Chapter 28 STOPWATCH TIME STUDY

Stopwatch Time study should be preceded by a methods analysis so the resulting standard is a“should take” time not a “did take” time.

OVERVIEWStopwatch time study is one of the two methods to establish a type I time standard.

The analyst observes one or more operators continuously and records the time taken to accomplish a task. This is called Observed Time

Observed Time x Rating = Normal Time

OVERVIEWStandard time = (Normal time) * (100/{100 – pct Allowances})

Example:

Observed time = .01 hr./unit

Rating = 120 %

Normal time = .012 hr./unit

Allowances = 10%

Standard time = (.012 hr./unit * 100/90) =.0133hr./unit

Time Study Sheets (from ERGO)

Acrobat Document

PREPARATION

There are basically two steps involved in Preparation

1. Methods Analysis

2. Operator Selection

METHODS ANALYSIS

From a productivity standpoint, supervisors of industrial engineering department have to do job design.

•The primary reason for doing a methods analysis before doing a time study is to establish a safe, productive job.

•The secondary reason is to leave a permanent record of the methods for future audits and improvements.

The typical items that are recorded are :

Date of observation(Improvement curve)Person observed (Skilled…..)Person observing (Viewpoint)Machine used (Improvement curve)Tools used (Improvement curve) Part no. processed etc..

METHODS ANALYSIS

METHODS ANALYSIS

After a good method has been established (using checklists), the job should be broken into Elements

METHODS ANALYSIS

Five Reasons to divide the tasks into elements:

•Elements make it possible to reuse the data

•Elements permit different ratings for different elements(Machine time and manual time)

•Elements permit consistency checks, within the study and between studies

•Elements improve methods descriptions

•Data collection is flexible

METHODS ANALYSIS

•After the task is broken into elements, we write the element description on the time study form with a description of its EP (End points ) or also called TP (Termination point)

(Example)

OPERATOR SELECTION

It is very important to select the right operator for performing the time study

There are two reasons:

•Rating Accuracy(average worker)

•Worker Acceptance( do the study at different times)

TIMINGTiming Techniques (example)•Videotape

•One watch, continuous

•One watch, snapback

•Three watch system

•Electronic watches

TIMINGVideotape:

•The primary advantage is having a permanent record of the method.

•Videotaping is less intrusive so there might not be any discrepancies.

•The tape counter does not give very accurate data as it gives continuous timing; use a stopwatch.

•The elements can also be performance rated

•If any dispute occurs then the tape can also be replayed

TIMINGOne watch, continuous

•The stop watch does not stop, it is continuously run (Example)

•As the clock never stops, there is no time omitted and workers like that

•The disadvantage is that the observer does not know how individual elements vary and the observer tries to read a moving target.

TIMINGOne watch, Snapback

•As the element ends, the time is noted and the stop is reset (set back to zero).

•The advantage is that no subtraction to be done and the observer is able to see the pattern.

•If the observer is confused then he might stop the watch.

•Continuous is preferred over snapback.

TIMINGThree-watch system

As in the title there are three watches and it is a combination of snap back and continuous type

Initially the hands of the first watch are moving, the second’s are stopped at some value, and the third’s are stopped at zero.

The only disadvantage is that there are three watches.

TIMINGElectronic watches

•These watches can be used either the snapbackor the continuos mode

•The key feature is that, when the user depresses thebutton, the display time is frozen while the clockcontinues timing.

•Electronic watches with a computer built into theboard, generally have replaced the traditional mechanical stop watch.

NUMBER OF OBSERVATIONS

There are two approaches to determining the number of observations

•Statistical

•Importance of Decision

NUMBER OF OBSERVATIONS

Statistical

A time study of sequential observations is a sample from a population of times. The goal is to estimate the population mean from the sample mean.

To minimize the differences between the sample and population means, increasing the sample size is one of the answers….

The number of sample size depends on three factors

•Accuracy Desired (absolute or relative)

•Confidence Desired (based on Z score)

•Data Variability (use subsample to determine)

Calculation formula: (See Box 28.1)

-Westinghouse/ General Electric and Niebel’s approaches are in Tables 28.2 and 28.3

NUMBER OF OBSERVATIONS

Irregular and Foreign Observations

•Irregular element (exp. Breakdown)

•Foreign element (exp. Customized part)

NUMBER OF OBSERVATIONSRecording Techniques

•Missed Readings

•Omitted Readings

•Element out of order

•Unexpected element

RATING

Normal Pace

During the time study, the observer will rate the worker, that is, determine the adjustment to convert the observed time to a time that a normal, experienced worker would take

APL = MPL - Expectancy

RATING

MPL (Motivated productivity level) : The work pace of a motivated worker possessing sufficient skill and effort to do the job, physically fit to do the job after adjustment to it, and working at an incentive pace that can be maintained day after day without harmful effect.

RATING

Acceptable productivity level (APL): The work pace established by management or jointly by management and labor at a level that is considered satisfactory; it is established at a given relationship to motivated productivity level.

Expectancy is the expected level of productivity, it is also related to allowance, if allowance is low expectancy discount tends to be high and vice-versa.

RATING TECHNIQUES

•There cannot be a set method to rate as different tasks within an activity requires different levels of skills and ways

•All tasks cannot be rated at a same scale

(example)

RATING TECHNIQUESPace Rating:

The observer estimates the speed and concentrate on dynamic micromotions such as reach or move rather then stationary like position and grasp.

Objective Rating: (three steps) (example)

•The observer rates the speed

•Observer estimates the task difficulty

•task difficulty factor is multiplied with speed to get actual pace.

RATING PROCEDURES•Divide the elements and take multiple readings

•Categorize mental, fine manipulative and muscular jobs

•Categorize skilled, unskilled and semi skilled labor

•Categorize time of the day

•Rating is a very specialized task and enough training via videotapes, practice tests, different paces etc should be carried out before actual assignment

RATING TECHNIQUES

Actual pace

Est

imat

ed P

ace

0 20 40 60 80 100 120 140

120

100

80

60

40

20

0 Identity Line

Cte Error

Flat Rating

Consistency