CALIBRATION STANDARD FOR AN INDUSTRIAL COMPUTER TOMOGRAPH

Description

[0001] The invention relates to a calibration standard for an industrial computer tomograph, wherein the calibration standard has a base body with a longitudinal axis, wherein the base body has an outer surface which is designed to be continuously circumferential around the longitudinal axis with respect to a circumferential direction and extends along the longitudinal axis, wherein a plurality of calibration ball elements are fastened to the base body distributed over the radially outwardly directed outer surface, wherein the calibration ball elements are distributed over a plurality of axial positions with respect to the longitudinal axis, wherein the base body tapers in the region of the outer surface along the longitudinal axis, and wherein the calibration ball elements are distributed over a plurality of radial positions with respect to the longitudinal axis.

[0002] Such a calibration standard is known from JP 2001 149363 A.

[0003] Industrial computed tomography (ICT) is used to measure components with high precision in areas that are inaccessible with conventional measuring methods. In particular, the interior of a component can be measured using ICT to check for correct internal dimensions and material defects, such as blowholes or pores. During ICT, X-ray images ("shadows") of the component are taken in various rotational positions. The three-dimensional X-ray density of the component can then be calculated from the X-ray images from the various rotational positions. A typical ICT measuring apparatus comprises an X-ray source, a rotating holder for the component to be measured, and a two-dimensional (=2D) X-ray detector.

[0004] To ensure high precision of the ICT, the measurement accuracy of the ICT apparatus must be checked. In particular, it must be ensured that the ICT apparatus does not produce any imaging errors such as distortions. For this purpose, it is known to measure test bodies with previously known dimensions, also known as calibration standards, in the ICT apparatus. If the dimensions of the calibration standard determined using the ICT apparatus sufficiently agree with the previously known (true) dimensions of the calibration standard, the ICT apparatus can be released. If necessary, differences between the dimensions determined using the ICT apparatus and the previously known dimensions of the calibration standard can be used to readjust the ICT apparatus. Typically, an ICT apparatus is checked before the first start of measurement operation and then at regular intervals.

[0005] In order to determine the previously known (true) dimensions of the calibration standard, it is typically measured in advance using a tactile coordinate measuring machine, i.e. mechanical sensors (also called probes) are moved along the calibration standard.

[0006] Common calibration standards comprise several calibration sphere elements, and the coordinate measuring machine is used to determine the relative positions of the calibration sphere elements (or their centers) to each other, which then serve as previously known dimensions of the calibration standard for comparison.

[0007] Carl Zeiss IQS Deutschland GmbH, Oberkochen, Germany, offers a "METRO-TOM Check Set," available at https: / / shop.metrology.zeiss.de / INTERSHOP / web / WFS / IMT-DE-Site / de DE / / EUR / ViewProduct-Start?SKU=626106-9215-000&CategoryName=460410&CatalogID=400000, downloaded on September 22, 2022. This calibration standard represents a commonly used type of calibration standard. In this calibration standard, support rods protrude axially from the front of a base plate, each end of which has a ruby ​​sphere attached. The support rods are approximately 10 times the diameter of the ruby ​​spheres. Several rings of support rods are nested radially within each other, with the support rods of rings located radially further inside protruding axially further than those of rings located radially further outside.A disadvantage of this design is that elastic deformations of the support rods can occur during an initial tactile measurement, which can render the initial tactile measurement of the calibration standard inaccurate. The coordinate measuring machine measures this calibration standard including the noticeable elastic deformations caused by the coordinate measuring machine, which will not be present (or at least not reproducibly) in a subsequent X-ray measurement. Furthermore, depending on the rotational position, the ruby ​​spheres of a ring can overlap for X-rays propagating in the radial direction, which can complicate the position determination of the calibration spheres in the ICT apparatus.

[0008] A similar calibration standard from Carl Zeiss IQS Deutschland GmbH, Oberkochen, DE is also available from https: / / shop.metrology.zeiss.de / metrotom-check-set-fuer-metrotom-1500-g2-mit-hubtisch-zid626106-9212-000 became known.

[0009] Trapet Precision Engineering, Sarria, Spain, offers https: / / trapet.de / de / Downloaded on September 22, 2022, offers so-called "miniature dumbbells" as calibration standards. This calibration standard comprises two support rods, each with a calibration sphere at each end. The two support rods are attached to a bracket at right angles. Even with this design, there is a risk of elastic bending of the support rods during tactile measurements. Furthermore, the space covered by the calibration standard in the CT scanner is small.

[0010] Furthermore, on the same website, Trapet Precision Engineering, Sarria, Spain, shows "miniature spherical tetrahedra made of ruby ​​spheres" as calibration standards. In this calibration standard, four relatively large ruby ​​spheres are clamped in a tetrahedral arrangement with a holding cage on a base plate. This setup is expensive and complex, and there is a possibility that the tension of the holding cage changes during the tactile measurement or over time, thus rendering the initial tactile measurement inaccurate or even causing the dimensions of the calibration standard to be inconsistent over time. Furthermore, the lower ruby ​​spheres are always at least partially overlapped, and the degree of overlap of the ruby ​​spheres for radially propagating X-rays depends heavily on the rotational position, which can complicate X-ray measurement.

[0011] Another calibration standard has been introduced by Obaton, AF, Klingaa, CG, Rivet, C., Mohaghegh, K., Baier, S., Andreasen, JL, Carli, L., & De Chiffre, L. (2020). Reference standards for XCT measurements of additively manufactured parts. Paper presented at 10th Conference on Industrial Computed Tomography, Wels, Austria, page 2, table entry "Multi-sphere standard", METAS, Switzerland. In this calibration standard, calibration spheres are arranged on the outside of a cylindrical shell-shaped base body. The calibration spheres are arranged at a uniform radius, which makes it difficult to detect any distortions in the image in an ICT apparatus in the near-axis area of ​​the base body with this calibration standard. In addition, depending on the rotational position, the calibration spheres can overlap for X-rays propagating in the radial direction, which can complicate the position determination of the calibration spheres in the ICT apparatus.

[0012] A similar calibration standard is known from the above-mentioned publication by Obaton et al. on page 2, table entry "CT tube", DTU, Denmark, Ruby spheres on carbon fiber tube.

[0013] The above-mentioned publication by Oberton reveals in the Figure 7 Furthermore, a calibration standard with axially aligned, cylindrical sections, with the radius decreasing from section to section. Recesses for external inserts are formed on the annular end surfaces of the sections.

[0014] Furthermore, the above-mentioned Oberton publication mentions the PTB's "Mini Star Probe" in a table entry on page 3. This probe features four radially outward-facing spheres on a base body and a sphere at the tip.

[0015] From the above-mentioned publication by Obaton et al., numerous other calibration standards have also become known, even without calibration spheres (see, for example, page 2, table entry "Step cylinder", DTU Denmark).

[0016] From JP 2001 149363 A, there Fig. 4 , an X-ray calibration phantom has become known which has a plurality of metal balls arranged along a helical path on a rotating body tapering towards a center.

