Poka-yoke

Poka-yoke is a Japanese term for error-proofing. It uses devices and design features to help operators avoid mistakes such as using the wrong part, leaving out a part, or installing a part backwards. The purpose is to find defects at their source and work toward 100% quality.

Source checked2/2 values · 2026-10-25Methodology

Specification

1 source

Kind	methodology
Origin	Japanese term

Study notes

Poka means inadvertent error; yoke means prevention.
The purpose of poka-yoke is to achieve 100% quality by finding defects at their source.
The document contrasts poka-yoke with quality by sampling inspection and quality by 100% inspection.
The two types of poka-yoke are shutdown and warning.
Shutdown poka-yoke can prevent a machine from starting if a workpiece is set incorrectly.
Warning poka-yoke alerts to abnormal conditions by buzzer or light.
Criteria for good poka-yoke include simplicity, long life, low maintenance, high reliability, low cost, and design for the workplace situation.
Examples include product designs with physical shapes that make incorrect orientation impossible.
Examples include photocells above parts containers to prevent a product from moving to the next stage until the operator's hands break the light to obtain parts.
Examples include a parts monitoring system using photocells with additional logic to confirm the right combination of parts for the product being assembled.

Safety

Blind spot warning in a vehicle is given as an everyday example to prevent accidents.
Auto-stop on a table saw is given as an everyday example to prevent injury.
Auto-brake in vehicles is given as an everyday example to prevent collisions.
Washing machines will not start until the door is closed and will stop if opened mid-cycle.
Lawn mowers operate only when a safety bar is held down and switch off when released.