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IE 101-Industrial Engineering Orientation Fall 200 9 Motion and Time Study Engin Topan. Methodology. Methods Design. Outline of MTS Develop System Design work methods (sequence of operations and procedures) that make up the preferred solution Find better methods for work Standardize

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IE 101-Industrial Engineering Orientation

Fall 2009

Motion and Time Study

Engin Topan


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Methodology

Methods

Design

Outline of MTS

  • Develop System

    • Design work methods (sequence of operations and procedures) that make up the preferred solution

    • Find better methods for work

  • Standardize

    • Form written standards for operations

  • Time Standards

    • Determine a standard time for each operation

  • Training

    • Train the operators

Develop System

Standardize

Work

Meas.mnt

Time Standards

Training


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Defining Work Systems

Work

  • Is our primary means of livelihood

  • Serves an important economic function in the global world of commerce

  • Creates opportunities for social interactions and friendships

  • Provides the products and services that sustain and improve our standard of living


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Defining Work Systems

  • Work consists of tasks

    • Tasks consist of work elements

      • Work elements consist of basic motion elements


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Defining Work Systems

Task

  • An amount of work that is assigned to a worker or for which a worker is responsible

    • Repetitive task – as in mass production

    • Non-repetitive task – performed periodically, infrequently, or only once

      Work Element

  • A series of work activities that are logically grouped together because they have a unified function in the task

    • Example: assembling a component to a base part using several nuts and bolts


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Defining Work Systems

Basic Motion Elements

  • Actuations of the limbs and other body parts

    • Examples:

      • Reaching for an object

      • Grasping the object

      • Moving the object

      • Walking

      • Eye movement

    • A work element consists of multiple basic motion elements


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1.3 Defining Work Systems

  • “Time=Money”? How?

    • New product introduction

    • Product cost

    • Delivery time

    • Overnight delivery

    • Competitive bidding

    • Production scheduling

  • Increase profit using less time!


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Defining Work Systems

  • Importance of Time in Work

    • Time is the most frequently used measure of work

      • How many minutes or hours are required to perform a given task?

    • Most workers are paid by the time they work

      • Hourly wage rate

      • Salary

    • Workers must arrive at work on time

    • Labor and staffing requirements computed in units of time


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Defining Work Systems

  • A work system is a system consisting of humans, information, and equipment designed to perform useful work

    • Contributes to the production of a product or delivery of a service

    • Examples:

      • Worker operating a machine tool in a factory

      • Robotic welding line in an automobile plant

      • A receptionist answering incoming phone calls



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Productivity

Production as a function in Economics

Q=f(K,L)

  • Q: Output, K: Capital, L: Labor

  • Is there a way to change function f with a better function g?

  • Better Function=Higher Productivity


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Productivity

Productivity

  • The level of output of a given process relative to the level of input

  • Process can refer to

    • Individual production or service operations

    • A national economy

  • Productivity is an important metric in work systems because

    • Improving productivity is the means by which worker compensation can be increased without increasing the costs of products and services they produce


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Productivity

Labor Productivity

  • The most common productivity measure is labor productivity, defined by the following ratio:

    LPR =

    • LPR = labor productivity ratio

    • WU = work units of output

    • LH = labor hours of input


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Productivity

Labor Productivity Index

  • Measure that compares input/output ratio from one year to the next

    LPI =

    • LPI = labor productivity index

    • LPRt = labor productivity ratio for period t

    • LPRb = labor productivity ratio for base period


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Productivity

Example

  • During the base year in a small steel mill, 326,000 tons of steel were produced using 203,000 labor hours. In the next year, the output was 341,000 tons using 246,000 labor hours.

    Determine: (a) the labor productivity ratio for the base year, (b) the labor productivity ratio for the second year, and (c) the productivity index for the second year.


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Productivity

Solution

(a) In the base year, LPR = 326,000 / 203,000

= 1.606 tons per labor hour

(b) In the second year, LPR = 341,000 / 246,000

= 1.386 tons per labor hour

(c) Productivity index for the second year

LPI = 1.386 / 1.606 = 0.863

  • Comment: No matter how it’s measured, productivity went down in the second year.


