UNIVERSITA’ DEGLI STUDI DI GENOVA

FACOLTA’ DI INGEGNERIA _________

TESI DI LAUREA

Progetto di un dispositivo per la localizzazione di

mine anti-uomo

RELATORE: Chiar.mo Prof. Ing. Rinaldo C. Michelini

CORRELATORE: Prof. James Trevelyan

Ing. Matteo Zoppi

ALLIEVO: Emanuela Elisa Cepolina

A.A. 2001-2002

“Sol nella libertà l’anima è intera”

Ringraziamenti

Mamma mia! Finalmente la tesi è in stampa per l’ultima volta. Beh nonostante sia

stanchissima con gli occhi che mi stanno per cadere dalla testa, sono felice. Sarà la soddisfazione o la stanchezza che mi inebria, ma alla fine di ogni fatica condivisa con altri sono felice. E’ stato bellissimo lavorare in questo laboratorio con questi compagni. Vorrei ringraziare col cuore in mano tutte le persone con cui ho condiviso questo periodo intenso, prezioso e bello della mia vita: il Prof. Michelini, per le discussioni vivaci e per aver creduto in me, lasciandomi libera di scegliere l’argomento della tesi e permettendomi di esportare le mie idee in Australia. Tutte le persone con cui ho lavorato a Perth: in particolare il Prof. Trevelyan, per avermi accolta, istruita e consigliata gratuitamente, e Sabbia, per avermi fatto un po’ da sorella maggiore. Tutti i giovini del laboratorio che mi hanno sostenuto, aiutato e hanno condiviso con me questi mesi: Matteo per la disponibilità, la pazienza e la gentilezza che mi ha dimostrato, e per gli innumerevoli libri che mi ha evitato di consultare perché lui ha tutto in testa, Gabriele, Paolo Emanuele Sandro per avermi accolto tra loro come se ci fossi sempre stata e Andrea con cui mi ha fatto piacere condividere un sacco di fatiche in questi ultimi anni. Infine la mia famiglia che dice che io non dico mai grazie, per avermi curato e mantenuto. Mi scuso per l’età che accuseranno tutti adesso che anche la minima si laurea.

Desidero ringraziare, inoltre, tutte le persone con cui ho avuto il piacere di discutere le idee esposte in questa tesi, che mi hanno consigliato con esperienza e fatto coraggio:

Yvan Baudoin, Royal Military Accademy, Brussels, Belgium Sergio Rizzo, Ansaldo ricerche Ian McLean, Geneva International Centre for Humanitarian Demining (GICHD), Ginevra, Svizzera. Jan Dai, Kings College, Londra, Inghilterra Paolo Fiorini, Università di Verona

“I went with my cousins to see the place where NATO bombed. As we walked I saw something yellow. Someone told us it was a landmine. One of us took it and put it into a well. Nothing happened. Later I went back to the bomb and put it in this position (vertical). We began talking about taking the bomb to play with and then I just put it somewhere and it exploded. The boy near to me died and I was thrown a meter in the air. The boy who died was 14 – he had his head cut off. I was near him and another boy tried to help me.” 13-year-old boy in Pristine Hospital, having undergone a double leg amputation. “Near the start of this century, 90 percent of wartime casualties were soldiers. As the century wanes, 90 percent are civilians”. Madeleine K. Albright, Former Secretary of State, Washington.

SUMMARY

1 INTRODUCTION ......................................................................................................................... 1

1.1 GLOBAL LANDMINE PROBLEM ....................................................................................... 2 1.2 SOCIO-ECONOMIC IMPACT OF LANDMINES................................................................. 3 1.3 TYPES OF LANDMINES....................................................................................................... 5 1.4 DIFFICULTIES IN MINE CLEARANCE .............................................................................. 9 1.5 CURRENT DEMINING METHODS.................................................................................... 11

1.5.2 Manual demining............................................................................................................ 12 1.5.3 Use of trained dogs ........................................................................................................ 13 1.5.4 Use of machines ............................................................................................................. 15

2 PROJECT IDEA.......................................................................................................................... 18

2.1 NEW TECHNOLOGIES ....................................................................................................... 19 2.2 VEGETATION...................................................................................................................... 19 2.3 LIZARD................................................................................................................................. 22 2.4 MOBILE ROBOTS IN HUMANITARIAN DEMINING..................................................... 23

2.4.1 Detonating mine robots .................................................................................................. 24 2.4.2 Scanning platforms supported by vehicles ..................................................................... 26 2.4.3 Mobile sensor platforms................................................................................................. 27

2.5 LIZARD VERSUS OTHER MOBILE ROBOTS PROPOSED ............................................ 32

3 LIZARD DESIGN ....................................................................................................................... 34

3.1 SENSORS.............................................................................................................................. 35 3.2 ARTFICIAL ODOUR AND VAPOUR SENSORS .............................................................. 39

3.2.1 Explosives contained in landmines................................................................................. 39 3.2.2 Migration of explosive from mine casings into the soil. ................................................. 40 3.2.3 Transport of explosive in soil ......................................................................................... 41 3.2.4 KAMINA, electric nose................................................................................................... 43 3.2.5 FIDO, chemical nose...................................................................................................... 44

3.3 LIZARD EARLY SOLUTIONS............................................................................................ 48

4 SECOND IDEA: WORM............................................................................................................ 53

4.1 OTHER TECHNIQUES ........................................................................................................ 54 4.2 REMOTE EXPLOSIVE SCENT TRACING (REST)........................................................... 54 4.3 AUTOMATING THE SAMPLING PROCESS .................................................................... 57 4.4 FROM LIZARD TO WORM................................................................................................. 57 4.5 DIRECTIONAL DRILLING MACHINES ........................................................................... 59 4.6 WORM FEATURES.............................................................................................................. 62

5 WORM: FEASIBILITY STUDY ............................................................................................... 66

5.1 WORM KINEMATICS AND DYNAMICS ......................................................................... 67 5.1.1 KINEMATICS................................................................................................................. 67 5.1.2 DYNAMICS .................................................................................................................... 69

5.2 MODEL IN ADAMS............................................................................................................. 70 5.2.1 ADAMS working principles............................................................................................ 70 5.2.2 Setting up the model ....................................................................................................... 72

5.3 MODEL CHOICES ............................................................................................................... 77 5.3.1 Bodies............................................................................................................................. 77 5.3.2 Contact ........................................................................................................................... 78 5.3.3 Pushing machine ............................................................................................................ 80 5.3.4 Torsion springs............................................................................................................... 81

5.4 BASIC MODEL..................................................................................................................... 83

5.5 FROM BASIC MODEL TO GENERAL MODEL ............................................................... 85 5.5.1 Parameterization............................................................................................................ 85 5.5.2 Worm problems and solutions........................................................................................ 86

5.6 GENERAL MODEL.............................................................................................................. 93 5.7 USE OF MODEL................................................................................................................... 95

6 WORM DESIGN ......................................................................................................................... 98

6.1 JOINT DESIGN..................................................................................................................... 99 6.1.2 Joint requirements.......................................................................................................... 99 6.1.3 Pro/ENGINEER drawing of joint................................................................................. 100

6.2 FUNCTIONAL ANALYSES .............................................................................................. 103 6.2.2 Joints ............................................................................................................................ 104 6.2.3 Rods.............................................................................................................................. 107

6.3 PROCESS FOR PROJECTING WORM............................................................................. 108

7 CONCLUSIONS AND FUTURE WORK ............................................................................... 111

8 REFERENCES .......................................................................................................................... 113

9 WEB-SITES ............................................................................................................................... 116

10 CONTACTS ............................................................................................................................. 118

Introduction

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1 INTRODUCTION

• Presentation of the global landmine problem

• General picture of solutions adopted nowadays

Introduction

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1.1 GLOBAL LANDMINE PROBLEM

According to the Civil Right, a landmine is some object placed on or under the ground or any surface, conceived for exploding by the simple fact of the presence, the proximity or the contact of a person or a vehicle. There are two main types of landmines: - Anti Tank (AT), or Anti Vehicle, landmines, which are designed to detonate when a

vehicle drives over them. - Anti Personal (AP) landmines, which are designed to detonate by the presence, the

proximity or the contact of a person.

Usually AT landmines are bigger and contain more explosive charge than AP landmines.

Dimensions Expolsive charge(diameter) (mass)

AT landmines 300-350mm 5-10 Kg

AP landmines 70-150 mm 80-250 g

Landmines are used to deny enemy access to strategic areas. The objectives achieved are mainly two: causing immediate fatalities or disabling injuries to the people who approach the contaminated land and denying access to the resources the affected land could offer. Landmines have been used for more than 50 years. Because they are very simple and low-cost devices, landmines have been used in many different occasions: by the civilians during internal conflicts, by villages and group of people for self-defence and by the military forces as part of a widely accepted military strategy. According to current estimates1, more than 110 million landmines have been laid in 90 countries through-out the world; some of the most severe landmine problems exist in India, Nepal, Vietnam, Egypt, Angola, Afghanistan, Rwanda, Bosnia, Cambodia, Laos, Kuwait, Iraq, Chechnya, Kashmir, Somalia, Sudan, Ethiopia, Mozambique and the Falkland Islands.

1 Landmine Monitor Report,2002: Toward a Mine-Free World, International Campaign to Ban Landmines (http://www.icbl.org)

Introduction

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(Picture: Landmine Monitor Report,2002, http://www.icbl.org )

In these countries up to 60 percent of useful agricultural land in some regions is unusable. Landmines are also in other places like irrigation canals, ruined houses and bunkers that offer cover and protection, roads, confrontation lines that divided military factions as river banks, abandoned industrial sites and residential areas. Every month between 500 and 800 people are killed and 2000 others are maimed because of the explosion of landmines2. The number of other indirect casualties cannot be calculated.

1.2 SOCIO-ECONOMIC IMPACT OF LANDMINES

Landmines have an unacceptable post-conflict impact on civilians and act as a widely recognized obstacle to rehabilitation, resettlement, reconstruction and development of the affected countries.

The devastating toll on human lives and health is unquestionably the cruellest impact of mines and unexploded ordinances (UXO).

2 International Committee of the Red Cross (http://www.icrc.org)

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Although the number of casualties is very high, the toll on human lives is mainly due to indirect effects resulting from displacement of population, deprivation of earning capacity and poverty. Still, information on the human loss is to a large degree deficient, as most data collection on mine victims suffers from lack of reliability and coordination. Not only the number of mine victims is uncertain, but also the extent of the mined areas the accidents refer to. New areas still continue to be identified with their share of high priority fields. The loss of a high number of human lives considerably affects the economy of the contaminated countries. From data’s acquired in Afghanistan from Socio-Economic Impact Study of Landmines and Mine Action Operations in Afghanistan (SEIS) in 1999, it can be seen that a considerable share (about 40 percent) of the victims were educated, with at least completed primary education, and that about half of the victims were responsible for supporting their families. It can thus be assumed, generally, that a considerable number of mine victims belongs to the economically active age groups (18-65 years) and could have contributed positively to the Gross National Product (GNP) of their countries. Considering that each active, employed person in a poor country could contribute about US$ 750 annually to the GDP3, contaminated countries are considerably impoverished by the loss of human lives due to landmines. The situation in contaminated countries it’s made worst by the fact that about 34 percent of the victims are less than 18 years old4 and then next to come to productive age.

Moreover, the cost per unit area, to check that ground is free of mines, is very high. Approximately US$10,000,000 are required to clear 10 sq Km in a third world country, and US$ 2,000 to clear an house with garden in Croatia5. This is incredibly high comparing to the cost to buy and lay a typical landmine (approximately US$5). This makes the operations of removing landmines a very slow process for the countries already brought to their knees by the war, because they depends on the aids given by richer countries. Landmines are, thereafter, left in the lands for many years after the war; this affects the economy of the countries in which landmines lie in many ways: - The process of finding and removing landmines becomes longer, due to the changes the

time makes on the land (grown vegetation, movement of the earth because of flood, etc…)

- The number of people injured by the explosion of landmines doesn’t decrease with

time, making the cost of medical cures very high for many years.

3 Study Report: Socio-economic Impact of Mine Action in Afghanistan (SIMAA), 2001. 4 Socio-Economic Impact Study of Landmines and Mine Action Operations in Afghanistan (SEIS), 1999. 5 Prof.Trevelyan, 2002, personal communication.

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- Agricultural land is unusable for many years, increasing the dependency of the affected countries from humanitarian aid coming from advanced countries.

- Millions of refugees can not go back home for many years. There is a urgent need to solve the global landmine problem. On the 18th of October 1997 a “Convention on the Prohibition of Use, Stockpiling, Production and Transfer of Anti-Personnel Mines and on their Destruction”, known as Ottawa Treaty, has been signed from 146 countries; up now, the number of State Parties, having ratified the treaty is 1306. Although this is a good result, the major military power countries, like US, Russia and China haven’t signed the convention yet and mines have been still used after 1997; one of the largest scale mine laying operations anywhere in the world after 1997 has taken place along the border between India and Pakistan1. Nowadays landmines are still being laid.

1.3 TYPES OF LANDMINES

Many types of mines exist around the world, differing one from each other about type of victim they are addressed to, type of activation, size, explosive charge, type of explosion and location with respect to the ground. There are two main types of landmines: - Anti Tank (AT), or Anti Vehicle, landmines, which are designed to detonate when a

vehicle drives over them. AT mines are activated by force (>100kg), magnetic influence or remote control. AT mines are quite big, comparing to the AP mines, and contain between 5 and 10 kg of explosive charge. Usually, AT mines are laid in unsealed roads or potholes.

- Anti Personal (AP) landmines, which are designed to detonate by the presence, the

proximity or the contact of a person. AP mines are activated by force (3-20kg) directly exerted on them or by pulling tripwires. AP mines have a diameter between 7 and 15 cm and contain between 80 and 250g of explosive charge. AP mines can be buried into the ground, fixed to something over the ground or just laid on the ground.

Dimensions Expolsive charge Activation force(diameter)

AT landmines 300-350mm 5-10 Kg >100kg

AP landmines 70-150 mm 80-250 g 3-20kg

6 Landmine Monitor Report,2002(http://www.icbl.org)

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Although there are more than 700 known types of AP mines, only two types of explosion are enabled. We distinguish between: - Fragmentation mines; when they explode, metal fragments are propelled out at high

velocity to a radius of 30 or even 100 meters, penetrating up to several millimeters of steel, if close enough. Usually they detonate when the tripwire connected to them it is pulled.

- Blast mines, which are typically buried into the ground and detonate when a person

steps on them. The explosion usually destroys the foot and partially the leg. Two main types of Fragmentation mines exist, differing one from each other about the location with respect to the ground: - Stake mines, which are fixed to a knee-high wooden stake, in order to detonate when a

person pull the tripwire while is walking near by the stake. - Bounding mines, which are buried into the ground. When their tripwire is pulled, they

jump up to groin height before exploding.

(Drawn: Prof. J. Trevelyan)

Usually, mines of one type have been laid in combination with mines of another type, to make the mine clearance more difficult. Defensive minefields often employ Stake mines buried near to Blast mines; Stake mines are more effective but relatively easy to see because of the tripwire, while the Blast mines can not be seen because they are buried and deter any attempt to remove the Stake mines.

Fragmentation mine

Blast mine

Introduction

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Some of the most common Blast mines are: - PMN 1, this mine is: -extremely reliable: surveys in Cambodia have revealed over 90

percent in fully operational conditions after 20 years; -extremely sensitive: deminers tend to have more accident with this type of mine than others; and easy to detect with metal detectors because of the large amount of metal contained; the largest piece is the stainless steel retaining ring that holds the rubber cup in place over the top of the mine.

(Photos: Prof. J. Trevelyan)

- PMN2, this mine has much more complex design and is less reliable than PMN1:

surveys in Cambodia have shown that this mine causes relatively few civilian casualties when the ground is dry and hard. One of the reasons for this could be the small pressure sensitive area on the top of the mine; the rest of the surface is rigid and provides more support for the soil over the top of the mine.

(Photo: Prof. J. Trevelyan)

- 72 Blast Mine, this mine is a classic plastic mine, with very small metal components in it. Plastic mines are difficult to detect with a metal detector.

(Photo: Prof. J. Trevelyan)

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- AT mine, this mine has very small metal components but contains a large amount of explosive; it is easier to detect using advanced technology such chemical sensors or nuclear methods.

(Photo: Prof. J. Trevelyan) All anti-tank mines are blast mines, because the goal of the anti-tank mine is to destroy the tank's tracks and as much of its body as possible. The track wheel and other components close to the mine become high velocity fragments that extends radius of damage.

(Drawn: www.howstaffworks.com)

In addition to landmines, in most of the affected countries, there are also unexploded Cluster Bombs laying on the ground. A Cluster Bomb is a particular kind of bomb, which is dropped out from a plane over the target. Up to 200 cluster bombs can be dropped at the same time from a single plane over area of around 0.5 sq.km. Instead of landmines, Cluster Bombs are designed to explode when they impact on the ground, not to be victim initiated. Cluster Bombs affect the mine clearance operations only when they don’t work properly and they fail to detonate as they hit the ground. As they lie on the ground and can detonate very easy, sometimes just touching them, they act as landmines.

Introduction

9

Although the most commonly quoted failure rate of Cluster Bombs is 5 percent, recent studies conducted by the UK working group on Landmines, confirm that the failure rate is much higher, around 9.6 percent.

These unexploded cluster bombs add to the number of landmines laying through out the world.

(Photo: Prof. J. Trevelyan)

1.4 DIFFICULTIES IN MINE CLEARANCE

Humanitarian demining operations face many complications. First of all, the landmines locations are usually unknown. Because landmines are very cheap and easy to build weapons, they have been largely used in different types of conflict, by military or civilians. In most countries, mine contaminated areas are often discovered by associations like the Red Cross when they have to provide support for mine victims.

In some cases, the military forces are able to provide maps indicating the locations of the landmines placed by them. Although these maps can be well detailed, only in few cases they are useful during the mine clearance; in fact demining operations may not start until years after the minefield was laid and during this time the conditions of the affected lands can drastically change.

Mines that have been in place for years can be corroded, waterlogged or impregnated with mud or dirt, and then behave quite unpredictably.

(Photo: Prof. J. Trevelyan)

Introduction

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Floods and heavy rains may have occurred on landmines fields, causing mines to move from the original place to another or to move deeper into the ground.

Mines placed near buildings may lie deep under fallen rubble, with yet more mines laid on top.

(Photo: Prof. J. Trevelyan Sarajevo,1997)

The stakes supporting Fragmentation mines may fall over and may rot, leaving the fragmentation mines half buried lying on their sides. The tripwires will either be lying on the ground half buried in rotting vegetation, or will be lifted into the air as scrub and bushes grow in what was once a cleared area of land. When this has happened, the wires will run through the branches of the scrub and may pull the pins from the fragmentation mine as the branches sway in the wind.

The vegetation grown in many years after the landmines were laid can represent a very big obstacle to demining operations.

(Photos: Prof. J. Trevelyan,

border between Croatia and Republika Serbska, 8 years after mines were laid)

The type of terrain itself can cause many problems to mine clearance: terrain plenty of metal fragments, represent an obstacle for the use of metal detector. Uneven rocky terrains add complications to the mine removing operation.

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(Photo: MCPA, Afghanistan, courtesy of Prof. J. Trevelyan)

Mines buried in a sandy desert, can easy move deeper when the wind blows the sand.

(Photo: Prof. J. Trevelyan Western Desert, near to Al Alamein)

1.5 CURRENT DEMINING METHODS

Until 2001 the UN standard for an area declared cleared of mines was that there was at least 99.6 percent probability that all mines have been removed or destroyed. From 2001, the UN standard has changed in “Land shall be accepted as “cleared” when demining organization has ensured the removal and/or destruction of all mine and Unexploded Object (UXO) hazards from the specified area to the specified depth”7 . The issue is how thoroughly to check and verify that all mines and UXO have been removed or destroyed. Unfortunately, in most of the cases, after mine clearance operations have finished, the area cleared cannot be considered totally free of mines and the accuracy of the operation of landmines removal cannot be stated. 7 www.mineactionstandard.org

Introduction

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Although current demining methods cannot guarantee that the land is effectively free of mines after it has been cleared, they are still used; this means that by now, a solution that reduces the risk to a reasonable level is accepted as the best available. Current demining methods are based on manual demining. Depending on the different situations, machines and trained animals can be used in combination with manual demining. Before demining can start, surveys are needed to produce detailed maps of minefields to be cleared. The survey team verifies a one or two meter wide safe lane around each minefield in order to define the minefield itself. A minefield can be surrounded with unknown land or other minefields. Typical minefields are 100-200m across and 0.1-10ha in area.

