There are many examples of Poka Yoke. What is important and not discussed much is the foundation of Poka Yoke, which I call Poka Yoke System Design.
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Poka-Yoke, or Error-Proofing or Mistake-Proofing, is an essential aspect of process improvement. In fact, Poka-Yoke is the method by which we can actually get closer to a goal of zero defects without an exponential increase in the cost to detect and eliminate defects. In this article, I’ll discuss two types of situations that would benefit from the approach of Poka-Yoke and provide general guidelines on how to develop robust process and systems with the help of mistake proofing.
In general, the approach of Poka-Yoke should follow the following guidelines:
- Based on common sense and obvious to the person involved in the process
- It MUST eliminate Occurrence and Detection of the problem at the root cause
Occurrence is the situation as it happens, but sometimes after the fact. An example would be a buzzer or warning light. For example, a fire alarm is a type of Occurrence Poka-Yoke. In general Occurrence situation that merit Poka-Yoke can happen:
- There is a chance that the required action is not performed
- There is a chance that the required action is performed incorrectly
- There is a chance that information required to perform an action is not understood or misinterpreted
- There is a chance that complexity of process could lead to defects
For this situation, it’s important to follow these guidelines:
- At assembly, make sure that the wrong parts do not join together (think of Lego pieces that cannot join because they are not from the same Lego set).
- Use of 100% prevention devices such as contoured locators or fitted templates
In Detection, these situation should alert the operator at the point of mistake. For example, when one makes a mistake, an effective Poka-Yoke system will alert the operator that a mistake was made, where it was made, and even how the mistake was made.
Here are some techniques for detection oriented Poka-Yoke:
- Use color coded parts of graphics or images
- Before the fact, or before the defective part proceeds to the next step in the process, a Poka-Yoke system should alert the operator that 100% quality does not exist.
- It should be autonomous, or require almost zero intervention, but be an automatic response to a defect; almost reflexive.