Device for evaluating measurement error of CT device

Abstract

To provide a device for evaluating a measurement error of a CT device which can suppress change in a spatial position of a member for evaluation, between a state where a cover is removed and a state where the cover is mounted.SOLUTION: A device 10 for evaluating a measurement error of a CT device 100 for three-dimensional shape measurement is used while being arranged on a subject mounting part 106, and includes a base 20, a member 23 for evaluation which is provided on the base 20, a cover 24 which is arranged so as to cover the member 23 for evaluation, and a connection part 30 which allows the cover 24 and the base 20 to be attachable / detachable from each other, and connects the base 20 and the cover 24, wherein the connection part 30 is engaged with the base 20 so that a relative position changes, the cover 24 is not supported by the base 20, in a state in which the base 20 is arranged in the subject mounting part 106, and is supported by the subject mounting part 106 together with the connection part 30.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an instrument for evaluating measurement errors in a CT scanner. [Background technology]

[0002] 2. Description of the Related Art Conventionally, there is known a measurement error evaluation tool for a CT scanner that includes a base, an evaluation member, and a cover that is arranged to cover the evaluation member (for example, Patent Document 1).

[0003] The above-mentioned Patent Document 1 discloses an X-ray CT device as an observation device for the internal structure of an object to be inspected (subject), and a measurement error evaluation device (measurement error evaluation instrument). The X-ray CT device performs internal observation and three-dimensional shape measurement by placing the object to be inspected (subject) on a rotating stage (subject placement unit) arranged between an X-ray irradiation unit (X-ray source) and an X-ray detector. The measurement error evaluation device is used to evaluate the accuracy of three-dimensional data obtained by the X-ray CT device. The measurement error evaluation device is provided with a plurality of support rods extending vertically upward on a base, and a sphere (evaluation member) is attached to the tip of each support rod. For example, when evaluating a length measurement error by X-ray CT using the measurement error evaluation device, the coordinates of the sphere are measured in advance using a CMM (Coordinate Measuring Machine: contact type three-dimensional coordinate measuring device). Then, the measurement error evaluation device is placed on the rotating stage, X-ray CT imaging is performed, and three-dimensional data is obtained. The error in length measurement using X-ray CT is evaluated from the difference between the inter-sphere distance value obtained from the coordinate measurement results and the inter-sphere distance value in the 3D data obtained by X-ray CT. The evaluation of the error in length measurement using X-ray CT is performed, for example, in accordance with the German national guideline VDI / VDE2630-1.3.

[0004] Furthermore, the above-mentioned Patent Document 1 discloses that the measurement error evaluation instrument is covered with a cylindrical cover during storage and use so that the spatial position of the sphere is not shifted after coordinate measurement of the measurement error evaluation instrument by the CMM. The above-mentioned Patent Document 1 does not specify how the cover is fixed, but shows that the cover is placed on a base. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6901733 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the measurement error evaluation instrument (measurement error evaluation instrument) of the above Patent Document 1, it is considered that the base may be distorted due to the load of the cover placed on the base. When the base is distorted due to the load of the cover, the spatial position of the sphere (evaluation member) of the measurement error evaluation instrument with the cover removed during coordinate measurement of the sphere by CMM or the like and the spatial position of the sphere (evaluation member) of the measurement error evaluation instrument with the cover attached during X-ray CT imaging by the CT device may change. Therefore, it may be difficult to accurately evaluate the length measurement error by X-ray CT based on the difference between the value of the inter-sphere distance by the coordinate measurement of the sphere by CMM or the like and the value of the inter-sphere distance in the three-dimensional data by X-ray CT imaging. Therefore, there is a demand for a measurement error evaluation instrument for a CT device that can suppress the change in the spatial position (three-dimensional position) of the evaluation member between the state where the cover is removed and the state where the cover is attached.

