Prevent Mistakes with Poka-Yoke

Poka-yoke (pronounced POH-kah YOH-kay) is a Japanese term meaning “mistake-proofing.” It refers to designing a process so that errors are prevented, or caught and corrected the instant they happen. The technique was formalized by industrial engineer Shigeo Shingo as part of the Toyota Production System.

Mistakes versus defects

Shingo drew a key distinction: mistakes are inevitable because people are human, but a defect occurs only when a mistake is allowed to reach the customer. Poka-yoke focuses on the process, so that human mistakes are stopped or spotted before they turn into defects. The aim is to change the system rather than blame the worker.

Three functions of poka-yoke

A poka-yoke device generally does one of three things: it prevents the error from being made at all, it detects an error and stops the process so it can be corrected, or it warns the operator that something is wrong.

A classic example

In an early example Shingo described, workers assembling a device with two push buttons sometimes forgot to place a small spring under a button. The fix was simple: a tray was set up to hold exactly two springs for each unit, so any leftover spring instantly showed that one had been missed. The defect dropped to zero without extra training — the process itself made the mistake obvious.

Everyday examples

Mistake-proofing is all around us: a microwave that stops when the door opens, a car that will not start unless it is in park, a connector shaped so it only fits one way, or a form that will not submit until a required field is filled in.