Poka-Yoke was developed by Toyota, and was originally called baka-yoke (fool proofing), but was changed to the less demeaning poka-yoke (mistake proofing). Personally I like the term idiot proofing and use it e.g. when talking about stopping me doing something wrong before my morning coffee.
The idea is that ALL defects are stopped, whether by making it impossible to make the error, or that an alert activates if a defect occurs.
There are two types:
- Warning – Lets you know when an error occurs
- Control – stops the error from occurring or stops the process when errors occur
Why we need Poka-Yoke
People will always make mistakes. When looking at a process, if you see a way that someone can make a mistake, someone will at one point make that mistake. You will naturally do a process a little different each time, and sometimes that will be outside the acceptable parameters, and that’s not mentioning all the times you don’t get enough sleep, are distracted or (surely not) go to work a little worse for wear after the night before. That is not even covering where the machine or parts go wrong.
Errors will occur, and at best will lead to waste, at worst will be found by the customer. These errors can be prevented though. With enough training and the correct production methods, operating as if all errors can be prevented or easily detected will significantly reduce the number of errors that get through.
An example is right next to me as I type this – my filing cabinet would tip over if too many full drawers are opened, but the mechanism inside stops me opening more than one drawer at once, saving me from getting crushed. At lunch today, I couldn’t start the microwave unless I closed the door, so that I didn’t accidentally cook myself.
Types of Poka-Yoke
The methods of Poka-Yoke are limited only by you and your workforce’s creativity. There are some examples to get you started:
- Alarms that detect errors and notify you when something isn’t correct
- Checklists that you go through each time to make sure no steps have been missed
- Guides in the machinery so that the material can only be put in the correct place
- Limit Switches that won’t let you turn on the machine until everything is correctly aligned and placed (such as the microwave example above)
How to implement
It’s easy to start using Poka-Yoke to improve your processes, and work towards a zero defect workplace:
- Start from assuming you can make the mistake impossible – you have to work from the assumption that all mistakes and defects can be removed
- Stop doing it wrong – just because you’ve accepted things up to now, doesn’t mean that
- Good ideas come from everywhere – from my experience the best ideas have come from the most unlikely sources; get the team together and have a brainstorming session.
- Make removing errors part of the process, not an afterthought
- If you think you’ve got a good idea that may work, try it out – it may work better than you expect