Direct Time Study

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DIRECT TIME STUDY
Dr. Ahmed Elyamany
Time Study
• Is a study of the operational steps or
production procedure and the time
consumed by them, for the purpose of
devising methods of increasing efficiency or
productivity of workers
• Measures the time required to perform a task
so that an output standard of production for a
worker or a machine could be established.
2
Selecting the job
 New jobs.
 A change in material or method of working
 Worker complain about the time standard.
 A “bottleneck” operation
 Standard times are required before an
incentive plan.
 An idle equipment.
 The cost of a particular job appears to be
excessive.
3
Worker Approach
 A representative worker is one whose skill and
performance is the average of the group under
consideration, and who is not necessarily a
qualified worker.
 A qualified worker is one who has acquired
the skill, knowledge and other attributes to
carry out the work in hand to satisfactory
standards of quantity, quality and safety.
4
Steps of Time Study
1.
2.
3.
4.
5.
6.
7.
Obtain and record all the job information.
Break down the operation into “elements.”
Determine the sample size.
Record the time taken to perform each “element”.
Assess the effective working speed of the operator.
Extend the observed times to “basic times.”
Determine the allowances to be made above the
“basic time”
8. Determine the “standard time” for the operation.
5
1.Obtaining and recording information
A. identification Information :
 Study number
 Sheet number/number of sheets.
 Name of the analyst making the study.
 Date of the study.
 Name of the person approving the study.
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1.Obtaining and recording information
B. Product Information:
 Name of product/part
 Drawing or specification number.
 Part number
 Material.
 Quality requirements.
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1.Obtaining and recording information
C. Process/method/plant Information:
 Location of the operation.
 Description of the operation or activity.
 Plant or machine.
 Tools.
 Sketch of the workplace layout.
 Machine speeds.
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1.Obtaining and recording information
D. Operator’s Information:
 Operator’s name.
E. Duration of the study
 The start of the study (“Time on”).
 The finish of the study (“Time off”).
 Elapsed time.
F. Working conditions
 Temperature, humidity, adequacy of the lighting,
etc.
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2.Breaking the Job
 An element is a distinct part of a specified job selected
for convenience of observation, measurement and
analysis.
 A work cycle is the sequence of elements which are
required to perform a job or produce a unit of
production.
 A work cycle starts at the beginning of the first element
of the operation or activity and continues to the same
point in a repetition of the operation or activity.
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Detailed Elements Breakdown
• To distinguish between Productive work/effective
time and Unproductive activity/ineffective time.
 To permit the rate of working to be assessed
more accurately.
 To allow the different types of element to be
identified and distinguished.
 To allow elements involving a high degree of
fatigue to be separated.
 To facilitate checking the method for error.
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Types of Element
Eight types of element are distinguished:
1. Repetitive element is an element which occurs in every
work cycle of an operation.
2.Occasional element is an element which does not occur
in every work cycle.
3.Constant element is an element for which the basic
time remains constant whenever it is performed.
Examples: switch on machine.
4.Variable element is an element for which the basic time
differs in relation to some characteristics of the
product. Examples: sawing wood with handsaw.
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Types of Element
5.Manual element is an element performed by a worker.
6.Machine element is an element performed
automatically by any process.
7.Governing element is an element occupying a longer
time within a work cycle than any other element which
is being performed concurrently. Examples: boil kettle
of water while setting out teapot and cups.
8.Foreign element is an element observed which does not
form a part of the operation(s) being studied. Examples:
degreasing a part that has still to be machined more.
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Rules for Breaking Down Element
 Elements should be easily identifiable, with
definite beginnings and endings.
 These beginnings and endings can often be
recognized by a sound.
 A break point is the instant at which one
element in a work cycle ends and another
begins.
 Elements should be as short as can be easily
timed by a trained observer.
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3.Sample Size
• Determine the sample size or number of readings that
must be made for each element, with a predetermined
confidence level and accuracy margin.
