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IE 101-Industrial Engineering Orientation
Fall 2009
Motion and Time Study
Engin Topan
Methodology
Outline of MTS
• Develop System
– Design work methods (sequence
of operations and procedures)
that make up the preferred
solution
– Find better methods for work
• Standardize
– Form written
operations
standards
– Determine a standard time for
each operation
– Train the operators
Standardize
for
• Time Standards
• Training
Methods
Develop System
Design
Work
Time Standards
Meas.mnt
Training
Defining Work Systems
Work
• Is our primary means of livelihood
• Serves an important economic function in
the global world of commerce
• Creates opportunities for social interactions
and friendships
• Provides the products and services that
sustain and improve our standard of living
Defining Work Systems
• Work consists of tasks
– Tasks consist
elements
of
work
• Work elements consist of basic
motion elements
Defining Work Systems
Task
• An amount of work that is assigned to a worker or for
which a worker is responsible
– Repetitive task – as in mass production
– Non-repetitive task – performed periodically, infrequently, or only
once
Work Element
• A series of work activities that are logically grouped
together because they have a unified function in the task
– Example: assembling a component to a base part using several nuts
and bolts
Defining Work Systems
Basic Motion Elements
• Actuations of the limbs and other body parts
– Examples:
•
•
•
•
•
Reaching for an object
Grasping the object
Moving the object
Walking
Eye movement
– A work element consists of multiple basic motion
elements
1.3 Defining Work Systems
• “Time=Money”? How?
–
–
–
–
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New product introduction
Product cost
Delivery time
Overnight delivery
Competitive bidding
Production scheduling
• Increase profit using less time!
Defining Work Systems
• Importance of Time in Work
– Time is the most frequently used measure of work
• How many minutes or hours are required to perform a given
task?
– Most workers are paid by the time they work
• Hourly wage rate
• Salary
– Workers must arrive at work on time
– Labor and staffing requirements computed in units of
time
Defining Work Systems
• A work system is a system consisting of
humans, information, and equipment
designed to perform useful work
– Contributes to the production of a product or
delivery of a service
– Examples:
• Worker operating a machine tool in a factory
• Robotic welding line in an automobile plant
• A receptionist answering incoming phone calls
Defining Work Systems
Productivity
Production as a function in Economics
Q=f(K,L)
• Q: Output, K: Capital, L: Labor
• Is there a way to change function f with a
better function g?
• Better Function=Higher Productivity
Productivity
Productivity
• The level of output of a given process relative to
the level of input
• Process can refer to
– Individual production or service operations
– A national economy
• Productivity is an important metric in work
systems because
– Improving productivity is the means by which
worker compensation can be increased without
increasing the costs of products and services they
produce
Productivity
Labor Productivity
• The most common productivity measure is
labor productivity, defined by the following
ratio:
WU
LPR =
LH
– LPR = labor productivity ratio
– WU = work units of output
– LH = labor hours of input
Productivity
Labor Productivity Index
•Measure that compares input/output ratio from
one year to the next
LPI =
LPRt
LPRb
– LPI = labor productivity index
– LPRt = labor productivity ratio for period t
– LPRb = labor productivity ratio for base period
Productivity
Example
• During the base year in a small steel mill, 326,000
tons of steel were produced using 203,000 labor
hours. In the next year, the output was 341,000
tons using 246,000 labor hours.
Determine: (a) the labor productivity ratio for the
base year, (b) the labor productivity ratio for the
second year, and (c) the productivity index for the
second year.
Productivity
Solution
(a) In the base year, LPR = 326,000 / 203,000
= 1.606 tons per labor hour
(b) In the second year, LPR = 341,000 / 246,000
= 1.386 tons per labor hour
(c) Productivity index for the second year
LPI = 1.386 / 1.606 = 0.863
• Comment: No matter how it’s measured, productivity
went down in the second year.