1.5.2 Manual demining

Manual demining is a procedure in which mines are manually detected and neutralized by a human deminer. The tools used by human deminers are: - A thin rod, which is gently swung or lifted to check for tripwires - A metal detector, which is swung from side to side to check for metal object - A prodder (typically a bayonet, screw, driver or knife), which is used to probe the

ground at an angle of about 30 degrees to the horizontal position and to excavate earth around a suspected object. Usually a prodder is used to investigate a suspect metal object.

Details vary, but the procedure is more or less the same in most demining operations:

1. The team defines the minefield perimeter and mark it using painted wooden posts or stones and rope or tape.

2. The deminers prepare breeching lane entry points, marking the starting position with a (typically) 1 meter long wooden cleared-position-marker rod.

3. The deminer checks for tripwires in next 0.5 meters of his lane, both visually and using a thin rod to lift tripwires lying on the ground.

4. He cuts and removes vegetation in next 0.6 meters of his lane, checking for tripwires not removed already.

5. He lays a wooden marker rod 0.5 meters from current position to mark the area to search with the detector.

6. He searches the area between the two marker rods 0.5 meters apart for landmines using his metal detector

7. As he finds each signal, he lays the detector on the ground, places a marker on the location, and checks the detector signal again to ensure that the marker is in the right place. He determines where the signal is weakest between the marker and the current cleared position. He marks this point as well.

8. Using a prodder he carefully excavates the surface layer first, working forward from a point about 15-20cm from the main marker. If he finds no metal target he repeats this,

Introduction

13

excavating deeper in layers until the target is found or the depth reaches a preset limit. In some operations excavations continue to a depth of 30 cm.

9. If (as is usually the case) he finds a metal fragment he removes it and checks the position again with a detector before moving on.

10. In some operations in soft ground, he carefully searches the main marker by probing with a long steel rod. However one cannot be certain of clearance to a depth more than 10 cm in ideal sandy conditions.

11. If a mine is discovered, the mine is marked and the lane is closed off until a demolition charge can be used to destroy the mine in-situ.

12. Once the 0.5 meter deep area between the current position and the marker rod has been shown to be metal free, the deminer moves the lane markings forward to the marker rod location. He also moves the current cleared position marker rod. Then the deminer returns to step 3 unless the minefield has been completely cleared.

13. After every few meters of lane has been cleared, in many demining operations, the deminers re-check the most recently cleared section of the lane with detectors, marking and removing targets using steps 5-9. Clearly this procedure can only be used when metal targets are removed. If the probing procedure is used and targets are left in-situ the targets must be marked until this re-checking is completed.

Usually a team of 30 deminers is assigned to clear each minefield. Two-man clearance parties work together on clearing parallel lanes, 1m wide, across the minefield, with each lane about 25 m from the next (considered to be a safe distance). The manual approach to mine clearance poses a lot of problems: - The work of human deminers is dangerous and severe: human deminers can be killed

or seriously injured while working, they have to wear heavy special protective cloths while the weather can be very hot, they have to work laying on the ground and the work itself is tiring and boring.

- The time needed to investigate a minefield is very high: analysis of statistics from a selection of 70 Afghan minefields reveals that deminers typically find 1 to 30 suspect objects for every 10 square meters, and clear 6 to 50 square meters per hour; on average for a 30-man team, between 1 and 15 hours pass between finding each mine or unexploded ordinance, meaning that an individual deminer can work for months without finding a mine 8 .

- Metal detectors are not reliable: recent tests (ITC2001) have shown the weakness of this technology, several mines were missed even though the mines were well within the specified clearance limits used in most mine clearance operations.

1.5.3 Use of trained dogs So far, dogs are considered the best detectors of explosives. Their sensitivity to this kind of substance is very high. This enables the dogs to detect mines with low metal content that are undetectable by metal detectors.

8 UN Office for Coordinating Humanitarian Aid to Afghanistan, 1996

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Dogs work in combination with manual deminers. The manual deminer clears safe access lanes (usually a metre wide) around the minefield. The width of the minefield (across the wind direction) must be no longer than the length of the leash on the dog. In Afghanistan this is 8 meters. In Bosnia 10 meter and 15 meter lengths are common. Usually, the dog is introduced to the minefield and commanded by the handler to cross the upwind edge of the minefield. The handler then steps about 60 cm sideways, and the dog performs another traverse, and so on. If one dog completes an entire task area (see diagram), another dog is introduced with his handler and again checks the same task area. If neither dog indicates explosives, the task area is declared to be safe and clear.

(Drawing: Mine dog clearance task layout: Afghanistan, courtesy Prof.J.Trevelyan)

Dogs are trained to indicate the presence of explosive by calmly sitting a short distance from the location where the scent was discovered. When any dog indicates, the location is marked by placing markers on the edges of the minefield. If this is the first dog, another dog will be introduced and will cross the area up to the indicated location again. Manual deminers can safely approach the location across the zone which has been 'cleared' by both dogs. Maybe the second dog will indicate a location that was missed by the first dog. In this case, it is this location that is checked the first by manual deminers. In Afghanistan, procedures require deminers to check an area 2 metres square around the location point, to a depth of up to 50 centimetres, or greater if there is evidence showing a suspect target.

Introduction

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The false alarm rate is low, and the total clearance cost using dogs is about one quarter (or less) that of manual demining using conventional methods. (Approx US$0.15 per sq metre with dogs, $0.65 per sq metre using manual demining 9).

(Photo:A.Smith, Afghanistan, courtesy of Prof J.Trevelyan)

The use of trained dogs in mine clearance poses some problems: - The dogs effectiveness depends on their level of training, the skill of their handlers and

on their correct use. - Searching for landmines it’s a game for the dogs; their work depends on their mood

and interest in playing. Usually they work just few hours a day. - The cost to train a dog is very high: between 10,000 and 100,000 US$ . And dogs need

to be retrained often, specially when they have to work with different kinds of mines. - We don’t understand completely how dogs find mines; they could use their nose as

main sensor in combination with other sensors as paws. Thus is difficult for the deminers to understand in which conditions they work better and what their limits are.

1.5.4 Use of machines Usually, demining machines are adapted from military armoured vehicles, with the same or reduced size. In an early stage, machines were designed to clear a navigable path through a contaminated field to make the access possible for the military forces. Because machines work fast and are relatively safe for the operator who is protected in a armoured crew or drives the machine from a safe distance by remote control, they have been used in different applications. There are several types of machines employed in mine clearance in different ways.

9 . Trevelyan, “Technology and the Landmine Problem: Practical Aspects of Mine Clearance Operations”, Detection of Explosive and Landmines, 2002,pp.165-184.

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1.5.4.1 Machines with flails

(Picture: http://diwww.epfl.ch/lami/detec/rodemine.html – EPFL DeTeC Centre; Aadvark Flail, used in Afghanistan and Angola.)

The flail principle originated in the 1940's and has been used for mine clearance in many places. A rotating shaft has several chains attached. Hammers on the ends of the chains beat the ground, setting off mines. These machines can be used only on carefully selected areas. Avoid rocky, uneven and hard ground, tracks and roadways. Because of their limitations, machines have to be always assisted by human demining.

1.5.4.2 Milling machines

(Drawn: courtesy of Prof.J.Trevelyan)

The diagram illustrates the principle used by the UNO Corporation machines in the form of an hydraulically driven attachment to a large hydraulic excavator machine.

Buried mines are first struck on the edge by the high speed cutter bars which chip pieces off rather than operating the fuse mechanism. These machines can be used only on carefully selected areas. Avoid rocky, uneven and hard ground, tracks and roadways. Because of their limitations, machines have to be always assisted by human demining. Manual clearance can be easier after the vehicle has moved through because the ground is softened by the machine's action.

1.5.4.3 Machines for vegetation removal Different types of machines can be used for vegetation removal:

Introduction

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Either machines designed for mine clearance like machines adapted with short flails designed not to beat the ground but just to rotate over the ground in order to clear the vegetation or specially designed machines.

(Photo: Menshen Gegen Minen MgM website, http://wwww.mgm.org)

This is the MgM Mulcher machine. It reduces vegetation on overgrown roads to chips before dogs or metal detectors check the ground.

The use of machines in mine clearance poses some problems: - Machines can only work on regular flat terrain. - Machines are usually big and heavy: the transport of them to remote areas in countries

with a little infrastructure is difficult. - Big machines can not be used in small paths or thick bush. - Machines often do not destroy all mines in a contaminated area and some can be

thrown far away or pushed to the side or buried deeper. - Machines are expensive and need to be driven by skilled workers. Often they need to

be fixed after the explosion of a landmine, or adapted to face particular environmental conditions

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2 PROJECT IDEA

• Defining the possible applications

• First Idea: LIZARD

• Review of other proposed robots

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2.1 NEW TECHNOLOGIES

“We need to intensify research into better methods of demining…the most common tool we have for detecting landmines is still a stick attached to a person’s arm.”

Ambassador Karl Inderfurth, U.S. Special Representative

of the President and Secretary of State for Global Humanitarian

Demining, December 8, 1997

The general view of the problem of landmines, suggests that new technologies are required, to achieve proper effectiveness, safety and reliability.

The large use people have made of landmines, in different types of conflicts, in different countries, and the large production of landmines, in different shapes, with different metal contents, with different activation means, etc., make mine clearance a very complex task.

A lot of researches, who have been involved in projects about landmines, agree that a solution, which is able to solve all the problems relating to landmine clearance, is actually out of any reasonable match.

A combination of different technologies shall be adopted to solve the different problems arising in different minefields.

Probably, landmines removal will keep on relying mostly on human deminers, as humans are the most reliable and versatile machines, but technological improvements can be thought in order to make landmine clearance safer and faster in particular conditions.

In order to think about an useful aid, the technology can give to mine clearance, it’s necessary to analyse the methods of mine clearance currently used and to focus on a particular problem which needs to be solved.

2.2 VEGETATION

Vegetation represents a big obstacle to mine clearance.

In order to work properly, metal detectors have to be near to the ground. Also dogs work better when their nose is near to the ground.

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Therefore, the first step in mine clearance operations is always vegetation removal.

The work of removing vegetation has to be done with great care because tripwires may be hidden in the branches of the bushes and might be pull as the branches sway in the wind.

(Photo: Prof.J.Trevelyan)

In areas where it is possible, the use of machines for removing vegetation is particularly suitable. Armoured flails resist damage due to tripwire activated mines and the occasional blast mines that might also be activated. Using flail systems in combination with manual deminers sensibly lowers the unit cost of demining. Unfortunately, the cases in which machines for vegetation removal can be used, are limited because of two main reasons: - Machines work well only with regular and flat terrain; unfortunately, up to 53 percent

of minefields are unstructured terrain in uneasy accessible areas1.

- Machines are very big and heavy and cannot access a lot of contaminated lands; often the infrastructures that the contaminated countries can offer are very weak and therefore not able to carry big machines.

Places like these cannot be accessed by machines and are very expensive and slow going to be demined by hand:

1 Y. Boudoin, E. Colon, “Humanitarian demining and robotics state of the art, specifications and ongoing research activities”, Climbing and Walking Robots 2000, Professional Engineering Publishing, pp. 869-877.

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(Picture: courtesy of Prof.J.Trevelyan,recently cleared area around a culvert;(small bridge for a drainage channel)

only the immediate area around theculvert has been cleared, for

maintenance works, the other beingtoo expensive to clear by hand)

(Picture: Prof.J.Trevelyan, showing a house in a village. The house is completely obscured by high vegetation that has grown up in 8 years since fight has started in this area)

(Picture: Prof J.Trevelyan,Typical house in a Croatian or

Bosnian village)

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In countries like Croatia and Cambodia, where vegetation grows very fast, clearing vegetation to provide access for detectors takes as much as 75 percent of the total effort2. Considering that often, after demining operations are completed, mines are not found in the supposed contaminated areas, the operation of vegetation removal is not always needed, therefore, time and money wasting.

Finding a way to check large areas covered with thick vegetation for the presence and location of landmines and other unexploded ordinance without having to clear the vegetation first, it is an urgent need and an interesting challenge.

2.3 LIZARD

In order to check for landmines an area, a sensor system needs to be carried and

swept over the ground, covering the entire surface of the area. It’s very difficult to get in and move inside the vegetation when this is very thick.

Looking at the nature, the animals that are able to enter and to move over the ground inside thick vegetation are small with very short legs or without legs and they move keeping their stomach very near to the soil.

A robotic device, such as a mobile platform, mimicking the behaviour of this kind of animals like lizards or worms could be very useful in mine clearance of areas covered by thick vegetation. A machine of the same type could be employed either to carry sensor systems or devices to neutralise mines.

A mobile platform carrying sensors, moving on minefields, can be designed in two ways: - It can be heavy, but able to detect mines before running them over. - It can be light enough not to trigger mines. In the first case, the platform can be autonomous and therefore more agile because it carries also the batteries required to power the system, usually quite heavy, without having to be connected to a power source via umbilical. But an error in detecting a mine, causing the platform to move over it, will be very expensive, because the equipment will be destroyed. In the second case, the platform needs to be powered via umbilical, in order to avoid the big weight of the batteries on board. This results in a lack of autonomy and therefore a decrease of agility, but allows the data’s coming from the sensors solid to the platform to

2 J. Trevelyan, “Technology and the Landmine Problem: Practical Aspects of Mine Clearance Operations”, Detection of Explosive and Landmines, 2002,pp.165-184.

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be read in real time, avoiding the use of more expensive devices, like radio transmitting devices and GPS, needed to locate the vehicle and the detected mines.

The requirements for a lightweight sensor platform to be useful, apart from removing the operator from the hazardous area, are: - To be light enough not to trigger mines. - To be agile inside the thick vegetation. - To give back a detailed map of all the mines laying into the minefield. - To be fast; at least faster than the method currently used:

Moreover, while projecting such a platform, it has to be considered that complex solutions are difficult to be accepted by the local population, usually not technically skilled. Therefore additional requirements for a lightweight sensor platform to be suitable for use in real minefields are: - To be simple: - low cost, when possible, parts should be available on local market; - with a simple design, in order to be built in the mine affected countries; - easy to use; - easy to program, programs could be available from Internet; - easy to be maintained: with a suitable modularised mechanised structure. A lightweight sensor platform should be able to operate in different control modes, including remote-operated and semi-autonomous mode. It should have navigation capabilities over the area to be cleared, with efficient and flexible locomotion capabilities. The preliminary aim of this thesis is to conceive and design a biologically inspired, lightweight, sensor platform to be used in mine clearance operations in areas covered by thick vegetation, taking inspiration from lizards, which will be called Lizard.

2.4 MOBILE ROBOTS IN HUMANITARIAN DEMINING

Several different robots have been proposed to help humanitarian demining

operations. Although they have been the issues of long researches, no local deminer centre has adopted any of them.

Time for checking the area + Time for removing mines (by using a special designed mobileplatform or by hand, having removed thevegetation first, only the required)

Time for vegetation removal + Time for checking the area (by hand, or using dogs)

>

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The reasons why the proposed robots are not used could be a lot. Some of them have not been conceived taking the real minefield conditions in mind, so that they are suitable just in few cases, some are not enough reliable and they cannot guarantee a certain percentage of clearance, some cannot be easy introduced in current demining methods. But the main reason I think is that a robotic solution is difficult to be accepted by the local population, until it’s felt to be too complicated and too difficult to be operated. Three main types of mobile robots have been proposed: - Robots designed to mechanically detonate mines while passing over them. - Scanning platforms designed to be attached in front of vehicles. - Mobile sensor platforms.

2.4.1 Detonating mine robots Some of the proposed robots of this type are:

- DERVISH, designed by Prof Salter, Department of Mechanical Engineering,

University of Edinburgh, Scotland.

(Picture: Dervish, Edinburgh, February 1999 http://www.dervish.org )

The Dervish is a three-wheeled vehicle with wheel axles pointing to the centre of a triangle. If all wheels were driven at the same speed then the frame would merely rotate about this centre and make no forward progress. However, carefully-timed, small, cyclical variations of wheel speed make the Dervish progressively translate in a chosen direction so that every point in its path is covered, twice, by a loading of about 90 kg in a pattern of overlapping circles as shown in figure. Different motor speeds will make the Dervish's wheels describe spirals.

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(Drawn: the overlapping circles of the Dervish track. Every point in the 5- metre wide path is covered twice

by a load a little greater than that of a human foot., http://www.dervish.org)

This should fire every functional anti-personnel mine but, because of the low weight, not normal anti-tank mines. The Dervish has a very open steel frame with all members oblique to the path of blast fragments. It effectively has a zero-radius turning circle. The wheels are made from Swedish Steel Hardox 400 excavator plate and can survive explosive charges larger than the largest anti-personnel mine in service. In a test with a 10kg charge, damage was confined to one corner and the axle and bearings from that test are still in use. The repair cost would be a few hundred dollars. In normal mine-detonating mode, the Dervish advances at about one metre a minute, a rate set by the requirement that there should be no mine-sized gaps between its wheel tracks. Three machines can be stripped down packed in a one tonne van and assembled by a single person in 30 minutes with the minimum of tools. The separate parts can, if necessary, be carried on foot. A second version of the Mark III experimental unit would cost about $25,000 but in production it might costs less.

- Suspended Pole Robot, proposed by Prof. J. Trevelyan, Department of Mechanical & Materials Engineering, University of Western Australia.

(Drawn: http://www.demining@mech.uwa.edu.au )

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Here a tool (a simple probe is shown) is suspended above the minefield by a system of steel cables controlled by winches on three or more poles or towers at the corners of the minefield. This device could significantly improve detection techniques because the location of the detector is known for each measurement. Compared with conventional hand-held detectors, much more sophisticated signal processing can be enabled, and false alarm rates can be lowered on metallic mines and non-metallic mines with metal fuses. This device will work over any terrain where temporary poles can be erected. Therefore, it should work over hills and waterways as easily as within open agricultural or urban land. It would cost about $60,000 to $80,000 to build a field operable system. This would be capable of mechanically probing for mines across an area the size of a football stadium at a rate of about 1 position every second. Although these machines have many interesting features such as easy transportability, simple design and are not very expensive, generally, mine detonating robots are not reliable, because they cannot guarantee that all the mines in the “cleared” field have been detonated. Thus, a minefield already “cleared” by mine detonating robots has to be checked again with sensors. Both of the machines shown can be adapted to behave as sensor platforms. In this case, accessibility to most of the minefields is the main problem. The size of the Dervish robot and the concept of the Suspended Pole Robot, make these machines suitable for a limited number of actual minefields: they cannot access fields full of obstacles, notably if thick vegetation exists.

2.4.2 Scanning platforms supported by vehicles

Some of the proposed robots of this type are:

- VAMIDS, designed by SHIEBEL Corporation.

(Picture: Vamids sensor platform attached to a car http//www.shiebel.com/industries/vadims.htm)

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Vamids is designed to detect landmines, including those with minimal metallic content, and Unexploded Ordinance (UXO) from a vehicular platform. Additionally, with the use of special array segments, Vamids can detect buried UXO to depths of several meters. Although the system is designed to be used along established routes, it has good cross-country capability which depends on the terrain and the mobility of the platform. The Arrays are available as rigid or flexible panels which can either be mounted on a vehicle structure or be pulled over the ground. The individual segments provide overlap areas on either side and may be arrayed up to a maximum width of six meters.

- Scanner for systematic acquisition of multisensors data, developed by E.Colon, D.

Milojevic, H.Ping, I. Doroftei, Royal Military Academy, Free University Of Brussels

(Picture: Scanner mounted on a tracked vehicle, Hudem Symposium 1999,

courtesy of Prof. Y. Baudoin)

The acquisition system can be used as fixed or as a mobile system when mounted on a tracked vehicle. The scanner is a Cartesian robot with 3 degrees of freedom. Four sensors are used: a metal detector, a ground penetrating radar, a pyrometer and an infrared camera. The human interface is user friendly.

Scanning platforms are much better than a common single metal detector. But they are not suitable for uneven terrain with obstacles where machines cannot go. Their size, usually big, is another big limitation to their use; before using them vegetation clearance must first be done.

