Poka-Yoke

Dhon G. Dungca

What is Poka-Yoke?

Poka (Poh-Kah) Inadvertent errors

Yoke (Yoh-Kay) To avoid

Technique for avoiding simple human errors at work

“fool-proofing” “fail-safe” “mistake-proofing the process”

Shigeo Shingo

Developed the idea into a formidable tool for achieving zero defects and eventually eliminating quality inspections.

Poka-Yoke EVERYWHERE!

Elevator alarms 110V/220V plugs Low battery indicator Low fuel indicator Alarm clock

3.5 Diskette

Cannot be inserted unless diskette is oriented correctly. This is as far as disk can be inserted upside-down. The beveled corner of the diskette pushes a stop in the disk drive out of the way allowing the diskette to be inserted. This feature, along with the fact that the diskette is not square, prohibit incorrect orientation.

File Cabinets

Can fall over if too many drawers are pulled out. For some file cabinets, opening one drawer locks all the rest, reducing the chance of the file cabinet tipping.

Bathroom Sinks

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

Key Holder

In China, where electric power has been scarce, hotel rooms are equipped with a room key holder which turns off the power when the key is removed. This ensures no electricity flow to the room while it is vacant.

ATM Machines

New generation ATMs perform transactions without the card leaving your hand because of the beeping sound once your card comes out of the machine

Elevators

Many elevators are equipped with an electric eye to prevent doors from shutting on people. They also are equipped with sensors and alarms to prevent operation when overloaded.

Why Poka-Yoke?

FACT! Workers finish their shift & don’t

remember what they have done Even highly skilled workers get tired

and start committing mistakes Workers get distracted and forget on

a valve or switch

TIPCO Experience

Incidental Details Root CausesChemical valve at kneading machine left open

Wrong delivery to customer

Unaccounted requisition causes distorted inventory stock

Overflow of whitewater storage tank

Human Error

Wrong label generated and pasted on roll

Misplaced actual stock requisition form

Unable to monitor level

TIPCO Experience

Incidental Details Root CausesDelay at truck scale

Fresh water tank emptied

Truck ran out of fuel

Forgot to put the control value to auto after cleaning the strains

Fact!

To Err is Human!

Kinds of Human Errors

Forgetfulness We forget things when we are not

concentrating

Misunderstanding We make mistakes when we jump to

conclusion before we are familiar with the situation

Kinds of Human Errors

Identification We misjudge a situation because we

view it too quickly or are too far away to see it clearly.

Made by Amateurs We make mistakes through lack of

experience

Kinds of Human Errors

Willful Errors We decide that we can ignore rules

under certain circumstances

Inadvertent Errors We are absentminded and we make

mistakes without knowing how they happened

Kinds of Human Errors

Due to Slowness We make mistakes when our actions

are slowed by delays in judgement

Lack of Standards Errors occur when there are no

suitable instructions or work standards

Kinds of Human Errors

Surprise Errors Equipment runs differently than

expected

Intentional Errors We make mistakes deliberately

How to deal with errors

Errors happen “Errors are inevitable. The mark of

character is not refusing to recognize them, but acknowledging them and taking responsibility.”

Errors can be eliminated People make fewer mistakes if they are

supported by proper training and by a production system based on the principle that errors can always be prevented.

5 Best Poka Yoke

Guide pins of different sizes Error detection and alarms Limit switches Counters Checklists

Poka Yoke Devices

Vibration sensors Metal sensors Timers Computer-activated devices

Poka Yoke…

Approaching ZD (zero defects)

Sampling vs 100% Inspection

Sampling inspection “we maintain our quality at 99%”

100% Inspection “we won’t tolerate a single defect.”

3 Strategies for ZD

Don’t make it! The more products you make, the greater

opportunity for defects to sit in inventory. Make it to withstand any use!

Build safeguards into the production process to ensure that the product is robust from the user’s viewpoint

Once you’ve made it, use it right away Go for continuous flow production

Inspection Techniques

Judgment Inspection Separates defective products from

good ones after processing Informative Inspection

Uses data feedback to control the process and reduce the defect rate.

Source Inspection Determines before the fact whether the

conditions necessary for high quality production exist.

Prediction vs Detection

Prediction System acts before a defect occurs

Detection System does not allow continuation

Basic Poka Yoke Functions

Shutdown Normal operations are stopped when

defect is detected or predicted Control

Prevents defective items from passing on the next process

Warning System signals when an abnormality is

about to occur or that a single defect has already occured

Basic Poka Yoke Functions

Shutdown Normal operations are stopped when

defect is detected or predicted Control

Prevents defective items from passing on the next process

Warning System signals when an abnormality is

about to occur or that a single defect has already occured

Where “Mistake-Proofing” works well

Manual operations were worker vigilance is needed

Where mispositioning can occur Where adjustment is required Where SPC is difficult to apply Where special causes can reoccur Where external failure costs

dramatically exceed internal failure

Detection Method

By characteristics Weight, dimension, shape

Omitted processes Process sequence method

Fixed values Using counter