1. Mistake Proofing (PokaYoke)
Six Sigma Greenbelt Training
Dave Merritt

2. The Six Sigma Cookbook Process Map Y Measurement System Analysis Y
Focus
Process Map Y
Measurement System Analysis Y
Process Capability Y
Phase 1:
Define/Measure
Phase 2:
Analyze
Graphical Methods X’s
Hypothesis Testing X’s
Phase 3:
Improve
Analysis of Variance X’s
Design of Experiments Vital Few X’s
The analyze and improve phases help you understand your X’s (inputs) and to narrow down to the vital few X’s.
Statistical Process Control Vital Few X’s
Failure Mode and Effects Analysis Vital Few X’s
Phase 1:
Control

3. Learning Objectives By the end of this module, you will be able to:
Understand the concept of Mistake Proofing as a control method
Apply Poka-Yoke methods as a control on identified key Xs
Reduce and/or eliminate process errors from occurring
Reduce and/or eliminate process defects from occurring
Understand “red flag” conditions

4. Why Is Mistake Proofing Important?
Improves quality and customer satisfaction
Prevents error occurrence
Prevents defect occurrence
If defects occur, ensures effective action
Little or no formal training
Cost effective
Easy to implement
In Summary:
Mistake Proofing is one of the most cost effective and reliable controls that can be used to assure that our key input variables remain at our optimum project defined settings.
5 to 15 intervals
Used to evaluate process capability of a stable process. If not stable – no central tendency
See example with increasing trend.

5. What Is Mistake Proofing (Poka-Yoke)?
Japanese phrase:
Yokeru (to avoid), Poka (errors)
A strategy for preventing errors in processes
Makes it impossible for defects to pass unnoticed
Prompts correction of problems as soon as they are detected
Detects defects
Prevents defects from moving into next area
Developed by Dr. Shigeo Shingo to achieve zero defects

6. Common Examples Of Mistake Proofing
Mechanical:
Guide pins of different sizes
Automated Optical Inspection (AOI)
Limit switches
Error alarms
Asymmetric parts (square peg in round hole)
Software:
Field drop down menus for data entry
Spell check
Auto correct (really??)
Weight and/or Quantity counters
Required fields

7. Common Examples Of Mistake Proofing

8. Common Examples Of Mistake Proofing

9. Common Examples Of Mistake Proofing

10. Basics Of Mistake Proofing
Effective Mistake Proofing requires 2 basic concepts:
Controls the inputs that cause errors
Inspection which is effective and tireless
It IS NOT traditional 100% inspection by inspectors
It IS a physical barrier that automatically performs the inspection with little to no human interaction
A strong Poka-Yoke makes it nearly impossible for an error to occur. If one does occur, it is guaranteed to be detected. It can’t be passed into next area.

11. What Does Mistake Proofing Do?
•The ideal process is Mistake Proofed at 3 points:
Critical inputs into the process
Within the process
The output from the process
will not accept any bad inputs
will not make any bad parts
will not pass on any bad parts

12. Classroom Exercise 1 – Round Robin
Split into two teams:
List a common Mistake Proofing idea from each of the following:
• Home (ex. auto shut off on flat iron)
• Car (ex. car won’t start unless transmission is in park/neutral)
• Sport/Recreation (ex. dead man’s lanyard on treadmill)
• Computer Software (ex. Spell check)
20 Minutes

13. Classroom Exercise 2 – Round Robin
2. The second time around, you will be asked to list possible Mistake Proofing ideas for each of the critical inputs into your project.
20 Minutes

14. Ten Common Reasons Mistakes Happen
1. Forgetfulness
2. Errors due to misunderstanding
3. Errors in identification
4. Errors made by untrained workers
5. Willful errors (ignore rules)
6. Inadvertent errors (distraction, fatigue)
7. Errors due to delay in decision making
8. Errors due to lack of standards
9. Surprise errors (malfunctions)
10. Intentional errors (sabotage)

15. Critical Inputs
You will find in some projects, after you have identified the critical inputs and their optimal settings, one or more of them may be extremely difficult to control.
Some examples:
Training was found to be critical, but the operation has 150% turnover
Cycle Times are very long, so the operators tend to lose concentration
Finding ways to Mistake Proof in these situations would make your project successful

16. Common Examples of Ideal Mistake Proofing
• Frequent changes to a job
• Complex processes
• Lack of standards
• Lack of measurement systems
• Lack of training
• Long Cycle Times
• Infrequent jobs
• High output
• Environmental conditions
• Attitude (motivation)

17. Degree of Strength of Mistake Proofing
Defective input is identified, operator altered and process stopped automatically. No product made with the bad input.
Defective input is identified and operator alerted. Process detects input and alerts operator. Production continues.
Best!
Defective input is identified and operator alerted, but still allowed to enter into the process. Production continues.
Good

18. Q & A