why dimensional measurements don’t agree

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Dim

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Copyright 2007Digital Metrology Solutions, Inc.

Apples and Oranges:Apples and Oranges:

Why Dimensional Why Dimensional Measurements Don’t AgreeMeasurements Don’t Agree

Mark C. Malburg, Ph.D.Digital Metrology Solutions, Inc.

www.digitalmetrology.com

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es a

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Why

Dim

ensi

onal

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sure

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ts D

on’t

Agre

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hy D

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sion

al M

easu

rem

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Don

’t Ag

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Have you ever measured Have you ever measured anything that somebody else anything that somebody else has already measured or has already measured or will be measuring?will be measuring?

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Dim

ensi

onal

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sure

men

ts D

on’t

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hy D

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sion

al M

easu

rem

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The world in which we live…The world in which we live…

• Specifications• Instruments• Locations

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ensi

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sion

al M

easu

rem

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SpecificationsSpecifications

• The good old days…

Size/OrientationShapeSurface Texture

increasing scale

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SpecificationsSpecifications

• Things are getting messy…

Size/OrientationShapeSurface Texture

increasing scale

shrinking tolerances

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easu

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InstrumentsInstruments

• The good old days…

Micro-burrs &Torn Material

Roughness Form Errors Dimension(Size & Position)

Microscopy(Visual Assessment)

Sharp-Stylus(Roughness)Instruments

Special PurposeInstruments

Surface Plate(layout) Instruments& Gauges

λ

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ensi

onal

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sion

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easu

rem

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Micro -burrs &Torn Material

Roughness Form Errors Dimension(Size & Position)

Microscopy(Visual & DigitalAssessment)

Sharp-Stylus(Surface Texture)

Instruments

Waviness

Roundness & CylindricityInstruments

CoordinateMeasuringMachines(CMM's)

λ

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es a

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es a

nd O

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Dim

ensi

onal

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sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

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0.010


etc. …

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ensi

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on’t

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sion

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easu

rem

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LocationsLocations

• Globalization– Car (5,000 components, domestic% = ?)– Expanding Markets (global assembly)

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Measurements should adequately agree:Measurements should adequately agree:between between locationslocations,,

between between operatorsoperators,,and between and between devicesdevices..

Unfortunately, they don’t…Unfortunately, they don’t…

Ideally…Ideally…

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So where do we begin?So where do we begin?

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The Myth of RepeatabilityThe Myth of Repeatability

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• Repeatability and Reproducibility% R&R < 10%

Gage System is OK


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• A dead measurement system has perfectrepeatability!– And it can’t be “adjusted” into correlation.


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Beginning to understand…Beginning to understand…

Specification is a “language”.

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Beginning to understand…Beginning to understand…

• Unfortunately things get lost in translation.

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A couple of examples…A couple of examples…

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Example: Connecting RodExample: Connecting Rod

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The connecting rod “language” The connecting rod “language”

Twist

Bend

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easu

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Bend & TwistBend & Twist

• The “gauge” interpretation

“Bend“Bend--ometer”ometer”

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• The “gauge” interpretation


• The “scanning” interpretation

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• When “things go wrong” different interpretations can give wildly different results.

Apparent “Bend” with fixed gauging

?

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Example: Shaft leakageExample: Shaft leakage

• A “spiral” surface texture pattern can act like a pump.– To control this, a maximum “lead angle” is

specified.

Undesired Flow

RotationLead Angle

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Lead Angle AssessmentLead Angle Assessment

• “String test” • “Surface texture”

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Unfortunately…Unfortunately…

• Even in cases where the “language” is understood problems still arise.

