Did you notice that, you can NOT start your car without keeping the gear in neutral and pressing the brake. Why it is so? It is so protect you from accidentally starting and moving your car. That’s Poka Yoke, A mistake proofing logic to help you not doing any mistake. Let’s learn more about Poka Yoke, Poka Yoke Definition, meaning and some poka yoke examples in this article.
- Poka Yoke Definition: Poka Yoke Meaning
- History Of Poka Yoke
- Why Poka Yoke is needed: Benefits of Poka yoke
- Principles of Poka Yoke
- Approach Of Poka Yoke
- Types of Poka Yoke
- How to implement Poka yoke
- Example of Poka yoke
- Disadvantages of using Poka yoke
- Frequently Asked Questions ( FAQ’s)
Poka Yoke Definition: Poka Yoke Meaning
Poka Yoke is a Japanese term which means ” Mistake Proofing“. It is a mechanism in the process to avoid ( Yokeru) mistakes ( Poka).
Mistakes are unavoidable in a process. But what we can do is to reduce the chance of doing the mistakes. If there are less number of opportunity to do a mistake, there will be less number of mistake.
Poka Yoke triggers a modified process flow or a new process flow so that there are less chances of doing a mistakes. Following this, a product will have less defects as there are less chance of doing a mistake.
Recommended Read: Types of Fit in engineering
History Of Poka Yoke
The concept of Poka Yoke was initiated by Shigeo Shingo in 1960 as a part of Toyota Production System in Japan. We all know that ” Necessity is the mother of invention” . The same is true with Poka Yoke.
Below is one story of a real incidents which gave birth to Poka Yoke
That time in the production line of Toyota, There was a switch , under which the operator has to put two springs. Often, operator forgets to assemble one spring. Unfortunately since the spring was assembled under the switch, the issue was very difficult to diagnose which lead to switch rejection.
What Shigeo Shingo did is that he introduced a new placeholder in the production line where the operator has to keep the two spring first, and then the operator needs to assemble those springs. Since those two springs were placed in a placeholder, so operator never forgets to assemble both the screw. With this they could able to reduce defects. Though this whole concept looks very simple, but this solution helped Toyota to save millions of switches getting rejected.
With this you might have understood that the concept of Poka Yoke is very simple and straightforward, It just reduce the chance of doing the mistake and that yields in less defects.
Why Poka Yoke is needed: Benefits of Poka yoke
To understand why Poka Yoke is needed, we need to understand what implication a defective part can have on the consumer/ supplier/ distributor or any end user. No one likes defective parts. Right? Defective part is a waste in a production system. Below are few severe impacts of having a defective part.
- High rate of rejection
- Functional failure of a product
- Increased rate of service calls
- More product recalls
- Regulatory disapproval
- Blacklisting by product safety agencies
- High risk to end user
- Loss of market share
- Bankruptcy of business
Now that we know that a defective part or product has too much of impact, let’s understand how Poka Yoke can help on those matters specially in the production line.
- Reduce part rejection
- Less chance of product failure
- Less quality inspection cost
- Improved product safety
- Improved production flexibility
- No risk of disapproval from regulatory and safety agencies
- Better customer satisfaction
- Better market share
Principles of Poka Yoke
Poka Yoke works on two broad principles.
- Prevention of occurance of human error
- Detection of error after occurance of human error
Now this broad principles are further decided into multiple pricicples as shown below.
Principle of occurance of human error has couple of sub principles.
The detection principle also has few sub principles.
Elimination works on the methodology to eliminate any process that might cause the human error. It can be done done either by redesigning the product or process work flow.
When a error prone process can not be eliminated or redesigning the product is too costly than the error itself, then prevention is the only solution. Prevention make the process so robust that their will be no chance of any human error.
When both elimination or prevention does not work, a more reliable process get introduced to replace the existing process. That when the Poka Yoke for replacement comes into picture.
Faciliation encourage to have a better and simplified process flow so that there is less chance of an error.
When already an error has occurred, it is always better to stop it as soon as possible. Detection in Poka yoke works on that principle.
When it is impossible to detect and stop the error, the next best solution is to mitigate the risk by reducing the number of error.
Recommended Read: Welding Defects: Types and how to avoid those defects
Approach Of Poka Yoke
Typically there are mainly two approach of Poka Yoke system that industries use.
- Warning Poka Yoke approach
- Control Poka Yoke approach
Warning Poka Yoke
Warning Poka Yoke alerts operator that an error is about to happen so that they can take action.
