PSYCH-105 Industrial Psychology
Chapter 3: Time and Motion Study
Unit 1
Unit 2
Unit 3
Unit 4
Appendix
Therbligs
A system of analyzing the motions involved in performing a task. A small part of job. The term Therblig is an anagram of “Gilbreth” and was coined by Frank and Lillian Gilbreth for their system of studying, timing and analysing the motions of workers. Therbligs are usually aimed at manual tasks and are often used in the field of time and motion studies. Gilbreths gave the name therbligs to the analysis and breakdown of a task into basic elements of motion. The theory is that by analysing and optimising the steps involved in a task, time can be saved. In a factory, saved time means higher productivity. In the home saved time on chores means more leisure time. Lillian Gilbreth used motion picture to study worker motions – developed 17 motions called “therbligs” that describe all possible work.
To use Therbligs, the activity of workers is first recorded and analysed. The individual sequences of motions can be broken down into their component Therbligs and timed. The timing is usually performed in milliseconds. The times taken can then be compared to industry norms (there are published tables for these). If workers are routinely taking longer than expected for a particular Therblig then there might be a reason that can be easily fixed, for example by investing in better equipment or rearranging the workspace.
The Therbligs would then be plotted on a Simo Chart (Simultaneous Motion Chart) along with the time each motion took. The following table lists the Therbligs, along with their mnemonic symbols and standard colours for charting.
|
Therblig |
Colour |
Symbol/Icon |
Abbreviation |
|
Search |
Black |
|
Sh |
|
Find |
Gray |
|
F |
|
Select |
Light Gray |
|
St |
|
Grasp |
Lake Red |
|
G |
|
Hold |
Gold Ochre |
|
H |
|
Transport Loaded |
Green |
|
TL |
|
Transport Empty |
Olive Green |
|
TE |
|
Position |
Blue |
|
P |
|
Assemble |
Violet, Heavy |
|
A |
|
Use |
Purple |
|
U |
|
Disassemble |
Violet, Light |
|
DA |
|
Inspect |
Burnt Orange |
|
I |
|
Pre-Position |
Sky Blue |
|
PP |
|
Release Load |
Carmine Red |
|
RL |
|
Unavoidable Delay |
Yellow Ochre |
|
UD |
|
Avoidable Delay |
Lemon Yellow |
|
AD |
|
Plan |
Brown |
|
Pn |
|
Rest |
Orange |
|
R |
Use of Therbligs
Therbligs have been used for every form of work imaginable. Indeed, the system has been applied to work in robotics and interactive computer systems. Where not used directly, the method has been a model for systems analyzing other aspects of work.
In Ergonomics, where reducing fatigue and injury producing motions is a main goal, the Therblig System is invaluable. Indeed, as motion analysis systems have become more sophisticated and expensive, Therblig analysis (which requires only a video camera and some training) is one of the most cost-effective tools available.
In computer software design, the possible use of Therbligs remains largely uncharted territory. For example, if, when using the mouse, the Search and Select Therbligs could be reduced, in both time taken and frequency of pointing and clicking, computer efficiency would improve at the same time we reduced the exposure to fatigue from using the mouse (a proven source of cumulative injuries). If we Pre-Positioned text or functions, using single-key Macros, again, Use and Assemble times would be reduced.
From these few examples, you can see that the Therblig method is a work in progress, with many new and yet to be explored applications.
