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History of Poka-Yoke

Origins of the Term: Poka-Yoke. The term “Poka-Yoke” was coined by Shigeo Shingo, a key contributor to the Toyota Production System (TPS); in the 1960s. Shingo noticed that in one process at the Toyota plant the workers often forgot to place a required spring under a switch button. He redesigned the process to be completed in two steps:

First placing the required springs in a placeholder, then inserting the springs into the switch. As a result, if a spring remained in the placeholder, it would be clear to the employee that they had unremembered to place it in the switch. Then, they could correct their mistake immediately. Shingo originally called the technique “Baka-yoke,” or “idiot-proofing,” but changed it to the milder “poka-yoke,” or “error-proofing,” after an operator became offended.

The principles of Poka-yoke (Mistake Proofing)have applies across industries. For example, preventing mistakes before they occur is critical in the medical industry; failing to prevent even a tiny mistake can have tragic consequences. Having measures in place to mark the correct body part for surgery, and even enforcing the washing of one’s hands, can prevent serious consequences. Poka yoke (Mistake Proofing)is also present in our everyday lives. For example, microwaves are designed to stop running if the door is open to prevent waves from escaping, and many new cars have error-proofing features such as alerts that let the driver sence if the car is leaving a lane. Some examples of Poka yoke (Mistake Proofing)are so common place that we generally would not think of them. For example, we often take for granted the spell-checking functions on our phones, internet browsers, and software that prevent us from making spelling mistakes in our communications.

What are Poka-yoke (Mistake Proofing)and their types?

Poka yoke (Mistake Proofing)is a method for avoiding simple human error in the workplace. Also known as mistake-proofing, idiot-proofing methods, Poka-yoke (Mistake Proofing)is simply a system designed to prevent unintentional errors made by employees performing a process. The idea is to take over repetitive tasks that depend on memory or attention and guard against any error in focus. Poka yoke (Mistake Proofing)can be seen as three usual components of Zero-Defect, source inspection and feedback.

Poka-yoke (Mistake Proofing)is used to prevent and resolve errors during the production process, eliminating the need for quality control after the process. Poka-yoke (Mistake Proofing)is a frequently used method in Lean Practices and Six Sigma to ensure as little errors in a production process as possible. A ‘poka’ is an ‘unintentional error’ and ‘yokeru’ is Japanese for ‘preventing’.

Poka yoke (Mistake Proofing)makes it practically impossible to make mistakes. It forces actions to be carried out correctly, leaving no room for misunderstandings. It’s about measures that prevent further errors from being made. Many solutions in Poka-yoke (Mistake Proofing)tool to be simple, cheap, and effective. They can be integrated into the product design or in one of the process steps. The most famous examples are smartphone SIM cards. After all, there’s only one way to place the SIM card in the phone. It’s impossible to do it wrong.

Poka-yoke (Mistake Proofing)distinguishes between defects and mistakes.  A defect is an error in a process that continues until it reaches the customer (at great cost to the company). A mistake, on the other hand, can be detected and corrected immediately.  Poka-yoke (Mistake Proofing)seeks to eliminate defects at the source, by removing the possibility of a mistake occurring or alerting the operator immediately.

There are three types of Poka yoke (Mistake Proofing)for detecting and preventing errors in a process:

The contact method identifies defects using a part’s shape, size, color, or other physical attributes. The contact method can also include limit switches and proximity sensors. For example, if we want to avoid placing a part backward or upside down in a fixture. This part should have an asymmetrical design with a receptacle only allowing the part to fit in the correct orientation. Alternately, a pin can stick-out from the part which will only allow the part to fit when correctly oriented providing a contact method poka-yoke.

The constant number (or fixed-value) method alerts the operator if a certain number of movements are not made.  Counters could also be a fixed number of parts that must be used at each step. Similar to building Ikea furniture, if when you’re finished there is a screw left over, you know you have done something wrong (although in that case, it’s probably too late). In manufacturing or service processes the operator is provided with a bin containing the exact number of parts to complete the stage of the task. A part leftover or one missing will highlight a defect at this stage. The part will not allow it to go to the next stage, where it would increase the associated cost of the defect.

The sequence (or motion step) method aims to ensure the prescribed steps of the process have been followed before starting the next stage. Not allowing the mistake to be made in the first place. This could include part boxes only opening in sequence. Colour coding and tagging are other examples of sequence poka-yoke, these are then inspected to ensure that critical previous steps were performed.


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Why is Poka-yoke (Mistake Proofing)important?

A Poka-yoke (Mistake Proofing)is that they help people and processes work right the first time, which makes mistakes impossible to happen. These techniques can significantly improve the quality and reliability of products and processes by eliminating defects. This approach to production place perfectly the culture of continuous improvement, which is also part of the Lean management arsenal. It can be used to fine-tune improvements and process designs from six-sigma Define – Measure – Analyze – Improve – Control (DMAIC) projects. Applying Poka-yoke (Mistake Proofing)ideas and methods in product and process design can eliminate both human and mechanical errors.

