Thursday, January 10, 2013

Poke Yoke – Preventing Inadvertent Errors

By Al Norval

We talk a lot about the House of Lean with its foundation of Standards & Stability and the two pillars of Just In Time and Jidoka supporting a roof of Customer and Strategic Direction which together encompass engaged Team Members continually solving problems.

All of this makes sense but what is this Japanese word – Jidoka?

It’s built in quality at the source. Rather than try to inspect and test quality in by looking for defects on finished product, a losing cause at best, lean organizations build in quality at the actual value added operation. That way defects can be caught early and they don’t have to reply as heavily on final inspection testing.

The big advantage to Jidoka is that by catching defects early in the process, they are closer to the actual process conditions that caused the defect and therefore closer to root cause. They can launch problem solving faster with a higher chance of getting to root cause since the process conditions wouldn’t have changed as much.

Jidoka has four parts:
  • Detecting defects
  • Alerting or signaling a problem
  • Immediate response - temporary countermeasures to get running again
  • Root cause problem solving and countermeasures to prevent the occurrence of the defect.

This is where Poka Yoke comes in. It’s about the final step in Jidoka of preventing the re-occurrence of the defect. Lean organizations realize that errors are inevitable. Human beings make errors that cause defects. By eliminating the possibility of the error being made, defects could be eliminated. Poka Yoke is used to prevent these errors being made. Translated it means “Preventing inadvertent mistakes” since it’s believed people don’t make mistakes on purpose. This is consistent with the lean principle of “Respect for People”

The best Poka Yoke devices are physical devices that eliminate the possibility of an error occurring. Weaker Poka Yoke countermeasures would be signs and warning systems but these could be overridden and the error could still occur.

Organizations are always looking for ways to get employees involved and having teams develop Poka Yoke devices that prevent errors from being made is a great way to do this. It’s a win-win. Employees are engaged in problem solving, quality gets better for customers.

For more on Poke Yoke, see The Lean Pathways “LEAN MANIFESTO


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