- Mistake Proofing is also known as Poka Yoke or Error Proofing.
- It used to be referred to as Baka Yoke, Japanese for fool proofing. This name has dropped out of favour as more is understood about the causes of defects. Rather than blaming a defect on an employee, we now look at it from the perspective that wherever people are involved, there is a risk of error.
It is the errors that give rise to the defect.
- Shigeo Shingo developed this philosophy while he was working for the Toyota Motor Corporation in 1961.
- A Mistake Proofing device is any device or mechanism that either prevents an error from being made or detects when an error has been made. The key is that we are looking to prevent or detect the error that leads to the defect.
- The ultimate goal of Mistake Proofing is to eliminate the wastes associated with errors.
To help explain the last two points let’s use an everyday occurrence, beautifully illustrated by a talented student who went on to use their skills in vehicle design.
Consider the image at the start of this blog, the lorry stuck under the bridge. What are the wastes involved here?
You may have come up with; operating time for the lorry and driver, the time lost by all the people stuck behind the incident, the damage to the lorry and the goods inside it, even damage to the bridge. Each of these has an associated cost.
What was the error that the driver made, to end up with the defect of the lorry stuck under bridge?
You could list many different causes of the error, but for this example we will choose process error – not following Standard Operations. The driver did not follow the height warning signs before the bridge.
How could we prevent or detect this error from occurring?
We could replace the low bridge with an alternative route, like this flyover bridge with no height limit. Expensive, but it prevents the error of not following the height warning.
Or we could install a cheaper detection device in front of the bridge.
The driver would hear and feel the clunk of the suspended pole. This alerts them to the fact they have made an error, before the defect occurs.
Some waste would still occur. The driver has to stop and reverse and there may be some minor scrapes. However these are not as drastic as the quantity of waste in the initial scenario.
The benefits of well-designed Mistake Proofing devices include; making the job simpler for the employee and improved Quality, Cost and Delivery performance, as defects and other wastes are eliminated.
Improved safety is another benefit. Preventing or detecting errors before they result in an accident is not only beneficial in manufacturing operations but for any process that can be performed incorrectly.
This includes processes the end user of the product may carry out or processes in a different field altogether, like medicine. Who wouldn’t want to prevent incidents like amputating the wrong limb or administering an incorrect dose of a drug?
Over the years I have seen many excellent Mistake Proofing devices, and some that really should not be classed as such. I would love to hear about your encounters, so send in your stories.