Poka-Yoke

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POKA-YOKE

One of the common quality concepts in statistics that can be used in continuous improvement is Poka- Yoke, which means “mistake proofing.” Poka-Yoke, pronounced (POH-kah YOH-kay) and developed by Japanese industrial engineer Shigeo Shingo in the early 1960s, uses devices, methods, or inspections in order to avoid machine error or simple human error. There are two main types of poka-yokes:

prevention-based poka-yokes and
Detection-based poka-yokes.

Prevention-based poka-yokes are mechanisms that sense that an error is about to occur and send some sort of signal of the occurrence or halt the process. Detection poka-yokes identify when a defect has occurred and stop the process so that the defect is not “built-in” to the product or service and sent downstream. Shingo believed that “The causes of defects lie in worker errors, and defects are the results of neglecting those errors. It follows that mistakes will not turn into defects if worker errors are discovered and eliminated beforehand.” As an example, suppose a worker is assembling a device that contains two push-buttons. A spring must be placed under each push-button in order for it to work. If either spring is not put in place, the associated push-button will not work, and an error has been committed. If the worker does an on-the-spot inspection by looking at the device or by testing it, then the cost of fixing the device (rework) is minimal, both in terms of the time to fix it and the time lost due to inspection. If, on the other hand, the error is not identified and the device goes on down the assembly line and is incorporated as a part into a product, the cost of rework, scrap, repair, or warrantee claim can become quite high.

A simple poka-yoke solution might be that the worker first counts two springs out of the supply bin and places them both in a small dish before each assembly. If the worker is not paying attention, is daydreaming, or is forgetful, he/she merely needs to...
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