2.4.3 Mobile sensor platforms Some of the proposed robots of this type are:

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- PEMEX robot, designed by Prof. J. Nicoud, Microprocessor and Interface Laboratory, Swiss Federal Institute of Technology.

(Picture: http://diwww.epfl.ch/lami/detec/pemex.html )

The Personal Mine Explorer Robot (PEMEX) weighs 16 kg and exerts a force of 6 kg on the ground, which should not trigger AP mines. Two wheels (bicycle wheels have been used for the prototype) give the motion. When searching for mines, the Pemex head oscillates right and left, covering a 1 metre wide path It climbs 30° slopes and stairs, making it suitable for checking destroyed urban areas, and floats on the water, propelled by paddles. The robot has one hour of autonomy, has a speed of 2 m/s and costs about 5000 euros. At the moment no suitable sensor has been found for the robot. The work on the Pemex will be resumed in cooperation with a company when a sensor system will be available. Work progresses anyway with students to improve of the structure, motors, and navigation sensors.(most recent data’s are from 1997) This robot offers several practical advantages: first of all it’s light enough to no trigger AP mines; it is very agile and the structure may be assembled with pieces from bicycles; the electric actuator and the electronic control are protected by an epoxy casing and could be reused in case of explosion.

- TRIDEM 3, developed by The Free University of Brussels (ULB)

(Picture: Hudem Symposium 1999, courtesy of Prof. Y. Baudoin)

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Tridem is a three-wheeled electrical robot. The three independent driving / steering wheels, which are connected to a frame as a regular three arms star (120 degrees between each arm) allow the robot to have a very large mobility The frame connecting the wheels supports also the control, electronics and the batteries. Each wheel has two degrees of freedom actuated by two electrical motors. The robot has been designed to have a 35 kilograms payload and a maximum speed of 0.3 m/sec This robot is similar to the Pemex robot because the motion is given by wheels but present the disadvantage of supporting the sensors at a certain distance from the ground. As seen above, sensors work better when they are swept very near to the ground. Moreover it has not being designed light enough no to trigger landmines.

- WHEELEG, developed by The University of Catania (UoC).

(Picture: Hudem Symposium 1999, courtesy of Prof. Y. Baudoin)

Wheeleg is an hybrid robot, between a wheeled and a legged robot. This robot has two pneumatically actuated front legs, each one with three degrees of freedom, and two rear wheels independently actuated by using two distinct DC motors. The main idea is to use wheels to carry most of the weight of the robot and the two legs to improve the grip with the surface to climb and to overcome obstacles. During walking, obstacles up to 20 cm high can be overcame and the robot can also climb over irregular terrain. A problem of this structure is the need of synchronising the motion of the leg with the two rear wheels, which leads to a complicated control system. Another kind of wheeled robots proposed are all-terrain rover robots adaptable for mine clearance operations.

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Examples of all terrain rover robots adaptable for mine clearance operations are ATRV robots and FETCH II:

- ATRV family of robots, developed by IS Robotics.

(Picture: http://www.isr.com)

ATRV family of robots can easy access every type of terrain thanks to four-wheel drive, differential steering, pneumatic knobby tires, long run times and a wide range of optional equipment and accessories.

- FETCH II vehicles, developed by IS Robotics.

(Picture: http://www.isr.com)

FETCH II is a team of robotic vehicles designed to cooperatively clearing a field of land mines under the supervision of a single operator. They move autonomously, using a relative coordinate positioning system and task-specific sensors mounted on a mobile platform. Cooperating together these robots can accomplish different tasks simultaneously, but they are expensive and difficult to operate and repair. All the wheeled systems work well, but are not suitable for moving inside the vegetation because wheels can easy stick in leaves or branches.

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A lot of tracked vehicles have been proposed, some of them are capable of traversing a wide variety of terrain, but, again, they cannot enter and move inside the thick vegetation without getting stuck. A very good example of them is:

- TALON, developed by Foster-Miller Company.

(Picture: http://www.foster-miller.com)

- TALON is an all-terrain, all-weather platform with day/night capability. It is controlled through a two-way RF or fiber optic link from an attaché-sized Operator Control Unit (OCU). The OCU displays video from up to seven cameras with audio and data feedback for accurate vehicle positioning and control at distances up to 1.6 km. The vehicle speed is 4 m/h. TALON can carry more than 90Kg. It uses a two-stage arm that can reach a maximum length of 1.6 m and a gripper attachment to manipulate hazardous materials or ordnance.

A lot of researches think that legged robots, rather then wheeled vehicles, might accomplish better mine clearance operations. Some of the advantages of legged robots over wheeled robots are: high adaptability on uneven and rough ground, modularity lightweight replaceable legs, omni-directional motion or orientation, and attitude and altitude control. Walking machines only need a finite number of contact points with the floor, on the contrary that the wheels that need a continuous trajectory. These characteristics enable them to walk over detected mines simply avoiding to place the feet on the forbidden zones (a forbidden zone is the area occupied by a detected landmine).

- ARIEL, developed by IS Robotics.

(Picture: http://www.isr.com/projects/ariel)

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Modelled after a crab, Ariel is designed to remove mines and obstacles on land and underwater in the surf zone. Its unique brand of legged locomotion capitalizes on a crab's agility, stability, and efficiency, and will allow Ariel to scramble over obstacles and crevices that traditional wheeled vehicles would find insurmountable. Ariel is impact resistant and completely invertible, manoeuvring equally well right side up and upside down. Its integrated system of body status sensors and control systems allow it to react quickly to changing conditions by modifying its posture and the grip on the ocean floor. Each leg has two degrees of freedom. In an amphibious assault operation, a fleet of these expendable bottom crawlers are deployed to collectively search a zone. Each will find and secure itself next to a mine, then wait for a detonation signal. For non-destructive operation, modifications can be made to allow the robots to place an explosive in a predetermined location and move to safety before detonation.

- RHIMO, developed by Instituto de Automatica Industrial-CSIC.

(Picture: http://www.iai.csic.es/dca/index_i.htm)

Rhimo is a four-legged robot that may be classified as an insect type. Its legs are based on a three dimensional Cartesian pantograph mechanism, which consists of four links that provides three degrees of freedom. The body of the RIMHO is 736 mm long, 710mm wide, and 344 mm high and the machine weighs about 65 Kg. The longest link in a leg is 500 mm. Chassis and links are mainly made of aluminium alloy.

2.5 LIZARD VERSUS OTHER MOBILE ROBOTS PROPOSED

The aim of the collection of robots previously shown is not to be exhaustive, but to give a general picture of the types of robots proposed for humanitarian demining.

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As we can see, researchers have suggested different approaches to the problem of locating and neutralising landmines in minefields already cleared from vegetation, but none of them has focused his attention on the extra cost caused by vegetation removal. In countries where vegetation grows very fast, clearing vegetation to provide access for detectors takes as much as 75 percent of the total effort. It’s difficult to adapt a machine for operating inside the thick vegetation, if it has not been designed for this specific task. Wheeled and tracked vehicles present difficulties in going forward when they are in the middle of tall grass and scrubs; legged vehicles can easier move forward but as well they stick into the leaves and branches. Therefore, I think that a mobile sensor platform specially thought for moving inside the thick vegetation could be useful. Experts of the United States Robotics community, focusing on possible use of their techniques in the domain of the Humanitarian Demining, recently identified “The design of small, cheap, reliable, modular platforms for UXO sensors” as a technical area requesting investment in research activities. Developing a mobile platform having these features and able to move inside the thick vegetation would be an important achievement.

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3 LIZARD DESIGN

• Sensors

• Design

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3.1 SENSORS

In order to design the lightweight sensor platform, capable to move inside the thick vegetation, it is first necessary to choose the sensors the platform shall carry.

Sensor improvements have been research topics in the past years. The task is to replace current metal detector technology with some more advanced means of sensing. The needs for this is to reduce the number of false alarms associated with the use of metal detector. Several different sensor technologies have been proposed and are still under study and tests. The sensor technologies available belong to two big families:

- Sensors detecting explosives; there are two main types of this kind of sensors:

· sensors detecting explosives by analysing their bulk · sensors detecting traces of explosive

- Sensors detecting something else than explosives i.e. trip wires and metal parts of

mines.

To the second family belong:

- Metal Detector (MD), it works by measuring the disturbance of an emitted electromagnetic field caused by the presence of metallic objects into the soil.

This type of detector cannot differentiate a mine from metallic debris. In most battlefields, but not only there unfortunately, the soil is contaminated by large quantities of shrapnel, metal scraps, cartridge cases, etc., leading to 100-1000 false alarms for each real mine. Each alarm means a waste of time and induces a loss of concentration

- Ground Penetrating Radar (GPR), it works by emitting into the ground, through a

wide band antenna, an electromagnetic wave covering a large frequency band. Reflections from the soil caused by dielectric variations such as the presence of an object are measured. By moving the antenna, it is possible to reconstruct an image representing a vertical slice of the soil; further data processing allows horizontal slices or 3D representations to be displayed.

This system lack automatic recognition algorithms, is expensive and, in order to cope with small metal objects, needs a high resolution which limits the penetration depth and increases the image clutter.

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- Infrared (IR) Camera, it works by measuring the thermal contrast between the soil over a buried mine and the soil close to it. In fact mines retain or release heat at a different temperature than their surrounding, and during natural temperature variations of the environment it is possible, using IR cameras, to measure this thermal contrast.

Rather sensitive cameras have to be employed, with sufficient spatial resolution and maximum burial depth is estimated at 10-15 cm. In addition, results obtained by passive infrared imagers depend quite heavily on the environmental conditions and there are cross over periods (in the evening and in the morning) when the thermal contrast is negligible and the mine undetectable. Foliage is also an additional problem.

- Passive Millimetre Wave (MW) Radiometer, it works by measuring the emissivity

and reflectivity contrast between the metal contained in mines and the soil. In fact, in the millimetre wave band, soil has a high emissivity and low reflectivity. On the other side, metal has a low emissivity and strong reflectivity. Soil radiation depends therefore almost entirely on its temperature and metal reflection mostly on the low level radiation from the sky. It is possible to measure this contrast using a millimetre wave radiometer device.

Millimetre wave radiometer devices lack automatic recognition algorithms, as GPR and are very expensive.

- Acoustic Detection, consists in the emission of a sound wave with a frequency higher

than 20kHz into a medium. This sound wave will be reflected on boundaries between materials with different acoustical properties.

At high frequencies ultrasound does practically not penetrate soil, while using pulses of 1 ms in duration the problem arising lies in isolating small object pulses from other, often dominant, signals, and coping with ground contours and irregularities. A kind of "background signal subtraction" procedure is therefore necessary. All the sensor belonging to this family, are not designed specifically to find mines but object buried into the ground. This leads to high false alarm figures. Moreover, they are complex: instead of measuring the change in their status, while they are in proximity to a mine, they measure a change occurring in an external signal disturbed by the presence of a mine.

To the first family of sensors detecting explosives, belong:

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Some of the techniques used in sensors detecting explosives by analysing their bulk are:

- Thermal Neutron Activation (TNA), which relies on the activation, via neutrons emitted by a radioisotopic source or an accelerator, of the nitrogen nuclei, abundantly contained in most explosives. Specific gamma rays are emitted and detected.

With this technique AP mines are difficult to detect reliably, because of their very reduced explosive volume.

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- Neutron Backscatter: fast neutrons are thermalised by the explosive’s hydrogen nuclei, and the resulting backscattered slow neutrons are detected.

This system will probably work only in dry environments.

- Nuclear Quadrupole Resonance (NQR), it has been described as "an electromagnetic

resonance screening technique with the specificity of chemical spectroscopy", and relies upon the resonant response of certain nuclei possessing electric quadrupole moments. It is being developed in particular for airline security applications and has the fundamental advantage of not needing an external (static) magnetic field, contrary to Nuclear Magnetic Resonance NMR.

Presently encouraging results have been obtained with cyclotrimethylenetrinitramine (RDX) and not with TNT, which is found in the majority of mines.

All the sensors belonging to this family are complex: instead of measuring the change in their status, while they are in proximity to a mine, they measure a change occurring in an external signal disturbed by the presence of a mine.

None of the technologies presented, except for metal detectors, is mature yet and meets the requirements of simplicity and low cost.

A NATO report1 has classified some new sensor technologies in terms of maturity and cost and complexity, as follow:

IR MW GPR Acoustic TNA NQR MD

Maturity near far near mid near far available

Cost and Complexity medium high high medium high high low

Sensors detecting traces of explosive are more promising. They are simple because they work by directly measuring the change in their status while exposed to vapours of explosive. Moreover they perform a job similar to the one performed by dog noses. So far, dogs are considered the best detectors of explosives. Although we don’t understand completely how they find mines, it is reasonable to think that they use their nose as a main sensor, maybe in combination with other sensors as paws. Therefore, artificial odour and vapour sensors with high sensitivity could be expected to be detectors with high reliability. They have been developed and are already used in chemical industries or in airports

1 “Peacetime Mine Clearance (Humanitarian Demining )”,1996, NATO Defence Research Group.

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3.2 ARTFICIAL ODOUR AND VAPOUR SENSORS

There are two main types of artificial odour and vapour sensors, electrical and chemical. Both of them work by directly measuring the change in their status while exposed to vapours of explosive.

In order to understand how they work, it is necessary to analyse the explosives contained in landmines, their process of migration from the mine casing into the soil and the way of transport trough the soil to the surrounding atmosphere.

3.2.1 Explosives contained in landmines

Nearly 80% of the types of mines manufactured worldwide contain Trinitrotoluene (TNT) or mixtures of explosives containing TNT. TNT-containing mines account for about 85% of the total number of landmines manufactured and now deployed2. Of the mine types that contain TNT, approximately 86% contains at least 50 grams of TNT3. This mass of TNT is sufficient to yield vapours of signature compounds that can be released into the soil for decades.

Military grade TNT is manufactured by the nitration of toluene. This process produces many nitroaromatic compounds, obtained by the substitution of hydrogen atoms with –NO2 groups, some of which may remain in the TNT as contaminants at up to several percent by mass. Some of these Explosive-Related Compounds (ERC) are significant contributors to the chemical fingerprint of a landmine.

Of the ERCs found in TNT, those that are prevalent in the vapour phase chemical signature of landmines include 2,4-dinitrotoluene (2,4-DNT), 2,6-dinitrotoluene (2,6-DNT), 1,3-dinitrobenzene (1,3-DNB), and 1,3,5 trinitrobenzene (1,3,5-TNB)4. The equilibrium vapour concentration of TNT is very low (70 pg/ml of air at 298 K). However, several of the contaminants present in TNT have equilibrium vapour pressures greater than TNT.

2 “Jane’s Mines and Mine Clearance”, Colin King ed.,(Fourth Edition)1999-2000 3 “Mine Facts” CD-ROM, v.1.2, United States Department of Defence. 4 V. George, T. F. Jenkins, D. C. Leggett, J. H. Cragin, J. Phelan, J. Oxley, and J. Pennington, “Progress on Determining the Vapor Signature of a Buried Landmine,” Proc. SPIE, Detection and Remediation Technologies for Mines and Minelike Targets IV, vol. 3710, part 2, p. 258, 1999.

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Because their vapour pressures are higher, the concentration of these contaminants in the vapour phase signature may be several orders of magnitude larger than that of TNT even though there is much more TNT in the explosive charge. In the environment, TNT and DNT both degrade. In addition to being a contaminant in TNT, 1,3,5-TNB is a photochemical degradation product of TNT. 2-amino-4,6-dinitrotoluene and 4-amino-2,6-dinitrotolune are microbial degradation products of TNT. The amino-DNTs have vapour pressures that are extremely low and are, therefore, of little use for vapour sensing. However, they are frequently found in the soil over landmines, particularly during warm weather when microbial activity is high. While 2,4-DNT is the most likely analyte to be detected in the vapour phase5, any of these compounds shows the presence of TNT and, hence, a landmine. It is therefore advantageous for chemical sensors to detect all these compounds.

3.2.2 Migration of explosive from mine casings into the soil. Signature compounds of explosive are released into the surrounding soil through surface contamination of landmine cases, by vapour phase diffusion of analyte through the mine structural materials, and by leakage through cracks, seams, and holes in the mine. The latter two are the primary long-term release mechanisms. Surface contamination on the mine at the time of burial is quickly dispersed into the soil matrix surrounding the mine. The total vapour-phase flux of signature compounds from several types of landmine cases has been studied5. The flux was the total flux due to diffusion through structural materials and leakage through cracks and holes. The flux was measured into air and into water. For the PVC-cased PMA-1A landmine, the vapour-phase flux of 2,4-DNT into air was 3.4 micrograms per mine per day at 296 K, while the flux for the less volatile TNT was only 0.3 micrograms per mine per day. The flux rates into water were larger because of more favourable partitioning of ERC into water than into air. The flux rate of 2,4-DNT from a polystyrene-cased PMA2 AP mine into water was a factor of 30 larger than into air, and for TNT was a factor of 400 larger. It was estimated that the flux rate into wet soil would be intermediate between the air and water values. This has important implications for sensing mines, since the soil moisture content will strongly influence the rate of release of ERC from mines.

5 V. George, T. F. Jenkins, D. C. Leggett, J. H. Cragin, J. Phelan, J. Oxley, and J. Pennington, “Progress on Determining the Vapor Signature of a Buried Landmine,” Proc. SPIE, Detection and Remediation Technologies for Mines and Minelike Targets IV, vol. 3710, part 2, p. 258, 1999.

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Note that of the mass of analyte released into the soil from the mine per day, only a small fraction will eventually reach the surface of the ground.

The vapour phase flux through a mine case varies depending on the type of material from which the mine is built and the structural design of the mine6. Depending on the type of plastic used, flux rates from plastic-cased mines are typically higher than from metal cased mines. For a metal-cased Yugoslavian TMM-1 AT mine, the flux rate for 2,4-DNT is 2.3 micrograms per mine per day at 296 K. This compares with 3.4 micrograms per mine per day for the plastic-cased PMA-1A whose total surface area is approximately 6.5 times smaller than that of the TMM-1. Release of ERC through intact metal-cased mines is presumably through seams, seals, and other non-metallic structural materials. Flux rates are also somewhat temperature dependent, with the TNT flux rate from a PMA-1A increasing by a factor of 36 over a 31-degree temperature range spanning 276 K to 307 K.

3.2.3 Transport of explosive in soil

Vapours of signature compounds escaping from the mine are quickly adsorbed onto soil solids or dissolved in soil water. Molecules of explosives such as TNT are strongly adsorbed by most surfaces. Due to the relatively large surface area presented by soil particles and because of the adsorptive properties of explosives to solid surfaces, the majority of the ERC partitions onto the soil particles stops immediately around the buried mine. The partitioning of ERC into liquid and gas phases is governed by partition coefficients that are primarily a function of soil moisture content, and secondarily a function of temperature and soil type6. For a typical soil, approximately 95% of the total mass of ERC is adsorbed onto soil solids, followed by approximately 5% into soil water, with a trace (approximately 1 x 610− %) partitioning into the vapour phase7. ERC accessibility and accumulation are further limited by irreversible binding to soil solids and by processes such as microbial degradation.

6 V. George, T. F. Jenkins, D. C. Leggett, J. H. Cragin, J. Phelan, J. Oxley, and J. Pennington, “Progress on Determining the Vapor Signature of a Buried Landmine,” Proc. SPIE, Detection and Remediation Technologies for Mines and Minelike Targets IV, vol. 3710, part 2, p. 258, 1999.

7 J. M. Phelan and S. W. Webb, “Environmental Fate and Transport of Chemical Signatures from Buried Landmine�Screening Model Formulation and Initial Simulations,” Sandia Report SAND97-1426, Sandia National Laboratories, June 1997.

