Chapter 13
Predetermined Time
Systems
Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
Ch.13 – Predetermined Time Systems
Key Points:
• Use predetermined time systems to predict
standard times for new jobs or improve
methods analysis
• They are a database of basic motion times
• Consider interactions with other motions
• Accurate systems require more effort
• Quick, simple systems are less accurate
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Ch.13
Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
Predetermined Time Systems
PTS – technique for obtaining a standard
time (vs. time study, work sampling) via:
1) Analyze and subdivide a task into
elemental motions (therbligs)
2) Assign pre-set time values for these
elements
3) Summate times to obtain a standard time
for whole task (no direct timing)
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Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
History of PTS
•
•
•
•
•
Based on Gilbreths’ therbligs
Time added in for each therblig
First – Work Factor in 1930’s
Now over 200 PTS systems
Focus on MTM based ones
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Ch.13
Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
13.1 Methods Time Measurement
(MTM)
• Maynard, Stegemerten, Schwab in 1940s
• Westinghouse jobs, broken down into
elements, rated, timed
• Time Measurement Unit (TMU) = 0.00001
hr = 0.0006 min = 0.036 sec
• Main variations: tradeoff of speed &
accuracy = MTM-1, 2, 3
• Specialized variations for jobs: MTM-C for
clerical, MTM-V for machines, MTM-M for
magnification
Ch.13
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Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
Comparison of MTM-1,-2,-3
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Accuracy vs. Length of Cycle
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Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
Use MTM-2 When:
1)
2)
3)
4)
Cycle time > 1,600 TMUs (~ 1 min)
Cycle is not highly repetitive
No complex finger motions used
Ex: dealing a deck of 52 cards
•
•
•
Time =
Repetitive =
Finger motions =
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Ch.13
Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
9 Elemental Motions
1) GET (G): gain control of object
•
•
•
Reach for an object
Grasp object
(eventually) Release object
2) PUT (P) = move object (when under
control) to new location
•
•
Move object to new location
Position object to proper location
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Ch.13
Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
Variations of GET & PUT
• Case = type of grasping or correcting
motion, amount of control needed
• Distance reached
• Weight of object or resistance
• Type of PUT
– Insertion difficulty (one object into another)
– Surface alignment
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Ch.13
Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
Cases
for
GET(G)
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Cases for PUT (P)
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Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
Clearances (in.) for
Insertion vs. Alignment PUT
PA
PB
PC
Insertion
>0.4
<0.4
Tight fit
Alignment
>0.25
<0.25
>0.0625
<0.0625
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Ch.13
Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
Distance Code
Range (in)
Code
Classification
0-2
2
1-finger
2-6
6
2-wrist
6-12
12
3-forearm
12-18
18
4-arm
18-32*
32
5-torso
* >32 → step
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Ch.13
Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
Weight Factor
• If significant weight moved, additional time
is needed
• GET Weight (GW) = + 1 TMU for each 2
lbs up to 40 lbs
• Values are per hand (20 lb box → 5 TMU)
• PUT Weight (PW) = + 1 TMU for each 10
lbs (above 4 lbs) up to 40 lbs
• Resistance: Ffriction = 0.4 N
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Ch.13
Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
Other Elemental Motions - 1
3) Apply Pressure (A) = 14 TMU
•
•
•
Exert muscular force on object
Without moving it (otherwise G or P)
Ex: push button
4) Regrasp (R) = 6 TMU
•
•
•
Change position of object
Without relinquishing control (otherwise G)
Ex: reorient tool
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Ch.13
Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
Other 7 Elemental Motions - 2
5) Eye Action (E) = 7 TMU
•
•
•
Recognize an object or
Shift line of sight out of normal area of vision
Don’t over do, G and P have already
6) Crank (C) = 15 TMU/rev
•
•
•
•
Hand/fingers move in circular path > ½ rev
If < ½ rev, use G and/or P
May need GW to overcome stiction
May need PW for sticky crank
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Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
Other 7 Elemental Motions - 3
7) Steps (S) = 18 TMU/step
•
•
Leg motion to move body,
Distance > 12”
8) Foot Motion (F) = 9 TMU
•
•
Short foot motion, to press pedal
Distance < 12”
9) Bend & Arise (B) = 61 TMU
•
•
•
Vertical displacement of body
Squat, stoop, kneel on one knee
Kneel on both knees = 2B
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Ch.13
Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
MTM-2 Application
1)
2)
3)
4)
5)
Use MTM Methods Analysis Chart
Summarize motions by hand (L & R)
Add TMUs (no ratings needed)
Add allowances
Consider special cases
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Summary of MTM-2 Data
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Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
Insertion vs. Alignment PUT
RH
TMU
P
P
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Ch.13
Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
Continuous vs. Intermittent Crank
Continuous C
GB 18
18
GW 10
5
3C
45
3PW 10
3
Total
71
Intermittent C
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Ch.13
Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
1) Simultaneous Motion
• Simo difficult motions
require more time
• Add a penalty
Ch.13
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Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
Other Special Cases
2) Principle of limiting motion
– For two different motions for each hand
– Use the longer time
3) Principle of combined motion
– For two combined motion in one hand
– Use longer time
4) R is included in C-type motions
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Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
Examples
Ch.13
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Sources of Error
• Discreteness – tabular data
– No interpolation
– Hopefully, this averages out
• Synthesis assumes correct process
• Need correct application - practice
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Ch.13
Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
Ex #1: U-bolt (Cable
clamp) assembly
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Ch.13
Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
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Ex #2: Flashlight assembly
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Comparison of
MTM and Time Study
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Ch.13
Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.
Ch. 13 Summary
• Use predetermined time systems to predict
standard times for new jobs or improve
methods analysis
• They are a database of basic motion times
• Consider interactions with other motions
• Accurate systems require more effort
• Quick, simple systems are less accurate
31
Ch.13
Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.