[0017] US 2016 / 0095569 A1 describes a phantom for checking the quality of CT images. Spherical balls are attached to or embedded in the interior of a container of the phantom. The container can, in particular, have a conical or ellipsoidal shape. Object of the invention

[0018] The object of the invention is to provide a calibration standard with which the measurement accuracy of an ICT apparatus can be checked with high precision in a simple manner. Description of the invention

[0019] This object is achieved according to the invention by a calibration standard of the type mentioned above, which is characterized in that the calibration standard further comprises a base plate, that the base body is fastened to an upper side of the base plate, and that a three-point bearing and a holding magnet are formed on an underside of the base plate.

[0020] Within the scope of the invention, the calibration standard comprises a base body having an outer surface continuously circumferential around the longitudinal axis. The calibration spherical elements are arranged on the base body, distributed over the outer surface, which is directed radially outward (at least with a directional component of the respective local surface normal).

[0021] The base body tapers toward a front end in the area of ​​the outer surface. This makes the base body particularly suitable for absorbing external forces with both a radial and an axial component. External forces with both of these components occur particularly during tactile measurement of the calibration spherical elements.

[0022] The outer surface of the base body forms a closed surface, regardless of any holes in the outer surface or the base body, which are closed with pins for ball retention (see below). Any external forces are distributed accordingly over the entire circumference of the base body and over the axial length of the base body, at least in the area of ​​the outer surface.

[0023] Overall, the base body therefore has a high mechanical rigidity and is difficult to deform due to external forces.

[0024] The calibration sphere elements are attached to the base body in a distributed manner along the outer surface. To this end, the calibration sphere elements either sit directly on the base body or the radially outward-facing outer surface (e.g., in a recess in the outer surface), or they are attached to the base body in close proximity to the radially outward-facing outer surface (typically at a distance A equal to or less than twice the diameter D of the calibration sphere elements, e.g., with a pin, see below).

[0025] Any mechanical loads exerted by a tactile coordinate measuring machine on the calibration sphere elements are transmitted practically directly into the base body, resulting in no noticeable mechanical deformation of the calibration standard. The force of the tactile coordinate measuring machine is optimally absorbed by the base body with its high mechanical stability and dissipated via the base body. The (relative) position of the calibration sphere elements is not changed, or at least not noticeably so, during a tactile measurement by the coordinate measuring machine. Accordingly, the true dimensions of the base body can be determined, as they will also be present during a subsequent (mechanically non-stressful) X-ray measurement in an ICT device.

[0026] Since the base body tapers along the longitudinal axis in the area of ​​the outer surface, the calibration sphere elements can be easily arranged to be distributed over a variety of axial and radial positions. This ensures that the measurement volume of the ICT apparatus can be reliably and essentially continuously checked for aberrations, particularly distortions, over both a certain axial and a certain radial range.

[0027] The circumferential base body can also be measured quickly and easily in a computed tomography scanner. In particular, such a base body requires comparatively little computing power for the reconstruction of the 3D X-ray density distribution. This is especially true in the case of a hollow, rotationally symmetric base body with a uniform wall thickness along the outer surface.

[0028] According to the invention, the calibration standard further comprises a base plate, in particular wherein the base plate is made entirely or predominantly of metal, and wherein the base body is fastened, in particular glued, to an upper side of the base plate. The structure with base plate and base body easily enables the use of different materials for the base plate (usually entirely or predominantly made of metal) and the base body (preferably a low-density / low-X-ray-absorbent material such as carbon fiber composite or a plastic or ceramic). The base plate, in particular made of metal, enables a stable and robust fastening of the base body, in particular on a coordinate measuring machine (or on an ICT device), or also a stable fastening of a hood arrangement.

[0029] The invention further provides for a three-point bearing and a holding magnet to be formed on the underside of the base plate. The three-point bearing and the holding magnet enable a particularly low-stress attachment of the calibration standard to a tactile coordinate measuring machine (or to an ICT device). Accordingly, the introduction of elastic stresses that could distort the geometry of the calibration standard can be minimized.

[0030] Each calibration sphere element consists of a complete calibration sphere or a portion of a complete calibration sphere. Each calibration sphere element exposes a convex, spherically curved surface section in front of the outer surface.

[0031] The calibration spheres typically have a roundness of Grade 05 or better (according to DIN 5401, ISO 3290). The roundness deviation of the calibration spheres is preferably 0.13 µm or less. Typically, the calibration spheres are made of ruby ​​or another ceramic material. The size and quantity of the calibration spheres can be selected depending on the application and the desired size of the calibration standard. Typically, the calibration standard has at least six, preferably at least eight, calibration spheres.

[0032] In addition to the outer surface in whose (axial) region it tapers, the base body can have further outer surfaces, for example a further outer surface axially below the outer surface in whose (axial) region the base body is cylindrical. Preferred embodiments of the invention Embodiments concerning the base body

[0033] A preferred embodiment of the calibration standard according to the invention is one in which the base body tapers continuously in the region of the outer surface along the longitudinal axis. This continuous taper (without jumps in the outer radius) allows for particularly high mechanical stability of the base body and also allows for a material-saving construction of the base body. Preferably, the base body tapers continuously in a linear manner in the region of the outer surface along the longitudinal axis. This is particularly simple in terms of construction.

[0034] Particularly preferred is an embodiment in which the base body is rotationally symmetrical with respect to the longitudinal axis, at least in the region of the outer surface.

[0035] This is particularly simple in design and avoids changes in the irradiation of the material of the base body when the calibration standard is rotated, thus simplifying the measurement of the calibration standard in the ICT apparatus.

[0036] In a preferred development of this embodiment, the base body is conical, at least in the area of ​​the outer surface. This ensures favorable, low-deformation force introduction into the base body in typical tactile coordinate measuring machines and is simple to manufacture. A particularly high mechanical rigidity of the base body is achieved. In addition, the conical shape allows approximately constant wall thicknesses (material thicknesses) of the base body to be penetrated over a wide axial area to be established with a uniform wall thickness of the base body, at least in a region close to the axis, thereby enabling particularly precise measurement of the calibration standard or the measurement volume of an ICT apparatus. In this design, the outer surface corresponds to at least part of the lateral surface of a cone. The cone angle is preferably between 30° and 60°, particularly preferably between 35° and 55°, most particularly preferably approximately45°.

[0037] In an alternative development of the above embodiment, the base body is designed, at least in the area of ​​the outer surface, to resemble a portion of a spherical surface. This design also allows the calibration standard or the measurement volume of an ICT device to be precisely checked for distortions.

[0038] In another embodiment, the base body has, at least in the area of ​​the outer surface, a rotational symmetry with respect to the longitudinal axis, with the longitudinal axis being an N-fold rotational axis, with N≥6. With such a design of a calibration standard, the measuring volume of an ICT device can also be checked for imaging errors.

[0039] Particularly preferred is an embodiment which provides that, at least for a majority of the calibration sphere elements, no further calibration sphere elements extend in an axial interval in which a respective calibration sphere element extends along the longitudinal axis, in particular wherein, for all calibration sphere elements, no further calibration sphere elements extend in an axial interval in which a respective calibration sphere element extends along the longitudinal axis. In other words, the calibration sphere elements do not overlap in the axial direction (regardless of the rotational position). During X-ray images of the calibration standard with an essentially radial X-ray propagation direction and rotation about the longitudinal axis of the calibration standard, the calibration spheres are always irradiated individually.This avoids distortions or imaging errors caused by calibration sphere elements overlapping in the propagation direction, which can be a difficulty when calculating the 3D X-ray density of the calibration standard.