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The half-life of TNT in certain soils when the conditions for microbial degradation are favourable is short, on the order of a few days, while 2,4-DNT is much more stable in the environment8. The primary mode of transport of ERC to the soil surface is through the movement of water in the soil. Precipitation tends to draw ERC downward through the soil. Conversely, water evaporating from the surface of the ground brings contaminated subsurface water to the surface (evapotranspiration). As the water evaporates, it deposits the semi-volatile signature compounds preferentially on the comparatively drier soil particles at the surface of the ground. Molecules of signature compounds then escape from contaminated soil particles at the surface of the ground and into the boundary layer of air near the surface of the ground. The concentration of ERC in the boundary layer of air depends on the solid-to-vapour partition coefficient, which is, as previously described, a function of soil moisture content, temperature, and soil type. Photochemical degradation of some analytes may occur in soil exposed to sunlight. Some of these products such as 1,3,5-TNB are more volatile than the parent compound and escape from the soil more readily. These more transient compounds may not offer the consistent signature needed for reliable vapour detection. Analyses of numerous surface soil samples from minefields have revealed the presence of several different ERCs in the soil near mines. However, three of these compounds (2,4-DNT, 4-amino-2,6-DNT, and 2-amino-4,6-DNT) are found much more frequently than the other compounds9. Of these three, only 2,4-DNT is a realistic candidate for vapour-phase sensing due to the extremely low vapour pressure of the amino-DNTs. Researchers have estimated the concentration of ERC present in the air over landmines by assuming ERC adsorbed on soil particles and ERC in the vapour phase can attain equilibrium in the thin boundary layer of air near the ground. These estimates put the concentration of TNT present in the air over a landmine at three to six orders of magnitude below its equilibrium vapour concentration10. This places the concentration of TNT in the air over a landmine in the parts-per-trillion (ppt) to parts-per-quadrillion (ppq) range. In terms of mass of analyte per milliliter of air, the concentrations range from femtograms (10 -15 g) to low attograms (10 -18 g) per milliliter of air.

8 C. L. Grant, T. F. Jenkins, and S. M. Golden, “Experimental Assessment of Analytical Holding Times for Nitroaromatic and Nitramine Explosives in Soil,” SR 93-11, US Army Corps of Engineers, Cold Regions Research and Engineering Laboratory, June 1993. 9 T. Jenkins, M. Walsh, P. Miyares, J. Kopczynski, T. Ranney, V. George, J. Penningtion, and T. Berry, “Analysis of Explosives-Related Signature Chemicals in Soil Samples Collected Near Buried Landmines,” ERDC Technical Report, Cold Regions Research and Engineering Laboratory, 2000. 10 J. M. Phelan and S. W. Webb, “Environmental Fate and Transport of Chemical Signatures from Buried Landmine�Screening Model Formulation and Initial Simulations,” Sandia Report SAND97-1426, Sandia National Laboratories, June 1997.

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Because of the migration process of the chemical signature escaping from mines, pinpointing the location of a mine using trace chemical sensors is difficult.

3.2.4 KAMINA, electric nose

KAMINA, is a gas sensor chip developed by the Research Center Karlsruhe. The sensor is constituted of an array of semiconducting metal oxide elements. The conductivity of such elements is influenced by interactions of ambient gases with oxygen ions present in the atmosphere, on the surface of the elements. When an organic gas is present, its oxidation leads to a reversible decrease of the oxygen ions in the atmosphere and to the release of electrons by the metal oxide elements, which results in an increase of conductivity. When a gas releases electron acceptors, electrons in the metal oxide elements are immobilized and the conductivity of the elements lowers. Almost all gases, except noble gases, show an effect depending on the differences in the adsorption or the reaction of the gases at the metal oxide surface. A signal pattern typical of a single gas or gas mixture is established that allows the detection and quantitative assessment of gas components. To obtain gas-typical conductivity patterns the gas-sensing properties of the elements have to be differentiated; this is achieved with the temperature gradient method. With the temperature gradient method, heating elements providing inhomogeneous heating changes the surface temperature of the chip. Usually, the operation temperature is varied by 50 degrees across the chip, so that each sensor element shows a temperature slightly different to the adjoining one. Thus, both single gases and gas mixtures (groups of gases with a fixed composition, e.g. odours) contained in the air can create characteristic signal patterns. The data established in the measurement are evaluated by comparing them to signal patterns of gases or gas mixtures previously obtained in calibration runs.

The sensor is manufactured in this way: a monolithic metal oxide layer is partitioned by 41 parallel platinum electrode strips, these strips together with two temperature sensors are accommodated on a substrate of oxidised silicon of approx. 100 mm2. On its back, the silicon substrate is equipped with four meandering heating elements to provide the required operation temperature. So, at present, the gas sensor chip is equipped with 40 sensor elements, each one consisting of two strips, which measure the conductivity of the metal oxide in between them. The sensor is approximately 10mm2 and weights 250 g. The detection limit depends on the gas mixture and on the sampling arrangements, i.e. gas flow rate and volume above the micro chip array. Generally, for inorganic gases, the detection limit is 1 part per million (ppm). The response time depends on the gas mixture, on the operating conditions and on the sampling arrangements, i.e., on gas flow rate and volume above the micro chip array.

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If the sampling arrangement is optimised and concentration is greater than 1 ppm, the response time is around the order of some seconds. The estimated price is about 3000 euros11.

(Picture: (a) The gas sensor chip mounted in the housing. The electric contacts are made of thermosonically bonded gold wires. (b) The reverse side of the chip is equipped with four meandering

platinum elements for controlled inhomogeneous heating, http://ifiawww.fzk.de)

3.2.5 FIDO, chemical nose

FIDO is a chemical vapour sensor developed by Nomadics Inc., under the Defense Advanced Research Projects Agency (DARPA) Dog’s nose program for the detection of nitroaromatic explosives. The sensor is based on fluorescence detection; it measures the change in fluorescence intensity of a fluorophore when it interacts with the explosive analyte. In order to achieve the great sensitivity necessary to detect landmines by vapour sensing, the sensor uses novel fluorescent polymers specifically engineered for TNT detection by Massachusetts Institute of Technology (MIT). Conventionally, fluorescence detection measures an increase or decrease in fluorescence intensity, or an emission wavelength shift that occurs when a single molecule of analyte interacts with a single fluorophore. In order to amplify the signal produced by a single TNT molecule, individual fluorescent monomers are linked forming a conjugated polymer. When a polymer molecule with a conjugated backbone absorbs a photon of light, the backbone of the polymer can act as a “molecular wire,” enabling the propagation of the excitation along the polymer backbone. If the exciton (excited state electron) samples every receptor site in the entire polymer chain consisting of N repeat units before transitioning back to the ground state, binding of a single electron-deficient (i.e. electron accepting) molecule such as TNT to a receptor site of the chain, results in quenching of N repeated units. By comparison, if the entire polymer chain consisting of N repeated units were broken into N monomeric units, one binding event would quench only one of the repeat units, resulting in a emission reduction of only 1/N.

11 Dr. Joachim Goschnick, personal communication, November 2002.

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The here described amplification effect is the mechanism responsible for the high sensitivity of the sensor. The polymers produce an amplification of between 100 and 1000 as compared to conventional (monomeric) quenching mechanisms12. Thin films of these materials coated onto a suitable substrate form the sensory element. These films are engineered to be preferentially responsive to specific target analytes via three mechanisms. The first of these mechanisms is through steric constraints. Small molecules such as the target Explosive Related Compounds (ERC) fit into the cavities in the films, while larger molecules are excluded. The second mechanism providing selectivity is electrostatic complementarity between the polymer and target analytes. It is postulated that the polymers, which are electron-rich, bind reversibly to electron-deficient nitroaromatics through an electrostatic-type interaction. Receptor sites are specifically synthesised to be electrostatic mirror images of the target analytes. This further increases selectivity via enhanced electrostatic interaction between the polymer and target ERCs. Finally, additional selectivity is attained by matching the reduction potential of the analyte and the effective ionisation energies of the polymer. These factors are important since the ability to establish an energy trap is defined by the strength of the binding complex formed between the polymer and the analyte. When molecules of nitroaromatics bind to the polymers, the intensity of the fluorescence is greatly reduced due to the amplifying effect of the polymer. This reduction is proportional to the mass of quencher adsorbed by the films and is measured by the sensor system. A schematic of FIDO is shown:

(Drawn: http://www.nomadics.com)

12 M. Fisher, C. Cumming, Nomadics, Inc., “Detection of Trace Concentrations of Vapour Phase

Nitroaromatic Explosives by Fluorescence Quenching of Novel Polymer Materials”,7th International Symposium on the Analysis and Detection of Explosives, June 2001, Edinburgh Scotland, UK.

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A blue light emitting diode (LED) serves as the fluorescence excitation source. Light from the LED goes through a lens that focuses the beam and directs it onto an interference filter that transmits a narrow band of light centred at the excitation wavelength, ca. 370 nm. The filtered light then passes at normal incidence through two borosilicate glass substrates coated with thin films of the polymer. The glass substrates act as planar waveguides for light emitted by the polymer and define the sensor sample chamber. A significant fraction of the fluorescence couples into the substrates and is waveguided to the edges of the substrates. Additional light is reflected back into the waveguide paths by reflective coatings on three edges of the substrate. Emitted light is detected by a small photomultiplier tube (PMT) or avalanche photodiode.

The response of FIDO is almost instantaneous. Experiments were done to measure its time response to TNT in the headspace over a TNT contaminated soil sample held in a glass bottle. The concentration of TNT in the headspace over this sample was 56 femtograms (15 x 10-15 g) of TNT per millimetre of air, i.e. 6 parts per trillion. FIDO was able to detect TNT in this sample in less then 1 second with no sample preconcentration13.

FIDO can detect as little as 1 femtogram (1 x 10-15 g) of vapour phase TNT in 1 millilitre of air. This corresponds to a TNT concentration of 10 parts per quadrillion (ppq)1.

Comparing with other existing technologies, FIDO has very high sensitivity:

(Drawn: Nomadics FIDO versus other explosive sensors: High Performance Liquid Chromatography-Ultraviolet (HPLC-UV), Mass Spectrometer (MS), High Performance Liquid

Chromatography-Electrochemical (HPLC-EC), Thermal Energy Analysis (TEA), Mass Spectrometer-Chemical Ionisation(MS_CI), Airport Sniffers, Electron Capture Detector(ECD), Micro Electron Capture

Detector(µECD), Ion Mobility Spectrometer(IMS), http://www.nomadics.com)

13 M. Fisher, C. Cumming, Nomadics, Inc., “Detection of Trace Concentrations of Vapour Phase Nitroaromatic Explosives by Fluorescence Quenching of Novel Polymer Materials”,7th International Symposium on the Analysis and Detection of Explosives, June 2001, Edinburgh Scotland, UK.

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Presently, FIDO is still under development. The current size approximately is 10 *10*43 cm and the weight is 1.7 Kg. The estimated price is between US$ 2500-500014. As representatives of electronic and chemical nose type sensors, KAMINA and FIDO are compared here:

KAMINA (Tungsten chip) FIDO

Size 10 mm2 10*10*43 cm

Weight 250 g 1.7 Kg

Detection limit 1ppm 10 ppq

Response time > 50 s 1 s

Price(approximate) 3000 euros US$ 2500-3000

(Data’s: Dr. Joachim Goschnick, Dr. J. Sikes, 2002) In opposition to KAMINA, FIDO has been designed specially for explosive detection; this allows it to have a simpler human interface, meaning a simpler output. In fact, while a presence of explosive can be revealed by KAMINA only after a comparison between the output signal and the signal patterns of gases or gas mixtures previously obtained in calibration runs, using FIDO, a simple decrease in fluorescence under a certain value indicates the presence of a mine.

Moreover FIDO has higher sensitivity and lower response time. Although KAMINA could easy be fit on a mobile platform thanks to its small size and low weight, the actual better characteristics of FIDO make it preferable. Unfortunately, the size of the actual FIDO prototype does not allow the sensor to be fit on a mobile platform, without loosing agility. Because the ability of moving inside the thick vegetation is a basic requirement for the platform, FIDO cannot be fit, presently, on board of very small self powered devices. Unfortunatley, none of the sensors available on the market, by now, is suitable for a mobile sensor platform designed to move inside thick vegetation.

I hope that a smaller version of FIDO that can be fit on a Lizard-kind robot will be developed soon. I think that a robot with the features of Lizard would be very useful in landmines removing operations and in a lot of other applications such as explosive detection in security services (on airplanes, trucks, etc.).

14 Dr. J. Sikes, Product Manager Nomadics, Inc., personal communication, November 2002.

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3.3 LIZARD EARLY SOLUTIONS

While investigating the sensors available to locate landmines, some early solutions of Lizard were drawn and analysed. Lizard is a lightweight sensor carrier able to move inside thick vegetation inspired to the Australian blue tongue lizard. This particular kind of lizard is very common in Australia and present bigger body dimensions then European lizards, still compatible for dexterous motion within the thick vegetation.

(Picture: blue tongue lizard, http://members.shaw.ca/cloose/diet.htm) The big size of blue tongue lizard makes it a good reference for Lizard machine drowns. Until the mobile platform has dimensions comparable to the real animal and good agility, it can easy move inside thick vegetation. The design of Lizard machine has to take into account the simplicity requirements that make it really suitable to be used in poor countries, by untrained personnel. Lizard has to be: - low cost, when possible, parts should be available on local market; - with a simple design, in order to be built in the mine affected countries; - easy to use; - easy to program, programs could be available from Internet.

The bigger efforts in the solutions studied are put into the design of the mechanism to achieve forward motion. In all the solutions proposed motion is achieved by a sequence of actions leading to a sequence of machine states. This is very easy to be controlled, e.g. using Programmable Logic Controller (PLC), and to be monitored in order to know the trajectory the machine is following without the need of expensive devices as GPS. No paws or arms are used in order to reduce the possibility to get stuck into the vegetation. The machines go forward by extending and contracting their bodies.

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Only simple actuators are used, such as pneumatic cylinders and stepper motors. They can be found easy everywhere and are cheap. The first solution proposed is :

The machine is mainly constituted by two parts: the nose, the yellow cone part, and the back, the orange part. During motion the nose is at the front, while the back is at the back. The machine uses 3 actuators: - 2 pneumatic cylinders, colored in blue. - 1 stepping motor, colored in green. The pneumatic cylinders give the motivation power to go forward. The stepping motor rotates the nose: when the nose surface faces the ground, the friction generated allows the nose to adherence to the ground and, during a step forward, the cylinders can contract; when the nose surface faces upward, the nose it’s free to move forward and, during a step forward, the cylinders can extend. One step forward is achieved by a sequence of 5 actions:

a)

b)

c)

d)

e)

1 step

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Where a dark color means that the actuator is active. The sequence of actions that need to be performed to obtain one step forward is: a) Stepper motor rotates; the nose it’s free to move on. b) Cylinder extend; the nose move forward. c) Stepper motor rotates; the nose adherence to the ground. d) Cylinder contract; the back moves forward.

The last state is the same as the first one. The machine is ready to move another step forward. This machine has too limited mobility: - Although there are 2 pneumatic cylinders the machine is not able to move aside. - The mobility in the up and down direction is limited to a slope with the same angle as

the nose angle. The machine has only one degree of freedom in the forward direction and a limited degree of freedom in the up and down direction. The second solution investigated has better mobility then the first one.

The machine is mainly constituted by two parts: the tongue, the green part, and the back, the pink part. During motion the tongue is at the front, while the back is at the back. The machine uses 3 actuators: - 1 pneumatic cylinders, coloured in blue. - 1 stepping motor, coloured in pink. - 1 stepping motor, inside one wheel. The pneumatic cylinder gives the motivation power to go forward. While the cylinder extends, the green wheels rotate together with the segmented tongue. The first tongue segment is solidly connected to the wheel tree while the other segments are connected each other and to the first segment by revolute joints. In this way, while the cylinder extends the tongue rolls off over the ground surface.

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The pink stepping motor rotates the cylinder and the tongue, allowing movements on the right and left direction. The stepping motor inside the wheel allows the tongue to go back in the initial position after one step forward. One step forward is achieved by a sequence of 4 actions:

1 step

a)

b)

c)

d)

Where a dark color means that the actuator is active. The sequence of actions that need to be performed to obtain one step forward is: a) Cylinder extend; the wheels rotate and the tongue rolls off. b) Cylinder contracts; the back move forward. c) The stepper motor inside the wheel rotates; the tongue rolls back. The last state is the same as the first one. The machine is ready to move another step forward. Although this machine presents some advantages over the first one proposed, it has a lot of limitations as well. The main advantage is the capability to move forward over any kind of ground surface. In fact while the tongue rolls off, it lays down over any shaped ground surface and sticks to it. The cylinder can, then, contracts moving the beck forward. The limitations as the advantages are due to the tongue.

)

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The space occupied by the tongue retracted is too much considering that the machine is designed to move inside thick vegetation. The pink stepper motor can not realistically move the wheels on the right or left. Moreover both of the solutions proposed present problems due to the transmission of pneumatic air through a long distance via umbilical wire.

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4 SECOND IDEA: WORM

• Investigation of other sensing techniques

• Second idea: WORM

• Review of existing machinery

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4.1 OTHER TECHNIQUES

“If Maometto doesn’t go to the mountain, the mountain goes to Maometto.”

Because none of the sensors available on the market is suitable for a mobile platform able to move inside the thick vegetation, other explosive detection techniques need to be investigated. Looking at the systems currently used by demining organizations throughout the world, we can see that beside the commonly used demining methods there is a special one called REST, which consists in a manual approach used in combination with trained dogs, adopted by two important organizations, Mechem and Norwegian People Aid (NPA). Remote Explosive Scent Tracing (REST) is the process of collecting target substances (usually traces of explosive vapour) from the surface of a mine suspected area, using filters that are subsequently analyzed by specially trained sniffer dogs. Using this technique, the explosive trace sensor, a dog nose or an artificial odour and vapour sensor, does not have to be swept over the ground of a suspected contaminated area. Samples of air and dust are collected from the headspace over the minefield and then transported to the sensor. While introducing a dog inside the thick vegetation or fitting an artificial vapour sensor on a mobile platform is not realistic, to fit scent trapping filters on a mobile platform is possible. The filters used in REST process are small (cylinders of 54 mm height and 25 mm diameter) and light (they are made by hard plastic and they are designed to contain only air and dust particles).

4.2 REMOTE EXPLOSIVE SCENT TRACING (REST)

The REST method was developed by the South African government at the end of the 1980s, in the hands of Mechem Consultants, a division of Denel (Pty) Ltd. The method was first referred to as MEDDS (Mechem Explosives and Drug Detection System). It has subsequently also been called EVD (Explosives Vapour Detection) by NPA-Angola, and Checkmate in the USA.

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The primary purpose of this method was to detect drugs, explosives and weapons at border crossing checkpoints. The system was utilized at the many checkpoints in South Africa at the borders with Swaziland and Lesotho, but also at the main border crossings to Mozambique, Zimbabwe and Botswana. The first time REST was used to carry out a complete demining survey contract was at the Cahorra Bassa Power Transmission Line. The contract was for Hydroelectricidade de Cahorra Bassa, Mozambique, in 1994. This was the very first time contracts for demining and survey were carried out by detecting and analysing vapours from the area to be surveyed. The results showed that only 10% of the total area to be surveyed had to be cleared of mines. At the moment, the REST technique is used by Mechem and Norwegian People Aid (NPA) just for mine clearance operations on roads. The whole process can be divided in three stages: - Stage one, involves the sampling of explosive traces near the road surface.

Typically samples are taken using a portable sampling machine that can suck air through filter cartridges fitted in plastic tubes. The tubes are placed at the end of the suction pipe. The filter cartridge is made from a coiled polyvinyl chloride (PVC) netting which has the ability to attract TNT molecules. Usually two filter cartridges are used at the same time at the end of the same suction pipe. The filters are replaced after 300 meters (Mechem) or 100 meters (NPA) of steady walk with the sampling machine. The suction pipe is systematically moved side to side in a 2-4 meter wide pattern. When the filters are changed, they are marked and stored in plastic tubes, each filter and tube representing a particular stretch of road. The sampling operation can be done by hand or with vehicle mounted vapour-sampling machines. In the second case the process is faster but less accurate. In the first case safety has to be guaranteed to the operator. Usually this is achieved by driving a mine proof vehicle, Casspir or Wolf, up the road before samples are taken. The tracks created by the vehicle wheels are considered to be safe to walk in due to the high pressure applied to the ground from the vehicle.

- Stage two, involves the analysis of filters. This is done using specially trained sniffer dogs to analyze the filters and indicate if some of them contain traces of TNT or other explosive compounds. The filters are placed in holders or stands and typically 6-8 stands will be placed in a row. Each stand contains two filters, each one collected from each side of the road stretch. A dog will seat near to a sample if it contains traces of TNT or other explosive substances. Usually several different dogs are employed at the same time to ensure satisfactory results. If one or more dogs have indicated an explosive, the filter would be considered as possibly TNT contaminated and the relative stretch of road will be rechecked.

