md. imrul kaes - time study
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TIME STUDY
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Qualified worker:
A qualified worker is a person who has the right
knowledge or right skill of doing the specific task, the
right effort, high motivation and other attributes to
accomplish a job up to satisfactory level of quality,quantity and safety.
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Definition of Time Study
Time study is a technique for determining as
accurately as possible, the time required on an
average to carry out a specific task by a
qualified worker. at a defined level of
performance.
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Objective of Time Study
1. Determines the standard time which should
be required to do a specific job by all
workers.
2. Decides manpower required for the job, it
helps in manpower economy.
3. Decides machines/equipments requirement.
4. Provide information for effective production
planning.
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5. Aids in calculating exact delivery dates.
6. Decides realistic labor wage/budgeting and
provides a basis for standard costing system.
7. Provides a basis for fair and sound incentive
schemes.
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Operation cycle:
Most of the works conducted on a mass scale have a
repetitive nature. For example, a worker in an apparel factory
performs her job again and again, she takes a bundle of cut
parts, open the bundle, takes a part from it, position it to the
machine, completes sewing, ties up the bundle, keep it asideand takes another bundle. This process continues all alone.
The series of movements from taking a part from bundle,
putting under the needle, sewing the part and disposing the
part to the bundle of sewn part is called operation cycle.
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Observed time:
An operator in an apparel industry performs one or
more operations. The time she requires to complete
the operation as determined by a work study officer
by observing her time with aid of a stop watch iscalled observed time.
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Calculation of an observed time of
an operation of an operator:Apparel comprises a large number of operations, in
order to determine the standard time of an
operation, it is necessary to record observed time of
the operation. Standard time is made of basic timeand allowance time. Basic time is the observed time
multiplied by operator rating. So it is the job of a
work study officer to record time of each operation
allotted to an operator and to asses her rating.
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Types of operations in terms of
length:
Operations vary in respect of length, difficulty and
quality etc.
They may be large (15 seconds or more), medium (7-
15 seconds), or small if below 7 seconds.
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Attaching pocket of a shirt or hemming
bottom of a shirt is relatively large process.
They can be divided in to element
movements. Time of these element
movements can be measured.
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Attaching labels on two edges is relatively
medium processes (more than 7 seconds).
The whole process as a whole can be
measured but its elements are too fast to
measure.
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There are some other small operations, such as bar
tacking on one position, as a single cycle cannot be
measured but a number of cycles say 15-20 cycles
may be measured. These are very important featuresof a process which are taken account at the time of
recording.
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Time measurement for larger
processesRelatively large processes are those which take more
than 15 seconds. Their elements movements are
clear and can be measured. Collar top stitching is
such an example. Collar is lifted, sewing iscompleted and then it is placed in the bundle. The
process continues. In this case all movements
should be recorded individually.
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Subdivision of work - Therbligs
Name Code Color
Search SH Black
Grasp G Red
Transport TL Green
Position P Blue
Assemble or sewing A Violet
Disassemble DA Light Violet
Inspect I Burnt Brown
Release RL Carmine Red
Rest R Orange
Unavoidable Delay UD Yellow
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Operator ProcessElement
movementStart time
Record completion time for each cycle given
below
RahimCollar top
stitch
Cycle 1 2 3 4
Lift/grasp
start0 20 40 61
Lift time 7 7 8 7
Sew start 7 27 48 68
Sew time 10 10 10 10
Place start 17 37 58 78
Placing
time3 3 3 3
Place end 81
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Time measurement for medium
processesMedium processes are those which take time
between 7 to 15 seconds each. These operations as
a whole are clear but their element movements
cannot be measured accurately. Time is measuredby stop watch. An example is collar band bottom
cutting by an overlock machine. A time recording
format for such processes is given below:
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SL operator process Start
time
Record of time for each cycle
1 2 3 4 5
1 Moyna Collar
bottom
cutting
0 12 25 38 51 64
Cycletime
12 13 13 13 13
2 Nazmun Collar
bottom
cutting
0 12 26 38 51 71
Cycle
time
12 14 12 13 20
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Time measurement for small
process:Small processes are those which generally take time
less than 7 seconds. These processes go so fast that
even individual operations cannot be measured. So a
definite lot of operations are allowed to pass whenmeasurements are taken. Attaching loops to
trousers or bar tacking are examples. A bundle has
10 trousers and each trouser has 5 loops. Time is
measures for the whole bundle and stop watchrecords 310 seconds. Thus each loop takes 310/50 =
6.20 seconds. Observed time for a trouser = 6.2 x 5 =
31 seconds.18Monday, April 15, 2013
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SL Operator Process Start
time
Finish
time
Time for
whole
lot
Pieces in
a lot /
bundle
Observed
time
1 Rohima Stay
sewing
0 100 100 20 5
2 Nazmun Collar
fitting
0 60 60 20 3
3 Moyna Collar
sewing
0 120 120 20 6
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Performance Rating
Different workers perform their jobs with different
efficiencies. Some workers are cleaver; they learn
their jobs quickly and attain a very high efficiency.Some other may be mediocre and many others may
be lenient to learn or may be dull. Thus workers
widely vary in their performance.