[0040] A particularly preferred development is one in which no further calibration sphere elements extend in the axial direction upstream and downstream of this axial interval in an axial adjacent interval, in particular wherein each adjacent interval has an axial length NIL for which NIL ≥ 0.2*RKK applies, where RKK is the radius of curvature of the respective calibration sphere element. This further facilitates precise imaging of the calibration standard in an ICT apparatus.

[0041] Particularly preferred is an embodiment in which at least some of the calibration sphere elements, which are distributed over the outer surface of the base body, are arranged according to a spiral, preferably wherein successive calibration sphere elements in the spiral are each spaced equally apart along the longitudinal axis and offset from one another by the same angle of rotation around the longitudinal axis. For example, all calibration sphere elements are arranged in only one spiral. It is also possible to arrange some of the calibration sphere elements or all of the calibration sphere elements in several spirals that are offset from one another, typically both by a certain angle of rotation around the longitudinal axis and by a certain distance along the longitudinal axis (the latter to avoid axial overlap of the individual calibration sphere elements).Due to the tapering of the base body in the area of ​​the outer surface along the longitudinal axis, both the radial and axial positions of the calibration spherical elements vary in a spiral arrangement around the longitudinal axis. The spiral arrangement therefore allows for a simple, reliable and virtually continuous examination of both a larger radial interval and a larger axial interval of the measurement volume of the ICT apparatus for distortions.

[0042] An advantageous embodiment is one in which the base body is designed as a hollow body. This saves material and reduces X-ray absorption by the base body, which in turn simplifies the measurement of the calibration standard in the ICT apparatus. Preferably, the hollow body is designed to be closed toward the end where the base body tapers along the longitudinal axis; this improves the mechanical stability of the base body.

[0043] In a preferred development of this embodiment, the wall thickness of the base body in the region of the outer surface is constant along the longitudinal axis. The (local) wall thickness is the (local) thickness of the (hollow) base body measured perpendicular to the (local) outer surface. Due to the constant wall thickness, in the case of a conical outer surface, an approximately equal thickness of material of the base body in overlap with a respective calibration sphere element can be achieved for the calibration sphere elements, at least in a region near the longitudinal axis, and thus very similar imaging ratios for all calibration sphere elements in the region near the longitudinal axis. This allows the calibration of the ICT apparatus in the measurement volume near the longitudinal axis (which usually corresponds to the axis of rotation of the computed tomography scanner) to be carried out particularly precisely and reliably.

[0044] An alternative development of the above embodiment provides that the wall thickness of the base body in the region of the outer surface along the longitudinal axis increases in the direction along which the base body tapers. In the regions further away from the longitudinal axis, the larger the local radius, the more material of the base body tends to overlap with a calibration sphere element. By increasing the wall thickness towards the taper, the average thickness of material overlapping with a respective calibration sphere element can be evened out, thereby making the imaging conditions even on average. This allows the calibration of the computed tomography scanner in the measurement volume further away from the longitudinal axis (which usually corresponds to the axis of rotation of the computed tomography scanner) to be carried out particularly accurately and reliably.

[0045] An advantageous embodiment is one in which depressions, in particular spherical depressions, are introduced into the outer surface of the base body, into which the calibration sphere elements are inserted. In this case, the calibration sphere elements are typically designed as complete calibration spheres. This design is structurally simple and mechanically particularly stable. It should be noted that the depth of the depressions (perpendicular to the local outer surface) typically corresponds to a maximum of 1 / 3 of the diameter of the calibration sphere elements. The calibration sphere elements are typically glued into the depressions. In the case of spherical depressions, the radius of curvature of the depressions corresponds to the radius of curvature of the calibration sphere elements, and a particularly secure fit can be achieved. Alternatively, conical depressions, for example, can also be provided.

[0046] In a likewise advantageous embodiment, the calibration ball elements are each fastened to plug pins, each of which has a recess, in particular a spherical recess, at one end face, into which a respective calibration ball element is inserted, and each of which is inserted with a different end into a respective bore on the outer surface of the base body, with a partial section of the plug pin protruding from the outer surface. The plug pins can improve accessibility of the calibration ball elements for a mechanical sensor of a tactile coordinate measuring machine. The calibration ball elements are typically designed as complete spheres that sit in the preferably spherical recesses.Note that the pins typically have a (greatest) length L protruding from the outer surface, which corresponds to a maximum of twice the diameter D of the calibration sphere elements. This minimizes moments or lever lengths during tactile measurement of the calibration sphere elements. The pins are typically aligned perpendicular to the local outer surface. Furthermore, the pins are typically directed radially outward (at least with one directional component).

[0047] A preferred embodiment is one in which the base body is made of a carbon fiber composite material. This material offers high mechanical stability for the base body while simultaneously exhibiting relatively low X-ray absorption (especially compared to most metals) and retains its shape even over long periods (several years). The carbon fibers are typically embedded in an epoxy resin matrix. A base body made of carbon fiber composite material can be molded, in particular, in an injection mold. Embodiments concerning the base plate and a hood arrangement

[0048] Furthermore, an embodiment of the calibration standard according to the invention is preferred which provides that the base plate is made entirely or predominantly of metal, and / or that the base body is glued to the top of the base plate.

[0049] A preferred embodiment provides that the calibration standard further comprises a hood assembly that can be screwed onto the top side of the base plate, wherein the hood assembly forms a hood thread, in particular an internal thread, in the region of its underside, and the base plate forms a matching base plate thread, in particular an external thread, and wherein the hood assembly, when screwed on, completely covers the base body together with the base plate. The hood assembly can be used to protect the calibration standard, in particular from plastic deformation or material breakage, so that the calibration standard precisely retains its geometry (i.e., its previously known dimensions) after its initial tactile measurement.The screw-on attachment of the hood assembly to the base plate is particularly stress-free, so that no noticeable (elastic or even plastic) deformation of the calibration standard occurs when the hood assembly is attached (after the tactile measurement of the calibration standard). Large-area threads, in particular, can be used to minimize mechanical stress.

[0050] A further development of this embodiment is advantageous, which provides that the hood arrangement has a base ring on which the hood thread is formed, in particular wherein the base ring is made entirely or predominantly of metal, and that the hood arrangement has a hood cup which is fastened, in particular glued, in the region of an upper side of the base ring, in particular wherein the hood cup is made at least partially of a transparent material and / or of plastic, preferably of a transparent plastic. By dividing the hood arrangement into a base ring and a hood cup, materials particularly well suited to the respective requirements can be used. The hood cup can be attached in a floating manner to the base ring, preferably by gluing, which minimizes the introduction of mechanical stresses into the base ring.The metal base ring can ensure a very robust and reliable threaded attachment, and the hood cup can be made of a material with low X-ray absorption but sufficient mechanical protection, such as plastic (especially polymethyl methacrylate). Transparent hood cups allow the user to easily identify which calibration standard is protected by the hood cup (without opening the cup). Adhesive attachment of the hood cup to the base ring is particularly stress-free.