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- Stage three, involves the clearance/area reduction of the minefield. Filters with explosive traces represent stretches of road that need to be rechecked for mines. Normally the rechecking operation is carried out using free running dogs to pinpoint the exact location of mines. Filters with no explosive trace represent mine free road stretches. These road stretches will be considered safe without further need for mine clearance.

REST as a system is not a method for demining, but rather a system for eliminating areas of ground suspected to contain mines where no scent or target substances of explosives can be found. The system has proven to be very cost-effective, as it greatly reduces the areas to be demined. Typically between 90 and 97 % of a total road length can be eliminated without further requirements for mine clearance .

There are still problems to be solved related to MEDDS/EVD technique. The problems arising during the sampling stage are mainly related to the filters; the concentration of strategic scent substances attached to soil particles is 1 million times higher than in the air directly over the ground. However, if the filter is subjected to excessive volumes of dust and soil particles, it will clog and will not be able to collect further trace substances from the ground. Therefore the suction pressure and the frequency of changes of filter cartridges have to be calculated carefully. The maximum height the filter has to be swept over the ground has been specified as 20 cm and it is recommended to be passed near to the vegetation, where the concentration of scent substances are believed to be higher.

The problems arising during the analyzing stage are related to dog training and to air conditions around the filter during investigation; in fact the TNT/DNT concentration in the filters is often marginal and difficult to be detected by a dog under some circumstances. It would be very important to find a way to manipulate substances in the filter in order to cause a chemical reaction with new and easy detectable scent. From the beginning the REST system has principally been used to search roads during demining operations. “Obtaining EVD samples from a minefield rather than a road is a problem that we have already identified and it is unsolved”1.

I believe that a mobile system carrying filter cartridges for REST-vapour sampling, able to move inside the thick vegetation on uneven terrain, could give an important help to mine clearance operations by reducing the time needed to investigate suspected contaminated areas for landmines.

1Ian G. McLean, Geneva International Centre for Humanitarian Demining, personal communication, November 2002.

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4.3 AUTOMATING THE SAMPLING PROCESS

The sampling process is the most important stage. When it is properly done the time needed for future work is drastically reduced. Moreover the sampling process is very tedious and doesn’t require especially skilled personnel. The operator has only to walk along the mine proof vehicle trucks holding the sampling machine, changing filters at certain intervals stated by the demining agency. Comparing to the job of manual deminers, who have to pay great attention to the metal detector signals in order to recognize between false alarms and real mines, the sampling job is much easier. However, as almost all the operations related to mine clearance, sampling is very dangerous. Many aspects of the sampling process make it suitable to be automated. Automating the sampling process would be an important achievement. Moreover, up now, sampling is only done on roads already cleared from vegetation. Removing the man from this operation would allow being able to sample also uneasy accessible areas such as uneven terrain covered by thick vegetation, suspected to be minefields.

4.4 FROM LIZARD TO WORM

Due to their small size and lightweight, sampling filters could easy fit into a mobile platform inspired to lizards. The mobile platform can easy get in and move inside thick vegetation keeping filters near to the ground. New filters could be drawn in order to catch more dust particles, which contain more TNT then air particles and allow a better recognition of contaminated areas by trained dogs during the analysing process. For example new filters looking like “curlers” could be useful:

(Filter scheme: the proposal)

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If they are free to rotate while the platform is moving because of the friction between the filter and the ground, the brushes will move off the dust particles from the ground surface to the filter.

A big problem arising using a lizard inspired platform for sampling is due to the need to change filters. After fixed intervals, filters have to be removed, sealed and new filters have to be put in place. The path checked from each filter has to be recorded and the filter has to be changed only when it has passed over the fixed length of path. The filter changes can be operated automatically or manually. In the first case complex equipment need to be fixed on board: - mechanism to change filters - sensors to know the path length already sampled - covers for filters - new filters In the second case, after one sampling interval, the machine has to come back to the start point, where the operator can change the filter manually, and go back to the point where it stopped sampling to start sampling again. Although the machine can just be pulled back to the start point using the umbilical wire, it needs to carry sensor equipment to find the point at which start sampling again. In both of the cases, the machine design is very complex. A mobile platform carrying sampling filters does not satisfy the basic requirement of simplicity and therefore is not suitable to be operated in poor countries, in a short period. A way to avoid the complex operation of changing filters, is to provide the lizard inspired platform with a long tail containing filters; in other words to project a long worm. By this way, the head of the worm can contain the mechanism needed to go forward inside the vegetation and the tail can contain filters at a fixed distance one from the other. While the head goes forward, the tail follows after. When the head had reached the most remote point it can reach, the tail lays down all over the distance covered by the head from the starting point to the arrival point. The filters can, then, be activated while the tail is pulled back and deactivated when the last filter introduced has reached the starting point. In this way, each filter samples the same path length and all the path is sampled when the last filter introduced is pulled back. The tail will be pulled all back until the head come back as well. The worm will be ready to check another path.

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filters

head

Path length sampled by the first filter

Pulling back

(Drawing: scheme of tail sampling of a straight path)

4.5 DIRECTIONAL DRILLING MACHINES

Before starting to project a new machine, it’s always useful to review the existing technologies. Time it’s worth spent on improving existing machines then on devicing new ones from the beginning. Under suggestion of Prof. James Trevelyan, I had the possibility to visit a directional drilling machine operating in Perth, Western Australia, from the Western Power company. Directional drilling machines are very simple and effective machines and they can be adapted to work for humanitarian demining. Directional drilling machines are used to drill holes in the ground. Usually holes are used to host electricity or telephone cables. Holes have very small diemater and can be very long. The technique used to drill holes is to push, while rotating, a steel rod into the ground with a pushing machine, to insert another rod into the machine and push again the first with the last one introduced and so on. The rods are connected by screwing one into the other. The basic elements needed in directional drilling are: - the power source or motor, - a bit and a set of rods, - a drill head - a mounting platform - assorted equipment which includes small tools for coupling or uncoupling the rod

string. The drill head and the mounting platform will be later referred to as pushing machine.

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Power source. A power source or motor is required to push the rod or to provide rotary motion to the drilling head. For sake of availability compressed air or hydraulic motors are preferred. A drive train, which consists of gears or hydraulic pumps, is used to convert the power supply to speed and torque for hoisting and rotating the drilling equipment Drill head. The primary functions of the drill head include rotating and hoisting or pull down the drilling tools. A solid drill head-sliding table can be moved forward or back to permit removal of the drill rods. Drilling tools are connected to the drill head by a fluted or square thick-walled pipe or kelly rod which runs through the drive head. The kelly is designed to move up and down through the drill head as it is rotated. Torque is applied to the kelly through bevel gears in the drive head. The speed of rotation varies over a wide range. When the drive head has been moved a distance equal to the stroke of the hydraulic cylinders, which is usually 0.6 to 0.9 m of travel, the kelly is unchucked, the cylinders are raised, and the kelly is rechucked for another drive.

(Picture: drill head, www.comacchio-industries.it )

Mounting platform. It permits levelling of the drill head before drilling and to prevent movement out of alignment during drilling operations.

(Picture: mounting platform, www.comacchio-industries.it )

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Remote Control drill. Drilling by remote control methods has received much interest. For remote control drilling operations, air cylinders or electric motors are attached to the operating levers of the rig and to the remote console. The function of the remote control system is to advance or withdraw drilling tools or samplers from the borehole. Other drilling functions such as making or breaking the drill string must be performed by the crew at the rig. Some automatic solutions have been proposed for the rods loading and unloading. In figure a low degrees of freedom robot has been designed for this tasks: it takes the rods from a simple buffer, that offers the rod in the pick, lowest, position by gravity. During the pull, disassembly, phase the robot pick the free rod from the table and place it on the top of the buffer.

(Drawn:PMAR lab, University of Genova)

Drill bits. A variety of bits are available for drilling operations. The types of bits include those for chopping and percussion drilling in soils and soft rocks and those for rotary drilling in soils and rocks. Drill bits may be made of hardened metal, carbide alloy, or diamond.

(Picture: drill bit, PMAR lab, University of Genova)

BUFFER ROBOT

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Drag bits. Drag bits, such as fishtail bits, bladed bits, replaceable blade bits, and carbide insert bits, can be used for drilling soils and soft rock. For softer materials, larger and fewer teeth are used.

Rods and coupling. Rods usually are hollow cylinders that present at each end some device ore features allowing the assembly and disassembly with other identical rods to make a rod cue of suitable length.

(Drawn: rod and coupling, , PMAR lab, University of Genova)

4.6 WORM FEATURES

Directional drilling machines are very simple (modular) and effective machines and they can be adapted to sample air from suspected mine affected areas, within REST method. The same pushing machine used in directional drilling can be used to push rods contatining filters into the thick vegetation over the ground surface.

Rods similar to the ones used in directional drilling can be used. They only need to be adapted to contain sampling filters. Filters are very simple: they are small cylinders made by hard plastic, usually fitted at the end of a suction pipe where the air is sucked. Sampling filters can be inserted into modules located inside the rods. Modules need to be controlled in order to expose filters to the ground surface or to cover them. The suction force can be supplyed from a station on the pushing machine through all the rods, or from fans directly fitted over each filter. Sampling process can be done while the rods are pulled back, once the number of rods introduced over the minefield has reached the maximum. The filters are activated as soon as the rods start to be pulled and deactivated when the last rod introduced is totally retracted.

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In this way, each filter samples the same path length and the entire path is sampled when the first filter is pulled back. Joints are introduced to connect rods. In this way, rods can follow better the ground surface and therefore sample air and dust particles nearer to the ground profile.

x

y

In order to make the head going forward also when there is an obstacle on the way or the vegetation is particularly thick, it’s necessary to limit the mobility of the joints connecting one rod to each other. In this way when a joint reaches the maximum mobility, the force applied to the first rod is transmitted to the second rod connected by the joint and then to the following rods, allowing the entire worm to go on.

x

y

In order to make the machine as simple as possible revolute joints leaving only one degree of freedom in the up and down direction (around z axis) connect one rod to the other. Joints do not leave any mobility in the right and left direction (around y axis). In this way worm follows straight lines and only small deviations due to rod elasticity are allowed, in the (x, z) plane. The machine is more rigid and the pushing force is better transmitted from the last rod introduced to the head. Two actuators are introduced: a motor driving the joint connecting the head module to the following one, called head joint, and a rotating drilling motor on the head of the head module, to allow penetration in very thick vegetation as bamboo’s. Two sensors are introduced: a GPS fitted on the head module to allow head position to be known at all time, and a video camera fitted on head rod to allow the motor driving the head joint to be tele-controlled by an operator at the minefield border. A rectangular minefield can, therefore, be sampled pushing Worm along parallel straight lines. Where Worm cannot go further, since there is a big obstacle on its way, it stops. Only the area sampled will be possible object of area reduction process. The regions not sampled, because unaccessible for Worm, will need to be checked for the presence of landmines with traditional methods or sampled from another starting point.

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At the end of the sampling process a map of the sampled area will be done, as shown in the figure below.

(Drawing: sampled area map)

Where the yellow colour indicates the sampled area and the red colour indicates the area not sampled.

Worm is an hyper-redundant mechanism. It is adaptable to the terrain because of its chain reconfiguration, it is robust and modular. Its configuration is biologically inspired (worm oriented) realised by a serpentine mechanism. It is semi-autonomous: its forward movement and head tilting are remote-operated but terrain adaptation is passive. The dexterity covers only the progress plane. The on-board sensors and equipment are limited as much as possible to comply with cost and robustness constraints. Its locomotion is achieved by adapting the natural snake motions to the multi-segment robot configuration: the robot has only one possible gate that results in a forward rectilinear motion without lateral ondulation ( changes of direction are not allowed). In this motion the segments displace themselves as waves on the vertical plane. Worm is intended for direct collaborative work with a human operator. It can be classified into the class of collaborative robot cobot2. To complete the sampling task, the cobot and human share in the determination of its motion. The cobot, by design, cannot move on its own, it is inherently passive, which confers a degree of safety to the operation. The human operator will be responsible for producing the forward motion of the cobot and the tilting of the head by applying forces and moments through telemanipulation, according to some given rules. I think that Worm can effectively help humanitarian demining. Using worm in REST technique, the time needed to investigate suspected mine affected areas for mines can be drastically reduced. It’s the long time needed to clear land from mines that makes landmines such a big problem. 2 R. B. Gillespie, J. E. Colgate, M. A. Peshkin, “A General Framework for Cobot Control”, Ieee Transactions On Robotics And Automation, Vol. 17, No. 4, August 2001 391

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Reducing the time needed to clear lands from mines, means giving back the country to the people and allowing their economy to start again earlier. Worm satisfies all the requirements that make a machine suitable for use in real minefields. It’s a very simple machine with very few electrical components. It’s easy to run and to maintain. Moreover it’s low cost and parts are easy to find on the local market. The main disadvantage Worm presents is the low agility. Worm is able to follow only straight lines; this makes it unusable in areas with many obstacles such as forests. The low agility it’s due to the extremely simple design. A simpler design has been preferred to a more complex but more flexible one. The choice was made considering two important factors: - The areas that have been mined were strategically important at the time they have been

mined. Usually, areas are important if they are accessible to people; in fact, typically mined areas are: agricultural lands, residential areas, confrontation lines that divided military factions as riverbanks and abandoned industrial sites. In these areas, usually, at the time they have been mined, there were not many obstacles, such as trees. Moreover the vegetation, overgrown in years after the areas have been mined, is mainly constituted by bush, thorny bush, plants with small diameter and bamboos, depending on the climate; this kind of vegetation can easy be breached by Worm just by pushing it or by pushing and drilling.

- Low cost devices are easier to be well accepted in poor countries.

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5 WORM: FEASIBILITY STUDY

• Worm kinematics and dynamics

• Worm model in ADAMS

• Use of model

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5.1 WORM KINEMATICS AND DYNAMICS

5.1.1 KINEMATICS

Worm is an hyper- redundant, re-configurable, planar mechanism. The reference model of Worm is given in figure. The re-configurability concerns both the adaptability to the terrain and the number of the actual segment of the operative chain. This second characteristic, if considered off-line, is peculiar of modular robotics but is very peculiar if it is working on line. A generic chain of n segments is considered. Each segment is a module. All the modules have identical lenght l.

x

Y

R1

P

R2

RiRi+1s

θ1

θi

θn-1

The origin of the coordinates coincides with the pushing machine end point and is represented by a prismatic joint: s indicates the free coordinate at this joint. All the other joints are revolute joints around an axis parallel to Z. The free coordinates are called θi and are numbered starting from the head. These coordinates represents the joint relative angle, as indicated in figure. The position equation is:

1 1

1

1 1

1 1

( ) cos ( )

( ) sin

n n

ji j i

n n

ji j

x n l s t

y n l

θ

θ

− −

= =

− −

= =

= +

=

∑ ∑

∑ ∑

where,

x(n) and y(n) are the coordinates of the head end when the nth segment is added.

0<s<l.

θmin< θi< θmax. Obviously the maximum and minimum values of x(n) are:

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xmax(n) = (n-1)l+s xmin(n) = (n-1)l cos [max(θmin , θmax )]+s The above equations represent the direct kinematics model that links the external

coordinates [x.y]T to the internal generalised coordinates [θ1 ,… θi,… θn-1, s]T.

( )1 2 1.. .n n

xf s

yθ θ θ −

=

The Jacobian matrix of the worm with n segments is:

1 1 2 1 1

1 1 1

1 1 2 1 1

1 1 1

sin sin ... sin 1

cos cos ... cos 0

nn

i

n n n n n

j j ji j i i j i j

n n n n n n

j j ji j i i j i j

fJq

l l lJ

l l l

θ θ θ

θ θ θ

− − − − −

= = = = =

− − − − −

= = = = =

∂=

∂

− − −

=

∑ ∑ ∑ ∑ ∑

∑ ∑ ∑ ∑ ∑

during the pushing phase. The velocity of the first segment depends on the pushing machine operability. To work with constant velocity a ramp thrust is applied. In this case each pushing cycle is composed by a ramp of applied force followed by a rest period necessary for rod loading and joint assembly. The corresponding position is represented in the same figure.

t

t

1 cycle

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5.1.2 DYNAMICS

The model used in dynamics is a n-link model as the one used for kinematics. All the revolute links, other than the first one (head) are passive. Mass, length, moment of inertia of each link are m, l, and J, respectively, and the centre of gravity is placed at the middle of the link; (x , y ) and (xi , yi) denote position of the head and position of the i-th link respectively. Only essential equations are shown.

)+ + + =M(q)q C(q,q)q D(q)q G(q Q where:

[ ][ ]

1 1

2

... T nn

T

s R

F R

θ θ

τ−= ∈

= ∈

q

Q

where,

q is the internal generalized coordinates vector, M is the inertia matrix, C is a centrifugal and Coriolis coefficient matrix, D is a frictional coefficient matrix. G is the gravity term vector

The above vectorial equation represents the dynamic equilibrium of the n rigid bodies composing the kinematic chain. The equation is non linear in q and dynamically coupled. Moreover the model of this underactuated, hyper redundant mechanism has to be solved taking into account the contact constraint disequations. The classical method of Lagrange multipliers can be adopted, considering a new generalised coordinates vector including the lagrange multipliers. The number of scalar equations (and of variables) encreases each time a new segment (and a new contact constraint) is added. Summarising, even admitting the simplifying hypothesis of rigid bodies, the model cannot be analitically solved, presenting difficulties due to many factors: - the high non linearities of centrifugal, Coriolis, gravitational and contact forces: - the dynamics couplings; - the application of intermittent discontinuous thrusting force by the pushing machine; - the varying number of model equations that can be very high for a long worm. To overcome these difficulties a different approach will be considered and a molti-body simulation tool will be used.

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5.2 MODEL IN ADAMS

In order to study Worm behaviour in different situations, a parametric model will be created using ADAMS software, a multi-body simulation tool.

5.2.1 ADAMS working principles

ADAMS is a multi-body simulation tool; is a modelling and simulating environment that lets you:

-Build and simulate multi-body models of mechanical systems And

-Analyse multiple design variations until the optimal design is found.

In order to understand better ADAMS working principles is necessary to define some concepts. We define: System, the part of the space object of studying. A system is constituted by Objects interacting one with the others, by performing Actions. At each moment a system is defined by its State (the set of State variable values). Model, the system equivalent to the real system in the field of function under studying. In order to pass from the system to the model is necessary to make approximations. A model behaves according to physical laws, logical-mathematical relations. Simulation, the progress in time of the mathematical model of the system. The mathematical model of the system is constituted by logical-mathematical relations. A simulation is a sequence of States in time.

Three types of entities constitute a multi-body system: Bodies, Constraints and Forces. A multi-body system is a model. The simulation performed by ADAMS/Solver on a multi-body system let us know the trajectory, speed and acceleration of the bodies belonging to the system, and the reaction forces acting on the system.

When a body is created, by defining its geometry, a local reference frame is automatically generated. In ADAMS the local reference frame is called Local Part Reference Frame (LPRF). Body position is located by the vector going from the world reference frame origin to the LPRF origin and by the angle by which the LPRF x axis is rotated with respect to the world reference frame x axis. In 2D, the vector is:

x

y x

y

World

LPRF

φ

i ri

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The vector locating the i body position is called generalized vector and is indicated with iq :

i

i

x

i y

i

rq r

= ϕ

ADAMS uses geometry to determine mass and inertia properties of the bodies. Once a body is created, by defining its geometry, and a material is assigned, its mass and inertia properties are automatically calculated by ADAMS.

Bodies are connected one to the other by constraints: each constraint is expressed by a number of scalar equations equal to the number of degrees of freedom the constraint removes. The system of equations representing system constraints is a system of algebraic non linear equations, with the generalized vectors locating the centre of gravity of each body belonging to the mechanical system as unknowns. The system of equations representing system constraints is indicated with:

( ), 0q tΦ =

The process for finding trajectory, speed and acceleration of the bodies belonging to the system, and the reaction forces acting on the system, performed by ADAMS /Solver during simulation is here schematically reported.

In the scheme,

- q is the generalized vector containing all the generalised vectors locating the centre of gravity of each body belonging to the mechanical system with respect to the world reference frame. -Q is the generalized vector containing all the generalised vectors representing the forces and the torques acting on each body. The vector Q can be considered sum of two vectors, AQ , representing the active forces and torques acting on the system

and RQ , representing the reactive forces and torques acting on the system.

