1 robotics

8/13/2019 1 robotics

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Dr Atul Sidola


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Contents1. Fundamental of Robotics

2. Robot Drive Systems and End Effectors

3. Sensors and Machine Vision4. Robot Kinematics and Robot Programming

5. Implementation and Robot Economics


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Fundamental of Robotics


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Who introduced the word robot? The term robot was first introduced by a Czech

dramatist, Karel Capek in his 1921 play "Rossum'sUniversal Robots". He was referring to a perfect and

tireless worker performing manual labour jobs forhuman beings.

Robota in Czech is a word for worker or servant.

Isaac Asimov, coined the word robotics as the science

of the study of robots, in his science fiction storiesabout robots in 1940s.


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Definition Robot term from Webstersdictionary:- An automatic

device that performs function ordinarily ascribed tohuman being

'Automation' refers to a mode of operation in whichany machine or piece of equipment is capable ofworking without human intervention.


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Robotics Timeline(1/2)Date DevelopmentMid- 1 700s J. de Vaucanson built several human-sized mechanical dolls

that played music.

1922 Czech author Karel Capek wrote a story called RossumsUniversal Robots and introduced the word Rabota(meaning

worker)

1940s Isaac Asimov, coined the word robotics as the science of thestudy of robots

1954 George Devol developed the first programmable Robot.

1955 Denavit and Hartenberg developed the homogenoustransformation matrices


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Robotics Timeline(2/2)Date Development

1962 Unimation was formed, first industrial Robots appeared.

1971 The -Stanford Arm," a small electrically powered robot arm,developed at Stanford University.

1973 Cincinnati Milacron introduced the T3 model robot, whichbecame very popular in industry.

1979 Development of SCARA type robot (Selective Compliance Arm for RoboticAssembly) at Yamanashi University in Japan for assembly. Severalcommercial SCARA robots introduced around 1981

1990 Cincinnati Milacron was acquired by ABB


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Social and Economic Issues(1/2) In the social area, what are the main issues related to

robotics? How will the labour and manpower market be affected

by robotics? How many workers are likely to bedisplaced?What are the impacts on the professional and semi

professional work force who are employed inmanufacturing? Also, will robotics affect productivity

and international economic competition?


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Social and Economic Issues(2/2)What kind of retraining and education is needed to

upgrade the present work force?Will foreign investors still choose certain countries for

manufacturing(as cheap labour will not be neededwhen factories are run by robots)? Such as: Some 90 percent of Malaysian industry is in

the SMI (Small and Medium Industry) category. CanSMIs afford installation of robotics in the near future?

Or will robotics benefit only MNCs (MultinationalCorporations)?


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Three Laws of Robotics1. A robot may not harm a human being, nor through

inaction, allow a human being to come to harm.

2. A robot must obey the orders given to it by humanbeings except where such orders would conflict withthe First Law.

3. A robot must protect its own existence, as long as

such protection does not conflict with the First orSecond Law.


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Robot Anatomy and Work Volume

Robot anatomy deals with:

The types and sizes of joints and links

and other aspects of the manipulators physicalconstruction


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Robot Anatomy Robot manipulator consists of joints and links

Joints provide relative motion

Links are rigid members between joints

Various joint types: linear and rotary

Each joint provides a degree-of-freedom

Most robots possess five or six degrees-of-freedom

Robot manipulator consists of two sections:

Body-and-arm for positioning of objects in the robot's work

volume Wrist assembly for orientation of objects


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What is a joint(kinematic pair)? The connection between

links that permitconstrained relativemotion are called joints.

A joint of robot is similarto a joint in the humanbody

Each joint gives the robotwith a degree-of-freedom(d.o.f)of motion

In the nearly all cases, only1 d.o.f is allowed to a joint

Joint


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What is a robot link? Links are rigid components

that form a chain connectedtogether by joints

A link is one of the rigidbodies or members joinedtogether to form a kinematicchain.