[0051] In a preferred embodiment, the three-point bearing comprises three pairs of bearing balls or three hard metal rollers that are attached, in particular glued, to the underside of the base plate, and the holding magnet is attached, in particular screwed, centrally between the bearing balls or hard metal rollers to the underside of the base plate. This design has proven successful in practice and can ensure a particularly secure fit of the base plate on a corresponding counterbearing. The pairs of bearing balls or hard metal rollers are typically located at a uniform radial position. The holding magnet can, for example, be formed by a circular blank.

[0052] In a further development of this embodiment, the holding magnet is formed by a round plate. Calibration standard system with adapter plate

[0053] Also within the scope of the present invention is a calibration standard system, comprising a calibration standard according to the invention with a three-point bearing and holding magnet on the underside of the base plate as described above, and an adapter plate, wherein a three-point counter bearing and a counter holding magnet are formed on an upper side of the adapter plate, corresponding to a position image of the three-point bearing and the holding magnet of the base plate of the calibration standard, and wherein the adapter plate further forms a clamping pin in the region of its underside for clamping in a clamping bearing of a coordinate measuring machine. By means of the adapter plate, it is possible to fasten the calibration standard to a conventional clamping bearing of a (tactile) coordinate measuring machine without elastic stresses being introduced into the calibration standard; accordingly, the geometry of the calibration standard remains unaffected by the clamping bearing.The clamping bearing can reliably provide a sufficiently secure mechanical hold for the calibration standard system on the coordinate measuring machine for tactile measurement. This design enables stress-free fixation of the calibration standard on the clamping system of a tactile coordinate measuring machine. The three-point counter bearing can comprise three carbide rollers or three pairs of bearing balls that are attached, in particular glued, to the top of the adapter plate. The carbide rollers or pairs of bearing balls are typically located at a uniform radial position. Furthermore, the counter-holding magnet can be attached centrally between the bearing balls or carbide rollers on the top of the adapter plate, in particular screwed or glued. Uses of a calibration standard system

[0054] The present invention also includes the use of a calibration standard system according to the invention as described above, comprising the following steps: Step a) The calibration standard is attached to the adapter plate in any order via the three-point bearing, the three-point counter bearing, the holding magnet and the counter-holding magnet, and the adapter plate is fastened to a clamping bearing of a coordinate measuring machine using the clamping pin; Step b) The geometric dimensions of the calibration standard are measured tactilely using the coordinate measuring machine; Step c) The calibration standard is removed from the adapter plate; Step d) The calibration standard is taken to an industrial computer tomograph; Step e) The geometric dimensions of the calibration standard are measured x-ray using the industrial computer tomograph, with the calibration standard rotating around a rotational axis of the computer tomograph that runs parallel to the longitudinal axis of the calibration standard.is rotated; Step f) the X-ray measured geometric dimensions of the calibration standard and the tactile measured geometric dimensions of the calibration standard are compared to check the function of the industrial CT scanner and / or to adjust the industrial CT scanner. With this procedure, the geometric dimensions of the calibration standard can be measured tactilely on the coordinate measuring machine with virtually no stress, even though the coordinate measuring machine uses a clamping bearing. The tactile measured dimensions then correspond very precisely to the actual dimensions of the calibration standard during the X-ray measurement of the calibration standard, and the imaging accuracy of the ICT apparatus can be checked or readjusted with high precision. Typically, steps a) to d) are only performed once, and steps e) and f) are repeated regularly on the CT scanner. Note:that an adapter plate can be used for a variety of calibration standards for their tactile measurement. The geometric dimensions typically include distances between the centers of the calibration sphere elements (or pairs of centers of the calibration sphere elements) of the calibration standard.

[0055] In a preferred variant of the inventive use of the calibration standard system, it is provided that the calibration standard is further configured with a hood assembly that can be screwed onto the base plate, that the hood assembly is unscrewed in step b), that the hood assembly is screwed on after step b) and before step d), and that the hood assembly is screwed on in step e). The calibration standard is measured tactilely without the hood assembly, and then the screwed-on hood assembly protects the calibration standard from external influences, in particular unintentional plastic deformation. This allows the ICT apparatus to be checked with particularly high reliability.

[0056] In a preferred further development of this variant, it is provided that, when the hood arrangement is screwed on, a part of the hood arrangement, in particular a first, radially outer, circumferential surface, and a part of the base plate, in particular a second, radially outer, circumferential surface, adjoin one another at a contact surface, in particular adjoin one another flush with one another, that after step b) and before step d), after the hood arrangement has been screwed on, a seal is applied to these two parts of the hood arrangement and the base plate, which seal engages over the contact surface, and that before step e) it is verified that the seal is undamaged. The seal can be used to ensure that the hood arrangement has not been accidentally or unauthorizedly removed in the meantime.If the seal (and the cover assembly) are intact, it is ensured that the calibration standard has not been (unnoticed) deformed when the cover assembly was removed. This can further increase the reliability of the ICT device inspection.

[0057] Further advantages of the invention will become apparent from the description and the drawings. Likewise, the above-mentioned and further-described features can be used individually or in combinations according to the invention. The embodiments shown and described are not intended to be exhaustive, but rather are exemplary in nature for describing the invention. Detailed description of the invention and drawing

[0058] Fig. 1shows a schematic exploded view of a first embodiment of a calibration standard according to the invention, viewed obliquely from above, wherein the base body tapers conically in the region of an outer surface; Fig. 2 shows a schematic exploded view of the first embodiment of the calibration standard of Fig. 1 , diagonally from below; Fig. 3 shows a schematic view of the first embodiment of the calibration standard of Fig. 1 in the assembled state, from above, without the hood cup; Fig. 4 shows a schematic view of the first embodiment of the calibration standard of Fig. 1 in the assembled state, obliquely from below, without the hood cup; Fig. 5 shows a schematic longitudinal section through the first embodiment of the calibration standard of Fig. 1 , without base plate and without hood arrangement; Fig. 6 shows a schematic side view of the first embodiment of the calibration standard of Fig. 1 , without base plate and without hood arrangement; Fig. 7 shows a schematic plan view of the first embodiment of the calibration standard of Fig. 1 , without base plate and without hood arrangement; Fig. 8 shows a schematic view of a second embodiment of a calibration standard according to the invention, obliquely from above, wherein the tapered base body has a hexagonal cross-section in the region of the outer surface; Fig. 9 shows a schematic longitudinal section through a third embodiment of a calibration standard according to the invention, wherein the tapered base body is spherical in the region of the outer surface; Fig. 10 shows a schematic longitudinal section through a fourth embodiment of a calibration standard according to the invention, wherein the tapered base body is conical in the region of the outer surface, and wherein the calibration ball elements are arranged on support pins; Fig. 11shows a schematic view of an exemplary adapter plate for a calibration standard system according to the invention, obliquely from above; Fig. 12 shows a schematic view of the adapter plate of Fig. 11 , diagonally from below; Fig. 13a schematically illustrates an exemplary use of a calibration standard according to the invention, in a step a), wherein the calibration standard is mounted on an adapter plate, and wherein the adapter plate is mounted on a coordinate measuring machine; Fig. 13b schematically illustrates the use of Fig. 13a , in a step b), whereby the calibration standard is measured tactilely; Fig. 13c schematically illustrates the use of Fig. 13a , in a step c), wherein the calibration standard is removed from the adapter plate; Fig. 13d schematically illustrates the use of Fig. 13a, in a step d), wherein the calibration standard including a hood arrangement is arranged on an ICT apparatus; Fig. 13e schematically illustrates the use of Fig. 13a , in a step e), whereby the calibration standard is measured X-ray; Fig. 13f schematically illustrates the use of Fig. 13a , in a step f), whereby the tactile measured dimensions and the X-ray measured dimensions of the calibration standard are compared with each other.