• The statistical method, we have first to take a number
of preliminary readings (n’). We then apply the
following equation for the 95.45 confidence level and a
margin of error of ±5 per cent:
•
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Example
• Let us suppose that we take five readings for a given
element, and find that the value of the elapsed time in
1/100ths of a minute is 7, 6, 7, 7, and 6. We can then
calculate the squares and the sum of the squares of
these numbers:
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3.Sample Size
 Number of preliminary readings (n’) < the required
sample size  the sample size must be increased.
 However, we cannot simply say that four more
observations are needed. When we add the values
obtained from these four additional observations, the
values of x and x2 will change, and this may affect the
value of n.
 Consequently it may be found either that a still larger
sample is required, or that the sample taken was in fact
adequate or more than adequate.
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4.Timing Each Element
 There are two principal methods of timing
with the stop-watch:
 Cumulative timing
 Fly back timing
 Cumulative timing has the advantage that,
even if an element is missed or some
occasional activity not recorded, this will have
no effect on the overall time.
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4.Timing each element
• In the fly back method, errors in reading the
watch may be added to the slight delay which
occurs when the hand is snapped back to zero.
The percentage error becomes greater for short
elements.
• Cumulative timing is therefore likely to be more
accurate for short-element and cycle work, while
fly back timing can be more safely used in jobs
with long elements and cycles, since the error
becomes too small to matter.
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13.1
20
13.2
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5.Performance Rating
• Assessing the effective speed of working of the
operator relative to the observer’s concept of the
rate corresponding to standard rating.
• Most time studies in industry are used to
determine standard times for setting workloads
and as a basis for incentive plans.
• Rating (the assessment of a worker’s rate of
working) and the allowances to be given for
recovery from fatigue.
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5.Performance Rating
• A qualified worker is one who has acquired the skill,
knowledge and other attributes to carry out the work in
hand to satisfactory standards of quantity, quality and
safety
• Time studies should be made on a number of qualified
workers; and that very fast or very slow workers should be
avoided.
• Different jobs require different human abilities. For
example, some demand mental awareness, concentration,
visual perception; others, physical strength; some acquired
skill or special knowledge.
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5.Performance Rating
• A representative worker is defined as one whose skill
and performance is the average of a group under
consideration and who is not necessarily a qualified
worker.
• If 500 qualified workers in a given project do the same
operation by the same methods and under the same
conditions, the whole operation being within the
control of the workers themselves, the times taken to
perform the operation would be distributed in the
manner shown in the table and figure below.
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25
26
Standard rating and standard
performance
• The principal use of work measurement is to set time
standards
• Time standards can be used in planning, estimating
and as a basis for incentives.
• Setting standards so high will be achievable only by
the best workers.
• Setting standards too low will not improve worker
efficiency.
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How does the analyst obtain such a
fair time from time studies?
• We have already said that, studies should be taken on qualified
workers to obtain a reliable average time.
• It is not always possible to time a job on an average qualified
worker.
• People do not work consistently from day to day or even from
minute to minute.
• The analyst should assess the rate of the working operator and
relating it to standard pace.
• This process is known as Rating.
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Rating
• Rating is the assessment of the worker’s rate of working relative to
the observer’s concept of the rate corresponding to standard pace.
• The standard level is the average rate at which the qualified
workers will naturally work at a job.
• The standard rating is denoted by 100.
• Standard performance is the rate of output which a qualified
workers will naturally achieve without over-exertion as an average
over the working day or shift.
• The Standard performance is denoted as 100.
29
How the rating factor is used
• It is usual practice to round off ratings to the
nearest multiple of five on the scale.
• If the rate is judged to be 13% above standard,
the rate is 115.
• If the study person’s ratings were always perfect,
the results should be:
Observed time x rating = a constant
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6.Basic Time
• The basic time represents the time taken by
the operator to perform an element if the
operator were working at the standard rate.
• If the operator was working slower than the
standard, basic time is < observed time.
• If the operator was working faster than the
standard, basic time is > observed time.