[0007] The present invention has been made to solve the above-mentioned problems, and one object of the present invention is to provide a measurement error evaluation tool for a CT scanner that is capable of suppressing changes in the spatial position of an evaluation component between a state in which the cover is removed and a state in which the cover is attached. [Means for solving the problem]

[0008] A measurement error evaluation tool for a CT device in a first aspect of the present invention is a measurement error evaluation tool for a CT device for three-dimensional shape measurement, which is placed on a subject placement section arranged between an X-ray source and an X-ray detector and used to place a subject on the subject placement section, and comprises a base, an evaluation member arranged on the base, a cover arranged to cover the evaluation member, and a connecting section connecting the base and the cover, wherein the cover and the base are detachable from each other and the connecting section is engaged with the base so that its relative position changes, and when the base is placed on the subject placement section, the cover is not supported by the base, but is supported by the subject placement section together with the connecting section.

[0009] A measurement error evaluation tool for a CT device in a second aspect of the present invention is a measurement error evaluation tool for a CT device for three-dimensional shape measurement, which is placed on a subject placement section arranged between an X-ray source and an X-ray detector and used, and comprises a base, a base support leg section arranged on the back surface of the base and supporting the base, an evaluation member arranged on the base, a cover arranged to cover the evaluation member, and a connecting section which connects the base and the cover, the cover and the base being detachable from each other, and which includes a base contact section which contacts the base at a corresponding position on the surface of the base or in the vicinity of the corresponding position corresponding to the base support leg section, and when the base is placed on the subject placement section, the cover is supported on the base via the base contact section of the connecting section. Effect of the Invention

[0010] In the measurement error evaluation tool for the CT device in the first aspect, as described above, the tool includes a cover arranged to cover the evaluation member, and a connecting part that connects the base and the cover, and the cover and the base are detachable from each other, and the connecting part is engaged so that the relative position with respect to the base changes, and when the base is placed on the subject placement part, the cover is not supported by the base and is supported by the subject placement part together with the connecting part. In this way, when the base is placed on the subject placement part, the relative position of the connecting part with respect to the base changes, so that the cover can be supported by the subject placement part without being supported by the base. Therefore, when the measurement error evaluation tool with the cover arranged thereon is X-ray CT-photographed by the CT device, when the base is placed on the subject placement part, the load of the cover is applied to the subject placement part without being applied to the base. In addition, when the measurement error evaluation tool is used to measure the coordinates of the evaluation member by the CMM, the cover is detached from the measurement error evaluation tool, so that the load of the cover is naturally not applied to the base. Therefore, it is possible to suppress the change in the state (distortion) of the base caused by the load of the cover between a state in which the cover is removed and a state in which the cover is attached, and as a result, it is possible to suppress the change in the spatial position (three-dimensional position) of the evaluation member between a state in which the cover is removed and a state in which the cover is attached.

[0011] In the measurement error evaluation tool for a CT apparatus in the second aspect, as described above, the connecting part includes a base contact part that contacts the base at a corresponding position on the surface of the base or in the vicinity of the corresponding position corresponding to the base support leg, and when the base is placed on the subject placement part, the cover is supported on the base via the base contact part of the connecting part. This allows the load of the cover to be received by the base support leg from almost directly above via the base contact part of the connecting part, so that the base can be prevented from being distorted due to the load of the cover, unlike when the position where the base contact part of the connecting part contacts the base is significantly separated from the position of the base support leg in a plan view. As a result, it is possible to prevent the state (distortion) of the base caused by the load of the cover from changing between a state where the cover is removed and a state where the cover is attached. Therefore, it is possible to prevent the spatial position (three-dimensional position) of the evaluation member from changing between a state where the cover is removed and a state where the cover is attached. [Brief description of the drawings]

