Poka-Yoke

Poka-Yoke or Mistake Proofing devices

Japanese words:      Poka = inadvertent Error                Yokeru = Avoid

By undertaking repetitive tasks that depend on vigilance or memory, Poka-Yoke frees the workers’ mind and allows them time to focus on more creative tasks with greater added value.

It took Shigeo Shingo a quarter of a century to develop its “Zero Quality Control, source Inspection and the Poka-Yoke System”.

By studying the operations of several factories, he discovered two important facts at the base of Zero Defects:

  • Regardless of your ability to discover defects, whatever the rigor with which you follow your corrective action plans, the improvement in your inspection will not prevent the defects to occur.
  • To prevent defects, you must look at the process of determining which condition leads to defects, then control this condition

The basic elements of a Poka-Yoke are

  •      It uses source inspection to catch errors before they become defects
  •      It uses 100% inspection to verify all product and all parts (not just a sample)
  •      It provides immediate feedback, thus reducing the time to implement appropriate corrective action

Poka-Yoke is inexpensive and requires little effort.

However, it is its design and implementation which can be quite complex.

Five families of defects have been identified:

  1.      Inadequate procedures or standards
  2.      Excessive change in the method
  3.      Defective materials or having excessive variation
  4.      Worn components machinery
  5.      human error

“The simple errors are the most common cause of defects and are the most difficult to detect.” “If the error causes defects, the idea is to discover the error before it produces a defect. “Shigeo Shingo

Almost all the defects are caused by human error which were subdivided into 10 categories, from simple forgetfulness to the intentional “error”.

There are more than a dozen families of anti-errors, most are very simple and easy to use and designed locally by people operating according to their specific problem.

  • As an approach, do we need a system that warns us or that controls the process?
  • Or a physical contact device, an energy sensor, a sensor that detects physical change (T°, volume, pressure, brightness, etc.)  Motion, flow, speed, etc.. that would be most appropriate?
  • Should we control a chronology of events?
  • Would one of the 4 Visuals devices do the job?
  • Are there restrictions related to the specific environment (temperature, smoke, vibrations, danger, etc.).
  • Do we want the machine to stop if an error is detected, or the part rejected, etc..?

This is the kind of questioning we need to do before deciding if we need a template, a locating pin, a fall detector, a counter, a limit switch, etc.

To the question: Is there anything that can go wrong in my process?

If the answer is Yes, Poka-Yoke can help you avoid unpleasant surprises.