Lean Six Sigma Improvement and Work Design, Part 2

This is the second post in a series taken from a lesson in Pyzdek Institute Lean Six Sigma Black Belt training. Future posts will continue the topic. You can find all of the articles by searching this site for the title. You can read Part 1 here.

Principles of Motion Economy

The rigorous study of efficient work design predates Lean Six Sigma by several decades. As a Lean Six Sigma Black Belt or Green Belt you should take advantage of this by learning the principles discovered long ago. Here are those principles most relevant to the design of work cells. You will see that we draw on these principles heavily when we discuss specific recommendations for work cells. Knowing the principles on which Lean Six Sigma is based will help you understand why the recommendations are made, and it will make it possible for you to go beyond Lean Six Sigma to discover improvements of your own.

Use of the Human Body

• The two hands should begin as well as complete their motions at the same time.
• The two hands should not be idle at the same time except during rest periods.
• Motions of the arms should be made in opposite and symmetrical directions and should be made simultaneously.
• Hand and body motions should be confined to the lowest classification with which it is possible to perform the work satisfactorily.
• 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.
• Smooth continuous motion of the hands are preferable to straight line motions involving sudden and sharp changes in direction.
• Ballistic movements are faster, easier and more accurate than restricted (fixation) or controlled movements.
• Work should be arranged to permit an easy and natural rhythm wherever possible.
• Eye fixations should be as few and as close together as possible.

Arrangement of the workplace

• There should be a definite and fixed place for all tools and materials.
• Tools, materials and controls should be located close to the point of use.
• Gravity feed bins and containers should be used to deliver material close to the point of use.
• Drop deliveries should be used wherever possible.[2]
• Materials and tools should be located to permit the best sequence of motions.
• Provisions should be made for adequate conditions for seeing. Good illumination is the first requirement for satisfactory visual perception.
• The height of the work place and the chair should preferably arranged so that alternate sitting and standing at work are easily possible.
• A chair of the type and height to permit good posture should be provided for every worker.

Design of tools and equipment

• The hands should be relieved of all work that can be done more advantageously by a jig, a fixture, or a foot-operated device.
• Two or more tools should be combined wherever possible.
• Tools and materials should be pre-positioned whenever possible.
• 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.
• 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.

[1] Ralph M. Barnes (1937,) Motion and Time Study Measurement of Work, reprinted by John Wiley & Sons, New York, 1980. This is the classic, seminal work on the subject and these principles are still relevant today.

[2] Gravity feed bins, gravity chutes, and other mechanisms that “drop” the needed parts and tools to the proper place for use by the worker or for moving the part(s) to the next operation.