error-proofing techniques (poka-yoke) concept · eprefer.ppt - 09 2/13/00 error-proofing techniques...

EPREFER.PPT - 012/13/00

ERROR-PROOFING TECHNIQUES(Poka-Yoke) CONCEPT

SENSOR INFORMATION:BASIC TYPES OF SENSORS• Discrete sensors• Analog sensors

TYPES OF PRESENCE SENSORS• Physical contact• No physical contact

TYPES OF NON-CONTACT SENSORS• Reed relays• Inductive• Capacitive• Photoelectric sensors

ADVANTAGES OF THE VARIOUS TYPES• Functionality• Costs• Areas of application



BASIC TYPES OF SENSORS:ANALOG SENSORS• Answer the question: “Where is the part?”

or• “To what level have we filled the container?”

DISCRETE SENSORS• The part is present or is not present.• Most frequently asked question in a manufacturing

operation.



TYPES OF PRESENCE SENSORS:PHYSICAL CONTACT• e.g. Limit switches• Advantages - Can carry more current

- Gap between terminals

NO PHYSICAL CONTACT• Advantages - No physical contact

- Better for counting sensitive surfaces,e.g. painted or polished surfaces

- No moving parts- Faster



TYPES OF NON-CONTACT SENSORS:REED RELAYS• Target is magnetic• Will not respond to non-magnetic targets

with reliability.

INDUCTIVE• Based on metal targets; will not respond

to non-metallic targets with high reliability.

CAPACITIVE• Cannot distinguish between the real target

and something else in the target region. Must control what comes close to the target.

PHOTOELECTRIC• Can be fooled by a non-target.



TYPES OF NON-CONTACT SENSORS:REED RELAYSTypical range: Up to 1.5 in. (approx. 4 cm)• Two hermetically sealed metal foil reeds which make contact

with each other to close the circuit, when in the vicinity of amagnet (permanent or electro-magnet).

• The differential is determined by differencing the point of firstcontact from the point of last contact.

• Magnet approach must be in a direction parallel to the directionof the line connecting the tow reeds.

Best applications for magnetically actuated switches in general:• Security and safety

• to avoid false tripping• security door interlock for heavy machinery; end of travel

for elevators, cranes, and the like.• Sensing through walls (non-ferrous, e.g. Aluminum and

Magnesium).• Pallet identification in synchronous automated assembly lines.• Relative dirty environments (e.g. dust, dirt, sand, oil, or coolant

fluids).• Whenever high response speeds are required.

Disadvantages - poor long-term reliability (moving parts)



TYPES OF NON-CONTACT SENSORS:INDUCTIVE SENSORS• Principle of Operation:

• Eddy currents are induced in the target (metallic)by the electromagnetic.

• The target reacts with the Eddy currents as afunction of the distance from the field.

• Inside the field, the target attenuates the magnitudeof the Eddy currents.

• Outside the field, the target does not impede theEddy currents.

• This type of oscillator is referred to as a ECKO(Eddy Current Killed Oscillator).



TYPES OF NON-CONTACT SENSORS:CAPACITIVE SENSORS• Principle of Operation:

• Senses all materials• Contain a high frequency oscillator with one of its

capacitor plates built into the sensor.

• Method of Application:• All materials are sensed through a change on the

dielectric characteristics.• Ideal applications include bulk materials and liquids

in containers of glass and plastic.

• Characteristics:• Poor choice for metal targets.• Is very sensitive to environmental factors.• Sensing range depends greatly on the material being

sensed.• Can be misled and therefore it is important to control

the material which is presented to the sensor.



TYPES OF NON-CONTACT SENSORS:PHOTOELECTRIC SENSORSPhotoelectric controls need no physical contact and are ideal where sensedobjects must remain untouched. Photoelectric controls respond rapidly toparts moving quickly and in varying positions along a conveyor, yet operatedependably if actuated only infrequently. There are controls for indoor oroutdoor use, for varying ambient light conditions, for high vibration, for areasrestrictive in space, and even for explosive locations.

