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Company ConfidentialCopyright NN, Inc. 2004

Poka-Yoke Systems

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Mistake Proofing

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POKA YOKE

Inadvertent

Mistakes To Avoid( Yokeru )

The Poka-Yoke Concept was developed by Shigeo Shingo ,

who also developed the SMED System.

Poka-Yoke Systems

POKA-YOKE

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Human Errors are usually inadvertent.

Poka-Yoke devices help us to avoid defects

before they occur, even when human errorsare made.

Poka-Yoke is a too l that bui lds Qual i ty into th e

process and shi f ts the attent ion from detect ionand inspect ion to bui ld ing i t r ight the f irst t ime.

Poka-Yoke Systems

POKA-YOKE

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Two Arguments :

Errors are Inevitable:Humans always will make mistakes.

Where Do You Stand ?

Poka-Yoke Systems

ERRORS AND DEFECTS

Errors can be Avoided:Any kind of mistake people make

can be avoided one way or another!!

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Sampling Inspection vs. 100 Percent Inspection:

Sampling Inspection:Is an Average Quality Level (AQL) of0.10% good enough? One Customer in a thousand will get a

defective part !!

100 Percent Inspection:Can it efficiently become part of

your standard operation?? How??

INSPECTION

Poka-Yoke Systems

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Strategies for Zero Defects:

Dont Make Products You Do Not Need!!

The more parts you produce, the greater the opportunity for

defects to happen. Therefore, make only what you need,

when you need it, one piece at a time.

Build Quality into the ProcessPut safeguards into the production process to ensure quality.

Moreover, standardize the process and always think of

mistake proofing.

Cont inuous Flow

Make sure that continuously value is added to the product

until it is a finished product.

ZERO DEFECTS

Poka-Yoke Systems

This is where Poka-Yoke comes in!

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1. Forgetfulness: Forgetting a step or a part.

Safeguard:Checklist, Visual Standard Operating Procedure

2. Errors due to Misunderstanding: Not very familiar with

the required operation.

Safeguards:Continuous Training, Visual SOP

3. Errors in Identification: Problems in identification orclearness of required steps or parts.

Safeguards:Training, Visual Training, Standardization

Poka-Yoke Systems

TYPES OF ERRORS

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4. Errors due to Lack of Experience: New Employees.

Safeguard:Skill Building & Training, Work Standardization

5. Errors due to Lack of Standards: No clear way to perform

the task or job.

Safeguards:Standard Operations, Visual Instructions

6. Errors due to Machine Readability: Machine out of spec.Safeguards:TPM , Critical Parts List, Maintain Equipment

History List.

Poka-Yoke Systems

TYPES OF ERRORS

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Keep in Mind :Mistakes do happen for many reasons, but

almost all can be prevented if we take the timeto identify WHEN & WHY they happen and take

steps to prevent the recurrence of these errors

and mistakes by using a systematic approach

to Mistake Proofing aimed at eliminatingforeseeable errors.

Poka-Yoke Systems

TYPES OF ERRORS

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Defective Product

Material DefectsProcessing Defects

Processing

Omissions

Processing

Errors

Missing

Parts

Wrong

Items

Adjustment

Errors

Operation

Errors

Wrong

Piece

Wrong

Set-Up

Other

Errors

Poka-Yoke Systems

TYPES OF DEFECTS

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Information Material

People

Methodology / Procedure

The fou r elements of pro duc t ion determine whether a

produc t is correct ly manufactured or not .

Defect Free Products are a result of Contro l led Standardsof Operat ion in each of these pr incip le areas.

Poka-Yoke Systems

ELEMENTS OF PRODUCTION

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Omitted Processing

Processing Errors

Set-Up Errors

Missing Parts

Wrong Parts

Processing Wrong Work-Piece Adjustment Errors

Tools and Jigs improperly prepared

Poka-Yoke Systems

SOURCES OF DEFECTS

There are many sources o f defects ,

the fol lowing are a few to look for :

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Standardized Guiding Pins

Alarms

Lim i t Switches

Counters

Checkl is ts

Poka-Yoke Systems

FIVE BASIC CONCEPTS OF POKA-YOKE

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Detection

Prevention

Prediction

Warning

Have

Happened

About to

Happen

Poka-Yoke Systems

POKA-YOKE STRATEGY

A

ctions

Errors

Focus on this

first .

