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What is Poka-yoke?

Shigeo Shingo(external link) advocates the concept of zero quality control by arguing that inspection processes or the use of statistical control should be completely eliminated. He believes that quality should be controlled at the source of the problem and not after the problem has manifested itself. He recommends that inspection should be incorporated within the process and at the point where the problem has been identified and from where it should be eliminated.

Poka yoke (pronounced poh-kah yoh-kay) comes from two Japanese words
  • yokeru means to avoid
  • poka means inadvertent errors.
Thus, poka yoke more or less translates to avoiding inadvertent errors.


Three types of systems

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

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

Three levels

  • Level 3 : Eliminating/prevent the defect opportunity at design level (or at the source) e.g. One-way assembly (Electrical three pin top only put in one way, A USB drive can be inserted one way only).
  • Level 2 : Put the control system it will detect the defect as it is being made & remove or quarantine. e.g. alarms sound (Spell checks in MS office)
  • Level 1 : Stop the defect from reaching the next operation (e.g. Inspection, checklist, color coding)

Advantages:

  • Preventing bad products getting passed customer.
  • Detect mistakes as they occur.
  • Eliminating defects before they occur.
References:

http://www.qualitygurus.com/courses/mod/forum/discuss.php?d=2790

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