How Poka Yoke can help you prevent mistakes? Mistake Proofing

Poka-yoke is one of the powerful lean manufacturing tools that help the organization to achieve zero defects targets in the process by preventing and eliminating errors. As a result, this tool removes waste in the process and helps to increase the process efficiency.

Making mistakes is very common in all types of organizations but making effective mistakes is not common. The errors/mistakes are responsible for more than 90% of the defects in the processes in an organization.

So all types of organizations need a tool that can prevent errors/mistakes from happening in the process. That powerful tool is the Poka-yoke or mistake-proofing.

In this article, I will share the complete details of this tool like what actually it is, the history of mistake proofing, types of poka-yoke, different examples of this lean tool, and its application in different organizations, etc.

In the end, you will get complete clarity on how useful this tool is for mistake/error prevention. So let’s start…

What is the Poka-yoke technique?

Poka-yoke is a Japanese term that means (poka – Mistake, yoke – proofing) mistake proofing. When somebody hears it the first time, it looks like some kind of video game name but in reality, this is one of the powerful lean tools used for 100% defect prevention in organizations.

This tool was first introduced by the key contributor of the Toyota Production System (TPS) Shigeo Shingo in 1960. Shingo emphasized more on the concept of zero quality control which means the situation where inspectors are no longer needed because process quality issues are prevented.

He actually builds the quality in the process rather than inspects the quality out of it. He wrote two books on this defect prevention method where he explained how Toyota used this method and later it became popular in all industries.

Let’s understand the concept of this tool with one example, you have seen the USB cable wire, in that wire both the ends are different. Because one end you insert in mobile phone and other you insert in a charger.

Due to the differences between the two ends, it becomes easy for you to understand the use of USB accurately.

If both ends of the USB cable wire are the same then you can’t understand which end to insert in the mobile and which end to insert in the charger.

That’s why USB wire is designed in such a way that both ends have a different design that helps you easily understand which end to insert where.

This is a real concept example of poka-yoke in which 100 % of defects/errors are prevented. Simply it is a fool-proofing device that prevents incorrect parts from being made or assembled or easily identified a flaw or error.

It is used to prevent defects from occurring in the process and resolve errors during the process and eliminate the need for quality control at the end of the process.

This tool is frequently used in Lean Six Sigma problem-solving for error prevention because this tool makes it practically impossible to make mistakes in the process.

Most of the poka-yoke solutions are very simple, effective, and cheap. It can be integrated into the product at the time of design or in one of the process steps while improving the process.

This tool basically ensures that the right conditions exist before the process step is executed or before the product is designed by focusing on preventing 100% of the defects from occurring in the 1st place.

Related content – What is Lean Manufacturing? Complete guide for 2022

Why Mistake proofing is so important?

As we know the main purpose of mistake proofing is to eliminate the product/process defects either by preventing them in the 1st place or by correcting them or by drawing attention to human errors as soon as they occur.

It acts as a safeguard that prevents a process from proceeding to the next step until the present process run without any mistakes/defects.

Any mistakes/errors/defects are critical aspects of the business because all these lead to a loss in terms of money and affect the bottom line of the business.

Just think about miscalculations in the excel sheet or spelling mistakes in the presentation such minor mistakes may affect the business in terms of breaking relationships with customers/suppliers.

Another example – by mistake, your company sends a defective product to the market, which may destroy the customer’s trust in your company.

That’s why to prevent such errors or defects poka-yoke is a necessary aspect to have in any type of organization. By integrating this technique into the process, mistakes/defects are easily prevented and high-quality products are produced.

This mistake-proofing mechanism figures out the root cause of problems and prevents them from becoming bigger problems in the future. It reduces the need for rework and repair activities by making the product defect free at the first attempt.

Characteristics of the poka-yoke technique – 

• It is a simple, easy-to-understand technique and cheaper to implement for any type of organization.
• It is mistake proofing technique that is mainly designed to avoid mistakes/defects in the products or process.
• It is placed in the process where the actual defects/errors have occurred. That’s why it is not necessary to make changes in the whole process, only focus on the mistake or defect area.
• It helps improve the quality of products/processes effectively due to 100% defect prevention.
• It removes the need for continuous inspection by the operators because this mechanism focuses on the instantaneous prevention and detection of defects.

Principles of the poka-yoke technique – 

All the Poka-Yoke mechanisms are based on the 6 important principles which are divided into two categories. Elimination, Prevention, Replacement, and Facilitation principles belong to 1st category i.e. Prevent the occurrence of human error.

