23 timestudy

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Time study procedure - overview

Perform methods analysis. Identify elements. Observe one or more operators to find observed time. Give a rating to adjust observed time and find normal

time. Add allowances to normal time to find standard time. Procedures attempt to reduce inaccuracies of going

from the sample to the population and from the present world to the future world.

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Step 1: Methods analysis

Purposes: Establish a safe, productive job. Leave a permanent record of method for future use.

Most of effort should be in job design and productivity rather than time standards.

Once the best method is established, break the job into elements.

Use the following forms as needed …

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Forms

Flow chart product / people flow motion patterns

Process chart Right and left hand chart Multi-activity chart Operator / Machine chart

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In-class exercise

Time to fill peg board – old method Follow the method given in the handout Determine the time to completely fill one board Repeat 5 times and calculate the average …

Redesign workspace and work method … (5 minutes)

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Step 2: Break the job into elements

Why … Makes it possible to reuse the data. Permits different ratings for different elements. Permits consistency checks. Improves methods descriptions. Makes incomplete data useful.

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Step 2: Break the job into elements

How … Identify complete actions, e.g.

Get a part Assemble two pieces together

Define action endpoints (EP) or terminal points (TP) Easily recognizable Logical in context Example: Get part A, TP is part A at center

Assemble two parts, TP is release of assembly in bin

Endpoint of one action is beginning of the next Always keep manual and machine time separate

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Operator selection

Treat the operator with dignity and respect. Try to make the sample representative of the

population. Select experienced rather than inexperienced

workers. Select average or typical workers. Vary the times and days of studies.

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Timing techniques

Stopwatch Use snapback mode. Use electronic watches. Avoid using continuous mode.

Videotape Provides a permanent record of the method. Analysis can be done by person other than

camera operator. Elements can be performance rated.

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Snapback recording

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Statistical approach – pg. 492

Number of observations depends on: Accuracy desired Confidence desired Data variability

Example: A time study is being planned. A preliminary sample of 20 times is shown to have a mean of 16 seconds and a standard deviation of 0.4 seconds. If a relative accuracy of 10% and a 95% (round to 2σ) confidence interval are desired, how many observations are required?

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Statistical approach – example (cont.)

Standard deviation method:

Alternatively, use range method (see box 25.1)

=

=

2'' xA

ZN σ

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Importance-of-decision approach

Number of observations depends on: Importance of accuracy of the time standard Cycle time Activity/year Cost of an inaccurate standard

See table 25.2, pg. 493

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Irregular and foreign observations

Irregular elements: operator activity that the observer did not anticipate include like other elements determine how often per unit produced example: clear hopper, change blade, etc.

Foreign elements: operator activity that is outside normal work

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Delays

Avoidable delays will not be included in standard. Drinking coffee Chatting with coworker

Unavoidable delays will be included in standard. Talking to supervisor about work Waiting for supplies Breaking a tool

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Recording technique for unusual events

Missed readings ‘M’ in time slot

Omitted elements ‘-’ in time slot

Elements out of order see columns 6-8, next page

Unexpected elements code events (A, B, C, etc.) explain code elsewhere in short (1-3 word) note

16ISE 311 - 23 Sample time study form (fig. 25.2, pg. 495)

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Rating

Ensures that the standard is based on the method, not the operator.

To improve rating accuracy, study an average operator.

Studying average operators also improves worker acceptance of the standard.

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Normal pace

Normal pace must be defined prior to observation.

Define motivated productivity level (MPL) first. Acceptable productivity level is within

expectancy of MPL. MPL is the work pace of a motivated, skilled,

physically fit worker.

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Motivated productivity level

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Rating techniques - problems

Micromotions change their proportions of the total task as the pace changes. Low-skill micromotions change less than the overall

task. High-skill micromotions change more than the overall

task.

Levels of methods detailLevel 1: Management-controlled

Level 2: Management attempts to control

Level 3: Operator-controlled

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Rating techniques: solutions Pace rating: Observer estimates the pace. Objective rating:

1. Observer rates the speed.

2. Observer estimates task difficulty.

3. Observer multiplies speed factor by difficulty factor to get pace.

Improve accuracy number of observations skilled operator observer skilled at job

Train raters

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Setting allowances

Personal and fatigue allowances are set from tables.

Delay allowances are set from delays actually occurring on the job.

Delays during a time study may provide estimate for the delays to allow for the standard.