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Dim

ensi

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01

01

01

00

11

Dig

ital

Met

rolo

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olut

ions


The Problem ParetoThe Problem ParetoRel

ativ

e Er

ror

Mag

nitu

de Stupidity

3rd Shift

Calibrati

onEnviro

nment

Definition

Dynamics

27

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

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01

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11

Dig

ital

Met

rolo

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olut

ions


The Problem ParetoThe Problem Pareto

• “Stupidity” Errors

28

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

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11

01

01

01

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11

01

00

01

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01

00

11

01

01

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11

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00

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00

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11

Dig

ital

Met

rolo

gyS

olut

ions



• “Stupidity” Errors– Wrong Part Program– Wrong Units

• Mars Explorer

– Typos • Applying calibration• Data transfer

29

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

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11

01

00

01

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11

01

01

01

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11

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00

01

00

01

00

11

01

01

01

00

11

Dig

ital

Met

rolo

gyS

olut

ions



• “3rd Shift” Errors

30

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

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11

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00

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01

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11

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00

11

Dig

ital

Met

rolo

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olut

ions



• “3rd Shift” Errors– Must have happened

before I got here.• Broken/Bent Stylus• Crashed probe

31

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

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11

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11

01

00

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11

01

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00

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00

01

00

11

01

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01

00

11

Dig

ital

Met

rolo

gyS

olut

ions



• Calibration Errors

32

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

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11

01

00

01

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01

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11

01

01

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11

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00

01

00

01

00

11

01

01

01

00

11

Dig

ital

Met

rolo

gyS

olut

ions



• Calibration Errors– Adjustment?– Validation?

33

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

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11

01

00

01

00

01

00

11

01

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11

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11

01

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01

00

11

Dig

ital

Met

rolo

gyS

olut

ions



• Environment

34

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

Dig

ital

Met

rolo

gyS

olut

ions



• Definition Errors

35

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

Dig

ital

Met

rolo

gyS

olut

ions



• Dynamics

36

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

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01

00

11

01

01

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01

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11

Dig

ital

Met

rolo

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olut

ions


Errors cost money!Errors cost money!Rel

ativ

e Er

ror

Mag

nitu

deTime & Money

spent diagnosing

and fixing

Stupidity

3rd Shift

Calibrati

onEnviro

nment

Definition

Dynamics

37

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

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11

01

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Dig

ital

Met

rolo

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olut

ions


A Closer Look at “Dynamics”A Closer Look at “Dynamics”

Since nobody likes to talk about it.

38

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

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11

01

00

01

00

01

00

11

01

01

01

00

11

Dig

ital

Met

rolo

gyS

olut

ions


Contrary to popular belief…Contrary to popular belief…

The world is not round.

www.spectrum3d.com

39

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

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11

01

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01

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11

01

00

01

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01

00

11

01

01

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11

01

00

01

00

01

00

11

01

01

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00

11

Dig

ital

Met

rolo

gyS

olut

ions


An “out of round world”…An “out of round world”…

• Perfect geometry is a bad assumption when dealing with the “last 10%”.


40

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

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11

01

00

01

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01

00

11

01

01

01

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11

01

00

01

00

01

00

11

01

01

01

00

11

Dig

ital

Met

rolo

gyS

olut

ions


An “out of round world”…An “out of round world”…

• Dimensional measurements must accommodate imperfect geometry.– Specification implications– Instrumentation implications

41

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

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00

11

01

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01

00

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00

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00

11

01

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00

11

Dig

ital

Met

rolo

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olut

ions


SpecificationSpecification

• How do you deal with bumpy surfaces?– Size?– Orientation?

42

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

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11

01

00

01

00

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00

11

01

01

01

00

11

Dig

ital

Met

rolo

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olut

ions


SpecificationSpecification

• Conventional Wisdom

Size

Form

SurfaceTexture

Size

Form

Surf

ace

Text

ure

43

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

Dig

ital

Met

rolo

gyS

olut

ions


Brake RotorsBrake Rotors

• Flatness ~2-5 µm• Peak-to-Valley Roughness ~10-15 µm

44

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

Dig

ital

Met

rolo

gyS

olut

ions


Cylinder BoresCylinder Bores

• Line element straightness: 1-3 µm• Peak to Valley Roughness: 4-8 µm

45

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

Dig

ital

Met

rolo

gyS

olut

ions


Wavelength Based SpecificationWavelength Based Specification

46

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

Dig

ital

Met

rolo

gyS

olut

ions


Wavelength Based SpecificationWavelength Based Specification

47

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

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01

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11

Dig

ital

Met

rolo

gyS

olut

ions


Can we see the same surface?Can we see the same surface?

