Poka-Yoke

Poka-yoke is a device or design choice that makes a mistake impossible, or catches it the moment it happens so it goes no further. The Japanese term translates as "mistake-proofing". Shigeo Shingo, an engineer who advised Toyota, made it part of the Toyota Production System in the 1960s.

Shingo first used the word baka-yoke, "fool-proofing", and dropped it around 1963 because it insulted the workers. Poka-yoke means avoiding inadvertent errors. For Shingo, everyone makes slips when tired or interrupted, so the fix belongs in the design of the work rather than in blaming the operator.

Two kinds of poka-yoke

A control poka-yoke stops the process until the error is corrected, like a machine that refuses to start while a part sits in the wrong position. A warning poka-yoke signals the error with a light or a sound and leaves the person to act, like the chime that sounds when a seat belt is unbuckled.

Everyday examples

A keyed plug only fits one way. The cut corner of a SIM card prevents inserting it upside down. A microwave stops when its door opens. In hospitals, each medical gas has its own connector shape, so oxygen and another gas cannot be swapped by mistake. Online, a form that refuses a date in the wrong format works as a control poka-yoke.

A defect caught at its source costs less than one found at final inspection or by the customer. Lean counts defects among its seven wastes, or muda. A poka-yoke also differs from a checklist: the checklist relies on someone reading it, while the poka-yoke keeps working when attention drops.