Quality
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Canada's premiere source for Poka Yoke
Training and Consulting Services.
Shigeo Shingo was one of the industrial engineers at Toyota
who has been credited with creating and formalizing Zero
Quality Control (ZQC), an approach to quality management
that relies heavily on the use of poka-yoke (pronounced POH-kah
YOH-kay) devices.
Poka-yoke is Japanese for mistake-proofing.
These devices are used either to prevent the special causes
that result in defects, or to inexpensively inspect each
item that is produced to determine whether it is acceptable
or defective.
A poka-yoke device is any mechanism that either prevents a
mistake from being made or makes the mistake obvious at a glance.
The ability to find mistakes at a glance is essential because,
as Shingo writes, "The causes of defects lie in worker
errors, and defects are the results of neglecting those errors.
It follows that mistakes will not turn into defects if worker
errors are discovered and eliminated beforehand.
He later continues that "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". We
suspect that Shingo and Deming would have a protracted discussion
about whether workers or management are responsible for defects.
No resolution of that issue is undertaken here.
An example cited by Shingo early in the development of poka-yoke
shows how finding mistakes at a glance helps to avoid defects.
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. This example also demonstrates that
poka-yoke performs well when corrective action involves trying
to eliminate oversights and omissions. In such cases, poka-yoke
devices are often an effective alternative to demands for greater
worker diligence and exhortations to "be more careful."
Shingo identified three different types of inspection: judgment
inspection, informative inspection, and source inspection.
Judgment inspection involves sorting the defects out of the
acceptable product, sometimes referred to as "inspecting
in quality." Shingo agreed with the consensus in modern
quality control that "inspecting in quality" is not
an effective quality management approach, and cautioned against
it.
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Group consists of full-time trainers and consultants with industry-diverse
experience. While we do use industry proven approaches and
methodologies, we tailor these to fit your organization’s
specific needs.
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and financial expertise, and a "hands-on" approach
creates a recipe for our clients' success. We not only identify
and prioritize opportunities to add significantly to your bottom
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exploiting those opportunities to achieve financially measurable
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