What is Poka Yoke

Guide: Error-Proofing (Poka Yoke)

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Daniel Croft

Daniel Croft is an experienced continuous improvement manager with a Lean Six Sigma Black Belt and a Bachelor's degree in Business Management. With more than ten years of experience applying his skills across various industries, Daniel specializes in optimizing processes and improving efficiency. His approach combines practical experience with a deep understanding of business fundamentals to drive meaningful change.

Error-proofing, also known as mistake-proofing or poka-yoke, is a highly effective technique for preventing errors and mistakes in a variety of processes. Error-proofing is critical in improving quality, reducing defects, and increasing efficiency in manufacturing, assembly, and service procedures.

This step-by-step guide will guide you through the error-proofing process, assisting you in identifying potential errors, analyzing their causes, and implementing effective error-proofing techniques. By following these steps, you can build a more dependable and error-free system, reducing errors and ensuring consistent results. Accept error-proofing as a way to create a more streamlined and error-free process.

Table of Contents

What is Poka Yoke?

Poka Yoke was originated and popularized by Shigeo Shingo in the 1960s. The term Poka Yoke translates into “Avoiding mistakes.”

Poka = Inadvertent mistakes

Yokeru = Avoid

The philosophy of Poka Yoke is that it is more effective to design processes in a way that makes mistakes impossible, or at least easy to detect and correct, rather than to find and fix them later. 

Poka Yoka works by setting up mechanisms that either prevent errors from happening or make them immediately obvious once they occur. These can be as simple as a jig that only fits a part in one orientation or as complex as barcode verification systems. By ensuring that the process or equipment is designed in a way that makes errors almost impossible, Poka Yoke contributes to more robust, efficient, and safe systems.

One such example of this that is referred to in training that 99% of people have come across without realizing it Poka Yoke is the SIM card shape and SIM card tray. If the SIM card did not have that notch, it could be put into the phone in eight different ways. However, by simply adding a notch there is only one possible way to put a SIM card in the tray. A simple change has saved billions of people from stress and confusion.

Poka-Yoke-Example-Sim-card

Poka-Yoke-Example-Sim-card

Types of Poka Yoke

Contact Method

This method uses physical attributes to prevent or detect errors. The SIM card is an example of this, but others include USB plugs, which can only be inserted one way, preventing errors by inserting them upside down. 

Other examples include:

  • Keyed Connectors: Connectors designed to fit only one way to prevent incorrect assembly.
  • Size Sorting: Holes or slots that allow only parts of a specific size to pass through.
  • Color-Coding: Parts that must be matched (like resistors or wires) are color-coded to prevent mix-ups.
  • Safety Guards: Physical barriers are placed around hazardous areas to prevent accidental entry.
  • Fuel Nozzle Diameter: Different nozzle sizes for diesel and gasoline are needed to prevent wrong fueling; at least diesel cannot be put into a petrol car.

Poka Yoke example of what it is

Constant Number (or Fixed Value) Method

This method ensures that a set number of actions have been performed before moving on to the next step. For instance, a checklist that requires confirmation of five completed tasks before proceeding ensures that no step is missed

Sequence Method

This method is often used in complex processes where tasks have to be performed in a specific order. For instance, software wizards that guide you through installation steps in a certain sequence, ensuring that all prerequisites are met before installation.

The first step when wanting to implement Poka Yoke in your process is to identify a process if you have not already. The key consideration for selecting a process is to prioritize those with high error rates and a history of defects. Another consideration should be of processes which are critical, with priority given to processes where errors have significant impacts on Safety, Quality, Delivery and Cost (SQDC).

This can be done by using process mapping to document the process and using a concentration chart of the process map to highlight at which stage of the process errors occur. This will give you a good indication of where to focus poka yoke actions first.

Step 2: Analyze

The next step in the process is to conduct some error analysis to identify the types of errors that occur and the frequencies of the errors. This can be done with some data collection and methods to analyze the data, such as Pareto charts, to see what causes 80% of errors.

For example, in the image below, the focus would be on poka yoking errors that cause incorrect assembly, documentation errors, and misbalance, and they will have the largest impact on reducing errors.

