Poka Yoke

In this article we will discuss all about Poka Yoke. Poka Yoke is a method or tool for avoiding mistakes or error. You can imagine what will happen if there is no error or mistakes in this world !!!. Yes, that’s the importance of poka yoke.

We will be discussing about mistakes, principles of error, examples of poka yoke, importance of poka yoke, how to implement poka yoke and benefits of poka yoke.

Before we move further some words about mistake…

What is mistake or error

A mistake is an action or judgement which will adversely affect our objective or aim.

An example : Suppose we are going for a journey and in our journey we took a wrong way and we were 4 hours late to our destination. Here mistake is taking wrong way.

What will happen if we do a mistake

You can see in our example, we lost our precious enjoying time and fuel.

Hope you understood about mistakes.

Let’s see some examples related to manufacturing…

1. Processing error
2. Operation error
3. Missing parts
4. Missing information
5. False or wrong parts
6. Damaged Materials
7. Human Errors

All the above activities adversely affects:

1. Customers (Defects)
2. Employees (Injuries)

Which finally will results in waste or increase in cost

Now we are ready to discuss about poka yoke.

Let’s dive in…

What is Poka Yoke

Poka Yoke is the Japanese term, meaning: “mistake-proofing”

This term represents, methods or tools which avoid mistake or error

The main purpose of this tool is to prevent or eliminate the product defects by taking correct preventive measures.

Poka Yoke is also called as: Mistake proofing, Fail-safe, Idiot proofing, Fool-proofing

Principles of Poka Yoke

Mistake proofing or Poka yoke mainly focuses on following points…

1. Elimination: Eliminate the possibility of defects or errors by redesigning the product or process. Example: 1) Redesigning of mobile chargers i.e. from micro USB OTG chargers to new C cable chargers, which can be pugged to mobile in any of two ways instead of one way in micro usb otg chargers. If we try to plugin the micro usb otg in wrong way it may results in damage. 2) Also as an another example, if a welding process is causing error, eliminate the welding process by finding another solution for welding.
2. Replacement: Implementation of more reliable process or equipment to improve repeatability. Example: Use of automation instead of manual work
3. Prevention: Objective is to eliminate any chance of committing mistakes; To make sure things never go wrong. Example: 1) Electronic machines gets shutdown when overheating is observed with the help of sensors. 2) Some vehicles do not start when clutch is not engaged.
4. Facilitation: Actions taken or improvements done for making the work easy and mistake proof. Example: 1) Using visual controls like color coding and labelling to make work easier to perform 2) Using templates for fixing labels on a product.
5. Detection: An arrangement for detecting an error when it occurs and prevents further processing. Example: Use of sensors to detect any missing parts or incorrect assembly.
6. Mitigation: Mechanism that reduces the impact of errors or defects. Example: Electric fuse: When overloading is observed, fuse protects from over current as safety device

Examples of Poka Yoke

1. Car safety features: Car door alarms, seat belt alarms
2. USB drive: One cannot insert USB drive upside down, it is designed to prevent mistakes
3. C-Cable charger: Can insert in mobile by any side to prevent error
4. Elevator: Alarm system when lift door is open
5. Spell check: Grammar and spell check feature in Microsoft
6. Smoke detector: It detects smoke and prevents major accidents

Why to use Poka-Yoke:

1. Prevention is better than cure (in this case: Detection)
2. This tool can be applied in any process
3. It mainly focuses on critical functions and actions
4. Source of defect can be identified and permanently eliminated
5. Every inspection methods has weakness and loop hole

When to use Poka-Yoke:

1. Processes where there are more chances of human errors, especially when process relies on skill, attention or experience of human
2. In service sector, where customers can make mistakes by giving wrong details to representatives which can cause errors
3. When minor errors in beginning are not addressed, it can result in major problem later in process
4. When consequences of small error are dangerous to human life
5. During the development of new product to reduce cost in design

How to implement Poka Yoke

There is no particular guidelines or standard procedure to apply poka yoke. It can be implemented at any time and any step of the process, where one can find mistakes or something goes wrong.

Step 1 : Identify the defect and track it down: This can be done by using some of the most common problem solving techniques. For instance: Data gathering, Statistical methods, Simulations.

Step 2 : Review the existing Standard operating procedure (SOP): By studying the regular practices followed by workers, their behaviour and various theories can be studied to find the source of mistakes

Step 3 : Study if there are any deviations or variations in the process and calculate the efficiency of the process and man power

Step 4 : Use “Root cause analysis” like 5 whys or fish bone diagram to identify the main causes of the events.

Step 5 : Identify the point where the deviation is formed and make a checklist and study the circumstances that triggers the creation of variation.

Step 6 : Take actions considering the principles of poka yoke and develop the error proofing devices based on following poka yoke methods.

Contact method: The contact method identifies the shape, size, color, weight etc using sensors or locating pins and detects and prevents the abnormalities to occur. Some method in contact method not only detects the error but also it will prevent the error to occur. For example, if a part comes with different shape or dimensions it will not be able to locate in specified place when locating pins are properly located.

Counting method: This method is used when there are particular steps or fix number of operations within a process. It develops such an error proofing sensors which counts the number of times procedure takes place and release the product only, when the count matches the right count.

Motion- Sequence method: It uses sensors to determine, if a particular motion is occurred or not. If step do not occur, sensor gives signal to machine or alarm, and machine is stopped immediately.

Benefits of Poka-Yoke:

1. Elimination of errors before they occur
2. Elimination of accidents
3. Eliminate Non-Value activities
4. Helps to implement continuous improvement approach : The use of poke yoke is to prevent mistakes and help people to do work right and correctly in the first time. Because of this approach it helps to improve quality also by saving time and increases reliability of the process and product by eliminating defects.
5. Reduce number of rework and defects
6. HAPPY CUSTOMERS !!!
7. Helps to implement “ZERO DEFECT STRATEGY”

A word from my heart

Ideally, Mistake proofing should be considered at the start of any process or at the developing stage of new product to take maximum benefit of this tool. It gives more chance to eliminate or prevent or detect any errors at the beginning of process. Once the product is designed and manufacturing is started, it becomes more limited to implement error proofing methods.

However, Removing Human errors or any kind of errors are crucial for any type of business. If not eradicated on time, it costs money and impact customers satisfaction. Just by implementing and introducing small and simple measures to stop errors, organisation can save tons of money and man power as well as company becomes more efficient.

Thank You.

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About the Author

Jay Desai has over 4 years of experience in Lean Six Sigma, Operations Management and Production Engineering. A post graduate in Computer Integrated Manufacturing from Nirma University. He has successfully delivered Lean deployment, training and project coaching at many levels within customers organization as well as delivered educational programmes.