[0059] The Figures 1 to 7 schematically illustrate an exemplary first embodiment of a calibration standard 1 according to the invention.

[0060] As best seen from the exploded views of Fig. 1 and Fig. 2 As can be seen, the calibration standard 1 comprises a base body 2, which in the embodiment shown has its lower / rear end 13a (in Fig. 1 and Fig. 2left side) is mounted on a base plate 3. The base body 2 can be covered with a hood assembly 4, which has a base ring 5 on which a hood cup 6 is mounted. The calibration standard 1 extends along a longitudinal axis LA.

[0061] The base body 2 has a front / upper section 2a, in which the base body 2 is conical. The cone angle here is 45° (see also Fig. 6). In this partial area 2a, the base body has an outer surface 7 which is directed radially outwards (with a directional component of its respective local surface normal) and on which calibration spherical elements 9 are inserted and fastened, here glued, in recesses 8. The recesses 8 are spherically rounded here. A total of eight recesses 8 and eight calibration spherical elements 9 are provided in the embodiment shown. The calibration spherical elements 9 are designed here as ruby ​​spheres with a roundness of grade 05. The recesses 8 and calibration spherical elements 9 are also arranged here in the form of a spiral 36 on the conical outer surface 7.

[0062] In the embodiment shown, the base body 2 further comprises a rear / lower partial region 2b, which is essentially cylindrical in shape. No calibration ball elements are arranged on the corresponding, further outer surface 10 of this partial region 2b. A rounded transition region 2c is also provided between the rear partial region 2b and the front partial region 2a, on whose further outer surface 11 no calibration ball elements are arranged.

[0063] The base body 2 is rotationally symmetrical with respect to the longitudinal axis LA (notwithstanding the recesses 8). In the area of ​​the outer surface 7, the base body tapers continuously and linearly, corresponding to its conical shape.

[0064] As from Fig. 2 (and also Fig. 5) clearly shows, the base body 2 is hollow, with the base body 2 being open towards its rear end 13a (but closed by the base plate 3) and closed towards its front, blunt end 13b. The base body 2 is made of a fiber-reinforced composite material. The orientation of the fibers (usually carbon fibers) can be optimized for expected mechanical loads. In many cases, it is advantageous to orient the fibers in a braid, with some of the fibers running in the circumferential direction. Typically, the composite material has a matrix made of epoxy resin.

[0065] In the embodiment shown, the base plate 3 has an annular groove 12 on its upper side 14, into which the rear end 13a of the base body 2 is inserted and glued. Furthermore, a base plate thread 15 in the form of an external thread is formed on the radial outer side of the base plate 3.

[0066] A matching hood thread 16 in the form of an internal thread is formed on the base ring 5 of the hood assembly 4. This allows the hood assembly 4 to be screwed onto the base plate 3 from the side of the top side 14; typically, the base plate 3 and the base ring 5 are made of metal, for example, stainless steel. The hood cup 6 is made of a transparent plastic, such as polymethyl methacrylate. This makes the base body 2 clearly visible to the naked eye even when the hood assembly 4 is screwed on, and also easily accessible for X-rays.

[0067] The hood cup 6 is pushed with its rear, open end 19 onto an annular base ring socket 17 and sits on a shoulder 18 of the base ring 5 on the upper side 37 of the base ring 5; in this position, the hood cup 6 is glued to the base ring 5. In the embodiment shown, the hood cup 6 is cylindrical. At its front end 20, the hood cup 6 is closed.

[0068] When the hood assembly 4 is screwed onto the base plate 3, the hood cup 6 can protect the base body 2 and the calibration ball elements 9 from mechanical influences, in particular deformations and damages.

[0069] As again especially from Fig. 2As can be seen, a three-point bearing 25 is formed on the underside of the base plate 3 by means of three pairs of bearing balls 22. The bearing ball pairs are arranged around the longitudinal axis LA and offset from one another by 120°. A holding magnet 23 is screwed centrally between the bearing balls 22 on the underside 21. The holding magnet 23 has the shape of a round plate with a flat magnetic disc through which a bore runs for the passage of a fastening screw 24, which is screwed into the base plate 3.

[0070] The Fig. 3 shows the calibration standard 1 of Fig. 1 and Fig. 2 in the assembled state with base plate 3, base body 2, and screwed-on base ring 5 in an oblique view (obliquely from above), but with the hood cup omitted. The oblique view clearly shows the arrangement of the calibration ball elements 9 in a spiral 36 on the outer surface 7 of the base body 2.

[0071] The base body 2 tapers in the area of ​​the outer surface 7 according to its conical shape towards its front / upper end 13b.

[0072] In the Fig. 4 is the calibration standard 1 of Fig. 3 shown in another oblique view (obliquely from below). In this oblique view, the three-point bearing 25, which is formed by the three pairs of bearing balls 22, is clearly visible, as is the holding magnet 23 attached to the underside 21 of the base plate 3 with the fastening screw 24.

[0073] The underside 21 of the base plate 3 and an underside 27 of the base ring 5 are flush with one another here. A seal 26 is glued to the underside over the contact surface 28 (i.e., over the adjacent threads on the lower end face) between the base plate 3 and the base ring 5. An undamaged seal 26 can be used to verify that since the seal 26 was applied, the base ring 5 or the hood assembly has not been unscrewed from the base plate 3, and accordingly, the base body and the calibration sphere elements were continuously protected by the hood assembly, so that deformation or damage to the base body and the calibration sphere elements due to external forces has been virtually impossible since that time.

[0074] The Fig. 5 shows in a longitudinal section the base body 2 of the calibration standard of Fig. 1 and Fig. 2. In the longitudinal section it can be clearly seen that the base body 2 has a substantially uniform wall thickness WS, in particular in the area of ​​the outer surface 7. As a result, in a computer tomograph the imaging of calibration spherical elements 9 near the longitudinal axis (in the respective rotational position) under very similar conditions, in particular approximately the same wall thickness of the base body 2 irradiated in the beam propagation direction, is possible over a large axial range, and is therefore particularly accurate.

