Definition
A complete set of verdict and device methods designed to make errors impossible or to ensure errors are detected before they become defects; the core proposition is that errors are inevitable but defects are avoidable. Devices have three capability levels (prevent occurrence / detect the error / detect the defect); the verdict prioritizes the level first, and only then whether the seven steps were completed.
In detail
Poka-Yoke is a method that makes errors impossible or ensures errors are detected before becoming defects through design. The core principle is "errors are inevitable, but defects can be avoided." It addresses quality issues caused by human error. Unlike inspection, Poka-Yoke emphasizes prevention at the source rather than post-event detection. Devices have three capability levels: preventing occurrence, detecting errors, and detecting defects; priority is determined by the level. Typical outputs include Poka-Yoke devices, checklists, and process improvements, often used in conjunction with FMEA and PSP.
Example in practice
On a certain assembly line, parts were frequently installed in reverse. An engineer designed an asymmetric locating pin so that parts could only be installed in the correct orientation, making the error impossible. After implementation, the defect rate at that station dropped to zero, and no additional inspection was needed.