Lecture Operations management: Creating value along the supply chain (Canadian edition) - Chapter 8S

Chapter 8 supplement, work measurement. In this supplement, you will learn about time studies and work sampling. Work measurement is determining how long it takes to do a job. Managing human resources requires managers to know how much work employees can do during a specific period.

Robert S Russell, Bernard W Taylor III, Ignacio Castillo, Navneet Vidyarthi

Lecture Outline

Work Measurement

—Services tend to be labor-intensive

—Service jobs are often repetitive

—Standard time

• time for average worker to perform a job once

—Incentive piece-rate wage system based on time study

Stopwatch Time Study - Steps

Stopwatch Time Study - Steps

Normal Cycle Time = NT = Nt

Normal Time = (Elemental average) x (rating factor)

Nt = (t )(RF)

ST = (NT)(1 + AF)Standard Time = (normal cycle time) x (1 + allowance factor)

Performing a Time Study

Time Study Observation Sheet

Identification of operation Sandwich Assembly Date 5/17

Operator Approval Observer Smith Jones Russell

Cycles Summary

1 2 3 4 5 6 7 8 9 10 t t RF Nt

Place ham, cheese,

and lettuce on bread

1

2

3

4

Grasp and lay

out bread slices

Spread mayonnaise

on both slices

Place top on sandwich,

Slice, and stack

t

t

t

t R R R

R

.11 44 79 1.13 1.47 1.83 2.21 2.60 2.98 3.37

.04 05 05 04 06 05 06 06 07 05 53 053 1.05 056 04 38 72 1.05 1.40 1.76 2.13 2.50 2.89 3.29

.07 06 07 08 07 07 08 10 09 08 77 077 1.00 077

.11 12 14 12 13 13 13 12 14 14 1.28 1.28 1.10 141

.93 23 55 1.25 1.60 1.96 2.34 2.72 3.12 3.51 12

.10 08 09 11 11 10 10 12 10 1.03 1.03 1.10 113 33 67 1.01 1.34 1.71 2.07 2.44 2.82 3.24 3.61

Performing a Time Study

Normal time = (Elemental average)(rating factor)

Performing a Time Study

How many sandwiches can be made in 2 hours?

= 269.7 or 270 sandwiches

120 min

0.445 min/sandwich

Incentive Piece-Rate System

Average worker makes 135 sandwiches per hour

Example Worker Wages

Observed worker average cycle time = 0.361, no RF

Time Study With Excel

z = number of standard deviations from the mean

in a normal distribution reflecting a level of statistical confidence

T = average job cycle time from the sample time study

s = = sample standard deviation from

sample time study

Σ(xi - x)2

n - 1

Number of Cycles

• Average cycle time = 0.361

• Computed standard deviation = 0.03

• Company wants to be 95% confident that computed time is within 5%

of true average time

n = = = 10.61 or 11 zs eT

2

(1.96)(0.03) (0.05)(0.361)

2

Number of Cycles With Excel

Sample size

Developing Time Standards

Without a Time Study

• workplace uninterrupted

• performance ratings unnecessary

• consistent

• ignores job context

• may not reflect skills and

MTM Table for MOVE

A Move object to other hand or against stop

B Move object to approximate or indefinite location

TIME (TMU) WEIGHT ALLOWANCE

Source: MTM Association for Standards and Research.

• percentage of time a worker or machine is delayed or idle

—analyze jobs that have non-repetitive tasks

Steps of Work Sampling

sample

n = p(1 - p) z e

2

where

n = sample size (number of sample observations)

z = number of standard deviations from mean for desired level of confidence

e = degree of allowable error in sample estimate

p = proportion of time spent on a work activity estimated prior to calculating work sample

Steps of Work Sampling

observations

n = p(1 - p) = (0.38)(0.62) = 2263 z e

2

1.960.02

2

Work Sampling With OM Tools

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