[0075] In the side view of Fig. 6 and the supervision from above of Fig. 7 on the base body 2 of the calibration standard of Fig. 1 and Fig. 2The spiral positioning of the calibration ball elements 9 of the first embodiment can be clearly seen. The calibration ball elements 9 form a spiral 36 in one revolution around the longitudinal axis LA. Calibration ball elements 9 adjacent in the circumferential direction have a uniform distance AA (from center to center) in the axial direction (along the longitudinal axis LA). The cone angle KW of the base body 2 in the partial area 2a is also 45° here. In addition, calibration ball elements 9 adjacent in the circumferential direction have a uniform relative angle of rotation to one another in the circumferential direction, also called angular offset WV, which is 45° here.

[0076] The diameter D of the calibration ball elements 9 is significantly smaller than the axial distance AA, i.e. D <AA. Die Kalibrier-Kugelelemente 9 überlappen somit nicht in axialer Richtung, unabhängig von der Drehposition, so dass ein in radialer Richtung propagierender Röntgenstrahl (in Fig. 6X-ray beam propagating perpendicular to the plane of the drawing) never has to pass through two calibration spherical elements in succession. In an axial interval 29 in which a calibration spherical element 9 extends, no further calibration spherical element 9 extends. In the present case, D = 0.67 * AA also applies. Thus, between two axially successive calibration spherical elements 9 there is a free, axial neighboring interval 30 of axial length NIL, with NIL = 0.33 * AA here, in which no calibration spherical element 9 extends. The diameter D corresponds to twice the radius of curvature of the calibration spherical element 9, i.e. D = 2 * R K K. Thus, in the present embodiment, NIL = 0.33 * (D / 0.67) and further NIL = 1 / 2 * D and further NIL = 1 * R K K. Note that generally at least NIL≥0.2*RKK is preferred, and particularly NIL≥0.5*RKK is preferred.

[0077] The Fig. 8shows a schematic oblique view of a calibration standard 1 according to an exemplary second embodiment. Note that in Fig. 8 the base plate, the three-point bearing and the holding magnet are not shown in detail (see Fig. 1 and 2 ).

[0078] In this embodiment, the base body 2 has a hexagonal cross-section in the region of the outer surface 7, which tapers continuously and linearly towards the upper, truncated end 13b of the base body 2. Accordingly, the base body 2 has a 6-fold rotational symmetry in the region of the outer surface 7 with respect to the longitudinal axis LA. The calibration ball elements 9 sit directly on the outer surface 7 and form a spiral 36 with 1.5 revolutions.

[0079] The Fig. 9 shows in a schematic longitudinal section an exemplary third embodiment of a calibration standard 1. Note that in Fig. 9the base plate, the three-point bearing and the holding magnet are not shown in detail (see Fig. 1 and 2 ).

[0080] In this embodiment, the base body 2 is spherically shaped in the region of its outer surface 7 in the upper portion 2a, and accordingly tapers continuously toward the upper end 13b. The base body 2 is also rotationally symmetrical with respect to the longitudinal axis LA.

[0081] In the embodiment shown, the local wall thickness WS of the base body 2 increases slightly axially upwards. This makes it possible to achieve that, for calibration spherical elements 9 that are located further away from the longitudinal axis LA (in the respective rotational position of a CT image), approximately the same imaging conditions prevail over a larger axial interval, and in particular, an approximately equal wall thickness is irradiated in the beam propagation direction.

[0082] The Fig. 10shows in a schematic longitudinal section a base body 2 of a calibration standard 1 according to an exemplary fourth embodiment of the invention, similar to that in Fig. 5 shown base body with conical taper. Only the essential differences are explained. Please note that in Fig. 10 the base plate, the three-point bearing and the holding magnet are not shown in detail (see Fig. 1 and 2 ).

[0083] In the fourth embodiment, the calibration ball elements 9 are arranged on pins 31. The pins 31 have recesses 32 at their front (outward-facing) end 33, which are spherical in shape here, corresponding to the radius of curvature of the calibration ball elements 9. The other, rear end 34 of the pin 31 is inserted into a bore 35 in the base body 2 and glued into the bore 35. The bores 35 are designed as through bores here, but blind bores can also be provided alternatively. The bores 35 are closed by the pins 31.

[0084] The pins 31 protrude here by a length L relative to the outer surface 7. In the embodiment shown, approximately L=D applies. Generally preferred is L≤2*D, particularly preferred is L≤1.5*D, in order to keep mechanical moments low during mechanical scanning of the calibration spherical elements 9. In the embodiment shown, the pins 31 and the associated bores 35 are oriented along the respective local surface normals of the conical outer surface of the base body 2; accordingly, the pins 31 protrude from the base body 2 or from the outer surface 7 in a direction that has a radial directional component. The pins 31 have a pin diameter SD that is smaller than the diameter D of the calibration spherical elements 9, i.e. SD <D, bevorzugt wobei SD≤0,75*D.

[0085] The plug pins 31 make the calibration ball elements 9 more accessible for a mechanical probe of a coordinate measuring machine; in particular, a certain degree of rearward engagement of the calibration ball elements 9 is also possible.

[0086] The Fig. 11 (from diagonally above) and the Fig. 12 (obliquely from below) illustrate an adapter plate 40 for an exemplary calibration standard system comprising the adapter plate 40 and a calibration standard, for example as in Fig. 1 and Fig. 2 shown.

[0087] The adapter plate 40 is essentially disc-shaped and rotationally symmetrical with respect to the longitudinal axis LA.

[0088] In order to attach the base plate of the calibration standard to the upper side 41 of the adapter plate 40, a three-point counter bearing 42 is formed on this upper side 41. In the embodiment shown, this comprises three hard metal rollers 43, which are arranged around the longitudinal axis and offset by 120° in the circumferential direction. The axes of the hard metal rollers 43 are directed towards a common center. The hard metal rollers 43 can each engage between a pair of bearing balls of a three-point bearing on the underside of the base plate of the calibration standard (see Fig. 4(top). A counter-holding magnet 44 is also arranged in the center area between the hard metal rollers 43. The counter-holding magnet 44 is disc-shaped here and is glued and / or pressed into a corresponding recess on the top side of the adapter plate 40. The counter-holding magnet 44 can interact with the holding magnet on the underside of the base plate of the calibration standard, thereby pulling the base plate onto the adapter plate 40. The magnetic force holds the base plate or the three-point bearing securely and without play on the adapter plate 40 or on the three-point counter-bearing 42.

[0089] It should be noted that alternatively the three-point bearing can be designed with the hard metal rollers 43 and the three-point counter bearing 42 with the pairs of bearing balls (not shown in detail).

[0090] A clamping pin 46 is formed on the underside 45 of the adapter plate 40, with which the adapter plate 40 can be clamped to a clamping bearing of a tactile coordinate measuring machine. Mechanical stresses acting on the adapter plate 40 through the clamping bearing via the clamping pin 40 are decoupled with respect to the calibration standard at the transition from the three-point counter bearing 42 of the adapter plate 40 to the three-point bearing of the base plate.

[0091] The Figures 13a to 13f schematically illustrate the use of a calibration standard 1 according to the invention as in Fig. 1 and Fig. 2 shown or a calibration standard system 50 comprising the calibration standard 1 and an adapter plate as in Fig. 11 and Fig. 12 represented within the scope of the invention in successive steps.

