Poka-yoke, or mistake proofing, is the use of a device, method or process design that either prevents an error from occurring or makes the error immediately obvious. The objective is to control the source of defects rather than relying only on final inspection.
Prevention vs Detection
| Approach | What it does | Example |
|---|---|---|
| Prevention | Makes the incorrect action impossible or very difficult | A connector that fits only in the correct orientation |
| Detection | Identifies an error immediately so it can be corrected | A barcode scan rejecting the wrong SKU before packing |
Supply-Chain Examples
- Receiving: system will not post receipt unless a valid PO line is selected.
- Picking: scanner rejects a product that does not match the order.
- Packing: scale check detects a missing item before carton close.
- Procurement: mandatory approval field prevents an unauthorized PO release.
- Transport: loading application prevents dispatch until required dangerous-goods documentation is confirmed.
A Practical Mistake-Proofing Method
- Map the process and identify where errors occur or could occur.
- Trace the error back to its source rather than only the final defect.
- First ask whether the error can be eliminated or prevented.
- If prevention is impractical, design immediate detection and containment.
- Test the method with the people doing the work.
- Monitor whether defects and rework actually fall.
Poka-Yoke Is Better Than Extra Inspection When Possible
Inspection finds some defects after they have already been created. A strong poka-yoke changes the process so the error cannot occur or is caught at the source. This is usually more effective than adding another manual check that depends on attention.
Poka-Yoke vs Jidoka
Poka-yoke is a specific mistake-proofing technique. Jidoka is the broader principle of detecting abnormalities and stopping or containing the process. A poka-yoke device can be one way to enable Jidoka.
Interview Question
Question: Give a supply-chain example of a prevention-type poka-yoke.
Answer: In receiving, the system can prevent a user from confirming a quantity against an item code that is not present on the PO. That is stronger than allowing the posting and finding the mismatch later.
Reference
American Society for Quality (ASQ) — Mistake Proofing / Poka-Yoke.
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