C8.2 - CT measurements of microparts: Numerical uncertainty determination and structural resolution

AMA Conferences 2015
2015-05-19 - 2015-05-21
Nürnberg, Germany
Proceedings SENSOR 2015
C8 - Calibration & Testing
M. Fleßner, M. Blauhöfer, E. Helmecke, T. Hausotte - Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen (Germany), A. Staude - BAM Federal Institute for Materials Research and Testing, Berlin (Germany)
483 - 488


Numerical uncertainty determination for X-ray computed tomography (X-ray CT or CT) measurements is a topic of recent research. For this approach, a realistic model of the real CT system within a simulation tool is prerequisite. Therefore, all relevant properties of the CT system, including all significant error sources, have to be modelled realistically within a Virtual Metrological CT (VMCT).
For dimensional measurements of microparts, the structural resolution has a strong influence on the measurement result. It is mainly induced by the finite size of the X-ray focal spot and the detector unsharpness. These effects superimpose within the 2D projection data. By examining projection data acquired at varying geometrical magnification and varying tube power, it is possible to separate these error sources and adjust the VMCT accordingly.
For a reliable determination of measurement uncertainty, a verification of the VMCT is necessary. As the final measurement results are derived from the extracted surface data, it is favourable to examine characteristics of the surface data instead of characteristics of the projection or volume data. A possible approach is to use an Aperiodic Spatial Frequency Standard (ASFS) to determine the structural resolution of the real and simulated CT system. The ASFS allows comparing the structural resolution for a variety of sensors by investigating the frequency response of the sensor on geometrical structures of different spatial frequency. This is demonstrated on measurements of an ASFS with four different sensors (CT, fringe projection, stylus profilometer, chromatic aberration probe).