Basic Motion Elements Basic Motion Elements(continued)ie202.cankaya.edu.tr/uploads/files/Ch10-Motion...

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

Chapter 10




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 such as

workholders, fixtures, power tools, etc.




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”

� Basic building blocks of virtually all manual work performed at a single location (so the primary interest is the hand motions)

� With modification, used today in several work measurement systems, e.g., MTM (Methods-Time Measurement)




Basic Motion Elements (continued)

� “Therblig”s – 17 basic motion elements

� Some of the motion element names and definitions

have been revised

� 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

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 toolWork Systems and the Methods, Measurement, and Management of Work



17 Therbligs (continued)

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

operation

8. Position (P) – position object in defined

location

9. Assemble (A) – join two parts

10. Disassemble (DA) – seperate multiple parts

that were previously joined

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

eyes or hand




17 Therbligs (continued)

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 in the motions)

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

the eyes

15. Unavoidable delay (UD) – waiting due to

factors beyond worker control

16. Avoidable delay (AD) – worker waiting

17. Rest (R) – resting to overcome fatigueWork Systems and the Methods, Measurement, and Management of Work



Therbligs




Therbligs




Therbligs




Therbligs




Therbligs




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

� Method study at the therblig level seeks to

eliminate or reduce ineffective therbligs.




Micromotion Analysis

� The main idea of method study at the therblig

level: seeks to eliminate or reduce ineffective

therbligs.

� Each therblig represents time and energy

expended by a worker.

� If task is repetitive, this will be performed many

times. Then, it becomes meaningul to analyze

therbligs.

� Known as micromotion analysis Work Systems and the Methods, Measurement, and Management of Work



Micromotion Analysis

� Analysis of therbligs that make up a repetitive task

� Objectives:� Eliminate ineffective therbligs if possible

� Avoid holding objects with hand – Use workholder

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

� Simplify overall method

� Reduce time for a motion, e.g., shorten distance

� Checklists: � Checklist1 (discussed in the in class)

� Checklist2 (given in the book – Table 10.3)




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

� Many people don’t understand why these principles are necessary, but you know that these principles are violated in work systems (think about your summer training).




Three Categories of 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




Use of Human Body

Most applicable to manual work

1. Design work to fully utilize both hands

2. The two hands should begin and end their motions at the same time to distribute the work equally to hands

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

� Avoid different independent motions of hands/arms

4. Design work to favor preferred hand

� Work units should enter the workplace on the side of the worker’s preferred hand

5. Worker’s two hands should not be idle at the same time

� except for the rest breaks

� Don’t forget that not all tasks can be organized according to these principles.




An experiment

� 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.




0.72 sec /

work unit

0.54 sec /

work unit




Use of Human Body

Utilize laws of physics

6. Method should consist of smooth continuous curved motions rather than straight motions with abrupt changes in direction

� Although shortest distance between two points is a straight line

� Because straight-line path sequence includes start and stop actions (accelerations and decelerations) consume worker’s time and energy

7. Use momentum (mass * velocity) to facilitate task

� Carpenter using a hammer to strike a nail

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

9. Method should achieve a natural rhythm of the motions involved




Use of Human Body

10. 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.




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.




V The entire arm and shoulder as when

turning around to reach for equipment

from adjacent fixed cabinetry.




Use of Human Body

For using body members other than the hands,

and arms

11. Minimize eye focus and travel

� Minimize the distance between the object

12. Design method to utilize feet and legs where

appropriate

� Since they are stronger than arms




Workplace Arrangement

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





� 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 Work Systems and the Methods, Measurement, and Management of Work



Illustration of First Three Principles

Good arrangement of parts and tools in workplace

Numbers indicate the sequence of operations





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. Use gravity drop chutes for completed work units where appropriate

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

light source are important

7. 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




Adjustable Chair for Workplace




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

3. Combine multiple functions into one tool where possible

� Pencils designed for writing and erasing

4. Perform multiple operations simultaneously rather than sequentially

� Multiple-spindle drill presses to drill holes in PCBs




Design of Tooling and Equipment

5. Where feasible, perform operation on multiple parts simultaneously

� Machines in a cake factory

6. Design equipment controls for operator convenience and error avoidance

� Controls should be located within easy reach to minimize the body motions required to access them

7. Hand tools and portable power tools should be designed for operator comfort and convenience

� e.g. tools that can accomodate both right-handed and left-handed workers

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

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