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5.2.2 Setting up the model Worm behaviour in different situations is analysed. Worm behaviour is known once analyses on the model are performed. The system to be modelled is constituted by: ground, Worm and vegetation. Ground is simply modelled as a body with parametric surface. Worm rods are modelled as hollow cylinders and the connections between them as revolute joints; their limited mobility is modelled by torsion springs acting on them. It’s not possible to model the pushing machine as it really works; in fact no bodies can be added to the model during simulation. Therefore all the worm modules that will be pushed one after the other until the head module would have passed all over the strip lenght, have to be in the model from the beginning. A long flat surface is added to the modelled ground

q*

nF independent equations

q

dq/dt

M QAg

ddq/ddt

t = t0ngl initialcondition

t = t0ngl initialcondition

ngl conditionfrom numericalanalysis

ngl conditionfrom numericalanalysis

t = t0 + Dt

Motion equations and Acceleration analysis[M]ddq/ddt - QR = QA

[F,q (q)]ddq/ddt = g(nq + nF independent equations / nq + nF independent unknowns)

Calculations ofg=g(q,dq/dt, t)[ M(q,dq/dt) ]QA = QA (q,dq/dt, geometry, dynamics characterists)

Speed analysis[F,q (q)]dq/dt = F,t(nF independent equations)(nq unknowns)

Position analysisF (q,t) = 0(nF independent equations)(nq unknowns)

Redundant constraints removalcalculation of [F,q (q*)]factoring of [F,q (q*)]

Assembly analysis

INPUTbodiesconstraints, forcesinitial conditions

t<tfin

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surface in order to host all the Worm modules that wait to be pushed inside the pushing machine. The pushing machine is simply modelled as a prismatic joint and a force applied with constant direction. The prismatic joint, defined between the last Worm module and the ground, costrains the force applied to the last Worm module to be horizontal over the ground surface. Vegetation is implicity modelled by two different forces: a friction force occuring during contact, between modules and ground, and a constant force acting on the head rod in direction opposite to the movement. Therefore, the entities involved in the model are: Bodies Forces Constraints Ground Contact Revolute joints Worm rods Pushing machine Prismatic joint (Pushing machine) Vegetation (Vegetation) Every situation is defined once all variable values are stated. Variables involved in the model include bodies, constraints, and forces characteristics that vary from situation to situation. Variables can be divided in In variables and Out variables, referring to the variables characterising Worm as Out variables and to the variables characterising the ground Worm is going to sample as In variables. Where, the variables reported on the left hand side are IN variables. Beside the understanding of Worm behaviour in different situations, the model will allow, also, to verify if Worm behaviour in a specific situation is correct; it can, therefore, be introduced into an iterative cycle to determine optimum Out variable values on each type of minefield, characterised by a specific ground surface and a vegetation type. In order to obtain general results from simulations of Worm behaviour in different environments, the possible In variable values have been classified. In this way, when similar terrain are analysed, the same model can be reused. Because mines have been spreadly used throughout the world, minefields are present in many different countries and they might vary very much one from each other. Many combinations of ground surface and vegetation type are possible. Unfortunately, while the vegetation covering a minefield can be seen and easily classified in order to be introduced into the model, most of the times, the ground surface is unknown

Rod length Max mobility angle Pushing force

Ground surface Vegetation type

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until the work is completed. The areas that will be sampled by the machine are covered by thick vegetation and might not have been walked in for years. Therefore exact data’s related to the ground surface of each minefield can not be introduced into the model and approximated data’s have to be used instead. The ground surface profile of the field that need to be checked can be assumed to be similar to the one of the sorrounding areas. The ground surface is characterized by two variables: the maximum hight of little edges over the horizontal, that depends on the obstacles present, such as stones and debris, and the frequence of the small edges, that depends on the climate. The former is deducted from the use people were used to make of land before it was mined. From a database of minefields cleared in Afghanistan from 1990, already analyzed from Chris Bartley1, land uses of minefields are classyfied as: agricultural, grazing, irrigation, residential, and road. The maximum height of little hills associated to these land uses are considered as:

Land use Little edges (rims and

dithces) Max height

Agricultural little stones, roots, fallen

branches 0.5 m

Grazing little stones 0.15 m Irrigation big stones, debris 0.6 m Residential walls, debris 1 m Road little stones 0.3 m

The frequence of small edges on the ground surface can be considered function of the climate; in areas where rains are heavy, the frequence of small edges it’s likely to be low because rains bring small objects, such as fallen branches, from the surface, under the ground; where it is windy, the frequence of small edges it’s likely to be high because wind moves the small objects until they get in contact with other objects and the wind blow is not strong enough to move both of them. From databases of minefield pictures collected by Adopt-A-Minefield2 and by Prof. James Trevelyan throughout the world, the overgrown vegetation over suspected contaminated areas can be classified as: - Grass - Bush - Thorny bush - Plants - Bamboos

1 C. Bartley, J. Trevelyan, “Modelling Minefield Clearance Data Statistical Analysis of Minefield Clearance Data”, Mine Action Information Centre (MAIC), James Madison University (JMU), 2002.

2 http://www.landmines.org.uk, Adopt-A-Minefield, program of the United Nations Association (UNA) Trust.

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The vegetation is modelled by two different forces: a friction force occuring during contact and a constant force acting on the head rod in direction opposite to the movement. The friction force will be unique for all the models that will be simulated while the constant force acting on the head rod will have different values in the diferent cases which will be analyzed. In order to consider realistic values for the forces modelling the vegetation, practical experiments were done on real fields similar to the ones found in the minefield pictures. Reference pictures for different vegetation types are:

(Afghanistan, http://www.mech.uwa.edu.au )

(Croatia, http://www.mech.uwa.edu.au )

GRASS

BUSH

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(Cambodia, http://www.mech.uwa.edu.au )

(Cambodia, http://www.mech.uwa.edu.au )

(Cambogia, http://www.mech.uwa.edu.au )

Environments similar to the ones present on real minefields, shown in the pictures, were found in a big garden in Genova.

THORNY BUSH

PLANTS

BAMBOOS

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The reaction forces exerted by different types of vegetation found in Genova have been calculated.

The force values, which will be considered to model the different overgrown vegetation types present in minefields, are:

Vegetation type Force acting on head rod

(diameter: 8 cm) [kg] Force acting on head rod (diameter: 3.5 cm) [kg]

Grass 0.6-0.8 0.5-0.6 Bush 4 3 Thorny bush 4.5 3.5 Leaves 5 3 Bamboos + Plants Motion stops Motion stops

5.3 MODEL CHOICES

In order to use the model for the feasibility study, it’s necessary to make it realistic first. IN variable values corresponding to the easiest case were assumed and the basic behavior of Worm was modeled. While Worm and its environment were modeled, a lot of problems arose and choices between different solutions have been taken. Every time a problem arose, a less realistic solution, than the one first considered, has been adopted. The considerations, which leaded to every choice taken, are here reported.

5.3.1 Bodies

The model adopted for Worm modules is very simple. Each rod is represented by a hollow cylinder. The rods are equal, with same length and diameter. The material chosen for the modules is steel. The ground surface was first modelled as a continuously varying surface. The only way to build such a surface in ADAMS is to extrude construction geometry. Because contact can be defined only between solids, the construction geometry to be extruded, representing the ground surface, has to be closed. Because it’s not possible to create a closed spline, a drawn has been imported from Pro/ENGINEER. Using Pro/ENGINEER it’s possible to draw any kind of surface. Unfortunately, the contact defined between a complex surface such as one imported from Pro/ENGINEER and another solid is very complex and long to simulate. This is due to the high number of points that define geometry in Pro/ENGINEER; at each one of these points, contact is calculated.

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In order to avoid long calculations, a simpler surface was drawn extrapolating a polyline directly built in ADAMS. The geometry created in this way is less realistic but from the point of view of the simulation little changes. In fact, modules are rigid and the best they can follow the ground surface is by laying tangent to it in each point. A polyline tangent to a spline representing the ground surface line can always be built.

(Image: bodies in ADAMS model: terra_dolce_dipiu)

5.3.2 Contact

In ADAMS the contact normal force magnitude is function of the penetration between the two bodies that get in contact. If there is no penetration there is any contact force. Two models for contact force calculations are available: - Impact function model - Restitution function model

The general form of the Impact force function is:

max max( ) ( , , , , ) dgFn Step g d cdt

= ⋅ + ⋅e k g 0 0

where: g, represents the penetration of one geometry into another. dgdt

, is the penetration velocity at the contact point.

e, is a positive real value denoting the force exponent.

maxd , is a positive real value specifying the boundary penetration to

apply the maximum damping coefficient .

maxc , is the maximum damping coefficient.

k, is a stiffness parameter, modeling the elasticity of the surfaces of contact.

Step (A, x0, y0, x1, y1), is a function that returns an array of y values, on a step

curve, corresponding to the A array of x values.

x0, is the value of x at which the step starts ramping from y0 to y1 and

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x1, is the value of x at which the step function reaches h1.

The values that can be defined by the user are: k, e, dmax, cmax. Using Impact function model, the contact normal force is sum of two terms: a spring force, proportional to the penetration between contacting bodies, and a damping force, proportional to the velocity of penetration between contacting bodies.

The general form of the Restitution force function is:

[( ) ( ) ] p dg dgFndt dt+ −= ⋅ −

where, p, is a scalar penalty parameter that defines local stiffness between the contacting

material.

dgdt

, is the penetration velocity at the contact point.

( )dgdt + , is the penetration velocity immediately before contact.

( )dgdt − , is the penetration velocity immediately after contact.

The penetration velocity immediately after contact is implicit related to the penetration velocity immediately before contact by a coefficient of restitution e, which can varies between 0, for perfectly plastic contact, and 1, for perfectly elastic contact. The values that can be defined by the user are: p and e. Using Restitution function model, the contact normal force is proportional to the penetration velocity and the constant of proportionality is p. The larger the penalty parameter, the smaller is the penetration between the contacting bodies. When using penalty methods to enforce contact constraints, large penalty (or stiffness) parameters cannot be used without the risk of making the equations of motion ill conditioned. Ill conditioning manifests itself in a loss of numerical accuracy during the solution process, causing either slowed convergence or even divergence. However, softening the penalty parameter compromises the accuracy of the unilateral contact constraint by permitting excessive penetration between interacting bodies. To circumvent penalty sensitivity, ADAMS/Solver offers an augmented Lagrangian solution technique. The method involves an iterative process to calculate the unknown contact force. The augmented Lagrangian iterations are:

( ) ( ) ( )

max[( ) ( ) ] 1,2,3,...k k kn

dg dgF p for k kdt dt

λ + −= + ⋅ − =

where,

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(1)λ = 0, for the first iteration, k=1

( )kλ =( 1)k

nF −, for k >1

The restitution force model was chosen, because in dynamic contact problems is more consistent with conservation laws and conserves and dissipates energy appropriately. Because restitution contact was chosen, initial conditions had to be stated accurately at the beginning. Cylinders representing rods were positioned right on the ground surface edge. This required a bit more attention but it was preferred to make falling down the Worm over the ground surface, which required to set first impact force model and after restitution force model. The values set for the penalty and the restitution coefficient are:

Penalty coefficient, p = 10000

Restitution coefficient, e = 0

Friction force was added to the contact model. The friction force model available in ADAMS is velocity based. Coefficient of static and dynamic friction can be defined, varying with slip velocity. An example is shown in the figure below.

(Drawn: Example of how friction coefficients vary with slip velocity, Using ADAMS/Solver)

5.3.3 Pushing machine

The role of the pushing machine is to apply a force over the last rod introduced into the machine, keeping it horizontal over the ground surface and constraining it from rotating under contact forces. Modelling the machine is complicated, but modelling what the machine really does is easy.

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Because no bodies can be add to the model during simulation, all the worm modules that will be pushed one after the other until the head module would have passed all over the strip lenght, have to be in the model from the beginning. Because forces in ADAMS can be applied only on bodies, a number of forces equal to the number of modules have to be defined; these forces should be step functions of rod displacement. Each force function has to rise from zero to the force value when the rod virtually enters the pushing machine and go back to zero when the rod exits the machine. Moreover, while each rod is pushed by the force, it has to be constrained to be horizontal over the ground surface and not to rotate. Unfortunately, all the step functions available in ADAMS library only define a smooth change from one level to one other. Therefore they are not suitable to describe the pushing force. A constant force applied to the last rod was chosen instead. Because the surface where all the rods are laying at the beginning of the simulation is flat, the force is totally transmitted to the head rod. While the simulation runs, all the rods that are waiting to virtually enter the pushing machine keep on laying over the flat surface and the force is still totally transmitted to the rod that is inside the machine at each particular moment, apart from the loss due to friction. In order to constrain the rods to be horizontal over the ground surface and not to rotate, a prismatic joint is defined between the last rod and the ground.

(Image: pushing machine, particular of ADAMS model, terra_dolce_di piu)

5.3.4 Torsion springs

As it was predicted, without constraining revolute joints connecting rods, when Worm finds a little obstacle and its body is not totally flat, is not able to go forward.

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In fact, when a force in direction opposite to the forward movement is applied to the head rod and a joint is rotated from the initial flat position, the resultant force of the pushing force and the force opposed to the forward movement acting on the rotated joint is directed towards top. In order to limit the joint mobility, bending elements simulated by local torsion springs were added to joints. The general form of the torsion spring force is:

0 0( )daT CT KT a a Tdt

=− ⋅ − ⋅ − +

where:

T, is the torque applied from the torsion spring.

T0, is the torque applied by the torsion spring in its preload position.

CT, is the torsion damping coefficient.

a, is the angle between the x axis of the second body and the x axis of the first body

connected by the joint.

a0, is the preload position of the spring.

da/dt, is the rotation velocity.

KT, is the torsion stiffness coefficient.

The values that can be defined by the user are: CT, KT, a0, T0. In ADAMS the torque applied by a torsion spring, can also be defined using a spline defining the relationship of torque to rotational deformation. Using a spline shaped as a step function it's possible to model the limited joint mobility. The spline adopted is like this:

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(Drawn: Spline diagram defining stiffness of the torsion springs modelling limited joint mobility)

Where, along the horizontal axis there is the angular displacement in degrees, a, and along the vertical axis there is the opposite of the torque applied by the torsion spring, T*. When the joint angle reaches the maximum defined value a*, the stiffness of the torsion spring turns from 0 to a very high value. The very high value is calculated to ensure that the torque applied from the spring on the last joint, between the last rod and the second last rod, it's enough to win the torque exerted by the weight of all the other modules.

5.4 BASIC MODEL

The model showing the actual behavior of Worm on a smooth surface is given hereafter. The irregularity of the surface was only due to a single ditch, 40 cm depth. The material of the terrain was wood; this was the material more similar to ground, which was already available from the material library. The force applied on the head rod modeling vegetation, was 100 N. The rod length was 2.5 m and the joint maximum mobility angle was +/-20 degrees with respect to (w.r.t.) the axis of the following rod. At the time, cylinders modeling Worm modules were not hollow but solid and their material was titanium giving a weight of 57.13 kg for each one. Therefore the force applied from the pushing machine was very high, 2000 N.

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(ADAMS Model: ic_imposed-restit_gcoeff_6modul_0smorz_units_F2000)

This model came after many other models, in which contact, applied forces, joints and torsion springs were studied. The behavior of Worm on this ground surface was good. It was able to follow the ground surface very well and the torsion springs acting on joints connecting rods worked well in limiting the joint mobility angles. In the picture, contact points and joint limited mobility can be seen. The picture is taken from the animation done after the simulation had run.

Contact points

Joint limited mobility

(ADAMS Model: ic_imposed-restit_gcoeff_6modul_0smorz_units_F2000; particular of animation)

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5.5 FROM BASIC MODEL TO GENERAL MODEL

The general model is intended to be a tool: once all the variables involved in the model are stated, the behavior of Worm on each specific minefield can be simulated and important variable values can be monitored. Therefore, the model can be introduced into an iterative cycle to determine optimum Out variable values on each type of minefield, characterised by a specific ground surface and a vegetation type.

5.5.1 Parameterization In order to have different simulation results from the same model by changing IN variable values, the model needs to be parametric. Once the basic model has been developed, it became object of parameterization study. First, design variables were introduced in bodies and forces definitions. Once a design variable has been created, it can be referred to in every definition only by assigning the name and not the numeric value. Whenever its value is modified, all the fields where it appears update automatically. In order to use the same model for different simulations, the ground surface needs to be defined parametrically. The ground surface is an IN variable to the model and therefore has to be changed every time the model is used. It is characterized by the small edges height and their frequency. In order to classify a ground surface, it’s necessary to measure its characteristics. There were two possibilities to obtain a ground surface in which small edges can be varied and measured: -drawing the surface in Pro/ENGINEER sketcher first, and import it in ADAMS

later. -drawing the surface directly in ADAMS.

In the first case, proper drawing software is used; drafts are more accurate and modifications can be done easier, but every time the surface is imported in ADAMS new contacts have to be defined. In the second case, the surface directly drawn in ADAMS is less accurate and its characteristics can be measured only by using the measuring tool. Because only distances between triads are measured, many triads have to be defined. However, the surface can be easy changed just by moving the hot points that define it, without having to redefine contacts every time a new ground surface is studied. Therefore the second option was preferred. In both of the cases, ground surface is obtained by extruding a polyline, for the reasons stated before. Although in ADAMS model there were joints connecting one rod to the other, when a rod was moved the other didn’t follow. This is due to the fact that joints are defined between 2 bodies at one location and a location is defined relatively to the absolute reference frame, by default. Therefore when one rod was moved, the joint connected to it stayed in the place where it was defined.

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In order to define joints and forces, applied to Worm modules, relatively to body reference frames, design points had to be added to the model. When the position of a design point is changed the position of all objects defined relative to it, automatically changes. All the points defined in the model belong to the Worm module last entering the pushing machine, at distances that are multiple of the design variable representing the module length.

5.5.2 Worm problems and solutions In order to develop the general model, the behavior of Worm had to be studied carefully. From many models developed between the basic one and the general one, the conditions to make Worm working properly on each type of ground surface were found. While Worm was behaving properly on a regular terrain, in the basic model, it presented three main problems on more irregular surfaces: - The head module got stuck, when approaching the ground in a direction perpendicular

to the ground profile.

- The head module moved backward, when approaching the ground in a direction

forming an angle >90° with the tangent to the ground surface.

- The Worm modules formed an arc over the ground surface.

5.5.2.1 Motor in the head joint

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The first two problems occur when the force applied from the head module to the ground surface has no components in the direction of motion. In the first case the force is perpendicular to the ground and therefore there are no components along the ground surface. The reaction force exerted from the ground to the head module is equal and opposite to the force applied from the head module. In the second case the force applied from the head module has component in direction opposite to motion.

(Image: force applied from head module is perpendicular to the ground surface, simulation verme_60gradi, modelterreno_agricolo_prova1)

As it was predicted, a motor driving the joint connecting the head module to the following one (head joint), is needed. In fact, by driving the position of the head module in the plane perpendicular to the ground surface, situations in which the contact occurs along a straight line forming an angle minor or equal to 90° with the ground surface can be avoided. Because a camera will be fixed on Worm head module, the motor can be activated only when it is needed, leaving the degree of freedom of the head joint uncontrolled for the rest of the time. The motor can be modeled in two ways: - it can be activated only when it is needed - it can be always active, rotating in order to make the head rod following the surface

profile The first solution is preferable because it’s simpler, but cannot be realized. In fact, the movement the user can define for a joint modeled in ADAMS, has to be function of time. The situation in which the contact between the head module and the ground occurs along a straight line forming an angle minor or equal to 90° with the ground surface is an event, not time dependent. Although a dependency of these events on time can be stated for each specific modeled minefield, because the time at which they occur can be calculated or extrapolated from simulations, a general dependency of these events on time cannot be stated.

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The second solution cannot be realized as well. The head joint should rotate every time the surface profile changes tangent. This means that the movement applied to the joint has to be function of displacement; displacement is a function of time if velocity is constant. The Worm velocity changes depending on the ground surface. None of the solutions proposed could be adopted. Other ways had to be investigated. First, the use of a sensor was considered. Sensors can be used in ADAMS to stop a simulation. A sensor is an event; it occurs when a function assumes a defined value. The function can be a measure of model performances. A sensor can be used to stop simulation when the head module gets stuck, having approached the ground surface along a straight line forming an angle minor or equal to 90° with it, and another simulation can be run once the head joint has been rotated enough to make the Worm moving on. The sensor could be defined by a function measuring contact between head rod nose and the ground.

