Mistake proofing

1. May 26, 2012 1

2. INTRODUCTION
What is a Poka- yoke?
 Shigeo shingo defined poka-yoke as POKA- ‘Inadvertent
mistake that anyone can make’ and YOKE- ‘To prevent or
proof’
 Poka-yoke is a tool to have “zero defects” and even reduce or
eliminate quality control.
 Poka-yoke is a Japanese name for “fool-proofing”.
 Poke-yoke represents the intelligence of the operator by
excluding repetitive actions that require a thinking process.
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3. MISTAKE PROOFING
 Mistake-Proofing a product's design and its manufacturing
process is a key element of design for manufacturability /
assembly (DFM/A)
 Mistake proofing is also a key element of improving product
quality and reliability
FACTORS CONTRIBUTING TO MISTAKE PROOFING:
 Attention
 Perception
 Memory
 Logical reasoning
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4. PRINCIPLES OF MISTAKE-PROOFING
There are six mistake-proofing principles or methods.
 Elimination seeks to eliminate the possibility of error by
redesigning the product or process so that the task or part is
no longer necessary.
 Replacement substitutes a more reliable process to improve
consistency.
 Prevention engineers the product or process so that it is
impossible to make a mistake at all.
 Facilitation employs techniques and combining steps to
make work easier to perform.
 Detection involves identifying an error before further
processing occurs so that the user can quickly correct the
problem.
 Mitigation seeks to minimize the effects of errors.
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5. 2-STATUS & 3-FUNCTIONS OF POKA-YOKE
POKA-YOKE HAS 2 STATUS AND 3 FUNCTIONS:
 Status:
1.The fault will happen or
2.The fault has happened
 Functions:
1.Stop
2.Check or
3.Alarm
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6. THREE STRATEGIES FOR ZERO DEFECT
 Only make the product when required!
 Make the product so it can not be used for anything else.
 If the product is ready use it immediately.
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7. POKA-YOKE CLASSIFICATION
Poka-yoke is classified into the following types:
Server Poka-Yokes Customer Poka-Yokes
Task Preparation
Encounter
Treatment Tangibles Resolution
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8. PROVIDER(SERVER) ERRORS
 Task Errors
• Doing the work incorrectly
• Doing work not requested
• Doing work in the wrong order
• Doing work too slowly
 Treatment Errors
• Not acknowledging the customer
• Not listening to the customer
• Not reacting appropriately to the customer
 Tangible Errors
• Failure to clean facilities
• Failure to control noise
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9. CUSTOMER ERRORS
 Preparation Errors
• Failure to bring necessary materials to the encounter
• Failure to engage the correct service
 Encounter Errors
• Failure to remember steps in the service process
• Failure to follow system flow
• Failure to follow instructions
 Resolution Errors
• Failure to learn from experience
• Failure to adjust expectations appropriately
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10. SEVEN STEPS TO POKA-YOKE ATTAINMENT
 Quality Processes
 Utilize a team environment
 Elimination of Errors
 Eliminate the “Root Cause” of The Errors
 Do It Right The First Time
 Eliminate Non-Value Added Decisions
 Implement a Continual Improvement Approach
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11. POKA-YOKE APPROACH
 Proactive Approach :
 A fully implemented ZERO DEFECT QUALITY system requires
Poka-Yoke usage at or before the inspection points during the
process.
 Poka-yoke will catch the errors before a defective part is
manufactured 100% of the time.
 Reactive Approach :
 Check occurs immediately after the process.
 Can be an operator check at the process or successive check at the
next process.
 Not 100% effective, will not eliminate all defects.
 Effective in preventing defects from being passed to next process.
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12. Two Poka-Yoke System approaches are utilized in
manufacturing which lead to successful ZERO DEFECT
QUALITY:
1.Control Approach:
 Shuts down the process when an error occurs.
 Keeps the “suspect” part in place when an operation is
incomplete.
2.Warning Approach
 Signals the operator to stop the process and correct the
problem.
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13. CONTROL SYSTEM
 Takes human element out of the equation ; does not depend
on an operator or assembler.
 Has a high capability of achieving zero defects.
 Machine stops when an irregularity is detected.
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14. WARNING SYSTEMS
 Sometimes an automatic shut off system is not an option.
 A warning or alarm system can be used to get an operators
attention.
 Color coding is also an effective non-automatic option
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15. TEN TYPES OF HUMAN MISTAKES
 Forgetfulness
 Mis-understanding
 Wrong identification
 Lack of experience
 Willful (ignoring rules or procedure)
 Inadvertent or sloppiness
 Slowliness
 Lack of standardization
 Surprise (unexpected machine operation, etc.)
 Intentional (sabotage)
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16. POKA-YOKE DEVICES
 Poka yoke is implemented by using simple objects like
fixtures, jigs, warning devices and the like to prevent people
from committing mistakes, even if they try to!.
 The main feature of poka-yoke devices is their exceptional
suitability for reducing or eliminating defects through
effective feedback and instantaneous corrective action.
 These devices are capable of being used all the time by all
workers; simple and usually installed with low
implementation cost.
 Poka-yoke devices help eliminate errors and defects by giving
machines the “intelligence” to stop and signal when a error
occurs.
 Poka-yoke devices stop machines and alert workers when a
problem exists.
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17. THE THREE LEVELS OF POKA-YOKE:
There are three levels at which your company can effect poka-
yoke:
 Eliminating errors defects and losses at the source or
prevention of a mistake from being committed..
 Detection of a loss or mistakes it occurs,allowing correction
before it becomes a problem.
 Detection of a loss or mistakes after it has occurred,just in
time before it blows up into a major issue(least effective).
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18. EXAMPLES OF POKA-YOKE PRODUCTS
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20. IMPLEMENTATION IN MANUFACTURING
Poka-yoke can be implemented at any step of a
manufacturing process where something can go wrong or an
error can be made.
Shigeo Shingo recognized three types of poka-yoke for
detecting and preventing errors in a mass production system:
 The contact method identifies product defects by testing the
product's shape, size, color, or other physical attributes.
 The fixed-value (or constant number) method alerts the
operator if a certain number of movements are not made.
 The motion-step (or sequence) method determines whether
the prescribed steps of the process have been followed.
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21. ADVANTAGES
 They are simple and cheap.
 They are part of the process, implementing what Shingo calls
"100%" inspection.
 They are placed close to where the mistakes occur, providing
quick feedback to the workers so that the mistakes can be
corrected.
 Once put in place, they require minimal supervision.
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22. CONCLUSION
Poka-yokes deals with understanding why
people make errors and how to analyze the process to
know where errors are likely to occur and what root
causes contribute to them.
Since the poka-yoke devices detect errors at their
roots n prevent them from blowing up to become
bigger problems, there is consistency in the quality of
the products, saving the cost and time spent in
subsequent quality inspection processes.
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23. THANK YOU
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