Typical applications include:• Counting• Labeling• Conveyor control• Bin level control• Parts inspection• Feed and/or fill control• Package handling• Thread break detection

• Edge guide• Web break detection• Regristration control• Food processing• Parts monitoring and sorting• Batch counting• Robotics• Parts handling



TYPES OF NON-CONTACT SENSORS:PHOTOELECTRIC SENSORSConveyor ControlThis application involves sorting brown cardboard boxes which are coded with up to four black marks per box. The application is to sense the number of marks on each box.

Package HandlingA diffuse scan photoelectric control is used to detect the light reflected from the object in this application. The control detects the light reflected off the box, turning ON and OFF the gluing machine.

LabelingThis application is designed to detect the leading edge of a black bar code on a read and write label. The labels are edge to edge on a spool. When the bar code is detected the sensor output triggers a laser bar code reader which reads the bar code.

Food ProcessingThis application monitors the level of an accumulator in a meat processing facility. A photoelectric control detects a fill level of hot-dogs in the accumulator then turns on the conveyor for a preset time period. Side walls of the accumulator are polished stainless steel. The equipment is subject to daily washdown.

Fill Level ControlThis application inspects the fill level of various jars of food products. The photoelectric system produces an output when either an under or over fill condition is detected.

Parts HandlingFiber optics are ideal for areas too small for a standard photoelectric control. The fiber optic cables direct the light from the base to where the sensing is needed.


Target

Thru:• Light source (emitter) and

receiver are placed opposite each other.

• The object to be detected passes between the two.

Advantages:1. Most reliable when target is opaque2. Long range scanning, most excess gain3. Use in high contamination areas, dirt, mist,

condensation, oil film, etc.4. Precise positioning or edge-guiding of opaque

material5. Parts counting

Types of Non-Contact Sensors

Photoelectric Sensors

Emitter Receiver

THRU




Diffuse:• Light beam is directed at the

object to be detected.• Light will be reflected off the

object in many directions.• Some of the light reflected from

the object will be sensed by the receiver.

Advantages:1. No reflector required.2. Convenient for installation.3. One sided scanning.4. Senses clear materials when

distance is not fixed.5. Ease of alignment



Target



TYPES OF NON-CONTACT SENSORS:PHOTOELECTRIC SENSORS

Proximity (diffuse) Background Suppression

Background suppression utilizes 2 receivers behind the receiving lens. They areaimed at a precise point in front of the unit and sense the presence of a targetwhen the output of both receives are equal.

Applications:

• Material handling - conveying systems• Collision detection for AGV’s (Automatic Guided Vehicles)• Car / truck wash• Level sensing


Retroreflective:• Light beam is directed at a reflective target

(reflector, tape or other reflective object) -one which returns light along the same path it was sent.

• The object to be detected passes between photoelectric control and reflective target.

Advantages:1. One-sided scanning2. Ease of alignment3. Immune to vibration



Target

Retroreflective

Reflector



Convergent:• Light beam is directed at object to be

detected (ignores background surfaces)

• Object must be at a given distance in relationship to photoelectric control before light will be reflected to receiver

Advantages:1. First choice for detecting clear

materials2. Ignores unwanted background

surface reflection3. Detects objects with low reflectivity4. Detects height differential



Target

Convergent Beam

FixedDistance




TYPES OF NON-CONTACT SENSORS:PHOTOELECTRIC SENSORSFiber Optic Sensors

What do you do when the physical constraints of the application don’t allow forinstalling regular, self-contained sensors? Maybe the target is in a high temperatureor chemically aggressive environment. Perhaps the target is small or very fast-moving.Fiber-optics, applied to photoelectric scanning, solves these problems.

Fiber Optics and SensingAll fiber optic sensing mode are implemented using one type of amplifier which containsboth emitter and receiver in one housing.

Fiber Optic Thru-beam ScanningUsing two opposed, individual fiber optic cables, the object to be detected breaks thebeam. The target must be at least the same dimension as the effective beam, which inthis case, is the bundle diameter. Because the beam is very small, the detection can bevery precise. A typical application might be edge detection for a web printing press.Needle tips reduce the beam dimension for use with extremely small targets, typical forapplication in semiconductors and pharmaceutical industries.

Typical application:• Small parts detection• Edge detection• High temperature environment (600 degrees F+)


Fiber Optic:• Not a scanning technique but rather another way of transmitting light beam.

