Poka Yoke is a Japanese phrase that means error prevention. It was developed in the sixties of the previous century by Shigeo Shingo from Japan. He was an engineer at the Toyota car factory. Toyota is still the most famous multinational business using Poka Yoke today.
Poka Yoke is used to prevent and resolve defects during the production process, eliminating the need for quality control after the process. Poka Yoke is a frequently used method in Lean Manufacturing and Six Sigma to ensure as little errors in a production process as possible. A ‘poka’ is an ‘inadvertent error’ and ‘yokeru’ is Japanese for ‘preventing’.
Poka Yoke makes it practically impossible to make mistakes. It forces actions to be carried out correctly, leaving no room for misunderstandings. It’s about measures that prevent further errors from being made. Many solutions in Poka Yoke tend to be simple, cheap, and effective. They can be integrated into the product design or in one of the process steps.
Poka Yoke Stages
In order to carry out Poka Yoke as well as possible, it’s a good idea to work in stages. The example at the end of this article will also refer to those stages.
During this phase, the problem causing the defect is described and defined. It needs to be an objective description that doesn’t draw conclusions right away. It’s possible to monitor the shop floor during the production process. This is also indicated with the word ‘Gemba’, which is Japanese for shop floor. The shop floor is where the process happens, and that’s where the causes of problems may also be hiding. If the problem occurs at the end user, it’s a good idea to define the problem objectively from this perspective.
Usually, the measuring stage is applied in case of complex problems in the production process. A test is used to discover how often the problem occurs. A percentage is then calculated based on the results. The higher the percentage, the more important it is to solve the problem at its source. Apart from a production error, it may also be a case of user error. In such a case, a so-called test group would be used that tests the product over a certain period. The outcome of this determines how the problem will be dealt with and solved.
During this stage, it becomes clear whether a Poka Yoke measure can be applied. The process is analysed thoroughly, and the cause of the defect is tracked down. Only when the source of the issue is clear, can the search for a solution begin.
During this phase, analysis is used to deal with the cause of the problem. A solution is developed and implemented. In many cases, Poka Yoke solutions seem obvious, but have a significant positive impact. They prevent the same mistake from being made in the future
During this stage, the effect of the changes is measured. If the Poka Yoke measure in question works well, and the chance of further potential error is negligible, it concludes with the ‘Zero Quality Control’ and Zero Defects.
3 types of Poka Yoke
Three types of Poka Yoke can be identified for quickly and easily delivering solutions for production problems.
1. Visual aids
These aids are clear and show the work instructions. These may be pictograms in a user manual or a traffic sign that shows a restriction or warning.
2. Visual control
These refer to directing behaviour and warning in case of deviations. One example would be a traffic sign that lights up red when drivers are speeding and green if they stick to the speed limit.
They force the user to either do or not do something. This can be road closures for motorway maintenance, for instance. Arrows on signs force drivers to go from 3 to 2 and from 2 to 1 lanes. The arrows are followed by red Xs on the signs until 2 of the 3 lanes are closed.