[0092] In Fig. 13ais illustrated in a first step a). The calibration standard 1, which comprises the base body 2 and the base plate 3, is placed on the adapter plate 40. The three-point bearing 25 and the three-point counter bearing 42 are fastened to each other by magnetic holding force. The calibration standard 1 and the adapter plate 40 together form a calibration standard system 50 (see also Fig. 13b for the assembled state). In addition, the adapter plate 40 is inserted into the clamping bearing 51 of a tactile coordinate measuring machine 52 and clamped in the clamping bearing 51. Clamping jaws 53 are moved onto the clamping pin 46 of the adapter plate 40 arranged in the clamping bearing 51. It should be noted that the order of these two described sub-steps is irrelevant.

[0093] In Fig. 13bThe assembled calibration standard system 50 is arranged and securely held in the clamping bearing 51 of the coordinate measuring machine 52. Then, in a second step b), the coordinate measuring machine 52 uses a mechanical sensor (also called a probe) 54 to tactilely measure the geometric dimensions on the surface of the calibration standard 1. For this purpose, the sensor 54 is attached to a cross-slide system 55 and can typically be moved in three orthogonal spatial directions. The tactile measurement of the calibration standard 1 determines, in particular, the relative positions of the calibration spherical elements 9 of the calibration standard 1.

[0094] In a third step c), illustrated in Fig. 13c ,The calibration standard 1 is then removed from the coordinate measuring machine 52. In the variant shown, a hood assembly 4 is then placed and screwed onto the base plate 3 of the calibration standard 1. In the screwed-on state, a seal 26 is also attached, which overlaps a contact surface between the base plate 3 and the hood assembly 4 (see also Fig. 4 ). Typically, the adapter plate 40 is also removed from the coordinate measuring machine 52 (the latter not shown in detail).

[0095] Then, in a fourth step d), as in Fig. 13dAs shown, the calibration standard 1, together with the hood assembly 4, is transported to an industrial computer tomography scanner 56 (also called an ICT apparatus) and placed on a rotating holder 57 of the ICT apparatus 56. Special fastening to the rotating holder 57 is generally not necessary, but is possible if desired. The ICT apparatus 56 is to be checked for its imaging accuracy and readjusted if necessary.

[0096] In a subsequent, fifth step e), an X-ray measurement of the calibration standard 1 is carried out, as in Fig. 13eshown. The calibration standard 1 is rotated by means of the rotary holder 57 about a rotation axis DA, which corresponds to the longitudinal axis LA of the calibration standard 1. An X-ray image of the calibration standard 1 is taken in different rotational positions. For this purpose, an X-ray tube 58 emits X-ray radiation 59 in the direction of a 2D spatially resolving X-ray detector 60; the X-ray radiation 59 propagates essentially in a horizontal direction or perpendicular to the rotation axis DA. The calibration standard 1 is penetrated by the X-ray radiation 59, and an X-ray shadow of the calibration standard 1 is created on the X-ray detector 60. The hood cup 6 of the hood arrangement is penetrated by the X-ray radiation 59, which causes only a slight attenuation.

[0097] In a sixth step f), shown in Fig. 13f ,The radiographically measured dimensions of the calibration standard (which were calculated from the plurality of x-ray images from step e) and in particular include the relative positions of the calibration sphere elements 9) are then compared with the tactilely measured dimensions of the calibration standard, which are assumed to be true. The comparison is typically carried out on a computer 61. If the two dimensions sufficiently agree, the ICT apparatus can be released. If the two dimensions do not sufficiently agree, the ICT apparatus cannot be released; this typically results in readjustments of operating parameters on the ICT apparatus, and possibly also further maintenance and repair work. Steps e) and f) are then usually repeated until sufficient agreement between the tactilely measured dimensions and the (re)radiographically measured dimensions is obtained, and the ICT apparatus can be released. List of reference symbols

[0098] 1Calibration standard 2Base body 2Front / upper section of the base body 2bRear / lower section of the base body 2cTransition area of ​​the base body 3Base plate 4Cover assembly 5Base ring 6Cover cup 7Outer surface 8Recess (in the base body) 9Calibration ball element 10Further outer surface 11Further outer surface 12Ring groove 13aRear end of the base body 13bFront end of the base body 14Top of the base plate 15Base plate thread 16Cover thread 17Base ring socket 18Shoulder of the base ring 19Rear end of the cover cup 20Front end of the cover cup 21Underside of the base plate 22Bearing balls 23Holding magnet 24Fastening screw 25Three-point bearing 26Seal 27Underside of the base ring 28Contact surface 29Axial interval (extension of a calibration spherical element) 30(free) axial adjacent interval (extension of the intermediate area between calibration spherical elements) 31Pin 32Recess (at the front end of the pin) 33Front / front end (of theplug pin) 34rear / other end (of the plug pin) 35bore 36spiral 37top of the base ring 40adapter plate 41top of the adapter plate 42three-point counter bearing 43carbide rollers 44counter-holding magnet 45bottom of the adapter plate 46clamping spigot 50calibration standard system 51clamping bearing 52(tactile) coordinate measuring machine 53clamping jaws 54(tactile) feeler / probe 55cross-slide system 56industrial computer tomograph / ICT apparatus 57rotary holder 58X-ray tube 59X-ray radiation 60(2D-resolving) X-ray detector 61computer AAaxial distance (from center to center) Ddiameter of a calibration spherical element DArotational axis of the rotary holder KWcone angle Lprojecting length of the Pin LALongitudinal axis NILaxial length of the axial adjacent interval RKKRadius of curvature of the calibration spherical element SDDiameter of the pin WSWall thickness WVAngle of rotation / angular offset

Claims

1. Calibration standard (1) for an industrial computer tomograph (56), wherein the calibration standard (1) has a main body (2) with a longitudinal axis (LA), wherein the main body (2) has an outer surface (7) which is continuously circumferential around the longitudinal axis (LA) with respect to a circumferential direction and which extends along the longitudinal axis (LA), wherein a plurality of calibration sphere elements (9) are attached to the main body (2) distributed over the radially outward-directed outer surface (7), wherein the calibration sphere elements (9) are distributed over a plurality of axial positions with respect to the longitudinal axis (LA), wherein the main body (2) tapers along the longitudinal axis (LA) in the region of the outer surface (7), and wherein the calibration sphere elements (9) are distributed over a plurality of radial positions with respect to the longitudinal axis (LA), characterized in that the calibration standard (1) further has a base plate (3), that the main body (2) is attached to an upper side (14) of the base plate (3), and that a three-point bearing (25) and a holding magnet (23) are formed on an underside (21) of the base plate (3).

2. Calibration standard (1) according to claim 1, characterized in that the main body (2) tapers continuously along the longitudinal axis (LA) in the region of the outer surface (7).

3. Calibration standard (1) according to any of claims 1 or 2, characterized in that the main body (2) is rotationally symmetrical with respect to the longitudinal axis (LA) at least in the region of the outer surface (7).

4. Calibration standard (1) according to claim 3, characterized in that the main body (2) is conical at least in the region of the outer surface (7).

