Patent Description:
In recent years, the measurement of dimensions including those of the internal shape of a test object has been performed using an X-ray CT device developed as a device for observing the internal structure of a test object. Methods for evaluating the measurement accuracy of an X-ray CT device designed to measure a three-dimensional shape have been discussed in order to develop international standards; however, regarding current devices, for example, on the basis of measurement accuracy calculated in accordance with the Germany's domestic guideline VDI/VDE2630-<NUM> (guideline on dimensional measurement by X-ray CT), accuracy assurance is provided for the devices. In addition, as a utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement (hereinafter referred to as a utensil) corresponding to VDI/VDE2630-<NUM>, a utensil made by Cael Zeiss Inc. is known (see Non-Patent Literature <NUM>).

The utensil described in Non-Patent Literature <NUM> is one of a type referred to as a forest gauge. In the utensil referred to as the forest gauge, spheres are arranged in a space by installing upright support rods supporting the spheres on a stepwise base. One having <NUM> spheres and one having <NUM> spheres as the number of spheres are known.

Also, Patent Literature <NUM> proposes a calibrator of an X-ray CT device, which intends to accurately calibrate the dimensions of shapes including the internal shape of a test object from projection images obtained by the X-ray CT device. In a utensil described in Patent Literature <NUM>, spheres are arranged in a space by firmly fixing the spheres on the outer circumference of a cylindrical body.

Before X-ray CT imaging of such a utensil, the coordinates of the respective spheres are measured by CMM (coordinate measuring machine: contact type three-dimensional coordinate measuring machine) or the like. In addition, from the difference between the value of an actual inter-sphere distance obtained by a coordinate measurement result and the value of an inter-sphere distance in an imaging space measured at the time of the X-ray CT imaging, a length measurement error by X-ray CT is evaluated.

<CIT>) is directed at a method for determining at least one parameter that describes the geometry of a measuring arrangement in the form of a computer tomography sensor system, at least consisting of a radiation source, a flat detector and a mechanical axis of rotation for rotating the workpiece or for rotating the radiation source and detector.

The present invention is defined by the features described in the independent claims.

The calibrator described in Patent Literature <NUM> has the problem of being able to evaluate only a cylindrical region in an imaging space because no sphere can be arranged in the cavity inside the cylindrical body. On the other hand, in the utensil referred to as the forest gauge, it is possible to arrange spheres on the central axis; however, there is the following problem.

<FIG> is a schematic diagram illustrating an evaluation range in an imaging visual space when performing X-ray CT imaging on a conventional forest gauge. In addition, <FIG> illustrates the case where the <NUM>-sphere forest gauge made by Carl Zeiss, Inc. is targeted for the X-ray CT imaging. In <FIG>, the imaging visual space of a cylindrical shape is indicated by virtual lines, and in <FIG>, an evaluation range at one time of X-ray CT imaging is illustrated. Also, <FIG> schematically illustrates evaluation ranges and unevaluable ranges in the imaging visual space when the X-ray CT imaging was performed three times at switched Z positions, and <FIG> is a diagram illustrating the mutual positional relationship among three conical spaces in the imaging visual space when the X-ray CT imaging was performed three times at the switched Z positions.

In a measurement space (X, Y, Z) specific to an X-ray CT device, the following distortion occurs. Firstly, a length reference in the X axial direction and a length reference in the Y axial direction are different, and for example, a perfect circle is deformed into an ellipse on a cross-sectional image orthogonal to the Z axis. Secondly, the length reference in the X axial direction and the length reference in the Y axial direction are gradually changed depending on the position of the Z axis, and thereby for example, a cylindrical shape is deformed into a truncated conical shape. Thirdly, local deformation occurs around a specific point. Fourthly, depending on the intersecting position of the X-Y plane with the Z axis, the X-Y plane is gradually rotated and twist-like deformation occurs in the space.

In a utensil like the forest gauge, spheres are arranged on a conical surface with the central sphere as the apex, and therefore a conical space as illustrated in <FIG> serves as an evaluation range where comparison with the value of an inter-sphere distance obtained from a coordinate measurement result by CMM is possible. For this reason, among the above-described first to fourth types of spatial distortion specific to an X-ray CT device, the second to fourth types of spatial distortion are difficult to capture.

Also, in the <NUM>-sphere forest gauge made by Carl Zeiss Inc. , the support rods supporting the spheres are installed upright on the base provided with steps, and a range where the shadow of the base part is imaged at the time of X-ray CT imaging is widened. In addition, only a space above the top step serves as an evaluation range (see <FIG>). For this reason, as compared with an evaluation range on the X-Y plane, an evaluation range in the Z axial direction in measurement by one time of X-ray CT imaging is narrowed. For example, in three times of X-ray CT imaging, as indicated by hatching in <FIG>, the unevaluable ranges remain between the conical spaces. In order to eliminate such unevaluable ranges, it is necessary to measure an inter-sphere distance by repeatedly performing X-ray CT imaging while finely changing the position of a utensil in the Z axial direction many times within a height range corresponding to the longitudinal direction of the light receiving area of an X-ray detector. That is, it takes time to evaluate the measurement accuracy of an X-ray CT device.

Further, in the <NUM>-sphere forest gauge made by Carl Zeiss Inc. , since the spheres are arranged on a conical surface, the Z axis is aligned only with the sphere at the apex of the conical space, and therefore the mutual positional relationship among conical spaces each serving as an evaluation target at one time of X-ray CT imaging among multiple times of repeated X-ray CT imaging cannot be evaluated. Accordingly, as illustrated in <FIG>, the deformation of the conical spaces can be captured, but the mutual positional relationship of a conical space at each time of X-ray CT imaging cannot be captured.

The present invention has been made in order to solve the above-described problems, and a first object is to provide a utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement, which makes it possible to sufficiently capture spatial distortion specific to the X-ray CT device and evaluate the three-dimensional shape measurement accuracy of the X-ray CT device.

<FIG> is a schematic diagram illustrating conventional methods for fixing a support rod supporting a sphere to a base. In a conventional forest gauge, when arranging spheres in a space by installing upright support rods supporting the spheres to a base, as a method for fixing the support rods, a method referred to as so-called split clamping has been employed. In <FIG>, a fixing member <NUM> formed with a hole insertable with a support rod <NUM> is attached to a base <NUM> by screwing, and by operating a clamping screw <NUM> to narrow a clearance <NUM> in a split part, clamping force is given to the support rod <NUM> to fix the support rod <NUM> to the base <NUM>. Also, in <FIG>, a support rod <NUM> is fixed to a base <NUM> by using a fixing member <NUM> provided with a hole to be inserted with the support rod <NUM> and a male screw part <NUM>, and screwing the male screw part <NUM> into a screw hole (female screw) formed in a base <NUM> in a state where the support rod <NUM> is bonded and fixed into the hole.

