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Poka-Yoke Mistake Proofing Log

Poka-yoke makes errors impossible or immediately visible. This log pairs each mistake with the device that stops it and shows the risk before and after, so you can prove the device is worth installing.

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RPN before	RPN after	RPN reduction
240	16	224
252	36	216
126	14	112
120	6	114

Total RPN before

738

Total RPN after

Total RPN removed

666

Overall RPN reduction

90.2%

Highest remaining RPN

Use the same rating scales as your PFMEA so the numbers match. RPN is a ranking aid; always review high severity items on their own, whatever the RPN.

Rank mistakes from real defect history

Optional review of how ERP scrap and NCR data can seed your mistake-proofing priorities.

Optional. The tool and every export work without this. No spam.

How to use the log

List each process step and the mistake an operator could make. Score severity, occurrence and detection from 1 to 10 using your PFMEA scales. Choose the type of device you plan, then rescore occurrence and detection as you expect after installation. The log multiplies the three scores into RPN before and after and sums the reduction. Update the status column from Idea to Verified once the device has been tested with a defect sample on the line.

Severity stays the same unless the design changes
Rescore only after a verification run
Keep the device description specific enough to rebuild

Prevention versus detection

The strongest poka-yoke prevents the mistake: a connector that only fits one way, a fixture that cannot hold the part backwards. Next best is stopping the process the moment the error happens, such as a sensor that blocks the next step. Weakest is detecting the defect afterwards and asking someone to react. Prevention lowers the occurrence score; detection lowers the detection score. The device column helps classify which approach you chose.

Common mistakes

Do not claim occurrence of 1 for a checklist or training alone; these are administrative controls and operators can still err. Do not remove a device without a risk review. Make sure the device itself is verified: use a known bad part at the start of each shift to test sensors. Link the finished item to your control plan and PFMEA so the change is recorded in the quality system.

Frequently Asked Questions

What is poka-yoke?

Poka-yoke is a Japanese term from the Toyota Production System for mistake-proofing. It means designing the process so an error cannot happen or is caught immediately at the source, rather than relying on operator attention.

What are the types of poka-yoke devices?

Shigeo Shingo described contact methods that use shape or position, fixed-value methods that check a count, and motion-step methods that check a sequence. Modern examples add sensors, vision and software interlocks.

Is RPN the right way to rank?

RPN is common and easy but has limits. Different combinations can produce the same number. Always review high severity items regardless of RPN, and consider the newer AIAG and VDA action priority method if your customers require it.

How do I verify a poka-yoke works?

Run a known defective sample through the device at the start of each shift and record the result. Keep the verification step in the work instruction and control plan so the device cannot silently fail.

Netray can help connect scrap and nonconformance data in your ERP to this log so rankings come from actual defect history.

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