Papers by Markus Bartscher
Achieving Traceability of Industrial Computed Tomography
Key Engineering Materials, 2010
Achieving traceability is crucial for complex measurement techniques, especially for coordinate m... more Achieving traceability is crucial for complex measurement techniques, especially for coordinate measuring machines (CMMs). For CMMs using tactile probes, traceability can for certain measurements be achieved using model-based uncertainty budgets. Up to now, uncertainty simula-tions could be used applicable only for tactile CMM measurements of regular geometries, but are available as an add-on for different CMMs. This procedure is accepted by guidelines and inter-national standards (VDI/VDE 2617-7, supplement 1 [1] to GUM). Furthermore, empirical ap-proaches to assess the measurement uncertainty by means of calibrated workpieces or prior know-ledge exist or are under development. These approaches can as a matter of principle also be used for CMMs featuring computed tomography (CT). In this paper, the empirical assessment of the mea-surement uncertainty of the upcoming measurement technology CT [2, 3] will be discussed uniting the present approaches and the current knowledge, with the...
This paper presents a method for evaluating measuring errors in a CT system using information fro... more This paper presents a method for evaluating measuring errors in a CT system using information from quality of reconstruction images. In particular, spatial resolution and pixel noise are considered in this work. Both factors can be theoretically described using formulas, and can be expressed as a combination of scanning setting parameters. A 3 2 full factorial design of experiment (DOE) was carried out to determine the influence of the two factors on dimensional measurements. For quantification of the influence, an evaluation parameter sphere distance error was selected. Results show that the spatial resolution is a dominant factor. Analysis of the reconstruction images is carried out, showing image artifacts occurring on the spheres visible under large opening angle, which are usually more significant for CT scans at high magnification. Theoretical formulation of pixel noise was validated through the experimentation.
Application of an Industrial CT Reference Standard for Cast Freeform Shaped Workpieces
ABSTRACT
Untersuchungen zur Messung von Mikrogeometrien mit großen taktilen KMGs und Anwendung bei einem Prüfkörper für Mikro-CT-Messsysteme (Investigations of the Measurement of Micro Geometries with Large Tactile CMMs and Application at a Micro-CT Artefact)
tm - Technisches Messen, 2008
... Norbert Gerwien, Michael Krystek, Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, ... more ... Norbert Gerwien, Michael Krystek, Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Carsten Schwehn, Michael Trenk, FEINMESS ... Kalibrierlaboratorium FEINMESS (DKD-K-25901) Untersuchungen an Kugelkalottenwürfeln zur Kalib-rierung mit großen KMGs ...
Up to now methods using artifacts to inspect large coordinate measuring machines (CMMs) are suita... more Up to now methods using artifacts to inspect large coordinate measuring machines (CMMs) are suitable only for interim checks and verification (1,2). For a full-scale error analysis of larger CMMs (at least one axis > 2 m) no readily applicable methodology exists so far, thus VDI and ISO have recently started activities yielding traceability of large CMMs. Regarding this background methods for a full-scale error analysis of large CMMs (calibration, error correction & performance tests) were developed under the EC funded SM&T Programme (project SMT4-PL97-2330). Methods are based on calibrated artifacts, which are described here: Light weight ball plates, disassemblable ball plates and disassemblable multi-ball bars. CMM manufacturers and users are testing methods and artifacts. Error models were extended to include non-rigid-body errors, typical of large CMMs (methods for error assessment and algorithms for numerical correction).
Phase-contrast x-ray tomography using synchrotron radiation
The principle and experimental l realization of x-ray phase- contrast in compute assisted microto... more The principle and experimental l realization of x-ray phase- contrast in compute assisted microtomography ((mu) CT) at the micrometer resolution level is described. The camera used is a modification of a setup previously developed by us for attenuation-contrast (mu) CT using synchrotron x-rays. Phase detection is accomplished by employing the x-ray interferometer. By using x-ray phase contrast it is possible
Einsatz von Computertomographie in der Reverse-Engineering-Technologie
Materials Testing, 2006
Dimensional Control of Micro Components with Synchrotron Computed Tomography
ABSTRACT An advantage of Computed Tomography (CT) is the coordinate measurement capability of sma... more ABSTRACT An advantage of Computed Tomography (CT) is the coordinate measurement capability of small inner structures, which are not accessible with classical measurement techniques. Using the advantages of synchrotron radiation CT measurements of parts with sizes of a few millimeters are performed at BAMline of BESSY II and are expected to be used as references for further dimensional measurements with micro CT. Previous investigations were focused on external gears, which are accessible with standard Coordinate Measurement Machines (CMMs). To obtain information about the accuracy of dimensional measurements of internal gears with CT, reference data have been measured by a tactile-optical CMM. This information is used to evaluate the performance of the CT. In addition to the first results for the evaluation of internal gear flanks, new measurements of different gear materials (steel and zirconium dioxide) will be presented. For functional evaluation, gear flanks are a matter of particular interest. Form deviations are analyzed with respect to the different gear materials to establish CT measurements as technology in the field of quality assurance and to compare the different manufacturing processes.
