Also called mistake-proofing, error-proofing, baka-yoke
What is poka-yoke?
Designing the job so the mistake is physically impossible, instead of asking people to be careful.
What else it is called
- Other names
- mistake-proofing, error-proofing, baka-yoke
- In French
- détrompeur
Related entries
Understanding poka-yoke
A fixture that will not accept the part backwards. A connector that only mates one way. A bin with a sensor that will not let the cycle start until the right number of fasteners has been taken. The principle is that human attention is unreliable by nature, and that designing the error out is more effective than asking people to concentrate harder.
There are two grades. Prevention stops the mistake happening at all and is always worth more. Detection catches it immediately, at the station rather than three operations later, which is the second-best outcome. Writing a work instruction is neither of these, though it is what most plants do after a defect escapes.
In practice
After a defect gets out, the first question should be what would have made it physically impossible. "Retrain the operator" is the answer that guarantees you will see the same defect again.
Frequently asked
Does mistake-proofing have to be expensive?
Almost never. The best examples cost very little: a locating pin, a jig cut so the part only sits one way, a different coloured fastener for the one position that differs. Expensive sensing systems are usually a sign that the design question was skipped.