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Factsheet: ‘Poka Yoke’ Error proofing

by Chris Turley

Process excellence through Poka Yoke

In order to achieve Operational Excellence it is vital to have processes capable of delivering Zero defects.
Poka Yoke
is the concept of eliminating process errors, ensuring the output is defect free. Eliminating errors and preventing defects not only improves quality but enables improvements in productivity and delivery and increases process capacity.

Why do we need Poka Yoke? (Errors Vs Defects)

An ERROR is any deviation from the intended process, they can be made by machines or people and can be caused by errors that occurred previously (knock on effect)

A DEFECT is a product that deviates from specification or fails to meet the customers expectation.

All DEFECTS are caused by ERRORS so ERRORS = DEFECTS

If ERRORS can be prevented / eliminated, DEFECTS will not be created

The concept of Poka Yoke was developed by the Japanese industrial engineer Shigeo Shingo, who is closely linked to the development of TPS (Toyota Production System) with Taiichi Ohno during the 1950’s onwards. Derived from the Japanese words Yokeru, meaning avoiding and Poka, meaning inadvertent errors, Poka Yoke is commonly translated as error or mistake proofing, and has become an integral part of problem solving.

Poka Yoke is based on the concepts of Prediction and Detection and clearly targets Zero Defects, Right First Time (RFT) and the reduction of waste.

There are 3 methods of Poka Yoke:
Contact

The contact method is based on detecting the shape, colour or other physical properties or features.
Fixed Value

The fixed value method is based on the completion of a preset number of actions or movements.
Motion Step

The motion step method is based on the completion of prescribed steps performed in a sequence by a single person

Requirements:
•  Prevent errors from occurring or immediately detect abnormalities in real time as they occur.
•  Stop the process from producing further errors.
•  Address the root cause of the process problem before resuming.

What makes a good Poka Yoke:
•  Robust & Reliable  (CRITICAL)
•  Inexpensive
•  Easy to implement
•  Doesn’t require continuous attention from the user
•  Specific to the need
•  Developed with the user
•  Simple basic engineering (Shapes & holes, Colour coding, Keyway, Nesting, Dowel & pin)
•  Technology (cost effective?)

The 10 Steps: Following the principle of PDCA

  1. Identify the process that needs to be improved.
    (target areas where there are high numbers of errors or where even single errors are very costly).
  2. Use QC Tools, Cause & Effect & 5Why analysis to get to the root cause of the problem.
  3. Decide whether to use a control or warning type.
    (There may be technical or financial reasons why you have to go for the latter)
  4. Decide whether a contact, fixed value or motion step method is best (this will hinge on the nature and purpose of the activities).
  5. Design an appropriate Poka Yoke.
  6. Test it to see if it works and will be reliable.
    (I mean really test it…try to make it fail. Don’t assume anything, make sure this thing really is ‘fool’ proof by trying anything and everything to ensure it really does what its supposed to).
  7. Once you have a working method then ensure you have the right tools/checklists/software, etc for it to work robustly, consistently and correctly.
  8. Train everyone to use it.
  9. Monitor its effect to ensure errors have been eliminated.
  10. Take whatever steps are needed to improve on what you have done.

KEY POINT:
If you are using a Warning or Attention type Poka Yoke your process is now dependent on this device or action detecting the error in real time.
How do you know it’s in place and working correctly?
Check and test it regularly
This validation forms a part of your Standard Operation, be it an hourly, shiftly, daily or weekly check depending on the process, product and potential risk to you.

The ideal solution:
Zero Defect and Right First Time are the goals of any process, the ideal is that new products and processes are designed to include the principles and thinking of Poka Yoke from the outset. The concept of Poka Yoke is that it forms an integral part of the process, not as an add on.

To see Poka Yoke in the service sector

Examples of Poka Yoke:



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Poka Yoke:

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