Poka-Yoke Error-proofing

Poka-Yoke Error-proofing is the act of making errors impossible through great design. Defining requirements or ensuring continuous flow are good things but are not entirely part of error-proofing.

A great example for anyone driving in the US is gas pump nozzles’ different shapes and sizes. I can remember one bleary-eyed road trip in college. Half awake, I tried to fill my 1986 Buick Regal with diesel instead of regular! Fortunately for me, the designers of the gas nozzles used poka-yoke. The diesel nozzle is wider than the unleaded nozzle, so it would not fit in the narrower filler neck my car had! That was great error-proofing.

History of Poka-Yoke Error-proofing

Coined in the 1960s in Japan, Poka Yoke means “mistake-proofing.” Shigeo Shingo renamed it from the earlier “baka-yoke,” or fool-proofing. It is a tool for avoiding inadvertent errors. The tool ensures that proper conditions are in place for every step of the process, so there is no room for defects while operating. In other cases, it detects and fixes the defects as early as possible.

Poka-Yoke is a vital tool in lean manufacturing since it helps the people and processes work the first time correctly. It helps to phase out defects during the process and in the products by improving quality and reliability. It is worth noting that it does reduce both machine and human errors in the work processes and products.

When to use Poka-Yoke Error-proofing?

The ideal time to use the technique of Poka-Yoke is when a process or product is likely to have an error or something may go wrong. You can easily introduce the Poka-Yoke technique in both the manufacturing and service industries. Poka-Yoke captures errors like poor process operations, improperly adjusted machines, or incorrectly used tools (setup errors).

Secondly, it flags missing parts on the production line (missing parts errors) and incorrectly used parts (improper parts error). It also flags processes or products that fall below quality standards (operations errors), and unadjusted machines and parts (measurement errors). Consequently, this last example includes improper dimensions of the supplies or parts used.

How to use Poka-Yoke Error-proofing?

There are several steps that one can follow to use Poka-Yoke in their work operations:

Step 1: Identify the process or operation that needs fixing, using a Pareto chart and analysis.

Step 2: Assess and understand the defects in the process that may lead to failure. Keep in mind the 5-whys during this stage.

Step 3: Decide the strategy to use for effective Poka-Yoke. Some of the options include:

• Shut-out strategy: this is a strategy that prevents anyone from committing the error
• Attention strategy: which brings attention to the defect while someone is committing it
• Comprehensive approach: which is a combination of options

Step 4: First, determine the appropriate strategy needed for the situation. You can do this using a contact, constant number, or sequencing method. A contact is any physical trait that can catch an error. Constant number finds errors in cases where the trigger behind the error is the absence of a certain number of actions. Finally, a sequencing method uses a checklist to tally the completion of steps in the process without error.

Step 5: Run a trial test to ensure the chosen method is appropriate and effective.

Step 6: Once you are sure the chosen method is good, train the operators on it. Then review the performance and measure the success to verify the Poka-Yoke strategy.

Poka-Yoke Videos

ASQ Six Sigma Black Belt Certification Poka-yoke Questions:

Question: A company has bought a system that prevents orders with incorrect information from being sent to production schedules. This is an example of which of the following lean tools? (Taken from ASQ sample Black Belt exam.)

(A) Standard work
(B) Kanban
(C) Poka-yoke
(D) Visual factory

Answer:

C: Using color coding as an error signal is an example of mistake-proofing, specifically an Attention Strategy (see Step 3 above). It brings attention to a defect as someone commits it. It does not physically prevent it the way a Shut-out Strategy would. (This isn’t the best example, as anyone who suffers from color blindness can tell you! Additionally, a better example of a Shut-out Strategy is the pumps at the gas station. Notice how different fuel types get differently shaped nozzles? That makes putting the diesel pump into your gasoline tank physically impossible, not just noticeable!)

An X Bar R chart can reveal when your process is out of control, but it will not make it mistake-proof. Using inspection to detect and contain defects can lead to better quality but will not prevent those defects in the first place.

Having a team that creates errors directly repair them may lead to learning and error- prevention in the future – or it may not.

For example, having a color-coded system where only people with red badges may enter a certain hospital floor can prevent defects before they happen.