Advantages:1. High temperature applications 4. Corrosive areas2. Where space is limited 5. Noise immunity3. Size and flexibility of fiber leads 6. Color sensing



Target orReflector

Thru



Polarized:• Will work only with comercube

reflector or special polarized reflective tape.

• Will not false trigger when sensing shiny object.

Advantages:1. One-sided sensing2. Does not false trigger off

highly reflective object3. Senses clear materials4. Ease of alignment5. Immune to vibration



Target

Polarized

SpecialReflector




APPLICATION SCAN TECHNIQUESmall parts detection Fiber optics or Thru scan with aperaturesLong distance scanning Thru scanHigh temperature sensing Fiber opticShiny object or film detection Polarized scanSevere environment (Extreme dust or dirt) Thru scanLimited mounting space Fiber opticExplosive environment Thru scan or RetroWashdown environment Thru, Retro-reflective or DiffuseAnalog position sensing Diffuse or Fiber OpticConveyor Monitor - Jam detection - Part count - Part position

Polarized, Diffuse or Retro

Vibratory Feeder Fiber opticLid or Cap detection Convergent beam or Fiber OpticClear bottle detection Polarized or Fiber OpticTransparent material Polarized scanLabel detection Diffuse or Fiber OpticBin or hopper level Thru when using window Diffuse from aboveMold or die clear to close Thru scan or Fiber Optic (high temp)Max height monitor (i.e. Fork trucks) Thru scanOpaque material on semitransparent carrier Thru scanMotion detection All scan type

APPLICATIONS FOR PHOTOELECTRIC SENSORS



ADVANTAGES DISADVANTAGES APPLICATIONS

Magnet Operated - Inexpensive - Magnet required - Security and safety(reed relay) - Very selective target - Sensitive to welding interlocking

identification fields - Sensing thru metal

Hall Effect - Complete switching - Magnetic target only - Keyboard function is in a single - Extremely sensitive to integrated circuit industrial environment- Operates up to 150khz- High temperature (150 degrees C)- Good resolution

Ultrasonic - Senses all materials - Resolution - Anti-collision on AGV- Repeatability Doors- Sensitive to background and environment changes- Distance limitation to 60mm

Inductive - Resistant to harsh - Presence detection on all environments kinds of machines- Easy to install - Very popular- Very predictable

Capacitive - Senses all materials - Very sensitive to - Level sensing with liquids- Detects through walls environment changes and non-metallic parts

Photoelectric - Senses all materials - Subject to contamination - Parts detection- Material handling- Packaging- Very popular

Piezo-electric - Torque (automated or manual)



NEW APPLICATIONS:• Pressure sensing

• Shape sensing

• Weight sensing

• Presence sensing

• Color sensing (dark vs light)

• Torque sensing (Piezo-electric)

• Position sensing• Custom / adaptive size parts

• Vacuum sensing

• Flow sensing (e.g. gallon / minute)



POKA-YOKE Sensors at a Deming Prize Winner1. Mechanical 9. Heat Sensor

2. Magnetic 10. Gas Sensor

3. Beam Cut 11. Force Sensor

4. Super Sonic 12. Torque Sensor

5. Image Sensor 13. Meter Relay

6. Counter 14. Vibration Sensor

7. Beam Reflector 15. Automatic Measurement

8. Pressure Sensor



THE MOST EFFECTIVE TYPES OF ERROR NOTIFICATION MEANS

Getting the Operator’s Attention:

• Visual Signal (flashing light is best)• Audio Signal (loud and persistent, e.g. burglar alarm)• Protective Barrier (to prevent defect or operator injury)• When used: low defect occurrence rate and when

repairs can be made.

Shutting Down the Operation:

• Upon detecting a “non-conformance” the operationis simply shut down, i.e. the next part will not beprocessed.

• When used: relatively higher occurrence rates andwhen repairs are not possible.



Problem Type Error ProofingInstalled

Type ofSensor Used

Type ofIntervention Used

Missing Components Counter to verify Micro-switch Machine interlockcorrect number ofcomponents

Pre-counting the None Nonenumber of components

Fixture at the operation Proximity switch Machine interlockto detect the presenceof component from theprevious operation

Incorrect Processing Process sequence None (all fixtures Nonefixturing specially designed)

Wrong Components Verifying component Light transmission Video or audio alarmsshape, weight, ordimension switches

EXAMPLES OF POKA-YOKE’SFOR THE THREE MOST COMMON PROBLEMS



What is the best method for sensing fluid levelsfor a machine?