Detection and Mitigation principles belong to the 2nd category i.e. To minimize the effects after the occurrence of human error. Let’s understand these 6 principles one by one – 

1. Elimination – This principle focuses on the elimination of the possibility of error either by redesigning the product or process so that the process step or part is no longer necessary which means removing those process steps or product parts that cause defects/errors. Eg- Product or Process simplification.
2. Prevention – This principle focuses on the design of the product or process so that it becomes impossible to make a mistake in the process/product. Eg – Mobile charging socket and charger pin.
3. Replacement – This principle focuses on the use of substitute for a more reliable process to improve the consistency of process flow. This is useful when the operator can’t reduce the defects/errors produced by any process, so it is better to replace that process step with another. Eg – Automation.
4. Facilitation – This principle of Poka-yoke focuses on the implementation of new techniques and a combination of steps to make it easier to perform the process. Eg –  At the workplace, visual color aids help the workers mark different parts to ensure that parts get assembled together easily.
5. Detection – This principle focuses on the identification of errors/defects before further processing occurs in the process. This is done so that the operator can quickly correct and solve the problem in the process. Eg – A light indicator near the assembly line which shows a signal when the final assembly is ready.
6. Mitigation – This principle focuses on the minimization of the effects of the errors this means mistakes are not avoided but defects are minimized to a certain level. Eg – A stabilizer in the machine which maintains the fluctuation from low to high voltage.

Types of Poka-Yoke technique – 

The goal of the poka-yoke technique is to achieve zero defects in the process or products. It mainly has two approaches that you need to understand before learning about its types – 

• Control type approach – The goal of this approach is to make mistake proofing mechanism that makes it mechanically impossible for mistakes to be made. That means this approach focuses on controlling mistakes as far as possible.
• Eg- There is only one way you can insert your mobile charger plug into the electric board. So here there is no chance for any mistakes or errors.
• Warning type approach – This approach is useful when mistakes cannot be controlled in a human’s hand. The goal of the approach is to detect errors or mistakes instead of controlling them.
• Eg – A message pop-ups on your mobile screen when your battery gets low, it is nothing but the warning signal that you should charge your mobile before it gets switched off.

Now let’s see the 3 types of methods that are used in the mistake-proofing mechanisms to ensure the detection and prevention of mistakes. All these three methods can be applied in both types of error-proofing approaches i.e. control and warning approaches.

Contact method –

In the contact method. the physical attributes measurements (like size and color) are done by using sensors. This type of poka-yoke method detects any deviation in shapes, dimensions, color, or physical characteristics through the mechanisms that are kept in direct contact with the part.

This type of mistake-proofing mechanism is used in settings with environmental constraints such as inadequate illumination, poor visibility, critical temperature, etc. It is also a good method for situations where there is rapid repetition or intermittent production.

While designing a new product the contact method refers to adding asymmetrical appendages or modifying the part design to restrict the use of the product in only one orientation.

For example – In order to get a cache from the ATM,  ATM machines allow inserting the card in only one direction so that there is no room for mistakes.

2nd example – Inserting a USB cable into the laptop or computer can have two directions, but contact method mistake proofing helps you in showing the right way to insert the cable.

Fixed value method – 

This method is useful in processes where the same activities or tasks are repeated multiple times. In this method, the supervisor can fit an automatic counting device that helps the operator keep an accurate count at all times like the number of actions, rate, length of movement, etc.

For example – In an assembly line, if the operator requires 6 bolts to assemble a component then he gets only 6 bolts in the box (not more than or less than 6).

2nd example is the counter device that counts the number of products that passed through the device in the given amount of time.

Motion step method – 

When any process includes a huge number of steps and there is a probability of skipping them by mistakes then you can use this method of mistake proofing.

This method ensures that the operator does not mistakenly skip the important step of the process as well as prevents the operator from performing a step that is not part of the actual process. 

Example – The supervisor provides the checklist to the operator, so that the operator can finish his job in the right way by following the checklist and that checklist includes all the tasks written in sequence format.

2nd example – The operator can use color coding and tag the completed things/tasks at the workplace which means he can highlight all the completed tasks.

Now let’s see some of the important poka-yoke techniques that can help you prevent mistakes – 

1. Design for better efficiency –  This means the system must remove all the defects present in the product and then produce a higher quality product.
2. Use sensors to prevent the processing of defective products – By making use of sensors you can get to the defective parts of products and then it can be easy to remove all those which are found unnecessary.
3. Visual system to rectify the abnormalities – It can be seen that the visual method is better than any other method in understanding a system that means with the help of a visual system you can easily identify abnormalities. 
4. Prepare a checklist to outline the steps – With the help of a checklist you can easily understand how many steps can be completed in a process or a system.
5. A creative solution to avoid or detect errors – By doing this elimination of defects can happen and then directly leads to producing better quality products.
6. Verification to avoid the rework process – It is better to verify and evaluate each process so there will not be room for waste production.

