3D Printed Poka-Yoke is a Gateway Drug for 3D Printing


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Recently, 3NTR‘s Davide Ardizzoia mentioned “poka-yoke” in a LinkedIn comment about a vacuum forming post I wrote. It inspired me to reconsider just how Lockout Tag Out (LOTO) tooling could be a gateway drug for 3D printing and how poka-yoke could, as well.

We have a problem in engaging and permeating our technology through large organizations. So far, something that has really worked for us is to get started with jigs and fixtures and, through that application, find more use cases where we can inexpensively solve problems that that company has. Through this method jigs and fixtures have been a gateway drug for 3D printing to grow inside businesses in a friendly, problem-solving way. In addition to our technology acting as industrial Duck Tape for solving your problems, I think that jigs and fixtures, LOTO tooling and 3D printed poka-yoke could be very valuable entry paths into companies that could help them industrialize 3D printing later on. All of these paths into firms demonstrate how we can make parts that solve problems and help the business and employees get ahead quickly and at a low cost .

An example is your SIM card.

So, what is poka-yoke? Poka-yoke is a methodology that finds its roots in the Toyota Production System (TPS) which itself is an integrated approach to produce less waste, fewer mistakes, and manufacture more efficiently. A key evangelist and teacher of the Toyota Production System was Shigeo Shingo who wrote the book “Zero Quality Control Source Inspection and the Poka-Yoke System.”

A positioning system by Volkswagen.

In it, he mentions that the goal of a poka-yoke is to, “Use source inspections, ie, inspections for preventing defects, to eliminate defects entirely. This does not mean dealing with the results of defect generation, it means applying control functions at the stage where defects originate” and urges us to “make a clear separation between errors and defects. Defects arise because errors are made; the two have a cause-and-effect relationship” while telling us to, “recognize that people are human and set up effective poka-yoke devices accordingly. Pokayoke devices fulfill control functions that must be effective in influencing execution functions.” 

There are six general principles,

  1. “Elimination (“don’t do it anymore”) is to eliminate the possibility of error by redesigning the product or process so that the task or part is no longer necessary.
  2. Prevention (“make sure it can never be done wrong”) is to design and engineer the product or process so that it is impossible to make a mistake at all.
  3. Replacement (“use something better”) is to substitute a more reliable process to improve consistency.
  4. Facilitation (“make tasks easier to perform”) is to employ techniques and to combine steps to make work easier to perform.
  5. Detection (“notice what is going wrong and stop it”) is to identify an error before further processing occurs so that the user can quickly correct the problem.
  6. Mitigation (“don’t let the situation get too bad”) is to seek to minimize the effects of errors.

Elimination, Prevention, Replacement, and Facilitation are to avoid the occurrence of mistakes. Detection and Mitigation are to minimize the effects of mistakes once they occur.”

Generally there are two main types of this type of device:

“The control poka-yoke does not allow a process to begin or continue after an error has occurred. It takes the response to a specific type of error out of the hands of the operator. For example, a fixture on a machine may be equipped with a sensing device that will not allow the process to continue unless the part is properly inserted. A 3.5-inch floppy disk will not work if inserted backwards or upside down. As a matter of fact, it won’t fit into the drive at all unless properly inserted. A second type of poka-yoke provides some type of warning when an error occurs. This does not prevent the error, but immediately stops the process when an error is detected. This type of poka-yoke is useful for mass production environments with rapid processing as the device prevents mass production of scrapped material. For environments where large losses of time or resources do not result, a warning poka-yoke is warranted. All that is needed is a way to ensure that the error is investigated and corrected in a timely manner.”

How delightful it is to think of floppy disks again.

These students show us a poka-yoke example whereby a corner of a sheet is cut and a 3D printed part matches up with it so people don’t put the sheet in the machine incorrectly.

The above is a “contact” method while “fixed value” methods of implementing poka-yoke focus on their being, for example, a vacuum-formed tray that holds exactly the right amount of screws. “Motion step methods” could give off a warning if a certain step hasn’t been completed. “Self-checks” are quick methods for verifying whether or not something has been done correctly by letting a worker run through what she just did for example.

