Error Proofing

Error proofing, also referred to as mistake proofing or poka yoke, is the art of building processes that make it nearly impossible to make a specific mistake. Error proofing is targeted at specific errors—they are not general in nature.

This concept is predicated upon the concept that errors cause defects. To remove defects from your products or services, you must first identify the process step where the error is occurring and eliminate the possibility of that mistake happening at all.

Mistake proofing can come in a variety of forms. Shigeo Shingo breaks them down into three main categories.

1. Contact Method: Essentially, this means that the physical characteristics of a process are checked automatically. For example, a fixture might be keyed to only accept a part in the correct orientation.
2. Fixed-Value Method: This category counts to make sure the operator completes the required number of movements. (i.e. reaches into parts bins the correct number of times)
3. Motion-Step Method: This category entails checking that the operator has followed the correct process steps.

In practice, there are many methods that fall into each category. The contact method can have parts designed to only fit together one way, or a limit switch can be installed to make sure parts are oriented correctly on a conveyor.

Likewise, you can apply creativity for the other categories as well. Making custom parts racks can limit overproduction, which falls under the fixed-value method.

>>Learn more about error proofing in our poka yoke term.