11 - Mistake Proofing

04/11/23 1Confidential Company Information

MISTAKE-PROOFING AND

DEFECT PREVENTION(POKA-YOKE)


Module Objectives

• Understand concept of mistake proofing and its relationship to defect prevention and product quality.

• Review the tools associated with Mistake-Proofing.

• Discuss opportunities to most effectively utilize these tools.


Quality

We are 99%

Good!

Is this good enough?


Practical Meaning

99% Good (3 Sigma Process) 99.99966% Good(6 Sigma Process)

U.S. Postal System

20,000 Lost Articles Of Mail / Hr 7 Lost Articles / Hr

Airline System

Two Short/Long Landings / Day 1 Short / Long Per 5 Years

Medical Profession

200,000 Wrong Drug Prescriptions / Year 68 Wrong Drug Prescriptions


IRS - Tax Advice

7

Sigma Level

1,000,000

100,000

10,000

1,000

100

10

1

PPM

Restaurant Bills

Payroll Processing

Prescription Writing

Baggage Handling

AirlineSafety Rate

3 4 5 621

What Does 6 Sigma Mean In Your Daily Life ?


Defects and its impact

• Defect free product is a necessity to compete in the market place. Every Customers has a right to demand 100% good product /service and every provider has an obligation to provide the same.

• Bad products hurt both reputation and bottom line (Scrap, rework, warranty….etc.,.)

• Defects have a direct impact on process yield affecting speed and flow of the product to the customer.


Poka-Yoke

• Poka-Yoke in Japanese means mistake proofing. It is the creation of devices that either makes it impossible to make mistakes or makes the mistake obvious or detect errors that have occurred.

• Mistake-Proofing techniques can drive defects out of products and processes and substantially improve quality and reliability.

• Any defect or non-conformance to CTQ can be major sources of customer dissatisfaction and hidden cost for the producer.

• A mistake or an error becomes a defect when it is undetected or prevented and makes it way to the next operation or to the customer.


Typical Errors

• Processing errors

• Missing Operation

• Inappropriate procedures

• Missing parts

• Missing information

• Wrong parts

• Damaged materials

• Tools or equipment improperly prepared or setup

• Human Errors


1. Forgetfulness: Sometimes we forget things when we are not concentrating. Example: Air line ticking agent forgets to ask for an ID

2. Errors due to misunderstanding: Sometimes we make mistakes when we jump to the wrong conclusion before we’re familiar with the situation. Example: A person not used to a car with automatic transmission steps on the brake, thinking it is the clutch.

3. Errors in identification Sometimes we incorrectly asses a situation because we view it too quickly or are too far away to see it clearly. Example: A $1 bill is mistaken for a $100 bill.

Ten Types of Human Error


Ten Types of Human Error (Contd.)

4. Errors made by amateurs Sometimes we make mistakes because of our lack of experience. Example: New worker does not know the process or is just barely familiar with it.5. Willful errors

Sometimes errors occur when we decide that we can ignore rules under certain circumstances. Example: Crossing a street against a red light because there are no cars in sight.

6. Inadvertent errors Sometimes we make mistakes inadvertently or without realizing it. Example: Someone lost in thought tries to cross the street without noticing that the light is red.



7. Errors due to slowness Sometimes we make mistakes because our actions are slowed down by our delays in judgement. Example: A person learning to drive is slow to step on the brake.

8. Errors due to lack of standards Some errors occur when there are no suitable instructions or work standards. Example: A measurement may be left to an individual worker’s discretion.

9. Surprise errors Errors sometimes occur when equipment runs differently than expected. Example: A machine malfunction without warning.


10. Intentional errors Unfortunately, some people make mistakes deliberately, in an attempt to sabotage or commit a crime. These are least common, and should be dealt with as special cases.

Mistakes happen for many reasons, but almost all can be prevented if we take the time to identify when and why they happen and then take steps to prevent them by using mistake proofing methods.



Inspection

Can we Eliminate defects only by Inspection?


The Inspection Exercise

Count the number of times the 6th letter of the alphabet appears in the following text:

The necessity of training farm hands for the first class farms in the fatherly handling of farm live stock is foremost in the eyes of the farm owners. Since the forefathers of the farm owners trained the farm hands for first class farms in the fatherly handling of farm live stock, the farm owners felt they should carry on with the family tradition of training farm hands of the first class farmers in the fatherly handling of farm live stock because they believe it is the basis of good fundamental farm management.