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Rating is the speed of an operator doing a job
relative to observers idea of standard speed
of work.Rating is thus a comparison of the rate of
work observed by a work study executive with theidea of some standard level of working in his mind.
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The standard rate is the average rate with which thequalified workers are assumed to be able to work provided
they are motivated to do the job and if the right method of
work is applied. Such rate of work is called standard rating.
This is called standard rating, because it is assumed that
majority of the qualified workers will be able to achieve such
speed of working. If appropriate allowances are provided, a
worker can retain standard performance over the whole
working hours.
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Scale of rating:
There are several scales in use. We normally use
British Standard Scale 100 BSI which is also known
as 0-100 scale. The advantage of this scale isthat 0 designates no activity while 100 which
represents standard rating which is normal for an
average qualified worker.
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Rating Description Comparable speed
0 No activity or
movement
50 Very slow clumsy
movement
2 miles/hr 3.2 km/hr
75 Speedy, purposefulbut unhurried
movement
3 miles/hr 4.8 km/hr
100 Speedy, business like
movement of
qualified motivated
worker
4 miles/hr 6.4 km/hr
125 Very speedy
movement, operator
shows higher degree
of effort, dexterity
and coordination
higher than that of an
average qualifiedworker.
5 miles/hr 8 km/hr
150 Exceptionally fast
movement which
cannot be retained for
the whole of working
time.
6 miles/hr 9.6 km/hr
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How work study officer uses a
rating:Rating of an operator is usually a very difficult task. It requires
long experience in the floor, patience, intelligence etc. If the
work study executive things that the operation is being
performed at a rate less than the standard, a factor less than
100 say, 75 is used. If he considers that the rate of doing isabove standard he will use a factor greater than 100, say 110
or 115 or 120 etc. Ratings are used normally as an
increment of 5. For example, a rate of 77 is not normallyused. It is generally rounded 80.
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Westinghouse Method of Rating
Westinghouse system utilizes a set of criteria to measurethe performance of the operators. The factors are:
Skill Measures the workers proficiency in performing theoperation.
Effort Measures the speed with which the skill is applied.
Consistency Measures the factors which affect theconsistency of the operator to perform the work cycle
repeatedly.
Conditions Measures the extent to which the conditionslike temperature, vibrations, light and noise affect performance.
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Performance Rating Table (Westinghouse Method)
Skill Effort
+ 0.15 A1
Super skill
+ 0.13 A1
Excessive+ 0.13 A2 + 0.12 A2
+ 0.11 B1Excellent
+ 0.10 B1Excellent
+ 0.08 B2 + 0.08 B2
+ 0.06 C1
Good
+ 0.05 C1
Good+ 0.03 C2 + 0.02 C2
0.00 D Average 0.00 D Average
- 0.05 E1Fair
- 0.04 E1Fair
- 0.10 E2 - 0.08 E2
- 0.16 F1
Poor
- 0.12 F1
Poor- 0.22 F2 - 0.17 F2
Conditions Consistency
+ 0.06 A Ideal + 0.04 A Perfect
+ 0.04 B Excellent + 0.03 B Excellent
+ 0.02 C Good + 0.01 C Good
0.00 D Average 0.00 D Average
- 0.03 E Fair - 0.02 E Fair
- 0.07 F Poor - 0.04 F Poor 27Monday, April 15, 2013
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Example:
An observed time for an operation is 0.05
minutes and the factors are as follows:
Skill is excellent
Effort is goodCondition is good
Consistency is good
What is the performance rating for the
operator?
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Solution:
The values for the ratings are as follows:
a) Performance rating factor = 1 + 0.13 = 1.13 = 113%
Criteria Rating Value
Skill B2 + 0.08
Effort C2 + 0.02
Condition C2 + 0.02Consistency C + 0.01
Total + 0.13
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Basic Time
Basic time is the time required by a qualified
operator to complete a job had she worked at
standard speed (at 100% rating) all the time
without any allowance. Basic time is obtainedby multiplying observed time with rating of
the worker. Thus
Basic time = observed time x rating of theoperator.
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Example: An operator attaches top center of the left
front. Her observed time shows 28 seconds. Work
study executive considers her of 80% rating.
Calculate basic time of the operation.Ans: observed time 28 seconds and rating of the
operator 80%.
So her basic time = observed time x her rating
= 28 x 80% = 28 x 0.80 = 22.4 seconds.
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Basic time is operation depended
not operator dependent:
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Operator Observed
time(seconds)
Operator rating Basic time
(seconds)
Julie 16 75% 16 x 75% = 12
Jesmin 12 100% 12 x 100% = 12
Kariman 10 120% 10 x 120% = 12
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Thus whatever may be the ratings of different
operators, for the same job the basic time will be the
same. In this way, standard time of any operation is
also constant irrespective of different rating ofoperators for the same operation and if allowance
time for the whole floor is same, say 20%.
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Example 1: an operator was found to have 900 seconds to
complete 300 pieces of her work as observed by a work study
officer. Calculate the observed time.