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Productivity

Labor Factor in Productivity

  • Labor itself does not contribute much to improving productivity

  • More important factors:

    • Capital - substitution of machines for human labor

    • Technology - fundamental change in the way some activity or function is accomplished


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Horse-drawn carts

Steam locomotive

Telephone operator

Manually operated milling machine

Railroad trains

Diesel locomotive

Dial phone

Numerically controlled (NC) milling machine

Productivity


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Productivity

Measuring Productivity

  • Not as easy as it seems because of the following problems:

    • Nonhomogeneous output units

    • Multiple input factors

      • Labor, capital, technology, materials, energy

    • Price and cost changes due to economic forces

    • Product mix changes

      • Relative proportions of products that a company sells change over time


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Productivity

Productive Work Content

  • A given task performed by a worker can be considered to consist of

    • Basic productive work content

      • Theoretical minimum amount of work required to accomplish the task

    • Excess nonproductive activities

      • Extra physical and mental actions of worker

      • Do not add value to the task

      • Do not facilitate the productive work content

      • Take time


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Productivity

  • Excess Nonproductive Activities can be classified into three categories:

    • Excess activities due to poor design of product or service

    • Excess activities caused by inefficient methods, poor workplace layout, and interruptions

    • Excessive activities cause by the human factor



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Work Systems

  • Manual work system

    • Worker performing one or more tasks without the aid of powered tools

  • Worker-machine system

    • Human worker operates powered equipment

  • Automated work system

    • Process performed without the direct participation of a human worker


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Work Systems

Manual Work Systems

  • Human body accomplishing some physical task without an external source of power

    • With or without hand tools

      • When hand tools are used, the power to operate them is derived from the strength and stamina of a human worker

    • Other human faculties are required, such as hand-eye coordination and mental effort


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Manual Work Systems

Work Systems


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Work Systems

Pure Manual Work

  • Material handler moving cartons in a warehouse

  • Assembly worker snap-fitting two parts together

    Manual Work with Hand Tools

  • Material handling worker using a dolly to move furniture

  • Assembly worker using screwdriver


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Work Systems

Worker-Machine Systems

  • Worker operating a piece of powered equipment

  • Examples:

    • Machinist operating a milling machine

    • Construction worker operating a backhoe

    • Truck driver driving an 18-wheeler

    • Worker crew operating a rolling mill

    • Clerical worker entering data into a PC



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Work Systems

Automated Work Systems

  • Automation is the technology by which a process or procedure is accomplished without human assistance

    • Implemented using a program of instructions combined with a control system that executes the instructions

    • Power is required to drive the process and operate the control system


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Automated Work System

Work Systems


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Methods

Design

Develop System

Standardize

Time Standards

Training

Methods Design

  • Motion study - analysis of the basic hand, arm, and body movements of workers as they perform work

  • Work design - design of the methods and motions used to perform a task

  • Includes:

    • Workplace layout and environment

    • Tooling and equipment used in the task


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Motion Study

Basic Motion Elements

  • Therbligs – 17 basic motion elements

    • Basic building blocks of virtually all manual work performed at a single location

    • With modification, used today in several work measurement systems, e.g., MTM and MOST

      • Some of the motion element names and definitions have been revised


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Motion Study

17 Therbligs

  • Transport empty (TE) – reach for an object

  • Grasp (G) – grasp an object

  • Transport loaded (TL) – move an object with hand and arm

  • Hold (H) – hold an object

  • Release load (RL) – release control of an object

  • Use (U) – manipulate a tool


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Motion Study

  • Pre-position (PP) – position object for next operation

  • Position (P) – position object in defined location

  • Assemble (A) – join two parts

  • Disassemble (DA) – separate multiple parts that were previously joined

  • Search (Sh) – attempt to find an object using eyes or hand


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Motion Study

  • Select (St) – choose among several objects in a group

  • Plan (Pn) – decide on an action

  • Inspect (I) – determine quality of object

  • Unavoidable delay (UD) – waiting due to factors beyond worker control

  • Avoidable delay (AD) – worker waiting

  • Rest (R) – resting to overcome fatigue


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Effective therbligs:

Transport empty

Grasp

Transport loaded

Release load

Use

Assemble

Disassemble

Inspect

Rest

Ineffective therbligs:

Hold

Pre-position

Position

Search

Select

Plan

Unavoidable delay

Avoidable delay

Classification of Therbligs

Motion Study


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Motion Study

Micromotion Analysis

  • Objectives:

    • Eliminate ineffective therbligs if possible

    • Avoid holding objects with hand – Use workholder

    • Combine therbligs – Perform right-hand and left-hand motions simultaneously

    • Simplify overall method

    • Reduce time for a motion, e.g., shorten distance


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Example: A repetitive Manual Task

  • Current method: An assembly worker performs a repetitive task consisting of inserting 8 pegs into 8 holes in a board. A sightly interference fit is involved in each insertion. The worker holds the board in one hand and picks up the pegs from a tray with other hand and inserts them into the holes, one peg at a time.


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Example: A repetitive Manual Task

  • Current method and current layout:


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Example A repetitive Manual Task

  • Improved method and improved layout:

    • Use a work-holding device to hold and position the board while the worker uses both hands simultaneously to insert pegs.

    • Instead of picking one peg at a time, each hand will grab four pegs to minimize the number of times the worker’s hands must reach the trays.