In a utensil where a sphere <NUM> is arranged by a conventional fixing method illustrated in <FIG>, when bringing a probe of CMM into contact with the sphere for coordinate measurement, the position of the sphere <NUM> has been slightly changed in some cases because of the insufficiency of the rigidity and strength of the fixing member <NUM>, <NUM>. Also, when tilting the utensil or turning it upside down at the time of moving the utensil, the position of the sphere <NUM> has been slightly changed in some cases because of the insufficiency of clamping force by split clamping in <FIG>, because of the engagement backlash of the screw in <FIG>, or the like. The utensil for evaluating a length measurement error in the X-ray CT device for three-dimensional shape measurement is one for evaluating a length measurement error by X-ray CT from the difference between the value of an actual inter-sphere distance obtained from a coordinate measurement result and the value of an inter-sphere distance in an imaging space measured at the time of X-ray CT imaging, and therefore a change in sphere position after measuring the positions of respective spheres in the utensil by CMM is not allowed even if it is slight.

The present invention has been made in order to solve the above-described problem, and a second object is to provide a utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement, which prevents a sphere position from being changed even when a significant amount of external force is applied to a sphere or a support rod by contact of a probe or the like, or even when tilted or turned upside down at the time of movement.

<FIG> is a schematic cross-sectional view illustrating conventional bonding structures of a sphere at the tip of a support rod.

In a conventional forest gauge, when arranging spheres in a space, the support of spheres by the support rods is achieved by bonding ruby spheres or sapphire spheres commercially available as probes for CMM to the tips of the support rods. Bonding structures of a sphere to a support rod include one in which as illustrated in <FIG>, the upper surface of a support rod <NUM> side is processed in a concave shape so as to fit to a spherical shape, and a sphere <NUM> is bonded in such a manner as to place the sphere <NUM> on the concave part. Also, as illustrated in <FIG>, there is one in which a perforated sphere <NUM> applied with hole drilling is prepared, the tip of a support rod is provided with a thin shaft <NUM> corresponding to the hole, and the thin shaft <NUM> on the support rod <NUM> side is press-fitted into the hole of the perforated sphere <NUM> and then bonded and fixed. It is considered ideal that the clearance between the processed surface of the concave part and the lower surface of the sphere <NUM> illustrated in <FIG>, or between the side surface of the thin shaft <NUM> and the inner wall surface of the hole of the perforated sphere <NUM> illustrated in <FIG> is uniform, and the clearance is filled with bond for fixation.

The bonding structure in <FIG> has the problem that it is difficult to smoothly and accurately process the processed surface of the concave part on the support rod <NUM> side so as to fit to the curved surface of the sphere <NUM>, and the mutual positional relationship between the sphere <NUM> and the contact surface of the support rod <NUM> is unstable because of the unevenness of the processed surface of the concave part. Also, when the curvature radius of the processed surface of the concave part on the support rod <NUM> side is larger than the radius of the sphere, the sphere <NUM> rolls in the concave part of the support rod <NUM>, and contrary when the curvature radius of the processed surface of the concave part is smaller than the radius of the sphere <NUM>, the sphere <NUM> contacts with the support rod <NUM> at multiple partial points, such as contacting with parts inside the concave part and the edge of the concave part. For this reason, even when the same length of support rod <NUM> is made to support the sphere, the height position of the sphere is slightly different.

Further, in the bonding structure in <FIG>, the thin shaft <NUM> made of a different material from the perforated sphere <NUM> is present inside the sphere. For this reason, there is a problem that a transmission image obtained by X-ray irradiation is disturbed. That is, non-negligible deviations occur between the central position of the X-ray CT image of the sphere itself and the shape of the sphere supposed to be detected, and the central position of the X-ray CT image of the sphere itself and the shape of the sphere obtained by actual X-ray irradiation.

The present invention has been made in order to solve the above-described problems, and a third object is to provide a utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement, which enables the positional relationships between respective multiple support rods and spheres supported by them to be made uniform.

The above problems are solved by the features of the independent claims. In a first example, multiple spheres are arranged in an XYZ space on a base; and multiple support rods support each of the multiple spheres and may be installed upright on the base, in which in the XYZ space on the base, multiple spheres having different Z positions are arranged, and among the multiple spheres, one or more spheres are arranged in a vicinity of a Z axis, and in each of multiple X-Y planes having different Z positions, multiple outer circumference side spheres are arranged along one outer circumference.

A second example is such that in the utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement according to the first example, outer circumference side spheres arranged in each of the multiple X-Y planes are cylindrically arranged.

A third example is such that in the utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement according to the first or second example, the spheres arranged in the vicinity of the Z axis are multiple inner circumference side spheres.

A fourth example is such that in the utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement according to any of the first to third examples, in each of the multiple X-Y planes, multiple outer circumference side spheres and one or more inner circumference side spheres are arranged.

A fifth example is such that in the utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement according to the third or fourth example, a distance between the inner circumference side spheres and the Z axis is set to be <NUM> % or less of a distance between the outer circumference side spheres and the Z axis.

A sixth example is such that in the utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement according to any of the first to fifth examples, an arrangement range of the multiple spheres is a range where a distance in a Z direction between an X-Y plane having a lowest Z position and an X-Y plane having a highest Z position among the multiple X-Y planes is larger than a distance from the Z axis in XY directions.

A seventh example is such that in the utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement according to any of the first to sixth examples, the outer circumference side spheres are arranged in such a manner that an average value of the distances between respective outer circumference side sphere in each of the X-Y planes and the Z axis is equal amount the multiple X-Y planes.

An eighth example is such that in the utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement according to any of the first to seventh examples, the multiple X-Y planes are at least three X-Y planes whose mutual distances in a Z direction are equally separated.

A ninth example is such that in the utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement according to any of the first to eighth examples, as the arrangement of the outer circumference side spheres, multiple sets of two spheres separated from the Z axis by a predetermined distance and oppositely arranged with respect to the Z axis are arranged in each of the multiple X-Y planes having different Z positions, and thereby at least four are arranged in each of the X-Y planes.

A tenth example is such that in the utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement according to the ninth example, the multiple X-Y planes are at least three X-Y planes whose mutual distances in a Z direction are equally separated, and among the multiple spheres, multiple sets of two spheres oppositely arranged with respect to the Z axis are arranged, and thereby spheres arranged in each of the three X-Y planes are equally arranged at intervals of substantially <NUM> degrees on a circle around the Z axis in a plan view where the three X-Y planes are superposed.

An eleventh example is such that in the utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement according to the ninth or tenth example, in each of the multiple X-Y planes, one or more inner circumference side spheres are also arranged, and the one or more inner circumference side spheres are arranged on lines connecting the outer circumference side spheres that are oppositely arranged.

A twelfth example is such that in the utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement according to any of the first to eleventh examples, the outer circumference side spheres are arranged at regular intervals on a circle around the Z axis in a plan view of one X-Y plane.

A thirteenth example is such that in the utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement according to any of the first to twelfth examples, the base has a flat surface on a top thereof, and the lengths of the multiple support rods are different each other so that the Z positions of the arranged multiple spheres are different each other.

