Dimensional Measurements with Micro- CT -Test · PDF filewith Micro- CT-Test Procedures and...
Transcript of Dimensional Measurements with Micro- CT -Test · PDF filewith Micro- CT-Test Procedures and...
‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Ulrich Neuschaefer-Rube, Markus Bartscher,
Marko Neukamm, Frank Härtig
PTB Physikalisch-Technische Bundesanstalt,
Braunschweig und Berlin, Germany
Karsten Ehrig, Andreas Staude, Jürgen Goebbels
BAM Bundesanstalt für
Materialforschung
und –prüfung Berlin, Germany
Dimensional Measurements
with Micro- CT
-Test Procedures and Applications20 mm
10 mm
1 mm
2 mm
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
1. Introduction
2. Test procedures
and error correction
3. Application examples
4. Conclusions
Content
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Set-up of industrial computed tomography (CT)Measurement object on rotary table between X-ray source and X-ray detector
Micro-CT: Cone-beam and area detector
Scale factor dependent on the distances between X-ray source, measurement object
and detector
Introduction
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
geometry fittingwall thickness
analysis
result report
measurement object
threshold process
CT measurement
voxel data
surface datareference data
(e.g. CAD model)
actual/nominalcomparison
Introduction
Flow chart of typicaldimensional CTmeasurement processes
�Each step contributes
to the measurementuncertainty of CT
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Introduction
Structural resolution depends on:Size of X-ray focus
Minimal distance between X-ray source and measurement object
Distance between measurement object and detector
Pixel size of detector
…
Smallest achievable voxel size (X-ray tube): approx. 1 µm (Ø object approx. 2 mm)
Smallest achievable voxel size (Synchrotron): approx. 0,5 µm (Ø object approx. 2 mm)
Further reduction possible with microscope set-up
Image:Andrei Tkachuk et. al:Z. Kristallogr. 222 (2007) 650–655
‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Carl Zeiss Fraunhofer-Gesellschaft Werth Messtechnik
RayScanTechnologies
GE sensing& inspection
YxlonInternational
Introduction
Industrial CT available and manufactured in Germany (examples)
WenzelVolumetric
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
� stability / drift� quantum efficiency � dynamics� contrast sensitivity � internal scattering� pixel variance, noise
detector
� spectrum� focus properties� stability� temperature� opening angle
X-ray source
� radial movement� axial movement� angular-position error� wobbling� linear-position error
rotary table / translation axis
� reconstruction� threshold & surface
generation � data reduction � data corrections
software / data processing
� penetrated depth� beamhardening� scattered radiation � multiple materials
measurement object
Micro CT-system of the BAMacceleration voltage: 30 - 225 kVflat panel X-ray detector: 2048 x 2048achievable voxel size: (3 µm – 200 µm)3
maximum object diameter: 180 mm
� source current� acceleration voltage� integration time� number of projections
� object orientation
user
� temperature / - gradients
� vibrations
environment
� guiding errors� squareness� local heating� intrinsic vibrations
geometry
Introduction - Influences on CT measurements
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Advantages of CT as dimensional measurement technique
� Non-destructive
� Determination of inner and outer geometry
� Achieves a very high point density in relative short time
Disadvantages of CT as dimensional measurement technique
� No accepted test procedures available so far (see following)
� Complex and numerous influence quantities
� Reduced form measurement capability due to measurement errors (artefacts)
� Measurement uncertainty in many cases unknown
Solution
� Apply material standards to correct measurement errors and achieve traceability
� Adopt experiences from coordinate metrology to CT:Use material standards and characteristics to qualify new technique
CT acts as coordinate measuring machine (CMM)
Introduction
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Test procedures
German standardisation activitiesVDI-GMA 3.33 technical committee
“Computed tomography in dimensional metrology”
Acceptance and reverification tests for
dimensional CT systems are described in:
VDI/VDE 2617 Sheet 13
= VDI/VDE 2630 Sheet 1.3 (Draft)
“Computed tomography in dimensional metrology -
Guideline for the application of DIN EN ISO 10360
for coordinate measuring machines with CT sensors”
International standardisation activitiesISO TC213, WG 10:
Dimensional CT accepted as a work item
