IE 366
Chapter 25
Time Study
Supplementary Material from:
Groover, M.P. (2007). Work Systems and the Methods, Measurement, and Management of Work,
Upper Saddle River, NJ: Pearson Prentice Hall, pp. 319 - 360.
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Time Study
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Also known as
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Involves
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direct, continuous observation of a task
using a time measurement instrument
to record time taken to complete task.
Allowances made for
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Direct Time Study
Stopwatch Time Study
personal needs
fatigue
unavoidable delays
Dates back to 1883
Inextricably connected with origins and early history of IE
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Direct Time Study Procedure
1.Define and Document Standard Method
2.Divide Task Into Work Elements
3.Time Work Elements
4.Rate Worker’s Performance
5.Apply Allowances
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Define and Document
Standard Method
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Goal: “one best method”
Seek worker’s advice, if appropriate
Elements of Document
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Procedure (steps, actions, work elements, hand/body
motions)
Tools, equipment
Machine settings (e.g., feeds, speeds)
Workplace layout
Frequency of irregular elements
Working conditions
Setup
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Reasons For Thorough
Documentation
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Batch production (likely to be repeated)
Methods improvement by operator
Disputes about method (too tight?)
Data for standard data system
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Divide Task Into Work
Elements
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Series of motion activities logically grouped because
of unified purpose.
Guidelines
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Each work element should consist of a logical group of
motion elements.
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Beginning point of one element should be end of previous.
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No time gap between elements.
Each element should have readily identifiable end point.
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e.g., reach, grasp, move, place
i.e., easily detected, no ambiguity
Work elements should not be too long.
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< “several” min
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Divide Task Into Work
Elements
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Guidelines (continued)
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Work elements should not be too short.
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Irregular elements should be identified & distinguished.
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i.e., not every cycle
Manual elements should be separated from machine
elements.
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> 3 sec
generally constant values
Internal elements should be separated from external
elements.
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i.e., performed by operator during machine cycle
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“Irregular” and “Foreign”
Elements
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Elements that occur routinely, but not every cycle – should be
included: irregular elements (Groover)
Elements that the observer didn’t anticipate –probably should
be included: irregular elements (Konz & Johnson)
Elements that are not normal work – should not be included:
foreign elements (Konz & Johnson)
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Time Work Elements
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Collect data on time study form (on clipboard).
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Time Work Elements (2)
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Collect data on time study form (on clipboard).
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Time Work Elements (3)
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Use stopwatch calibrated in 0.01 minutes:
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Snapback method
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Start watch at beginning of every element.
“Snap” watch back to zero at end of element.
Record time.
Advantages
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Element variations easily observable
No subtraction
Continuous method
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Start watch at beginning of observation (or beginning of each
cycle)
Record elapsed time at end of each element.
Let it run …
Advantages
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Not so much manipulation of stopwatch
Elements not so easily omitted
Regular/irregular elements more readily distinguished (?)
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Rate Worker’s Performance
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Standard performance = 100%
Rate
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Individual elements
Or entire work cycle
Most difficult & controversial step in time study
Requires analyst’s judgment
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Apply Allowance
Pure Manual Work
Work Element
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b
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d*
Obs. Time
0.56 min
0.25 min
0.50 min
1.10 min
Perf. Rating
100%
80%
110%
100%
* irregular element performed every 5 cycles
PFD Allowance = 15%
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Apply Allowance
Pure Manual Work
Work Element
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Obs. Time
0.56 min
0.25 min
0.50 min
1.10 min
Perf. Rating
100%
80%
110%
100%
* irregular element performed every 5 cycles
PFD Allowance = 15%
Normal Time:
NT = 0.56(1.00) + 0.25(0.80) + 0.50(1.10) + 1.10(1.00)/5
= 0.56 + 0.20 + 0.55 + 0.22 = 1.53 min
Standard Time:
ST = 1.53(1 +0.15) = 1.76 min
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Apply Allowance
Task Including Machine Cycle
Work Element
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Obs. Time
0.22 min
0.65 min
0.47 min
0.75 min
Perf. Rating
100%
80%
100%
100%
(idle)
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1.56 min
(idle)
(idle)
Mach. Time
PFD Allowance = 15%
Machine Allowance = 20%
* irregular element performed every 15 cycles
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Apply Allowance
Task Including Machine Cycle
Work Element
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b
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d*
Obs. Time
0.22 min
0.65 min
0.47 min
0.75 min
Perf. Rating
100%
80%
100%
100%
(idle)
m
1.56 min
(idle)
(idle)
Mach. Time
PFD Allowance = 15%
Machine Allowance = 20%
* irregular element performed every 15 cycles
Normal Time:
NT = 0.22(1.00) + Max{0.65(0.80), 1.56} + 0.47(1.00) + 0.75(1.00)/15
= 0.22 + 1.56 + 0.47 + 0.05 = 2.30 min
Standard Time:
ST = (0.22 +0.47 + 0.05)(1 + 0.15)
+ Max{0.52(1 + 0.15), 1.56(1 + 0.20)}
= 0.85 + 1.87 = 2.72 min
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Number of Cycles To Be
Timed
Let X be a random variable, time of one work element in a task.
