What is Poka Yoke and how to use it in the manufacturing industry for zero defects?


Poka Yoke means Mistake Proofing or Error Proofing. Poka Yoke is a mechanism to prevent the mistake,defects from being made or detect the mistake if not prevented. It is also called error proofing or fool proofing.

Dr. Shigeo Shingo developed the concept of Poka-Yoke. Poka-Yoke is based on the concept that people do not make mistakes intentionally. But for other various reasons, mistakes can happen. Also as per Toyota’s concept an error is the failure of the system & methods that are used to perform that work.
But in general, operators are blamed for any mistake. So there is a need for Poka-Yoke or mistake-proofing to be implemented in all methods or systems.

Shingo Statement about Errors & Defect relationship:

“The causes of defects lie in operator errors and defects are the result of neglecting those errors. It follows that mistakes will not turn into defects if operators errors are discovered and eliminated beforehand. Defects arise because errors are made; the two have a cause & effect relationship. Yet error will not turn into defect if feedback & action take place the error stage”

Poka-Yoke works as Zero Defect:

When we implement poka yoke in process (tools / machine) to prevent the defect to occur. Then we got a condition of zero defect. So poka yoke works as a zero defect in any process or system. Also defect prevention is the goal of IATF 16949. So we should focus on error proofing from new development to mass production.

Dr. Shingo identified 3 types of inspections:

100% Inspection:

This involves sorting the defects out of the acceptable products. Shingo said that inspection in quality is not an effective quality management approach. As it is very costly process to inspect 100% parts. After that also there are chances of human error. So we never prevent defect to pass by 100% inspection / segregation.

 Sampling Inspection:

This uses data gained from inspection to control the process & prevent defects. SPC is a type of sampling inspection. But as per Shingo’s concern that inspection may not occur soon enough after production. So there are chances to skip defects. So there are chances of rejection to be made in meantime of inspection frequency decided.

Source Inspection:

Operators check their own work while doing production. This gives current & real feedback. Self-check uses poka-yoke devices to allow operators to assess the quality of their own work. Because they check each part produced, operators may be able to recognize what conditions changed that caused the last unit to be defective. This concept is used to prevent further defects. 

In source inspection, poka-yoke devices ensure that proper operating conditions are available before actual production. The poka-yoke devices & inspection techniques are intended to increase the speed with which quality feedback is received. 

Mistake proof design : 

It is a method to avoid mistakes by designing items so that they can only be assembled (DFA) in a certain way. So it is called mistake-proof design because it does not take much skill to put the parts together.

Examples of foolproof design in daily use:

Poka Yoke of Mobile phone sim card
Credit Google
  • Mobile phone sim card : In mobile sim there is a cut in one corner, so it can be fit in the mobile sim cavity only in fix direction & location. There are no chance of sim to be fit in wrong orientation.
  • Pen drive in USB: Sam is the case of USB pen drive which can fit only in one direction.
  • Three-pin plug : Due to the design of 3 pin plug, there are no chance for plug to be fitted in wrong direction.
Poka Yoke as USB pendrive
Credit Google

Awareness about Poke Yoke :

To make poka-yoke a company-wide program, first you need to educate your operators on the concept of mistake-proofing. Also you need to empower them to make small improvements in their processes continuously (Kaizen). Then we will get an industry wasting less energy, time & resources in doing things wrong and then reduce the cost of poor quality ( COPQ).

Read the Story about Poka Yoke in Lean manufacturing.

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