The necessity of training farm hands for the first class farms in the fatherly handling of farm live stock is foremost in the eyes of the farm owners. Since the forefathers of the farm owners trained the farm hands for first class farms in the fatherly handling of farm live stock, the farm owners felt they should carry on with the family tradition of training farm hands of the first class farmers in the fatherly handling of farm live stock because they believe it is the basis of good fundamental farm management.


Theory of Escaping Defects

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pp ii nn

gg DD e

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tt ss

Escaping Defects

No matter how good your inspection and test processes are, the more defects you create, the more defects escape to the customer


The Inspection Exercise Count the number of times the 6th letter

of the alphabet appears in the following text:

The necessity in training hired hands in the strange handling of valuable live stock in premier operations is a priority in the eyes of the operations owners. Since the ancestors of the owners trained the hired hands in premier operations in the strange handling of valuable live stock, the operations owners thought they should carry on with the happy tradition of training hired hands in the premier operations in the strange handling of valuable live stock because they believe it is the basis of good basic operations management.




The necessity in training hired hands in the strange handling of valuable live stock in premier operations is a priority in the eyes of the operations owners. Since the ancestors of the owners trained the hired hands in premier operations in the strange handling of valuable live stock, the operations owners thought they should carry on with the happy tradition of training hired hands in the premier operations in the strange handling of valuable live stock because they believe it is the basis of good basic operations management.


Why Is Defect-Free Production So Important?

• What is the Rolled Throughput Yield if a product is built at five workstations and each has a yield of Y%?

Y = 95% Rolled Throughput Yield = _____%

Y = 99% Rolled Throughput Yield = _____%

#1 #2 #3 #4 #5

#1 #2 #3 #4#5

Workstations

A comparatively small improvement in yield

results in an enormous improvement in production.


results in an enormous improvement in production.


Why Is Defect-Free Production So Important?

• What is the Rolled Throughput Yield if a product is built at five workstations and each has a yield of Y%?

Y = 95% Rolled Throughput Yield = 77.3%

Y = 99% Rolled Throughput Yield = 95 %

#1 #2 #3 #4 #5

#1 #2 #3 #4 #5

Workstations


(from 95 to 99%) results in an enormous improvement in RTY (From

77% to 95%).


(from 95 to 99%) results in an enormous improvement in RTY (From

77% to 95%).


Financial Impact

REJECTION

Too Late

INSPECTION

After the FactBefore it Ships

DETECTION

Before It Escapes Your Process Step

PREVENTION

Before it Happens


Defect Detection and Prevention Strategies

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FeedbackFeedbackFeedback

Self-ChecksSelf-Checks

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Successive ChecksSuccessive Checks

Poka-YokePoka-YokePrevent the defect from occurring in the first placeor to make it immediately evident

Prevent the defect from occurring in the first placeor to make it immediately evident

• Find defects as they exit process, Immediate feedback & corrective action.• Stops adding value to defective product.

• Each process inspects previous process• Typically, 3 or less critical checks per step• Effective with small transfer quantities from process to process.


Some Mistake-Proofing Strategies

• Make it harder to create the error

• Make it possible to reverse the error

• Make it obvious that the error has occurred

• Detect deviations from procedures or fixed values (e.g., Number of parts)

• Design:

– Design process so it tolerates the error and doesn’t result in a defect– Design process to decrease complexity


Approaches to Mistake Proofing

• Control approach

• Shuts down the process when an error occurs• High capability of achieving zero defects (ie robust design that can tolerate

variation or eliminates variation or assembly mistakes)

• Warning approach

• Signals the operator to stop the process and correct problem or check for a problem (ie are parts still ok, is oil level ok)

• Sometimes an automatic shutoff is not an option• Dials, lights, and sounds to bring attention to the problem

– Automatic email or phone to inform issues– Safety scorecard that appears when you boot your PC when on the RS network that alerts you

to the plant’s safety metrics.


Mistake Proofing Devices

• Types of mistake proofing devices within control or warning approach can be of:

– Contact type:• The contact type makes contact with every product or has a physical

shape that inhibits mistakes.– Example: Fixed diameter hole through which all products must fall and an oversize

product does not fall through and a defect is registered.

– Fixed value type:• The fixed value method is a design that makes it clear when a part is

missing or not used. – Example: “Egg tray” used for supply of parts,

– Motion step type:• The motion step type automatically ensures that the correct number of

steps have been taken. – Example: An operator is required to step on a foot pedal every assembly cycle, Check

lists, Correct sequence for switches that do not work unless the order is correct.