What is the best method for sensing magnets forelectric motors?

What are three possible methods for sensing burson a cylinder bore?

What is the best method for detecting the presenceof an O-ring?

BEST SENSING IDEAS


Four Categories of Errors - Questions to Ask????

Missing Parts Is there a model mix such that some models require a part

while others require nothing at all in that location?

Is the part assembled as a small part after some main activity?

Is the part difficult to see after being assembled?


Missing PartsIs the part :

Unseen or untouched in subsequent process steps?Difficult to see during assembly?Difficult to assemble?Difficult to see after assembly?Difficult to differentiate between pre and post assembly?

Can anything be done to resolve this in design of product/process?Can the part be combined with another part?Can the part be eliminated?

What can be done to detect whether the part has been assembled?

Detection device - torque counter, photoelectric eye over container, limit switch at dispenser,....

Lock out subsequent operation if part is missing.

Lock out device - limit switch, conductivity sensor...

Implement operator instructions, visual aids and training as minimum requirement

YES

NO

NO

Implement Error Proofing(process/design change and/or

detect/lock out device)

Verify results

YES


Brainstorm Error Proofing Mechanism

Make visible/obvious if missing Color contrast Visible at numerous operations and pack Use mirrors Position of part as moves down line Visual aid/picture posted with part present and highlighted

Redefine process Assemble early in process Successive check Rearrange multiple write-up to eliminate “sometimes do/sometimes don’t”

Monitor part supply Only supply parts needed for that model (no questions-if there are parts

present, use them) Lot control, count parts-must equal # pieces produced

Sensors Photoelectric eyes to detect, lock out until corrected Limit switch to detect, lock out until corrected

Modify design Eliminate part

Missing Parts - Thought Starters


Misassembled Parts Is the operation difficult for the operator to see as they

perform the job?

Is there an assembly or positioning operation that can be completed incorrectly?

Four Categories of Errors-Questions to Ask????


Misassembled PartsIs the part :

Difficult to see during assembly?Difficult to assemble?Difficult to see after assembly?Difficult to differentiate between pre and post assembly?Lacking guides or fixtures for proper assembly or proper alignment?

Can anything be done to resolve this in design of product/process?(guides, fixtures, automation)Can the part be combined with another part?Can the part be eliminated?

What can be done to detect whether the part has been misassembled?

Detection device - torque counter, photoelectric eye, limit switch

Lock out subsequent operation if part is misassembled.



YES

NO

NOImplement Error Proofing

(process/design change and/or detect/lock out device)

Verify results

YES



Visual aids Visual aid/picture posted with correct position highlighted

Redefine process Assemble early in process Successive check

Workplace organization Organize for maximum ease and visibility


Modify/design fixture Unable to assemble incorrectly

Modify design Eliminate part Prevent misassembly - e.g. two sizes of studs Provide guides or references

Misassembled Parts- Thought Starters


Incorrect Processing Is there an operation that requires a recognition of some

characteristic to determine what to do with the part next?

REJECTSGOOD



Incorrect ProcessingDoes the operation require recognition of some characteristic to determine what to do with the part?

(e.g. Red light indicates place in reject pile, visual inspection for pre-defined defects)

Can anything be done to resolve this in design of product/process?(fixtures, automation)Can the part be combined with another part?Can the part be eliminated?

What can be done to detect whether the part has been incorrectly processed?

Detection device - reset button,photoelectric eye, limit switch

Lock out subsequent operation if part is incorrectly processed.



YES

NO

NO



Verify results

YES



Visual aids Quality alert indicating high potential for error Fixture or template outlining pre-defined defects Bogey or sample boards for visual inspection

Redefine process Reset or acknowledge but at the appropriate next operation Automate

Workplace organization Separate and clearly label reject locations/containers


Incorrect Processing- Thought Starters


Incorrect Parts Is there a selection of parts in front of the operator that would

allow for the wrong part to be chosen and assembled?



Incorrect PartsIs there a selection of parts available at the workstation?Are similar parts assembled onto the product at the same location?

Can anything be done to resolve this in design of product/process?(Consolidation, separate operations)Can the part be combined with another part?Can the part be eliminated?

