Motion Economy in Lean Manufacturing

Productivity in Workstation Design 

What Is Motion Economy?

Horizontal Reach zones and Motion EconomyMotion economy helps achieve productivity and reduce Cumulative Trauma at the workstation or sub-micro level. The Principles of Motion Economy eliminate wasted motion, ease operator tasks, reduce fatigue and minimize cumulative trauma such as Carpal Tunnel and tendonitis. Ralph M. Barnes codified these principles in the 1930's. They are still valid. Workstation designers should memorize them.

Lean Manufacturing & Motion Economy

Shigeo Shingo and Taiichi Ohno both had a thorough grounding in basics such as motion economy. Shingo used it in his SMED work and for workstation design. Ohno ensured that the concepts were applied throughout Toyota and its supplier system. The Western world pretty much forgot about Motion Economy in the rush to computerization of the 1960's and 1970's. In Lean Manufacturing the Toyota Production System (TPS) was re-introduced as Lean Manufacturing, Motion Economy was often left behind.

Limitations of Motion Economy

Motion economy has limitations. It does not account for physical limitations or differences in operators. Moreover, a movement that appears ineffective from a motion economy perspective actually may prevent fatigue and possible injury from static posture loading. However, using them alongside Principles of Ergonomics and a rationalized design procedure will ensure a productive, safe and optimum workstation.

Body Segment Classes

The principles are, for the most part, self- explanatory. However, Body Segment Class needs elaboration. In the table, each movement after class 1 involves body parts from the previous class(es), and more of the body participates in the motion. Tasks should have the lowest possible motion class. To do this, place the most frequently grasped objects near the operator. In addition, items should be close together, lightweight, and easily positioned at the end of the motion. 

References

BARNES, RALPH M., Motion and Time Study, Second Edition, John Wiley & Sons, New York, 1940.


Summarized From Ralph L. Barnes

1.0 Use of Human Body
2.0 Arrangement of The Work Place 
3.0 Design of Tools and Equipment 
4.0 Body Segment Classes 
Class Pivot Point Body Members
5 Trunk Torso, upper/forearm, wrist, fingers
4 Shoulder Upper/forearm, wrist and fingers
3 Elbow Forearm, wrist and fingers
2 Wrist Hand, and fingers
1 Knuckle Fingers

Note: This list does NOT include all of Barnes' principles. It also omits many details. It includes the most commonly applied principles that will help the occasional user.

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