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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