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Work Systems and the Methods, Measurement, and Management of Work by Mikell P. Groover, ISBN 0-13-140650-7.

©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Motion Study and Work Design

Sections:

1. Basic Motion Elements and Work

Analysis

2. Principles of Motion Economy and

Work Design Principles that apply to the use of the human body

Principles that apply to the workplace arrangement

Principles that apply to the design of tooling and

equipment

Chapter 10

Work Systems and the Methods, Measurement, and Management of Work by Mikell P. Groover, ISBN 0-13-140650-7.

©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Definitions

Motion study - analysis of the basic hand, arm, and

body movements of workers as they perform work

Work design - design of the methods and motions

used to perform a task

Design of the work system

Includes:

Workplace layout and environment

Tooling and equipment used in the task workholders,

fixtures, power tools, etc.

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Basic Motion Elements

Frank Gilbreth – first to analyze and classify the basic motion elements

“Therblig”s – 17 basic motion elements Spelled backward except for “th”

Therbligs are the basic building blocks of virtually all manual work performed at a single location (so the primary interest is the hand motions).

Therbligs involves both physical and mental elements.

Although it is first used in production and logistics, the

principles are also applicable to service industry.

17 Therbligs Basic Motion Elements

1. Transport empty (TE) – reach for an object with empty hand

– today we call it “reach”

2. Grasp (G) – grasp an object by contacting and closing the

fingers until control has been achived

3. Transport loaded (TL) – move an object with hand and arm

– today we call it “move”

4. Hold (H) – hold an object with one hand

5. Release load (RL) – release control of an object

6. Use (U) – manipulate/use a tool (use screwdriver or

hammer)

7. Pre-position (PP) – position object for next operation.

8. Position (P) – position object in defined location

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17 Therbligs (continued)

9. Assemble (A) – join two parts

10. Disassemble (DA) – separate multiple parts that were

previously joined

11. Search (Sh) – attempt to find an object using eyes or hand

12. Select (St) – choose among several objects in a group

(hand-eye coordination is involved)

13. Plan (Pn) – decide on an action (a short pause or

hesitation تردد in the motions)

14. Inspect (I) – determine quality of object using the eyes

15. Unavoidable delay (UD) – waiting due to factors beyond

worker control (e.g., waiting for a machine to complete its

feed motion)

16. Avoidable delay (AD) – worker waiting (e.g., use the

mobile)

17. Rest (R) – resting to overcome fatigue

Therbligs

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Therbligs

Therbligs

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Therbligs

Example (Right hand/left hand activity

chart from chapter 9)

Seq. Work element description Worker time

1 A worker picks up board with left hand and holds it. 0.08 min.

2 Worker picks peg from tray and inserts it into hole in board with right hand. 0.06 min.

3 Worker picks second peg from tray and inserts it into hole in board with right hand

0.06 min.

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Example

Classification of Therbligs

Effective therbligs:

Physical Basic Motion Elements: Transport empty

Grasp

Transport loaded

Release load

Use

Assemble

Disassemble

Mental Basic Elements: Inspect

Delay Elements: Rest

Ineffective therbligs:

Physical Basic Motion Elements: Hold

Pre-position

Physical and Mental Basic Motion Elements:

Position

Search

Select

Mental Basic Elements: Plan

Delay elements: Unavoidable delay

Avoidable delay

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Micromotion Analysis

Analysis of therbligs that make up a repetitive task

Objectives: Eliminate ineffective therbligs if possible; for

example, eliminate the need to search for parts or tools by positioning them in a known & fixed location in the workplace.

Avoid holding objects with hand – Use workholder

Combine therbligs – Perform right-hand and left-hand motions simultaneously

Simplify overall method resequence of therbligs in the cycle

Reduce time for a motion, e.g., shorten distance of therbligs such as transport loaded.

