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Bruce Hamilton


Seven Mistake-Proofing Mistakes That Promote Cynicism

Why poka-yoke isn’t seen as purposeful

Published: Monday, December 21, 2015 - 14:47

A piece of popular lore, provided by Shigeo Shingo, is that the original name for mistake-proofing (poka-yoke) was actually fool-proofing (baka-yoke). Shingo chided managers at Panasonic for using the latter term, as it disrespected workers by essentially calling them fools.

Shingo substituted the word “mistake” for “fool,” because, as he aptly noted, making mistakes is part of humanity. “Mistakes are inevitable,” Shingo said. “But the defects that arise from them are not.”

Notwithstanding Shingo’s admonitions, however, I still hear the term “fool-proofing” used regularly, and occasionally, with a little more venom I hear “idiot-proofing.” No doubt, these derogatory terms, along with others like “screw-up” and its less gentile derivatives, have given a bad name to one of the most energizing, empowering, and creative tools from the Toyota Production System toolbox. Many organizations never even get out of the blocks with this technique because of an overtly insulting, blame-focused environment. Who wants to report a mistake when the reward is blame and ridicule? Like Mr. T, managers tend to blurt out the wrong words when mistakes occur. Bad habits die hard.

Even for more enlightened managers, however, there are still some common hurdles to create a really powerful poka-yoke system. A few weeks ago I presented a short webinar on poka-yoke for the Association for Manufacturing Excellence, and received the following question from a viewer:

“How do I ensure the effectiveness in use of the poka-yoke device? People usually don’t want to continue using it.”

Here, with a few embellishments, was my response: “The general answer to this question is that if people don’t find a particular tool purposeful, they don’t use it. More specifically for poka-yoke, there are seven reasons that the tool is not seen to be purposeful by team members.”

Seven reasons poka-yoke isn’t seen to be purposeful

1. Sometimes, to ensure quality, an additional step is added to the operation to prevent or detect the defect, but this step is not considered in the standardized work (i.e., no additional time is allowed). If the device or method requires an extra step that takes more time (e.g., the use of a checklist or matching parts to a template) then employees will feel rushed and pressured to choose between rate and quality.

2. A corollary to the lack of standardized work is the lack of communication to team members, team leaders, and managers. An undocumented and untrained standard is not a standard.

3. If the device or method causes strain to the employee, it won’t last. Substituting muri for muda is not a good trade off.

4. For detect-type poka-yoke devices (i.e., a defect is created, but is detected before it can pass to the next operation), the concept involves swarming the defect when it’s trapped to understand its root cause. I see many cases where defects are trapped, but there is no follow-up. Defects pile up, or they are picked up occasionally by engineering or quality, and no feedback goes back to the production line. When problems don’t get fixed, this promotes cynicism. It’s not poka-yoke, just a scrap sorter.

5. Sometimes, as suggested in the question above, a device is put in place, but the defect persists. This could mean that the device isn’t used by the team member, but it could also mean that the device just doesn’t work. More plan-check-do-act (PCDA) is needed. If the device doesn’t work, team members will be the first to know. Telling them to use something that doesn’t work is disrespectful and disengaging.

6. The term poka-yoke is used too broadly to describe countermeasures that have nothing to do with human error, but relate more to providing proper tooling and fixturing to team members. For example, if a particular job requires superhuman sensor capability to complete (more muri), creating fixturing to make the job doable is not a poka-yoke solution. My father, who was a machinist by trade and an artist by avocation, could draw a straight line freehand around an entire room. Most of the rest of us would want a straight edge and a level to complete that task. The point is, when we refer to such countermeasures as “mistake-proofing”, we’re once again disrespecting team members.

7. Most important, if the employee who uses the device is not included in the solution, there is typically little commitment to use it, especially if any of points 1 through 6 apply.

That’s the long-winded answer to the short question. The short answer to that question is that the “technical” portion of poka-yoke doesn’t work if it is not grounded by a quality culture.

Perhaps you can think of some other common mistake-proofing mistakes to share with our readers. Please let me hear from you.


About The Author

Bruce Hamilton’s picture

Bruce Hamilton

Bruce Hamilton, president of the Greater Boston Manufacturing Partnership (GBMP), brings hands-on experience as a manager, teacher, and change agent. Prior to GBMP, Hamilton led efforts to transform United Electric Controls Co.’s production from a traditional batch factory to a single-piece-flow environment that has become an international showcase. Hamilton has spoken internationally on lean manufacturing, employee involvement, continuous improvement, and implementing change; and he has contributed to numerous texts ranging from visual control to variety reduction. Hamilton’s blog, Old Lean Dude, is an on-going reflection on lean philosophy and practices with an emphasis on keeping good jobs close to home.