Productivity
Labor Factor in Productivity
• Labor itself does not contribute much to
improving productivity
• More important factors:
– Capital - substitution of machines for human
labor
– Technology - fundamental change in the way
some activity or function is accomplished
Productivity
Horse-drawn carts
Railroad trains
Steam locomotive
Diesel locomotive
Telephone operator
Dial phone
Manually operated
milling machine
Numerically controlled
(NC) milling machine
Productivity
Measuring Productivity
• Not as easy as it seems because of the
following problems:
– Nonhomogeneous output units
– Multiple input factors
• Labor, capital, technology, materials, energy
– Price and cost changes due to economic forces
– Product mix changes
• Relative proportions of products that a company sells
change over time
Productivity
Productive Work Content
• A given task performed by a worker can be
considered to consist of
– Basic productive work content
• Theoretical minimum amount of work required to accomplish
the task
– Excess nonproductive activities
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•
•
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Extra physical and mental actions of worker
Do not add value to the task
Do not facilitate the productive work content
Take time
Productivity
• Excess Nonproductive Activities can be
classified into three categories:
– Excess activities due to poor design of product
or service
– Excess activities caused by inefficient
methods, poor workplace layout, and
interruptions
– Excessive activities cause by the human factor
Productivity
Allocation of Total Task Time
Work Systems
1. Manual work system
– Worker performing one or more tasks
without the aid of powered tools
2. Worker-machine system
– Human worker operates powered equipment
3. Automated work system
– Process performed without the
participation of a human worker
direct
Work Systems
Manual Work Systems
• Human body accomplishing some physical task
without an external source of power
– With or without hand tools
• When hand tools are used, the power to operate them is
derived from the strength and stamina of a human worker
– Other human faculties are required, such as hand-eye
coordination and mental effort
Work Systems
Manual Work Systems
Work Systems
Pure Manual Work
• Material handler moving cartons in a warehouse
• Assembly worker snap-fitting two parts together
Manual Work with Hand Tools
• Material handling worker using a dolly to move
furniture
• Assembly worker using screwdriver
Work Systems
Worker-Machine Systems
• Worker operating a piece of powered equipment
• Examples:
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Machinist operating a milling machine
Construction worker operating a backhoe
Truck driver driving an 18-wheeler
Worker crew operating a rolling mill
Clerical worker entering data into a PC
Work Systems
Worker-Machine Systems
Work Systems
Automated Work Systems
• Automation is the technology by which a
process or procedure is accomplished
without human assistance
– Implemented using a program of instructions
combined with a control system that executes
the instructions
– Power is required to drive the process and
operate the control system
Work Systems
Automated Work System
Methods
Design
Develop System
Standardize
Time Standards
Training
Methods Design
• 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
• Includes:
– Workplace layout and environment
– Tooling and equipment used in the task
Motion Study
Basic Motion Elements
• Therbligs – 17 basic motion elements
– Basic building blocks of virtually all manual
work performed at a single location
– With modification, used today in several work
measurement systems, e.g., MTM and MOST
• Some of the motion element names and definitions
have been revised
Motion Study
17 Therbligs
1. Transport empty (TE) – reach for an object
2. Grasp (G) – grasp an object
3. Transport loaded (TL) – move an object with
hand and arm
4. Hold (H) – hold an object
5. Release load (RL) – release control of an object
6. Use (U) – manipulate a tool
Motion Study
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) – separate multiple parts that
were previously joined
11. Search (Sh) – attempt to find an object using
eyes or hand
Motion Study
12. Select (St) – choose among several objects
in a group
13. Plan (Pn) – decide on an action
14. Inspect (I) – determine quality of object
15. Unavoidable delay (UD) – waiting due to
factors beyond worker control
16. Avoidable delay (AD) – worker waiting
17. Rest (R) – resting to overcome fatigue
Motion Study
Classification of Therbligs
Ineffective therbligs:
Effective therbligs:
• Hold
• Transport empty
• Pre-position
• Grasp
• Position
• Transport loaded
• Search
• Release load
• Select
• Use
• Plan
• Assemble
• Unavoidable delay
• Disassemble
• Avoidable delay
• Inspect
• Rest
Motion Study
Micromotion Analysis
• 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
Example: A repetitive Manual Task
• Current method: An assembly worker performs
a repetitive task consisting of inserting 8 pegs into
8 holes in a board. A sightly interference fit is
involved in each insertion. The worker holds the
board in one hand and picks up the pegs from a
tray with other hand and inserts them into the
holes, one peg at a time.
Example: A repetitive Manual Task
• Current method and current layout:
Example A repetitive Manual Task
• Improved method and improved layout:
– Use a work-holding device to hold and position
the board while the worker uses both hands
simultaneously to insert pegs.
– Instead of picking one peg at a time, each hand
will grab four pegs to minimize the number of
times the worker’s hands must reach the trays.
Motion Study
Principles of Motion Economy
• Developed over many years
experience in work design
• Guidelines to help determine
of
practical
– Work method
– Workplace layout
– Tools, and equipment
• Objective: to maximize efficiency and minimize
worker fatigue
Work Methods Design
To select preferred work method:
1.
2.
3.
4.
