POKA –YOKEYou can’t go wrong

SUBMITTED BY:AKSHITA PILLAIMCA IIIrd SEM.

ポカヨケ

CONTENTS• History• What is Poka Yoke• Why is it important?• Example• Key Principle• Types of Poka Yoke• Poka Yoke System Design• Fail Safe Device/Machine• Sensor for detecting defects• Reason of using vision sensor and its working• Cognex-Checker Vision Sensor• Vision Sensor Inspections• Vision Sensor example in motion• Conclusion• References

WHAT DOES ‘POKA-YOKE’ MEAN ???

POKA YOKE (yokeru)

“Mistake” “Avoid”

HISTORY This term Poka-Yoke was adopted by Dr.Shigeo Shingo as part of the Toyota Production System in 1960.

It was originally described as “baka-yoke”,but this name mean “Fool Proofing", so the name was changed to the Poka-Yoke.

WHAT IS POKA-YOKE?

Poka-Yoke is a Quality Assurance Technique, its purpose is to eliminate the product defects by preventing, correcting or drawing attention to human errors as they occur.

Its objective is to achieve “Zero Defects”.

WHY IS IT IMPORTANT ?

Poka Yoke refers to the technique which can drive the defects out of the products and improve quality and reliability.

By eliminating the defects at the source, the cost of mistakes within a company is reduced.

EXAMPLE OF AN ELEVATOR A traditional lift set up by an engineer in a building

has maximum weight capacity is 200 kg.

Person 1=60 kg

Person 2=90kg

Person 3=50 kg

LIFT CAPACITY=TOTAL

WEIGHT

CONTINUED… If more people enter the lift then weight will increase,

which increases the possibility of break down of lift’s wire because there is no warning mechanism on excess weight.

CONTINUED… Latest lifts are very advanced, because when it is

over weight the alarm will start & indicate light , until weight is not reduced, this is done through Poka yoke.

And lift will move without any fault.

Here people want to use lift but they can’t use it,

why ?Because lift can’t run on overload. This is good for our safety, so here no any defect comes out .

This is also called zero defect.

KEY PRINCIPLE Error is inevitable, but it should be eliminated.

Before Poka Yoke After Poka Yoke

TYPES OF POKA YOKE

Dr.Shingo recognized 3 types of Poka-yoke for detecting and preventing errors:

The Contact Method The fixed value (or constant number) The motion step (or sequence method)

THE CONTACT METHODThis method identifies product defects by testing the product’s shape,size,color or other physical attributes.

Example:

THE FIXED VALUE METHOD

This method alerts the operator if a certain number of movements are not made.

Example: Control or shut out Warning & Attention

THE MOTION STEP METHOD

This method determines whether the prescribed steps of the process have been followed.

Example: Control or shut out Warning & Attention

INEXPENSIVE

SIMPLE FAIL-SAFE MACHINEFOR

QUALITY CONTROL

SENSOR

FAIL-SAFE DEVICE Principle of Fail safe Device

It is designed in a way, so that when a failure does occur, the device will tend to fail in a predictable manner to a “safe state”.

Fail safe device is distinguished from Fail Secure device.

FAIL SAFE DEVICE IS DISTINGUISHED FROM FAIL SECURE DEVICE.

Fail-safe means that a device will not endanger lives or properties when it fails.

Fail-secure means that access or data will not fall into the wrong hands in a failure.

For example, if a building catches fire, fail-safe systems would unlock doors to ensure quick escape and allow firefighters inside, while fail-secure would lock doors to prevent unauthorized access to the building.

SENSORS FOR DETECTING DEFECTS

For detecting defects in products, the sensor which is used is “Vision Sensors” also known as Smart Inspection Cameras.

WHY VISION SENSORS?

Repetitive inspection of production lines is a labor-intensive activity that is being replaced by vision sensors which are not only cost-effective, but give consistency of judgment and documented traceability to the inspection process.

HOW DO THEY WORK? Vision sensors have huge numbers of photoelectric cells that

capture a complete image. After capturing the image, the vision sensor compares some,

or a number of characteristics of the image to the reference image stored in its memory.

It can inspect asymmetrical objects no matter how they are rotated within a full 360o range.

Reference image is set using software inspection tools built- into the sensor.

The sensor has been programmed to enable it to locate, analyse and measure the image and then compare the results with preset pass or fail criteria.

The result is communicated over Ethernet ports.

CHECKER VISION SENSORS

Cognex Checker vision sensors are very good at detecting defective parts reliably on the fastest production lines. Equally important is the vision sensor’s ability to stop the rejection of good parts. That’s exactly what Checker does.

Checker Vision Sensor is an industrial sensor with built-in camera,processors,lighting,optics capable of detecting and inspecting up to 6000 parts per min.

Developed by Cognex. Easy to setup and operate. Not expensive.

VISION SENSOR INSPECTIONS

The image display simplifies setup by enabling you to see what the sensor sees.

CHECKER’S UNIQUE INSPECTION SENSORS PROVIDE THE MOST RELIABLE WAY TO

INSPECT YOUR PART Brightness sensors look for dark or light areas on the part. Width sensors measure the width of a part, component, or

feature. Height sensors measure the height of a part, component, or

feature. Diameter sensors measure the diameter of a part, component,

or feature. Pattern presence sensors include “robust” and “fast” modes

to verify the presence of patterns.

VISION SENSOR MEASUREMENT TOOLS IN ACTION

Checker vision sensors have photoelectric sensors and even other vision sensors has ability to determine dimensions of parts and deliver simple pass/fail results.

Example given here – verifying component thickness after the machining of an automotive part component.

An automotive part component comes down a belt, is machined on the production line, and moves to the inspection station. 

The part can be in any position on the belt because Checker is always looking for the part so there is no need for the part to be fixture precisely. 

This means that you don’t have to adjust the sensor constantly (like you do with photoelectric sensors).

Once the part is found, the width, height and diameter measurement tools quickly measure the part and produce a pass/fail result.

Correct Thickness

Incorrect Thickness

In this example, Checker is performing part inspections that human eyes simply cannot.  The result for the user is 100% defect detection, more

quality control, and lower production costs.

APPLICATIONS

Label AlignmentObjective: To verify that the labels on a bottle are aligned with each other and both are straight.Sensors: Presence PLUS P4 EDGE, with LCF08 lens, HFFW12DC tubular fluorescent light, PLC used as a trigger.

Food Packing Inspection Objective: To inspect boxes of chocolates for missing or

damaged pieces to make sure each nest contains a candy and that the candies are not damaged.Sensors: Presence PLUS P4 OMNI with LEDR80x80M light and LCF16LMP lens.

CONCLUSIONIn many companies,poka yoke devices are created every week or even everyday. The ‘Kaizen’ idea implies that they don’t have to be expensive and should be simple. Every company, office or hospital, certain mistakes are unwanted, but where imperfect beings work or live, should give the idea of Poka-yoke.

It might make a big difference.

REFERENCES http://www.tektron.ie/vision_sensors.htm http://www.cognex.com/Connect/BlogMain.aspx?id=

12365&blogid=1825 http://en.wikipedia.org/wiki/Fail-safe www.hubpages.com http://www.thetoyotasystem.com/lean_inventions/pok

a_yoke-you-can%E2%80%99t-go-wrong.php

THANK YOU