Lean teams use poka-yoke because people make mistakes, and inspection catches defects too late. Preventing errors at the source protects quality without adding an inspection step.
Where it comes from
Shigeo Shingo developed poka-yoke while working with Toyota, as part of his approach to zero quality control.
At a glance
Mistake-proofing the four-bolt bracket
Swipe sideways to see the whole diagram.
How to apply Poka-Yoke
- 1
Pick a recurring defect
Start with an error that repeats or that causes serious harm. Use defect data and operator input to choose.
- 2
Find where the error starts
Trace the defect back to the step where the mistake happens. Ask why the process allows it.
- 3
Choose prevention or detection
Prefer a design that makes the error impossible. If that is not practical, detect it immediately and stop or warn.
- 4
Select the device type
Use contact methods for shape or position, fixed-value methods for counts and motion-step methods for sequence.
- 5
Test and standardize
Trial the device, confirm it catches the error without false alarms, and add it to standard work and maintenance checks.
Worked example
Operators sometimes skip one of four bolts on a bracket. The team adds a tray that holds exactly four bolts and a torque tool that counts tightenings. The next station will not release the part until the count reaches four.
Common mistakes
- Relying on warnings and signs, which people learn to ignore, instead of physical prevention.
- Installing devices without adding them to maintenance checks, so they fail without anyone noticing.
- Letting operators bypass a poka-yoke that causes false alarms rather than fixing it.
When Poka-Yoke is not the right tool
Some errors cost too little to justify a device, or happen too rarely. Rank error risks first, so effort goes where defects hurt most.
Poka-yoke also cannot fix a process that is unstable for other reasons, such as worn equipment or unclear standards.
Poka-yoke meaning
Poka-yoke is Japanese for avoiding inadvertent errors, usually translated as mistake-proofing. It is a device or design that makes a mistake impossible, or makes it obvious right away so it cannot become a defect.
Shigeo Shingo developed the idea at Toyota. He first used the term baka-yoke, fool-proofing, and changed it because the name was unfair to workers.
Poka-yoke examples
Everyday examples include a USB-C plug that fits either way up, a microwave that will not run with the door open, and a car that will not shift out of park unless the brake is pressed.
In factories, examples include a fixture that only accepts a part in the correct orientation, a sensor that stops the line if a part is missing, and a parts tray with one pocket per component so a leftover part signals a missed step.
Control and warning devices
A control poka-yoke stops the process or makes the error physically impossible, such as a fixture that only takes the part one way.
A warning poka-yoke alerts the operator with a light or sound but lets the process continue. Control devices give stronger protection where errors are costly.
Poka-yoke, jidoka and inspection
Inspection finds defects after they happen. Poka-yoke prevents the error that causes them. Jidoka stops the process when something abnormal happens.
Shigeo Shingo linked poka-yoke to source inspection in his book Zero Quality Control.