Control Poka Yoke
In control Poka yoke , a device or process is implemented so that the error can be stopped from happening even if the operator ignore the warning.
Types of Poka Yoke
There are mainly three types of Poka yoke.
- Contact method Poka yoke
- Fixed value Poka yoke
- Motion step Poka yoke
Contact Method Poka yoke
Contact method Poka yoke detects the defects of a part by measuring it’s physical charecterestics like length , height, volume etc. Since the Poka yoke mechanism comes in direct contact with the part, hence it is called contact method .
Fixed value Poka yoke
If any operation need to be performed multiple times then a Poka yoke device is installed to make sure that the operation is performed for that many times. Since it counts the number if repeated operation, hence it is called fixed value method.
Motion step Poka yoke
Motion step Poka yoke checks if an operator has performed all the required function or not. It ensures that the operator does not miss any step or does not do a step which is not required.
How to implement Poka yoke
To implement Poka yoke you need to consider following steps.
- Identify the defects
- Identify the source of defects
- Create a Poka yoke device or process
- Maintain the Poka yoke
Identifying the defects and the source of defects is very essential to implement Poka yoke. Once source of defects are found , all stakeholder should sit and discuss on a potential poke yoke method to stop the defect. Once a Poka yoke device or method is implemented, there should be a dedicated team to monitor the effectiveness of Poka yoke.
Creating a Poka yoke is different for different defects. Some company use their standard method to find a defect and implement a poke yoke. Although the Poka yoke philosophy is same but the implementation methods are different from company to company.
Recommended Read: AutoCAD Vs SolidWorks
Example of Poka yoke
Below are couple of Poka yoke example though which you can relate the Poka yoke philosophy in day to day life.
1. Press brake and put gear in neutral to start a car
This is a perfect example of Poka yoke. The system protects the driver from doing a mistake of moving the car accidentally. If the Poka Yoke was not implemented, there could have been numerous errors by drivers
2. Mobile phone charging stops when it is fully charged.
We all know that the even if you keep your mobile phone in charging, it does not overheat and does not catch fire. This is due to the mistake proofing mechanism kept in place to break the circuit when the phone is 100% charged.
3. Different size fuel nozzle for different fuel
Did you notice you can’t put a diesel fuel nozzle in a petrol car fuel tank? This is because the nozzle diameter is different for petrol and Diesel fuel injectors. This is saving the driver’s from injecting wrong type of fuel.
4. Washing machines shuts down when the lid is open
You might have noticed that if you open a washing machine lid, the machine stops automatically. This is to protect people from getting hurt and leverage the risk of water spillage.
5. Circuit breaker
Circuit breaker break the circuit when there is over voltage and there is a chance of fire. The circuit breaker automatically breaks the connection to save you.
Disadvantages of using Poka yoke
Although there is no such disadvantages of using Poka yoke but it affects the initial part or process setup cost. Since Poka yoke introduce new process or device in the system , so it add up the initial setup cost.
Also since Poka yoke uses additional control method to detect defects, it increases the cycle time of manufacturing. A dedicated expert team is also required to implement and maintain Poka yoke, which is again an additional cost and use if resource.
Though implementing Poka yoke increases initial setup cost, but ultimately it saves lot of money by reducing defects. It helps to make great products which ultimately increases customer satisfaction and confidence.
Poka yoke is a science as well as an art. When implemented properly and efficiently, it can give you the best outcome. Though I listed just a few Poka Yoke examples, but there are hundred of such examples you may find in your day to day life.
That’s all I have in this article. It’s next to impossible to cover such a huge and critical subject with only one article. But I just tried to cover as much as I can so that you Atleast get the basics.
If you do have any question or want to know more about Poka Yoke, please do let me know in the comment section and I will be happy to respond to all your questions.
Frequently Asked Questions ( FAQ’s)
What is Poka Yoke?
Poka Yoke is a mistake proofing methodology that reduce the chances or opportunities of doing any mistake.
Poka Yoke Can be used in product design?
Yes, Poke Yoke philosophy is used widely used in product design. In fact, now a days its a must to implement poka yoke in product design
Poka Yoke can be only used in Manufacturing?
No, Poka yoke can be used in service industry, software development industry or any industry where there is a chance of doing mistakes
Implementing Poka Yoke adds additional cost?
Yes, when you implement Poka Yoke, there is an initial set up cost. But in the long run it saves lot of money for companies by reducing defects.