. and then

on this!

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Identify Items by their Characteristics:

By Weight: Establish weight standards to determine defective

parts by pre-defining the weight for a good part.

By Dimension: Length, Width, and Diameteretc.

Use jigs, fixtures, stoppers, and limit switches to eliminate errors

associated with positioning.

By Shape: Angles, Projections, Position of Holes, Curvature..etc

and Identify standards, limit switches, and fixtures.

Poka-Yoke Systems

POKA-YOKE HINTS

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There are three main methods for using Poka-Yoke Systems:

1. Contact Methods2. Fixed-Value Methods

3. Motion-Step Methods

Each of these methods can be used with eitherContro l

SystemsorWarning System. Focus on your end objective and

select the proper system accordingly.

Poka-Yoke Systems

METHODS FOR USING POKA-YOKE

SYSTEMS

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Contact Methods work by detecting whether a

product makes physical or energy contact with

a single detection device.

Micro Switches

Limi t Sw itches

Displacement Senso rs

Metal-Passage Sensors

A Variety of other Mechanical

& Electro -Mechanic al devic es

Poka-Yoke Systems

CONTACT METHODS

Contact Devices :

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Prox imi ty Switches: Respond to changes in distance from objects andto changes in magnetic force.

Posi t ion ing Sensors: Control cylinder strokes or determine screwheights.

Transm ission Pho toelectr ic Switch: Light beam between twoobjects detects any obstruction of beam.

Reflect ing Photoelectr ic Switch: Responds to light reflected from anobject to detect its presence.

Poka-Yoke Systems

CONTACT METHODS

Contact Methods may also be energy sensing devices that do

not physically touch the product but sense when something is

not in the desired position.

Energy Sensing Devices:

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Contact Methods do not have to be high-tech in order to be

effective. Some of the best contact devices are passive devices

SUCH AS :

Poka-Yoke Systems

CONTACT METHODS

Guide Pins Blocks

Jigs

Fixtures

Color Coded Devices

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Contact Devices often take advantage of parts that are designed

with uneven shape, such as a work-piece with a bump or a hole on

only one end. Use a Jig that matches the shape or a limit switch

positioned to detect an abnormal shape.

Poka-Yoke Systems

CONTACT METHODS

Rule of Thumb:

We can also make design recommendations based upon

adaptability to manufacturing.

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Fixed Value Methods are used when a fixed number

of parts must be attached to the product or when a

fixed number of repeated operations needs to be

done at a process station.

In this method, a device counts the number of times

something is done and signals or releases the product

only when the required number is fulfilled.

Poka-Yoke Systems

FIXED VALUE METHODS

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The Fixed-Value Method may use Limit Switches that are

tripped with each movement. The switch sends a signal to a

counter that detects when the correct number of movements

has taken place.

Poka-Yoke Systems

FIXED VALUE METHODS

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The Motion-Step Methods are used to sense whether a motion or

step in the process has been carried out within a certain

expected time, such as a machines Cycle Time.

Devices normally used in the Motion-Step Method:

Sensors

Photo-electric Switches

Timers

Counters

Poka-Yoke Systems

MOTION-STEP METHODS

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Poka-Yoke Sheet

POKA-YOKE SHEET

Department / Machine :

Assembly

Product :Bearing

Date :14 Dec. 2004

Problem :Ball missing.

Prevent ErrorX Shutdown

Solution :Sensing the difference of weight against standard

weight. Control

XDetect ErrorKey Improvement :Weighing scale installed on line.

Alarm

Before After

No device was present to detect Ball missing from the

bearing in the assembly cell.

Weighing machine installed on line after Etching station

which detects any Ball missing bearing and the transfer

plate automatically stops if any bearing comes even withone Ball missing.

Poka-Yoke Sheet

POKA-YOKE SHEET

Department / Machine :

Assembly

Product :Bearing

Date :14 Dec. 2004

Problem :Ball missing.

Prevent ErrorX Shutdown

Solution :Sensing the difference of weight against standard

weight. Control

XDetect ErrorKey Improvement :Weighing scale installed on line.