Principles of Motion Economy

Developed over many years of practical experience in work design

Guidelines to help determine

Work method

Workplace layout

Tools, and equipment

Objective: to maximize efficiency and minimize worker fatigue

Note: Micromotion Analysis checklist for possible improvement in therbligs

(see Table 10.3, page 264 in textbook)

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Three Categories of Motion Economy

& Work Design Principles

1. Principles that apply to the use of the human

body

2. Principles that apply to the workplace

arrangement

3. Principles that apply to the design of tooling

and equipment

1. Use of Human Body

1. Design work to fully utilize both hands (the worker uses always the preferred hand to accomplish most of the work).

2. Hand and arm motions should be symmetrical and simultaneous to minimize hand/arm-eye coordination

Avoid different independent motions of hands/arms

3. Design work to favor preferred hand

Work units should enter the workplace on the side of the worker’s preferred hand (preferred hand is faster & stronger)

Most applicable to manual work. There are 12 principles related to the use of human body.

Important principles related to the worker hands

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An experiment (Example)

A relatively simple task

Reaching, selecting, grasping, transporting, releasing

small parts.

Two types of containers

A rectangular bin

A bin with a tray

The worker performed the work cycle with each container using

Only the right hand

Only the left hand

Both hands performing symmetrical and simultaneous motions.

bin with a tray rectangular bin

Note: Worker is a right-handed person

0.74 sec /

work unit

0.54 sec /

work unit (1.10/1.04)*100%

Since, the worker

is right-handed

worker

(base time)

1. Use of Human Body

4. Take advantage of gravity – Don’t oppose it

Important principles related to utilize laws of physics

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1. Use of Human Body

5. Use lowest classification of hand and arm

motion (five classifications)

1) Finger

2) Finger and wrist

3) Finger, wrist, and forearm

4) Finger, wrist, forearm, and upper arm

5) Finger, wrist, forearm, upper arm, and

shoulder

I Movement of the

fingers only as when

picking up a cotton roll.

II Fingers and wrist

motion as used when

transferring an

instrument to the

operator,

or manipulating a hand

instrument.

1. Use of Human Body

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III Fingers, wrist, and

forearm as when

reaching for a

handpiece.

IV

The entire arm when

reaching for

supplies away from

the work area, or to

adjust the operating

light.

1. Use of Human Body

V The entire arm and

shoulder as when

turning around to reach

for equipment from

adjacent fixed cabinetry.

1. Use of Human Body

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1. Use of Human Body

For using body members other than the hands,

and arms

6. Design method to utilize feet and legs where

appropriate

Since they are stronger than arms

2. Workplace Arrangement

Principles for Design of the workplace

1. Locate tools and materials in fixed positions within the

work area

2. Locate tools and materials close to where they are

used

To minimize the distances to be covered

3. Locate tools and materials to be consistent with

sequence of work elements

Decrease the time required for searching

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2. Workplace Arrangement

Normal and maximum working areas in the

workplace

Design for

average

user

Illustration of First Three Principles

Poor arrangement

of parts and tools

in workplace

Numbers indicate the sequence of operations

Good arrangement

of parts and tools

in workplace

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2. Workplace Arrangement

4. Use gravity feed bins to deliver

small parts and fasteners

Two types of bins used for small parts and

fasteners in the workplace:

(a) gravity feed bin

(b) conventional rectangular bin

5. Provide adequate illumination Also color, constrast among items, location of the

light source are important

2. Adjustable Chair for Workplace

6. A proper chair should be provided for the worker • Adjustable to the size of the worker • Seat height and back adjustments • Padded seat and back

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3. Design of Tooling and Equipment

1. Workholding devices should be designed for the task

2. Hands should be relieved of work elements that can be performed by the feet using foot pedals

sewing machine OR advance welding machine

3. Combine multiple functions into one tool where possible

Hammers designed for stick and remove nails

4. Perform multiple operations simultaneously rather than sequentially

Pneumatically powered, multiple-spindle lug nut to attach tires to the car assembly.

Design of Tooling and Equipment

5. Design equipment controls for operator convenience and error avoidance

Controls (e.g., switches and push buttons) should be located within easy reach to minimize the body motions required to access them

6. Mechanize or automate manual operations if economically and technically feasible