PokaYoke

Poka-yoke, from the Japanese poka meaning "inadvertent error" and yokeru meaning "to avoid," is a quality assurance concept that aims to prevent human errors in manufacturing and related processes by designing devices, tools, or procedures that either prevent mistakes from occurring or immediately detect them and stop the process. The purpose is to reduce waste, rework, and defects.

Origin and scope: The approach was developed in Japan as part of the Toyota Production System in the 1960s and 1970s by Shigeo Shingo. It has since become a standard technique in lean manufacturing and quality management, and is widely applied beyond manufacturing to service industries and software interfaces.

Techniques: Classic poka-yoke methods are grouped into three categories: contact-based detection that checks the physical relationship or shape of components; fixed-value devices that require a part's presence or a specific state (e.g., a part that must be assembled before the next step); and sequence or processing checks that enforce correct order of operations. Other implementations include interlocks, sensors, data input validation, color coding, and fixtures that physically prevent incorrect assembly.

Examples: A fixture that only allows a component to be inserted in the correct orientation; a plug that won’t mate unless aligned; a machine that automatically stops if a required fastener is missing; a bin whose color or position signals a correct part; software forms that reject invalid input.

Impact and limitations: Poka-yoke reduces defects, scrap, and downtime, and supports Jidoka (automation with a human touch) and continuous improvement. It is not a complete substitute for other quality tools; effective poka-yoke relies on careful process design, ongoing monitoring, and integration with other lean and quality practices.