What can be done to detect whether the incorrect part has been assembled?

Detection device - bar code,photoelectric eye, limit switch

Lock out subsequent operation if the incorrect part is detected



YES

NO

NO



Verify results

YES



Make visible/obvious if incorrect part Color code - match part to product Visible at numerous operations and pack Position of part as moves down line Visual aid/picture posted with correct part present and highlighted

Redefine process Assemble early in process Successive check Rearrange multiple write-up to separate assembly of like parts

Monitor part supply Only supply parts needed for that model


Modify/design fixture Unable to assemble incorrect part

Modify design Eliminate part Prevent assembly of incorrect part

Incorrect Parts- Thought Starters


The Error Proofing Process:– Utilizes a multi-functional approach– Is driven by Customer Satisfaction and allows for

Quick response and implementation of solutions– Is used to “Kill” problems– Is documented in the ‘Problem Solving Document’

(PSD)– Supports Continuous Improvement Methodology– Is the ‘Contain’ step in the 5 Step Problem Solving

Process

People&

Teamwork

5. Evaluate 1. Identify

2. Analyze

3. Plan

4. Implement

Prevent Select

ContainCorrect

Error-Proofing Process“Quick Response / Quick Implementation”

Institutionalizethe Solution

and the OngoingControl

Institutionalize ContinuousImprovement Opportunity

Problem Solving Documentation

First TimeQuality(F.T.Q.)

atOperation

DepartmentalContainment

StationNetwork

InternalPlantAudit

CustomerRejects(PPM)

SystematicProblemSolvingProcess

Candidates for Error Proofing

WarrantyInformation


1% DEFECT RATE (99% YIELD)OF ALL STATIONS

RESULTS IN 78%CONFORMING PRODUCTS

Cell 1

Cell 3

Cell 2

Cell 4

1%DefectRate

1%DefectRate

1%DefectRate

1%DefectRate

1%DefectRate

1%DefectRate

1%DefectRate

1%DefectRate

1%DefectRate

1%DefectRate

1%DefectRate

1%DefectRate

1%DefectRate

1%DefectRate

1%DefectRate

1%DefectRate

1%DefectRate

1%DefectRate

1%DefectRate

1%DefectRate


PROCESS FALLOUT TABLECentered Process

Process capability ratio Parts per million defective0.50 133,600.000.75 24,400.001.00 2,700.001.10 967.001.20 318.001.30 96.001.40 26.001.50 6.801.60 1.601.70 0.341.80 0.062.00 0.0018


DIDN’T WASHHANDS


Implementation Procedure:• Product Tooling Design Phase

¶ Predict Potential Quality Defects during Product Tooling Design Stage.

Use DFM to modify Tooling Design to Prevent Potential Defects from Occurring in Production based on Potential Defects Identified.

Build Poka-Yoke Devices into the Process where Design “Fixes” can not be Incorporated.

ERROR PROOFING


• Production Phase¶ Retro-fit Poka-Yoke Devices into Existing

Tooling Use Quality History to Target Potential Error

Proofing Application Sites Obtain Set-Up Operator Input as to Where to

Apply “Error Proofing” Devices as well asthe Type of Devices to Use.

Implementation Procedure (Continued):

ERROR PROOFING


Some Error Proofing Guidelines:• Standardize Press Shut Heights• Utilize Digital Process Parameter Gages• Apply Locating Devices to Dies, Fixtures, Etc.• Gages Pre-calibrated prior to Start of Set-Up• Utilize Common/”Quick Connect Fittings and

Clamping Hardware• “One Way” Loading• 100% Component Presence Check• Verify “Machine Cycle Completed”• Detected “Error” Stops Process

ERROR PROOFING


CASUAL CONNECTIONS BETWEEN DEFECTS AND HUMAN ERRORS

Causesof Defects

Omitted Processing

Processing Errors

Errors Setting Up Workpieces

Missing Parts

Wrong Parts

Processing Wrong Workpiece

Misoperation

Adjustment Error

Improper Equipment Setup

Improper Tools and Jigs

HumanErrors

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SOURCE: NKS/Factory Magazine “Poka-Yoke”

error-proofing techniques (poka-yoke) concept · eprefer.ppt - 09 2/13/00 error-proofing techniques...

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