A fourteenth example is such that in the utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement according to any of the first to thirteenth examples, the multiple support rods are respectively provided with support rod holding mechanisms inserted into holes that are formed in the base so as to correspond to the number of the multiple support rods, and each of the support rod holding mechanisms includes: a bottomed cylindrical member that is inserted into one of the holes of the base, whose side surface is provided with multiple through-holes, and that is provided with a space into which a one of the support rods is inserted; a loading bolt whose central part is provided with a hole through which the support rod is made to penetrate and whose outer circumferential part is provided with a male screw part screwed into a female screw formed on the inner wall of an opening of the cylindrical member; fixing block inserted into one of the through-holes of the cylindrical member and having a convex part that abuts on the side surface of the support rod whose end part on a side opposite to a side where a sphere is supported abuts on the bottom of the cylindrical member, and a load transmitting block that is inserted into one of the through-holes of the cylindrical member and in two directions, transmits force generated when the loading bolt is fastened to the cylindrical member by screwing the female screw and the male screw part together, the two directions being a direction to constrain the degree of freedom of the support rod in a translation direction in an X-Y plane and a direction to constrain the degree of freedom of the support rod in a translation direction on the Z axis.

A fifteenth example is such that in the utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement according to the fourteenth example, the through-holes of the cylindrical member are provided in three positions of the side surface of the cylindrical member at regular intervals around a cylinder axis, and in two of the through-holes, the fixing blocks are arranged, and in one, the load transmitting block is arranged.

A sixteenth example is such that in the utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement according to the fourteenth or fifteenth example, the load transmitting block includes three wedge-shaped members mutually joined via a tilt surface.

A seventeenth example is such that in the utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement according to any of the first to sixteenth examples, one end of each of the support rods is provided with a conical concave part, and a sphere is supported in contact with the conical tilt surface of the conical concave part.

An eighteenth example is such that in the utensil for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement according to the seventeenth example, a bottom of the conical concave part of the support rod is provided with a through-hole.

According to the first to eighteenth examples, since in the XYZ space on the base, one or more spheres are arranged in the vicinity of the Z axis, and in each of the multiple X-Y planes having different Z positions, multiple outer circumference side spheres are arranged along one outer circumference, not only from a region where the multiple outer circumference side spheres are arranged in the space, but also to a region where one or more spheres are arranged in the vicinity of the Z axis on the inner side of the region where the outer circumference side spheres are arranged, an imaging space can be evaluated. Also, since in each of the multiple X-Y planes having different Z positions, multiple outer circumference side spheres are arranged along one outer circumference, the problem that an unevaluable region remains between conical spaces as in a conventional forest gauge where spheres are arranged on conical surfaces can be solved.

According to the fourth example, one or more inner circumference side spheres are arranged in each of the multiple X-Y planes, and thereby multiple spheres having different Z positions are arranged in the vicinity of the Z axis, so that multiple measurement points can be given in the Z direction at the center of an evaluation range. In doing so, the mutual positional relationship among cylindrical spaces each serving as an evaluation target at each time of X-ray CT imaging among multiple times of repeated X-ray CT imaging can be evaluated.

According to the sixth example, since the arrangement range of the multiple spheres is set as a range where the distance in a Z direction between an X-Y plane having the lowest Z position and an X-Y plane having the highest Z position among the multiple X-Y planes is larger than a distance from the Z axis in XY directions, a cylindrical imaging visual space can be isotropically evaluated by a smaller number of times of X-ray CT imaging than before. The number of times of performing repeated measurement with a Z axis position changed can be reduced than before, and therefore imaging time for evaluating the measurement accuracy of an X-ray CT device can be shortened.

According to the ninth example, since as the arrangement of the outer circumference side spheres, at least four spheres are arranged separated from the Z axis by a predetermined distance in each of the multiple X-Y planes having different Z positions, a conventional structure where spheres are arranged on conical surfaces is not formed, and therefore spatial distortion specific to an X-ray CT device can be sufficiently captured. Accordingly, the three-dimensional shape measurement accuracy of the X-ray CT device can be evaluated.

According to the thirteenth example, since by forming the top of the base as a flat surface and differentiating the lengths of the multiple support rods, the arrangement of the spheres having different Z positions is achieved, the shadow of a step appearing when a base is formed stepwise as conventional is not imaged, and a range evaluable at one time of imaging is widened, thus making it possible to reduce the number of times of performing repeated measurement with a Z axis position changed than before.

According to the fourteenth to eighteenth examples, since each support rod can be constrained in the three-dimensional space by the support rod holding mechanism, a utensil that even when a significant amount of stress is applied to a sphere or a support rod, or even when turned upside-down during transportation or installation, prevents a change in sphere position can be fabricated.

According to the seventeenth and eighteenth examples, since in a support rod, the tip supporting a sphere is shaped as the conical concave part, the sphere comes into line contact with the conical tilt surface of the conical concave part, and individual differences among spheres can be made less influential to uniform the positional relationships between spheres and corresponding support rods.

According to the eighteenth example, by providing the bottom of the conical concave part of the support rod with the through-hole, bond can be allowed to escape, and force for further pulling the sphere toward the support rod side is generated when the bond cures, making it possible to increase force for holding the sphere.

In the following, an embodiment of the present invention will be described on the basis of drawings. <FIG> is a schematic diagram of an X-ray CT device for three-dimensional shape measurement.

The X-ray CT device for three-dimensional shape measurement (hereinafter referred to as an X-ray CT device) includes an X-ray irradiation part <NUM>, an X-ray detector <NUM>, and a rotation stage <NUM>. The X-ray CT device is one that performs nondestructive internal observation and three-dimensional shape measurement with a test object placed on the rotation stage <NUM> disposed between the oppositely arranged X-ray irradiation part <NUM> and X-ray detector <NUM>.

The X-ray irradiation part <NUM> is provided inside with an X-ray tube as an X-ray source, and from the X-ray tube, generates X-rays corresponding to tube voltage and tube current supplied from a high voltage generator <NUM>. The high voltage generator <NUM> is controlled by an X-ray control part <NUM>, and the X-ray control part <NUM> is connected to a personal computer PC installed with control software for controlling the whole of the X-ray CT device. The X-ray detector <NUM> is one in which an image intensifier (I. ) is combined with a CCD camera, or an FPD (Flat Panel Detector), and connected to the personal computer PC via a CT image reconstruction arithmetic unit <NUM>. In addition, the X-ray detector <NUM> is configured to be separable/approachable with respect to the rotation stage <NUM> in order to scale a fluoroscopic imaging region. Further, the rotation stage <NUM> is also separable/approachable with respect to the X-ray irradiation part <NUM>.

The rotation stage <NUM> is adapted to rotate with a Z-axis orthogonal to an X-axis along an X-ray light axis L connecting from the X-ray irradiation part <NUM> to the X-ray detector <NUM> as a rotation axis R, and also be movable in the horizontal direction corresponding to XY directions and the vertical direction corresponding to a Z direction by a stage driving mechanism <NUM>. In addition, the stage driving mechanism <NUM> is connected to the personal computer PC via a stage control part <NUM>.

When performing X-ray CT imaging, rotation is given to the rotation stage <NUM> around the rotation axis R while irradiating the test object placed on the rotation stage with X-rays from the X-ray irradiation part <NUM>. Then, transmitted X-rays from all directions over <NUM> degrees around the test object are detected by the X-ray detector <NUM>, and the resulting X-ray transmission data is retrieved into the CT image reconstruction arithmetic unit <NUM>.

