Lean Mistake Proofing (Poka-Yoke)

To prevent mistakes from occurring or making it impossible to pass mistakes on to the next step in the process


Mistake Prevention

• Machine operations that make it impossible or very difficult to produce a defective product. Does not require human assistance
• Electronic checklist built into a product or process/procedure

Mistake Proofing

• Devices or systems that either prevent the defects or inexpensively inspect each item to determine if it is defective
• Software programming that makes it impossible to move onto the next step without accurately completing prior steps

When to use it

• When rework to correct errors or process delays downstream are hurting Process Cycle Efficiency
In situations critical to life and limb or cost

How to do it

There are two basic Poka-yoke approaches

A. Control/Warning Approach
• Shuts down the process or signals personnel when an error occurs
• Dials, lights and sounds bring attention to the error
• Prevents the suspect work from moving on until the process step is complete
• Process stops when irregularity is detected (may be necessary if too costly to implement mistake proofing)
• High capability of achieving zero defects

B. Prevention Approach
• Employs methods that DO NOT ALLOW an error to occur or be produced
• Gives 100% elimination of mistakes (100% zero defects)

Steps to Mistake Proofing

1. Describe the mistake and its impact to customers
2. Identify the process step where the defect is discovered and the step where it is created
3. Detail the standard procedures where the defect is created
4. Identify errors in or deviations from standard procedure
5. Investigate and determine the root cause of deviations
6. Brainstorm methods to eliminate or detect the deviation early
7. Create, test, validate, and implement mistake proofing devices/procedures