Poka-Yoke is a Japanese phrase that means mistake-proofing. A poka-yoke device is any mechanism that either prevents a mistake in production from occurring or makes the mistake obvious immediately. Shigeo Shingo is credited with formalizing poka-yoke as the main tool in establishing zero quality control. In other words, poka-yoke aims at achieving zero defects in the manufacturing process.

A poka-yoke device is put into place to enable an operator to achieve 100% inspection of the products s/he is producing. There are three different types of inspection:

• Judgment Inspection: This involves sorting the detective products out after production.
• Informative Inspection: This uses data gained from inspection to control the process and prevent defects.
• Source Inspection: This determines "before the fact" whether conditions necessary for high quality production exist.

In other words, Source Inspection is the most effective form of inspection to prevent defects from occurring in the first place. In this case operating conditions are checked before the operation is performed and a poka-yoke device is put in place to halt the process until such time as the error or fault is corrected before the process continues. Halting of the process at this stage results in down time but, is far less expensive than having to "rework" a product. In effect, therefore, the poka-yoke device increases the speed with which quality feedback is received and also reduces the costs associated with reworking, or inspecting quality in by identifying defects after they occur. Rather, with a poka-yoke device, quality is "controlled in."