QualiPedia: Poka-yoke

Mistake proofing your processes

Published: Monday, June 15, 2009 - 13:14

The term, poka-yoke (pronounced poh-kah-yoh-keh), may sound vaguely familiar and kind of fun, and even conjure up images of a dance at wedding receptions; however, poka-yoke is a quality tool that has prevented incalculable waste in the manufacturing industry for more than 40 years. Poka-yoke, a Japanese term roughly translated as “mistake proofing,” is the use of a method or device that prevents a mistake from being made or makes the mistake obvious at a glance.

Here’s a good example of poka-yoke in manufacturing: At a Toyota truck plant in India, workers were sometimes forgetting to tighten certain bolts on a vehicle. To prevent this, wrenches were kept in a bucket of brightly colored paint. If a bolt had been missed, it lacked the splash of colored paint, thus reminding the worker to tighten the bolt.

For a completely different example, here’s one of poka-yoke working in healthcare. The error was esophageal intubation—putting a tube into a patient’s stomach which was intended for their lungs. The poka-yoke prevention was this: After the tube has been inserted into the patient, take the bulb in hand, squeeze the bulb then attach the bulb to the end of the tube. If the bulb inflates, the tube is in the lungs, if not, the tube is incorrectly placed in the esophagus.

Although the concept of fool-proofing and fail-safe devices has been around a long time, it is Japan’s “Dean of Quality Consultants,” Shigeo Shingo, who was most influential for developing it into a defect prevention system.

During the 1960s Shingo worked closely with Toyota Motor Co. as an industrial engineer, creating tools and techniques for improving their manufacturing process. Working toward a means of zero defects, Shingo developed poka-yoke. He believed that the causes of defects lie in the inadvertent errors made by workers, and that defects would be prevented if these errors were avoided or caught when they occur.

In his book, Zero Quality Control: Source Inspection and the Poka-Yoke System (Routledge, 1986), Shingo writes, “Defects arise because errors are made; the two have a cause and effect relationship…. Yet errors will not turn into defects if feedback and action take place at the error stage.”

If you’re thinking of poka-yoke as merely limit switches or automatic shut-offs on a factory floor, think again. Poka-yoke devices or methods can be inexpensive and in any form you can imagine (i.e., mechanical, electrical, procedural, visual, human). It can apply to any type of process in many industries, such as in healthcare for drug dispersion in hospitals, in retail for customer service, in business offices to process orders and invoices, or in aviation for maintenance (particularly with processes where failure can be catastrophic).

Poka-yoke is a quality tool within quality tools. Consider it an extension of failure mode and effects analysis (FMEA), a tool used in combination with other problem-solving tools to evaluate and document potential failures according to their risk, and identifying actions that could reduce or eliminate potential failures. Poka-yoke supports the effectiveness of the problem-solving method, define, measure, analyze, improve, control (DMAIC) used in Six Sigma projects. These are just two examples where poka-yoke fine tunes process analysis and defect prevention tools.

Poka-yoke is invaluable wherever mistakes can be made.

http://forvo.com/word/poka-yoke (audio pronunciation)

www.poka-yoke.org.uk

http://thequalityportal.com/pokayoke.htm

http://facultyweb.berry.edu/jgrout/tutorial.html

http://elsmar.com/Error_Proofing

Modern Approaches to Manufacturing Improvement: The Shingo System (Manufacturing and Production), by Shigeo Shingo, edited by Alan Robinson (Productivity Press, 1990)

Zero Quality Control: Source Inspection and the Poka-Yoke System, by Shigeo Shingo, Ph.D. (Productivity Press, 1986)

Poka-Yoke: Improving Product Quality by Preventing Defects, edited by Nikkan Kogyo Shimbun Ltd. (Productivity Press, 1989)

About The Author

Laurel Thoennes @ Quality Digest

Laurel Thoennes is an editor at Quality Digest. She has worked in the media industry for 33 years at newspapers, magazines, and UC Davis—the past 25 years with Quality Digest.