5. Calibration standard (1) according to claim 3, characterized in that the main body (2) is formed at least in the region of the outer surface (7) corresponding to a part of a spherical surface.

6. Calibration standard (1) according to any of claims 1 or 2, characterized in that the main body (2) has, at least in the region of the outer surface (7), a rotational symmetry with respect to the longitudinal axis (LA), with the longitudinal axis (LA) as an N-fold axis of rotation, with N≥6.

7. Calibration standard (1) according to any of claims 1 to 6, characterized in that, at least for a plurality of the calibration sphere elements (9), no further calibration sphere elements (9) extend in an axial interval (29) along the longitudinal axis (LA) in which a respective calibration sphere element (9) extends, in particular, wherein, for all calibration sphere elements (9), no further calibration sphere elements (9) extend in an axial interval (29) along the longitudinal axis (LA) in which a respective calibration sphere element (9) extends.

8. Calibration standard (1) according to claim 7, characterized in that, additionally, no further calibration sphere elements (9) extend in the axial direction in front of and behind this axial interval (29) in each case in an axial adjacent interval (30), in particular wherein each adjacent interval (30) has an axial length NIL for which NIL ≥ 0.2*RKK, where RKK is the radius of curvature of the corresponding calibration sphere element (9).

9. Calibration standard (1) according to any of the preceding claims, characterized in that at least some of the calibration sphere elements (9), which are distributed on the outer surface (7) of the main body (2), are arranged according to a spiral (36), preferably wherein, in the spiral (36), successive calibration sphere elements (9) are each at an equal distance (AA) from one another along the longitudinal axis (LA) and are offset from one another by the same angle of rotation (WV) around the longitudinal axis (LA).

10. Calibration standard (1) according to any of the preceding claims, characterized in that the main body (2) is designed as a hollow body.

11. Calibration standard (1) according to claim 10, characterized in that a wall thickness (WS) of the main body (2) in the region of the outer surface (7) is constant along the longitudinal axis (LA).

12. Calibration standard (1) according to claim 10, characterized in that a wall thickness (WS) of the main body (2) in the region of the outer surface (7) increases along the longitudinal axis (LA) in the direction along which the main body (2) tapers.

13. Calibration standard (1) according to any of claims 1 to 12, characterized in that, in the outer surface (7) of the main body (2), recesses (8), in particular spherical recesses (8), are introduced, into which the calibration sphere elements (9) are inserted.

14. Calibration standard (1) according to any of claims 1 to 12, characterized in that the calibration sphere elements (9) are each fastened to pins (31), each of which has, on an end face (33), a recess (32), in particular a spherical recess (32), into which a corresponding calibration sphere element (9) is inserted, and each of which is inserted with another end (34) into a corresponding bore (35) on the outer surface (7) of the main body (7), wherein a partial portion of the pin (31) protrudes with respect to the outer surface (7).

15. Calibration standard (1) according to any of the preceding claims, characterized in that the main body (2) is made from a carbon fiber composite.

16. Calibration standard (1) according to any of the preceding claims, characterized in that the base plate (3) is made entirely or predominantly of metal, and / or that the main body (2) is glued to the upper side (14) of the base plate (3).

17. Calibration standard (1) according to any of the preceding claims, characterized in that the calibration standard (1) further comprises a hood arrangement (4) which can be screwed onto the base plate (3) on the upper side (14) of the base plate (3), wherein the hood arrangement (4) in the region of its underside (21) forms a hood thread (16), in particular an internal thread, and the base plate (3) forms a matching base plate thread (15), in particular an external thread, and that the hood arrangement (4) completely covers the main body (2) together with the base plate (3) in the screwed-on state.

18. Calibration standard (1) according to claim 17, characterized in that the hood arrangement (4) has a base ring (5) on which the hood thread (16) is formed, in particular wherein the base ring (5) is made entirely or predominantly of metal, and that the hood arrangement (4) has a hood cup (6) which is fastened, in particular glued, in the region of an upper side (37) of the base ring (5), in particular wherein the hood cup (6) is at least partially made of a transparent material and / or of plastic, preferably of a transparent plastic.

19. Calibration standard (1) according to any of the preceding claims, characterized in that the three-point bearing (25) comprises three pairs of bearing balls (22) or three hard metal rollers (43) which are attached, in particular glued, to the underside (21) of the base plate (3), and that the holding magnet (23) is fastened, in particular screwed, centrally between the bearing balls (22) or hard metal rollers (43) on the underside (21) of the base plate (3).

20. Calibration standard according to claim 19, characterized in that the holding magnet is formed by a round blank.

21. Calibration standard system (50), comprising a calibration standard (1) according to any of the preceding claims and an adapter plate (40), wherein, on an upper side (41) of the adapter plate (40), a three-point counter bearing (42) and a counter holding magnet (44) are formed, corresponding to a position image of the three-point bearing (25) and of the holding magnet (23) of the base plate (3) of the calibration standard (1), and wherein the adapter plate (40) further forms, in the region of its underside (45), a clamping pin (46) for clamping in a clamp mount (51) of a coordinate measuring machine (52).

22. Use of a calibration standard system (50) according to claim 21, with the following steps: Step a) in any order, the calibration standard (1) and the adapter plate (40) are fastened to each other via the three-point bearing (25), the three-point counter bearing (42), the holding magnets (23) and the counter holding magnet (44), and the adapter plate (40) is fastened with the clamping pin (46) in a clamp mount (51) of a coordinate measuring machine (52); Step b) geometric dimensions of the calibration standard (1) are measured tactilely with the coordinate measuring machine (52); Step c) the calibration standard (1) is removed from the adapter plate (40); Step d) the calibration standard (1) is transferred to an industrial computer tomograph (56); Step e) geometric dimensions of the calibration standard (1) are measured with x-ray imaging using the industrial computer tomograph (56), wherein the calibration standard (1) is rotated about an axis of rotation (DA) of the computer tomograph (56) which runs parallel to the longitudinal axis (LA) of the calibration standard (1); Step f) the geometric dimensions of the calibration standard (1) measured using x-ray imaging and the tactilely measured geometric dimensions of the calibration standard (1) are compared with each other in order to verify the function of the industrial computer tomograph (56) and / or to adjust the industrial computer tomograph (56).

23. Use of the calibration standard system (50) according to claim 22, characterized in that the calibration standard (1) is further designed according to any of claims 17 or 18, that, in step b), the hood arrangement (4) is in an unscrewed state, that, after step b) and before step d), the hood arrangement (4) is being screwed on, and that, in step e), the hood arrangement (4) is in a screwed on state.

24. Use of the calibration standard system (50) according to claim 23, characterized in that, in the screwed-on state of the hood arrangement (4), a part of the hood arrangement (4), in particular a first, radially outer, circumferential surface, and a part of the base plate (3), in particular a second, radially outer, circumferential surface, adjoin one another at a contact surface (28), and in particular sit flush against each other, that, after step b) and before step d), after the hood arrangement (4) has been screwed on, a seal (26) is applied to these two parts of the hood arrangement (4) and the base plate (3), which seal overlaps the contact surface (28), and that, before step e), it is verified that the seal (26) is undamaged.