SaukValley.com – Serving Dixon, Sterling & Rock Falls:
Here's a news story about career day at a High School and someone talking about Lean (I guess Wahl, the clipper company, is using Lean):
“‘Poka yoke … allows you to dummy-proof something to guarantee your success' and ‘Takt time' is when a company makes only enough product to fill its orders. The new language is part of a Japanese-inspired, lean manufacturing philosophy that helps companies produce products with the least amount of labor, equipment, materials and power – ‘so, you're working smarter, not harder,' Segura said.”
I'll nitpick (because I can) about the Poka yoke definition. I really dislike the phrase “dummy proof” or “fool proof.” There's another Japanese phrase, “Baka Yoke,” I believe, that translates to dummy proof. Poka yoke means mistake proof… a less judgmental phrase. Maybe this is urban legend, but there's a story about how Ohno (or Shingo) used the phrase “dummy proof” and somebody started crying at the factory, so they moved to error proof.
But, the phrase “Baka Yoke” is still in Ohno's book Toyota Production System: Beyond Large-Scale Production
Either way, I think the phrase “dummy proof” misses the point, and ranks low on the “respect for people” scale. Errors aren't made because people are dummies, or because they don't care. The system made it too easy for an error to occur, that's the assumption we have to go by, so solutions are most often with the system. This is different than Western management, which typically points the finger of blame first.
Update: Corrected “bakta” to “baka” per comments. I've seen it both ways in print, but will assume baka yoke is correct since it's spelled that way in the Ohno book.
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I can’t comment on the history part, but I think poka yoke isn’t really about changing a process to avoid human errors as much as it is about changing a process so that it can be performed with a REALISTIC level of human vigilance. A lot of the things that I have seen poka yoke’d were things that were really pretty easy to do once, but if you had to do them a bunch of times in a shift with time constraints then it got hard to do. The error was designing a processes that didn’t repect humanity.
I recall hearing that the shop floor workers objected (quite correctly) to being called “idiots” or “fools.”
By the way, I highly recommend the books by Sidney Dekker on Human Error. Although most of his stuff relates to aviation, it all applies to human-interaction in complex environments. If you follow the philosophy he outlines, “human error” is almost never a root cause. Rather, it is caused by factors in the situation and the environment which led a person to make the wrong decision, or to omit a step. Either way, you must assume as a starting point that the person intended to do it right, and probably is sure he did. Then look at what in the environment and process failed to stop the process or at a minimum penetrate consciousness and alert the person that something is off.
I am reading your question about Poka-yoke versus Baka-yoke
You can find the story on page 45 of Shingo’s:” Zero Quality control: Source inspection and the Poka-yoke System”
I a typing it just in case you don’t have the book:
In the early days, I used the term “foolproofing” (in Japanese, bakayoke ), but in 1963, when Arakawa Auto Body adopted a “foolproofing” device to prevent seat parts from being spot-welded backwards, one of the company’s part-time employees burst into tears when her department head explained that a “foolprooving { mechanism had been installed because workers sometimes mixed up left- and right-hand parts. “Have I really been such a fool?” she sobbed. She ended up staying home the following day and the department head went to see her there.
He tried all sorts of explanations. “It’s not that you’re a fool,” he told her. “We put the device in because anybody can make inadvertent mistakes.” Finally, he managed to persuade her.
When the department head told me this story, it was clear to me that “foolproofing” was a poorly chosen term. But what name would be suitable? After some thought, I gave the name Poka-yoke (mistake-proofing) to these devices because thy serve to Prevent (or “proof;” in Japanese, yoke) the sort of inadvertent mistakes (poka in Japanese) that anyone can make.
Anonymous has given a terrific history of this phrase. And to point out something in his comment, the Japanese expression is “baka yoke,” not “bakta yoke.”
The word “baka” means “fool” and is formed by the characters for “horse” and “deer.” Legend has it that two people were arguing over which animal is more elegant and handsome. Obviously a stupid argument – hence the word “baka.”
[…] There’s an old Toyota story about how the term “fool proofing” upset an employee, they switched to using the equivalent of “mistake proofing” or “error proofing.” Read more about the story in a comment on an old blog post of mine. […]