Poka-yoke

Origin. Shigeo Shingo at Toyota (1960s); originally "baka-yoke" (fool-proofing), renamed to the less offensive "poka-yoke" (mistake-proofing).

Mechanism. Design the process or artifact so that errors are impossible or immediately detected. Prevention is better than inspection: rather than checking for defects after production, prevent the defect from occurring. The mechanism is physical or procedural constraint that makes the wrong action harder than the right action.

Procedure. Identify error-prone steps. For each, ask: can the step be eliminated? If not, can it be designed so the wrong action is physically impossible (asymmetric connectors, interlocks, forced sequences)? If not, can the error be detected immediately and automatically (sensors, checklists, confirmation dialogs)? If not, can the consequences be contained? Implement the strongest poka-yoke possible for each step.

Applies to. Manufacturing, software interfaces, safety-critical systems, any process where human error is probable and consequential.

Limitations. Over-engineered poka-yoke that slows the process more than the errors cost. Also: poka-yoke for the expected errors, not the actual ones — the constraint prevents errors no one makes while leaving the real Limitationss open. Study actual errors before designing constraints. Poka-yoke can also reduce learning; operators protected from all mistakes never develop judgment.