Summary of Mistake Proofing Types

Control Warning

Contact Parking height bars Shop entrance bell

Fixed Value French fry scoop Trays with indentation

Motion Step Foot pedal operated Machine Beepers on ATM


Breakout

• Break into Teams• In 10 minutes, name mistake proofing devices

that exist inside an automobile:

_________________________________________

_________________________________________

_________________________________________

_________________________________________

_________________________________________

_________________________________________


Everyday Examples of Mistake Proofing

• Home– Automated shut-offs on electric coffee pots– Child-Proof caps on mediations– Ground fault circuit breakers for bathrooms or outside electric

circuits

• Office– Spell check in word processing– Question prompt “Do you want to delete?” after depressing the

“Delete” button on your computer.

• Factory:– Dual palm button and light curtains on machines– Loc-out / Tag-out

• Retail:– Tamper-Proof packaging– Bar coding at checkout.


Control Approach

Automobile controls have a mistake-proofing device to insure that the key is in

the on position before allowing the driver to shift

out of park. The keys cannot be removed until

the car is in park.

Electronic door locks can have three mistake-proofing devices: • Insures that no door is left unlocked. • Doors automatically lock when the car exceeds 18 miles an hour. • Lock won't operate when door is open and the engine is running.


Stove burner turns off automatically when pot or pan is removed.

Control Approach (Contd.)


Manhole covers are round because if they were of any other shape (Ex: Square) it would be possible to accidentally drop one through the hole while removing it.

Control Approach (Contd.)


Warning Approach

Warning lights alert the driver of potential problems. These devices employ a warning method instead of a

control method. (Seatbelts, High engine temperature, Low oil pressure)


Furnace Blower Door Latch

Will only engage on 1 side.


Badge plate holes of different sizes prevent

assembly of names plates upside down and insure plate is level for

appearance CTQ

Name Plate


AMP Connectors on IFC Boards

Shape of mating holes allows for only one way to assemble the

connector


IFC Board Standoffs that prevent shorting due to IFC flexing if excessive force is used to install a harness connector or wire terminal

IFC Board


Silicon Nitride IgnitorSilicon Carbide Ignitor

The reversed male and female pins prevent assembly of Silicon Carbine Ignitor wiring harness

and Silicon Nitride Ignitor and vice versa

Wiring Harness for Silicon Carbide Ignitor

Wiring Harness for Silicon Nitride Ignitor


Areas Where Mistake Proofing Should be Considered…..

Where: worker attention is needed (manual operations) mispositioning is likely. adjustment is required. SPC is difficult to apply or ineffective. training cost and employee turnover are high. mixed model production occurs. Opportunity for customers to make mistakes

exist. field failures are extremely expensive.


Examples of Some Useful Mistake-Proofing Devices

• Guide pins, to assure that parts can only be assembled in the correct way.

• Limit switches, that sense the presence or absence of a part.

• Mistake-proofing jigs, detect defects immediately upstream of the process ensuring that only the correct part reach the process.

• Counters, that verify that the correct number of parts or steps have been taken.

• Checklist, that reminds operators to do certain actions.• Parts are designed to be robust. (i.e rounded corners to

reduce lacerations. Part standardization to reduce assembly choices, Parts purchased with gaskets pre-applied so they can not be omitted due to operator error )


Mistake-Proofing

• What are some of the mistake-Proof devices in your area?

_____________________________________

_____________________________________

_____________________________________

_____________________________________

_____________________________________

_____________________________________


Levels of Mistake-Proofing

• Level 1 (Best): Process can only be performed correctly. 100% prevention and make it impossible for errors to occur.Example:– Name plate can not be printed or Air handler can not be packed

until the unit has passed Run Test & Mass Spec. – Can not “run test” an Air handler unless the blower, Wrapper and

coil bar code matches.– Inlet and outlet of Driers are of different size preventing assembly

of driers in reverse.

• Level 2 (Better): Detect any mistake as being produced. (Ex: Auto spell checker in word processor )

• Level 3 (Good): Detect before passing to next operation. (Ex: Mass spec of coils)


Auto Spell check is not foolproof

Human Brain Not Yet ObsoleteEye have a spelling checker,

It came with my PC.

It plainly marks four my revue

Mistakes eye can knot sea.

I’ve run this poem threw it

I’m sure your please two no.

Its letter perfect in it’s weigh,

My checker tolled me sew.

Check Assumptions of the Control Plan

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Seven Step Mistake-Proofing ProcessDefineDefine::

(1)(1) Identify and describe the defect or potential defect

Measure:

(2) Document defect rates.

