Poka-Yoke — Mistake-Proofing in Manufacturing
Poka-yoke (ポカヨケ) is a Japanese term meaning 'mistake-proofing' — designing processes, tools, or fixtures that prevent errors from occurring or immediately detect them when they do. Developed by Shigeo Shingo as part of the Toyota Production System, poka-yoke devices range from simple physical guides (a part that only fits one way) to sensor-based detection systems. The goal is zero defects through prevention, not inspection.
Anatomy of the Chart
- Prevention
- The error cannot physically occur — a part that only fits one way.
- Detection
- The error occurs but is caught immediately, before it moves downstream.
- Contact method
- Shape, size or position decides whether the part can be fitted at all.
- Fixed-value method
- A set count must be met — every screw accounted for before release.
- Zero defects by design
- The goal is prevention, not inspection; inspection finds defects, poka-yoke stops them.
How to Create
- 1
Record the task as it is actually performed
Error-prone steps show up as hesitation, re-checking and inconsistent sequence — none of which appear in a procedure document.
- 2
Find the steps where a mistake is possible
Look for moments that depend on the operator remembering, judging or noticing rather than on the part or fixture.
- 3
Decide: prevent or detect
Prevention stops the error happening; detection catches it immediately. Prevention is stronger, detection is often faster to fit.
- 4
Design the device
From a physical guide that lets the part fit only one way, through to a sensor that will not release the cycle.
- 5
Verify by recording again
The device works when the error can no longer be produced — not when it is merely less likely.
Example
Video analysis of a connector assembly operation revealed that operators occasionally installed a gasket upside-down — a defect caught only at final test. A simple asymmetric fixture (poka-yoke) was designed that only accepted the gasket in the correct orientation. Post-implementation video analysis confirmed zero orientation defects.
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