This is the classic poka-yoke example:

“Suppose a worker must assemble a device that has two push-buttons. A spring must be put under each button. Sometimes a worker will forget to put the spring under the button and a defect occurs. A simple poka-yoke device to eliminate this problem was developed. The worker counts out two springs from a bin and places them in a small dish. After assembly is complete, if a spring remains in the dish, an error has occurred. The operator knows a spring has been omitted and can correct the omission immediately. The cost of this inspection (looking at the dish) is minimal, yet it effectively functions as a form of inspection. The cost of rework at this point is also minimal, although the preferred outcome is still to find the dish empty at the end of assembly and to avoid rework even when its cost is small.”

Keyence also shows us modern methods for poka-yoke, such as checking an industrial recipe using a barcode scanner or cameras for verification.

Everyday examples of poka-yoke include the clip on a treadmill that stops the machine if you fall off or microwaves that won’t function when the door is open. Plugs that can only be inserted in one manner are an oft-cited example. Others include that light that turns on when your seatbelt is not on and the ATM “eating” your money should you forget to take it. A lovely example mentioned in the below video is the U bend below your sink, which has been designed so that things dropped in stay there, lest you lose your wedding ring in the drain.

On this 3D printed inspection jig, the extruder can only be mounted in one way.

Simply put, a poka-yoke device is something that has been designed to aid the employee so that this person is less likely to make a mistake. Rather than monitor errors through inspectors or by going over statistics, we’re going to go to the root cause to stop them from occurring in the first place. In another context, we could perhaps see poka-yokes used to create very good ergonomics or thoughtful design. We could also see them as the signifiers, mapping, and affordances as expressed by Donald Norman in the excellent Design of Everyday things.

In a manufacturing context and especially within the lean, six sigma community poka-yoke is the term of choice, however. Interestingly, I could only find two parts explicitly mentioning the use of 3D printing and poka-yoke here and here. We only had it mentioned on two article, this Aaron Hurd story and one in which Beyond Vision used Stratasys machines to make a fixture to aid the blind in manufacturing. Generally, publications discussing poka-yoke are few and far between, as well. But it is happening, and some people talk discuss it. There’s even a paper on how to apply it to making your HDMI plugs easier to use.

The Beyond Vision fixture.

Poka-yoke is valuable, since it engenders safety, saves money, can increase productivity, and can make workers’ lives easier. 3D printing poka-yoke is valuable because we can easily and inexpensively make many forms that can be used to nudge machine operators and other workers towards the correct behavior. If an inspector or manager has a poka-yoke idea, 3D printing is simply the fastest way to implement that idea. Whatever type of new poka-yoke they want to implement, 3D printing is also going to be one of the lowest cost methods to produce it, as well. In this way, we can help make your factory more efficient and safer, one poka-yoke at a time.

But, it gets even better, because who cares about poka-yoke? Quality assurance and quality control people. And who hates 3D printing? Quality assurance and quality control people! We have a chance here to engage the individuals most resistant to adopting 3D printing in any organization. Open loop, finicky, porous, problematic surface textures, run to run rates all over the place, different results at different parts of the print bed, part changes due to humidity, build failures, unpredictable part properties—we’re a perfect nightmare for quality control teams. We’ll parachute into their neat, orderly, statistically sane lives and take an ax to everything.

Imagine having a garden party where everything is orderly and zen with teacups and cucumber sandwiches, We are a mad gang of orcs that have just been catapulted into that garden party and we’re now boisterously exclaiming to everyone that they need to learn our language, DfAM. But, through engaging quality managers by 3D printing their poka-yoke, we can introduce them to the wonders of 3D printing, in a drip fed way.

Therefore, quality control teams will be much more likely to understand our technology and see us as more of an ally. Through extending our jigs and fixtures engagement with poka-yoke, creative solutions we will also extend our reach throughout the organizations that we work with using the same printers, practices and materials. By demonstrating more value to more people we can bit by bit spread 3D printing in that company and industry.

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