Principles of Motion Economy
The principles of motion economy form a set of rules and suggestions to improve the manual work in manufacturing and reduce fatigue and unnecessary movements by the worker, which can lead to the reduction in the work related trauma.
The principles of motion economy were first used by Frank Gilbreth, who listed them as ‘rules for motion economy and efficiency from time to time other investigators have added to and amplified the principles.
The principles of motion economy are grouped under three headings:
- use of the human body
- arrangements of the workplace
- design of tools and equipment
It is necessary for a productivity analyst to know the laws of motion economy that are useful in both workshops and offices, since they cannot develop an effective new method without such knowledge. These are as follows:
Use of the human body
- The two hands should begin and complete their movements at the same time.
- The two hands should not be idle at the same time except during periods of rest.
- Motions of the arms should be symmetrical and in opposite directions and should be made simultaneously.
- Hand and body motions should be made at the lowest classification at which it is possible to do the work satisfactorily.
- Momentum should be employed to help the worker but should be reduced to a minimum whenever it has to be overcome by muscular effort.
- Continuous curved movements are to be preferred to straight-line motions involving sudden and sharp changes in direction.
- ‘Ballistic’ (i.e. free-swinging) movements are faster, easier and more accurate than restricted or controlled movements.
- Rhythm is essential to the smooth and automatic performance of a repetitive operation. The work should be arranged to permit easy and natural rhythm whenever possible.
- Work should be arranged so that eye movements are confined to a comfortable area without the need for frequent changes of focus.
Arrangement of the workplace
- Definite and fixed stations should be provided for all tools and materials to permit habit formation.
- Tools and materials should be pre-positioned to reduce searching.
- Gravity fed bins and containers should be used to deliver the materials as close to the point of use as possible.
- Tools, materials and controls should be located within the maximum working area and as near to the worker as possible.
- Materials and tools should be arranged to permit the best sequence of motions.
- ‘Drop deliveries’ or ejectors should be used wherever possible so that the operator does not have to use his hands to dispose of the finished work.
- Provision should be made for adequate lighting and a chair of the type and height to permit good posture should be provided.
- The height of the workplace and seat should be arranged to allow alternate standing and sitting.
- The colour of the workplace should contrast with that of the work and thus reduce eye fatigue.
Design of Tools and Equipment
- The hands should be relieved from ‘holding’ the workpiece where this can be done by a jig, fixture or foot-operated device.
- Two or more tools should be combined wherever possible.
- Where each finger performs some specific movement, as in typewriting, the load should be distributed in accordance with the inherent capacities of the fingers.
- Handles such as those on cranks and large screwdrivers should be designed so as to permit as much of the surface of the hand as possible to come into contact with the handle. This is especially necessary when considerable force has to be used on the handle.
- Levers, crossbars and hand-wheels should be placed so that the operator can use them with the least change in body position and the greatest mechanical advantage.