The principles of motion economy form a set of rules or suggestions which, if applied by one trained in the technique of motion study and the problem solving process, will make it possible to increase the output of the manual labor with a minimum of fatigue.
These principles have the following three sub-divisions:
(I) Principles of motion economy as related to the use of the human body.
(II) Principles of motion economy as related to the arrangement of the place.
(III) Principles of motion economy as related to the design of tools and equipment.
Principles of Motion Economy as Related to the Use of the Human Body:
1. The two hands should begin as well as complete their motions at the same time.
2. The two hands should not be idle at the same time except during rest periods.
3. Motions of the arms should be made in opposite and symmetrical direction and should be made simultaneously.
It is advantageous to arrange similar work on the left and right hand sides of the workplace, thus enabling the left and right hand to move together, each performing the same motions. The symmetrical movements of the arms tend to balance each other, reducing the stock and jar on the body enabling the worker to perform the task with less mental and physical effort. There is apparently less body strain when the hands move symmetrically than when they make nonsymmetrical motions, because of this matter of balance.
4. Hand and body motions should be confined to the lowest classification with which it is possible to perform the work satisfactory.
General Classification of Hand Motion:
(A) Finger motions.
(B) Motions involving fingers and wrist.
(C) Motions involving fingers, wrist and forearm.
(D) Motions involving fingers, wrist, forearm and upper arm.
(E) Motions involving fingers, wrist, forearm, upper-arm and
shoulder. This class necessitates disturbance of the posture.
Finger motions are more fatiguing, less accurate and slower than motions of the forearm. Forearm is the most desirable member to use for light work and that is highly repetitive work, motions about the wrist and elbow are superior to those of the fingers or shoulders.
5. Momentum should be employed to assist the worker wherever possible, and it should be reduced to a minimum if it must be overcome by muscular effort.
The momentum of the object is its mass multiplied by its velocity. I most kinds of factory work the total weight moved by the operator may consist of three components, the weight of the material moved, the weight of the tools or devices moved, and the weight of the part of the body moved. It is often possible be employ momentum of hand, the material or the tool to do useful work. When a forcible stroke is required, the motions of the workers should be so arranged that the stroke is delivered when it reaches its greatest momentum.
In laying a brick wall, for e.g. if the brick are conveyed fro the stock platform to the wall with no stops, the momentum can be made to do valuable work by assisting to shove the joints full of mortar. If instead of being utilized, the momentum must be overcome by the muscles of the bricklayer, and fatigue will result.
6. Smooth continuous curved motions of the hands are preferable to straight line motions involving sudden and sharp changes in direction.
The abrupt changes I direction are both time consuming and fatiguing to the operator e.g. Folding paper.
7. Ballistic movements are faster, easier and more accurate than restricted (fixation).
Voluntary movements of hands may be grouped into:
I) Fixation movements
Here opposing groups of muscles are contracted, one group against the oher example finger and thumb method of writing.
II) Ballistic movements
It is fast, easy motion caused by a single contraction of a positive muscle group with no antagonistic muscle group contracting to oppose it.
It is less fatiguing, for the muscles contract only at the beginning of the movements and are relaxed during the remainder of the movement. It is more powerful, faster, more accurate, and less likely to cause muscle cramp example the skilled carpenter swinging a hammer in driving a nail. The carpenter aims his hammer, then throws or swings it. The muscles are contracted only during the first part of the movement they idle along the rest of the way.
8. Work should be arranged to permit an easy and natural rhythm whenever possible.
9. Eye fixations should be as few and as close together as possible.
All though some kinds of work can be performed with a little or no eye direction, but where visual perception is required it is desirable to arrange the task so that eyes can direct the work effectively that is work place should be so laid out that the eyes fixations are as few and as close together as possible.