Head rod

In fact when the head rod nose touches the ground, the force applied from the head rod to the ground doesn’t have any component in direction of motion. Two main problems arose, while trying to define the sensor: -None of the functions available in ADAMS library can be used to measure contact between the head rod nose and the ground. In order to define a function measuring contact between two bodies is necessary to define a triad on each body first. Because the body modeling the terrain is big, define a triad on each point it’s impossible. The same problem arose defining a function measuring distance between head rod nose and ground: many ADAMS functions measure distances and forces between two triads. -Is not possible to start an interrupted simulation imposing an initial model configuration different from the one obtained from the previous simulation. Secondarily, a system to keep the head rod horizontal was studied. In fact, until there are not ground surface profile lines vertical or having negative tangent, the angle at which the head module, kept horizontal, approaches the ground surface will always be smaller then 90°. Not to consider profile lines vertical or with negative tangent is reasonable; usually ground surfaces don’t present vertical slopes. If vertical surfaces are approached by Worm while crawling its way trough vegetation, they belong to obstacles. The presence of obstacle on ground surface cannot be predicted and therefore is not modeled. When an obstacle is found, the only way to overpass it is to remotely operate the head motor using the camera fit on head module as sensor. If the obstacle cannot be over passed Worm is pulled back and another strip of land can be analyzed. A mechanism to keep the head rod horizontal was developed.

Head rod nose

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(Image: mechanism to keep head rod horizontal, simulation:pantografo_gcontatto, model. Terreno_agricolo_irregolare_prova_7)

This solution worked, but not in a realistic way; therefore the final solution was investigated. A more realistic model taking into account the presence of the motor in the head joint was developed. It was obtained by changing a little bit the torsion spring applied to the head joint. The head joint mobility was restricted from -20°/20° to 0°/20°, by changing the spline defining the spring stiffness in this way:

(Spline diagram defining stiffness of the torsion spring applied to the head joint)

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As it can be seen from the diagram, the spring stiffness reaches a very high value when the joint angle approaches –5° instead of 0°. This is due to the fact that imposing a very high stiffness value at 0° results in a very high torque applied to the head module when it is horizontal; as soon as the simulation starts, the joint moves.

5.5.2.2 Hump inequality The third main problem Worm presented on more irregular surfaces was to form an arc over the ground. Usually an arc is formed when a sharp small edge is approached; the head module goes over and the other modules follow, but because the edge is sharp and the joints connecting rods have limited mobility, the modules overpass the edge forming an arc over the ground. As all the joints connecting the rods forming the arc have reached the maximum joint mobility angle, under the rod weights, the part of Worm involved in the arc can be considered as a rigid body.

αα

α

(Drawing: Worm forming an arc)

Assuming the hypothesis of static equilibrium and the hypothesis of having the first joint of the arc and the last joint of the arc at the same height, a simplified model was studied and the general equation governing this phenomenon (hump) was obtained. Worm can be assumed to be in static equilibrium, because its speed is very low and its motion can be considered as a sequence of static states. If Worm is always in static equilibrium, the sum of the forces acting on it is zero at every time.

(Drawing: Worm forming an arc in the hypothesis of having the first joint of the arc and the last joint of the

arc at the same height)

As it can be seen, the problem of finding the general equation governing this phenomenon is made easier by the fact that the Worm modules involved in the arc are sides of a regular polygon, having the same length and the same angle with respect to the previous side. The angle between one module and the previous is equal to the maximum joint mobility angle, α.

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The momentum equilibrium equation for the case in which only two modules are forming the arc is here reported:

αα/2

L Fs

Fs

pFs

sLF ' L sin p cos

2 2 2α α

⋅ ⋅ = ⋅ ⋅

where, Fs’, is the pushing force, reduced of the amount lost for friction along Worm body L, is rod length α, is the maximum joint mobility angle p, is rod weight Only half of the arc is considered because it is symmetric. Because of the hypothesis of static equilibrium, the same force acting on the Worm in direction of motion, Fs’, is applied to Worm head in the opposite direction. The momentum equilibrium equation for the case in which four modules are forming the arc is here reported:

α/2L

Fs

Fs

p

Fs

α

α

p

s3 1 3 3 1F ' L (sin sin ) p L [( cos ) (cos cos )

2 2 2 2 2 2 2α α

⋅ ⋅ + α = ⋅ ⋅ ⋅ α + α +

where, Fs', is the pushing force, reduced of the amount lost for friction along Worm body L, is rod length α, is the maximum joint mobility angle p, is rod weight

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Only half of the arc is considered because it is symmetric. Because of the hypothesis of static equilibrium, the same force acting on the Worm in direction of motion, Fs’, is applied to Worm head in the opposite direction. A general form of the momentum equilibrium equation, for the simplified model, in the case in which a generic even number, 2n, of rods are involved in the arc was obtained:

n n k 1

sk 1 k 1 j 1

1F ' L [ sin( (n k) )] p L { [ cos( (n k) ) cos( (n j) ]}2 2 2 2

−

= = =

α α α⋅ ⋅ + − ⋅α = ⋅ ⋅ ⋅ + − ⋅α + + − α∑ ∑ ∑

Therefore, the inequality that has to be satisfied in order not to have arc is:

n n k 1

sk 1 k 1 j 1

1F ' L [ sin( (n k) )] p L { [ cos( (n k) ) cos( (n j) ]}2 2 2 2

−

= = =

α α α⋅ ⋅ + − ⋅ α < ⋅ ⋅ ⋅ + − ⋅ α + + − α∑ ∑ ∑

The equation states a relation between several design variables of the model: - number of rods involved in the arc, 2n - weight of each rod, p; as all the modules are made by steel, p is function of rod length,

L - joint maximum mobility angle, α - pushing force, Fs, through Fs’, which can be calculated from Fs A similar equation could be obtained for the case in which a generic odd number of rods are involved in the arc. From the inequality, once the values of rod length, L and the value of pushing force, Fs are stated, the value of joint maximum mobility angle, α can be known. As it can be seen, the value of joint maximum mobility angle, α, obtainable from the equation, is the maximum: all the smaller α values are good in order not to have an arc. In fact, once the equilibrium is achieved, if α increases the arc does not collapse, if α decreases the arc collapses. Here it is shown for the case in which 4 rods are forming the arc:

α/2L

Fs

Fs

p

Fs

α

α

p

h Arm ofpuschingforce Fs

Arms of weights

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While α increases, the height of the arc, h, increases. This means that the arm of the pushing force increases, while the arm of the rod weight forces decreases. Therefore, the arc does not collapse. It can be demonstrated that as the number of rods involved in the arc increases while their length and pushing force are constant, the joint maximum mobility angle decreases. In fact, as the number of sides of a regular polygon increases, the angle between one side and the previous decreases. Therefore, the worst case in which to calculate the maximum joint mobility angle is when the minimum number of rods are involved in the arc. In fact, the bigger is α, the more stable is the arc and the more difficult is to make it collapsing. Because, as seen previously, in order to sample correctly, filters have to be swept over the ground at a maximum height of 20 cm, the inequality that has to be satisfied in order not to have arc, has to be satisfied by the minimum number of rods, 2n, whose possible arc height is higher than 20 cm:

n 1

k 1L [sin sin(k )] 20

2

−

=

α⋅ + ⋅ α >∑

The general inequality, that has to be satisfied in order not to have arc, obtained, calculated for the number of rods specified from the equation above, 2n, will be called Hump inequality.

5.6 GENERAL MODEL

The general parametric model, able to reproduce the behavior of Worm on any type of surface covered by any type of vegetation, is here presented. The bodies involved in the model are: - ground - Worm modules Ground is characterized by its surface. Ground surface was obtained by extruding a closed polyline, created before. The polyline was defined using many points, called hotpoints. In this way changing position of the hotpoints defining the polyline can largely modify the ground surface and a better approximation of a real surface can be obtained.

2n: n:

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(Image:surface hotpoints, particular of ADAMS model: terra_dolce_dipiu)

The material of ground is wood, as this material is the most similar to ground already contained in ADAMS material library. Worm modules are represented with hollow cylinders made by steel. Their length, external diameter and thickness are defined using design variables, equal for all the modules. Modules are connected by revolute joints. In order to make changes in modules position and length, joints are located on design points belonging to the last module entering the machine. Restitution type contact and friction force are defined between Worm modules and ground. Contact and friction parameters are defined using design variables equal for all the contacts between each module and ground. The pushing machine is modeled as a prismatic joint and a force. The prismatic joint is defined between the last module and the ground while the force is applied to the last module and is defined using a design variable.

(Image: design points, particular of ADAMS model: terra_dolce_dipiu

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design points belonging to the last rod are red cubes)

Joint limited mobility is modeled with torsion springs acting on joints connecting rods. The torsion spring stiffness is defined using a spline. All the torsion springs have the same spline except for the torsion spring acting on the head joint, whose spline is slightly different in order to model the presence of the motor. By changing the splines, the joint maximum mobility angle of each rod is modified. The force exerted by vegetation on head module is defined using a design variable. The list of design variable names used in the model is here reported:

Design variable name Variable name DV_1 (Design Variable 1) Rod length, L DV_2 Contact penalty parameter, p DV_3 Contact restitution coeff., e DV_4 Static friction coeff., µs DV_5 Dynamic friction coeff., µd DV_6 Static slip friction velocity,vs DV_7 Dynamic slip friction vel.,vd DV_8 Pushing force, Fs DV_9 Vegetation force DV_10 External rod diameter, D DV_11 Rod thickness

5.7 USE OF MODEL

There are many variables involved in the model. Beside the IN and OUT variables, several others need to be specified in order to obtain results from the model. The variables involved are:

Variables Origin MODULES External diameter, D Structural analysis Internal diameter, d Structural analysis Length, L Output from model JOINTS Joint maximum angle, α Output from model PUSHING MACHINE Pushing force, Fs Output from model

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MINEFIELD Ground surface Input to model Vegetation Input to model

Once the structural analyses are completed and the values of external and internal module diameter are known, the model together with hump inequality can be used to determine OUT variable values. Because the relationships between variables are complicated, the process of determining the OUT variable values, Fs, L and α was difficult to be defined. The iterative process found can be easier explained using a flow diagram:

Fs L

' 'n n k 1' ' '

sk 1 k 1 j 1

1F L [ sin( (n k) )] p L { [ cos( (n k) ) cos( (n j) ]}2 2 2 2

−

= = =

α α α⋅ ⋅ + − ⋅α < ⋅ ⋅ ⋅ + − ⋅α + + − α∑ ∑ ∑

α

Simulation

NO YES

YES NO

YES NO

n ‘

'n 1

k 1l (sin sin(k )) 20

2

−

=

α⋅ + ⋅ α <∑ Set n’ higher

Height ofmodulesfrom ground

< 20Set L smaller

Fs is enough to makeWorm moving

Set Fs lower Set Fs higher

STOP

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First, values for Fs and L are stated. Although these values can be any, if they are chosen with appropriate considerations, they make shorter the process of determining OUT variable values. The value chosen for Fs should be the minimum necessary to make Worm moving. A low Fs is needed in order to have low torque applied on joints both in the plane perpendicular to ground, and in the ground plane. In fact, while in the plane perpendicular to ground a low torque on joints means lower possibility to have arc, in the ground plane a low torque on joints means a lower possibility for Worm to deviate from straight lines. The value chosen for L should be low but the time necessary to assemble all the Worm modules to cover the desired length has to be taken in account as well. A low L is needed in order to make Worm better following the ground surface. Because modules are made by steel and their diameter is known from structural analysis, once their length is determined, their weight is known as well. Then, the number of modules for which the hump inequality has to be satisfied is set to the minimum, 2n’=2. This corresponds to the worst case; in fact, the joint maximum mobility angle obtained in this way is the maximum. A high value for joint maximum mobility angle means a bad force transmission throughout the Worm. The value of joint maximum mobility angle for 2n’=2 is, then, determined. A verification follows: if the height of the arc formed by 2 modules connected by the joint with α mobility is smaller then 20 cm, that arc can be ignored and the arc formed by 4 modules is considered. All the data’s obtained are now introduced into ADAMS model. A simulation is run and the height of each module from ground at the end is measured. Two verifications follow: if the height of any module over the ground is higher then 20 cm, the process has to be started again with a smaller initial L; if the pushing force is not enough to make the Worm moving, the process has to be started again with a higher initial value for Fs; if the pushing force is enough, the process has to be started again with a lower initial value for Fs. After the first iteration, if the pushing force is not enough the process is completed and the Fs value obtained before is taken. At the end of the process, the force the pushing machine has to exert on modules, Fs, the module length, L and the joint maximum mobility angle, α are known. In order to be sure to make Worm passing over small obstacles, the pushing force that will be exerted from the pushing machine will be higher then Fs obtained.

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6 WORM DESIGN

• Joint design

• Functional analysis

• Rod design

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6.1 JOINT DESIGN

Worm design includes rod design, pushing machine design and joint design. Because Worm is adapted from directional drilling machines, pushing machine and rods similar to the ones used in directional drilling machines can be adopted. While pushing machine and rods need only to be modified from already existing ones, joints have to be designed from the beginning. All the joints are equal except from the head joint, which contains a motor.

6.1.2 Joint requirements Before starting to design Worm joint, it’s necessary to state the rquirements that the joint has to satisfy. Joints give mobility to the mechanism: each rod can rotate with respect to the following one in the plane perpendicular to ground. While the joints used in directional drilling give continuity to the structure formed by rods because they allow each rod to be screwed into the next without leaving any degree of freedom, joints used in Worm introduce discontinuities in Worm body. As in directional drilling, Worm modules will be assembled together on field; the pushing machine has the role to host the next rod that is going to be introduced in the vegetation while it is connected to the last one introduced and, then, to push it. Although this operation requires time: the time needed to add each rod to Worm body multiply for the number of rods introduced, it is necessary. In fact, Worm is designed to operate in mine affected countries where, often, infrastructures are weak; the transport of big machine to these areas can represent a big problem. Particularly the transport of Worm already assembled could be impossible; the space occupied by worm modules is very big because of the limited joint mobility. Therefore, as Worm need to be assembled on field and joints represent discontinuities in Worm structure, I think that joints have to be used to assemble one rod to the other. In this way no more discontinuities are add to Worm body. As Worm is designed to operate in a dirt enviroinment where mud, water, little stones, little tree branches , etc., can be present, it has to be designed in order to work properly also in these conditions. While rods need only little protection for filters, joints have to be well protected. Their mobility has to be guaranteed and moreover no dirt has to enter inside modules. Therefore joints have to be protecetd and cannot be hollow. While directional drilling machine are almost just mechanincal, having all the electricity concentarted in the pushing machine, electricity power has to be brought to Worm modules. In each module electricity is needed to operate filters and in the head module electricity is needed to operate head joint motor, drilling motor and the camera needed to drive the head joint motor, as well as the filter. Therefore, electricity has to be transmitted trough joints.

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Joints should be air resitant if the pressure drop trough filters would be obtained with pressurized air. Joints don’t have to be air resitant if the pressure drop trough filters is obtained with electric fans directly fitted over filters. Electric fans were preferred to pressurized air. They present the advantage of not having to transport an air compressor on minefield. Therefore, the Worm joints have to be: - Easy to be assembled - Not hollow - Protected from water and dirt - Able to transmit electricity

6.1.3 Pro/ENGINEER drawing of joint

A drawing of Worm joint was made using Pro/ENGINEER software. The drawing is only a proposal because there was not enough time to do a structural analysis. The drawing has been corrected many times until the final form seemed well dimensioned to our eyes. Every time Worm is modified in order to sample a specific minefield, joints have to be redrawn because joint maximum angle changes. As all the joints along Worm body are the same, only one joint has to be redrawn each time. The joint drawing developed using Pro/ENGINEER is parametric: a new joint drawing with a different joint maximum mobility angle can be obtained just by changing the joint maximum mobility angle variable. The joint is mainly composed by 3 parts: - 2 parts that will be connected to the rods connected by the joint - 1 pin The drawing was intended to be as simple as possible. In order to allow only a limited mobility of one part with respect to the other in the plane perpendicular to ground, a cavity was obtained in the first part. The cavity has two sides perpendicular to the ground plane and two sides forming the desired joint maximum mobility angle with the horizontal. The second part has a prismatic protrusion designed to be inserted into the cavity. A pin allows the prismatic protrusion to rotate with respect to the other part until the protrusion sides get in contact with the cavity angled sides.

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(Image: first part and second part shapes, particular of joint) As it can be seen from the particular of the joint drawing, contact between the first part and the second part occurs only along a limited part of cavity sides. This was done in order to have contact along a concentrate area far away from the pin. in this way, the maximum torque the joint can transmit is higher; in fact, the arm of the contact force is bigger. Moreover, in this way, there is enough space to allow the protrusion of the second part to be introduced into the cavity. As it can be seen from the particular of the joint drawing, the top surfaces of both parts are curved with the same radius. This was done in order to keep the cavity covered along all joint excursions. This helps to keep joint free from dirt that could limit joint mobility. However, an external cover is needed in order to keep water away. In this drawing the maximum joint mobility angle is 10°and the external diameter of both of the parts is equal to rod external diameter, 72 mm. When joint maximum mobility angle is changed, external diameter of both of the parts has to be changed as well, in order to keep the cavity covered. It could happen to have rod external diameter different from joint external diameter. In order to make the joint easy to be assembled there were two possibilities: - Build every rod with one part of the joint already connected to one end and the other

part of the joint to the other end and assemble two following rods together by inserting the joint pin

- Build every rod with the whole joint already connected to one end and only a little cavity in the other end and assemble two following rods together by inserting the joint into the little cavity

First part Second part

Pin

Cavity sides

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The second possibility was preferred. In this way the pin can be better fixed in the joint and joint gap can be smaller. A system to make the free part of the joint connected to one rod easy and fast to insert into another rod was studied. Two little cylinders and one spring were adopted. The cylinders and the spring are fitted in a hole obtained in the joint part that waits to be inserted in the apposite rod cavity.

(Image: system to connect joint to rod, particular of joint ) By pushing the cylinders, and therefore the spring, interposed between the two cylinders, until they retract inside the hole, the joint can be inserted into the rod next to be assembled. When cylinders find the cavities appositely obtained into the rod, they are pushed by the spring until they fit inside the cavities. In order to disassembly two following rods, cylinders have to be pushed again while joint is pulled. Worm joints need to be able to transmit electricity. The easiest way to transmit electricity through the joint is to use external electrical wires. Because Worm is designed to operate in thick vegetation and wires can easy get stuck into it, this is not a good solution. Another solution was thought. Joints first part and second part can present a little hole in which electrical wire can be fit. A little place has been created on both part top surfaces to host connectors between the two sets of electrical wires fitted in each part. Connectors can be electrical brushes touching each other or just small electrical wires just long enough to follow joint excursion.

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(Image: place for electricity connectors, particular of joint) The whole joint is represented here.

(Image: joint)

6.2 FUNCTIONAL ANALYSES

While during feasibility study equations were stated and technical solutions were adopted in order to make Worm able to follow any desired ground surface, covered by vegetation, close to it enough to satisfy sampling requirements, during functional analyses intrinsic limits of Worm were detected and formalized.

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6.2.2 Joints As joints are not ideal, they present a clearance. The entity of joint clearance is important. In fact, looking at the minefield where Worm is working from the top, it can be seen that the presence of a small clearance in each joint can cause a big deviation from the straight line Worm is supposed to follow and this deviation increases as the number of rods introduced in the field increases. The worst case, when all Worm modules rotates with respect to the previous module by an amount equal to joint clearance, in the same direction, is shown here:

The deviation of Worm from the straight line it is supposed to follow is not desirable for two main reasons: - The torque applied by the pushing force on joints can be very high; it increases as the

number of modules introduced into the minefield increases - Sampling along straight lines allows not to cover twice the same area and to cover at

least once the area that could be sampled As torque applied on joints increases as the number of modules introduced into the minefield increases and joints can support a maximum torque, whose value can be known from structural analysis, the joint clearance needs to be calculated in order to know the maximum number of modules can be introduced into the minefield without making Worm collapsing. Assuming that the coupling between first joint part and pin, considered solidly connected to second joint part is: H7/g6, the maximum gap between the hole and the pin is given by the sum of the maximum gap of the hole and the maximum gap of the pin and is equal to 41µm, equal to 0.041mm.

