Motion%20Study%20and%20Work%20Design

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Motion Study and Work Design

• Sections
• Basic Motion Elements and Work Analysis
• Principles of Motion Economy and Work Design

Chapter 10
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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.

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Basic Motion Elements

• Frank Gilbreth first to analyze and classify
  the basic motion elements
• Therbligs 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)
• 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.

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17 Therbligs

• Transport empty (TE) reach for an object with
  empty hand today we call it reach
• Grasp (G) grasp an object by contacting and
  closing the fingers until control has been
  achived
• Transport loaded (TL) move an object with hand
  and arm today we call it move
• Hold (H) hold an object with one hand
• Release load (RL) release control of an object
• Use (U) manipulate/use a tool
• Pre-position (PP) position object for next
  operation
• Position (P) position object in defined location

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17 Therbligs (continued)

• Assemble (A) join two parts
• Disassemble (DA) separate multiple parts that
  were previously joined
• Search (Sh) attempt to find an object using
  eyes or hand
• Select (St) choose among several objects in a
  group (hand-eye coordination is involved)
• Plan (Pn) decide on an action (a short pause or
  hesitation ???? in the motions)
• Inspect (I) determine quality of object using
  the eyes
• Unavoidable delay (UD) waiting due to factors
  beyond worker control
• Avoidable delay (AD) worker waiting
• Rest (R) resting to overcome fatigue

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Therbligs
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Therbligs
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Therbligs
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Therbligs
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Therbligs
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Therbligs
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Example
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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
• 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

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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

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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

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1. Use of Human Body

• Most applicable to manual work
• Design work to fully utilize both hands
• The two hands should begin and end their motions
  at the same time to distribute the work equally
  to hands
• Hand and arm motions should be symmetrical and
  simultaneous to minimize hand/arm-eye
  coordination
• Avoid different independent motions of hands/arms
• Design work to favor preferred hand
• Work units should enter the workplace on the side
  of the workers preferred hand
• Workers two hands should not be idle at the same
  time
• except for the rest breaks
• Dont forget that not all tasks can be organized
  according to these principles.

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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.

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0.72 sec / work unit
0.54 sec / work unit
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1. Use of Human Body

• Utilize laws of physics
• 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 workers time and energy
• Use momentum (mass velocity) to facilitate task
• Carpenter using a hammer to strike a nail
• Take advantage of gravity Dont oppose it
• Method should achieve a natural rhythm of the
  motions involved

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1. Use of Human Body

• Use lowest classification of hand and arm motion
  (five classifications)
• Finger
• Finger and wrist
• Finger, wrist, and forearm
• Finger, wrist, forearm, and upper arm
• Finger, wrist, forearm, upper arm, and shoulder

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1. Use of Human Body
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.
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1. Use of Human Body
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.
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1. Use of Human Body
V The entire arm and shoulder as when turning around to reach for equipment from adjacent fixed cabinetry.
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1. Use of Human Body

• For using body members other than the hands, and
  arms
• Minimize eye focus and travel
• Minimize the distance between the object
• Design method to utilize feet and legs where
  appropriate
• Since they are stronger than arms

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2. Workplace Arrangement

• Design of the workplace
• Locate tools and materials in fixed positions
  within the work area
• Locate tools and materials close to where they
  are used
• To minimize the distances to be covered
• 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
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Illustration of First Three Principles
Good arrangement of parts and tools in workplace
Poor arrangement of parts and tools in workplace
Numbers indicate the sequence of operations
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2. Workplace Arrangement

• 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

• Use gravity drop chutes for completed work units
  where appropriate
• Provide adequate illumination
• Also color, constrast among items, location of
  the light source are important

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2. Adjustable Chair for Workplace

• 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

• Workholding devices should be designed for the
  task
• Hands should be relieved of work elements that
  can be performed by the feet using foot pedals
• sewing machine
• Combine multiple functions into one tool where
  possible
• Pencils designed for writing and erasing
• Perform multiple operations simultaneously rather
  than sequentially
• Multiple-spindle drill presses to drill holes in
  PCBs

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Design of Tooling and Equipment

• Where feasible, perform operation on multiple
  parts simultaneously
• Machines in a cake factory
• 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
• 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
• Mechanize or automate manual operations if
  economically and technically feasible