Alarm

Before After

No device was present to detect Ball missing from the

bearing in the assembly cell.

Weighing machine installed on line after Etching station

which detects any Ball missing bearing and the transfer

plate automatically stops if any bearing comes even withone Ball missing.

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Poka-Yoke Sheet (blank)

POKA-YOKE SHEET

Department / Machine : Product :

Date :

Problem :

Prevent ErrorShutdown

Solution :

Control

Detect ErrorKey Improvement :Alarm

Before After

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POKA-YOKE

8 MAIN PRINCIPLES

Bu i ld Quali ty into the pro cess.

All in advertent errors and defects can be el iminated.

Stop doing i t wrong and s tar t doing i t r ight - now !!!

Do not th ink up excuses, th ink about doing i t r ight .

An80% chance of success is good enough - focus

on implementat ion.

Attack d efects and errors as a team .

Ten heads are better than one - B rainsto rm id eas,Discus s, Think.

Seek out the root cause, use the 5 Whys.

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Poka-Yoke Systems

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The Sensing Devices used in the Poka-Yoke System can be

divided into three broad categories:

Physical Contact Sensing Devices

Energy Sensing Devices

Sensors that detect change in Physical Condition

- Pressure: Pressure Gauges

- Temperature: Thermometers

- Electrical Current: Meter Relays

Poka-Yoke Systems

TYPES OF SENSING DEVICES

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Physical Contact Sensing Devices

limit switches

microswitches

touch switches

trimetrons

Energy Sensing Devices

transmission types

reflection typestransmission types

reflection types

proximity switches

fiber sensors

area sensors

position sensors

dimension sensorsvibration sensors

displacement sensors

tap sensors

metal passage sensors

color-mark sensors

double-feed sensors

weld position sensors

photoelectric

switches

beam sensors

line plane

Passage

Presence

BreakConfirmation

ofPosition

Measurement

Overlap

Shape

Foreign

Matter

Damage

Color

Mismatch

What They Detect

Types of Sensors

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Physical Contact Sensing Deviceswork by physically touching the product

or machine part. In many cases, particularly in automated processes, physical

contact sensing devices send an electrical signal when they are touched. This

signal can be a command to start or stop a machine or a warning. Here are

some common examples:

Limit Switches and Microswitches are the most common devices. They areused to confirm the presence and position of objects that touch the small lever

on the switch.

Touch Switches have the same basic function as a limit switch, but they are

activated by a light touch on a thin antenna. Touch switches are more

sensitive than limit switches and can detect whether an object is present,properly positioned, broken, or of proper dimensions.

Trimetrons are needle-type gauges that send out signals to sound alarms or

stop machinery when the conditions they measure are not within acceptable

limits.

Poka-Yoke Systems

PHYSICAL CONTACT SENSING DEVICES

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Energy Sensing Devicesuse energy rather than physical contact todetermine whether an error is occurring. Here are some examples:

Photoelectric switches use beams of light to inspect transparent objects,judge welds, or verify conditions such as proper size and color.

Beam sensors use electron beams to verify conditions such as the

proper level of liquid in a container or the passage of an object on aconveyor.

Proximity switches respond to changes in distance from objects and tochanges in magnetic force.

Fiber sensors detect motor revolutions, color coding marks, or marks on

translucent objects or printed matter.

Area sensors detect random breaks in a fixed area, such as handsplaced in hazard areas or parts dropping from a conveyor.

Position sensors control cylinder strokes or determine screw heights.

Poka-Yoke Systems

ENERGY SENSING DEVICES

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Dimension sensors ensure correct product dimensions.

Vibration sensors detect product ejection areas, width distortion, seam

position, or start of processing.

Displacement sensors detect and measure warping, thickness, and fluid

level heights.

Tap sensors detect incomplete tap screw machining.

Metal passage sensors detect metal in motion.

Color-mark sensors detect colored marks or differences in color.

Double-feed sensors detect two products fed at the same time.

Weld position sensors detect joints such as weld lines in coil stock,

seams in pipes and cans, or splices in wires.

Poka-Yoke Systems

ENERGY SENSING DEVICES

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