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Ch. 26: Predetermined Time Systems

Frank and Lillian Gilbreth broke work into therbligs (elements).

The next step is to assign time values to the elements.

Times for elements are added to obtain a total time. Independence and additivity are assumed.

PTS are based on the concept that there are basic, universal units of work with standard amounts of time.

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Therbligs

The smallest unit of activity in a task.

“Gilbreth” backward (sort of)

from: http://gilbrethnetwork.tripod.com/therbligs.html#Chart

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Methods-Time Measurements (MTM)

Developed in 1946 Simplified versions are available. A training course is required for using the

system correctly.

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MTM-1 10 categories of movements Times in TMUs (1 TMU = .000 010 h) Times are for an experienced worker working at

a normal pace. No allowances are included in the times.

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Reach (table 26.1, pg. 503)

Reach to an object in a fixed location or in the other hand.

Reach to a single object whose general location is known.

Reach to an object jumbled with others in a group.

Reach to a very small object or where accurate grasp is required.

Reach to an indefinite location.

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Move (table 26.2, pg. 504)

Move object to the other hand or against stop. Move object to an approximate or indefinite

location. Move object to an exact location.

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Turn (table 26.4, pg. 506)

A movement that rotates the hand, wrist, and forearm about the long axis of the forearm.

Time depends on degrees of turn, weight of the object, and resistance against turn.

Apply Pressure (table 26.5, pg. 506)

Application of force without resultant movement.

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Grasp (table 29.6, pg. 567)

Pickup grasp Regrasp Transfer grasp Jumbled grasp Contact, sliding, or hook grasp

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Position (table 26.7, pg. 508)

Aligning, orienting, or engaging one object with another

Position times vary with: Amount of pressure needed to fit Symmetry of the object Ease of handling

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Disengage (table 26.8, pg. 509)

Breaking contact between one object and another

Times vary with: Class of fit Ease of handling Care in handling

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Release (table 26.9, pg. 509)

Relinquishing control of an object by the hand or fingers

Two types: Simple opening of the fingers Contact release

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Other Motions

Body, leg, and foot motions Eye motions Combined motions Limited motions

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MTM Form

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MTM-2

Takes about 40% of the time of MTM-1 to analyze a task.

Has only 37 times in all. Key categories are GET and PUT. Provides decision trees to determine case. User estimates distance and uses time from

table. Includes 7 other motions.

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MTM-2 Analysis

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MTM-3

Takes about 15% of the time of MTM-1 to analyze a task.

Has only 10 times. Key categories are HANDLE and TRANSPORT. Provides decision trees to determine case. User estimates distance (< 6 in. or > 6 in.) and

uses time from table. Includes 2 other motions.

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MTM-3 Analysis

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MOST Work Measurement System

Based on observation that the majority of activities are associated with a limited number of motion sequences.

Significantly reduces time required to perform an analysis.

4 sequence models (pp. 513 – 516) General move sequence [A B G A B P A] Controlled move sequence [A B G M X I A] Tool use sequence [A B G A B P use* A B P A] Manual crane sequence [A B G M X I A, specific to

crane use.]

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General Move Sequence Model

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Your turn …

Perform a MOST analysis of the peg board task.

Perform a MOST analysis of writing “MOST” on your notes with a pencil (assume the pencil is picked up from the desk at the beginning and returned to the desk at the end of the task.)

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MODAPTS

Based on the concept that the body member used is the key variable.

All body movements are multiples of a MOD (1 MOD = .129 s).

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Comments about PTS

In theory, PTS can accurately predict task times. Evidence shows reality and theory don’t agree.

One problem is that analyst judgment is required. For the most part, consistency and cost are

more important than accuracy. a consistent deviation from reality can be adjusted for

Purpose of a PTS study use methods analysis to determine an efficient work

method determine the amount of time necessary to do the job