The CT image reconstruction arithmetic unit <NUM> includes a computer including: a ROM, RAM, hard disk, and the like as storage devices for storing programs, detection data from the X-ray detector <NUM>, and the like; and a CPU as an arithmetic unit. In the CT image reconstruction arithmetic unit <NUM>, the retrieved X-ray transmission data covering the <NUM> degrees is used to construct a tomographic image (CT image) of the test object, which is sliced along a plane parallel with the X-Y plane. The CT image is transmitted from the CT image reconstruction arithmetic unit <NUM> to the personal computer PC, and used for three-dimensional imaging by a three-dimensional image construction program installed in the personal computer PC.

The personal computer PC is connected with a display device <NUM> such as a liquid crystal display and input devices <NUM> including a keyboard 22a and a mouse 22b. In addition, the keyboard 22a and the mouse 22b are ones for providing inputs by an operator in various operations. The display device <NUM> displays a CT image transmitted from the CT image reconstruction arithmetic unit <NUM> to the personal computer PC, as well as displays a three-dimensional image constructed using the CT image. In addition, the functions of the CT image reconstruction arithmetic unit <NUM> may be integrated with the personal computer PC and implemented as computer's peripheral devices and software by one computer.

Next, the utensil <NUM> for evaluating a length measurement error used when evaluating the X-ray CT device as one for three-dimensional shape measurement will be described. The X-ray CT device obtains volume data referred to as a reconstruction image from multiple projection images detected by the X-ray detector <NUM>, and therefore when evaluated as one for three-dimensional shape measurement, is required to be able to confirm length measurement accuracy over a wide range relative to the X-ray detection region of the X-ray detector <NUM>. Also, the X-ray CT device changes the positional relationship among the X-ray source, the rotation stage <NUM>, and the X-ray detector <NUM> in order to change the magnification ratio of a projection image, and is therefore required to be able to evaluate a geometric error due to displacement from a state where respective components are ideally assembled. Further, the X-ray CT device performs X-ray imaging with the rotation stage <NUM> rotated, and is therefore also required to be able to evaluate the motion error of the rotation stage <NUM>.

<FIG> is a perspective view of the utensil <NUM> for evaluating a length measurement error in the X-ray CT device for three-dimensional shape measurement according to the present invention.

The utensil <NUM> for evaluating a length measurement error in the X-ray CT device for three-dimensional measurement (hereinafter referred to as a utensil <NUM>) is such that support rods <NUM>, <NUM>, <NUM> whose tips are fixed with spheres <NUM> and whose lengths are different are attached to a base <NUM>, and thereby <NUM> spheres <NUM> are arranged in an XYZ space on the base <NUM>. On a flat surface <NUM> on the top of the base <NUM>, the support rods <NUM>, <NUM>, <NUM> supporting the spheres <NUM> and having different lengths are installed upright at predetermined intervals. The base <NUM> is formed of a low thermal expansion metallic material whose thermal deformation is extremely small. Also, as the spheres <NUM>, spherical bodies whose shape error is small (sphericity is high) are employed, and for the support rods <NUM>, <NUM>, <NUM>, a material such as ceramic is employed.

The arrangement space of the sphere <NUM> on the top of the base <NUM> is adapted to be covered with a cylindrical cover <NUM> at the time of storage and at the time of use so as to prevent the spatial arrangement of the respective spheres <NUM> after coordinate measurement by CMM from being disordered. The cover <NUM> is formed of a material having relatively high X-ray transmittance, such as an acrylic resin. In addition, the cover <NUM> is not required to be transparent to visible light, but is desirably transparent to visible light. When it is transparent, an operator can directly view the inside, and therefore structural understanding can be facilitated.

The support rods <NUM> has a dimension longer than the support rods <NUM> by <NUM>, and the support rods <NUM> has a dimension longer than the support rods <NUM> by <NUM>. Using the support rods <NUM>, <NUM>, <NUM> whose lengths are different from each other by <NUM> enables the multiple spheres <NUM> to be arranged at three Z positions (e.g., five per one Z position). That is, by differentiating the lengths of the support rods <NUM>, <NUM>, <NUM> used to support the spheres <NUM> in the three-step manner, the sphere <NUM> are arranged in three X-Y planes having different Z positions. In addition, in the present embodiment, by setting the difference in length between the shortest support rods <NUM> and the intermediate-length support rods <NUM> and the difference in length between the intermediate-length support rods <NUM> and the longest support rods <NUM> to have the same length, the intervals between the three Z positions are equalized.

<FIG> and <FIG> are schematic diagrams illustrating the arrangement of the spheres <NUM>. <FIG> is a three-dimensional image illustrating the arrangement of the respective spheres <NUM> in a cylindrical imaging space indicated by dashed-two dotted lines, and <FIG> is a schematic plan view. In <FIG>, projection coordinates (Xi, Yi) obtained by projecting the positions of the respective spheres <NUM> parallel to the Z axis toward the X-Y plane at the Z position of the spheres <NUM> supported by the shortest support rods <NUM> are illustrated. Here, triangles (Δ) in the view represent the positions of the five spheres <NUM> supported by the shortest support rods <NUM>, quadrangles (□) represent the positions of the five spheres <NUM> supported by the intermediate-length support rods <NUM>, and circles (∘) represent the positions of the five spheres <NUM> supported by the longest support rods <NUM>.

As illustrated in <FIG> and <FIG>, in this utensil <NUM>, on a circle (inner circle) having a radius of approximately <NUM> around the origin (<NUM>, <NUM>) of the projection coordinates, one sphere <NUM> at each of the three Z positions is arranged, and on a circle (outer circle) having a radius of approximately <NUM>, four spheres <NUM> at each of the three Z positions are arranged displaced from each other by approximately <NUM> degrees in a substantially cross shape to thereby arrange the <NUM> spheres <NUM> in total. Since the origin (<NUM>, <NUM>) of the projection coordinates also corresponds to the Z axis, in each of the three X-Y planes having different Z positions, five spheres are arranged, i.e., the <NUM> spheres in total are arranged in total. Since the differences in length between the respective support rods <NUM>, <NUM>, <NUM> are the same length such as <NUM>, the three X-Y planes are equally mutually separated in terms of distance in the Z direction. In addition, in one X-Y plane, the arrangement of spheres arranged at positions away from a sphere arranged on the inner circle in the vicinity of the Z axis and on the outer circle separated from the Z axis by the predetermined distance is such that by arranging multiple sets of two spheres oppositely arranged with respect to the Z axis, i.e., in the present embodiment, by arranging the two sets of two spheres oppositely arranged with respect to the Z axis, four spheres <NUM> are arranged. Further, by adjusting the positions of the two sets so that two line segments each connecting between two spheres on the same line passing through the Z axis have an orthogonal relationship, the arrangement of the four spheres <NUM> is made substantially cross-shaped, in which the four spheres <NUM> are displaced from each other by approximately <NUM> degrees.

