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Poka-Yoke (Mistake-Proofing)

What is Poka-yoke?

Poka-yoke is Japanese tern which means “mistake-proofing” or “inadvertent error prevention”. The word Poka-yoke is made of two Japanese words poka (mistakes) and yokeru (avoid). Poka-yoke is any mechanism used in a lean manufacturing process that helps an equipment operator avoid mistakes. It’s purpose is to eliminate product defects by preventing, correcting or drawing attention to human errors as they occur. This concept was earlier adopted by Shigeo Shingo as part of Toyota Production System. It was originally named as baka-yoke which means “fool-proofing” or “idiot proofing”.

Implementation in manufacturing

Poka-yoke can be implemented any manufacturing process where something can be go wrong or an error can be made.
For example, digital counter might track the number of spot welds on each piece to ensure that the worker executes the correct number of welds.

Shigeo Shingo recognized three types of poka-yoke for defecting and preventing errors in mass production system:

1.   The contact method identifies product defects by testing the product’s shape, size, colour or other physical attributes.
2.   The fixed value (or constant number) method alerts the operator if a certain number of movements are not made.
3.   The motion—step (or sequence) method determines whether the prescribed steps of the process have been followed.

Either the operator is alerted when a mistake is about to be made, or the poka-yoke device actually prevents the mistake from being made. In Shingo's lexicon, the former implementation would be called a warning poka-yoke, while the latter would be referred to as a control poka-yoke.
Shingo argued that errors are inevitable in any manufacturing process, but that if appropriate poka-yokes are implemented, then mistakes can be caught quickly and prevented from resulting in defects. By eliminating defects at the source, the cost of mistakes within a company is reduced.[citation needed]

A methodic approach to build up poka-yoke countermeasures has been proposed by the Applied Problem Solving (APS) methodology, which consists of a three-step analysis of the risks to be managed:

  1. identification of the need
  2. identification of possible mistakes
  3. management of mistakes before satisfying the need

This approach can be used to emphasize the technical aspect of finding effective solutions during brainstorming sessions.

Benefits of Poka-yoke
  • Less training requirement to operators
  • Less Rejection
  • Immediate intimation or error/defect/problem occurs
  • 100 % built in quality control
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