Each joint has two links,known as an input link and

an output link

Link


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Types of robot joints

Joints

Translationalmotion

Linear joint(type L)

Orthogonaljoint(type O)

Rotary motion

Rotationaljoint(type R)

Twisting

joint(type T)

Revolvingjoint(type V)


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Linear jointThe relative movement

between the input link

and the output link is alinear sliding motion,

with the axes of the two

links being parallel


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Orthogonal jointThis is also linear

sliding motion, but the

input and output linksare perpendicular to

each other during the

move


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Rotational jointThis type provides a

rotational relative

motion of the joints,with the axis ofrotation perpendicularto the axes of the input

and output links


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Twisting jointThis joint also involves a

rotary motion, but the

axis of rotation isparallel to the axes ofthe two links


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Revolving jointIn this types, the axis of

the input link isparallel to the axis of

rotation of the joint,and the axis of theoutput link isperpendicular to the

axis of rotation


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Joint Notation Scheme The joint symbols (L, O, R, T, V) to designate joint typesused to construct robot manipulator

Separates body-and-arm assembly from wrist assembly

using a colon (:)

Example: TLR : TR


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This joint-link numbering scheme of robot

BaseLink0

Joint1

Link2

Link3Joint3

End of Arm

Link1

Joint2


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Degree of Freedom Degree of freedom or axes can be defined as the

direction in which a robot moves when a joint isactuated or the various movements made by the

manipulator of robots in different direction.

Six degree of freedom may be possible

3 linear motion (in X,Y and Z)

3 rotational motion (yaw, pitch and roll)


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Work Volume or Work EnvelopWork volume is the space within which a robot can

manipulate its wrist end.

The work volume is determined by the followingcharacteristics of the robot.

Size of body, arm, and wrist components.

Robots physical configuration.

The limits of robots joints movements.


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Working Envelope


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GENERAL CLASIFICATION OF ROBOTSo Low technology

o Medium technology

o

High technology


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Low Technology Material handling, using simple assembly

2 axes of movement

Stop at extreme


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Medium technology Pick-and-place

Material handling

4 axes


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High Technology

Material handling

Pick-and-place

Loading and unloading Painting and welding

6 axes


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Robot Classification Based on Kinematic

StructureNormally, robot manipulators are classifiedaccording to their arm geometry or kinematicstructure. The majority of these manipulatorsfall into one of these four configurations:

1. Cartesian Type Configuration (PPP)2. Cylindrical Type Configuration (RPP)3. Spherical Type Configuration (RRP)

4. Revolute Type Configuration (RRR)


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Cartesian Type Configuration (PPP)


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Cartesian Coordinate Body-and-Ar

Assembly Notation LOO: Consists of three sliding joints, two

of which are orthogonal

Other names include rectilinearrobot and x-y-z robot


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Cartesian Type Configuration (PPP) Manipulator whose first three joints are prismatic are

known as a Cartesian manipulator.. Cartesian manipulatorare useful for table-top assembly applications and, asgantry robots for transfer of material and cargo

Advantages:

- 3 linear axes- Easy to visualize- Rigid structure- Easy to program off-line

- Linear axes make for easy mechanical stops


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Cartesian Type Configuration (PPP) Disadvantages:

- Can only reach in front of itself- Requires large floor space for size of work envelop- Axes hard to seal


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Cylindrical Type Configuration (RPP)


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Cylindrical Body-and-Arm

Assembly Notation TLO:

Consists of a vertical column,relative to which an armassembly is moved up or down

The arm can be moved in orout relative to the column


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For cylindrical type manipulator, its first joint isrevolute/twisting/rotational which produces a rotationabout the based, while its second and third joints areprismatic.

Advantages:- 2 linear axes, 1 rotating axis- Can reach all around itself- Reach and height axes rigid

- Rotational axis easy to seal.


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Disadvantages:- Cannot reach above itself- Base rotation axis is less rigid than a linear axis- Linear axes hard to seal

- Will not reach around obstacles- Horizontal motion is circular


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SCARA Robot(a cylindrical type) Notation VRO

SCARA stands for SelectivelyCompliant Assembly Robot

Arm

Similar to jointed-arm robotexcept that vertical axes areused for shoulder and elbow

joints to be compliant inhorizontal direction for verticalinsertion tasks


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Spherical Type Configuration (RRP)


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Polar Coordinate Body-and-Arm

Assembly Notation TRL:

Consists of a sliding arm (L joint) actuated relative tothe body, which can rotate about both a vertical axis(T joint) and horizontal axis (R joint)


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Spherical Type Configuration (RRP)

The first two joints of this type of manipulatorsare revolute, while its third Joint is prismatic.

