The Use of "Poka Yoke" with Medical Device Design and Manufacturing

In 1961, a Japanese manufacturing engineer named Shigeo Shingo working at Masushita Electric developed the idea into a formal tool for achieving zero defects and eventually eliminating quality control inspections. The term "poka-yoke" generally translates as "mistake proofing" or as "to avoid inadvertent errors."

The value proposition to implement Poka Yoke into Medical Device Manufacturing is an increase in product yields and a reduction in rework and scrap. The great thing about poka-yoke is that implementation can be very simple and very effective.

The idea is to respect the intelligence of workers by taking over repetitive tasks or actions that depend on vigilance or memory, and free a worker's time and mind to pursue more creative and value-adding activities.¹ A poka-yoke device is any mechanism that either prevents a mistake from being made or makes the mistake obvious at a glance.²

The concept is widely used in everyday examples but you may not have noticed:

• USB and HDMI cables are designed so they can only be connected one way.
• The irritating sound that is triggered when you leave your lights on in your car and take the keys out of your ignition (it beats a dead battery any day)
• When you put together toys for your kids, the parts are designed so they can only go together one way (okay, they're not always perfect but they have gotten better over the last several years).

Why Should I Implement It?

The value proposition to implement Poka Yoke into Medical Device Manufacturing is and increase in product product yields and a reduction in rework and scrap. The great thing about poka-yoke is that implementation can be very simple and very effective.

What about the bottom line?

• Lucent Technologies reported that half of their 3,300 mistake-proof devices cost less than $100 while creating a net savings of $8.4 million.
• Varian Ion Implant Systems saved over $1 million dollars on installation, start ups and warranties on their new product launch.
• If the product is recalled from distribution, what does that cost in your company?

As more products are provided in the home care setting, the need to implement this methodology is even more important. Imagine you have an insulin pump and require a 0.5 mg bolus; would you happy to know that you could give yourself 5.0 mg instead?

Where Can I Implement Poka Yoke?

Poka yoke is the most effective when a company's attitude is that it's better to have one million one-dollar improvements than one million-dollar improvement. If the company culture asks everyone to identify at least one improvement per week, this can quickly accumulate to a large cost savings.

Mistake-proofing can be implemented into the manufacturing process but it is certainly the most effective when it is incorporated into the design of the product. If the parts can only be assembled one way, then you've eliminated errors (and assembly time) within the production area. If it can't be implemented into the design, the tooling or manufacturing aids may be another area for implementation. If it can't be integrated into the tooling then other items like sensors, limit switches or counters can be very effective.

Poka Yoke is most effective when it falls into two major categories: prevention and detection. In a prevention approach, the design makes it impossible to commit a mistake at all. A classic example of a prevention design is the USB plug design. The connection is carefully engineered to be slightly asymmetrical so that it will not fit into the mating connection in any orientation other than the correct one. Prevention designs remove the need to correct a mistake, since the user cannot make the mistake in the first place.

A detection design signals the user when a mistake has been made, so that the user can quickly correct the problem. Line clearance methods that verify the number of components used equal the total number of finished devices completed. As an example, the number of pouches are counted to equal the lot quantity to be shipped. When the last device is sealed in the pouch, the worker should not have any pouches left. If there are too many or not enough, this alerts the worker that something was forgotten. Detection devices typically warn the user of a problem but they do not enforce the correction.

How Do I Implement It?

• Start by picking one of these three points of view: the actual user of the device, the manufacturing and assembly process or the design. Most likely, your review will cover the other items but trying to keep it focused on one element will help you be more effective.
• Get the right people together to discuss the review of the product. If it's the end user, try to get a clinician or someone that uses your device. One recommendation is to have the Manufacturing Technician in these conversations. Once they hear how and why the device is used, they will have some great ideas for improvement.
• From the design perspective, review the features of the components and how they are assembled. Are there parts that are symmetrical but have to be put together in a certain orientation? Here is a great example of looking at what assembly issues might happen and adding features into the design to prevent them.⁴
• Don't wait to the end of the process to perform the inspection of a critical process or attribute. The inspection can be done with a simple template or overlay but the most effective method is when the solution is part of the tooling. As an example, the fixture used to bond the two parts together as designed so that the part can only be put into the fixture in the correction orientation.

What is the Best Book for Poka Yoke?

"Poka-Yoke, Improving Product Quality by Preventing Defects" also known as "the Big Red Book" (Productivity Press), is one of my favorites. The book is full of practical examples and diagrams of great ideas, showing preventative error examples as well as the Poka Yoke functions (shutdown, control and warning). Sometimes, these concepts are best explained with pictures and examples.

What are the Five Best Poka Yoke?

The idea of poka yoke is that the workers don't go to work thinking that they are going to make a mistake. "Mistakes are inevitable; people are human and cannot be expected to concentrate all the time on the work in front of them or to understand completely the instructions they are given. Defects result from allowing a mistake to reach the customer, and defects are entirely avoidable.¹"

As described in the "Big Red Book," there are five examples for detecting or avoiding defects caused by human error:

1. Guide pins of different sizes - prevents the two mating parts being put together incorrectly, such as a stamping die


2. Error detection and alarms - if a door to a CNC machining center is opened, the lights starts to flash


3. Limit switches - the worker needs to push down on a special cutter so it will cut through the material. When the cutter touches the limit switch, the light on the machine illuminates


4. Counters - digital counters are great tools to help workers. These devices can be attached to machines and will count repetitions so the worker can cross-verify against the total output of components.


5. Checklist - this is an easy tool to implement and very effective to highlight important items to verify

Summary

The Poka Yoke method is something that improves your daily life; why not use it to make your product better, as well? The best solutions are simple, quick to implement and 100 times more effective than a 100-percent final inspection.

References

1. "Poka-Yoke; Improving Product Quality by Preventing Defects," Hirano, Hiroyuki, Productivity Press, 1987.
2. "A Brief Tutorial on Mistake-proofing, Poka-Yoke, and ZQC," John R. Grout, and Brian T. Downs, www.isixsigma.com.
3. "Poka-Yoke; Improving Product Quality by Preventing Defects," Page 24-25, Hirano, Hiroyuki, Productivity Press, 1987.
4. "Poka Yoke designs make assemblies mistake proof," Paul Dvorak, Machine Design, Page 181-184, March 10, 1998.