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Over the past decade computed tomography (CT) with conventional x-ray sources has evolved from an imaging method
in medicine to a well established technology for industrial applications in fields such as material science, light metals and
plastics processing, microelectronics and geology. By using modern microfocus and nanofocus X-ray tubes, parts can be
scanned with sub-micrometer resolutions. Currently, micro-CT is a technology increasingly used for metrology
applications in the automotive industry. CT offers big advantages compared with conventional tactile or optical
coordinate measuring machines (CMMs). This is of greater importance if complex parts with hidden or difficult
accessible surfaces have to be measured. In these cases, CT offers the advantage of a high density of measurement
points and a non-destructive and fast capturing of the sample's complete geometry.
When using this growing technology the question arises how precise a μCT based CMM can measure as compared to
conventional and established methods for coordinate measurements. For characterizing the metrological capabilities of a
tactile or optical CMM, internationally standardized parameters like length measurement error and probing error are
defined and used. To increase the acceptance of CT as a metrological method, our work seeks to clarify the definition
and usage of parameters used in the field of metrology as these apply to CT. In this paper, an overview of the process
chain in CT based metrology will be given and metrological characteristics will be described.
For the potential user of CT as 3D metrology tool it is important to show the measurement accuracy and repeatability on
realistic samples. Following a discussion of CT metrology techniques, two samples are discussed. The first compares a
measured CT Data set to CAD data using CMM data as a standard for comparison of results. The second data second
realistic data set will compare the results of applying both the CMM method of measurement and the CT method of
measurement within the same CT data set. A comparison of these results to the data obtained by means of CT shows
that state of the art high resolution CT can provide measurement accuracy on the order of established coordinate
measurement techniques.
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