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Analysis and comparison of the surface filtering characteristics of computed tomography and tactile measurements

: Salzinger, Mario; Hornberger, Peter; Hiller, Jochen

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6th Conference on Industrial Computed Tomography, iCT 2016. Online resource : 9-12 February 2016, Wels, Austria
Wels, 2016
Paper id73, 8 pp.
Conference on Industrial Computed Tomography (iCT) <6, 2016, Wels>
Conference Paper, Electronic Publication
Fraunhofer IIS ()
dimensionales Messen; CT-Metrologie; CT-Bildqualität; Computer-Tomografie (CT)

The use of industrial computed tomography for dimensional measurements is still met with considerable suspicion because of the numerous factors that influence the measurement uncertainty, which thus is hardly describable by a mathematical model. As a consequence, reference measurements with a tactile coordinate measuring machine (CMM) are usually performed. Image unsharpness when using computed tomography (CT) can be seen as low pass filter and therefore is one among many factors that influence the metrological performance of a CT system. However, it is also known that the geometry of the probe tip acts as a mechanical filter when using tactile CMMs. The studies in this work are performed with the help of a simple specimen which includes a number of surfaces of different waviness and roughness. Capturing the surfaces using both systems and comparing the results allows a deeper analysis and understanding of the filtering effects. The measurements are performed with probe balls of different diameters on a CMM. The CT measurements are performed using various spatial resolution settings, resulting in different surface filtering characteristics. Additionally, surface measurements using a stylus instrument are performed. The comparison of these measurements shows that the CMM is more accurate when measuring form deviations of higher order. However, it also shows that the metrological performance, when measuring dimensional and geometrical measurands using the two systems, is comparable in many cases.