Poka-Yoke

Poka-yoke is a mechanism built into a manufacturing process that helps an operator avoid mistakes, by preventing an error outright, correcting it automatically or drawing immediate attention to it, so a human mistake never becomes a defect that reaches a customer. The Japanese industrial engineer Shigeo Shingo formalized the concept and gave it its name in the 1960s as part of the Toyota Production System; it was originally called baka-yoke, or fool-proofing, before the milder term poka-yoke, meaning avoiding an unthinkable mistake, replaced it. Shingo's own founding example came from a factory assembly line where workers kept forgetting to insert a spring into a switch button: he had them first set aside the required spring in a small placeholder tray and only then install it, so a spring left sitting in the tray immediately showed that a step had been skipped and let the worker correct it before the part moved on.