In cone-beam computed tomography, the reconstruction process is usually described solely by the source-to-object distance (SOD) and the source-to-detector distance (SDD). The ratio of these two distances determines the magnification and thus defines the length scale. In a previous work [1], the authors proposed considering the finite thickness of the detector’s sensitive layer and the finite penetration depth of the electrons into the target of the X-ray source. Initial experimental results of the absorption spectrum-dependent variation of the SDD were shown. In this article, a new method is introduced in which – by means of a laser interferometer and a calibrated perforated thin metal foil – the positions of the source, the object and the effective detector plane can be determined absolutely depending on the source cathode voltage with an accuracy of a few micrometres. This enables the quantitative evaluation of the spectral dependence of these positions for a possible future correction.

Industrial X-ray Computed Tomography (CT) has evolv ed as an alternative measurement method to tactile nd optical coordinate measurement systems (CMSs). Acce ptance testing e.g. according to ISO 10360 standard s is a common method to assess locally and globally CMS er rors as probing measurement errors P and length measurement errors E, respectively. This paper explores in an experimen tal approach aspects of performing combined, i.e. simultaneous, P and E acceptance tests in the field of dimensional CT. T his combined test approach was proposed in ISO standardization in ear ly 2014. Prospective benefits of combined P/E testing are the potential reduction of time and costs. However, the combined P/E test is a completely new concept in the field of coordinate metrology and needs to be analy zed for its metrological characteristics. Thus, thi s work – performed within the framework the European Marie C urie project INTERAQCT – discusses this new approac h on the basis both of real CT scans and simulations and tries to create input for the international sta ndardization of dimensional CT.

Abstract High-temperature solid particle erosion (SPE) is a major threat to efficiency in power plants and jet engines, potentially reducing turbine efficiency by 7-10% and causing significant CO2 emissions. The sources of these particles vary widely, from volcanic ash in engines to fly ash in boilers and scale in turbines. While better surface engineering and coatings offer solutions, their development is hampered by a lack of standardized test methods and reliable models. To address this, the METROSION initiative aims to establish a comprehensive framework for characterizing the high-temperature SPE performance of new materials and coatings. This framework will require a step change in test methods and control, focusing on accurately measuring key parameters like temperature, flow rate, particle properties, and impact angles. This paper outlines the initiative’s goals, with a particular focus on the techniques used for in-situ measurements of temperature, particle velocity, and 3D shape/size.

We present a modified aluminium casting which is especially suited as test piece for measuring casting defects and the geometry by means of cone-beam micro-focus X-ray systems, and which may become a reference standard for dimensional measurements and defect detection.To obtain a test piece with inner geometries measured by tactile means, we divided a small aluminium cylinder head into four pieces in such a way that most inner surfaces can be reached with a tactile probe. Reference geometries (spheres and cylinders) were applied to define a coordinate system for aligning the measurements in the disassembled and re-assembled state. The four pieces were re-assembled after the tactile measurementThe test piece also contains casting defects. In order to be able to use the assembled cylinder head as reference sample for defect detection, measurements with higher spatial resolution and better signal-to-noise ratio were performed on the single parts. For improving the reliability of the reference measurements, CT measurements of each part were carried out in three different orientations, and the individual defect detections were combined to obtain a reference data set with a high probability of defect detection and a low rate of erroneous detections.A new method for comparing the defect detection in a CT measurement to a reference data set is demonstrated, which provides individual information on every detected flaw.We discuss the results of measurements in the assembled state with respect to the reference data for flaw detection. (C) 2011 Elsevier Ltd. All rights reserved.

The paper gives a survey of the upcoming use of X-ray computed tomography (CT) for dimensional quality control purposes: i.e. for traceable measurement of dimensions of technical (mechanical) components and for tolerance verification of such components. It describes the basic principles of CT metrology, putting emphasis on issues as accuracy, traceability to the unit of length (the meter) and measurement uncertainty. It provides a state of the art (anno 2011) and application examples, showing the aptitude of CT metrology to: (i) check internal dimensions that cannot be measured using traditional coordinate measuring machines and (ii) combine dimensional quality control with material quality control in one single quality inspection run. (C) 2011 CIRP.

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.

We present a modified aluminium casting, which is especially suited as test piece for measuring the geometry and casting-defects with cone-beam micro-focus X-ray systems, and which may become a reference standard for dimensional measurements and defect detection. The accuracy of dimensional measurements of outer surfaces with CT can be determined by comparison with tactile measurements. But CT is the only non-destructive method to measure inner surfaces which are inaccessible with tactile or optical methods. To get a test piece with inner geometries measured by tactile means, we divided a small (roughly 12 cm x 9 cm x 6 cm) aluminium cylinder-head (casted by the company ACTech in Freiberg, Germany) into four pieces in such a way that most inner surfaces can be reached with a tactile probe. Reference geometries (spheres and cylinders) were applied to define a coordinate system for aligning the measurements in the disassembled and re-assembled state (see Fig. 1). The four pieces were re-assembled after the tactile measurement (see Fig. 2). The test piece also contains casting defects. For being able to use the assembled cylinder-head also as reference sample for defect detection, measurements with higher spatial resolution and better signal-to-noise ratio were performed on the single parts. For improving the reliability of the reference measurements, CT-measurements of each part were carried out in three different orientations, and the individual defect detections were reconciled to obtain a reference data-set with a high probability of defect detection and a low rate of erroneous detections. We discuss the results of measurements in the assembled state with respect to the reference data for both, dimensional measurement and flaw detection.