Eliminate all unnecessary work
Combine operations or elements
Change the sequence of operations
Simplify the necessary operations
Develop System
Standardize
Work
Meas.mnt
Time Standards
Training
Time Study and Work
Measurement
Time Is Important
• 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
Time Study and Work
Measurement
• Work measurement – evaluation of a task in
terms of the time that should be allowed by
an average worker to perform the task
• Time study – all the ways in which time is
analyzed in work situations
• Standard time – amount of time that should
be allowed for an average worker to process
one work unit using the standard method
and working at normal pace
Time Study and Work
Measurement
Standard times
• define a “fair day’s work”
• provide a means to convert workload into staffing
and equipment needs
• provide a basis for wage incentives and evaluation
of worker performance
• provide time data for:
– Production planning and scheduling
– Cost estimating
– Material requirements planning
Time Study and Work
Measurement
Task Hierarchy & Work Measurement
Time Study and Work
Measurement
Prerequisites for Valid Time Standards: Factors that must be
standardized before a time standard can be set
Time Study and Work
Measurement
Normal Performance
• A pace of working that can be maintained by a
properly trained average worker throughout an
entire work shift without deleterious short-term
or long-term effects on the worker’s health or
physical well-being
– Normal performance = 100% performance
– Common benchmark of normal performance:
• Walking at 3 mi/hr
Time Study and Work Measurement
Performance Rating
• Analyst judges the performance or pace of
the worker relative to the definition of
standard performance used by the
organization
– Standard performance Pw = 100%
• Slower pace than standard Pw < 100%
• Faster pace than standard Pw > 100%
– Normal time Tn = Tobs(Pw )
Time Study and Work
Measurement
Normal Time
• The time to complete a task when working
at normal performance
Tn = Tobs(Pw )
where Tobs = observed time, Tn = normal
time, and Pw = worker performance or pace
Time Study and Work
Measurement
Example: Normal Performance
• Given: A man walks in the early morning for
health and fitness. His usual route is 1.85
miles. A typical time is 30 min. The
benchmark of normal performance = 3 mi/hr.
• Determine: (a) how long the route would take
at normal performance and (b) the man’s
performance when he completes the route in
30 min.
Time Study and Work
Measurement
(a) At 3 mi/hr, time = 1.85 mi / 3 mi/hr
= 0.6167 hr = 37 min
(b) Rearranging equation, Pw = Tn / Tc
Pw = 37 min / 30 min = 1.233 = 123.3 %
Time Study and Work
Measurement
Reasons for Lost Time at Work
Work-related interruptions
Non-work-related interruptions
• Machine breakdowns
• Waiting for materials or parts
• Receiving instructions from
foreman
• Talking to co-workers about
work-related matters
• Rest breaks for fatigue
• Cleaning up at end of shift
• Personal needs (e.g., restroom
breaks)
• Talking to co-workers about
matters unrelated to work
• Lunch break
• Smoke break
• Beverage break
• Personal telephone call
Time Study and Work
Measurement
How to Allow for Lost Time
• Two approaches used by companies:
1. Scheduled rest breaks during the shift
• Typical - one 15-minute break in mid-morning and
another in mid-afternoon
2. A PFD allowance is added to the normal time

This allows the worker to take a break on his/her
own time
Time Study and Work
Measurement
PFD Allowance
• Personal time
– Rest room breaks, phone calls, water fountain stops,
cigarette breaks (5% typical)
• Fatigue
– Rest allowance to overcome fatigue due to work-related
stresses and conditions (5% or more)
• Delays
– Machine
typical)
breakdowns,
foreman
instructions
(5%
Time Study and Work
Measurement
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
Time Study and Work
Measurement
Standard Time
• Defined as the normal time but with an allowance
added in to account for losses due to personal
time, fatigue, and delays
Tstd = Tn (1 + Apfd)
where Tstd = standard time, Tn = normal time, and
Apfd = PFD allowance factor
where pfd = personal time, fatigue, and delays
• Also called the allowed time
Time Study and Work
Measurement
Standard Performance
• Same as normal performance, but
acknowledges that periodic rest breaks must
be taken by the worker
– Periodic rest breaks are allowed during the
work shift
– Other interruptions and delays also occur
during the shift
Time Study and Work
Measurement
Standard Method
• Must include all of the details on how the task is
performed, including:
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–
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Procedure - hand and body motions
Tools
Equipment
Workplace layout
Irregular work
Working conditions
Setup
Time Study and Work
Measurement
Tc
cycle
time
Pw rating
Tn
normal
time
Apfd allowances
Tstd
standard
time
Time Study and Work
Measurement
Irregular Work Elements
• Elements that are performed with a
frequency of less than once per cycle
• Examples:
– Changing a tool
– Exchanging tote pans of parts
• Irregular elements are prorated into the
regular cycle according to their frequency
Time Study and Work
Measurement
Example: Determining Standard Time
• Given: The normal time to perform the regular
work cycle is 3.23 min. In addition, an irregular
work element with a normal time = 1.25 min is
performed every 5 cycles. The PFD allowance
factor is 15%.