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Motion Study

Principles of Motion Economy

  • Developed over many years of practical experience in work design

  • Guidelines to help determine

    • Work method

    • Workplace layout

    • Tools, and equipment

  • Objective: to maximize efficiency and minimize worker fatigue


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Work Methods Design

To select preferred work method:

  • Eliminate all unnecessary work

  • Combine operations or elements

  • Change the sequence of operations

  • Simplify the necessary operations


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Develop System

Standardize

Work

Meas.mnt

Time Standards

Training

Time Study and Work Measurement

Time Is Important

  • Most workers are paid for their time on the job

  • The labor content (cost of labor time) is often a major factor in the total cost of a product or service

  • For any organization, it is important to know how much time will be required to accomplish a given amount of work


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Time Study and Work Measurement

  • Work measurement – evaluation of a task in terms of the time that should be allowed by an average worker to perform the task

  • Time study – all the ways in which time is analyzed in work situations

  • Standard time – amount of time that should be allowed for an average worker to process one work unit using the standard method and working at normal pace


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Time Study and Work Measurement

Standard times

  • define a “fair day’s work”

  • provide a means to convert workload into staffing and equipment needs

  • provide a basis for wage incentives and evaluation of worker performance

  • provide time data for:

    • Production planning and scheduling

    • Cost estimating

    • Material requirements planning


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Task Hierarchy & Work Measurement

Time Study and Work Measurement


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Time Study and Work Measurement

Prerequisites for Valid Time Standards: Factors that must be standardized before a time standard can be set


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Time Study and Work Measurement

Normal Performance

  • A pace of working that can be maintained by a properly trained average worker throughout an entire work shift without deleterious short-term or long-term effects on the worker’s health or physical well-being

    • Normal performance = 100% performance

    • Common benchmark of normal performance:

      • Walking at 3 mi/hr


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Time Study and Work Measurement

Performance Rating

  • Analyst judges the performance or pace of the worker relative to the definition of standard performance used by the organization

    • Standard performance Pw = 100%

      • Slower pace than standard Pw < 100%

      • Faster pace than standard Pw > 100%

    • Normal time Tn = Tobs(Pw )


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Time Study and Work Measurement

Normal Time

  • The time to complete a task when working at normal performance

    Tn = Tobs(Pw )

    where Tobs = observed time, Tn = normal time, and Pw = worker performance or pace


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Time Study and Work Measurement

Example: Normal Performance

  • Given: A man walks in the early morning for health and fitness. His usual route is 1.85 miles. A typical time is 30 min. The benchmark of normal performance = 3 mi/hr.

  • Determine: (a) how long the route would take at normal performance and (b) the man’s performance when he completes the route in 30 min.


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Time Study and Work Measurement

(a) At 3 mi/hr, time = 1.85 mi / 3 mi/hr

= 0.6167 hr = 37 min

(b) Rearranging equation, Pw = Tn / Tc

Pw = 37 min / 30 min = 1.233 = 123.3 %


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Work-related interruptions

Machine breakdowns

Waiting for materials or parts

Receiving instructions from foreman

Talking to co-workers about work-related matters

Rest breaks for fatigue

Cleaning up at end of shift

Non-work-related interruptions

Personal needs (e.g., restroom breaks)

Talking to co-workers about matters unrelated to work

Lunch break

Smoke break

Beverage break

Personal telephone call

Time Study and Work Measurement

Reasons for Lost Time at Work


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Time Study and Work Measurement

How to Allowfor Lost Time

  • Two approaches used by companies:

    • Scheduled rest breaks during the shift

      • Typical - one 15-minute break in mid-morning and another in mid-afternoon

    • A PFD allowance is added to the normal time

      • This allows the worker to take a break on his/her own time


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Time Study and Work Measurement

PFD Allowance

  • Personal time

    • Rest room breaks, phone calls, water fountain stops, cigarette breaks (5% typical)

  • Fatigue

    • Rest allowance to overcome fatigue due to work-related stresses and conditions (5% or more)

  • Delays

    • Machine breakdowns, foreman instructions (5% typical)


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Time Study and Work Measurement

Allowances in Time Standards

  • Normal time is adjusted by an allowance factor Apfd to obtain the standard time

  • Purpose of allowance factor is to compensate for lost time due to work interruptions and other reasons


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Time Study and Work Measurement

Standard Time

  • Defined as the normal time but with an allowance added in to account for losses due to personal time, fatigue, and delays

    Tstd = Tn (1 + Apfd)

    where Tstd = standard time, Tn = normal time, and Apfd = PFD allowance factor

    where pfd = personal time, fatigue, and delays

  • Also called the allowed time


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Time Study and Work Measurement

Standard Performance

  • Same as normal performance, but acknowledges that periodic rest breaks must be taken by the worker