1 linear axis, 2 rotating axes

Long horizontal reach

Cannot reach around obstacles

Generally has short vertical reach


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Revolute Type Configuration (RRR)


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Revolute manipulator is also called articulated oranthromorphic manipulator. These type of robot resembles human arm. Two common revolute designs are the elbow type

manipulator such as the PUMA and the parallelogram

linkage such as the Cincinnati Milacron T3 735.


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PUMA(Programmable Universal Manipulator for Assembly) Robot


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Cincinnati Milacron T3


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Advantages:- 3 rotating, axes- Can reach above or below obstacles- Largest work area for least work space- Two or four ways to reach a point

Disadvantages:- Difficult to program off-line- The most complex manipulator


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Robot Wrist


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Wrist Configurations Wrist assembly is attached to end-of-arm End effectors is mounted on the wrist

Function of wrist assembly is to orient the end effector

Body-and-arm determines global position of end effector

Two or three degrees of freedom:

Roll

Pitch

Yaw

Notation :RRT


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Robot components

RobotManipulator

EndEffector

Actuator

Sensor

Controller


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Robot Components Manipulator: Main body consisting of links and joints


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Robot Components End- Effector: Part mounted on the last link to carry

out the robots task; example: gripper.

Wrist and end-effector together sometimes referred toas a hand.


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End Effectors

The special tooling for a robot that enables it toperform a specific task

Two types:

Grippers to grasp and manipulate objects (e.g.,

parts) during work cycle Tools to perform a process, e.g., spot welding, spray

painting


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Grippers and Tools


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Robot ComponentsActuators: Provides force/torque for robot motion. Controllable electric/hydraulic/pneumatic drivers to

change the robots configuration.


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Electric Uses electric motors to actuate individual joints

Preferred drive system in today's robots

Hydraulic

Uses hydraulic pistons and rotary vane actuators

Noted for their high power and lift capacity

Pneumatic

Typically limited to smaller robots and simple materialtransfer applications


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Robot Components Sensors: Reads actual variables in robot motion for use

in control.

Elements that detect and collect information about

internal and environmental states, such as jointposition, velocity, acceleration, force

Controller: Collects and processes sensor information,plans motions of the robot structure, and organizes

information.


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Robot SensorsAllow for perception.

Sensors can be active or passive:

Active derive information from environmentsreaction to robotsactions, e.g. bumpers and sonar.

Passiveobservers only, e.g. cameras and

microphones .


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Sensor Classes Range finders: these sensors are used to determinedistances from other objects, e.g. bumpers, sonar,lasers, whiskers, and GPS.


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Sensor Classes Imaging sensors:

these create a visualrepresentation of the

world.

From NOVA, www.pbs.org


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Sensor Classes Proprioceptivesensors: these provide information

on the robots internal state, e.g. the position of itsjoints.

Shaft decoders count revolutions, allowing for

configuration data and odometry.


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Robot Components Controller: Collects and processes sensor information,

plans motions of the robot structure, and organizesinformation.


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Robot Controller

Controllers direct a robot how to move.

Two type of control systems

Open-loop controllers

Closed-loop controllers


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Open-loop controllers execute robot movement withoutfeedback.

Closed-loop controllers execute robot movement and

judge progress with sensors. They can thus compensatefor errors.


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Coordinate Systems

World coordinate system Tool coordinate system


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Robot SpecificationsGeometric configuration

Degree of freedomPay load

Reach

Precision

Speed of motionSpatial resolution

Positional accuracy

Repeatability

Programming methods

Work volume


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Part load or payload The lifting capacity of the manipulator is called its

payload.

The payload refers to weight of a work piece carried or

tool external to robot and does not include thegripper, which is considered as a part of robot.

It may vary from several kilogram to tons.


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Reach Reach is the maximum distance a robot can reach withinits work envelope.

Many points within the work envelope of the robot maybe reached with any desired orientation (called

dexterous). However, for other points, close to the limit of robot's

reach capability, orientation cannot be specified asdesired(called non-dexterous point).

