Mistake proofing, or its Japanese equivalent Poka-yoke (pronounced PO-ka yo-KAY), is the use of any automatic device or process that either makes it infeasible for an error to occur or makes the error immediately obvious once it has occurred.

1. Mistake Proofing

2. Mistake Proofing
• Mistake Proofing is devoted to the implementation of devices or
methods that prevent an error, provide notification of an error or
prevent the defect from moving to the next step.
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3. Introduction to Mistake Proofing / Error Proofing
• Competition in business is constantly increasing.
• More than ever before, providing high quality products and services is the key
to survival and growth in today’s marketplace.
• Whether it is in manufacturing, healthcare or service industries, companies are
striving to achieve zero defects.
• While zero defects sounds great, it seems almost impossible to achieve. The
fact is mistakes happen and errors can occur in all types of processes.
• A machine operator or office worker may get distracted or forget to complete a
task or a machine can break a tool and cause an error.
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4. • Many companies rely on training and work instructions to prevent errors.
• Historical information indicates that no matter how much training the operator
receives or how well the process is documented, human error occurs.
• While application of standard work practices and operator training are valid methods
for reducing the frequency of errors, they will not prevent errors from occurring.
• Mistake Proofing or Poka-Yoke methodologies can detect errors and prevent the non-
conforming part from moving to the next process or leaving your facility.
• Furthermore, by implementing Error Proofing techniques to detect the error at the
source, we can prevent the non-conforming part or product from being produced.
• Then we are truly on the road towards zero defects.
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5. What is Mistake Proofing / Error Proofing
• Many practitioners consider the terms Mistake Proofing, Poka-Yoke and
Error Proofing one and the same.
• No matter what title you choose, the fundamental purpose of all three is
to prevent errors that cause defects, notify the operator if an error has
occurred or prevent the defect from moving to the next step in the
process or reaching the customer.
• While they are the same in many ways, when you investigate the history
and deeper meanings of the terms, you discover there are slight
differences between them.
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6. • Mistake Proofing and Poka-Yoke consist of three levels of application
• True Error Proofing consists of only one level, which is the equivalent of the highest
level in Mistake Proofing or Poka-Yoke
• Mistake Proofing is devoted to the implementation of devices or methods that prevent
an error, provide notification of an error or prevent the defect from moving to the
next step
• Error Proofing is the act of implementing “fail-safe mechanisms” to prevent
production of non-conforming parts – Error Proofing focuses on error prevention at
the source or point of creation
• Poka-Yoke is very similar to Mistake Proofing except that it is centered on the human
factor
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7. • Poka-Yoke focuses on reducing or eliminating human error, which
cause defects
• The heart of Poka-Yoke is more of a concept than a procedure.
• Therefore, implementation of Poka-Yoke is governed by what people think
they can do to prevent errors in their workplace, and not by a set of step-
by-step instructions on how they should do their job.
• The Poka-Yoke philosophy is based upon two fundamental observations
about human behavior:
• Mistakes are inevitable
• Errors can be eliminated
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8. Mistake Proofing three levels of application
• Level 3 – Cannot Produce:
• Level three is the highest level of Mistake Proofing and
encompasses all controls implemented to prevent the defect from
occurring.
• Therefore, non-compliant parts cannot be produced. Examples:
• USB slots that only allow connection in one position
• Assembly fixtures that prevent parts from being inserted incorrectly
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9. Level 2 – Cannot Process:
• Level two is sometimes referred to as the warning level as it
provides a notification (Light, Sound, etc.) to the operator that a
defect has occurred. Examples:
• DC torque tool that activates a red or green light depending on whether the
correct torque is achieved
• Automated counters that will not allow the part to proceed down the line
until the correct number of screws are tightened
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10. Level 1 – Cannot Accept or Pass:
• Level one focuses on keeping the defective product from reaching
the next operation, or the customer. Examples;
• Inspection sheets or checklists
• End of-line functional testing
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11. • The most effective way of reducing or eliminating defects due to
errors is to prevent them at the source, at the point of creation.
• Tools which help identify where Error Proofing can be applied are
• Failure Mode and Effects Analysis (FMEA),
• Fault Tree Analysis (FTA), and
• Advanced Product Quality Planning (APQP).
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12. • Error Proofing philosophy promotes a mindset of zero defects.
• The only way to have zero defects is to prevent any defects from
ever happening.
• If we examine error proofing closely, we discover that it is actually
a form of 100% inspection at the source of the error.
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13. Why Implement Mistake Proofing / Error Proofing
• To achieve the highest levels of quality in our products or processes and reduce cost we must
reduce errors and prevent defects.
• Errors and defects incur very high costs in many industries through wasted production time,
rework, and increased scrap.
• Reducing or eliminating errors in a process can be achieved by either adding more detection
controls or through the implementation of preventive controls.
• Implementing mistake proofing or error proofing devices are often less costly than most
detection controls.
• In addition, error proofing reduces or eliminates risk in the process by preventing failures at
the point of origin, prior to further expensive processing.
• The age-old saying “An ounce of prevention is worth a pound of cure” is just as true today.
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14. When to Mistake Proof / Error Proof
• There are many situations or circumstances when application of Mistake
Proofing would be beneficial. Mistake Proofing should be applied when there
is sufficient risk in the process so that failure would adversely affect the
customer. Mistake Proofing should be applied when:
• Heightened alertness is required while performing manual operations
• Errors early in a process are causing problems in a subsequent process
• Missed operations or other errors could cause a potential safety issue
• Operator turnover is high or retraining is frequently required
• Failures occur frequently or the process capability is low
• Incorrect placement of components causing errors that result in defects
• Process step where human error, due to the operators attention, skill level or experience,
can cause defects
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15. Where to Mistake Proof / Error Proof
• There are several locations where Mistake Proofing devices or
methods are routinely placed within a process workflow.
• The location in the workflow can affect the level of effectiveness.
• Best –
• The very best location for a mistake proofing device is before the operator
or the machine starts the task. Prevent the error by not allowing the
process to start unless a particular set of conditions exist.
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16. • Better –
• The second best location is during the process step or cycle.
• Provide feedback or notification to the operator or machine when an error has occurred
and physically prevent the part from moving to the next operation.
• Some applications provide notification that the operation was performed correctly prior to
advancing the part.
• Good –
• The final location for a device is downstream at an inspection or test station after the
operation or process step is complete.
• In this scenario, we are completely dependent upon detection controls.
• The objective is to detect any defects prior to proceeding to the next step in the process.
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17. Implement Mistake Proofing / Error Proofing
Form
the
Team
Select
the
Process
Map the
Process
Identify
Risk
Locate
the
Source
Review
Options
Select
the
Method
Impleme
ntation
Validatio
n
Continu
ous
Improve
ment
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18. Reference
• https://quality-one.com/mistake-proofing/
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19. B.Varun
9787608011
bvarun.me@gmail.com
varun.me@srit.org
varunnelson bvarun.me
varunme bvarunme
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