Poka-yoke is a Japanese term for mistake-proofing: designing a part, fixture or process so that an error either cannot happen or is caught at once. Some poka-yoke devices prevent the mistake, such as a fixture that only accepts the part the right way round. Others detect it and stop the process or warn the operator, such as a sensor that counts screws and will not release the part until all of them are in. The aim is to stop defects at the source rather than rely on attention or later inspection.
Example: Operators sometimes loaded a bracket upside down in a welding fixture. The team added a pin that matches an off-center hole in the bracket, so an upside-down part no longer sits in the fixture and cannot be welded.
Training, reminders and inspection all depend on someone noticing, and people miss things when they are tired or rushed. A good poka-yoke removes that dependency, which is why a mistake-proofing change is usually a stronger corrective action than retraining.
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