16759875 Work Measurement (VG)

WORK WORK MEASUREMENTMEASUREMENT

Rodger Koppa, P.E., Ph.D.Rodger Koppa, P.E., Ph.D.

Industrial and Systems Industrial and Systems EngineeringEngineering

Uses of Work MeasurementUses of Work Measurement

1.1. Compare efficiency of alternative Compare efficiency of alternative methodsmethods

2.2. Balance work among team membersBalance work among team members

3.3. Optimize number of machines per Optimize number of machines per operator (e.g., in a work cell)operator (e.g., in a work cell)

4.4. Establish basis forEstablish basis for• Production planning and controlProduction planning and control• LayoutLayout• Process planningProcess planning• JITJIT

More UsesMore Uses

5.5. Pricing estimationPricing estimation

6.6. Standards for labor performance Standards for labor performance and machine use for 1-5 and for and machine use for 1-5 and for incentivesincentives

7.7. Information for labor cost control – Information for labor cost control – enable standard costs to be fixed enable standard costs to be fixed and maintainedand maintained

Basic Six PackBasic Six Pack SELECT what to studySELECT what to study RECORD that activity or operationRECORD that activity or operation EXAMINE the recorded data and modify EXAMINE the recorded data and modify

procedures/task allocation/layout using procedures/task allocation/layout using Work Study to get the best methodWork Study to get the best method

MEASURE quantity of work with respect to MEASURE quantity of work with respect to time with the best method or ESTIMATE time with the best method or ESTIMATE using predetermined time data using predetermined time data

COMPILE a standard time for activity, COMPILE a standard time for activity, including allowances including allowances

DEFINE activity and standard timeDEFINE activity and standard time

Work Measurement Techniques

1. Work Sampling2. Structured Estimation3. Time Study4. Predetermined Motion Time

Standards (PMTS)5. Standard Data Systems (SDS)

Technique 1: Work Sampling

Definition—Work Sampling

Work sampling is a method of finding the percentage occurrence of a given activity by statistical sampling and random observations

Also known as: Activity sampling Ratio-delay study Random observation Snap-reading method Observation ratio study

When to Use Work Sampling

Lots of time available (weeks) More than one worker and/or

machine Long cycle times Non-repetitive work cycles (but

must be distinct number of categories)

Statistical Approach

Best Case: observe activity all the time Worst Case: observe activity once and

jump to conclusions based on that one experience

Realistic Case: observe often enough to draw some conclusions with a given level of confidence (80%, 90%, 95%, 99%.....)

How Often?

Setting How Often

How much confidence you need determines how many times you must observe and go through the six-pack

Sometimes the target operation will be going on, sometimes not

Spend a period of hours or visit 5 times or more to estimate % time activity happens

Sample Size Estimation

Where σp = SE of

proportionp = % idle timeq = % working timen = Number of

observations needed (sample size)

n

pqp

Sample Size Estimation (Cont’d)

Suppose 95% confidence level 10% margin of error Then 1.96 x (σp) = 10; so σp ≈ 5 Preliminary study says machines idle 25% Substitute these values of σp, p,q in

binominal sample equation and solve for n

n = 75 observations with margin of +/- 10% (if +/- 5%, you need 300 observations!)

Randomized Observations(Play the game right)

Randomize with respect to time Divide shift into time slots Use random number table (or Excel)

and assign random numbers to each time period, re-order time slots 1-n

Observe in that order (will take quite a few days or maybe weeks)

For Each Observation

Record what is happening to level of detail required:

Machine working? Cutting Boring Grinding

Machine Idle? Maintenance Waiting for materials Worker in restroom

Rated Work Sampling

Equal-appearing rating (≤ 10 intervals) can be applied to pace of operation if machine not idle

Can set fixed intervals (no random sampling) and rate pace at those times

Interval must be short with respect to total cycle time

Can be used with more than one worker and/or machines

Work Sampling: So What?