AnalyzeAnalyze::

(3)(3) Identify:

Where the defect is made

Where the defect is discovered

(4)(4) Detail the Sequence of events documented in the standard where the defect is made and determine the deviation from standard.

(5)(5) Determine the root cause of the defect or error condition that is contributing to the defect. (Refer to the observations in step 4 and Why (5 Whys) the error happens until the root cause is identified). Do not try to develop device yet!!!

Improve and Control:

(6)(6) Identify mistake-proof ideas / devices to prevent the error or defect.

(7)(7) Create a mistake-proof device or implement other mistake-proof solution and try-storm it.

Mistake proof the mistake proof and establish relevant control plan. Ensure that the proposed change is evaluated against “Process change management” and safety criteria.


Mistake-Proofing

• Post-It notes or cards of different colors can be used for this purpose.

• Example:– White Post-it can be used to record each element of the operation

where the defect is made in Step 4– Yellow Post-it to record specific errors, deviation from sequence

or other possible causes of the defect– Blue Post-it to record ideas for defect prevention that could lead to

mistake-proof devices.

Error and idea writing guidelines

1. Write only one element, cause or idea per note or card2. Be specific and concrete3. Use a full sentence – not a phrase or word4. Write so that other can read


Safety, Quality and Productivity

• When arriving at Mistake proofing solution, it is essential to carefully review impact of the proposed solution on Safety, Quality and Productivity (Ex: Process change management criteria) in addition to ease of implementation, effectiveness of the device and cost-benefit impact.


Team Work (Proposal 1)

• Each team identify a process from your work area that is producing defects or has an opportunity for mistake.

• Teams will develop a mistake proof solution based on 7 steps of mistake proofing (Use the concepts of Poka Yoke strategies, approaches and devices).

• Use the Post-it note method to run the exercise

• Recommend an optimum mistake proofing solution based on effectiveness, cost-benefit and ease of implementation.


Mistake Proofing Example

1. Define and describe the defect: Wrong compressor 2. Measure: (Defect or Incident rate)Current defect rate at final inspection = 2.5%

3. Location at which Defect is:Discovered Final Inspection

Produced Station 14. Detail the process steps at which defect is made:

5. Analyze: (Investigate and analyze root causes for error)Factor

Method Not verifying the compressor

6. Improve (Ideas to eliminate or detect early)Levels of Mistake Proofing: Level 1: 100% Prevention Level 2: Level 3: Detect before pass to next operation

Cause Level Cost(<1 wk, 1-4wk, 4-12 wk, 12-24 wk)

Not verifying the compressor - Auto verify unit model &compressor Level 2 Medium $500- Unit will not be moved to the next station without postively verifying compressor.

7. Create Mistake Proof device:Current conditon:

Mistake proof device:

Product: Impack Process: Assembly

Mistake Proofing IdeaDetect as being produced

Implementation Difficulty

Read the compressor model number from the computer screen - Obtain compressor - Assemble on to the base pan - Move unit to next station

Factor CauseCause

EXAMPLE OF MISTAKE PROOFING WORK SHEET

Operator picks the compressor by reading the model number off the label and places it on the basepan.(The model number is shown by the computer) - Exclusively human verification

Scanner with system (soft) and conveyor (hard) lock. Operator scans lay-in card and compressor bar code. System does auto-verification validating right compressor for the unit and accepts only valid compressor bar code. If there is a wrong compressor bar code scanned, the system will not allow operator to initiative lay-in of the next unit. Further, it will lock the conveyor gate thus not allowing operator to release the unit to the next station.

(Easy, Medium, High)Time required

4-12 weeks

Date:


Set a Standard

• Errors are not acceptable

• Use cross-functional teams to design and maintain processes to be robust

• Make it right the first time

– Good: Design products and processes so that we make it right the first time

– Best: Design products and processes so we CAN’T make it wrong any time and get a concurrent productivity improvement


Summary

Why Mistake-Proof?

• Judgment inspection cannot eliminate all defects

• It is natural for humans to make errors

• Errors can be eliminated or stopped from becoming defects by using mistake proofing concepts and devices.

What are the costs and benefits?

• Devices tend to be inexpensive

• 10:1, 100:1, 1000:1 rates of return cited


Team Work (Proposal 2)

• Business, quality or OF leader will propose an area to apply Mistake proofing.

• Teams will be assigned to the area.

• Teams will go through the methodology and recommend an optimum solution.

• Winning team is selected. (Ex: Based on effectiveness, cost-benefit and ease of implementation).

Documents

11 - Mistake Proofing