[0012] [Figure 1] 1 is a block diagram showing an example of an X-ray CT apparatus according to a first embodiment. [Diagram 2] FIG. 1 is a block diagram showing an example of a three-dimensional coordinate measuring device. [Diagram 3] FIG. 1 is a perspective view showing an example of a measurement error evaluation instrument according to a first embodiment. [Figure 4] FIG. 2 is a perspective view illustrating a cover and a connecting portion in the measurement error evaluation instrument according to the first embodiment. [Diagram 5] FIG. 1 is a plan view of a measurement error evaluation device according to a first embodiment. [Figure 6] 13 is a schematic cross-sectional view for explaining the positional relationship between a base and a connecting portion. FIG. [Figure 7] FIG. 13 is a schematic diagram for explaining distortion of a base of a measurement error evaluation instrument according to a comparative example. [Figure 8] FIG. 11 is a perspective view showing an example of a measurement error evaluation device according to a second embodiment. [Figure 9]FIG. 11 is a plan view of a measurement error evaluation device according to a second embodiment. [Figure 10] FIG. 11 is a perspective view of the measurement error evaluation instrument according to the second embodiment, seen from the rear side of the base. [Figure 11] 13 is a schematic cross-sectional view for explaining the positional relationship between a base and a connecting portion. FIG. [Figure 12] FIG. 11 is a perspective view showing an example of a measurement error evaluation instrument according to a third embodiment. [Figure 13] FIG. 13 is a schematic front view showing an example of a measurement error evaluation instrument according to a fourth embodiment. [Figure 14] 13 is a schematic plan view for explaining the positional relationship between the base, the connecting portion, and the cover. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments embodying the present invention will be described with reference to the drawings.

[0014] [First embodiment] (X-ray CT device) The overall configuration of an X-ray CT apparatus 100 according to the first embodiment will be described with reference to FIG.

[0015] The X-ray CT apparatus 100 includes an X-ray source 101, an X-ray detector 102, a control unit 103, an image processing unit 104, and a rotation mechanism 105 including a subject placement unit 106. The X-ray CT apparatus 100 is, for example, a CT apparatus for measuring the three-dimensional shape of a subject.

[0016] The X-ray source 101 is configured to irradiate an object with X-rays. Specifically, the X-ray source 101 is configured to generate X-rays by colliding electrons, which are generated by applying a high voltage to an electrode, with a target. The X-ray source 101 is, for example, an X-ray generating device including an X-ray tube and a power supply.

[0017] The X-ray detector 102 is configured to detect X-rays irradiated from the X-ray source 101. The X-ray detector 102 is also configured to convert the detected X-rays into an electric signal (image signal). The X-ray detector 102 includes a light receiving unit that receives X-rays and a conversion unit that converts the received X-rays into an image signal. The X-ray detector 102 is, for example, an FPD (Flat Panel Detector). The X-ray detector 102 is configured with a plurality of conversion elements (not shown) and pixel electrodes (not shown) arranged on the plurality of conversion elements. The image signal of the X-ray detector 102 is sent to an image processing unit 104.

[0018] The control unit 103 is configured to control the X-ray source 101 and the rotation mechanism 105. The control unit 103 includes a processor including a central processing unit (CPU), a read only memory (ROM), and a random access memory (RAM).

[0019] The image processing unit 104 is configured to control the X-ray detector 102. The image processing unit 104 is also configured to acquire X-ray image data based on X-rays detected by the X-ray detector 102. The image processing unit 104 is also configured to generate CT data (three-dimensional data) based on a plurality of X-ray image data acquired by capturing an image of a subject while rotating the subject around an axis 110 using a rotation mechanism 105. The image processing unit 104 includes a processor such as a CPU, a field-programmable gate array (FPGA), or an application specific integrated circuit (ASIC). The image processing unit 104 is configured in software as a functional block realized by the processor executing various programs. The image processing unit 104 may be configured in hardware by providing a dedicated processor (processing circuit) in the X-ray CT device 100.

[0020] The rotation mechanism 105 is configured to rotate the subject around an axis 110. The rotation mechanism 105 includes a subject placement unit 106 on which the subject is placed, a rotation unit 107 that rotates the subject placement unit 106, and a drive unit (not shown) that imparts a drive force to the rotation unit 107. The rotation unit 107 includes, for example, a pulley for transmitting the drive force from the drive unit. The drive unit includes, for example, a motor.

[0021] The measurement error evaluation tool 10 is placed on the subject placement unit 106. The measurement error evaluation tool 10 is used to evaluate the accuracy of the three-dimensional data acquired by the X-ray CT scanner 100. The measurement error evaluation tool 10 will be described in detail later. For example, when evaluating the length measurement error by X-ray CT using the measurement error evaluation tool 10, the coordinate measurement of the evaluation member 23 provided on the measurement error evaluation tool 10 is performed in advance by the three-dimensional coordinate measuring device 200 (see FIG. 2). Then, the measurement error evaluation tool 10 is placed on the subject placement unit 106 of the X-ray CT scanner 100, and X-ray CT imaging is performed to obtain three-dimensional data. Then, the length measurement error by X-ray CT is evaluated from the difference between the value of the distance between the evaluation members 23 obtained from the coordinate measurement result and the value of the distance between the evaluation members 23 in the three-dimensional data by X-ray CT imaging. The three-dimensional coordinate measuring device 200 and the measurement error evaluation tool 10 will be described in detail later.