<title>Measurement of micro gears: comparison of optical, tactile-optical, and CT measurements</title>
Three-Dimensional Imaging, Interaction, and Measurement, 2011
ABSTRACT Micro gears are applied in an increasing quantity in many applications. Therefore, preci... more ABSTRACT Micro gears are applied in an increasing quantity in many applications. Therefore, precise measurements are of growing importance to ensure their quality. This contribution describes the measurement of gears of a micro planetary gear set with a tactile probe, a tactile-optical probe, an optical sensor, and computed tomography (CT). For the tactile measurements, a high precision piezoresistive microprobe was used. A so-called fiber probe was applied for tactile-optical measurements. This probe applies image processing to determine the position of the tactile probing element. For all tactile and tactile-optical measurements, single point probing was used. The optical measurements were carried out with an imaging sensor based on focus variation. Due to limited accessibility, on some gears not all regions could be measured by the optical sensor and the tactile-optical probe. In contrast to this, with CT the whole part could be measured with high point density. We used a micro-CT system and carried out measurements with Synchrotron-CT. All the sensors used deliver measurement data in Cartesian coordinates. It is a challenge to transfer these data into coordinates in which gear parameters are defined. For this, special attention must be paid to the determination of the gear axis and to the orientation of the teeth. The applied procedures are detailed for different micro gears. The comparison between data of different measurements was carried out successfully. The deviations between the CT data and the tactile or tactile-optical data lie in the range of only a few micrometers.
X-ray and Neutron Interferometry and the Measurement of Fundamental Constants
Metrologia, 1994
Current state of standardization in the field of dimensional computed tomography
Measurement Science and Technology, 2014
ABSTRACT Industrial x-ray computed tomography (CT) is a well-established non-destructive testing ... more ABSTRACT Industrial x-ray computed tomography (CT) is a well-established non-destructive testing (NDT) technology and has been in use for decades. Moreover, CT has also started to become an important technology for dimensional metrology. But the requirements on dimensional CTs, i.e., on performing coordinate measurements with CT, are different from NDT. For dimensional measurements, the position of interfaces or surfaces is of importance, while this is often less critical in NDT. Standardization plays an important role here as it can create trust in new measurement technologies as is the case for dimensional CT. At the international standardization level, the ISO TC 213 WG 10 is working on specifications for dimensional CT. This paper highlights the demands on international standards in the field of dimensional CT and describes the current developments from the viewpoint of representatives of national and international standardization committees. Key aspects of the discussion are the material influence on the length measurement error E and how E can best be measured. A respective study was performed on hole plates as new reference standards for error testing of length measurements incorporating the material influence. We performed corresponding measurement data analysis and present a further elaborated hole plate design. The authors also comment on different approaches currently pursued and give an outlook on upcoming developments as far as they can be foreseen.
Procedure and reference standard to determine the structural resolution in coordinate metrology
Measurement Science and Technology, 2014
ABSTRACT A new procedure and reference standards for specifying the structural resolution in coor... more ABSTRACT A new procedure and reference standards for specifying the structural resolution in coordinate metrology traceable to the SI unit the metre are proposed. With the definition of the structural resolution, a significant gap will be closed to complete &#39;acceptance and verification tests&#39; of the coordinate measuring systems (CMSs) which are specified in the ISO 10360 series dealing with tactile sensors, optical sensors, and x-ray computed tomography measurement systems (CTs). The proposed new procedure uses reference standards with circular rounded edges. The idea is to measure the radius of curvature on a calibrated round edge structure. From the deviation between the measured and the calibrated radius, an analogue Gaussian broadening of the measurement system is determined. This value is a well-defined and easy-to-apply measure to define the structural resolution for dimensional measurements. It is applicable to CMSs which are based on different sensing principles, e.g. tactile, optical and CT systems. On the other hand, it has a physical meaning similar to the classical optical point-spread function. It makes it possible to predict which smallest details the CMS is capable of measuring reliably for an arbitrary object shape. The theoretical background of the new procedure is given, an appropriate reference standard is described and comparative, quantitative measurement data of CMSs featuring different sensors are shown.
Tactile and optical microsensors: test procedures and standards
Measurement Science and Technology, 2008
ABSTRACT This paper presents procedures and standards for the testing of tactile and optical micr... more ABSTRACT This paper presents procedures and standards for the testing of tactile and optical microsensors and micro-computed tomography (micro-CT) systems for coordinate metrology. The tests are analogue to the well-established tests for classical coordinate measuring machines (CMM) and assess local and global sensor characteristics. For this purpose, adequate and miniaturized reference standards were manufactured, calibrated and tested. In addition, task-specific reference standards have been realized to determine special sensor characteristics, such as the maximum slope angle measurable by optical sensors or specific errors of tactile–optical microprobes measuring deep micro-holes.
Quantification of the capability of micro-CT to detect defects in castings using a new test piece and a voxel-based comparison method
NDT & E International, 2011
... References. [1] Bartscher M, Neukamm M, Koch M, Neuschaefer-Rube U, Staude A, Ehrig K, et al.... more ... References. [1] Bartscher M, Neukamm M, Koch M, Neuschaefer-Rube U, Staude A, Ehrig K, et al. ... Fachhochschule Oberösterreich, Wels, Shaker Verlag GmbH, Aachen (2010), pp. 85–91. [6] R. Schmitt, P. Hafner and S. Pollmanns, Kompensation von Metallartefakten in ...
CIRP Annals - Manufacturing Technology, 2011
Data processing is an essential part of the evaluation of measurement results, e.g. in X-ray comp... more Data processing is an essential part of the evaluation of measurement results, e.g. in X-ray computed tomography (CT). Some of these calculations are denoted as "filtering". Filtering is always a trade-off between an enhancement of data quality and a loss of information. The standard reconstruction technique for CT data is t he filtered back-projection. Additionally to the high-pass filter inherent to this technique, a suppression of high-frequency noise is in most cases also necessary. Many different possible filter algorithms are found in the literature. Although their effect on the signal-to-noise ratio and the spatial resolution is well-studied, it is not obvious how the different filters affect the determination of the object's surface in the reconstructed data and, thus, the results of dimensional CT measurements. We compare the results of industrial dimensional CT measurements obtained at the same data set of a calibrated reference standarda calotte cube -when using different filters and discuss the implications. Filters under investigation are mainly median filters on projections and as well filters during filtered backprojection and filters on the reconstructed volume.
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Papers by Markus Bartscher