ct devices for dimensional metrology
TRANSCRIPT
CT devices for Dimensional Metrology
Filip Geuens
CTO - Nikon Metrology
Symposium on Computed Tomography
KULeuven – Group T
4th June 2013
Content
1. Vision about Metrology CT
2. Benefits of Metrology CT
3. Traceability of Metrology CT
4. Needs for Research
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4. Needs for Research
2
New production technology requires new metrology
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Metrology CT measurement process
NM CT Pro
3D volume reconstruction
NM Inspect-X
2D data collection
Feature inspection + CAD compare
MCT will lead to integrated
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Defect analysis
integrated material and dimensional
analysis
X-ray history of Nikon Metrology
The company began as
X-Tek Systems Ltd specialising
in real-time micro-focus X-ray
Acquired in 2007 by Metris, a
metrology company and
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metrology company and
KULeuven spin-off
Became part of Nikon group as Nikon Metrology in 2009
Legacy Method - Measurement in a non-metrology system
Measure with traceable touch probe to get calibrated value
Measure with system and measure the
Compare the values and calculate the error
Adjust the scaling based on minimising the error of the calibration piece scan
Scan the specimen and the calibration artefact at the same position and under the same X-ray conditions
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and measure the same distance
piece scan
Advantages:•Simplicity•Any CT system can make measurements
Disadvantages:•Difficult to determine measurement uncertainties•Must be performed for every new manipulator position•Slow•Calibration artefact must have similar radiographic properties to part
Example - Specialised blade inspection
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Research new material and production techniques
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2D CT slice of carbon fiber plate with impact region
De-lamination below impact
Research new material and production techniques
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How are the carbon fibers woven?
Benefits MCT over traditional metrology
Reduce total measurement time
• Measurement + reconstruction time independent from
number of features
• Very easy machine programming & operation
Provide better insight in problem to reduce number of
iterations
• 3D image provides better insights
• Higher productivity
• Shorter time to market
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• 3D image provides better insights
But also
• Avoid destroying sample
• Do any analysis at any time without remeasuring
10
Current Metrology CT
Temperaturecontrolled enclosure
20OC ±±±±1OC
Strengthened
manipulator for
maximum stability
MPESD = 9 + L/50
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High resolution
detector
200 µm pixel size
Precision manipulator
•High resolution encoders
•Error mapping using laser
interferometer
In-house
designed micro-
focus source for
sharp low-noise
images
How do we verify accuracy of performance VDI/VDE 2630
– not quite a standard but all we have for now
What is VDI 2630?
VDI/VDE 2630 is a guideline for verifying the accuracy of a CT metrology system.
It is published in Germany and is being adopted by CT Metrology manufacturers.
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It is not an agreed standard, there is scope for variation within the Guidelines.
Forms the basis of the current ISO draft. TC213 WG10
Verification - A standard is needed
– “the missing link”
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Method and Artefact with reference to
VDI/VDE 2630 part 1.3
Spatial Resolution
Using calibration piece suggested by University of
Padua.
Scan piece with main calibration piece
D
d
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Fit spheres and calculate diameter of circle of confusion
on co-tangent plane
Using circle diameter calculate the spatial resolution
DR
22dDDR −−=
Many factors influence the accuracy of CT measurement tools
�Specimen surface condition, shape, topology and material(s).
�Data handling - Reconstruction methods, introduction / suppression of artefacts, data filtering techniques, 3D model creation, surface finding and thresholding.
�Radiographic factors, kV, mA, magnification and filtering – effect of scatter.
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�Detector physics: incl. sensitivity, resolution and geometry.
�Environmental temperature and vibration
�X-ray source: focal spot size and shape, spectral content
�Specimen mounting, stability and orientation.
Major issue - Multi-material assemblies
Optimised for low density
Optimised for high density
Compromise
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Measurement
possible, accuracy
depends on object
No accurate
measurement possible
Accurate
measurement
possible
•CT has evolved from a qualitative inspection tool to a quantitative measuring instrument.
•The ability to verify accuracy and repeatability in a traceable way is essential to enable more widespread adoption.
•A recognised standard is needed.
Summary and Conclusions
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•Metrology CT will have an impact on the market of dimensional inspection and merge it with material inspection.
But …
•Still more research needed for better understanding and making it applicable to a wider range of applications and parts
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