Poka Yoke

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What is Poka Yoke?

  • Developed by Toyota Motors as a tool to achieve Zero Defects
  • Originally called Baka Yoke (idiot proof) but recognized that this label could offend workers so changed to Poka Yoke (Mistake Proofing)

One serious obstacle to extending equipment life is the unexpected failure that occurs as a result of operating or repair errors. This irksome problem can not be resolved by maintaining optimal conditions or correcting design weaknesses, no matter how much effort is exerted in these areas. Also the fact that human error is involved makes these failures difficult to resolve quickly. The only way to deal with them is through comprehensive, sustained training in operating and maintenance skills and the use of visual control and error-proofing (poka yoke) measures.

It is rarely one individual device which prevents the production of defects but often the hundreds and thousands of these very simple “fail-safing” mechanisms that day after day deliver high quality goods.

The devices can be used to achieve zero defects and to eliminate quality control inspections. The expression “fool proofing” is avoided as this can offend many workers, hence the expressions “mistake-proofing” or “fail-safing” were introduced. By taking over repetitive tasks or actions that depend upon vigilance or memory, poka yoke can free workers time and mind to pursue more creative and value adding activities.

Many things can go wrong in the complex environment of the workplace; every day there are opportunities to make mistakes that will result in defective products. Defects are wasteful and if they are not discovered they disappoint the customers expectations of quality a company must adopt not only a philosophy but a practice of producing zero defects. Poka yoke methods are simple concepts of achieving this goal.

When to use Poka Yoke?

Tackling different kinds of errors:

Almost all defects are caused by human errors. There are many different kinds of human errors, below are a few examples with some potential safeguards.

  1. Forgetfulness: Sometimes we forget things when we are not concentrating. Eg; The stationmaster forgets to lower the rail crossing gate. Safeguard: Alerting operator in advance or checking at regular intervals.
  2. Errors due to misunderstanding: Sometimes we make mistakes when we jump to the wrong conclusion.Eg; A person not used to automatic transmission steps on the brake, thinking it is the clutch. Safeguard: Training, checking in advance, standardising work procedures
  3. Errors in identification: Sometimes we make mistakes when we view it too quickly. Eg; A $10 note is mistaken for a $20 note. Safeguard: Training, attentiveness, vigilance.
  4. Errors made by amateurs: Sometimes we make mistakes through lack of experience. Eg; New operator does not know the operation or is barely familiar with it.Safeguard: Skill building, work standardisation.
  5. Wilful errors: Sometimes we make mistakes when we decide we can ignore rules under certain circumstances.Eg; Crossing a street against a red light because there are no cars in sight.Safeguard: Basic education and experience.
  6. Inadvertent errors: Sometimes we make mistakes without knowing how they happened.Eg; Someone lost in thought tries to cross the street without noticing the light is in red. Safeguard: Attentiveness, discipline, work standardisation.
  7. Errors due to slowness: Sometimes we make mistakes when are actions are slowed down by delays in judgement.Eg; A person learning to drive is slow to step on the brake. Safeguard: Skill building, standardisation.
  8. Errors due to lack of standards: Sometimes we make mistakes when there are no suitable standards or work instructions.Eg; A measurement may be left to an individual workers discretion. Safeguard: Work standardisation, work instruction.
  9. Surprise errors: Sometimes we make mistakes when equipment runs differently than expected. Eg; A machine may malfunction without warning. Safeguard: Total Productive Maintenance, work standardisation.
  10. Intentional errors: Sometimes we make mistakes deliberately. Eg; Crimes and industrial sabotage! Safeguard: Fundamental education, discipline.

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