When a consultant shows a factory how to implement a poka-yoke (mistake-proofing) system to get rid of frequent mistakes committed by operators, they are often surprised by the benefits of mistake-proofing. However, anybody with a dose of creativity and an understanding of the main types of poka-yokes can come up with good ideas.
Here are the 6 main types of mistake-proofing techniques:
6 Commonly-Implemented Poka-Yoke (Mistake-Proofing) Techniques You Might Have Missed
1. Changes to Die Design for Efficiency
In some operations, a die is necessary, e.g. a stamping die, and can be placed incorrectly. That error can result in product quality issues and in damage done to the die.
How to avoid this? By only making it possible to place the die in one way. This can be realized in many ways. One approach is to have guide pins of different sizes so that they can only “fit” in one direction. There are many other methods for fixing the die position.
2. Changes to Fixture Design for Consistency
This is relatively similar to point 1, with a key difference: the part being worked on can be placed the wrong way into a fixture, resulting in quality issues.
The fixture can be modified in order to make it impossible to place the part incorrectly. (Sometimes, the design of the part itself has to be changed for the same effect.)
You can see a simple example in the short video here.
3. Sensors to Prevent Processing of Defective Products
The most common sensors are listed below:
- Limit switch – convenient when a part is in contact with a tool/fixture.
- Proximity sensor – a good solution when a part is/might be at a certain distance.
- Infrared sensor – appropriate for checking presence from a distance.
There are many scenarios in which a sensor can detect an issue. We show 3 mistake-proofing examples that use sensors in our free e-book.
Now, don't go overboard with sensors. There are sometimes lower-tech, cheaper, and easy-to-maintain approaches.
Let’s say some parts move on a conveyor. A few of them have a defect and are taller. The “obvious” countermeasure is a sensor that detects that abnormality. But a better approach is to place a stick that will block the way to all defective parts and push them into a red container on the side of the conveyor. It is faster and cheaper to implement, it is easier to maintain, and it immediately acts on its findings!
Enjoying reading about mistake-proofing? Explore the topic in more detail by reading our FREE eBook with 14 Mistake-Proofing Examples.
4. Vision System to Rectify Abnormalities
In simple terms, a vision system captures images, analyzes them, and triggers an action in pre-determined cases. It does not require contact with the product.
For example, it might detect that a part is poorly positioned, that a component (or labeling element) is missing, that a step was done before another, etc. As a response, it might sound an alarm, or it might make it impossible to proceed (often by stopping a piece of equipment) until a positive change is made.
This approach appeared in the 1980s in a simple form and has kept improving since then. It doesn’t appear in the Poka-Yoke red book that seems to include examples dating back to the 1960s.
I have seen vision systems that use consumer electronics (cheap webcams if the environment is not very dusty) and require relatively little programming. With the advances in artificial intelligence/machine learning, vision systems will get better and better. Remember, a Tesla car can pretty much self-drive based on cameras alone!
5. A Checklist to Outline Steps
By any standard, a checklist is one of the weakest mistake-proofing techniques. It does help a lot when no other approach listed above is possible and when operators are trained and careful – think pilots in a plane.
The more a checklist’s elements are integrated into the work content, the better. Think of color codes where a checklist step matches a certain tool. Or a form to fill out that contains the steps in the right order.
6. Creative Solutions to Avoid or Detect Errors with Minimal Investment
Poka-yokes are a science but also an art. Think this way and you will see many opportunities that will take different shapes depending on the application.
For instance, some errors are made when pressing the wrong button, if the use interface is unclear. A very simple change can help prevent those errors, as shown in this short video.
Here is another example. A tool might require much manual precision from the user. To improve quality and productivity at the same time, improving the tool is sometimes possible, as shown in this video.
We show 2 creative applications in our free e-book, but a researcher could probably list hundreds of them.
Is Mistake-Proofing Only Used in Manufacturing?
With many types of mistake-proofing systems improving product quality in factory processes, poka-yoke occurs in daily life too:
- Your washing machine won't start if the door is not closed.
- The pump at the gas station won't keep providing fuel once your tank is full.
- Airline pilots strictly follow a set of pre-flight checklists. Doctors and nurses do the same in hospitals.
- Forcing trucks to get under an obstacle at a certain limit, before they get under a bridge of the same height. It can be seen in Japan.
Poka-Yoke FAQs
How is Poka-Yoke Different from Defensive Design?
Poka-Yoke and Defensive Design both aim at error prevention but differ in scope and application. Poka-Yoke is a specific technique focused on mistake-proofing to eliminate errors or defects. Defensive Design is a broader concept that includes various approaches, including Poka-Yoke, to prevent issues or confusion across different contexts and industries.
Where Does the Poka-Yoke Concept Originate From?
The Poka-Yoke concept originated from Shigeo Shingo, a Japanese engineer who consulted for companies like Mazda, Mitsubishi, and Toyota during the 1940s to 1960s. Shingo aimed for "zero quality control," a state where quality issues are prevented or caught at the source, eliminating the need for inspectors. He initially termed it "baka yoke" (idiot proofing) but later refined it to "poka-yoke" to focus on preventing inadvertent errors.
Why Isn't Error-Proofing Applied More Systematically in Manufacturing?
Error-proofing isn't more systematically applied in manufacturing for three main reasons. First, people, including process engineers, are often optimistic and pressed for time, overlooking preventive measures. Second, there's a tendency to not address issues at their root; operators are blamed while designers move on to other projects. Third poka-yokes can add inconvenience or time to the process, leading operators to skip them, especially under tight deadlines.
What Are the Most Common Types of Poka-Yoke Devices?
The most common types of Poka-Yoke devices are physical guides, warning alarms, and automatic shutoffs. Physical guides ensure correct positioning or alignment, warning alarms alert operators about potential errors, and automatic shutoffs halt processes to prevent mistakes.
How Do You Measure the Effectiveness of a Poka-Yoke System?
The effectiveness of a Poka-Yoke system is measured by tracking key performance indicators such as error rates, product quality, and production efficiency. A successful Poka-Yoke system will show a decrease in errors and an improvement in overall product quality and process efficiency.
What Are Some Poka-Yoke Examples In a Factory Setting?
In a factory setting, common Poka-Yoke examples include color-coded components for easy identification, physical guides to ensure correct part alignment, and warning alarms for out-of-spec conditions. Using better manufacturing gloves and improving task division are examples of Poka-Yoke in an electronics manufacturing environment.
To Conclude
There are many other types of devices and systems that reduce human errors without requiring a heavy investment. Some of them actually add a step to the process (for example, kitting components together before assembling them usually results in fewer missing parts and in faster assembly) and typically don’t qualify as a method of mistake-proofing. Others cost virtually nothing and cut defects by 80%.
In many industries, this tool is the best way to reduce defects from about 3% to a tenth of that. That’s a major component of ‘jidoka’, which is one of the 2 pillars of the Toyota Production System.
If you are now ready to implement poka-yoke, you can learn how to do it effectively in this blog post on mistaking proofing effectively.
Do you have any questions about mistake-proofing, or examples of where it has worked for you to share with our community?
In this blog post I covered some mistake-proofing examples relatively briefly, but if you would like to explore it in greater depth, you can find 14 detailed examples in our FREE e-book below:
