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Predetermined Motion Time Systems
Sections:
1. Overview of Predetermined Motion
Time Systems
2. Methods-Time Measurement
3. MTM-1
4. Maynard Operation Sequence
Technique (MOST)
Chapter 14
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Overview-PMTS Defined
An alternative to direct time study that does not require performance rating.
PMTS is a database of basic motion elements and their associated normal time values, together with procedures for applying the data to analyze manual tasks and establish standard times for the tasks
Basic motions include:
o Reach
o Grasp
o Move
o Release
The time required to perform these basic motions usually depends on certain work variables (reach and distance; move and weight of object; etc.).
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PMTS Procedure
To apply PMTS to a task the analyst must accomplish the following steps:
1. Analyze method that would be used to perform the task
The method is described in terms of basic motion elements
2. Retrieve normal time values for each motion element
Sum the element times to determine the task normal time
3. Evaluate method to make improvements by
eliminating motions
reducing distances
using both hands simultaneously etc.
4. Apply allowances to determine standard time
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PMTS Levels and Generations
First-level PMT Systems use the basic motion elements
Reach, grasp, and move used separately to define
the task
Higher-level systems combine several motion elements
into motion aggregates
Reach and grasp combined into one element called
“get”, “Put” which combines move and position
There are various types of PMT systems, and these types
are variety in the basic motion elements.
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PMTS Levels and Generations (CONT.)
First-level systems were chronologically the first to be
developed and are called first generation PMTS (MTM-1)
MTM-2 is the second generation of PMT systems was
developed. MTM-3 is the third generations.
Some of Predetermined Motion Time systems:
• Method Time Measurements (MTM)
• Maynard Operation Sequence Technique (MOST)
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Comparisons
First-level PMTS
Most accurate
High application speed ratio
Most suited to highly repetitive short cycles
Basic motion elements
Very detailed
Highest flexibility
Higher-level PMTS
Less accurate
Less time to set standards
Longer cycle times feasible
Motion aggregate
Less detailed; easier to apply
Less flexible
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Methods-Time Measurement (MTM)
MTM is a procedure which analyzes any manual
operation or method into the basic motions required to
perform it and assigns to each motion a predetermined
time standard which is determined by the nature of the
motion and the conditions under which it is made
Time units are TMUs (Time Measurements Units)
1 TMU = 0.00001 hr = 0.0006 min = 0.036 sec
1 sec = 27.8 TMU
MTM is a family of products available through the MTM
Association (www.mtm.org) and the original MTM is now
called MTM-1.
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Methods-Time Measurement
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MTM-1
Operates at the basic motion element level in our pyramidal structure of work (same in therbligs)
Most MTM-1 basic motions involve hand and arm movements
Also includes elements for eye, leg, foot, and body actions
More appropriate for tasks that are highly repetitive and cycle times are less than 1 min
Time unit in MTM are called TMUs (time measurement units).
1 TMU = 0.00001 hr = 0.0006 min = 0.036 sec
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MTM-1: Motion Elements
1- Reach (R): Basic motion elements
involves moving the hands and fingers to the
new destination.
R1C takes 3.6 TMUs
Normal Time (Tn)= 3.6 * 0.036 = 0.130 sec
Example:
Motion element
Symbol
Case and
description
Distance
(inches)
Normal Time in
TMU
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G1C3 takes 10.8 TMUs
MTM-1: Motion Elements (Cont.)
2- Grasp (G): Use fingers and hands to
gain control on one object or more.
Example:
Normal Time= 0.389 sec
Motion element
Symbol
Case and
description
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M6B12.5 takes
TMU= Constant + Factor * (TMU value from
table)
= 3.9+1.11(8.9)=13.8 TMUs
MTM-1: Motion Elements (Cont.)
Normal Time= 13.8 * 0.036= 0.497 sec
Example:
3- Move (M): Using the hand and fingers to
relocate an object
Motion element
Symbol
Weight
up to Type of
case
Distance in
inches
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Round peg in a round hole: S(ymmetrical)
Key inserted in a lock: N(on)S(ymmetrical)
P3NSD takes 53.4 TMUs
Example:
Normal Time= 53.4* 0.036= 1.92 sec
4- Position (P): A relatively short hand motion employed to align, orient or engage
the object to another.
MTM-1: Motion Elements (Cont.)
Motion element
Symbol class
Symmetry Easy handle OR
Difficult
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RL1 takes 2.0 TMUs
Example:
Normal Time= 0.072 sec
5- Release (RL): A hand and finger
motion element in order to release
(free) an object
MTM-1: Motion Elements (Cont.)
