IE 101-Industrial Engineering Orientation Fall 2009 Motion and Time Study Engin Topan

IE 101-Industrial Engineering OrientationFall 2009

Motion and Time StudyEngin Topan

WorkMeas.mnt

MethodsDesign

MethodologyOutline 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

Time Standards

Training

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

Defining Work Systems• Work consists of tasks

– Tasks consist of work elements

• Work elements consist of basic motion elements


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


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

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!


• 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


• 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


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

ProductivityProductivity• 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

ProductivityLabor 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

LH

WU

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

b

t

LPR

LPR

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.

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.

Productivity

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

Productivity

Horse-drawn carts

Steam locomotive

Telephone operator

Manually operated milling machine

Railroad trains

Diesel locomotive

Dial phone

Numerically controlled (NC) milling machine

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

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

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

Allocation of Total Task Time

Productivity

Work Systems

1. Manual work system– Worker performing one or more tasks

without the aid of powered tools

2. Worker-machine system– Human worker operates powered equipment

3. Automated work system– Process performed without the direct

participation of a human worker

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

Work Systems

Manual Work Systems

Work Systems

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

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

Worker-Machine Systems

Work Systems

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

Automated Work System

Work Systems

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

MethodsDesign

Develop System

Standardize

Time Standards

Training

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

Motion Study

17 Therbligs 1. Transport empty (TE) – reach for an object2. Grasp (G) – grasp an object3. Transport loaded (TL) – move an object with

hand and arm4. Hold (H) – hold an object5. Release load (RL) – release control of an object6. Use (U) – manipulate a tool

Motion Study

7. Pre-position (PP) – position object for next operation

8. Position (P) – position object in defined location

9. Assemble (A) – join two parts

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

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

Motion Study

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

13. Plan (Pn) – decide on an action14. Inspect (I) – determine quality of object15. Unavoidable delay (UD) – waiting due to

factors beyond worker control16. Avoidable delay (AD) – worker waiting17. Rest (R) – resting to overcome fatigue

Classification of TherbligsEffective 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

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

Motion Study

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.

• Current method and current layout:

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.

Example A repetitive Manual Task

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

Work Methods Design

To select preferred work method:1. Eliminate all unnecessary work

2. Combine operations or elements

3. Change the sequence of operations

4. Simplify the necessary operations

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

WorkMeas.mnt

Develop System

Standardize

Time Standards

Training


• 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


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

Task Hierarchy & Work Measurement


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



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


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 )


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


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.


(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 %

Reasons for Lost Time at Work

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



How to Allow for Lost Time

• Two approaches used by companies:1. Scheduled rest breaks during the shift

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

2. A PFD allowance is added to the normal time This allows the worker to take a break on his/her

own time


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)


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


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


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


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


Pw ratingTc

cycle time

Tn

normal time

Apfd allowancesTstd

standard time


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


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.


(a) 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

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

Direct Time Study

Direct Time Study Procedure 1. Define and document the standard method2. Divide the task into work elements

3. Time the work elements to obtain the observed time Tobs 4. Evaluate worker’s pace relative to standard performance

to obtain normal time Tn

– Called performance rating (PR)

Tn = Tobs(PR)5. Apply allowance factor to compute standard time

Tstd = Tn(1 + Apfd)

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

Direct time study form

Direct Time Study

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 1.10Performance rating 100% 80% 110% 100%

• Determine (a) normal time and (b) standard time for the cycle

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

Work SamplingStatistical 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

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

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. Category No. 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?

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)

Category Proportion Hrs 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

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

Work Sampling Observation Form

Work Sampling

References

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

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

Documents

IE 101-Industrial Engineering Orientation Fall 2009 Motion and Time Study Engin Topan