Computed tomography (CT) is a well-established technology in medical diagnostics. For a few years now, dedicated CT systems have also been in use for dimensional measurements in industry. However, as far as the accuracy and reliability of the results is concerned, many problems are still unsolved. This paper describes concepts and first results for solving these problems. CT-specific reference standards and procedures for their application - similar to the acceptance and verification procedures of classical coordinate measuring technology - have been developed. In this paper, concepts and recent results are presented. They illustrate the technological and technical aspects and indicate the attractiveness of this new measurement technology.

Computed tomography (CT) using x-rays, originally developed to visualise inner human structure, has become an important tool for industrial applications. CT systems are at present not only used for the non-destructive defect analysis of parts. Only a few years ago CT started to be used for dimensional measurements. It is the only way to measure the inner and outer geometry of parts in a non-destructive way and with high data density. The article demonstrates the spread of applications of CT for quality control and production near measurements by selected examples. A drawback of CT is at present that measurement deviations caused by complex influence factors often cannot be quantified. Nevertheless, concepts exist to analyse measurement deviations and to correct them. One example is the correction of scaling factors e.g. by the measurement of reference bodies. For selected measurement tasks ISOfTS 15530-3 can be utilised to determine the measurement uncertainty.

We show that promising information about the three-dimensional (3D) structure of a peripheral nerve can be obtained by x-ray phase-contrast microtomography (p-μCT; Beckmann, F., U. Bonse, F. Busch, and O. Günnewig, 1997. J. Comp. Assist. Tomogr. 21:539–553). P-μCT measures electronic charge density, which for most substances is proportional to mass density in fairly good approximation. The true point-by-point variation of density is thus determined in 3D at presently 1 mg/cm3standard error (SE). The intracranial part of the rat trigeminal nerve analyzed for the presence of early schwannoma “microtumors” displayed a detailed density structure on p-μCT density maps. The average density of brain and nerve tissue was measured to range from 0.990 to 0.994g/cm3 and from 1.020 to 1.035g/cm3, respectively. The brain-nerve interface was well delineated. Within the nerve tissue, a pattern of nerve fibers could be seen that followed the nerve axis and contrasted against the bulk by 7 to 10mg/cm3 density modulation. Based on the fact that regions of tumor growth have an increased number density of cell nuclei, and hence of the higher z element phosphorus, it may become possible to detect very early neural “microtumors” through increases of average density on the order of 10 to 15mg/cm3 by using this method.

Funded by the EC under the SM&T Programme (project SMT4-PL97-2330), methods for performance tests, error correction, and calibrations of large coordinate measuring machines (CMMs) were developed, based on calibrated artifacts: Light weight ball plates, disassemblable ball plates, and disassemblable multi-ball bars. CMM manufacturers and users are testing methods and artifacts. Error models we extended to include non-rigid-body errors, typical of large CMMs (methods for error assessment, algorithms for numerical correction). For a full-scale error analysis of larger CMMs (at least one axis > 2 m) no readily applicable methodology existed so far.

The paper presents a new imaging method based on a refined and better stabilised X-ray Michelson interferometer [APPEL, BONSE]. Interference fringes are detected which mark local Angstrom-scale shifts of the lattice at the surface of the interferometer's phase-shifter crystal.Conventional double-crystal topography (DCT), lacking phase information of the beam reflected by the specimen crystal, does not detect mere lattice shifts. The new method appears to be also more sensitive to any combined lattice strain delta = Delta d/d + cot theta(B) Delta theta (theta(B): Bragg angle, d: lattice parameter) present in the crystal layer contributing to the surface Bragg reflection. delta is known to be the dominant part of the DCT image [BONSE, 1958; BONSE, HARTMANN].The technique presented here is the X-ray analogue to the well known light-optical interference microscope. A possible application is the testing of silicon crystals for minute lattice imperfections causing lattice-incoherent positions of atoms in a surface layer of typical 1 to 10 mu m thickness. For instance striations, which under certain conditions arise during crystal growth, cause such incoherence.

The principle and experimental realization of X-ray phase-contrast in computer 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 (SR)(1). Phase detection is accomplished by employing the X-ray interferometer. By using X-ray phase contrast it is possible to image structural details in low-Z biological tissues much better than with absorption contrast (Z: Atomic Number). The advantage of phase over attenuation contrast is not limited to light elements nor to low X-ray energies. Examples of applying phase contrast mu CT to the structural investigation of rat trigeminal nerve are given.

As is well known, in the wavelength range below 600 pm, dynamical diffraction by perfect crystals is best used to split and reflect beams of x-rays and thermal neutrons for interferometry without loss of coherence. Laue (L) geometries as well as Bragg (B) geometries may be employed for either purpose. Figure 1 shows six types of interferometer that have been constructed and successfully operated in the past. The triple-Laue case (LLL) interferometer [l] (Figure la) is the most commonly used. Its scanning version [2, 31 is applied to the precision measurement of the lattice parameter of silicon. Figure l b illustrates the measurement of the dragging effect for thermal neutrons [4] with the LLL interferometer. The polylithic skew-symmetric type [5] (Figure IC) offers much space for the accommodation of bulky samples. It has been also tried as a double interferometer for x-rays and neutrons [ 6 ] . Recently it was used in the precision measurement of angles down to 10-4’’ (5 x lo-’’ rad) [7]. Figure Id shows a BBB interferometer [8] which uses Bragg beam splitting by a very thin crystal in a slightly asymmetric orientation. The LBBL interferometer [9] in Figure l e mixes the L and B cases. The LLLL interferometer [lo, 111 of Figure If establishes the crossing of coherent beams in free space. It provides standing wavefields for probing the structure of objects [12].