Mecanichal coding and visual coding: leveraging Poka-yoke

Exemple de poka-yoke mécanique

What every manufacturing company is looking for is a quality production at a lower cost. The recent setbacks of Toyota and the numerous recalls of vehicles (all brands) remind us regularly. When assembling parts manually, how can you guarantee that the operator always mounts the right part in the right place? Keying, also called poka-yoke, is one of the solutions that can be made.

Poka-yoke definition

In the West, we are impregnated at a young age of these concepts.

The principle of poka-yoke or anti-error is the same as that of this toy. Each piece can only go to one place, the “good” one. Poka-yoke is a preventive method, which is therefore put in place upstream, in order to prevent an error.

Poka-yoke systems should be designed as simply as possible. They must ensure that all parts are good: 100% control.

The two main types of coding

Mechanical coding is more reliable than visual coding, but more complex and more expensive to implement. It is, in general, reserved for the most critical cases, when an error may have an impact on the security of property or people.

Thus the USB connection is mechanically coded, turning it impossible to connect a USB key upside down or in a bad connector.

The audio jacks such as the microphone and the speakers are visually coded. It is possible to reverse both. In this case, the system will not work properly, but will not be “endangered”. The sound will come out through the microphone without damaging it. It will then be possible to reverse the two cables.

In the industry, the mechanical coding can take place by differences in size, the addition of a protuberance at a specific location, a fastening system positioned differently for each piece, …

The choice between a visual or mechanical poka-yoke will be based on the risk of error, impacts for the customer and cost.

The coding system can be implemented at different stages of the product life cycle: during the design, during industrialization or during a process improvement activity. It is obvious that a product designed with the foolproof system is always the least expensive solution. However, simple solutions such as jigs or color codes can be implemented during a continuous improvement process. In addition to the anti-error aspect, this type of system reduces the cognitive load of the operator and intellectual fatigue, sources of stress.

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