POKA-YOKE OR MISTAKE PROOFING

-AN OVERVIEW

Ashish GuptaAsst. Officer QA

Parle Biscuit Pvt. Ltd., Pantnagar(Uttarakhand)

“Be more careful” not effective The old way of dealing with human error was to scold

people, retrain them, and tell them to be more careful… My view is that you can’t do much to change human nature, and people are going to make mistakes. If you can’t tolerate them... you should remove the opportunities for error.

Training and motivation work best when the physical part of the system is well designed. If you train people to use poorly designed systems, they’ll be OK for awhile. Eventually, they’ll go back to what they’re used to or what’s easy, instead of what’s safe.

You’re not going to become world class through just training, you have to improve the system so that the easy way to do a job is also the safe, right way. The potential for human error can be dramatically reduced.

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What Causes Defects?

1. Poor procedures or standards.2. Machines.3. Non-conforming material.4. Worn tooling.5. Human Mistakes.

Except for human mistakes these conditions can be predicted and corrective action can be implemented to eliminate the cause of defects.

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What to do now!!!

To avoid such mistakes here comes the tool that is called…

Mistake-proofing systems

Does not rely on operators catching mistakes

Quick feedback 100% of the time

Inexpensive ‘Point of Origin inspection’

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What is it?

Poka-yoke (pronounced POH-kah YOH-kay) was coined in Japan during the 1960s by Shigeo Shingo who was on of the industrial engineers at Toyota.

The initial term was ‘baka-yoke’, which means ‘fool-proofing’. This term ‘baka-yoke’ dishonorable and offensive connotation. Hence, the term was changed to poka-yoke, which means ‘mistake-proofing’.

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What the Poka-yoke is?

Techniques that help operators avoid mistakes in their work caused by choosing the wrong part, leaving out a part, installing a part backwards, etc.

It involves the implementation of fail-safe ways methods that detect or prevent human and machine error at or near the source.

It provides instant feedback and prevention of quality problems

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Poka-Yoke as a…

Poka Yoke as Prevention Device

Is a device or process that prevents errors from occurring or prevents these errors from creating defects.

Examples: part locators, part present sensors.

Poka Yoke as Detection Device

Is a device that will detect a defect or concern and initiate a corrective action.

Examples: vision system, limit sensors

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Why is it important?

Poka-yoke helps people and processes work right the first time.

Poka-yoke refers to techniques that make it impossible to make mistakes.

Poka-yoke techniques can drive defects out of products and processes and substantially improve quality and reliability.

It can be thought of as an extension of FMEA.

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Contd…

It can also be used to fine tune improvements and process designs from six-sigma Define - Measure - Analyze - Improve - Control (DMAIC) projects.

The use of simple poka-yoke ideas and methods in product and process design can eliminate both human and mechanical errors.

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When to use it?

It is a technique, a tool that can be applied to any type of process be it in manufacturing or the service industry.

Poka-yoke can be used wherever something can go wrong or an error can be made.

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Contd…

Errors can be of any type-i. Processing Error: Process operation missed or

not performed per the SOP.ii. Setup Error: Using the wrong tooling or setting

machine adjustments incorrectly. iii. Missing Part: Not all parts included in the

assembly, welding, or other processes.iv. Improper part/item: Wrong part used in the

process.v. Operations Error: Carrying out an operation

incorrectly; having the incorrect version of the specification.

vi. Measurement Error: Errors in machine adjustment, test measurement or dimensions of a part coming in from a supplier.  

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How to use it?

Step by step process in applying poka-yoke:1. Identify the operation or process - based on a Pareto

Analysis.2. Analyze the 5-whys and understand the ways a

process can fail.3. Decide the right Poka-yoke approach, such as using a,

Shut out Type: Preventing an error being made, or an

Attention Type: Highlighting that an error has been made.

Note: Take a more comprehensive approach instead of merely thinking of Poka-yoke as limit switches, or automatic shutoffs. A poka-yoke can be electrical, mechanical, procedural, visual, human or any other form that prevents incorrect execution of a process step.

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Contd…

4. Determine whether a Contact Method Constant Number or Counting Method Motion-Sequence Method

5. Trial the method and see if it works.6. Train the operator, review performance

and measure success.

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Methods in Detail

Contact Methods“Do not have to be high tech!”

Passive devices are sometimes the best method. These can be as simple as guide pins or blocks that do not allow parts to be seated in the wrong position prior to processing.

Take advantage of parts designed with an uneven shape!

A work piece with a hole a bump or an uneven end is a perfect candidate for a passive jig. This method signals to the operator right away that the part is not in proper position.

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Methods in Detail

Constant Number or Counting Method Used when a fixed number of operations are required

within a process, or when a product has a fixed number of parts that are attached to it.

A sensor counts the number of times a part is used or a process is completed and releases the part only when the right count is reached.

Motion-Sequence Method The third poka yoke method uses sensors to

determine if a motion or a step in a process has occurred. If the step has not occurred or has occurred out of sequence, the sensor signals a timer or other device to stop the machine and signal the operator.

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Day2Day Examples of Poka-Yoke

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Day2Day Example

3.5 inch diskettes cannot be inserted unless diskette is oriented correctly. This is as far as a disk can be inserted upside-down. The beveled corner of the diskette along with the fact that the diskette is not square, prohibit incorrect orientation.

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Day2Day Example

For some file cabinets, opening one drawer locks all the rest, reducing the chance of the file cabinet tipping.

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Circuit breakers prevent electrical overloads and the fires that result. When the load becomes too great, the circuit is broken.

Day2Day Example19

Day2Day Example

Even bathroom sinks have a mistake-proofing device. It is the little hole near the top of the sink that helps prevent overflows.

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Both the sink and the urinal are fitted with light sensors. These sensors insure that the water is turned off in the sink and that the urinal is flushed.

Day2Day Example21

Okay, So This Is Not An Everyday Example For

Anybody. I Hope You'll Find It Interesting Nonetheless…

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Bathyscaph Submarine

The bathyscaph is a deep water submarine used to explore the very lowest parts of the ocean. It is electrically powered. Once at the bottom, if the batteries or electrical system fail the best outcome would be for the sub to return to the surface. The designers made this outcome occur by holding the ballast in place with electromagnets. When power is lost, the ballast drops off automatically and the sub starts its ascent.

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Any Questions???

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Thanks For Keeping Patience

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