Ch. 26: Predetermined Time Systems

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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.
htmlChart
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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 (lt 6 in. or gt 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 dont 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