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105

gap

armFirst part

Second part

Therefore, joint clearance is approximately given by:

4gap 0.041 5.857 10 [rad] 0.0335arm 70

−γ = = ⋅ = °

Where, γ is joint clearance. The equation that states a relationship between joint clearance, pushing force, rod length, maximum torque joints can support and maximum number of modules can be introduced into the minefield, was found for the worst case:

Fs

Fs’

γ

Where, green arrows represent friction forces exerted by vegetation.

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106

Assuming the hypothesis of static equilibrium the sum of the forces acting on Worm is zero at every time. Worm can be assumed to be in static equilibrium, because its speed is very low and its motion can be considered as a sequence of static states. Therefore,

n ''

max s sk 1

1M L [F' sin (k ) p ( sin (k ) (k 1) sin )]2=

= ⋅ ⋅ ⋅ ⋅ γ + ⋅µ ⋅ ⋅ ⋅ ⋅ γ + − ⋅ γ∑

Where, Mmax, is the maximum torque joints can support L, is the module length n’’, is the maximum number of modules can be introduced into the minefield γ, is the joint clearance p, is the module weight; once the material and the external and internal diameter of

modules have been stated, p is function of L. µs, is the static friction coefficient Fs’, is the force applied to the head rod, equal to the force applied by the pushing machine minus all the friction forces exerted on each rod by vegetation.

The relationship between Fs’ and Fs was found:

n ''

s s sk 1

F ' F p cos ( (k 1) )=

= + ⋅µ ⋅ ⋅ ⋅ − ⋅ γ∑

Where, all the symbols are the same as before. By substituting the last expression into the second last, the relationship between joint clearance, pushing force, rod length, maximum torque joints can support and maximum number of modules can be introduced into the minefield, can be obtained. It will be later referred to as no collapse equation. While the torque applied on joints increases as the number of rods introduced into the minefield increases, i.e. when Worm is pushed inside the vegetation, it decreases when Worm is pulled back. In fact, the force applied from the machine and the friction forces acting on each rod change direction. Therefore, when the number of rods introduced into the minefield has reached the maximum, Worm has to be pulled back. While pulling back, joint clearances are corrected and modules are subject to a torque that constrains them to align themselves again. If the pulling force is high, the number of rods that need to be pulled back in order to have Worm aligned again along a straight line is smaller. These considerations have been done without taking into account the vegetation. In this case, the presence of vegetation is desirable; in fact, if the vegetation is thick it constitutes a barrier that constraints Worm to go on a straight line. Vegetation reacts to the torque exerted by Worm with a torque in the opposite direction.

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Considering the vegetation, the maximum number of modules can be introduced into the minefield before having to pull them back greatly increases.

6.2.3 Rods Rod variables are length, external diameter and internal diameter. As the material is steel, rod weight is function of rod length. While internal and external rod diameters are known from structural analysis, once the stress and the torque applied to the rods is known, rod length can be obtained from the iterative process described previously. Because Worm is designed to operate on minefields, its weight has to be contained. In fact, the pressure exerted by Worm per millimeter square has to be lower then the minimum pressure, per millimeter square, needed to trigger anti personnel (AP) mines. Therefore, in order to make Worm really useful for mine clearance operations, another equation, that relates rod variables, has to be satisfied. As seen previously, the force needed to activate an AP mine is between 3-20 kg. The diameter of an AP mine can be between 7-15 cm. Assuming that all the mine casing surface is pressure sensitive, which corresponds to the worst case, the minimum pressure, needed to trigger an anti personnel (AP) mine can be calculated. In order to obtain the minimum pressure, the smallest force and the biggest diameter were considered.

2

2 22 2 2 2

2

F Np [ ]S mm

F 3 [kg] 3 9.8 [N] 29.4 [N]D 15S R [cm ] 176.71 [cm ] 17671 [mm ]4 4

29.4 Np 0.00166 [ ]17671 mm

= ⋅⋅

= ⋅ ⋅ = ⋅ ⋅ ⋅ = ⋅ ⋅

= π ⋅ = π ⋅ = π ⋅ ⋅ ⋅ = ⋅ ⋅ = ⋅ ⋅

= = ⋅ ⋅

The pressure exerted by Worm on ground, per millimeter square, can be calculated considering the pressure exerted by one module, per millimeter square. As modules are cylinders, the area of contact between them and the ground is function of the type of ground. As the pressure increases if the area of contact decreases, a small area of contact was considered: module length multiplied by the external radius. Therefore the inequity that has to be satisfied in order not to trigger AP mines while Worm is working is:

2e

P N0.00166 [ ]L R mm

< ⋅⋅⋅

where, P, is the module weight

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L, is the module length Re, is the module external radius The inequity written above will be referred to as no explosion inequity.

6.3 PROCESS FOR PROJECTING WORM

From feasibility study and functional analyses important equations Worm variables have to satisfy were stated. From structural analyses of Worm joints and modules, other important equations could be obtained. Unfortunately, there was not enough time to carry out these analyses as well. However, the variables involved in the equations of structural analyses are known. Therefore, a scheme to represent the logical process to calculate Worm variable values, in order to project and to use Worm correctly, was obtained. In the scheme appear equations from feasibility study, equations from functional analyses, model simulation calculations and equations from structural analyses, which are not specified, and all Worm variables, already listed above.

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FsL

n ‘

Structuralanalysis

D/d

Tmax

α

Simulation

NO YES

Set n’higher

Hump inequalityf (Fs, L, n’, α, D/d) = 0

Is height ofmodules fromground

< 20 cm ?

Set Fs lower

STOP

YES NO

YES NO

Height ofmodulesfromground

< 20 cm?

Set Lsmaller

Fs is enough tomake Wormmoving ?

Set Fs higher

No collapse equation

f ( Tmax, L, n’’, Fs, γ, D/d, µs ) = 0n’’

Jointclearancecalculation

No explosioninequality f (L, D/d ) = 0satisfied?

YES NOSet L higher

γ

First, values for Fs and L are stated. Although these values can be any, if they are chosen with appropriate considerations, they can make the process of determining OUT variable values shorter. The value chosen for Fs should be the minimum necessary to make Worm moving. A low Fs is needed in order to have low torque applied on joints both in the plane perpendicular to ground, and in the ground plane. In fact, while in the plane perpendicular to ground a low torque on joints means lower possibility to have arc, in the ground plane a low torque on joints means a lower possibility for Worm to deviate from straight lines.

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110

The value chosen for L should be low but the time necessary to assemble all the Worm modules to cover the desired length has to be taken in account as well. A low L is needed in order to make Worm following better the ground surface. The value chosen for L has to satisfy the no explosion inequality as well; if the inequality is not satisfied, a new higher value for L has to be stated. Once structural analyses are done, the value of module diameter is known and can be introduced into the no explosion inequality and then to the no hump inequality. Then, the number of modules for which the hump inequality has to be satisfied is set to the minimum, 2n’=2. This corresponds to the worst case; in fact, the joint maximum mobility angle obtained in this way is the maximum. A high value for joint maximum mobility angle means a bad force transmission throughout the Worm. The value of joint maximum mobility angle for 2n’=2 is, then, determined. A verification follows: if the height of the arc formed by 2 modules connected by the joint with α mobility is smaller then 20 cm, that arc can be ignored and the arc formed by 4 modules is considered. All the data’s obtained are now introduced into ADAMS model. A simulation is run and the height of each module from ground at the end is measured. Two verifications follow: if the height of any module over the ground is higher then 20 cm, the process has to be started again with a smaller initial L; if the pushing force is not enough to make the Worm moving, the process has to be started again with a higher initial value for Fs; if the pushing force is enough, the process has to be started again with a lower initial value for Fs. After the first iteration, if the pushing force is not enough, the process is completed and the before obtained Fs value is taken. At the end of the process, the force the pushing machine has to exert on modules, Fs, the module length, L and the joint maximum mobility angle, α are known. In order to be sure to make Worm passing over small obstacles, the pushing force that will be applied from the pushing machine will be higher then the obtained Fs. All the assessed variable values can, therefore, be introduced into the no collapse equation, together with the maximum torque joints can support, Tmax, and joint clearance, γ, in order to obtain the maximum number of modules can be introduced into the minefield without making Worm collapsing, n’’. As it was said before, considering the vegetation, the maximum number of modules that can be introduced into the minefield before having to pull Worm back greatly increases.

Conclusions

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7 CONCLUSIONS AND FUTURE WORK

The ground recovery after landmine detection appeared as very challenging topicto be dealt with by conscious engineering development. Unfortunately, while developing this project I had to realize that it was too ambitious. Starting a new project is exciting: you need to learn a lot about a new problem you like, choose a particular aspect of the problem that is urgent and important to be solved, employ your creativity to find a possible solution and verify if you were right, but going towards the end of the project in a short period of time is really hard. Although I have done as much as I could there are still many things to do. Many aspects of the problem that are not treated in this report have been argument of discussions and ideas to solve them have been proposed, but a lot of future work needs to be done. Luckily, I know that the work started will be continued and the project will be developed further: maybe see it employed on real minefields is not a hope. In fact, professor James Trevelyan, recently informed me that an English student is interested in contributing to Worm project. This was wonderful news. The work done within the thesis can be divided in two parts: The first part regards the data’s collection, partly done in Genova but mainly done in Perth Western Australia under the super visioning of professor James Trevelyan, the understanding of the landmine problem from a technical and social point of view, which leaded to a great involvement, the review of the actually used demining methods, the research of a possible contribution to demining operations, the focus on a particular aspect of the problem which is urgent and important to be solved: the localization of mines in uneasy accessible areas covered by thick vegetation without the need to remove vegetation first, the proposal of a first solution: Lizard, the feasibility study, involving the review of sensor technologies available with particular attention to artificial odour and vapour sensors, the study of explosive migration into the soil surrounding a mine and the withdrawal of the first idea. The second part regards the project of Worm. First other sensor techniques were considered and Remote Explosive Scent Tracing (REST) method was analyzed. A less complicated solution was researched, directional drilling machines were studied and seen working on field and Worm was proposed, taking inspirations from them. Professor Trevelyan made me believe that simplicity was the most important requirement for a machine design to operate in poor countries, driven by people without technical skills. Worm feasibility study followed: it was carried out using ADAMS software. Because I never had the possibility to use it before, I had to learn it first. Then, many models were developed in order to obtain a realistic behavior of Worm and then to know if it could actually be used in demining operations. A general parametric model was obtained: it can be used as a tool to choose optimum Worm design variable values for the specific area that need to be checked for landmines. Worm design followed: a joint was proposed and a parametric Pro/ENGINEER drawing was made. Finally a logical scheme of the process which needs to be followed in order to project Worm correctly, taking into account that

Conclusions

112

Worm has to be light enough in order not to trigger Anti Personnel (AP) mines, that filters have to be swept over the ground at the maximum height of 20 cm and that as the number of Worm modules pushed over a minefield increases, the torque applied by the pushing force on joints, due to the presence of clearance in joints, increases, was made. The work that needs to be done regards head module design, filters design and the whole mechanism design, taking into account how to fit electrical wires along Worm and evaluating how to activate the head joint: a solution could be by pulling steel wires appropriately fitted along Worm body rather than by a motor fitted into the joint. While designing head module, it has to be considered that a camera will be fitted on it, which will allow to drive the head joint, and that a drilling part will be needed while operating in minefields covered by bamboos.

References

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8 REFERENCES

Landmine Monitor Report, 2002: Toward a Mine-Free World, International Campaign to Ban Landmines (http://www.icbl.org) Study Report: Socio-economic Impact of Mine Action in Afghanistan (SIMAA), 2001. Study report: Socio-Economic Impact Study of Landmines and Mine Action Operations in Afghanistan (SEIS), 1999. UN Office for Coordinating Humanitarian Aid to Afghanistan, 1996. Designer Dogs: Improving the Quality of Mine Detection Dogs, GICHD, Geneva, December 2001. J. Trevelyan, “Technology and the Landmine Problem: Practical Aspects of Mine Clearance Operations”, Detection of Explosive and Landmines, 2002,pp.165-184. Y. Boudoin, E. Colon, “Humanitarian demining and robotics state of the art, specifications and ongoing research activities”, Climbing and Walking Robots 2000, Professional Engineering Publishing, pp. 869-877. Hudem Symposium 1999, Brussels Belgium, Proceedings. J.-D Nicoud, “Vehicles and robots for humanitarian demining”, Industrial Robot, Vol.24, No. 2, 1997, pp.164-168. Rae McGrath, “Cluster Bombs, the military effectiveness and impact on civilians of cluster munitions”, Richard Lloyd ed., August 2000. “Hidden Killers, the global landmine crisis”, Office of Humanitarian Demining Programs, September 1998. Maki K. Habib, “Mine Clearance Techniques and Technologies for Effective Humanitarian Demining”, Journal of Mine Action, Issue 6.1 Winter 2002, pp. 62-65. J. Trevelyan, “Practical Issues in Manual Demining: Implications for New Detection Technologies”, Detection of Explosive and Landmines, 2002, pp.155-164. J. Trevelyan, “Robots and landmines”, Industrial Robot, Vol.24, No.2, 1997, pp.114-125.

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C. Bruschini, B. Gros, “A Survey of Current Sensor Technology Research for the Detection of Landmines”, International Workshop on Sustainable Humanitarian Demining (SusDem’97), 29 September-1 October 1997, Zagreb, Croatia. “Peacetime Mine Clearance (Humanitarian Demining )”,1996, NATO Defence Research Group. M. J. Randall, R. Jagadeesan, “Requirements for a walking machine for use in humanitarian de-mining”, Climbing and Walking Robots 2000, Professional Engineering Publishing, pp. 767-776. Mechanical Demining Equipment Catalogue 2002, Geneva International Centre for Humanitarian Demining, 2002. “Mine Facts” CD-ROM, v.1.2, United States Department of Defence. “Jane’s Mines and Mine Clearance”, Colin King ed.,(Fourth Edition)1999-2000. M. Fisher, C. Cumming, Nomadics, Inc., “Detection of Trace Concentration of Vapour Phase Nitroaromatic Explosive by Fluorescence Quenching of Novel Polymer Materials”, 7th International Symposium on the Analysis and Detection of Explosives, June 2001, Edinburgh Scotland, UK. http://www.nomadics.com/Landmine_Detector/Fido, M. Fisher, C. Cumming, M. Fox, M. la Grone, S. Jacob, D. Reust, M. Rockley, E. Towers “Sensing ultra-trace concentrations of landmine chemical signature compounds in the air over landmines using a man portable chemical sniffer”, May 2000. http://ifiawww.fzk.de, “KAMINA- A gas sensor system based on conductivity measurements with segmented metal oxide films to be used in mass products”. C. L. Grant, T. F. Jenkins, and S. M. Golden, “Experimental Assessment of Analytical Holding Times for Nitroaromatic and Nitramine Explosives in Soil,” SR 93-11, US Army Corps of Engineers, Cold Regions Research and Engineering Laboratory, June 1993. T. Jenkins, M. Walsh, P. Miyares, J. Kopczynski, T. Ranney, V. George, J. Penningtion, and T. Berry, “Analysis of Explosives-Related Signature Chemicals in Soil Samples Collected Near Buried Landmines,” ERDC Technical Report, Cold Regions Research and Engineering Laboratory, 2000. J. M. Phelan and S. W. Webb, “Environmental Fate and Transport of Chemical Signatures from Buried Landmine−Screening Model Formulation and Initial Simulations,” Sandia Report SAND97-1426, Sandia National Laboratories, June 1997.

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V. George, T. F. Jenkins, D. C. Leggett, J. H. Cragin, J. Phelan, J. Oxley, and J. Pennington, “Progress on Determining the Vapor Signature of a Buried Landmine,” Proc. SPIE, Detection and Remediation Technologies for Mines and Minelike Targets IV, vol. 3710, part 2, p. 258, 1999. C. Bartley, J. Trevelyan, “Modelling Minefield Clearance Data Statistical Analysis of Minefield Clearance Data”, Mine Action Information Centre (MAIC), James Madison University (JMU), 2002. “The European Union Mine Actions In The World”, Office for Official Publications of the European Communities, Luxembourg, 2002. “Remote Explosive Scent Tracing”, part of a series of studies on the use of mine detection dogs established by the Geneva International Centre for Humanitarian Demining (GICHD), informally given by Ian Mc Lean (GICHD), November 2002. M. De Biase, " Robot arrampicatore: progettazione del sistema di manipolazione", 1998. ADAMS/View guides, Mechanical Dynamics, Incorporated, 2002:

Learning ADAMS/View Basics, Building models in ADAMS/View, Using the ADAMS/View Function Builder, Using the ADAMS/View Controls Toolkit, Refining Model Designs in ADAMS/View.

S. Aoshima, T. Yabuta, “Simplified Dynamic Model for Amount of Directional Correction of Small-Diameter Tunnelling Robot”, Journal of Dynamic Systems, Measurement, and Control, September 1992, Vol.114, p. 476, 480. I. Gravagne, R. Woodfin, “Mine-Sniffing Robotic snakes and eels: Fantasy or Reality ?”, Journal of Mine Action, Summer 2002.

Web-sites

116

9 WEB-SITES

International Campaign to Ban Landmines (http://www.icbl.org) International Committee of the Red Cross (http://www.icrc.org) UN standards about landmines, http://www.mineactionstandards.org. Menshen Gegen Minen MgM, http://wwww.mgm.org Dervish robot, http://www.dervish.org. Demining Research at the University of Western Australia, http://www.demining@mech.uwa.edu.au Vadims, scanning platform, http//www.shiebel.com Demining Technology Center (DeTeC) at Ecole Polytechnique Federale de Lausanne (EPFL), http://diwww.epfl.ch/lami/detec/pemex.html Nomadics Inc., FIDO, http://www.nomadics.com/Landmine_Detector/Fido Research Centre Karlsruhe, http://ifiawww.fzk.de http://www.humanitydog.se James Madison University, Mine Action Information Centre, http://maic.jmu.edu/journal, http://www.mineaction.org, United Union, Technology, Research & Development, Mine Action, web site. http://www.itep.ws, International Test Evaluation Programme (ITEP). http://www.gichd.ch, Geneva International Centre for Humanitarian Demining (GICHD). http://www.ndrf.dk, Nordic Demining Research Forum (NDRF). http://www.ccmat.gc.ca, Canadian Centre for Mine Action Technologies (CCMAT). http://www.port.ac.uk/research/c&r/robotics, Smelly Robot, University of Portsmouth, UK.

Web-sites

117

http://www.chemistry.gatech.edu/staff/ishida.html, Hiroshi Ishida, School of Chemistry & Biochemistry, Georgia Institute of Technology, web page. http://www.rma.ac.be, Royal Military Academy(RMA), Brussels, Belgium. http://www.mech.uwa.edu.au, University of Western Australia, Mechanical Engineering Department website. http://www.howstaffworks.com http://www.landmines.org.uk, Adopt-A-Minefield, program of the United Nations Association (UNA) Trust. www.comacchio-industries.it, Directional Drilling Machines Company. http://members.shaw.ca/cloose/diet.htm, The blue tongue lizard homepage.

Contacts

118

10 CONTACTS

Associate Professor James P. Trevelyan, Department of Mechanical and Materials Engineering, The University of Western Australia, Perth, Western Australia, jamest@mech.uwa.edu.au Professor Yvan Baudoin, Royal Military Academy, Dpt Applied Mechanics, Brussels, Belgium, Yvan.Baudoin@rma.ac.be Ian G. McLean, Geneva International Centre for Humanitarian Demining 7bis, Avenue de la Paix CH-1211, Geneva 1, Switzerland, i.mclean@gichd.ch Havard Bach, Geneva International Centre for Humanitarian Demining 7bis, Avenue de la Paix CH-1211, Geneva 1, Switzerland, h.bach@gichd.ch Dr. J. Goschnick, Forschungszentrum Karlsruhe Institut fuer Instrumentelle Analytik Hermann-von-Helmholtz-Platz 1 D-761344 Eggenstein-Leopoldshafen , Germany achim.goschnick@ifia.fzk.de Dr. J. Sikes, Product Manager Nomadics, Inc., Fido, jsikes@nomadics.com Geir Bjørsvik, Norwegian People Aid (NPA), gb@npaid.org