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Test procedures
Characteristics in VDI/VDE 2617 Sheet 13 / VDI/VDE 2630 Sheet 1.3
Global error characteristics
Error of indication for length measurement (length measurement error)
Material standard: length standard, e.g. step gage, ball bar, ball plate, gauge block
Local error characteristics
Probing error (size and form) PS, PF
Material standard: reference sphere
CT-specific characteristics (optional)
Material- and geometry-dependent errors GS, GG, GF
Material standard: step cylinder
Structural resolution (additional to every specification)
Material standard: e.g. small spheres (under discussion)
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Material standardsfor conventional CMM
Material standardsfor micro-CT systems
Mini-Probe
Calottecube
Ballplate
Stepgage
10 mm
Test procedures
10 mm
10 mm
Development of material standards
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Test procedures - Material standards
1 mm
Microtetrahedron
10 mm
Miniprobe
20 mm
Spherecalotte plate
10 mm
Spherecalotte cube
Length standards / test spheres for CT application
300 mm
Step cylinder
CT-specific standards
Multi-material ringsRing / Cylinder pair
25 mm
10 mm
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Advantages
Increased information content compared
to 2D standard
Traceable tactile calibration available
Standard can be used with
others sensors, too (multisensor)
Sphere calotte cube made from titanium
Calottes manufactured by eroding (EDM)
Cube features 3 facets (x, y, z)
with 5 x 5 calottes
Calottes: Ø 0.8 mm
form deviation: nominal < 2 µm
Optional:
Cavity at the bottom
Modified calotte grid
Test procedures and error correction
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Application of sphere calotte cube to reduce scale errors
Sphere distance deviation of a CT measurement of calotte cubebefore (red squares) and after (black squares) scale correction
0 2 4 6 8 10 12 14 m m
-8
-6
-4
-2
0
2
46
810
12
1416
µm
sp
here
dis
tan
ce
de
via
tion
m easured length
voxel size 15 µm
2775 lengths
red = uncorrected
black = corrected
Recent result
(other CT system):
Max. deviation
< 1 µm
Test procedures and error correction
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Application of sphere calotte cube
Spatial distribution of the residual position errors of a corrected CT system Cone beam CT 180 kV, (18.4 µm)3 voxel size
measurement position
Test procedures and error correction
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Probing error form PF after correction ≈ 2 µm (voxel size)Probing error form PF before correction < 5 µm
Micro tetrahedron(Ruby balls 0,5 mm)
Manufactured by PTBusing micro mechanics
CT measurement BAM 100 kV, (2 µm)3 voxel size
µm
1 mm
Correction of geometry errors of involved CT axesapplying micro tetrahedron
Test procedures and error correction
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
No. of teeth 14
Normal modul mn 0.12 mm
Pressure angle α0 20°
Addendum modification coefficient x
0.12
Base circle radius rb 0.789 mm
Helix angle β0 0°
Tip diameter da 2.0 mm
Face width b 1.0 mm
Reference circle radius r0 0.840 mm
Example 1 – Micro spur-gear study
CAD of micro spur-gear
Parameters of micro spur-gear under study
Micro spur-gear
made from steel
2 mm
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Example 1 – Micro spur-gear study
Micro-CMM measurements (Carl Zeiss F25)using software Zeiss Calypso and Gear Pro
Tactile micro probeProbe diameter 120 µm
Analysis parameters:Tooth No. 1, 5, 8, 12
Flanks left and right
Radius / length of roll foot rSAP / lαSAP 0.845 mm / 0.301 mm
Radius / length of roll tip rEAP / lαEAP 0.985 mm / 0.589 mm
Reference for the height -0.05 mmof measurement (related to the datum face
of the gear)
Measurement range in height 0.7 mm
Measurements with F25 by Michael Neugebauer (PTB)
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Example 1 – Micro spur-gear study
used BAM micro-CT system
Voltage Filtering No. of angles Time Detector size
80 kV 0.25 mm Cu 1800 5 h 2048 x 2048
Data binning Reconstruction Voxel size Surface extraction No. of measurements
No Feldkamp (3.6 µm)3 adaptive 6
reconstructed volume reconstructed volumeconstant threshold surface with adaptive threshold
Parameters of micro CT measurement
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Example 1 – Micro spur-gear study
Registrationand analysisof data
Object
CMM-measurementwith Zeiss F25 CMM
Projection with µCT at BAM
Reconstruction
Voxel data
Adaptive threshold
Surface
Comparison
Best fit alignment
Report
Aligned flanks
Point Data
First:Define workpiececoordinate systemwith Calypso.
