In any type of business, mistakes and errors can happen. In processes where manual work is done, human errors can occur. Apart from human errors, machine errors or malfunctions happen. Both of these can cause defects. As a response, we install controls or use inspection points to prevent or catch these errors. This is what poka yoke is about.
What is Poka Yoke?
The Toyota Production System is built on the objective of establishing efficient and defect-free processes. Poka yoke is one of the pillars of the Toyota Production System and was established through jidoka. It translates to mistake-proofing or error-proofing in Japanese. It was Shigeo Shingo, one of the industrial engineers working with Taiichi Ohno, who developed and coined the technique in the 1960s. It has since been used not only on the shop floors of Toyota but in various manufacturing companies as well. The concept of mistake-proofing has also been used in other areas such as product and system design.
The purpose of poka yoke is to prevent errors from happening or catch them before they come out of the production line. Errors are detected through physical devices that determine whether products from a step in the process have passed quality standards or not.
Types of Poka Yoke
Poka yoke can be classified into two main categories:
- Control – Taking physical action to prevent defects or errors from occurring
- Warning – Sending signals when a defect or error has occurred
They can be further classified into three types: Contact, Fixed-value, and Motion-step.
Contact Poka Yoke
Contact type poka yoke uses methods to detect physical abnormalities or deformities such as size, shape, color, or weight, to prevent errors. An example is a three-pin plug that can only be inserted in a socket that matches its prongs. Another one is a USB which can only be inserted in a port when it’s following the desired orientation and size.
Fixed-value Poka Yoke
Fixed-value type poka yoke uses both physical and visual methods to detect whether all components of a part are present and are in the right quantities. They are often used together with contact type poka yoke to make errors more visible. An example is an egg tray container. An empty hole will mean the desired quantity has not been met. Another is a sensor that detects whether a box of crayons has all the colors needed. If not, then it will stop the line and signal the error.
Motion-step Poka Yoke
Motion-step poka yoke uses devices and methods that ensure all necessary steps have been taken before a part or product can go to the next step in the process. This type is particularly useful for processes where workers perform different steps repetitively to create a product.
Having all necessary steps done means that certain outcomes have been achieved. If the desired outcome is not achieved, it would mean that a step has been missed. When this happens, the production line is put to a halt to prevent succeeding defects and will only resume once the issue is resolved.
Poka Yoke Design Examples
Poka yoke devices provide fast and effective feedback to alert workers of defects. It’s used extensively in manufacturing. Some examples of poka yoke used in manufacturing include:
- Locator pins
- Guide pins
- Proximity switches
- Alarms
- Error detection systems
- Color codes
- Sensors
- Checklists
- Warning signs
This method is not only used by manufacturing or production-type companies. Unknowingly, we encounter poka yoke in our daily lives. The concept of mistake-proofing has become an essential part of product design. Companies now incorporate poka yoke design techniques to ensure end-consumers can use products without incurring mistakes or errors. Here are some examples of poka yoke in real life:
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- Elevator door sensors – Prevents the elevator door from closing when someone is between it.
- Child-resistant caps on medicine bottles – Prevents undesired consumption of the drug.
- Car safety features – There are a lot of mistake-proofing designs in a car. From the dashboard you can immediately see if something is not working as intended. Alarm sounds go off when the seatbelt is not fastened. The same happens when the car is in motion but the handbrake is activated.
- Washing machine control functions – A washing machine will only work when the door is closed. Preventing water from leaking while washing. It also has a safety lock that ensures the door can’t be opened until the cycle is complete.
- Spelling and grammar checker – Communication and documentation apps and software we use in our computers and mobile phones usually come with error-proofing functions. It highlights misspelled words and grammatical errors.
Benefits of Poka Yoke Method
Incorporating error-prevention and detection within the process helps ensure only quality products are delivered to customers. Other benefits of poka yoke include:
- Increase in customer satisfaction
- Decrease in customer complaints and warranty claims
- Lessen costs due to after-sales issues
- Easy and not expensive to implement
- Help ensure worker safety within the production floor
- Enables workers to have a kaizen or continuous improvement mindset as they devise ways to make the process error-proof
Error-free processes lead to higher levels of quality in products and services. By using poka yoke in your process design, you can strengthen your process efficiency and optimize your production capacity.