    • Periodic rest breaks are allowed during the work shift

    • Other interruptions and delays also occur during the shift


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Time Study and Work Measurement

Standard Method

  • Must include all of the details on how the task is performed, including:

    • Procedure - hand and body motions

    • Tools

    • Equipment

    • Workplace layout

    • Irregular work

    • Working conditions

    • Setup


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Time Study and Work Measurement

Tc

cycle

time

Tn

normal

time

Tstd

standard

time

Pw rating

Apfd allowances


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Time Study and Work Measurement

Irregular Work Elements

  • Elements that are performed with a frequency of less than once per cycle

  • Examples:

    • Changing a tool

    • Exchanging tote pans of parts

  • Irregular elements are prorated into the regular cycle according to their frequency


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Time Study and Work Measurement

Example: Determining Standard Time

  • Given: The normal time to perform the regular work cycle is 3.23 min. In addition, an irregular work element with a normal time = 1.25 min is performed every 5 cycles. The PFD allowance factor is 15%.

  • Determine (a) the standard time and (b) the number of work units produced during an 8-hr shift if the worker's pace is consistent with standard performance.


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Time Study and Work Measurement

  • Normal time Tn = 3.23 + 1.25/5

    = 3.48 min

    Standard time Tstd = 3.48 (1 + 0.15)

    = 4.00 min

    (b) Number of work units produced during an 8-hr shift

    Qstd = 8.0(60)/4.00 = 120 work units


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Direct Time Study

  • Direct and continuous observation of a task using a stopwatch or other timekeeping device to record the time taken to accomplish the task

  • While observing and recording the time, an appraisal of the worker’s performance level is made to obtain the normal time for the task

  • The data are then used to compute a standard time for the task


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Direct Time Study

Direct Time Study Procedure

  • Define and document the standard method

  • Divide the task into work elements

  • Time the work elements to obtain the observed time Tobs

  • Evaluate worker’s pace relative to standard performance to obtain normal time Tn

    • Called performance rating (PR)

      Tn = Tobs(PR)

  • Apply allowance factor to compute standard time

    Tstd = Tn(1 + Apfd)


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Direct Time Study

Document the Standard Method

  • Determine the “one best method”

    • Seek worker’s advice if possible

  • Documentation should include:

    • All of the steps in the method

    • Special tools, gauges, equipment and equipment settings (e.g., feeds and speeds) if applicable

    • Irregular elements and their frequency

  • Once the standard method is defined, it should not be possible for the operator to make further improvements


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Direct Time Study

Direct time study form


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Direct Time Study

Example

  • A direct time study was taken on a manual work element using the snapback method. 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) normal time and (b) standard time for the cycle


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Direct Time Study

(a) Normal time:

Tn = 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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Work Sampling

Statistical technique for determining the proportions of time spent by subjects in various defined categories of activity

  • Subjects = workers, machines

  • Categories of activity = setting up a machine, producing parts, idle, etc.

  • For statistical accuracy

    • Observations must be taken at random times

    • Period of the study must be representative of the types of activities performed by the subjects


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Work Sampling

When is Work Sampling Appropriate?

  • Sufficient time is available to perform the study

    • Several weeks usually required for a work sampling study

  • Multiple subjects

    • Work sampling suited to studies involving more than one subject

  • Long cycle times for the jobs covered by the study

  • Nonrepetitive work cycles

    • Jobs consist of various tasks rather than a single repetitive task


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Work Sampling

Example: How Work Sampling Works

  • A total of 500 observations taken at random times during a one-week period (40 hours) on 10 machines with results shown below.

    CategoryNo. of observations

    (1) Being set up 75

    (2) Running production 300

    (3) Machine idle 125

    500

  • How many hours per week did an average machine sped in each category?


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Work Sampling

  • Proportions of time determined as number of observations in each category divided by 500

  • Time in each category determined by multiplying proportion by total hours (40 hr)

    CategoryProportionHrs per category

    (1) Being set up 75/500 = 0.15 0.15 x 40 = 6

    (2) Running production 300/500 = 0.60 0.60 x 40 = 24

    (3) Machine idle 125/500 = 0.25 0.25 x 40 = 10

    1.00 40


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Work Sampling

Work Sampling Applications

  • Machine utilization - how much time is spent by machines in various categories of activity

    • Previous example

  • Worker utilization - how workers spend their time

  • Allowances for time standards - assessment of delay components in PFD allowance factor

  • Average unit time - determining the average time on each work unit

  • Time standards - limited statistical accuracy when standards set by work sampling



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References

  • Groover,Mikell P., Work Systems: The Methods, Measurement & Management of Work, 2007, Prentice Hall

  • Barnes,RalphM., Motion and Time Study: Design and Measurement of Work,1990, John Wiley & Sons Inc.