• Determine (a) the standard time and (b) the
number of work units produced during an 8-hr
shift if the worker's pace is consistent with
standard performance.
Time Study and Work
Measurement
(a) Normal time Tn = 3.23 + 1.25/5
= 3.48 min
Standard time Tstd = 3.48 (1 + 0.15)
= 4.00 min
(b) Number of work units produced during an
8-hr shift
Qstd = 8.0(60)/4.00 = 120 work units
Direct Time Study
• Direct and continuous observation of a task using
a stopwatch or other timekeeping device to record
the time taken to accomplish the task
• While observing and recording the time, an
appraisal of the worker’s performance level is
made to obtain the normal time for the task
• The data are then used to compute a standard time
for the task
Direct Time Study
Direct Time Study Procedure
1. Define and document the standard method
2. Divide the task into work elements
3. Time the work elements to obtain the observed time Tobs
4. Evaluate worker’s pace relative to standard performance
to obtain normal time Tn
–
Called performance rating (PR)
Tn = Tobs(PR)
5. Apply allowance factor to compute standard time
Tstd = Tn(1 + Apfd)
Direct Time Study
Document the Standard Method
• Determine the “one best method”
– Seek worker’s advice if possible
• Documentation should include:
– All of the steps in the method
– Special tools, gauges, equipment and equipment settings (e.g.,
feeds and speeds) if applicable
– Irregular elements and their frequency
• Once the standard method is defined, it should not be
possible for the operator to make further improvements
Direct Time Study
Direct time study
form
Direct Time Study
Example
• A direct time study was taken on a manual work element
using the snapback method. The regular cycle consisted of
three elements, a, b, and c. Element d is an irregular
element performed every five cycles.
Work element
a
Observed time (min) 0.56
Performance rating 100%
b
0.25
80%
c
0.50
110%
d
1.10
100%
• Determine (a) normal time and (b) standard time for the
cycle
Direct Time Study
(a) Normal time:
Tn = 0.56(1.00) + 0.25(0.80) + 0.50(1.0)
+ 1.10(1.0)/5 = 1.53 min
(b) Standard time:
Tstd = 1.53(1 + 0.15) = 1.76 min
Work Sampling
Statistical technique for determining the proportions of
time spent by subjects in various defined categories
of activity
• Subjects = workers, machines
• Categories of activity = setting up a machine,
producing parts, idle, etc.
• For statistical accuracy
– Observations must be taken at random times
– Period of the study must be representative of the types of
activities performed by the subjects
Work Sampling
When is Work Sampling Appropriate?
• Sufficient time is available to perform the study
– Several weeks usually required for a work sampling
study
• Multiple subjects
– Work sampling suited to studies involving more than
one subject
• Long cycle times for the jobs covered by the study
• Nonrepetitive work cycles
– Jobs consist of various tasks rather than a single
repetitive task
Work Sampling
Example: How Work Sampling Works
• A total of 500 observations taken at random times during a
one-week period (40 hours) on 10 machines with results
shown below.
Category
No. of observations
(1) Being set up
75
(2) Running production
300
(3) Machine idle
125
500
• How many hours per week did an average machine sped in
each category?
Work Sampling
• Proportions of time determined as number of
observations in each category divided by 500
• Time in each category determined by multiplying
proportion by total hours (40 hr)
Category
Proportion Hrs per category
(1) Being set up
75/500 = 0.15
0.15 x 40
= 6
(2) Running production
300/500 = 0.60
0.60 x 40
= 24
(3) Machine idle
125/500 = 0.25
0.25 x 40 = 10
1.00
40
Work Sampling
Work Sampling Applications
• Machine utilization - how much time is spent by
machines in various categories of activity
– Previous example
• Worker utilization - how workers spend their time
• Allowances for time standards - assessment of delay
components in PFD allowance factor
• Average unit time - determining the average time on
each work unit
• Time standards - limited statistical accuracy when
standards set by work sampling
Work Sampling
Work Sampling
Observation
Form
References
• Groover, Mikell P., Work Systems: The
Methods, Measurement & Management of
Work, 2007, Prentice Hall
• Barnes, Ralph M., Motion and Time Study:
Design and Measurement of Work, 1990,
John Wiley & Sons Inc.