A good poka yoke definition is simply ‘mistake proofing’. Of note, the term poka yoke is of Japanese origin and is one of the handful of the more commonly used Japanese terms that have become mainstream in Lean circles.
Poka yokes keep processes from producing errors. Preventing errors obviously improves quality, but it also plays a major role in improving productivity. With no rework, and easier production, cycle times and lead times both become much shorter. And, of course, faster production with fewer defects means lower costs.
While the term poka yoke originated on the shop floor, it is equally relevant in office, healthcare, and service settings.
Another similar term, baka yoke, meaning ‘fool proofing’, has fallen into minimal use, likely for reasons of political correctness. As an aside, the term poka yoke is also frequently used as a verb, as in ‘John, can you please poka yoke that fixture?’
Of note, the last ‘e’ in the term is often pronounced as a long ‘a’.
Mistake-proofing poka yoke devices surround people, preventing costly problems in their everyday lives.
The list could go on and on and on. As you can see, if you use the loose ‘mistake proofing’ definition, poka yoke devices are everywhere.
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A poka yoke device must make it physically impossible to make a mistake. While a poka yoke is often a physical device, such as a fixture that only accepts parts one way, processes and parts can also be designed to have a built-in poka yoke.
Safety switches are similar to poka yokes. The little switch that keeps the microwave from running when the door is opened is a safety device that keeps you from zapping yourself if you try to get your food before the ‘ding’. The same is true of dual hand switches on heavy machines that must be pressed for the machine to run. They are great—they keep your hands attached to your body. Just keep in mind that as important as these safety devices are, they don’t protect the output of the process. Poka yokes will protect you and deliver uncompromising quality.
Poka yokes can take some precision to fabricate. Identify a person that can become an expert on building mistake-proofing devices. Many manufacturing companies have a tooling group that is a source of great candidates. Just be careful that they don’t over-engineer solutions. Simple is better.
Most of these examples come from the shop floor where poka yoke has its roots. Because office processes tend to be more focused on people and software than on parts and machines, there tend to be fewer opportunities for mistake-proofing by frontline employees. Despite this, it is still very important in the office.
Computers and software are full of poka yokes. Field filters might ensure that the proper number of digits are entered for a phone number. A poka yoke in a call center may sign a person out of if his phone rings more than 4 times without an answer. This keeps the customer from waiting. Restricting functionality based on user type (administrator vs. user) is another example.
Become familiar with poka yokes. They contribute to your success in two important ways. First, they improve cycle times which clearly benefits standard work. After all, when a process is mistake-proofed, it gets far quicker.
The gas pump example illustrates the point. How much longer would it take to fill a tank if you had to know how much gas you had to start, and subtract that from the capacity of your tank, and then slow down the pump when you got close to being full? The zip code poka yoke example reduces rework for the customer service group. They have fewer lost orders to take care of. Mistake proofing also speeds up processes because it eliminates the need for inspections, since there is no way for bad parts to slip through.
The second benefit of poka yokes is improved quality. Obviously, if there is no way to make a mistake, defects can’t slip through.
Poka yokes are among the most beneficial Lean concepts for frontline workers. They keep you from making mistakes, but more importantly, they take the worry about making mistakes away from you. With less concern about problems, you can direct your energy in a more positive direction. Jobs where you are constantly concerned about missing production targets, or scrambling to change plans when you have to stay late to do rework are never any fun.
Develop a talent for identifying opportunities for mistake-proofing devices. They will prevent you from making errors that can be a major source of frustration and conflict with your co-workers. Processes where you must pay close attention to avoid mistakes are a good place to start looking.
If you recognize places where a device can help, even if you don’t have a fully developed idea, present it to your coworkers, your boss, or an engineer that supports you. They will be able to add to your thoughts, and will probably help you come up with a good solution to improve your quality.
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