Simulation-Based Planning of Optimal Conditions for Industrial Computed Tomography

We present a method to optimise conditions for industrial computed tomography (CT). This optimisation is based on a deterministic simulation. Our algorithm finds task-specific CT equipment settings to achieve optimal exposure parameters by means of an STL-model of the specimen and a raytracing method. These parameters are positioning and orientation of the specimen, X-ray tube voltage and prefilter thickness

A study on evaluation strategies in dimensional X-ray computed tomography by estimation of measurement uncertainties

Computed tomography has entered the industrial world in 1980’s as a technique for non-destructive testing and has nowadays become a revolutionary tool for dimensional metrology, suitable for actual/nominal comparison and verification of geometrical and dimensional tolerances. This paper evaluates measurement results using different measuring strategies applied in different inspection software packages for volume and surface data analysis. The strategy influence is determined by calculating the measurement uncertainty. This investigation includes measurements of two industrial items, an aluminium pipe connector and a plastic toggle, a hearing aid component. These are measured using a commercial CT scanner. Traceability is transferred using tactile and optical coordinate measuring machines, which are used to produce reference measurements. Results show that measurements of diameter for both parts resulted in smaller systematic errors compared to distance and height measurements. It was found that uncertainties of all measurands evaluated on surface data were generally greater compared to measurements performed on volume data

Semiclassical theory of surface plasmons in spheroidal clusters

A microscopic theory of linear response based on the Vlasov equation is extended to systems having spheroidal equilibrium shape. The solution of the linearized Vlasov equation, which gives a semiclassical version of the random phase approximation, is studied for electrons moving in a deformed equilibrium mean field. The deformed field has been approximated by a cavity of spheroidal shape, both prolate and oblate. Contrary to spherical systems, there is now a coupling among excitations of different multipolarity induced by the interaction among constituents. Explicit calculations are performed for the dipole response of deformed clusters of different size. In all cases studied here the photoabsorption strength for prolate clusters always displays a typical double-peaked structure. For oblate clusters we find that the high--frequency component of the plasmon doublet can get fragmented in the medium size region ($N \sim 250$). This fragmentation is related to the presence of two kinds of three-dimensional electron orbits in oblate cavities. The possible scaling of our semiclassical equations with the valence electron number and density is investigated.Comment: 23 pages, 8 figures, revised version, includes discussion of scalin

Методы измерения фазового сдвига с промежуточным преобразованием напряжение-частота

В статті розглянуті методи вимірювання фазового зсуву з проміжним перетворенням напруга-частота. Проаналізовано переваги й недоліки методів. Проведено оцінку похибки, обумовленої неточністю формування часових інтервалів.In article methods of measurement of phase shift with preliminary transformation a voltage-frequency are considered. Their merits and demerits are analyzed. The estimation of the error caused by discrepancy of formation of time intervals is made

Quality improvements by reference-free artefact reduction and surface normalisation in industrial 3-D computerized tomography

Die zerstörungsfreie Untersuchung komplexer Gussteile zur Prozessoptimierung ist eine wichtige Prüfaufgabe in der Automobilindustrie. Die dabei gestellten Anforderungen umfassen eine schnelle Verifikation der Maßhaltigkeit sowie die Analyse von Soll-Ist-Vergleichen. Für diese Erfordernisse ist die 3D-CT als zerstörungsfreie Prüfmethode bestens geeignet. Physikalische Effekte wie Strahlaufhärtung und Streustrahlung äußern sich in den rekonstruierten Schichten als Artefakte, die die Bildqualität verschlechtern und die genannten Prüfaufgaben erschweren oder verhindern. Die vorgestellte Iterative Artefakt Reduktion (IAR) kombiniert Verfahren zur Korrektur dieser physikalischen Effekte. Die referenzlose Berechnung einer Kennlinie zur Strahlaufhärtungskorrektur ersetzt die zeitaufwendige Aufnahme und Auswertung von Eichkörpern. Die Längenbasierte Streuapproximation (LBSA) ist ein einfaches, aber effizientes Streustrahlenmodell, welches Objektformen berücksichtigt und bei deutlich weniger Rechenzeit als Monte-Carlo-Simulationen vergleichbare Ergebnisse liefert. Schwierigkeiten bei der 3D-Digitalisierung bereitet wegen der oben geschilderten Artefakte die Festlegung des korrekten Schwellwertes für die Isoflächenextraktion. Die Iterative Oberflächennormierung (ISN) des artefaktreduzierten Volumens vereinfacht die problematische Flächenextraktion und steigert die Genauigkeit beim Dimensionellen Messen.The non-destructive inspection of castings for process optimization is an important task in the automotive industry. To meet the requirements a fast verification of dimensional accuracy and the analysis of the deviation of the real geometry from target data is necessary. For this purpose the most adequate NDT method is 3D-CT. Physical effects like beam hardening and radiation scattering become apparent as artefacts in the reconstructed slices and reduce the image quality vastly. The presented Iterative Artefact Reduction combines methods to correct these physical effects. The calculation of a function for beam hardening correction from the reconstructed volume itself replaces the time consuming scanning and evaluation of a reference object. The Length Based Scattering Approximation (LBSA) is a simple but efficient model for estimating radiation scattering, which takes the shape of an object into account and delivers comparable results to Monte-Carlo simulations in an obviously shorter computing time. Due to the above-mentioned artefacts 3D-digitalisation is a problem for the determination of a correct threshold for isosurface extraction. The Iterative Surface Normalisation (ISN) of volumes reduced by artefacts simplifies the difficult surface extraction and increases the dimensional accuracy

Registration concepts for the just-in-time artefact correction by means of virtual computed tomography

This article deals with the enhancement of accuracy in CT by just-in-time correction of artefacts (beam hardening, scattered radiation) caused by the interaction of X-rays with matter. The so called EAR method needs for simulation a registration of the object. Therefore the article presents two different registration concepts