I’ve heard Poka Yoke described as “Mistake Proof and Fail Safe” but as with most things in Lean it actually goes much deeper than that. The best translation of Poka Yoke that I’ve come across says that it means “To prevent inadvertent mistakes”. I really like this definition since it ties in several fundamental Lean principles.
The first is quality at the source. We do this by preventing the errors that lead to defects. Errors that are made when the work is being done. To err is human and to expect humans not to make errors is unrealistic. Recognizing this we need to look for ways to prevent the errors from being made. We do this through the use of physical devices that make it impossible to make the error. The best Poka Yoke devises are simple, reliable and designed by the teams themselves. Where we can’t use physical devices we resort to using visual aids such as signage, markings, alarms and check-sheets. By their very nature, these are not nearly as effective at preventing errors from being made.
Have you ever seen someone driving their car with the dashboard engine light on?
How about someone running a red light at an intersection?
Both errors can lead to very expensive defects.
The second Lean principle involved is “Respect for People”. By recognizing the purpose is to prevent “Inadvertent mistakes” a much greater respect is shown to people than to call it “Idiot Proofing” which is a common name I’m sure we have all heard of. We all make mistakes and we all make errors. Sometimes these lead to defects and sometimes they don’t. Have you ever had a close call and thought to yourself “Phew – I got away with one this time”?
Isn’t a better way – to surface the near miss and use the capabilities of the team to come up with ways of preventing the mistake/error from being made? I think so and I believe you’ll find it very empowering for the team. After a little practice, you’ll be amazed at what they come up with.