Ans: her observed time = 900 seconds / 300 = 3 seconds.
Example 2: the same operator found to have a rating of 90%.
Calculate her basic time.
Ans: basic time =observed time x rating
= 3 x 90% =3 x 0.90 = 2.7 seconds.
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Allowance Time
A worker cannot and does not work continuously throughout
her full working hours. She has to go to lavatory, take out
bobbin case, replace a blunt needle, talk to the supervisor or
line inspector, a small break to recover from fatigue etc. She
cannot avoid all these things, because they are beyond hercontrol. She needs some time for her own personal needs.
This is why workers are entitled to some type of extra time for
these types of circumstances. This type of non performing
time is called allowance. The allowance time ranges from 15-25%. Allowance time is taken into account during setting up of
standard time.
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There are different types of
allowances:
Relaxation allowances: it is the time allowed toan operator to attend to personal needs and to
recover from fatigue. Fatigue is a mental or physical
exhaustion developed in a worker due to continuouswork. It is assumed that a small rest or pause in work
lessens fatigue and as a result the person is
reenergized.
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Fixed relaxation allowance: Fixedallowance comprises time allowed for personal needs
and for basic fatigue. Time allowed for personal needsis around 5-7%. Example drinking water, smoking, going
to wash room etc.
Variable relaxation allowance: Variableallowance is added to take in to account a poor
working condition leading to higher stress and fatigue.
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There are some factories which encounter frequent
minor interruptions. They cover them by a
contingency allowance.
Machine delay allowance: this is the timeallowed for delay due to machine maintenance.
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Allowance time varies with the complexity of
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Allowance time varies with the complexity of
the machine. Some typical machine delay
allowances are shown below for references:
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Type of machine Allowance rate in %
1 needle lockstitches 9%
2 needle lockstitches 14%
1 needle 3 thread over lock 7%
2 needle 4 thread over lock 9%
2 needle 5 thread over lock 11%
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Process allowance: A process allowance is an
allowance of time given to compensate for enforced
idleness of an operator due to the character of the
process or operation on which he or she isemployed. For example, an operator may be the
member of an unbalanced line. These are all
unavoidable delay for which the operator is not
responsible.
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Style change allowance: allowance time ispermitted where frequent style changes occur.
Special allowance:some times special time
is given as start time allowance, shut down
allowance etc because time is wasted at start time or
change of work shift. Times are covered by special
allowance.Allowance is calculated on basic time.
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A job comprises following elements. The work is
done with a single needle lockstitch machine
equipped with auto thread trimmer. There are 50
pieces in the bundle. Calculate allowance time usingfollowing information:
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Description Basic time
(sec)
Machine used Occurrence
rate
Allowance
rate
Grip the part
and place on
the table
20 Manual 1 12%
Sew 29 1 needle lock
stitch
1 9%
Turn 15 Manual 1 12%
Top stitch 25 1 needle lock
stitch
1 9%
Tie up bundle 50/50 Manual 1 12%
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Here machine delay allowance time comprises SL. 1
&2 and personal need and fatigue allowance
comprise SL. 1,3 and 5.
Thus machine delay allowance= (29+25) x 9% =54 x 0.09 =4.86 sec.
Thus personal needs and fatigue allowance
= (20+15+50/50) x 12% = 5.04 sec. Total allowance time = 4.86 +5.04 sec = 9.90 sec
However most of the factories accept an average rate
of allowance to apply to basic time.44Monday, April 15, 2013
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STANDARD TIME
Standard time of an operation is the time which a
qualified operator should take to accomplish it if she
works at standard performance/speed (at the rating
of 100) and provided that she takes extra timeallowed to her as an allowance.
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If standard time is counted in seconds it is called
standard second but if it is calculated in minutes
standard time is referred to as standard minute or
standard minute value (SMV). Standard time of anoperation is also a constant value though different
operators take different observed time due to their
different speed or efficiencies and if the allowance
rate is fixed throughout the factory.
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Operator Observed
time(seconds)
Operator
rating
Basic time
(seconds)
Allowance
15%
(seconds)
Standard time
Julie 16 75% 16 x 75%
= 12
1.8 13.8
Jesmin 12 100% 12 x 100%
= 12
1.8 13.8
Kariman 10 120% 10 x 120%
= 12
1.8 13.8
The table shows that three operators are observed to have taken different
time to complete the same job to their different speed. But the basic andstandard time for the operation are constant.
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Example:
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Example:
The recorded time for a trousers hem for 10 observations is
given below:
If the performance rating is 85% and the allowance rate is 25%,then what would be the standard time for trousers hem?
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Observation Time1 0.42
2 0.425
3 0.408
4 0.412
5 0.415
6 0.418
7 0.414
8 0.411
9 0.419
10 0.410
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Solution:
Observed time = Average time for the mean observation
= 4.145 / 10 = 0.4145 minute
Basic Time = Observed Time Performance Rating
= 0.4145 0.85 = 0.35224 minute
Standard Time = Basic Time + Allowances
= 0.35224 + (0.35224 0.25)
= 0.44 minute
Thus standard time for trousers hem is 0.44 minute.