Poka-yoke

Poka-yoke was coined in Japan during the 1960s by Shigeo Shingo who was one of the industrial engineers at Toyota. Shigeo Shingo is also credited with creating and formalizing Zero Quality Control (poka-yoke techniques to correct possible defects + source inspection to prevent defects = zero quality control).

The initial term was baka-yoke, which means ‘fool-proofing’. In 1963, a worker at Arakawa Body Company refused to use baka-yoke mechanisms in her work area, because of the term’s dishonorable and offensive connotation. Hence, the term was changed to poka-yoke, which means ‘mistake-proofing’.

Ideally, poka-yoke ensures that proper conditions exist before actually executing a process step, preventing defects from occurring in the first place. Where this is not possible, poka-yoke performs a detective function, eliminating defects in the process as early as possible. This can be achieved using three rule.

Following are three rules of poka yoke:

1. Make the task more likely to to come right than wrong
2. Make errors evident right there on the spot
3. Make it possible for person to correct the error right then

Applying poka-yoke (steps)

• Identify the operation or process - based on a pareto.
• Analyze the 5-whys and understand the ways a process can fail.
  Decide the right poka-yoke approach, such as using a
  - shut out type (preventing an error being made), or an
  - attention type (highlighting that an error has been made) poka-yoke.
  Take a more comprehensive approach instead of merely thinking of poka-yokes as limit switches, or automatic shutoffs. A poka-yoke can be electrical, mechanical, procedural, visual, human or any other form that prevents incorrect execution of a process step.
• Determine which is appropriate
  - Contact - use of shape, size or other physical attributes for detection,
  - Constant number - error triggered if a certain number of actions are not made
  - Sequence method - use of a checklist to ensure completing all process steps
• Trial the method and see if it works
• Train the operator, review performance and measure success.
  

MISTAKE-PROOFING PRINCIPLES:

1. Hierarchy of Principles and Moving Upstream to Product & Process Design
   
2. Principle of Elimination
   Role of Product Design - Design out Potential Defects
   
3. Principle of Replacement
   Replace Error-Prone Product Features/Items
   Replace Error-Prone Process Steps
   
4. Principle of Prevention
   Prevent Errors with Product Design - Guidelines & Techniques
   Prevent Errors with Process Design - Guidelines & Techniques
   Poke-Yoke Devices - Sensors, Counters & Other
   
5. Principle of Facilitation
   Product Design Techniques to Facilitate Error Avoidance
   Process Design Techniques to Facilitate Error Avoidance
   Visual Controls
   
6. Principle of Detection
   Defect Detection - Poke Yoke Devices & Self-Checking
   
7. Principle of Mitigation