In the three different X-Y planes, the positional relationship among the respective spheres <NUM> arranged on the outer circle is such that in the plan view as illustrated in <FIG>, the spheres <NUM> are arranged on the same circle around the Z axis at regular intervals. That is, positions on the circle around the origin (<NUM>, <NUM>) in <FIG> are positions separated from each other by substantially <NUM> degrees. In the present embodiment, with the arrangement of the four spheres <NUM> indicated by the triangles (Δ) in the X-Y plane at the lowest Z position as a reference, the four spheres <NUM> indicated by the quadrangles (□) in the X-Y plane whose X position is displaced upward are arranged at positions rotated anticlockwise by substantially <NUM> degrees around the Z axis, and the four spheres <NUM> indicated by the circles (∘) in the X-Y plane whose Z position is further displaced upward from the previous one are arranged at positions rotated anticlockwise by substantially <NUM> degrees around the Z axis. That is, on the outer circumferential surface of the cylinder having a radius of <NUM> and a height of <NUM>, the spheres <NUM> are spirally arranged at every <NUM> degrees in the order of the triangle (Δ), the quadrangle (□), and the circle (∘) on the basis of the combination of the <NUM>-degree rotation with the Z axis as a rotation axis and the <NUM>-mm translation parallel to the Z axis. The multiple outer circumference side spheres arranged in the respective three X-Y planes are cylindrically arranged as evaluation points in the cylindrically-shaped region (indicated by the dashed-two dotted lines) of the imaging space. In addition, the multiple outer circumference side spheres are equally arranged at intervals of substantially <NUM> degrees on the circle around the Z axis in a plan view by rotating and arranging the arrangement positions of four spheres arranged in each of the three X-Y planes by substantially <NUM> degrees around the Z axis with respect to the arrangement positions of spheres in an adjacent X-Y plane.

Four among the five spheres <NUM> supported by the shortest support rods <NUM>, four among the five spheres <NUM> supported by the intermediate-length support rods <NUM>, and four among the five spheres <NUM> supported by the longest support rods <NUM> are equally arranged on the circle having a radius of <NUM> around the origin (<NUM>, <NUM>) of the projection coordinates as described above. In the present embodiment, by arranging four spheres <NUM> in each of the X-Y planes on the same circle as described, the distances between the respective spheres <NUM> and the Z axis are equalized. In addition, as long as among the respective spheres <NUM> excluding the three spheres <NUM> in the vicinity of the Z axis illustrated in <FIG>, the average value of the distances between the origin (<NUM>, <NUM>) and the respective triangles (Δ), the average value of the distances between the origin (<NUM>, <NUM>) and the respective quadrangles (□), and the average value of the distances between the origin (<NUM>, <NUM>) and the respective circles (∘) are equalized, the spheres <NUM> are not necessarily required to be arranged on the same circle. That is, regarding the spheres <NUM> arranged in the respective X-Y planes other than the three in the vicinity of the Z axis, the X-Y plane-based average values of the distances between the respective spheres <NUM> and the Z axis are only required to be roughly equalized.

One among the five spheres <NUM> supported by the shortest support rods <NUM>, one among the five spheres <NUM> supported by the intermediate-length support rods <NUM>, and one among the five spheres <NUM> supported by the longest support rods <NUM> are inner circumference side spheres of the present invention and arranged at equal intervals on the circle having a radius of approximately <NUM> or less in the vicinity of the Z axis. That is, on a substantially straight line in the Z direction, one sphere <NUM> is arranged at each of the three types of Z positions. In addition, the utensil <NUM> is configured to support the spheres <NUM> respectively using the support rods <NUM>, <NUM>, <NUM>, and therefore the three spheres <NUM> whose Z positions are only different cannot be strictly arranged on the origin (<NUM>, <NUM>) of the projection coordinates. For this reason, in the present embodiment, by arranging at equal intervals on the circle having a radius of approximately <NUM> or less in the vicinity of the Z axis, the equal arrangement of the multiple spheres in the Z axis direction (the equal arrangement of the spheres in the longitudinal direction) is achieved. In addition, a guide for the vicinity of the Z axis is a distance range where a distance from the Z axis is approximately <NUM> % or less of the diameter of the circle defining the arrangement positions of four spheres <NUM> in each of the X-Y planes. In the present embodiment, the three spheres <NUM> respectively supported by the support rods <NUM>, <NUM>, <NUM> having different lengths are arranged on the inner circumferential circle at equal intervals; however, as long as three sphere positions having different heights along the Z axis can be obtained, they are not required to be arranged on the same circle. The "vicinity" of the vicinity of the Z axis in the present invention includes being separated from the center by a distance enough to be regarded as a central position, and also includes being on the Z axis as the center. Further, by arranging a sphere <NUM> arranged in the vicinity of the Z axis on a line connecting two having a diagonal relationship interposing the origin (<NUM>, <NUM>) among four spheres <NUM> arranged on the circle having a radius of <NUM> in each X-Y plane at a corresponding Z position, grasping a displacement amount from the Z axis and equal arrangement around the Z axis in a plan view are facilitated.

<FIG> are schematic diagrams illustrating variations of the arrangement of spheres <NUM>. <FIG> and <FIG> are three-dimensional images illustrating the arrangement of the respective spheres <NUM> in an imaging space, and <FIG> and <FIG> are schematic plan views. In the variations, the positions of spheres <NUM> in an X-Y plane having a low Z position are indicated by black circles, and the positions of spheres <NUM> in an X-Y plane having a high Z position are indicated by white circles.

In the arrangement of the spheres <NUM> illustrated in <FIG>, arranging one sphere on the Z axis results in one evaluation point in the Z direction. In addition, two spheres <NUM> are arranged along one circumference around the Z axis in each of the two different X-Y planes. In the plan view illustrated in <FIG>, respective spheres <NUM> are arranged on the same circle at regular intervals.

In the arrangement of the spheres <NUM> illustrated in <FIG>, the one sphere <NUM> on the Z axis enables the imaging space to be evaluated in a region on the inner side of a region where the outer circumference side spheres are arranged. In addition, by oppositely arranging two spheres along an outer circumferential circle so as to be able to at least project the spheres <NUM> to positions near the maximum lateral X-ray detection region of the X-ray detector <NUM>, multiple evaluation points can be obtained in the imaging space of a cylindrical shape. Also, by arranging two outer circumference side spheres <NUM> in each of the two X-Y planes having different Z positions, the spheres <NUM> can be projected to positions near the maximum longitudinal X-ray detection region of the X-ray detector <NUM> and to different height positions. For this reason, when performing imaging multiple times with a Z position changed, the inside of the cylindrical imaging visual space can be evaluated by a small number of imaging times without creating an unevaluable range between single imaging spaces. Further, by arranging two spheres <NUM> in each of the X-Y planes having different Z positions, the evaluation of the motion error of the rotation stage <NUM> and the evaluation of a geometric error can be performed.

