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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