Frequency of errors pareto

Step 3: Choose the Right Method

Now that we know the process and the type and frequency of errors in the process, we need to choose the right method to address them. For this, we need to consider the nature of the errors and choose a method that will best address the errors. For this consider the physical and operational characteristics of the process.

Methods to consider include the Contact method which can be ideal for physical errors related to size, shape, or other physical attributes. 

For example, let’s say a regular error was due to incorrect product weights. A machine that checks the product weight could be called a check weigher. This could reject lightweight or overweight products or cause an automation that corrects the product weight if possible.

Other methods to consider have been covered above in the types of Poka Yoke section.

Step 4: Develop and Test

The next step is to design and test the Poka Yoke solution. For this, you can create a simple and cost-effective solution based on the chosen Poka Yoke method. To ensure success, make sure the solution is easy to understand and simple to use.

Testing should be done in a controlled environment to test the effectiveness of the method. Then, gather feedback from users and make any necessary adjustments.

Step 5: Implement

After successful testing, there should be a full-scale implementation in the actual process. This should be followed by any required training to educate employees on how to use the new system effectively.

Following this, there should be continued monitoring of the process immediately after the implementation to catch any unexpected issues.

Step 6: Review and Iterate

Finally, as always in continuous improvement, you should regularly assess the effectiveness of the poka-yoke solution in reducing errors and continue to adjust based on new insights or changes to the process. 

Conclusion

In conclusion, error-proofing through Poka Yoke is an indispensable strategy for enhancing quality and efficiency across diverse processes. By meticulously identifying high-risk areas, analyzing error patterns, selecting the appropriate Poka Yoke method, and rigorously developing and testing solutions, organizations can significantly reduce error rates. Implementation requires careful planning, employee training, and ongoing review to ensure that the solutions remain effective.

Embracing Poka Yoke not only streamlines processes but also fortifies them against the costs and disruptions of mistakes, aligning with the Lean Six Sigma philosophy of continuous improvement and operational excellence.

References

A: Error-proofing, also known as mistake-proofing or poka-yoke, is a technique used to prevent errors and mistakes in various processes. It involves implementing mechanisms, systems, or procedures that make it difficult or impossible for errors to occur or go unnoticed.

A: Error-proofing is important because it helps improve quality, reduce defects, and increase efficiency in processes. It minimizes the risk of errors and ensures consistent results, leading to improved customer satisfaction, cost savings, and a more streamlined operation.

A: To identify potential errors, conduct a thorough analysis of the process and involve all relevant stakeholders. Consider past incidents, collect data on defects or failures, and engage in discussions or observations to identify areas where errors are likely to occur. Also, review customer feedback, conduct risk assessments, and examine process documentation.

A: Common error-proofing techniques include using physical devices or mechanisms to prevent errors, implementing color coding or labeling systems, creating checklists or visual aids, employing poka-yoke devices that detect or prevent errors, and standardizing and simplifying processes and instructions.

A: Measuring the effectiveness of error-proofing involves collecting data on defect rates, error occurrences, customer complaints, or other relevant metrics. Compare the data before and after implementing error-proofing techniques to assess the impact. Additionally, seek feedback from employees and stakeholders involved in the process to gather qualitative insights.

A: Foster a culture of continuous improvement by encouraging employees to identify and report errors, suggest improvements, and actively participate in the error-proofing process. Provide training and development opportunities, regularly review and update error-proofing techniques, and celebrate successes and contributions to reinforce the importance of continuous improvement.

A: While error-proofing techniques significantly reduce the likelihood of errors, it may not completely eliminate all errors. Human error and unforeseen circumstances can still occur. However, by implementing robust error-proofing measures and continuously improving them, organizations can greatly minimize errors and their impact on processes.

Author

Daniel Croft

Daniel Croft

Daniel Croft is a seasoned continuous improvement manager with a Black Belt in Lean Six Sigma. With over 10 years of real-world application experience across diverse sectors, Daniel has a passion for optimizing processes and fostering a culture of efficiency. He's not just a practitioner but also an avid learner, constantly seeking to expand his knowledge. Outside of his professional life, Daniel has a keen Investing, statistics and knowledge-sharing, which led him to create the website learnleansigma.com, a platform dedicated to Lean Six Sigma and process improvement insights.

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