In addition, in this variation, in the two different X-Y planes, two spheres <NUM> are oppositely arranged in each of the X-Y planes; however, as long as respective spheres <NUM> in each of the two X-Y planes are arranged along one outer circumferential circle, it is not required to strictly arrange them at regular intervals, or oppositely arrange them in each of the X-Y planes. The "outer circumference" of the outer circumference side spheres in the present invention refers to a circumference such as a circle having a diameter or an ellipse having the major axis, which enables the spheres <NUM> to be projected to positions near the maximum lateral X-ray detection region of the X-ray detector <NUM>. By arranging two or more spheres in each of two or more X-Y planes having different Z positions, the problem that spheres are arranged on conical surfaces as in the conventional forest gauge described with reference to <FIG>, and thereby unevaluable ranges are created in a cylindrical imaging space is solved.

The outer circumference side spheres in the present invention refer to spheres arranged in multiple X-Y planes along outer circumferences enabling the spheres <NUM> to be projected to positions near the maximum lateral X-ray detection region of the X-ray detector <NUM>, and on condition of lying along circumferences, all the spheres are not required to be in a relationship where distances from the Z axis are equal. Also, cylindrically arranging the outer circumference side spheres in the present invention refers to the arrangement of the spheres in a state where among different X-Y planes, translating multiple spheres in each X-Y plane toward another X-Y plane in parallel with the Z axis makes it possible to form a cylindrical shape whose height is the difference in Z position between the two X-Y planes.

In the arrangement of the spheres <NUM> illustrated in <FIG>, there are two evaluation points in the Z direction. That is, one sphere <NUM> is arranged in the vicinity of the Z axis in each of the two X-Y planes, and the spheres <NUM> in the vicinity of the Z axis in the different X-Y planes have a positional relationship of lying along an inner circumferential circle in the vicinity of the Z axis in the plan view illustrated in <FIG>. The "inner circumference" of the inner circumference side spheres in the preset invention refers to a circumference on the inner side with respect to the outer circumference, and by making the positional relationship of the spheres in the vicinity of the Z axis in the different X-Y planes have a certain design regularity, uniformity in fabricating the utensil can be ensured. As compared with the variation of <FIG>, the evaluation points in the Z direction is increased in number, and thereby the mutual positional relationship among cylindrical spaces each serving as an evaluation target at each time of X-ray CT imaging among multiple times of repeated X-ray CT imaging can be evaluated.

The arrangement of spheres <NUM> can be modified in other ways than those described with reference to <FIG>. That is, depending on the size of the X-ray detector <NUM> or the necessity of multiple times of X-ray CT imaging performed with a Z axis position changed, the number of X-Y planes in which multiple outer circumference side spheres are arranged, and the number of spheres arranged there can be changed.

A structure for fixing the support rods <NUM>, <NUM>, <NUM> supporting the spheres <NUM> to the base <NUM> will be described. <FIG> is a diagram illustrating constraint conditions in a three-dimensional space at the time of fixing the cylindrical support rod <NUM> to the base <NUM>. <FIG> is a diagram illustrating force transmission by wedge-shaped blocks.

In order to fix the cylindrical support rods <NUM>, <NUM>, <NUM> to the base <NUM>, five degrees of freedom indicated marked with circled signs <NUM> to <NUM> together with outlined arrows in <FIG> are taken into account. That is, in an X-Y plane, constraint is performed at points <NUM> and <NUM> in <FIG> by force from a direction opposite to them (force from a direction <NUM>-degree opposite to the middle between <NUM> and <NUM>), and constraint is performed at points <NUM> and <NUM> by force from a direction opposite to them (force from a direction <NUM>-degree opposite to the middle between <NUM> and <NUM>). Translation in the Z axis direction is constrained at a point <NUM> in <FIG> by force from a direction opposite to it. Further, rotation in the Z axis direction can be constrained by frictional force due to surface contact in addition to the constraint at the points <NUM> to <NUM> in <FIG>.

In order to constrain the degree of freedom of the support rods <NUM>, <NUM>, <NUM> in the translation direction in the X-Y plane and the degree of freedom in the translation direction (vertical direction) on the Z axis, it is necessary to simultaneously apply bidirectional forces whose directions are different by <NUM> degrees as indicated by dashed line arrows in <FIG> to the support rod <NUM>. As a mechanism enabling such force transmission, a wedge-shaped block in which a block shape for constraining the support rod <NUM> is combined with a wedge shape having an acute angle of <NUM> degrees can be employed. As illustrated in <FIG>, in the wedge-shaped block in which three wedge-shaped members contacting with each other via a tilt surface are combined, from a load indicated by an outlined arrow bidirectional forces whose directions are different by <NUM> degrees as indicated by dashed line arrows in <FIG> can be generated by action of tilt surfaces.

<FIG> is an exploded perspective view illustrating a support rod holding mechanism <NUM>. <FIG> is a schematic diagram illustrating a state where the support rod holding mechanism <NUM> is inserted into the base <NUM>. <FIG> is a plan view of the support rod holding mechanism <NUM>, and <FIG> is an A-A' cross-sectional view in <FIG>.

The support rod holding mechanism <NUM> includes a bottomed cylindrical member <NUM> provided with a space insertable with a support rod <NUM>, <NUM>, or <NUM>, fixing blocks <NUM> and a load transmitting block <NUM> for constraining the support rod <NUM>, <NUM>, or <NUM>, and a loading bolt <NUM> for applying a load on the fixing blocks <NUM> and the load transmitting block <NUM>. In addition, since the support rods <NUM>, <NUM>, <NUM> are rod members having mutually different length but the same diameter, and will be described as the support rod <NUM> in the following description.

The inner wall of an opening of the cylindrical member <NUM> is formed with a female screw screwed with the below-described male screw part <NUM> provided on the outer circumference of the loading bolt <NUM>. Also, in the side surface of the cylindrical member <NUM>, through-holes <NUM> for arranging the fixing blocks <NUM> and the load transmitting block <NUM> are formed at regular intervals of approximately <NUM> degrees in three directions from a cylinder axis. In the through-holes <NUM> provided in three positions of the side surface of the cylindrical member <NUM>, the two fixing blocks <NUM> and the one load transmitting block <NUM> are respectively arranged. The fixing blocks <NUM> are provided with convex parts <NUM> abutting on the support rod <NUM> at positions corresponding to the points <NUM> and <NUM> and the points <NUM> and <NUM> illustrated in <FIG>. In addition, the fixing blocks <NUM> in the present embodiment are also provided with convex parts <NUM> at corresponding positions of a surface on the side opposite to the side abutting on the support rod <NUM>.

The load transmitting block <NUM> is a wedge-shaped block described with reference to <FIG>, includes three wedge-shaped members 46a, 46b, 46c mutually joined via a tilt surface, and is formed into a prism by combining the three wedge-shaped members 46a, 46b, 46c in such a manner as to bring their tilt surfaces into contact. When force in a compression direction along an axis of the prism is applied to the load transmitting block <NUM>, the three wedge-shaped members 46a, 46b, 46c are mutually moved by sliding on the tilt surfaces.

The base <NUM> is provided with holes that are slightly larger than the outside diameter of the cylindrical member <NUM> and for receiving cylindrical members <NUM> and whose number is equal to the number of spheres <NUM> desired to be arranged in the XYZ space. In addition, the cylindrical members <NUM> are inserted into the respective holes of the base <NUM> with the load transmitting block <NUM> and the two fixing blocks <NUM> arranged in the through-holes <NUM>.

