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PREDETERMINED TIME SYSTEMS (PTS)

PREDETERMINED TIME SYSTEMS (PTS). History and Development. Frank and Lillian Gilbreth: Broke work in to 17 micro elements called therbligs Assigned time values to each of these elements Totaled the times for each of the elements

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PREDETERMINED TIME SYSTEMS (PTS)

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  1. PREDETERMINED TIME SYSTEMS(PTS)

  2. History and Development Frank and Lillian Gilbreth: • Broke work in to 17 micro elements called therbligs • Assigned time values to each of these elements • Totaled the times for each of the elements Assumptions: Each element does not affect what happens before and after it (independence and additivity) • PTS are based on the concept that there are basic, universal units of work with standard amounts of time.

  3. Methods Time Measurement (MTM) is probably the most widely used PTS in the world It was developed by Maynard, Stegemerten, and Schwab (1948) in 1946 from motion pictures of sensitive drill operations at Westinghouse Simplified versions are available A training course is required for using the system correctly 2. Methods – Time Measurement

  4. 2.2. MTM-1 • The most detailed system. • 10 categories of movements: Reach, Move, Turn, Apply Pressure, Grasp, Position, Release, Disengage, Body (leg-foot, horizontal and vertical) Motions, and Eye Motions. • Times are given in time measurement units (TMUs). • 1 TMU = .000010 h = .000600 min = 0.036s. • Times are for an experienced worker working at a normal pace. • No allowances are included in the times.

  5. 2.2.1.Reach • Reach is usually movement with an empty hand or finger while move is generally movement with an object in the hand. • Reach is subdivided into five classes. • Reach to an object in a fixed location, or to an object in the other hand, or on which the other hand rests. (The concept is of minimum eye control and emphasis on proprioceptive feedback) . • Reach to a single object whose general location is known. (The concept is that some visual control is necessary and the following grasping motion will be simple and not slow down to reach). • Reach to an object jumbled with others in a group so that search and select occur. (The concept is that considerable visual, muscular, and mental control is necessary and that the following grasp motion will be complex, so the hand will slow down during the terminal motion of the reach to prepare for the complex grasp. It is the most difficult reach). • Reach to a very small object or where accurate grasp is required. (The concept is that considerable visual control is necessary and that the following location grasp motion will be precise., so the hand will slow down during the terminal portion of the reach to prepare for the careful grasp.) • Reach to an indefinite location to get the hand in position for body balance or next motion of out of way. (The concept is f minimum mental control. The movement often is “limited out” as other motions are done simultaneously.)

  6. The distances are for the motion of path of the hand knuckle or fingertip rather than the straight line distance between two points. • If a movement is not given in the table, the user can interpolate or just use the next higher value. • The MTM Association recommends interpolation when tables are given in inches but use of the next higher value when the tables are given in even cm or multiples of 5 cm. • Hands could be in motion either at the beginning or end of the cycle, so either an acceleration or deceleration time can be omitted. Time is decreased, as is shown by the hand-in-motion columns.

  7. 2.2.2. Move • In Move the hand is usually holding something; occasionally the hand is pushing or dragging an object. • Move is subdivided into three cases • Move object to the other hand or against stop. (The concept is there is little need to control the last portion of the move, except perhaps to prevent damage to the object.) • Move object to an approximate or indefinite location. (The concept is a move in which some control is needed at the end of the move, but not a great deal of control.) • Move object to exact location. (The concept is a move with considerable control needed at the end of the move. A case C Move very often is followed a position.)

  8. For example, mM6B, or M6Bm indicates that the hand acceleration or deceleration is omitted. • If both hands move a 5-lb object, no extra time is allocated. • If an object is slid rather than lifted, take the object weight times the coefficient of friction (.4 for wood-wood and wood-metal, 0.3 for metal-metal). • An M6B = 8.9. For a 5-lb weight, time would be M6B5 = 8.9(1.06) + 2.2 = 11.8 For an 18-lb weight moved 12 inches with both hands, time for an M12C would be M12C9 = 15.2(1.11) + 3.9 = 20.8 • Additional time for weight has a static component for obtaining control and dynamic component for additional time. • The static component in TMU = .975 + .345 (weight, lbs) • The dynamic time component is 1.1%/lb, at any given distance

  9. For example: For continuous cranking for 5 revolutions against a 10-lb load with a 6-inch diameter crank, the time would be 5 x 12.7 = 63.5 TMU plus 5.2 for start and stop = 68.7 TMU. Then the resistance is considered by multiplying by 1.11 (from Move table) and adding 3.9 (from Move table) , giving a total of 68.7 x 1.11 + 3.9 = 80.2 TMU. The code is 5C6-10

  10. 2.2.3. Turn • Turn is 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.

  11. 2.2.4. Apply Pressure • Apply pressure is the application of force without resultant movement.

