Mistake Proofing

Also called: Error Proofing, Poka' Yoke, Fail Safing, and Fail Proofing

Mistake Proofing

Mistake proofing, error proofing or Poka Yoke, it doesn't matter what someone calls it. What matters is this is one of the most effective methods to reduce product and process defects.

Study data shows excessive process input variation is the largest cause of manufacturing quality problems  This often times results from the fact that most manufacturing processes rely on people. And, people are the single greatest source of variation.

Mistake proofing, or its Japanese name poka-yoke, is the use of any automatic device or method that either makes it impossible for an error to happen or makes the error immediately noticeable when it does occur.

Variation Compensation

Mistake proofing compensates for the variation caused by people. It does not rely on people for quality. Mistake proofing is one of the most effective cost savings methods for improving quality.

When To Use Mistake Proofing

• When a process step has been identified where human error can cause mistakes or defects to occur, especially in processes that rely on the worker’s attention, skill or experience. 
• In a process, where the customer, internal or external, can make an error which affects the output.
• At a hand-off step in a process, when output or the customer is transferred to another worker.
• When a minor error early in the process causes major problems later in the process.
• When the consequences of an error are expensive or dangerous.

Mistake Proofing Methods

There are two methods of mistake proofing, the warning method and the control method. The control method is the most effective. The control method automatically stops the process when a defect is detected or separates the defective from good product.

The warning system alerts the operator that something is wrong. It does not stop the operation or separate defect from good product. Defects could occur if the operator ignores the warning. This happens because of the number of false-positive warnings given in the past.

In addition there are three setting functions: Inspection, Regulatory and Setting.

Inspection Method: Three kinds of inspection methods provide rapid feedback:

• Successive inspection is done at the next step of the process by the next worker. 
• Self-inspection means workers check their own work immediately after doing it. 
• Source inspection checks, before the process step takes place, that conditions are correct. Often it’s automatic and keeps the process from proceeding until conditions are right. 

Setting Method: Setting functions are the methods by which a process parameter or product attribute is inspected for errors:

• The contact or physical method checks a physical characteristic such as diameter or temperature, often using a sensor. 
• The motion-step or sequencing method checks the process sequence to make sure steps are done in order. 
• The fixed-value or grouping and counting method counts repetitions or parts or weighs an item to ensure completeness. 
• A fourth setting function is sometimes added: information enhancement. This makes sure information is available and perceivable when and where required. 

Regulatory Method: Regulatory functions are signals that alert the workers that an error has occurred:

• Warning functions are bells, buzzers, lights and other sensory signals. Consider using color-coding, shapes, symbols and distinctive sounds.
• Control functions prevent the process from proceeding until the error is corrected if the error has already taken place or conditions are correct, (if the inspection was a source inspection and the error has not yet occurred).

 Mistake Proofing Process Steps

Corrective Action Compliant

This course helps you comply with the corrective action clause (8.5.2) of ISO 9001:2008, AS9100:2004 and ISO/TS 16949:2002

You can have this class presented at your business for as little as $54.00 per person. Call us or click here to send a message.

Course content

This class is 1 day and includes:

1.         Introduction and overview

2.         Review of improvement strategies

3.         Defect sequence: root cause, error, defect

4.         Breaking the sequence

5.         Mistake proofing the operation

6.         Implementation of mistake proofing

7.         Workshops

8.         CEU and RU credits are awarded

This is the best book on mistake proofing I've read. It is my top pick and available through Amazon.

Additional Resources

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