Abstract

Mistake proofing eliminates defects rather than relying on inspections to correct or remove them. Inspections do not identify all defects. Inspections are expensive, and they can be unsafe when an injury occurs before a problem can be corrected. Mistake proofing is known as poka yoke in Japanese and was formalized by Shigeo Shingo. Poka yoke devices work by warning, controlling, or shutting down operations. For example, a warning buzzer can indicate that lights have been left on after a car engine is shut off. The control alternative is to use a timer that prevents the light from staying on too long. Shut down devices will stop operation before a defect occurs. The designer of poka yoke devices should consider characteristics like weight, shape, and dimension, as well as process deviations and value differences. Indications of improper weight or other characteristics can trigger the poka yoke device before a defective product is shipped. If a poka yoke system is programmed to detect process deviations, it can prevent continuation of a process that fails a mistake proofing test. Differences of value, for example, prevent improper parts kitting by detecting left over parts. Workers must be involved in implementing the poka yoke devices that are incorporated in their operations. Engineers are the coaches who bring workers� suggestions to implementation. First implementation of poka yoke might occur in situations that have the most defects or where defects are most costly.