Transcript MOTION STUDY AND WORK DESIGN

Motion Study
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Definition
Analysis of the basic
hand, arm, and body
movements of workers
as they perform work
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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”
 Basic building blocks of virtually all manual work
performed at a single location (so the primary interest
is the hand motions)
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17 Therbligs
1.
2.
3.
4.
5.
6.
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
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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
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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 fatigue
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Therbligs
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.
Therbligs
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.
Therbligs
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.
Therbligs
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.
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
 Method study at the therblig level seeks to
eliminate or reduce ineffective therbligs.
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Time Study
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Definition
all the ways in which
time is analyzed in
work situations
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Time is important, because;
 Most workers are paid for their time on the job
 The labor content (cost of labor time) is often a
major factor in the total cost of a product or service
 For any organization, it is important to know how
much time will be required to accomplish a given
amount of work
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When Are Time Standards Beneficial?
 Characteristics of industrial situations in which
time standards would be beneficial
 Low productivity
 Repeat orders
 Long production runs
 Repetitive work cycles
 Short cycle times
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Functions of Time Standards
 They define a “fair day’s work”
 They provide a means to convert workload into
staffing and equipment needs
 They allow alternative methods to be
compared objectively
 They provide a basis for wage incentives and
evaluation of worker performance
 They provide time data for:
 Production planning and scheduling
 Cost estimating
 Material requirements planning
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Average Worker
A worker who is representative of the persons
who usually perform tasks similar to the task
being measured
 If the work is performed mostly by men, then
the average worker is male
 If the work is performed mostly by women, then
the average worker is female
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Standard Performance
A pace of working that can be maintained by an
average worker throughout an entire work shift
without harmful effects on the worker’s health
or physical well-being
 The work shift includes periodic rest breaks
and occasional interruptions are experienced
by the worker
 Benchmarks of standard performance(EX:
 Walking at 3 miles/hr on level flat ground
 Dealing four hands of cards from a 52 card
deck in exactly 30 sec)
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Distribution of Worker Performance
Worker performance is expressed in terms of
daily output
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How a Standard Time is Defined
Distribution of worker performance, indicating
how standard time is defined so that it can be
readily achieved by most workers
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Allowances in Time Standards
 Normal time is adjusted by an allowance factor
Apfd to obtain the standard time
 Purpose of allowance factor is to compensate for
lost time due to work interruptions and other
reasons
 Standard time:
Tstd = Tn(1 + Apfd)
where pfd = Personal time, Fatigue, and Delays
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Rest Periods
 Common in industry
 Paid for by the employer as regular work
time
 Rest breaks usually included in allowance
factor built into the time standard
 Relatively short duration - 5 to 20 minutes
 Meal periods - not included
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ERGONOMY
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Definition
Ergonomics can be defined as
the application of knowledge of
human characteristics to the
design of systems
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Human Variability
 Differences in body dimensions exist among
people because of:
 Ethnicity and Nationality
 Heredity
 Diet
 Health
 Sex
 Age
 Living conditions
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Static Dimensions of Human Body
Standing
Seated
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Anthropometric Design Principles
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
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Design for extreme individuals
Design for adjustability
Design for the average user
Design different sizes for different size users
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Design for Extreme Individuals
 Designing for the maximum
 Doorway heights
 Automobile door openings
 Mattress sizes
 Designing for the minimum
 Heights of kitchen cabinets
 Locations of levers and dials on equipment
 Weights of portable power tools
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Design for Adjustability
 To accommodate a wide range of users
 Examples:
 Automobile driver seats
 Adjustable steering wheel in an automobile
 Office chairs
 Worktable heights
 Tilt angles of computer monitors
 Lawnmower handle heights
 Bicycle handlebars
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Adjustable Chair for Workplace
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Design for Average User
 For situations in which design for extreme
individuals and adjustability are not feasible
 Examples:
 Stair heights
 Stadium seats
 Sofas
 Heights of checkout counters at
supermarkets
 Lengths of shovel handles
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Workplace Arrangement
 Normal and maximum working areas in the
workplace
Design for
average
user
Work Systems and the Methods, Measurement, and Management of Work
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Different Sizes for Different Size Users
 When the only way to accommodate user
population is to make the product in different
sizes
 Examples:
 Clothing
 Shoes
 Elementary school desks and chairs
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The Physical Work
Environment
1.The Visual Environment and
Lighting
2.The Auditory Environment
and Noise
3.Climate Control in the Work
Environment
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Visual Environment and Lighting
 About 80% of the information input to the human
brain comes from visual stimuli
Relative possibility of being seen under prevailing
conditions of light, distance, and related factors
 Most important factor = level of illumination
 Other factors:
 Visual angle - angle subtended at the eye by the
smallest distinguishable detail
v = 3438 h/d
where v is measured in arc minutes
 Brightness contrast - relative luminance between
object and background
 Color
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Lighting Systems
 Lamp - a single artificial source of light (e.g., an
incandescent lamp, fluorescent lamp)
 Luminaire - complete lighting unit, including
 One or more lamps
 Reflectors and other apparatus to distribute
the light
 Means to connect to power supply
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Auditory Environment and Noise
 The second most important means by which
humans receive information
 Visual and auditory stimuli account for 95% or
more of a person's information input
 The auditory environment also includes:
 Noise - defined as unwanted sound
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Effects of Noise on Humans
 Distraction
 Negative emotions such as annoyance,
frustration, anger, and fear
 Interference with conversation, thinking, and
other cognitive processes
 Interference with sleeping
 Temporary hearing loss
 Permanent hearing loss
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Climate Control
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Four primary variables that define climate:
1. Air temperature
2. Humidity - usually relative humidity
3. Air movement
4. Radiation from surrounding objects,
including the sun
Most comfortable working environment (called
the comfort zone)
 Air temperature = 19 to 26C (66 to 79F)
 Relative humidity = 50%
 Slow air movement = 0.2 m/s (0.64 ft/sec)
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Heat Stress
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
Occurs when body absorbs more heat than it
gives off, raising the body core temperature
Illnesses resulting from heat stress:
1. Heat rash - areas of skin erupt into red or
white bumps due to inflammation of sweat
glands
2. Heat cramps - spasms of muscles in physical
labor
3. Heat exhaustion - muscle weakness, nausea,
dizziness
4. Heatstroke - fever, dry skin, convulsions,
coma (in extreme cases: death)
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Cold Stress
 Drop in core body temperature below normal
due to net heat loss from combination of low
temperature and air movement
 Windchill factor - estimates cooling effect of
moving air on exposed skin
 Jobs where cold stress is a problem:
 Refrigerated warehouses
 Construction jobs in wintertime
 Aboard ships in extreme northern climates
 Research in Antarctica
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