Time several cycles to estimate true mean:
close estimate
low estimate
high estimate
1-α
1-α
α/2
α/2
1-α
α/2
α/2
α/2
x
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α/2
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μX
Overall, P(μx lies within x + zα/2 [σ/√nc ]) = 1 – α
where nc = number of cycles timed
But σ unknown, so take preliminary sample of ns observations and use
s=
∑(x-x)2
ns-1
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Number of Cycles To Be
Timed (2)
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P(μ lies within x + tα/2 [s/√nc ]) = 1 – α
Interval size = x + kx
where k = proportion of sample mean
(e.g., if k = 10%, interval size = x + 0.10 x)
kx = tα/2 [s/√nc ] (remember, s is an estimate of σ based on preliminary sample of ns)
So, rearranging,
nc = (tα/2s / kx)2
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Number of Cycles To Be
Timed: Example
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From preliminary study, engineer has collected n s=10 samples on one work
element
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x = 0.40 min
s = 0.07 (an estimate of σ based on preliminary sample of ns=10)
How many cycles should be timed to ensure actual element time is + 10%
of the sample mean, with 95% confidence?
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df = (ns – 1) = 10 – 1 = 9
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α = 0.05, α/2 = 0.025
tα/2 = t0.025 = 2.262
Number of cycles = nc = (tα/2s / kx)2 = [2.262(0.07) / 0.10(0.40)]2
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= 15.7 ≈ 16 cycles
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If 16 observed cycles yields
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x = 0.45 min
P(μx lies within x + kx) = P(μx lies within 0.45 + 0.10(0.45))
= P(μx lies within [0.405, 0.495]) = 95%
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Performance Rating
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Also called performance leveling.
Performance relative to engineer’s concept of “standard” performance.
Most common method based on speed or pace: speed rating.
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> 100% means faster than standard pace
engineer must use judgment
must consider
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Standards
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degree of difficulty of work element
worker’s pace relative to standard
Walk 3 mi/hr on flat, level ground, no load, 27-in steps.
Problem: few work situations lend themselves to such precise measurement.
However, many situations in which experts judge (e.g., gymnastics, dog shows)
Solutions
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Experience (including feedback)
Training (e.g., using training films)
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Performance Rating (2)
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Pace depends on worker’s
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So, select skilled worker
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skill
experience
exertion level
attitude toward time study
familiar with job
Accepts time study as necessary management tool
Characteristics of good performance rating system
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consistency among tasks (one task to another)
consistency among engineers
easily understood
related to standard performance (well-defined concept)
machine-paced elements rated at 100% (no worker control of machine)
rating recorded during observation, not after
worker notification
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Time Study Issue
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Why is time study important to the
organization?
What are some worker concerns?
How can they be resolved?
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Time Study Equipment:
Mechanical Stopwatch 1
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Time Study Equipment:
Mechanical Stopwatch 2
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www.stopwatchesusa.com
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Time Study Results
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(from text)
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