Reach is a function of the robot's joint lengths and its

configuration.


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Precision

Precision is defined as how accurately aspecified pointcan be reached.

This is a function of the resolution of theactuators, as well as its feedback devices.

Most industrial robots can have precision of0.001 inch or better.


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Speed of Robot It determines how quickly the robot can complete the

work cycle.

It is required in mass production.

It depends on:

The weight of object being moved

The accuracy with which the end effecter need to be

positioned. The distance to be moved.


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Spatial resolution It is defined as the distance between two adjacent

addressable points in axis movements.

The spatial resolution of control resolution of a robot

is the smallest increment of movement, into which therobot divides its work volume.


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Positional accuracy It is defined as how closely a robot can position its

payload to a given programmed points.

It is the robots ability to position its wrist end at

desired point within its work volume.

Since this is done by servo control and servo are neverperfect, so there will be always be a error.


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Repeatability

Repeatability is how accurately the same position can be reached if themotion is repeated many times. Suppose that a robot is driven to the same point 100 times. Since many factors

may affect the accuracy of the position, the robot may not reach the samepoint every time, but will be within a certain radius from the desired point.

The radius of a circle that is formed by this repeated motion is calledrepeatability. Most industrial robots have repeatability in the 0.001 inchrange.

Repeatability is more important than precision. If a robot is not precise, itwill generally show a consistent error, which can be predicted and thuscorrected through programming.

As an example, suppose that a robot is consistently of 0.05 inch to the right.In that case, all desired points can be specified at 0.05 inch to the left, and

thus the error can be eliminated. However, if the error is random, it cannot bepredicted and thus cannot be eliminated.


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Industrial Robot Applications1. Material handling applications

Material transfer pick-and-place, palletizing

Machine loading and/or unloading

2. Processing operations Welding

Spray coating

Cutting and grinding

3. Assembly and inspection

l


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Example Sketch following manipulator configurations

(a) TRT:R, (b) TVR:TR, (c) RR:T.

Solution:

T

R

T

V

(a) TRT:R

R

T

RT R TR

R

(c) RR:T(b) TVR:TR


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Definitions Machine: A combination of interconnected partshaving definite motions and capable of performinguseful work may be called a machine.

Mechanism: A mechanism is a component of amachine consisting of two or more bodies arranged sothat motion of one compels the motion of the other.

Kinematics: This is the study of motion in mechanism

without reference to the forces that act on themechanism.


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Dynamics: This is the study of the motion ofindividual bodies and mechanisms under theinfluence of forces and torques.

Anthropomorphic: Designed or appearing like humanbeings.


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Basic Components Robot system is combination of multidiscipline area,

which includes implementation of mechanics, electricaland electronic systems, software engineering, andnumerous other fields of application interest.

Most of the industrial robots have Five basic components:manipulator, end effector, actuators, sensors, andcontroller.


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Manipulator Manipulator is a main bodyof the robot and consists of the

joints, linksand other structural elements of the robot.

It is a collection of mechanical linkages(or link) connectedby joints and included are gears, coupling devices, and so on.

Generally,joints of a manipulator fall into two classes:

rotary

prismatic (linear).

Each of the joints of a robot defines a joint axisalong whichthe particular link either rotates or slides (translates).

Every joint axis identifies a degree of freedom(DOF).No. of DOFs = No. of Joints.


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Manipulator.. Regardless of its mechanical

configuration, the manipulator defined bythejoint-link structuregenerally containsthree main structural elements as humanparts:

the arm

the wrist the end effector.Most robots are mounted on stationary base

on the floor and its connection to the firstjoint as called link 0. The output link of

joint 1 is link 1, and so on.


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Manipulator...

Besides the mechanical components, most manipulatorsalso contain the devices for producing the movement of thevarious mechanical members.

These devices are referred to as actuatorsand may bepneumatic, hydraulic, or electrical in nature.

They are either directly or indirectly, coupledto the variousmechanical links or joints (axes) of the arm.

In the latter case, gears, belts, chains, harmonic drives, orlead screwscan be used.

The interface between the last link and the end effector is

called the tool mounting plate or tool flange.

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1 robotics