Simple technique usable in plants, service operations, offices

Low cost Avoids controversial aspects of time

study Management gets good idea of where

inefficiencies may lie Can trigger method studies, travel

studies




Structured EstimationStructured Estimation

Most widely used and oldest approach Most widely used and oldest approach Based on past experience with Based on past experience with

same/similar operationssame/similar operations Very cheap to apply, but you get what Very cheap to apply, but you get what

you pay foryou pay for Much used for jobs/operations not yet Much used for jobs/operations not yet

implemented implemented

Analytical Approach to Analytical Approach to Structured EstimationStructured Estimation

Estimator should have experience in type Estimator should have experience in type of job being considered and in work study of job being considered and in work study techniques (tall order)techniques (tall order)

Alternatively the estimator derives Alternatively the estimator derives times/rates of production from times/rates of production from experienced workers by debriefingexperienced workers by debriefing

Analytical ApproachAnalytical Approach

Break job into elements than can Break job into elements than can estimated for timeestimated for time

Apply available estimates (experience, Apply available estimates (experience, Dodge Manual, other labor statistics)Dodge Manual, other labor statistics)

Time similar task elements or use Time similar task elements or use mockup/simulated workplacesmockup/simulated workplaces

SWAGSWAG




What is a “Time Study?”

“Time study is a work measurement technique for recording the times of performing a certain specific job or its elements carried out under specified conditions, and for analyzing the data so as to obtain the time necessary for an operator to carry it out at a defined rate of performance”

Introduction to Work Study 4th Ed

G. Kanawaty (Ed.) International Labor Office, Geneva Switzerland 1992

Basic Time Study Approach

Except for a Q&D study, don’t bother with a stop watch Heisenberg principle Requires practice and multiple runs

Acquire and use a video camera Digital video camera best and getting cheaper every

year Many digital (still) cameras have “movie” mode that

suffices for short cycles (5 min or less) “Movie Maker” software to analyze

Data Collection

Can make up your own or use a spreadsheet Basic sheet layout sketched in next slide Summary sheet also can be hand-hacked or

produced on a spreadsheet (much prefer using a spreadsheet!)

When to Do a Time Study

Don’t bother with time study until Method Study is done and as much inefficiency is wrung out as possible

Must optimize method before setting a standard!

Aim for what a “qualified” worker can do without “undue” fatigue (engineering judgment)

Caution

Don’t try to do covert observations either with stopwatch or with camera

Invasion of personal privacy May or may not meet criterion of “motivated”

worker Duck image of “efficiency expert”

8 Basic Steps

1. Identify background, operator, environmental factors that pertain to work

2. Do a Task Description down to “element” level of detail

3. Do a Methods Study and optimize the task 4. Time each task element from video data or

by direct observation with a stopwatch

8 Basic Steps (Cont’d)

5. Assess observed pace vs expected pace (IF past experience/standard times exist)

6. Extend observed times to Basic Times

7. Determine Allowances

8. Establish Standard Times

1. Background Information

Retrieval/catalog information Study number Analyst and approvals (if needed) Date, time, location

Product/part identification Process, method, plant, machine identification Worker’s identification or designation (do you really

need this?) Study duration Working conditions (temperature, humidity, lighting,

noise)

2/3. Task Description & Methods Study Element: lowest component of a specified job

being timed, selected for convenience of observation, measurement, and analysis

Work Cycle: sequence of elements required to perform a job or yield a unit of production

2/3. Task Description & Methods Study (Cont’d) Observe task being done several times Debrief worker based on observations to identify

subtasks and/or study videos Perform Methods Study Optimize task based on results of Methods Study Train worker(s) to perform optimized task Repeat task cycle until performance becomes

asymptotic in skill and time Complete task description down to element level

2/3. Task Description & Methods Study (Cont’d)Types of Elements: Repetitive – comes up each cycle Irregular – comes up every now and then Constant – takes same time every time Variable – basic time varies with respect to some characteristics

of product Manual – done by worker Machine – automatic once started, can only be terminated by

operator Governing – Takes more time than any other element within

work cycle performed concurrently

2/3. Task Description & Methods Study (Cont’d)

Picking elements to study: Define break points—distinct segments Elements should be 2-3 sec or longer

For timing purposes: Separate manual and machine elements Separate constant from variable elements Separate repetitive from irregular elements

4. Perform Time Study

How many repetitions to time or video?

2 Approaches:

1. Statistical estimation of sample size

2. Industrial practice (preferred)

Industrial Practice (source: General Electric) The shorter the cycle time, the larger the sample

size (Number of reps) Vary from 0.10 min = 200 reps to 40 or more min =

3 reps

Timing Each Element

Video Recording: Record as many cycle reps as needed for sample Use time scale in software (Windows Movie Maker)

Stopwatch (ugh): Cumulative timing: note start time of cycle and then

note time at end of each element Flyback timing: watch reset (but not stopped) at end of

each element and time noted Digital watch MUCH easier than analog Will have to go through cycle as many times as needed

for sample size and repeat for each concurrent element

Time Study Rating

Very subjective and full of pitfalls Helps if observation is as unobtrusive as

possible without being covert Helps if enough reps done so worker forgets

you are observing him AND if the worker is “qualified”

Qualified?