Related content –5 principles of Lean manufacturing that you need to know

Examples of Poka-Yoke – 

Until now you understood the concept of poka-yoke in detail. It is useful in industry as well as in everyday life. There are a lot of examples you can find about mistake proofing at your workplace as well as in your home. Let’s see some of the practical examples of mistake-proofing – 

• USB cable can only be connected to the laptop/computer facing one side.
• The washing machine only starts when the door is closed and the door will not open until the one washing cycle is over.
• The microwave oven only starts working when you close its door.
• Elevator electric eye to prevent the door from closing.
• Gas pumps with automatic shutdown of nozzles.
• Many cars have automatic braking systems to stop the car if the driver fails to brake when an obstacle suddenly appears.
• Seat belts and airbags in the car.
• Car engine warning light.
• Spell check in word processing software or in the dictionary.
• Questioning “Do you want to delete” after depressing the “delete button” on your computer/laptop.
• Childproof caps on medications.
• Electric sockets are shaped in such a way that only one way of plugging in is possible.

Benefits of Mistake Proofing – 

There are many benefits to the poka-yoke in the improvement initiatives that’s why it is used in many industries today. Implementing Poka yoke into the process not only prevents mistakes but also produces high-quality output.

These defect-prevention mechanisms get to the root cause of problems and prevent them from becoming bigger problems in the future. This mechanism actually encourages all the operator’s accountability for excellence.

It eliminates defects and increases customer satisfaction by focusing on waste reduction and defect prevention. So applying this defect prevention tool in your organization can lead to a lot of other benefits. – 

• Reduce waste – Products which is manufactured with even minor mistakes are also considered defective products so by applying mistake-proofing in the processes you can save time by spending less time reworking defective products. It’s always faster and better to fix the defects earlier rather than later so that waste gets reduced.
• Reduce time – With the help of mistake proofing if you prevent all the defect or mistakes means there is no mistakes present in the process then process steps like verification or inspection is not necessary to be done.
• Operators also don’t need to look out for as many problems and simultaneously you also don’t need to spend much time on training them for the inspection process. Because mistake proofing mechanism automatically prevents and corrects the defects.
• Increase productivity – Processes at your organization will function more smoothly when defects/mistakes are prevented or detected and also solved immediately.
• Due to this processes become more efficient and produce good products with few waste results. This results in productivity increment.
• Boost continuous improvement – Poka-yoke is one of the best lean tools for defect prevention, which encourages the workers to prevent problems and solve them immediately and also find out their root causes to prevent them from becoming bigger in the future. All these activities boost continuous improvement at the organization.
• Improve safety – Mistake proofing not only prevents defects but also improves the safety of your organization because defects/mistakes may lead to an unsafe situation at the workplace which can be dangerous to the workers.
• So by preventing defects in the first place, this mechanism makes the workplace safe for daily working and hence improves the safety at the workplace.
• Increases the quality of products – The final product’s quality improves because of poka-yoke and everyone’s trust in the final products also improves. Stakeholders in the process know that process eliminates or reduces the defects.
• So no defective items are produced at the end of the process and hence waste also gets reduced as the elimination of mistakes is built into the process. All these increase the quality of products.
• Simple and inexpensive way of defect prevention – This is one of the best and simple to implement lean tools which can be used in any type of industry for defect prevention.
• Mistake-proofing implementation is not expensive as it can help you avoid relying on human inputs knowing that people do make mistakes.

Related content –8 types of waste in Lean that you can remove using mistake proofing

Application of Mistake Proofing – 

Mistake proofing is used in any type of organization because where there is a chance of error/mistakes poka-yoke can be used to prevent those mistakes.

This defect-prevention technique is used when a process or product is likely to have an error. Let’s see some of the important applications of this powerful tool.- 

• It is useful in all types of industries like service, manufacturing, IT software, administration, healthcare, pharmaceutical, etc.
• It is useful when a minor error early in the process may cause major problems in the later stages of the process.
• It is useful at a hand-off step in a process when output has been transferred to another worker.
• It is useful when the consequences of an error are expensive or dangerous.
• It is useful during the assembling phase, the employee may forget to insert a part that should be in the final assembly.
• It is useful when faulty memory can cause an employee to miss a process step.
• It is useful where there are processing errors, missing parts errors, setup errors, production errors, measurement errors, operations errors, etc.

Conclusion – 

Poka-yoke is one of the most innovative and inexpensive tools from the set of all Lean tools. This tool is the best way to get quality outputs from the process by preventing defects or errors. There is no limitation to using this powerful tool, it can be applied in any type of industry.

In this article, I discussed poka-yoke in detail like its principle, characteristics, and importance in the industry, I also discussed 3 important types of mistake-proofing mechanisms along with the benefits and different applications of error-proofing. I hope this article helped you understand the mistake proofing.

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