August 18, 2015

Six Sigma: Improve Phase : 5 Poke Yoke

mistake proof Judgment Inspection  Informative Inspection Successive Check Self Check Source Inspection Poke Yoke Systems Control Warning Mistake proof

5. Poka-Yoke

Shigeo Shingo is widely associated with a Japanese concept called Poka-Voke(pronounced poker-yolk-eh) which means to mistake proof the process. Mr. Shingo recognized that human error does happen but it can be corrected before creating defects.

Human errors can occur in many ways. Any operation that relies on the human element will run into the problem of errors. The notion of concentrating 100% of the time on a task will not guarantee zerodefects in the product. Poka-yoke is the Japanese term for “mistake-proofing” or “fail-safing” a task. Poka-yoke devices can be installed at low costs.

Inspection and Quality (S. Shingo)

Types of Inspections
1.Judgment Inspection: Discover defects after the facts, Sort out bad products

Disadvantage:
•Costly
•Difficult to eliminate all defects if human inspection is used
•No feedback to process

2. Informative Inspection: Taking data from process, when defects/abnormal condition occurs, the information is feedback to the process, and corrective actions will be taken.

Statistical Process Control / Successive Check / Self Check

-The Pitfalls of SPC (Shingo) •It is a sample inspection, so if the process is not capable, it cannot catch All the defects
-The feedback is usually slow

Successive Check

Successive check is to let the immediate down stream process To check the output of the immediate upstream process. Basic Principles of successive check method
•Always 100% inspection
•Judgment about defect is done objectively
•When a defect occurs, the information will be immediately feed back to immediate Upstream, root cause will be immediately investigated
•Eliminate hidden root cause one at a time, until they are all gone.

Self Check

Successive check is to let current process to check itself and Trouble shoot the process immediate if defect occurs. Basic Principles of self check method
•Always 100% inspection
•When a defect occurs, the root cause analysis will follow instantly and corrective
action will be taken immediately
•Eliminate hidden root cause one at a time, until they are all gone.
•Inspection should be done at low cost and automatically

3. Source Inspection:

Source Inspection is based on the idea of discovering and correcting errors before errors become a defect

Basic Principles of self check method
•Always 100% inspection
•When a defect occurs, the source of errors will be traced in upstream and/or adjacent/related process elements and be identified
•Real time check mechanism will be implemented and whenever an error shows up, it will Be immediately identified and eliminated

Poke Yoke Systems
There are three types of regulatory mechanisms for Poke Yoke
1.Control: When abnormalities occur, the Poke Yoke system will halt the operations
2. Warning: When abnormalities occur, the Poke Yoke system will send warning
3. Mistake proof: When abnormalities occur, the Poke Yoke system Will make mistake impossible to happen

Poke Yoke device should be cheap, able to perform 100% inspection, and gives results instantly Poke Yoke system can detect abnormalities by detection technology and/or process procedures.

Other design improvements to “error proof’ the process include: .

Elimination of error-prone components

. Amplification of human senses

. Redundancy in design (back-up systems)

. Simplification by using fewer components

. Consideration of functional and physical environmental factors.

Providing fail safe cut-off mechanisms

. Enhancing product producibility and maintainability

. Selecting components and circuits that are proven