Benefits of Poka-Yoke

Poka-yoke (Mistake Proofing)stems from recognizing that making mistakes is part of being human. A Poka-yoke (Mistake Proofing)removes or majorly reduces the opportunities for us to make mistakes. They can make a process run more smoothly, reduce defect rates, decrease takt time, and even improve the quality of life. The term was initially applied in the manufacturing world but today examples can be seen in all sectors and many aspects of our lives. A can improve the yield and efficiency of many processes and above all reduce defect rates.

A second advantage of implementing a Poka-yoke (Mistake Proofing)is a better moral and improved atmosphere among employees and managers. This is achieved by removing a “blame culture”. In the working environment telling an employee to do better or penalizing them for mistakes is often unsuccessful in reducing error rates. Poka-yoke (Mistake Proofing)theory recognized that it is the process that is flawed and not the people. Companies should do everything they can to ensure the success of their employees. Small design features and visual cues can do just that. They can have a profound effect on safety, efficiency, and ensuring a product or service is right the first time. Giving those who work in the process the opportunity come up with clever solutions to greatly reduce the error rate or eliminate it is incredibly rewarding for everyone involved.

1. Reducing Time Spent on Training

Since workers won’t need to look out for as many problems, you won’t need to spend as much time training them on these issues. Promoting a Culture of Continuous Improvement

Poka-yoke (Mistake Proofing)fosters an improvement-oriented approach by encouraging employees to solve problems immediately and address the root cause of problems to prevent them from becoming bigger problems. It’s a great tool to implement within a larger lean manufacturing framework.

2. Improving Safety

You can improve the safety of your factory by putting measures in place to prevent workers from entering unsafe situations.

3. Reducing Waste

It may go without saying, but producing fewer defective products means you’re also wasting fewer materials. You also save time by spending less time reworking defective products: in addition to cutting down on the number of defects that need fixing, it’s faster to fix a defect earlier rather than later.

4. Higher Productivity

Your processes will run more smoothly when errors are prevented and defects are detected and solved immediately. As a result, quick, more efficient processes and less waste result in higher overall productivity.

  • elimination of set-up errors and improved quality.
  • decreased set-up times with associated reduction in production time and improved production capacity.
  • simplified and improved housekeeping.
  • increased safety.
  • lower costs.
  • lower skill requirements.
  • increased production flexibility.
  • improved operator attitudes.

How to implementation of Poka-yoke?

Poka-yoke (Mistake Proofing)is easy to implement because of its universal and practical nature. You can follow this step by step process to apply it:

  1. Identify the operation or process.
  2. Analyze the ways a process can fail
  3. Choose the right Poka-yoke (Mistake Proofing)approach.
  • Elimination – This seeks to eliminate the possibility of Mistake by redesigning the product or process so that the task or part is no longer necessary.

Example: Product simplification or part consolidation that avoids     a part defect or assembly Mistake in the first place

  • Replacement – Substitute a more reliable process to improve consistency.

Example: Use of robotics or automation that prevents a manual assembly Mistake, automatic dispensers, or applicators to ensure the correct amount of material such as an adhesive is applied.

  • Prevention – Design the product or process so that it is impossible to make mistakes at all.

Example – Limit switches to assure a part correctly placed before the process is performed; part features that only allow assembly the correct way, unique connectors to avoid misconducting wire harnesses or cables, part symmetry that avoids incorrect insertion.

  • Facilitation – Employ techniques and combining steps to make work easier to perform.

Example – visual controls including color-coding, marketing or labeling parts to facilitate correct assembly exaggerated asymmetry to facilitate correct orientation of parts; a staging tray that provides a visual control that all parts were assembled, locating features on parts

  • Quickly correct the problem.

Examples – sensors in the production process to identify when parts are incorrectly assembled built-in self-test (BIST) capabilities in products

  • Mitigation – Minimizing the effects of Mistakes.

Examples – fuses to prevent overloading circuits resulting from     shorts, products designed with          low – cost, simpler rework procedures     when a Mistake is discovered, extra design margin or redundancy in     products to compensate for the effects of Mistakes

  1. Take a comprehensive approach alternately of thinking of Poka-yoke.
  2. Determine the Poka-yoke (Mistake Proofing)method type.
  3. Test the method and see if it works.
  4. Train the operator, review performance, and measure success.

When to Use Poka-yoke (Mistake Proofing)and Identifying Errors? 

Poka-yoke (Mistake Proofing)can be implemented at any point in any process in which a mistake can be made. Here are some situations where it would be particularly important to mistake-proof a process:

  • At a hand-off step in a process, when output is transferred to another worker
  • When a minor error early in the process will cause major problems later in the process
  • When the consequences of an error are expensive or dangerous

Here are some common types of errors that can occur in manufacturing processes:

Processing Errors- Missing a process operation or not performing it according to the standard operating procedure

Setup Errors- Setting machine adjustments incorrectly or using the wrong tooling

Missing Parts- Not all parts incorporated in the assembly, welding, or other processes

Improper Parts/Items- Using the wrong parts in a process Interfaces

Operations Errors- Carrying out an operation incorrectly or having the incorrect version of the standard operating procedure

Measurement Errors- Making an error in measurement during a process, machine adjustment, or the dimensions of a part coming from a supplier

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