Friday, January 11, 2013

Chapter - Human Effort Engineering - 2013 Edition

Human Effort Engineering

Human effort engineering component of industrial engineering focuses on the efficiency of  human resource. Principles of motion economy guide this activity. Motion study is the principal technique to redesign human motions to carry out a task giving the desirable human input into a man-machine sytem. Frank Gilbreth initially developed the motion study technique and it was further developed by other industrial engineers

Method and Techniques of Human Effort Engineering

1. Principles of Motion Economy

2. Motion Study.
    Therbligs, SIMO chart, Chronocycle graph

3. Work Measurement
    Stop watch time study, worksampling, PMTS - MTM, MOST

4. Fatigue Study

5. Ergonomics - Human Comfort and Discomfort Studies, Health Issues - Musculo-skeletal problem elimination, Human-Computer Interaction related Studies

7. Safe Work Practice Design
    Personal protective devices

8. Wage Incentives

9.  Job Evaluation

10. Motion Economy Device Design

1. Principles of Motion Economy

Principles of motion economy were proposed by Frank Gilbreth. They stood the test of time and with slight modifications the list proposed by Gilbreth is the standard for application in motion study and improvement of motion economy.

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 directions and should be made simultaneously.
4. Hand and body motions should be confined to the lowest classification with which it is possible to perform the work satisfactorily.
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.
6. Smooth continuous motion of the hands are preferable to straight line motions involving sudden and sharp changes in direction.
7. Ballistic movements are faster, easier and more accurate than restricted (fixation) or controlled movements.
8. Work should be arranged to permit an easy and natural rhythm wherever possible.
9. Eye fixations should be as few and as close together as possible.

Arrangement of the workplace
10. There should be a definite and fixed place for all tools and materials.
11. Tools, materials and controls should be located close to the point of use.
12. Gravity feed bins and containers should be used to deliver material close to the point of use.
13. Drop deliveries should be used wherever possible.
14. Materials and tools should be located to permit the best sequence of motions.
15. Provisions should be made for adequate conditions for seeing. Good illumination is the first requirement for satisfactory visual perception.
16. The height of the work place and the chair should preferably arranged so that alternate sitting and standing at work are easily possible.
17. A chair of the type and height to permit good posture should be provided for every worker.

The currently popular 5S method is based on this group of motion economy principles

Design of tools and equipment

18. The hands should be relieved of all work that can be done more advantageously by a jig, a fixture, or a foot-operated device.
19. Two or more tools should be combined wherever possible.
20. Tools and materials should be prepositioned whenever possible.
21. Where each finger performs some specific movement, such as in typewriting, the load should be distributed in accordance with the inherent capacities of the fingers.
22. Levers, hand wheels and other controls should be located in such positions that the operator can manipulate them with the least change in body position and with the greatest speed and ease.

Motion economy device design given as a separate technique in human effort engineering is based on the principles 18.

These principles are further explained in some more detail in a separate chapter.


Ralph M. Barnes, Motion and Time Study Measurement of Work, John Wiley & Sons, New York, 1980

2. Motion Study

Motion study is the investigation and measurement of the movements involved in the performance of any work, their subsequent improvement, resulting in development of easier and more productive (efficient) methods. Specifying the  human input need in the man-machine system and understanding the present way of movement or proposed way of human movement is the starting point. The needs and problems of the current operators has to be ascertained. The purpose of the study is to enable operators to work with minimum effort and maximum efficiency. Minimum effort refers to the efficiency of the operator effort. Maximum efficiency refers to the output being produced by the operator. Motion study man has to study conditions in the man-machine system, machine where human inputs are given, movement of materials, tools and the layout of the work station. They have a bearing on the efficiency and well-being of the workers.

Recording the present or proposed practice is the beginning of the study. The two-handed process chart is commonly used to record movements of each hand separately and also movement of feet if present. Micromotion study records the movements in more detail and the fundamental motions termed as therbligs are used in the recording the micromotions. Gilbreth popularized filming the motions and doing the motion study using them.

F.B. Gilbreth and L.M. Gilbreth, Process Charts: First Steps in Finding the One Best Way to Do Work, paper presented to the Annual Meeting of th Amercian Society of Mechanical Engineers, New York, Dec. 5-9, 1921
The paper is in this collection also

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