DOORWAY 6: VISUAL GUARANTEES (POKA-YOKE SYSTEMS)
A visual guarantee is a mechanism that builds information so deeply into the process of work that it becomes the work itself. When that happens, it becomes impossible to do the wrong thing. We are only able to do the right thing. Such devices are already a part of process and quality control solutions in community settings. The credit card that functions only when inserted the correct way. The gas pump with its series of error proof devices to make it possible—in the United States at least—for even the most untutored citizen to pump his/her own gas (including my own 93-year old Mom), without blowing up the city. But such devices (aka, mistake-proof, error-proof or poka-yoke solutions) are far less current in the workplace—if not entirely absent.
Dr. Shigeo Shingo—co-architect of the Toyota Production System with Taiichi Ohno—nearly single-handedly brought visual guarantees to the world of work. I had the honor of working directly with Dr. Shingo through the 1980s. Three years before he passed on, he asked me to use his book, Zero Quality Control, as a base for creating a poka-yoke training and implementation curriculum for the West. It was a pleasure and a revelation.
While he had dubbed his approach poka-yoke, I choose to call them visual guarantees because of their amazing ability to pack in information—and therefore to address many, many levels of motion (moving without working). Coining the term “visual guarantees” was also my way of sending the message that mistake-proofing solutions are part of the same continuum of logic I call workplace visuality. This choice has held up nicely over the years. A closer look shows us that, as with all visual devices, visual guarantees are powerful imbedded answers to the six core questions, only on an extremely refined and minute level—which is to say: on the level of attribute.
- If you have been following my articles in this Visual Thinker e-newsletter, you will recognize motion as the lever we use to “see” the absence of information. As such, motion is the key to the deeper levels of splendid visual information sharing.
There is no manufacturing venue—discrete or continuous—that is not a ready and needy candidate for poka-yoke devices. Hand-assembly operations, however, surpass all others in the benefits that can accrue because of the likelihood of human error. Healthcare settings are also prime candidates where the history of life-threatening and life-taking error is legion.
Quality professionals tend to congratulate themselves too quickly for the introduction of a dozen—or even a hundred mistake-proof solutions. Instead, I urge you to consider the same target that I, my colleague, Dr. Martin Hinckley (author of Make No Mistake), and Toyota Motors itself uphold for the serious pursuit of mistake-proofing as a quality strategy: 12 poka-yoke devices per 60 seconds of work content. This metric provides us with a truer gauge of the level of physical and quality risk at work.
A visual guarantee translates attribute-level information into the process of work itself. Actual devices range from plain mechanical apparatus to sensors and limit switches to quality control as a result of product design. All of them are ingenious. Quality-forward companies train their designers in the principles and practices of mistake-proofing and thus commit to driving risk and error out of their products at the earliest stages.
It is for this reason that Doorway 6 is wholly owned by your designers and quality staff. And because they are also the subject matter experts in design, quality, and risk, these employees are, in my experience, the most accomplished and effective trainers of the modality. As recipients of poorly designed products and processes, operators and supervisors (to name but two of many other functions) make significant mistake-proof contributions, of course.
It is worth noting that Six Sigma is NOT a competing quality methodology, however useful its DAMAIC framework. Dr. Hinckley’s recent research study shows that, out of 320,000 reported poor quality events across a field of 600 suppliers, only five were due to variation. The rest were squarely rooted in human error, a phenomenon that Six Sigma is incapable of even noticing, let alone addressing. The eight-part on-demand Mistake-Proof Course Dr. Hinckley and I developed last year provides many such remarkable insights as well as a robust mistake-proof methodology for designers, quality staff, and CI specialists. Available here on our website. We encourage you to check it out.