As noted in our previous post, poka-yokes are meant to mistake-proof a process. They must be devised to prevent a particular type of error, which is why it is so important to thoroughly study the problem, the process, and the root causes.
Once you have all the facts and data about what goes wrong most frequently, in what way, and why, you can set your collective creative minds to designing a poka-yoke that most effectively and efficiently prevents the most frequent human errors or omissions.
To effectively design a poka-yoke, follow these simple steps.
Include the right people. Often the simplest and most effective poka-yokes are thought of by the people closest to the work.
For example, a port for the dry-docking and repair of supertankers needed to perfectly align the ship, and this was very time consuming and expensive with lots of engineers with sensitive measuring devices. A fellow working at the dock saw all this effort, and suggested a poka-yoke. His idea was that they move his shack to just the right position on the dock to line up with where the ships needed to align, then mount a scope on the shack in just the right position. He would then watch through the scope and tell them when the ship was in the right position.
It can also be helpful to include an outside perspective. Someone not immersed in the work every day may spot opportunities to eliminate problems or difficulties that the people executing the process every day may take for granted. Also, a good poka-yoke can often be created by borrowing from one industry or application to another, so diversity of experience is very useful in mistake-proofing.
Identify the specific mistakes you want to prevent. Poka-yokes are individually designed to prevent a specific mistake. Since you cannot mistake-proof everything at once, you must study the process and gather the data to identify what specific errors to address first.
Explore modifications to the work environment to reduce errors. The Five-S method identifies ways that the environment contributes to errors, often by making it hard to detect when a problem has occurred. Clutter makes it difficult to spot deviations in the location or condition of critical items. Sorting and cleaning help to mistake-proof. A bank greatly reduced the frequency of delays in processing mortgage applications by clearing off all the desks so each desk had only two applications at any one time, the one the processer was working on and one waiting in their in-box. Many organizations have found shadow-boarding ― creating outlines of tools that should be hanging on the board in that place ― to help them reduce time looking for the right tool or errors from using the wrong tool.
Explore modifications to machines or tools. Using jigs and automatic stops are changes to machines that make it much easier to execute the work to specification. Similarly, tools such as Excel are filled with poka-yokes, such as conditional formatting that can be used so that a cell’s color changes when the data in it meets certain criteria such as a date within a certain date range, quantities over a certain level, or even simply a required cell is blank.
The data validation feature is another handy mistake-proofing tool. This lets you prevent the entry of a wrong data type or an invalid name or a quantity that is too high or non-standard. This feature can be set to prevent entry that does not meet certain criteria or merely alert the user to re-examine the entry.
Explore modifications to materials. Changing materials can help to prevent an error or make a mistake readily visible so easy to catch before it causes trouble.
For example, one company gathered data on the types of errors people made on the forms they were using, and then redesigned the forms to make it much more obvious which fields were required and which were not. This greatly reduced the number of forms that had to go back to the customer for rework.
Explore modifications to the process to reduce errors. Changes to the process can be made to catch critical errors at the time they are made. Many hospitals have implemented a pre-surgical process poka-yoke that involves marking the point of incision ― in some cases having the patient sign off on the spot. To prevent the risk of an undiluted medication being delivered to a patient, a hospital changed the process so the medicine was diluted in the pharmacy rather than in the patient’s room.