August 9, 2015

Lean Process Optimization , Andon System , Error Proofing ( Poka Yoke ) & Defect vs Errors

Resource: About Process Optimization, Andon System, When does the Andon light up?, How the Andon is Activated?, Team Leader Call, Pre‐requisites for Andon Success, Error Proofing (Poka‐Yoke), What is Error Proofing?, Benefits of Error Proofing?, Defects ‐vs‐ Errors, Error Proofing

Lean Process Optimization , Andon System , Error Proofing ( Poka Yoke ) & Defect vs Errors Resource: About Process Optimization, Andon System, When does the Andon light up?, How the Andon is Activated?, Team Leader Call, Pre‐requisites for Andon Success, Error Proofing (Poka‐Yoke), What is Error Proofing?, Benefits of Error Proofing?, Defects ‐vs‐ Errors, Error Proofing










About Process Optimization
• Achieving man assignments and workload balance
• Optimizing process efficiency
• Reducing assembly system cost
• Trade‐offs in assembly process development, involving throughput (JPH), Cost, Facilities, Mfg. requirements and assembly quality
• Capturing different viewpoints of Product Engineering, Advanced Mfg. Engineering, Production, Facilities and Material Handling.

Andon System
• The Andon system provides Work instruction; the team member perform their standardized work based on the information received from the Andon board.
• The Andon system is a problem identification tool; problems are quickly pointed out, at the point of origin.

When does the Andon light up?
• To provide work instructions: Tool change, quality check, add material.
• To indicate when process is unavailable: Machine fault, work flow problem.
• To indicate when team member require assistance: Call buttons located at each station/machine.

How the Andon is Activated?
Automatic Equipment:
• Tool Change – by pre‐programmed counters in each machine for forecast and life expired (machine stop)
• Quality Check – by pre‐programmed counters on the automation or in the machines for forecast and expiration (machine stop)
• Fault – machine / level automation PLC’s signals fault condition to Andon
• Material Forecast – level detection devices signals Andon when material need is forecast
• Others as needed through the PLC to the Andon.

Team Leader Call
Each process / station is provided with a call button on the HMI to call for team leader assistance. Since machines are automatic (they stop on their own when problem is detected), this button does not have direct effect on the machines’ ability to run.

Pre‐requisites for Andon Success
• Small, Empowered Teams
• Team Leader / Problem Helper
• Standardized Work
• Automation / Fixed Position Stops
• Full Work Principle
• Zone and De‐coupling to Maintain Availability
• Scandalized Problem Solving Process
• Error Proofing

Error Proofing (Poka‐Yoke)
• Lean Manufacturing Error and Mistake Proofing Systems

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 not have to create resulting 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.

In control systems, operations are stopped when a fault is encountered. Root cause analysis starts immediately and corrective action is completed before work continues. This system requires fixing problems immediately and avoids the problem of setting aside a mountain of rejects until “maintenance” can repair the machine.

The success of poka-yoke is to provide some intervention device or procedure to catch the mistake before it is translated into nonconforming product. There are numerous adaptive approaches. Gadgets or devices can stop machines from working if a part or operation sequence has been missed by an operator. A specialized tray or dish can be used prior to assembly to assure that all parts are present. In this case, the dish acts as a visual checklist. Other service oriented checklists can be used to assist an attendant in the case of interruption.

Numerous mechanical screening devices can be used in fabrication. The author has seen applications based on length, width, height and weight. Cash registers at many fast food outlets have descriptions or schematics of the product purchased. This system and the use of bar codes at super markets avoids data entry errors and saves time. Obviously, mistake proofing is a preventive technique.

Other than eliminating the opportunity for errors, mistake proofing is relatively inexpensive to install and engages the operator in a contributing way. Work teams can often contribute by brainstorming potential ways to thwart error prone activities. A disadvantage is that, in many cases, technical or engineering assistance is required during technique development.

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 failsafe cut-off mechanisms . Enhancing product producibilityand maintainability . Selecting components and circuits that are proven

What is Error Proofing?
• People will occasionally make mistakes
• People need help to consistently perform their job correctly
• Reduces the chance of defects

Benefits of Error Proofing?
• Improve First‐time‐through capabilities
• Improved quality through reduced scrap & rework

Defects ‐vs‐ Errors
“Errors” are not same as “Defects.”
A “Defect” takes place after an “Error” occurs.
If “Errors” are caught before they lead to a “Defect”, then a “Defect‐free” environment becomes possible.

Error Proofing
• The intent of Poka‐yoke is to stop defects at source, to provide immediate feedback as to the cause, and to prevent passing on of defective products to the next customer in process.
• Error proofing is accomplished through the deployment of simple, inexpensive devices designed to catch errors so they do not become defects.
• These devices are placed in the process to ensure that it is impossible or difficult for operator to do the job incorrectly.
• The tools could be physical, mechanical or electrical.
Machine Operator Checklist = Error Proofing Devices