Poka Yoke is a Japanese concept aiming at preventing defects in a given process from being experienced by the customers. There are two effective ways to block the defects before they go to the customers. The first and most efficient way is to prevent the root causes of the process failures from happening: this is Prevention. The second way is to capture the defects coming out of the process before the products or services are sent to the customers: this is Detection.
Obviously, the second is not ideal because you still have a defect that has cost you some money to produce and for which you will not receive any income; and this defect will probably cost some more money to correct. Yet, at least, your customers are not seeing your internal problems, your reputation is preserved.
Furthermore, the detection process also becomes a powerful measurement system, allowing you to visualize and measure the defects – a first compulsory step before identifying the root causes. Once you have a good measurement of your defects thanks to your detection system or process, you have created some breathing space when you can spend the necessary time to deeply analyze the root causes, without having to exhaust you and your teams in addressing the always urgent customer complaints (since the customers do not receive the defects anymore). Little by little, the detection system is likely to become obsolete, as you will fix the root causes and build a robust preventive process; but still, you also have a good safety net in place, just in case.
Here are a few examples of bad processes, where either preventive or detective measures could be taken.
The bathroom sink:
Imagine the water control knob on a bathroom sink. You wash your hands with soap, and then you turn the knob to rinse. Easy. Now, imagine a knob about as smooth as glass and almost impossible to turn when your hands are full of soap… a real example!
Such design could have been avoided if the designer had tested the sink as a detective measure before selling it. Therefore, the root cause would have been identified and the design changed, preventing the customers from being stuck with their soapy hands.
Watch your step:
I’m sure you have already seen some examples of “Watch your step” signs behind the step… too late!
By putting the sign in front of the step, the root cause of people not seeing the step can be easily prevented.
The USB key:
Who has never tried to plug a USB key upside down? A slightly different shape up and down makes the mistake easy to prevent.
These examples show a combination of preventive and detective measures embedded into the process or system itself, so that defects cannot reach the customers.
In your opinion, is Poka Yoke meant to be Preventive, Detective, or both? What are your favorite examples illustrating how one can apply Poka Yoke to simplify and streamline processes while improving their quality?
The Process Excellence String of Ariadne 