Second:Measure the flanks with gear specific software Gear Pro.Orientation of the x-axes is unknown!
Tooth flanks
Define coord. system
Define Zeiss F25 CMM workpiece
coordinate system
Best fit alignment with restricteddegrees of freedom
Probe radius correction
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Example 1 – Micro spur-gear study
Deviation of CT measurement (data-set 1 of 6)
Distribution of deviations without strong outliers
me
asure
me
nt err
or
in m
m
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Example 1 – Micro spur-gear study
Histogram of all 6 assessed measurements
Analysis of deviations
95% of all observed absolute deviations are less 0.0037 mm
Due to the statistics of 6 measurements (correction with t-distribution) a value of 0.0048 mm can be attributed as a first measureof the uncertainty of measurement
0
500
1000
1500
2000
2500
3000
3500
-0.006 -0.004 -0.002 0 0.002 0.004 0.006
measurement error in mm
freq
uen
cy
0
500
1000
1500
2000
2500
3000
0 0.001 0.002 0.003 0.004 0.005 0.006
absolute value of measurement error in mm
freq
uen
cy
0%
20%
40%
60%
80%
100%
cu
mu
lati
ve p
erc
en
tag
efrequency
cumulative %
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Example 2 – Internal micro gear study
No. of teeth 40
Normal module mn 0.12 mm
Pressure angle α0 20°
Addendum modification coefficient x
-0.79
Base circle radius rb 2.615 mm
Helix angle β0 0°
Tip circle diameter da 4.8 mm
Root circle diameter df 5.23 mm
Internal micro gear
made from steel
lengthca. 11 mm
� Reference measurement with micro CMM
Werth VideoCheck HA 400 with tactile-optical probe
Probe diameter: 61 µm
Modus of operation: single point probing
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Reproducibility test of CMM measurement (7 measurements)Result of gear analysis: Profile deviations (example: tooth 10, left flank, z = -0.4 mm)
Reproducibility better than 1 µm in analysis interval
Example 2 – Internal micro gear study
-0.005
-0.0025
0
0.0025
0.005
0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 1.3
length of roll in mm
pro
file
dev
iati
on
in
mm
tooth tip tooth rootanalysis interval
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Synchrotron CT measurement
at BESSY BAMLine
Report
Object
Threshold
Voxel data
Surface
Comparison
Reconstruction
Segmented slice data
Gear analysis
CMM meas.
Gear analysis
Example 2 – Internal micro gear study
Energy: 60 keV
Voxel size: (2.2 µm)3
Detector: GdOS scintillator,
CCD-camera
(3209 x 801 pixel)
Exposure (each): 3 s
No. of angles: 2500 (0°-180°)
Projection
Point data
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Comparison of CT and CMM dataResult of gear analysis: Profile deviations (example: tooth 10, left flank)
Deviations < 2 µm in analysis interval
Example 2 – Internal micro gear study
-0.005
0
0.005
0.01
0.015
0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 1.3
length of roll in mm
pro
file
de
via
tio
n i
n m
m
CT, z = -0.4 mm
CT, z = -0.6 mm
CMM, z = -0.4 mm
CMM, z = -0.6 mm
tooth tip tooth rootanalysis interval
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
� Complete dimensional measurements of microparts possible with micro-CT
� Smallest voxel size without optics approx 0.5 µm
� Successful application of material standards
� Standardization of dimensional CT:
- VDI/VDE 2617 Sheet 13 = VDI/VDE 2630 Sheet 1.3
available as Draft
- Work item CT in ISO TC 213
� Achieving traceability of CT measurements
is still a challenge
First results: measurement uncertainties of several
micrometer for small complex objects
� Vision in future:
CT is a fully accepted measurement technique
which is used coequal to conventional coordinate metrology
Conclusions
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Contact:
Thank you for your attention !
Activities are supported by the German Research Foundation (DFG)
project No. NE 757/2-2
and by the German Federal Ministry of Economics and Technology
project No. AZ: II D 5 – 07/06