The loading bolt <NUM> is a bolt-like member that is provided in the central part with a hole through which the support rod <NUM> is made to penetrate and whose outer circumferential part is provided with the male screw part <NUM> screwed into the female screw formed on the inner wall of the opening of the cylindrical member <NUM>. The loading bolt <NUM> is different from general bolts in that the hole is formed in the central part, but adapted to be capable of being rotated by a wrench, which is a general tool, and attached to/detached from the cylindrical member <NUM> by forming parallel flat surfaces in parts where a male screw is not formed, or by other means.

When the loading bolt <NUM> is fastened to the cylindrical member <NUM>, the load transmitting block <NUM> is applied with force along the long axis direction of the block. In the present embodiment, the length of the load transmitting block <NUM> in the long axis direction, in which the three wedge-shaped members 46a, 46b, 46c are combined, is made sufficiently larger than the length of the fixing blocks <NUM> in the long axis direction. In doing so, when the loading bolt <NUM> is fastened, the loading bolt <NUM> does not abut on the upper end parts of the fixing blocks <NUM>, and a load at the time is transmitted only to the load transmitting block <NUM>. In addition, regarding the fixing blocks <NUM> in the present embodiment, the upper end parts of the fixing blocks <NUM> are adapted not to abut on the loading bolt <NUM> at the time of fastening the loading bolt <NUM> by making the length in the long axis direction smaller than the length of the load transmitting block <NUM>; however, the length in the long axis direction may be made the same as the load transmitting block <NUM>, and in order that the upper end parts of the fixing blocks <NUM> lie outside the diameter of the loading bolt <NUM>, the shape of the upper convex parts on the side abutting on the support rod <NUM> may be deformed.

The force applied to the load transmitting block <NUM> by fastening the loading bolt <NUM> is dispersed into horizontal force and vertical force with respect to the loading direction at the mutual joint part between the tilt surfaces of the wedge-shaped member 46a and wedge-shaped member 46b as described with reference to <FIG>. Further, the vertical force is dispersed into horizontal force and vertical force with respect to the loading direction at the mutual joint part between the tilt surfaces of the wedge-shaped member 46b and wedge-shaped member 46c. Such bidirectional forces whose directions are different by <NUM> degrees allow the support rod <NUM> to be applied with force toward the central axis of the support rod <NUM> and downward force. The force toward the central axis of the support rod <NUM> is transmitted to the fixing blocks <NUM> installed in +<NUM>-degree directions (see <FIG>) from the position where the load transmitting block <NUM> is arranged. In addition, the forces from the sides opposite to the abutting points between the convex parts <NUM> of the fixing blocks <NUM> and the support rod <NUM> constrain the support rod <NUM> on an X-Y plane. Also, the force downward of the support rod <NUM> is transmitted to the cylindrical member <NUM>. Such motion in the Z axis direction that the lower end of the support rod <NUM> floats from the bottom of the cylindrical member <NUM> is constrained by the force in the same direction as the loading direction applied to the load transmitting block <NUM> at the time of fastening the loading bolt <NUM>, which is force from the direction opposite to the motion. At this time, the wedge-shaped member 46a in direct contact with the loading bolt <NUM> slides and slightly moves to the support rod <NUM> side because of the tilts of the tilt surfaces with which the wedge-shaped member 46a and the wedge-shaped member 46b are in contact, and is thereby pressed against the outer circumferential surface of the support rod <NUM>. The motion of the support rod <NUM> in the rotational direction is constrained by the frictional force between the outer circumferential surface of the support rod <NUM> and the surface of the wedge-shaped member 46a.

Also, in a state where the loading bolt <NUM> is fastened to the cylindrical member <NUM>, among the wedge-shaped members 46a, 46b, 46c of the load transmitting block <NUM>, the wedge-shaped member 46c arranged in contact with the bottom of the cylindrical member <NUM> slides and slightly move outward of the cylindrical member <NUM> because of the tilts of the tilt surfaces with which the wedge-shaped member 46b and the wedge-shaped member 46c are in contact. This allows the wedge-shaped member 46c to be pressed against the inner wall surface of the base <NUM> on the outer side than the outer circumference of the cylindrical member <NUM>. At this time, the wedge-shaped member 46b tilts in association with the slight movements of the wedge-shaped member 46a and the wedge-shaped member 46c in the mutually opposite directions, and the upper edge is pressed against the inner wall surface of the base <NUM> on the outer side than the outer circumference of the cylindrical member <NUM>. Also, as a material of the fixing blocks <NUM> and the load transmitting block <NUM>, a soft metal as compared with iron is employed, such as aluminum, and therefore upon receipt of the load caused by fastening the loading bolt <NUM> via the load transmitting block <NUM>, the fixing blocks <NUM> are pressed by the support rod <NUM> and thereby slightly deformed as well, and the convex parts <NUM> of the fixing blocks <NUM> on the side opposite to the convex parts <NUM> facing the support rod side are pressed against the inner wall surface of the base <NUM>. By action of such force pressed against the inner wall of the base <NUM>, the support rod holding mechanism <NUM> including the cylindrical member <NUM> is fixed to the base <NUM>, and the support rod <NUM> is fixed to the base <NUM>.

In addition, in the present embodiment, as the shape of the load transmitting block <NUM>, the wedge-shaped one is employed; however, as long as a mechanism capable of dispersing a load from one direction in two directions, and applying lateral and downward forces to the support rod <NUM> is included, one of another shape may be employed.

Next, a structure for fixing a sphere <NUM> to the tip of a support rod <NUM>, <NUM>, or <NUM> will be described. <FIG> is a schematic cross-sectional view illustrating the bonding structure of the sphere <NUM> at the tip of the support rod. The following description relates not only to the support rods <NUM>, and the same applies to the support rods <NUM> and <NUM>.

The one end (tip) of the support rod <NUM> in the present embodiment is applied with conical concave processing in order to firmly fix the sphere <NUM>. The end part on the side opposite to the side where the sphere <NUM> is firmly fixed is formed in a flat shape contacting with the bottom surface of the cylindrical member <NUM>. As illustrated in <FIG>, when placing the sphere <NUM> on a conical concave part <NUM>, the sphere <NUM> contacts with the conical tilt surface of the conical concave part <NUM> on a circular line indicated by sign t. The depth of the conical concave part <NUM> and the tilt of the conical surface are determined by the diameter of the sphere <NUM> so that the upper end <NUM> of the support rod <NUM>, which is the edge of the conical concave part <NUM>, lies closer to the apex side of the cone in the conical convex part <NUM> than the equator e of the sphere <NUM>. The sphere <NUM> is fixed on the conical tilt surface of the conical concave part <NUM> by bond.

The sphere <NUM> is not required to be applied with hole drilling for inserting the thin shaft <NUM> as previously described with reference to <FIG>, and on the equator e of the sphere <NUM>, a structure that disturbs an X-ray transmission image is not present. For this reason, between the central position of an X-ray CT image of the sphere itself and the shape of the sphere, which are supposed to be detected, and the center position of an X-ray CT image of the sphere itself and the shape of the sphere, which are obtained by actual X-ray irradiation, no non-negligible deviation occurs.