(between instruments)

48

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

Dig

ital

Met

rolo

gyS

olut

ions


Understanding your instrumentUnderstanding your instrument

• Surface Texture Instrument Overlaps

1 mm

1 µm

1 nm

1 nm 1 mm 1 m

Hei

ght

Wavelength

AFM

InterferometricMicroscope

Stylus Instrument

1 µm

49

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

Dig

ital

Met

rolo

gyS

olut

ions


1 mm

1 µm

1 nm

1 nm 1 mm 1 m

Hei

ght

Wavelength

AFM

InterferometricMicroscope

Stylus Instrument

1 µm

Agre

emen

t is

Poss

ible


• Surface Texture Instrument Overlaps

50

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

Dig

ital

Met

rolo

gyS

olut

ions



• “Dynamic” calibrations

51

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

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11

01

00

01

00

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00

11

Dig

ital

Met

rolo

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olut

ions


A better dynamic assessment…A better dynamic assessment…

• Microphones…

52

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

00

11

01

01

01

00

11

01

00

01

00

01

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11

01

01

01

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01

00

01

00

01

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11

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A better dynamic assessment…A better dynamic assessment…

• A “chirp” waveform.Chirp Waveform

-1.5

-1

-0.5

0

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1

1.5

0 0.5 1 1.5

mm

µm

53

Appl

es a

nd O

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es:

Appl

es a

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es:

Why

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hy D

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easu

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“Chirp“Chirp--based” comparisons…based” comparisons…

• The “chirp” waveform– Current tool geometry causes deterioration of amplitude.

Measured Chirp Waveform

-1.5

-1

-0.5

0

0.5

1

1.5

0 0.5 1 1.5 2 2.5 3 3.5

mm

µm

54

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

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onal

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sure

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on’t

Agre

eW

hy D

imen

sion

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easu

rem

ents

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’t Ag

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• Tip radius implications– 5 µm tip radius

Measured Chirp Waveform (5 um tip radius)

-1.5

-1

-0.5

0

0.5

1

1.5

0 0.5 1 1.5 2 2.5 3 3.5

mm

µm

55

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

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ensi

onal

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sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

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• Tip radius implications– 0.5 mm tip radius

Measured Chirp Waveform (0.5 mm (500 µm) tip radius)

-1.5

-1

-0.5

0

0.5

1

1.5

0 0.5 1 1.5 2 2.5 3 3.5

mm

µm

56

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

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’t Ag

ree

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• Tracing speed implications– Doubling the speed

Measured Chirp Waveform (1.0 mm/second tracing speed)

-1.5

-1

-0.5

0

0.5

1

1.5

0 0.5 1 1.5 2 2.5 3 3.5

mm

µm

57

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

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• Filtering implications– 8.0 µm long-pass filter

Measured Chirp Waveform (8.0 µm short wavelength filter)

-1.5

-1

-0.5

0

0.5

1

1.5

0 0.5 1 1.5 2 2.5 3 3.5

mm

µm

58

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

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• Stylus arm dynamics– “Super small bore” stylus

Measured Chirp Waveform (miniature probe)

-1.5

3.5

8.5

13.5

18.5

0 0.5 1 1.5 2 2.5 3 3.5

mm

µm

59

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

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• Optical Methods– “White Light Interferometry” (shown in black)

Measured Chirp W aveform (W hite Light Interferometry - in black)

-1.5

-1

-0.5

0

0.5

1

1.5

0 0.5 1 1.5 2 2.5 3 3.5

mm

µm

60

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

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easu

rem

ents

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• AFM

Measured Chirp Waveform (AFM - segments in red)

-1.5

-1

-0.5

0

0.5

1

1.5

0 0.5 1 1.5 2 2.5 3 3.5mm

µm

61

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

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eW

hy D

imen

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easu

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ents

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’t Ag

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So what are we to do?So what are we to do?

1. Realize that the world isn’t round.

2. Accommodate “shape”in specifications andmeasurement.

3. Understand your instrument!

Measured Chirp Waveform (1.0 mm/second tracing speed)

-1.5

-1

-0.5

0

0.5

1

1.5

0 0.5 1 1.5 2 2.5 3 3.5

mm

µm

62

Appl

es a

nd O

rang

es:

Appl

es a

nd O

rang

es:

Why

Dim

ensi

onal

Mea

sure

men

ts D

on’t

Agre

eW

hy D

imen

sion

al M

easu

rem

ents

Don

’t Ag

ree

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Apples and Oranges:Apples and Oranges:

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why dimensional measurements don’t agree

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