6- Disengage (D): A hand and finger motion
element in order to separate one object from
another one (disassemble)
D3E takes 22.9 TMUs
Example:
Normal Time= 0.824 sec
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Example (MTM-1)
Q1. A worker seated at a table performs a REACH. The sought-after
object is jumbled with other objects in a tote pan, and the distance of
the reach is 18 in. Determine the MTM-1 symbol and normal time in
TMUs for this motion element.
MTM-1 symbol = R18C (From Reach table)
Solution:
So, the normal time (from Reach table) = 18.4 TMU
The normal time in sec = 18.4 TMU * 0.036 = 0.662 sec
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Example (MTM-1) (Cont.)
Q2. A work element in a manual assembly task consists of the
following MTM-1 elements: (1) R16C, (2) G4A, (3) M10B5, (4) RL1,
(5) R14B, (6) G1B, (7) M8C3, (8) P1NSE, and (9) RL1. (a) Determine
the normal times in TMUs for these motion elements. (b) What is the
total time for this work element in sec?
(a) The individual motion element times are given as follows:
(1) R16C, Tn = 17.0 TMU (2) G4A, Tn = 7.3 TMU
(3) M10B5, Tn = 2.2 + 1.06(12.2) = 15.1 TMU (4) Rl1, Tn = 2.0 TMU
(5) R14B, Tn = 14.4 TMU (6) G1B, Tn = 3.5 TMU
(7) M8C3, Tn = 2.2 + 1.06(11.8) = 14.7 TMU (8) P1NSE, Tn = 10.4 TMU
and (9) RL1, Tn = 2.0 TMU. Total = 86.4 TMU.
Solution:
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Example (MTM-1) (Cont.)
(b) The normal time of the manual assembly task in second:
Total normal time of the task in second = 86.4 TMU (0.036) = 3.1 sec
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Maynard Operation Sequence Technique
(MOST)
MOST is a high-level PMTS based on MTM
Same time units as MTM: TMU
MOST is a product of H.B. Maynard and Company (an educational and consulting firm), Pittsburgh, Pennsylvania
(www.hbmaynard.com)
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MOST in the Work Pyramid
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Basic MOST
Focused on work involving the movement of objects (e.g.,
parts, tools) from one location to another in the workplace
Uses motion aggregates
Called activity sequence models
Three activity sequence models:
General move – object moved freely in space
Controlled move – object remains in contact with a
surface
Tool use – use of hand tools (e.g., hammer,
screwdriver)
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Activity Sequence Model
Consists of sequence model parameters, which correspond roughly to basic motion elements
Sequence model parameters for General Move:
A – Action distance (move hands or feet) – horizontal body motions
B – Body motion (sit, stand up) – vertical body motions
G - Gain control (closely related to grasp)
P – Placement (e.g., position, lay aside, orient)
Standard sequence in General Move:
A B G A B P A
ABG: to get an object;
ABP: to move the object to a new location;
A: return to original position
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Normal Time in TMU = 10 * (sum of index values)
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Example: General Move
Develop the activity sequence model and determine the normal time for the following work activity: A worker walks 5 steps, picks up a small part from the floor, returns to his original position, and places the part on his worktable.
Solution
A10B6G1A10B0P1A0
where A10=walk 5 steps;
B6=bend and arise;
G1=gain control of small part;
A10=return back;
B0=no body motion;
P1:lay aside part on table;
A0=no motion
The sum of index values: 28.
Normal time: 10*28=280 TMUs = 280*0.036 = 10.1 sec
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Controlled move
Used when an object is moved through a path that is somehow constrained. In this case we need additional three new parameters beside previous parameters of the general move (A, B and G):
M-Move, used to describe any manual body motion require to move an object with controlled condition.
X-Process time: since it may include the operation of machinery.
I-Align: this parameters is used when the manual motions are performed at the end of the control move to align object
Standard sequence in controlled move:
ABGMXIA
ABG: to get an object;
MXI: to move the object followed by a process time and alignment,
A: to return
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Controlled move (Cont.)
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Controlled move (Cont.)
Type of Milling Machine
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Controlled move (Cont.)
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Example: Controlled move
Q1. Develop the activity sequence model and determine the normal time for the following work activity: A worker takes 2 steps, grasp the waist-level feed lever on the lathe in stand position, pulls up the lever approximately 15 cm to engage the feed. Process time to turn the part is 25 sec and aligns the lever with one specific speed and then he needs to return the original workstation with 5 steps.
Solution:
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Example: Controlled move
Q2. Develop the activity sequence model and determine the normal time for the following work activity in second: A machinist standing in front of his milling machine, grasps the waist level feed lever on the machine, and rotates the lever one crank to engage the feed. The process time to mill the part is 50 sec. There is no alignment and no action by the worker at the end of the process time.
Solution: