Mistake Proofing – Poka Yoke

“Your ability to mistake-proof of a process is only limited by your own lack of imagination.” Shigeo Shingo

Last week I was at week 2 lean six sigma training and learnt a concept that really made me think of my job differently. In testing we at times look for bugs and we also do activities that are risk based. For risk based activities we look at the risks that can occur and how we can test or plan for it during testing.
The other side to a defect is how to mistake proof it in such a way that if the defect does occur how do we prevent or detect it. Its a back up of a back up – Poka Yoke.

Poka Yoke is Japanese for mistake proofing. It is the creation of devices that either prevent special causes that result in defects or inexpensively inspect each item produced to determine whether it is acceptable or defective.

When this topic was introduced in class I was thinking oh this is hard. I didn’t understand it. Then the instructor gave examples. Automobile air bags – yes this is poka yoke. If the customer does have an accident then the car is helping reduce the impact. Another good example is auto door lock, seat belt warning, etc.

What is really happening in these cases are that a tester is being sent with every product. He or she warns the customer when a defect is occurring or going to occur. There are some cases where the customer can override it. Example of this is where you get a spell check error and you can still choose to over write it and use the different spelling than what is being recommended. When closing a word file a message is displayed do you want to save the file before closing and its up to the customer or end user to choose one option or the other.

After the class was completed we were given an assignment to come up with as many poka yoke’s we can see around us. We all went home thinking this is hard we don’t see as many of these mistake proofing as we think. Next morning we all came up with 200 poke yoke’s between 11 class participants.

Its really everywhere….My favorites from the class

  1. Garages have car clearance limits and have a height check before the cars go into the garage
  2. Dryer/washer switch off when the doors are open
  3. Garage doors do not close if there is an object that obstructs its closing path
  4. Drop downs for most online applications have a state drop down
  5. You have to enter email addresses twice when signing up online
  6. ABS (anti lock braking system)
  7. Bathroom sink have a little hole at the top of the sink to prevent overflows
  8. Iron’s auto switch off
  9. Auto sensor lights/flushes
  10. Keys enter the key hole only certain way

I love this concept and will be thinking of how to use this in our day to day activities be it how I write test plans, test cases or do my testing. After all I have to think of our customers everyday and add value for them.

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6 Responses to Mistake Proofing – Poka Yoke

  1. John Hunter says:

    >I completely share your positive attitude toward poka yoke. It is such a wonderful way to design in success. http://management.curiouscatblog.net/2010/05/19/mistake-proofing-deployment-of-software-code/

  2. >Its really cool. Am in love with POKA-YOKE since my engg days. We have had made an entire project on POKA-YOKE in my Engg Final Sem. :-)-Lalit

  3. shilpa says:

    >Yes I love this idea too. Thanks for stopping by Lalit.

  4. shilpa says:

    >Thanks John for your comment. Yes Poka Yoke so simple yet so effective.

  5. Anonymous says:

    >Just an observation. Have you noticed that the higher risk activity is related to progress, i.e., technology. While the backup poka yoke is a failsafe that is less technological. A simple offswitch, or a mechanical backup. So I think that is a maxim of all poka yoke's, that it requires by definition that it be more simple than that which it backs up.Thoughts?

  6. shilpa says:

    >Yes very nice observation. Also lean six sigma is about removing complexity and not adding any. Thanks for the note.

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