This paper examines the concept of Therbligs — a system for analyzing the individual motions involved in performing work tasks — developed by Frank and Lillian Gilbreth around 1908. Using micro-motion film study and Simultaneous Motion Charts (Simo Charts), the Gilbreths isolated discrete movements such as reach, grasp, search, and rest, measuring each in time measurement units (TMUs). Rather than imposing fixed time standards, they sought to eliminate unnecessary or fatigue-producing motions so that efficiency would emerge naturally from better work design. The paper also notes the humanistic dimension of their approach and its continued relevance in modern ergonomics.
What is the problem, one might be tempted to ask, with apportioning the workday according to simple units of seconds and hours when measuring worker efficiency? Why is there a need to create another system of measurement with respect to motion as well as time? The concept of Therbligs — a study of worker efficiency not in relation to time, but in relation to motion — provides the answer.
The concept of Therbligs was born at the turn of the 20th century, a period that oversaw the birth of both the modern factory and the modern motion picture. It was with the help of this latter invention that Frank and Lillian Gilbreth were able to embark upon their study of human kinesthetic behavior in the former. Thus, although the term "Therbligs" may "sound like a new computer term or some obscure part of the human anatomy," Therbligs in fact comprise a fairly old system for analyzing the motions involved in performing a task — almost as old as the modern industrial age of assembly lines. The Gilbreths' identification and isolation of individual worker motions, as well as moments of delay in the process, was designed to root out unnecessary or inefficient motions and to utilize or eliminate even split seconds of wasted time (Ferguson, 2000).
The concept of the Therblig was born around 1908 and has been continually refined and tested by ergonomics experts ever since. Its development was made possible by the use of systematic micro-motion stop-study of movie film. The Gilbreths were able to examine the smallest of motions by watching filmed depictions of workers at their tasks. They then isolated the individual motions and plotted such Therbligs on a Simo Chart (Simultaneous Motion Chart), along with the time each motion took.
"The sequences of motions of each hand were plotted, as was a foot, if used for pedal controls. Then, by examining the charts, one could determine which Therbligs were taking too long. One could also isolate individual motions that could be eliminated by rearranging the step-by-step procedures of the work" (Ferguson, 2000). Through such study, the Gilbreths identified periods of delay caused by tool and part layout, integrating the Therblig motion organization with that of the worker's arrangement of appliances.
"Time used only to quantify motion duration, not impose standards"
"Catalogue of motions includes rest and fatigue reduction"
For all of its coolness of tone, the use of Therbligs could make things easier for the worker — through the use of colors and shapes, to take just one example — as well as swifter and less costly for the producer. The Gilbreths' system, developed over a century ago, thus retains practical relevance in the fields of ergonomics and industrial engineering to this day.
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