Chapter 7: Maintenance Work Measurement

1
Chapter 7 Maintenance Work Measurement

• Coverage
• Work measurement techniques
• Work sampling
• Control charts
• Predetermined motion-time systems
• Standard data
• Estimating

2
Work Measurement Techniques
3
Time Study

• Time Study is performed by timing worker as the
  job is performed
• Summing the times for the pertinent elements of
  the job
• Standardize the observed times
• Add the allowances for personal and other
  variable working conditions

4
Time Study Procedures

• Select the job standardized
• Break the job into elements segments in work
  cycle
• Machine elements manual elements
• Easy to identify and time
• Actual maintenance work element other works
• Observe the job
• n (Z?/2?/A?)2 where n number
  of observations required to
  provide the desired accuracy ? the true
  mean of the time of activity

5
Time Study Procedures

• A accuracy desired, expressed as a fraction of
  the true value of the population
  parameter Z ?/2 Standardized
  normal deviate that has ?/2 as the area remaining
  in the tail of the standard normal distribution
  beyond it ? standard deviation of the
  population
• If ? is unknown, Sample standard deviation S is
  used
• Estimate ? and ? from S and by initial sample
  size n1
• Compute n with S and
• if n ? n1 , stop. Else set n1 n go to step 1

6
Time Study Procedures

• 4. Compute the basic times
• Basic time for a job is the time it should take a
  qualified worker to perform the elements of the
  job while working at a standard pace
• BT OT(rating/standard rating)
  where BT basic time OT observed
  time Standard rating 100
• 5. Determine allowances
• Allowance is the percentage of the basic time
  allowed for delays and fatigue
• Constant allowances personal needs and fatigue
• Variable allowances maintenance job
  characteristics
• Guidelines

7
General Guidelines for Computing Allowances
8
Time Study Procedures

• 6. Establish job standard
• Job standard BT(1 Allowances)

9
Work Sampling

• Work sampling is a technique for finding the
  percentage occurrence of a certain activity using
  statistical sampling.
• Make tours of the maintenance department at
  random intervals, noting which workers are
  working, idle, and their reasons for being idle
• Estimated worker idle time Where X
  number of times the worker was observed idle
  n total
  number of observations

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Work Sampling

• X is a binomial random variable
• is a random variable with
• when n is large, the distribution of can be
  approximated by a normal distribution with a
  (1-?) confidence interval from p is given by

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Number of observations required for work sampling
study
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Planning a Work Sampling Study

• Objective of study
• Population identification
• Activity definition
• Observation form design
• Observation route planning
• Study schedule
• Number of observations
• Observation time schedule
• Sample population preparation
• Observer training

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Control Charts

• Detect instability in a work sampling study
• p, and its upper and lower limits
• Instability ? errors methodology of
  study work environment change
• Instability ?correction actions

14
Control Chart Construction

• Start about three days into the beginning of the
  sampling study
• Compute new limit when ever there is a change in

15
Predetermined Motion-Time Systems

• PMTSs are use for setting job standards
• Common PMTSs the method time measurement (MTM)
  system
• The fundamental motion times? large sample of
  diversified operations
• Job standard? basic motions predetermined times
• MTM ? broad range of operations production
  , maintenance, etc. ? MTM-2

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MTM-2 System

• MTM-2 based on the categories of
  motions Category Allowed Get G Put P
  Get Weigh GW Put Weigh PW Grasp R
  Apply Pressure A Eye Action E Foot
  Action F Step S Bend and
  Rise B Crank C

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MTM-2 System

• A summary of MTM-2 data in time measurement
  units- TMUs (1 TMU 10-5h) Code GA GB
  GC PA PB PC - 5 3 7
  14 3 10 21 - 15 6
  10 19 6 15 26 - 30 9
  14 23 11 19 30 - 45 13
  18 27 15 24 36 - 80
  17 23 32 20 30 41 GW,
  1/kg, PW, 0.2 kg A R E C S F B 14 6 7 15 18
  9 61

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MTM-2 System

• Code Distance 5 0 2 inches
  15 2 ? . lt 6 30 6 ? . lt 12
  45 12 ? lt 18 80 18 ? .
• The MTM-2 system allows for simultaneous hand
  motions and takes into account cases when
  simultaneous motion requires additional time

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Procedure for Setting a Predetermined Standard

• Observe the job or think it through if it is yet
  to be established
• Break the job into elements and record each
  element
• Obtain time units for each job element from the
  tables
• Add the total motion units for all elements
• Estimate allowances for personal time, delays,
  fatigue
• Add the performance motion time and allowance
  units for a standard job motion unit together and
  compute the motion units to actual time in
  minutes, hours, and so forth

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Standard Data

• Basic time all elements in standard data
• Basic time allowances standard for the new
  job
• Standard data development is a desired activities
  of a maintenance department
• Advantages
• Eliminate the repetitive time study
• Save time to set job standards
• Provide greater consistency between similar job
  standards

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Steps for Developing Standard Data

• Gather data to identify jobs and job standards
• Form a master list of elements jobs and element
  time values
• Perform Curve fitting and formula development
  using standard techniques
• Evaluate and improve the standard data
• Calculate r time from standard data/ time
  from time study
• If r ? 98 confidence interval, stop
• Else adjust standard time by Index of
  comparison (IOC) job standard (standard data)/
  job standard (time study)

22
Estimating

• Measure work using experience-base knowledge
• Advantages
• Low cost
• Estimate job standard before the job is started
• Disadvantages
• Inconsistent estimation
• Method changes may not be taken into account
• Cannot used for jobs which experience is not
  available

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Estimating

• Classification of maintenance works for job
  standard
• Routine work of regular frequencyaverage past
  time
• Routine work of irregular frequency average past
  time
• One-of-a-kind work that requires lt 100hrs
  average time for each group 0 8hrs 9
  16hrs 17 32 hrs 33 50
  hrs 51 100 hrs
• Non-routine jobs that require gt 100hrs use
  stiem study or PMTS

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Comparative Estimating (Slotting)

• Comparative estimating is a work measurement
  technique used to measure the work content of
  low, repetitive maintenance work
• Experience worker can estimate a range of time
  during which a certain task can be completed most
  of the time
• Use a series of benchmark jobs work group
  or task areas
• Benchmarks are jobs, representative of a range of
  jobs which are similar in work requirements,
  tools used, and are capable of being measured by
  accepted time measurement techniques
• Position a new or unmeasured job into a group of
  benchmarks slotting

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Comparative Estimating (Slotting)

• Two methods of slotting
• Ranking allocate unmeasured job of similar
  requirements If slightly less work
  content than the benchmark ? any group.
  If slightly more work content ? same
  group, average time of that group
• Direct comparison compare the new jobs work
  content with a benchmark of similar work content
  ? the different gt basic time of the
  benchmark/group/ slot boundary ?move the new job
  out of that slot