Since the contact between the support rod <NUM> and the sphere <NUM> is limited to on the circular line of the conical tilt surface, difference in processing accuracy of each sphere <NUM> can be made less influential, and the attachment of the sphere <NUM> to the support rod <NUM> can be more stably performed than before. A certain clearance between the conical surface of the support rod <NUM> and an outer part of the sphere <NUM>, which is not in direct contact, can also be filled with the bond, and therefore force for holding the sphere <NUM> can be stabilized.

Another structure for fixing a sphere <NUM> to the tip of each support rod <NUM>, <NUM>, <NUM> will be described. <FIG> is a schematic cross-sectional view illustrating the bonding structure of the sphere <NUM> at the tip of the support rod. The following description relates not only to the support rods <NUM>, and the same applies to the support rods <NUM> and <NUM>.

At the tip of the support rod <NUM> illustrated in <FIG>, a conical concave part <NUM> for placing the sphere <NUM> is formed as in the structure illustrated in <FIG>. In addition, the tip of the support rod <NUM> illustrated in <FIG> is provided with a through-hole <NUM> passing from the bottom of the conical concave part <NUM> to the outer surface of the support rod <NUM>. The through-hole <NUM> is one for allowing bond at the time of fixing the sphere <NUM> to escape to the outside of the conical concave part <NUM>. By providing such a through-hole <NUM>, the bond between a conical tilt surface and the sphere <NUM> can be thinned. Also, by a shrinking action when the bond cures, force for pulling the sphere <NUM> toward the bottom of the conical concave part <NUM> is generated to improve force for holding the sphere <NUM>. In addition, an embodiment illustrated in <FIG> is adapted to allow the bond to more easily escape in such a manner that the through-hole <NUM> communicates to the outer surface of the support rod <NUM>; however, the through-hole <NUM> is not necessarily required to be made penetrate to the outer surface of the support rod <NUM>. Only by providing the bottom of the conical concave part <NUM> with a thin columnar concave part, the same degree of effect can be obtained.

Before performing X-ray CT imaging on the utensil <NUM>, the coordinates of the <NUM> spheres <NUM> are measured by CMM, and information on the coordinates of the respective spheres <NUM> and the values of inter-sphere distances obtained from the results of the coordinate measurement are stored in the personal computer PC.

Also, in the utensil <NUM>, the respective support rods <NUM>, <NUM>, <NUM> can be constrained in the three-dimensional space by the support rod holding mechanisms <NUM>, and the spheres <NUM> are stably fixed to the respective support rods <NUM>, <NUM>, <NUM> formed with the conical concave parts <NUM>. For this reason, even when the utensil <NUM> is tilted or turned upside down during transportation until the utensil <NUM> is placed on the rotation stage <NUM> or during installation, a change in sphere position can be reduced than before. Also, even when a significant amount of external force is applied to each support rod <NUM>, <NUM>, <NUM> because of the contact of the probe with a sphere <NUM> at the time of the coordinate measurement by the CMM, a sphere position can be prevented from being changed as conventional.

After the end of the coordinate measurement by the CMM, the XYZ space in which the respective spheres <NUM> are arranged is covered with the cover <NUM>. In the utensil <NUM>, the number of spheres <NUM> is suppressed to <NUM>, and therefore the coordinate measurement by the CMM can be quickly performed. Further, the number of parts can be reduced than before, and therefore the fabrication cost of the utensil <NUM> can also be suppressed.

When performing the X-ray CT imaging on the utensil <NUM>, the utensil <NUM> is positioned with the cover <NUM> attached on the rotation stage <NUM>, and the X-ray CT imaging is performed.

In the utensil <NUM> of the present embodiment, as illustrated in <FIG>, the projection coordinates (Xi, Yi) of the respective spheres <NUM> are almost uniform, and the positions of the three X-Y planes having different Z positions are also almost uniform in the Z direction, so that the <NUM> spheres <NUM> arranged in the XYZ space are not structured such that they are arranged on conical surfaces as conventional, and respectively have appropriate distance intervals. Such sphere arrangement enables spatial distortion specific to an X-ray CT device to be sufficiently captured.

In the utensil <NUM> of the present embodiment, by forming the upper surface of the base <NUM> as the flat surface <NUM>, and differentiating the lengths of the support rods <NUM>, <NUM>, <NUM> supporting the spheres <NUM>, an evaluation range in the Z axis direction in an imaging visual space by one time of X-ray CT imaging can be more widened than in a conventional utensil having a step-wise base.

Also, in the utensil <NUM> of the present embodiment, the difference in length (e.g., <NUM>) between the support rod <NUM> having the shortest length and the support rod <NUM> having the longest length is made longer than the radius (<NUM>) of the circle around the origin (<NUM>, <NUM>) of the projection coordinates illustrated in <FIG>. For this reason, the arrangement range of the multiple spheres is such that among the multiple X-Y planes, the distance in the Z direction between the X-Y plane having the lowest Z position and the X-Y plane having the highest Z position is larger than the distance from the Z axis in the XY directions. As described, in the present embodiment, the difference between the arrangement range of the spheres <NUM> in the X-Y planes and the arrangement range in the Z axis direction is made smaller than before, and therefore, for example, when the ratio between the vertical and horizontal sizes of the X-ray detector <NUM> is one, the cylindrical imaging visual space can be isotropically evaluated by two times of X-ray CT imaging, and when the ratio between the vertical and horizontal sizes of the X-ray detector <NUM> is vertical:horizontal = <NUM>:<NUM>, the cylindrical imaging visual space can be isotropically evaluated by one time of X-ray CT imaging. As described, the number of times of performing repeated measurement with a Z axis position changed can be reduced than before, and therefore imaging time for evaluating the measurement accuracy of an X-ray CT device can be reduced.

Claim 1:
A utensil (<NUM>) for evaluating a length measurement error in an X-ray CT device for three-dimensional shape measurement, the utensil (<NUM>) being configured for use on a rotation stage of the X-ray CT device for three-dimensional shape measurement such that a Z axis as a rotation axis of the rotation stage coincides with a center of a cylindrical imaging space, the utensil (<NUM>) comprising:
a base (<NUM>);
multiple spheres (<NUM>) arranged in an XYZ space on the base (<NUM>) corresponding to the imaging space; and
multiple support rods (<NUM>, <NUM>, <NUM>) supporting each of the multiple spheres (<NUM>) and installed upright on the base (<NUM>), wherein:
the multiple spheres (<NUM>) include multiple outer circumference side spheres (<NUM>) arranged on one outer circumferential circle around the Z axis in each of multiple X-Y planes having different Z positions, wherein:
one or more spheres are arranged in a vicinity of the Z axis,
a radius of an outer circumferential circle on which the multiple outer circumference side spheres (<NUM>) are arranged in each of the multiple X-Y planes is same and coordinates (X, Y) of multiple outer circumference side spheres arranged in all of the multiple X-Y planes are different; and
the multiple outer circumference side spheres (<NUM>) include two sets of two spheres (<NUM>) symmetrically arranged with respect to the Z axis.