A qualified worker is one who has acquired the skills, knowledge and other (?) attributes to carry out the work in hand to satisfactory standards of quality, quantity, and safety

Bootstrap?

You bet!

Experience to Become Qualified

May take only 1 shift May require 10,000 cycles for a complex

operation Motivation of worker key element Adversarial image of industrial engineer an

impediment: How do you make a win-win situation? How much do you know about the operation?

Fair Time

Come up with factor to multiply observed mean time to estimate “fair time”

“Standard performance” is what can be expected of an “average” worker over the shift period, assuming: Knowledge of the job (qualified) Motivation to do work in professional manner

Rating of such performance = 100

Rules of Thumb

Standard rating (100) is represented by the speed of motion of the limbs of a person walking at 4 MPH (6.4 kph)

Brisk, purposeful walk Standard rating, arm motion: Dealing a pack

of cards in 0.375 min

Rating Actual Performance

100 scale actually 10 scale Ordinal scale of measurement Rater must be experienced and very familiar

with operation

Intervening Variables

Variation in quality of materials or subassemblies

Changes in efficiency of tools and machines Method changes Worker attention and motivation Working environment Speed/accuracy tradeoff

0 – 100 Rating

Rating Performance Walking50 Very slow, clumsy 2 mph

fumbling, unmotivated75 Steady, deliberate, 3

unhurried100 Brisk, businesslike 4

piece work pace125 Very fast, assured, dexterous 5

coordinated150 Exceptionally fast, intense 6

concentration, hard to keep up pace

Deriving Standard Times for Elements

Convert observed times to Basic TimesBT = Observed Time x Observed Rating

Standard Rating (100) Derive “representative” BT

Mean (but consider outliers) Median or mode

Variable Elements

Compute SD as well as Mean Continue to observe until SD stabilizes Use mean as best estimate of time




Predetermined Motion Time Standards

“ An organized body of information, procedures, techniques, and motion times employed in the study and evaluation of manual work elements. The system is expressed in terms of the motions used, their general and specific nature, the conditions under which they occur, and their previously determined performance times”

--ANSI Standard Z94.11- 1989

History

1915: PMTS presaged by Gilbreth’s “Therbligs” 1927: A.B. Segur—”The time required for all

experts to perform the fundamental motions (of work) is a constant”

1934: J.H. Quick – Work Factor System 1946: H.B. Maynard and others develop MTM

(Method-Time Measurement) 1972: K.B. Zandlin develops Maynard Operations

Sequence Technique (MOST) from MTM approach

Basic PMTS Approach

1. Do task description in terms of basic motions in a defined workspace just as in Time Study

2. Perform work studies to improve task (unless task is in planning stage)

3. Retrieve from data base the basic times associated with each motion as modified by task conditions and work variables

4. Sum all of these times to form the basic time for the task (ratings automatically included)

5. Apply allowances (to be discussed) to arrive at standard time for the task

PMTS Levels

Level 1: Very elemental motions like Therbligs, suitable for short cycles

Level 2: Some motions combined, e.g., reach and grasp become get

Level 3: May only be 3 or 4 elements, e.g., handle, transport, step/foot motions, bend/rise

A Few PMTS Variants

Work-Factor (1930’s) WF Methods-Time Measurement (MTM-1, MTM-2, MTM-3, others) Basic Motion Time Study (BMTS) based on MTM-1 and

Therbligs Master Standard Data (MSD) based on MTM-1 Maynard Operation Sequence Technique (MOST) emphasizes

production and material handling at Level 1 and 2 Modular Arrangement of Predetermined Time Standards