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6.Basic Time
32
6.Basic time
• The most common method of selecting the
representative basic time is calculating the
average of the estimated basic times.
33
Example
• During a time study made on the operation of inspecting
and covering a book, one element was described as: “Pick
up one book, inspect, initial at end of paper (break point:
book closed)”.
• This element was observed 31 times, and the basic minutes
calculated (in 1/100 min) were as follows:
•
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Example
• Exclude the basic time of 0.49 minutes
because of a faulty operation.
• The total of the remaining 30 basic times is
7.97 minutes.
• The average basic time is 0.266 minutes per
occasion.
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Example
• At the end of the calculations, the basic time
finally selected would be rounded off to the
nearest two figures, in this case 0.27 minutes.
• The excess work observed (0.49 - 0.27 = 0.22)
would be carried down to the contingencies
record.
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Work content
• The work content of a job or operation is
defined as :
• Basic time + relaxation allowance +
contingency allowance
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38
7.Allowances
• Many jobs require spending of human effort, and
some allowance must therefore be made for
recovery from fatigue and for relaxation.
• Allowance must be made to allow a worker to attend
to personal needs.
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7.Allowances
• Relaxation allowances are intended to assist recovery from
fatigue.
• Relaxation allowances are the only essential part of the
time added to the basic time.
• Other allowances, such as contingency, policy and special
allowances are applied under certain conditions only.
• Contingency allowances may also have to be added to the
basic time in order to give the work content.
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Apply Allowances
• A PFD (personal time, fatigue, and delays) allowance is
added to the basic time to compute the standard time
Tstd = Tb(1 + Apfd)
where Apfd = allowance factor for personal time, fatigue,
and delays
• The function of the allowance factor is to inflate the
value of standard time in order to account for the
various reasons why the worker loses time during the
shift
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8.Standard time
• Standard time is the total time in which a job should
be completed at standard performance.
• The contingencies and relaxation allowances are
percentages of the basic time.
• The standard time is expressed in standard minutes
or standard hours.
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Example
 A direct time study was taken on a manual work
element. The regular cycle consisted of three elements,
a, b, and c. Element d is an irregular element
performed every five cycles.
Work element
a
b
c
d
Observed time (min)
0.56
0.25
0.50
1.10
Performance rating
100%
80%
110%
100%
Determine:
(a)Basic time
(b)Standard time for the cycle, using allowance factor of
15%.
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Solution
(a) Basic time:
Tb = 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
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Machine Cycle in the Task
• If the work cycle includes machine-paced
elements, then standard time may include a
machine allowance applied to the machine time
Tstd = Tbw(1 + Apfd) + Tm(1 + Am)
where
Tbw = basic time for worker (external) elements,
Tm = machine cycle time (assumed constant), and
Am = machine allowance
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Example
• An example of a time study - extracts from the two main
documents in time study follow:
Element
number
Rating
Observed time
(1/100 min)
Basic time
(1/100 min)
1
90
30
27.0
2
80
95
76.0
3
80
45
36.0
4
90
10
9.0
5
75
22
16.5
6
80
17
13.6
1
80
33
26.4
3
75
46
34.5
4
75
10
7.5
(etc.)
(etc. etc..)
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Example
• Time study analysis sheet
Element
number
Basic time
Relaxation
Basic time
Allowance%
X Frequency
Standard
time
(min)
Basic time
(1/100 min)
Frequency
1
29
1/1
0.290
10
0.319
2
75
1/8
0.094
10
0.103
3
38
1/1
0.380
10
0.418
4
9
1/1
0.090
10
0.099
5
15
1/1
0.150
10
0.165
6
17
1/1
0.170
15
0.196
7
96
1/12
0.080
18
0.094
Standard cycle time (min) =
• Cycles in one hour = 60 / 1.394 = 43 cycle/hour
1.394
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Contact:
Dr. Ahmed Elyamany
019-4100-824
[email protected]
QUESTIONS
48
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