Lean Manufacturing: Jidoka and Poka-Yoke

Jidoka and Poka-yoke form one of the two pillars in the house of Lean. (The other pillar is JIT, or Just-In-Time manufacturing.) Jidoka is defined as "providing the ability to detect abnormal conditions and immediately stop work". Poka-yoke is defined as "error-proofing or mistake-proofing a process".

Generally, mistake-proofing has three levels: preventing errors, reducing the impact of an error, and identifying errors. The following sections provide some real-world examples of each.

Preventing Errors

• Specially-shaped parts that can be installed in only one direction are designed to prevent installation errors.

• In the software world, many applications are programmed to prevent certain values from being entered into a form.

Reducing the Impact of an Error

• An airbag does not prevent an automobile accident from happening, but it can reduce greatly the human cost and anguish from a car accident.

• The SawStop®, a saw that can detect a human finger and immediately stop the saw, can save the operator from serious injury.

Identifying Errors

• Smart Bolts from Stress Indicator, Inc. are bolts that change color based on how much they are tightened. The help users avoid under tightening and over torquing conditions.

Learn from Deming

One of Edward Deming's 14 points is this: "Cease dependence on inspection to achieve quality. Eliminate the need for inspection on a mass basis by creating quality into the product in the first place."

Manufacturers mostly rely upon inspection (which usually occurs after a product is made) to determine the quality of the product. Often, the results of the inspection are not fed back to the process that created the error, or the cause of the error is not readily known. By building systems and cultures that immediately stop the process when an error is detected, the process can be improved to reduce or eliminate those errors from occurring in the future. This will eliminate waste and provide for satisfied customers in the long run.

How are errors and problems handled at your organization? Are your people rewarded for bringing attention to problems? Can you share any examples oferror-proofing where you work?

Additional Resources

Here are some links to additional resources for Jidoka and Poka-yoke.

A brief tutorial on mistake-proofing written by John R. Grout and Brian T. Downs

http://www.mistakeproofing.com/tutorial.html

Wikipedia Article

http://en.wikipedia.org/wiki/Autonomation

Society of Manufacturing Engineers – Lean e-newsletter

http://www.sme.org/cgi-bin/get-newsletter.pl?LEAN&20021209&1&

Previous Posts about Lean in CR4's Engineering Management Blog

http://cr4.globalspec.com/blogentry/7657/A3-Reports-Methodology-and-Process

http://cr4.globalspec.com/blogentry/7101/Lean-Manufacturing-Part-1

http://cr4.globalspec.com/blogentry/7106/Lean-Manufacturing-Part-2