(MODAPTS) based on MTM’s and MSD; finger motion is basic element

Basic MTM

Postulates: A given motion has a fundamental time to

accomplish that motion Each motion is independent of any other with

respect to time Simple chaining can provide a consistent and

accurate prediction of the basic time of a given operation

Time Units

Vary from system to system Most common: Time Measurement Unit

(tmu) = 0.00001 hour

0.0006 min

0.036 sec

MTM-2

Most widely used MTM Technique 15 basic motions Modify times by distance moved and

weight Not as complicated as it looks but requires

practice

Motions in MTM-2

Refer to handout, MTM-2 Basics

GET– reach, grab, release

GA –No grasp needed

GB – grasp, close hand

GC – thumb, finger only

GW – grasp and move mass

Motions in MTM-2

PUT – Move object from a to b

PA – ballistic motion

PB – Controlled motion

PC – Complex motion, obvious correcting

PW –Moving significant mass

Motions in MTM-2

REGRASP (P) –change mode of graspAPPLY PRESSURE (A) –Isometric application of forceEYE ACTION (E) – Examine object, searchFOOT MOTION (F) – Shift foot position less than 30 cmSTEP (S) –Displace trunk, leg motion more than 30 cmBEND & ARISE (B) – Lowering trunk, reach at/below

knees, returnCRANK (C) – Circular motion of handle

MTM -3

Bare-bones “quick and dirty” analysis Only 4 work elements:

Handle (HA and HB)Transport (TA and TB)Step and foot motions (SF)Bend and rise (B)

A and B for H and T refer to “light” and “heavy” loads

MOST

Maynard Operation Sequence Technique Basic MOST

Motion aggregates concerned with material handling and moving objects

General move-object is freely moved through space

Controlled move-object is slid or manipulated Tool use-hand tool operations

Basic MOST

General Move A – Action Distance: hand translation

loaded or unloaded, feet translation B –Body motion sit/stand G –Gain control (same as grasp) P –Placement: position, orient, lay aside

object

Basic MOST

Controlled MoveObject being moved is constrained (e.g., a contrtol

lever) A, B, G as in General Move M –Move, controlled: object is moved over a

certain path X –Process time associated with machine I –Align: motions at end of movement to ready

object for next operation

Basic MOST

Tool Use A,B,G,P as in General and Controlled Move Additional subtype is the specific use of the tool:

Fasten, Loosen Cut Surface treat Measure Record Think

Other MOSTs

MaxiMOST – for long, complex cycles, e.g., heavy assembly, machine setup

MiniMOST – Very short cycle, highly repetitive work (1.6 min or less)

Clerical MOST – For office operations

MOST for Windows

Basic, Maxi, or MiniMOST 2 Modules:

Quick MOST – Select work methods given application, canned procedures and times edited by user as needed. Similar to using standard data systems

Direct MOST – User provides data on industry and work situation, program generates possible work method. Method refined by user (intelligent system)




Standard Data Systems

Industry or company specific data base Common elements from different tasks are

grouped and summarized Industry sources may have data that can be

applied to make a good-enough estimate of cycle/operation times

MOST for Windows is such a data base Semi-quantified experience

Data Base Development Decide what to cover, what to omit (otherwise data

base will be too large) Break jobs into elements that are common enough

to group together Derive times from standard data handbooks,

previous time or PMTS studies on similar operations, or very limited observations (video tape if possible) of representative elements in each group May need to use mockups or “air guitar” to get a feel for the

times Estimates from workers familiar with the tasks can be very

helpful, but NOT sufficient

Elements to Include

Setup and Production Constant and variable Worker-paced and machine-paced Regular and irregular

Setup and Production Elements

How long does it take to set up for any batch and changeover from one to another?

Setup elements occur once per batch Production elements occur once per unit

output Total time to produce a batch is the sum of

setup time plus the product of number of units in batch times batch time

Constant and Variable Elements

Constant: replace bit in drill press; push 4 buttons to initiate process

Variable: material handling; place work piece in lathe and secure; unload parts from container

Worker-paced and Machine-paced Elements

Worker-paced: rebuild injector body; lay up ceramic for firing

Machine-paced: feed and speed, number of operations and how controlled

Regular and Irregular Elements

Regular: happen every cycle Irregular: not every cycle, so time must be

prorated based on expected frequency of occurrence

From Basic Time to Standard From Basic Time to Standard TimeTime

• Once you have basic times from any Once you have basic times from any of the 5 approaches for each element of the 5 approaches for each element of interest you’re not finished yet!of interest you’re not finished yet!