  12. 2.2.5. Grasp • Skill motions: Grasp, Position, Disengage and Release • Grasp is the motion used when the purpose is to gain control of an object or objects : it always is followed by Move • Grasp is subdivided into five categories • Pickup grasp: Usually follows an A or B reach • Regrasp: This grasp is used to change or improve control of an object that had previously been grasped • Transfer grasp: It is used to transfer control of an object from one hand to the other • Jumbled grasp: Follows a C reach • Contact, sliding, or hook grasp. It usually occurs between a Reach and a Move

  13. 2.2.6. Position • Original Position is the collection of minor movements (distance moved to engage no more than 1 inch) for aligning, orienting, and engaging one object with another object. It usually follows a C Move • Align is orienting the longitudinal axes of the two items • Orient is rotation about the long axis to align mating features (key in lock) • Engage is to move along the longitudinal axis to mate the parts • Disengage is the complement of the engage portion of position • Position times vary with: • Amount of pressure needed to fit • Loose • Close • Exact • Symmetry of the object • Symmetrical: No matter in which orientation the part might happen to be, no rotation is necessary for assembly • Nonsymmetrical: There is only and only one rotation in which the two parts will mate • Semisymmetrical: All positions that are neither symmetrical nor symmetrical are considered semisymmetrical • Ease of handling • Easy • Difficult

  14. 2.2.7.Disengage • Disengage is the breaking of contact between one object and another. • Times vary with: • Class of fit • Ease of handling • Care in handling • A complete disengage code includes both feed and ease of handling – for example, D1E, D1D, D2D.

  15. 2.2.8. Release • Release is the relinquishing of control of an object by the hand or fingers • Two types: • Simple opening of the fingers • Contact release: the release begins and is completed at the instant the following Reach motion begins

  16. 2.2.9. Other Motions • Body, leg and foot motions • Eye motions • Combined and Limited Motions

  17. Eye Motions • Eye focus is the focusing of the eye once it has an object in its line of sight. • Eye travel is the movement of the eyes from one point to another. • From geometry, when T/D = 1, the angle swept by the eyes is 45o; for T/D = 2, • the angle is 90o. Thus 15.2 TMU is allowed per 45o sweep (.33 TMU/degree) • with the limitation of a maximum allowable for Eye Travel of 20 TMU.

  18. Combined Motions • Combined motions are those that occur when the same body member performs two or more motions at the same time (Turn a part of the hand while moving it; Regrasp during a Move). • The time to allocate is the greater of the two times. Thus, a Regrasp (5.6) during an M3A (4.9) would be given 5.6 for time, with a slash line through the M3A.

  19. Motions also occur simultaneously, such as right and left hands, hands and feet, or eyes and hands. • If they are truly simultaneous, allow only the longer time. • If they are only apparently simultaneous, allow both times. • Use Table 29.12 to decide between truly and apparently simultaneous. Truly and apparently depends on which combinations are considered, on whether they are in the area of normal vision (objects within 4 inches of each other at a distance of 16 inches from the eye), and the amount of practice (one common definition is 500 cycles, although others use 1,000 or 2,000).

  20. For truly simultaneous motions such as an M8A with the left hand and M10A with the right hand, allow only the 11.3 of the M10A. • For difficult motions such as an M8C with the left hand an M8C with the right hand, allow 11.8 + 11.8 = 23.6 • In many cases where truly simultaneous motions are not allowed by Table 29.12, one hand can drift toward the target while the other does the motion. For example, while the right hand does an M8C, the left hand does an M8B. The M8B can be done simultaneously with the M8C and is “limited out”; it is conventional to circle limited motions. Then, when the M8C is completed, the left hand has only a small distance remaining (an MfC where f stands for fractional remaining). The time allowed is 11.8 for the right hand plus a 2.0 for the left – a total of 13.8.

  21. 2.3. MTM – 2 and MTM - 3 • How much error can be tolerated in the time determined for a specific task: 1%, 5%, 10%, 30%? • How much are you willing to pay for accuracy? • Two simplified systems called MTM-2 and MTM-3 were developed. • In MTM-1 it takes about 350 times the cycle time to analyze the task, while in MTM-2 it takes about 150 times, and in MTM-3 about 50 times.

  22. ±20% ±12% ±7%

  23. 2.3.1 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. • In the cases of GET, if necessary, add 1 TMU/2 lb moved if the object to be moved weighs 4 lb or more per hand • In the cases of PUT, if necessary, add 1 TMU/10 lb moved if the object to be moved weighs 4 lb or more per hand • Includes 7 other motions.

  24. Apply Pressure (A): An action with the purpose of exerting muscular force on an object • Regrasp (R): A hand action performed with the purpose of changing the grasp on an object • Eye Action (E): An action with the purpose of either recognizing a readily distinguishable characteristic of an object or shifting the aim of the axis of vision to a new waiving area • Crank (C): A motion with the purpose of moving an object in a circular path of more than half a revolution with the hand or fingers • Step (S): Either a leg motion with the purpose of moving the body or a leg motion longer than 12 inches • Foot Motion (F): A short foot or leg motion when the purpose is not to move the body • Bend and arise (B): A bend, stoop, or kneel on one knee, and the subsequent rise.

  25. Two key motions GET (reach + grasp + release) PUT (move + position)

  26. 2.3.2 MTM- 3 • Takes about 15% of the time of MTM-1 to analyze a task. • Has only 10 times. • Key categories are HANDLE (getting control over an object with the hand or fingers and the placing the object in a new location) and TRANSPORT (placing an object in a new location with the hand or fingers). • Provides decision trees to determine case. • User estimates distance (< 6 in. or > 6 in.) and uses time from table. • The seven additional elements of MTM-2 have been reduced to 2: SF (combining S and F categories of MTM-2) and B. • Crank would be a TRANSPORT, while Apply Pressure, Regrasp, and Eye Motion are included in the HANDLE and TRANSPORT.

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