Ch. 29: 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.
Ch. 29: 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.
Methods-Time Measurements (MTM) • Developed in 1946 • Simplified versions are available. • A training course is required for using the system correctly.
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.
Reach (table 29.1, pg. 563) • 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.
Move (table 29.2, pg. 565) • Move object to the other hand or against stop. • Move object to an approximate or indefinite location. • Move object to an exact location.
Turn (table 29.4, pg. 566) • 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 29.5, pg. 567) • Application of force without resultant movement.
Grasp (table 29.6, pg. 567) • Pickup grasp • Regrasp • Transfer grasp • Jumbled grasp • Contact, sliding, or hook grasp
Position (table 29.7, pg. 568) • 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
Disengage (table 29.8, pg. 569) • Breaking contact between one object and another • Times vary with: • Class of fit • Ease of handling • Care in handling
Release (table 29.9, pg. 569) • Relinquishing control of an object by the hand or fingers • Two types: • Simple opening of the fingers • Contact release
Other Motions • Body, leg, and foot motions • Eye motions • Combined motions • Limited motions
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. • see, for example, table 29.13, pg. 574 • Provides decision trees to determine case. • User estimates distance and uses time from table. • Includes 7 other motions.
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.
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. 577 – 580) • 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.]
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.)
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).
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. • Most managements are not concerned with a great deal of accuracy. • Managements are concerned with cost of analysis.
Purposes of PTS Studies • Make a methods analysis to determine an efficient work method • Determine the amount of time necessary to do the job