• To derive a standard time for To derive a standard time for planning, costing, and payroll, planning, costing, and payroll, allowancesallowances must be made must be made

• Then basic time is adjusted by Then basic time is adjusted by allowances to arrive at standard timeallowances to arrive at standard time

Allowances

1. Individual (e.g., disabilities)

2. Work Factors

3. Environmental Factors

Cycle time is adjusted (longer) by allowances to obtain Standard Time for cycle or activity

Rest periods may also be built into a shift or the time prorated over cycles as allowances

PFD Allowance

Personal, fatigue, and delay allowance Personal: 5% or more if stressful environment Fatigue: 5% up to 20% or more for heavy

labor (negotiated or use formulas) Delay: (unintentional, caused by breakdown

or inefficiencies) depends on company experience

Other Allowances

Contingency: Unscheduled maintenance, breakdowns, out of tolerance products, should NOT exceed 5%

Policy: machine part of cycle, training, OJT Special: Industry specific such as

exposure to toxic materials, radioactivity

Machine Allowance

A “Policy allowance” negotiated between management and labor

Pertains to wage incentive program

Machine time (automatic) “significant” part of cycle time

)1()1( mmpfdntstd ATATT

allowance Machine A

allowance PFD A

cycle during timemachine T

cycle during me worker ti T Where

m

pfd

m

nt

Allowance Example

Assembly of a framus Cycle basic time is 10 min PFD allowance is 10% (no definite breaks, worker is

free to go to restroom, water cooler) Contingency allowance is 10% (junky equipment up

the line) Machine allowance is 0 (hand and pneumatic tools

only in this operation) Training allowance is 5% (high turnover)Standard time = 10 x 1.25 = 12.5 min

Worker-Machine Standard Times

Some terminology: Unrestricted work: hand/power tool work

where output affected by factors under worker control during cycle. Person-machine relationship

Restricted work: Machine does some to most of work done, worker initiates, terminates, but cannot change machine part of cycle. Person-machine system

Basic Concepts

1. Machine maximum time—time machine available during given period

2. Machine idle time—machine theoretically available, but other factors preclude use

3. Machine ancillary time—machine out for cleaning, setting, programming

4. Machine down time—machine out for breakdown, maintenance, repair

5. Machine running time—time during which it is actually running/producing (Trt = 1 – (2,3,4)

6. Machine running time standard—(2,3,4) minimized

3 Indices

1. Machine Utilization Index: Running Time

Avail Time

2. Machine Efficiency Index: RT Standard

RT

3. Machine Effective Utilization Index:

RT Standard

Avail Time

Approach to Improving Restricted Work Maximize 3 indices (approx. 1) Do methods study with machine time in cycle

fixed Worker does part of work in cycle while

machine stopped (“outside” work) Worker does part of work while machine does

its thing (“inside” work) What outside work could be shifted to inside

work, thus shortening cycle time?

Allowances in Restricted Work

Personal needs PN – based on total cycle time, worker is at workplace even if he/she not actually doing anything

Fatigue FA—based on time (inside/outside) worker actually is doing something productive

Try to allocate during machine part of cycle BUT consider whether machine can be left

unattended, if not “floaters” may be necessary Most often, personal need times must be outside

cycle (cycle time too short to run to restroom!)

Fatigue Allowance (FA)

If 90 sec or more unoccupied time, charge it to FA

If 30-90 sec unoccupied time, deduct 30 sec and multiple by 1.5

4 Basic Situations

1. All PN and FA taken outside cycle

2. PN outside, FA inside

3. PN and some FA outside, some FA inside

4. PN and FA inside

Try to work DOWN this list to achieve # 4 by method study

Unoccupied Time “Allowance”

On some person-machine systems worker is unoccupied during the machine portion of a cycle much more than on other systems

Should worker be paid the same when he/she is working vs not working during cycle?

Paying same leads to perceived inequities in pay between high-manual vs high-machine jobs

Pay rate may be different for “work” vs. “unoccupied” time to compensate

Multiple Machines

1 worker may tend more than 1 machine 2 or more workers may tend 1 machine (e.g., power

plant) To study cycle, IE must do timelines for each worker

and each machine in cycle “Load factor” = proportion of cycle time required by

worker to carry out necessary work during machine process cycle

Reciprocal of Load Factor ~ Number of machines worker “could” tend during cycle

ResourcesResources

Beside the WEB, consider these publications:1. Groover, M.P. Work Systems and the Methods,

Measurement, and Management of Work Pearson Prentice Hall, 2007

2. Kanawaty, G. (Ed) Introduction to Work Study (4th Ed) International Labour Office, Geneva, Switzerland, 1992

3. Mundell, M.E. and Danner, D.L. Motion and Time Study: Improving Productivity (7th Ed) Prentice Hall 1994

16759875 Work Measurement (VG)

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