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Poka-Yoke - practical aspects of the mistake proofing method

Poka-Yoke - what requirements a system must meet & what are the Poka-Yoke security levels? Learn about practical examples of error proofing!

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Rafał B.

What does Poka-Yoke mean?

Poka in Japanese means “mistakes” and yokeru means “to avoid.” This combination resulted in the phrase Poka-Yoke, pioneered by Japanese engineer Shigeo Shingo.

Shigeo Shingo came to the conclusion that people will always make mistakes. Therefore, he was guided by the idea that tools and work methods should be used to prevent mistakes. These tools were just called Poka-Yoke. Poka-Yoke is also known by other names, such as error proofing or mistake proofing.

The first Poka-Yoke invented by Shingo was created in 1961 on a switch line. On that line, workers often forgot to put two springs on during assembly. Shingo suggested that there should be only two springs on a special feeder. When one was left on the feeder, the worker detected the error.

Nowadays, many companies have an ambitious goal – ZERO DEFECTS, ZERO COMPLAINTS. How to achieve it? Poka-Yoke solutions are the answer.

How to implement Poka-Yoke?

Poka-Yoke can be introduced right at the device design stage. How? It is possible to design the device in such a way that it is not possible to assemble it, replace worn parts or connect the plugs incorrectly.

Poka-Yoke examples

Other examples of mistake proofing

Another solution could be the introduction of a mechanical Poka-Yoke. A mechanical form of Poka-Yoke can be, for example, a gate that detects the physical size of products, checking their dimension and shape. The mechanical device can be set up in such a way that it passes on only those items that meet certain criteria. For this type of equipment, it is important to verify the device with good and bad patterns.

For example, having a device that verifies the dimension, a good dimension pattern and a bad dimension pattern should be run through before and during production. It’s also good to stock up on boundary patterns. Why? Because you may find that Poka-Yoke rejects products that are good, whose values are at the tolerance limit. Or conversely, it accepts products that have minimum values outside the tolerance limits.

Poka-Yoke can also be an electrical or electronic solution. For example, it can be: a vision system or various types of sensors (motion, proximity or using other physical phenomena sensors).

Most often, however, a mechanical device alone cannot function without electrical support and, conversely, an electrical device cannot function without a mechanical one.

Another form of Poka-Yoke can be a protection against an incorrect sequence of work being performed. In a situation where the operator is tasked with dozens of operations in a short period of time, it is important that he does not forget any and performs them in the correct order. Appropriate electronic and mechanical safeguards are used for this type of Poka-Yoke.

Poka-Yoke can also be a functional test. Instead of checking dimensions, angles and other geometric characteristics dozens of times, we check, among other things: whether the device is tight, whether it closes properly, whether it interacts with the component it will work with in the next stage of its “life cycle.”

Poka-Yoke requirements

A well-designed Poka-Yoke must meet several requirements.

  1. Specific objective. That is, the solution must prevent specific defects, errors (e.g. detecting a missing part in a device).
  2. Verified detection method. The method should be verified for correct detection (as mentioned above), stability and durability.
  3. The response system of the device to the detection of non-compliance. The detected irregularity should be communicated. This can be an audible or light signal.

It is also important that each employee knows how to act in the event of receiving a signal of irregularity (for example, stop the production line).

Poka-Yoke security levels

Poka-Yoke security levels

Benefits of introducing Poka Yoke:

  • Verification and detection of defects and irregularities at an early stage of production.
  • Inspection and detection of parameters and settings indirectly responsible for the defect (Preventive Poka-Yoke).
  • Checking the technical parameters and physical characteristics of products.
  • Verification of the suitability of the input material or semi-finished product (protection against mixed parts).
  • Possible 100% control of the production process or product.
  • Reduced financial outlay and time for process or product control activities by operators.
  • By responding quickly to the problem, it is possible to prevent the cost of poor quality.

Link to the product:

Mistake Proofing Course

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