POKA-YOKE, AS A QUALITY IMPROVEMENT TOOL

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. By this method the operator is more free creative thinking and added value activities.

BACKGROUND & HISTORY Shingo suggested a solution that became the first poka yoke device: In the old method, a worker began by taking two springs out of a large parts box and then assembled a switch. In the new approach, a small dish is placed in front of the parts box and the worker's first task is to take two springs out of the box and place them on the dish. Then the worker assembles the switch. If any spring remains on the dish, then the worker knows that he or she has forgotten to insert it. The new procedure completely eliminated the problem of the missing springs.

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

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.

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

THREE STRATEGIES FOR ZERO DEFECT Only make the product when required!  

THREE STRATEGIES FOR ZERO DEFECT Make the product so it can not be used for anything else.

THREE STRATEGIES FOR ZERO DEFECT If the product is ready use it immediately.

POKA-YOKE CLASSIFICATION Based on what is fail-safed poka-yoke is classified into the following types: Server Poka-Yokes Task Treatment Tangibles Customer Poka-Yokes Preparation Encounter Resolution

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

CUSTOMER ERRORS Preparation Errors Failure to bring necessary materials to the encounter Failure to understand role in the service transaction Failure to engage the correct service Encounter Errors Failure to remember steps in the service process Failure to follow system flow Failure to specify desires sufficiently Failure to follow instructions Resolution Errors Failure to signal service failures Failure to learn from experience Failure to adjust expectations appropriately

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 an Incremental Continual Improvement Approach

POKA-YOKE APPROACH Poke-yoke and Point of Origin Inspections( 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. Poka-yoke and Informative Inspection( 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.

POKA-YOKE SYSTEMS GOVERN THE PROCESS 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.

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. “There must have been an error detected, so the machine shut down by itself”

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. Below left is an example of an alarm system using dials, lights and sounds to bring attention to the problem. Color coding is also an effective non-automatic option I’m glad that the alarm went off, now, i’m not making defects

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)

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.

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). Of course, preventing a defect or loss in the first place is the most effective form of poka-yoke. However, devices for catching defects or losses and immediately stopping the action are also valuable. Eg.,warning lights in your automobile that alert you to a problem such as low oil or a nearly empty fuel tank before the problem affects the operation of your vehicle.

EXAMPLES OF POKA-YOKE PRODUCTS

EXAMPLES OF POKA-YOKE

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 proce ss have been followed.

IMPROVEMENT PRINCIPLES FOR POKA-YOKE Stop by doing wrong, do it right. Do it now! Build quality in the process. No excuses. If your poka yoke idea has better than 50% chance to succeed…Do it! Do it now….improve later! Team work Why, why, why, why, why ?????

ADVANTAGES They are simple and cheap. If they are too complicated or expensive, their use will not be cost-effective. 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. Judged by these criteria, the "small dish" solution to the missing-spring problem is an excellent poka-yoke device: It was simple. It was cheap, involving only the cost of a small dish. It provided immediate feedback about the quality of the work; corrections could be made on the spot.

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