[0022] When performing X-ray CT imaging of the measurement error evaluation instrument 10, the image processing unit 104 rotates the measurement error evaluation instrument 10 around the axis 110 by the rotation mechanism 105 to image the measurement error evaluation instrument 10. The measurement error evaluation instrument 10 is imaged by the X-ray CT device 100 in a state where a cover 24 for covering the evaluation member 23 is attached to the measurement error evaluation instrument 10 so that the spatial position of the evaluation member 23 is not shifted after the coordinate measurement by the three-dimensional coordinate measuring device 200. Here, the evaluation member 23 has a spherical shape, for example. The image processing unit 104 generates CT data (three-dimensional data) based on the acquired multiple X-ray image data. The accuracy of the three-dimensional data acquired by the X-ray CT device 100 is evaluated by comparing the diameter, sphericity, and distance between the evaluation members 23 in the generated three-dimensional data with the diameter, sphericity, and distance between the evaluation members 23 acquired by the three-dimensional coordinate measuring device 200. As an example of how the accuracy of 3D data can be evaluated, the indexes used are the inter-sphere distance accuracy, which is related to the distance between spheres, defined in the German domestic guideline VDI / VDE2630-1.3, and the probing error, which is related to the diameter and sphericity of the spheres.

[0023] (3D coordinate measuring device) The three-dimensional coordinate measuring device 200 will be described with reference to FIG. 2. The three-dimensional coordinate measuring device 200 includes a contact type measuring device that performs measurement by bringing a probe into contact with a measurement object, and a non-contact type measuring device that performs measurement by irradiating a measurement object with laser light or the like. In the first embodiment, the three-dimensional coordinate measuring device 200 is a contact type measuring device (Coordinate Measuring Machine). That is, the three-dimensional coordinate measuring device 200 brings a probe 202 into contact with a plurality of evaluation members 23 to acquire position coordinates of each of the plurality of evaluation members 23. The probe 202 is a contactor that contacts the evaluation members 23. The three-dimensional coordinate measuring device 200 includes a mounting table 201 on which the measurement object is mounted, the probe 202, a probe driving unit 203 that drives the probe 202, and a measurement control unit 204 that controls the probe driving unit 203 and acquires the position coordinates of the measurement object.

[0024] The three-dimensional coordinate measuring device 200 is used to measure the coordinates of the evaluation member 23 provided on the measurement error evaluation instrument 10. The coordinate measurement of the evaluation member 23 by the three-dimensional coordinate measuring device 200 is performed in a state where the cover 24 covering the evaluation member 23 is removed from the measurement error evaluation instrument 10. As an example, the three-dimensional coordinate measuring device 200 acquires position information of the evaluation member 23 including the position coordinates of the center point of the evaluation member 23. The three-dimensional coordinate measuring device 200 acquires a value of the distance between the evaluation members 23 based on the acquired position coordinates.

[0025] (Instrument for evaluating measurement error) The measurement error evaluation instrument 10 will be described with reference to Fig. 3 to Fig. 6. As shown in Fig. 3, the measurement error evaluation instrument 10 includes a base 20, a base support leg 21, a support 22, an evaluation member 23, a cover 24, and a connecting portion 30.

[0026] The base 20 is formed of a disk-shaped plate-like member, for example. The base 20 is formed of a material with a small thermal expansion coefficient. The base 20 is made of ceramics, for example. The material of the base 20 is not particularly limited, and may be a metal material such as aluminum or iron. A fitting hole 25 for fitting and holding the support 22 is formed on the surface of the base 20. A plurality of fitting holes 25 for fitting the support 22 are formed. The base 20 is placed on the subject placement unit 106 via base support legs 21 provided on the back surface of the base 20.

[0027] The base 20 is detachably connected to the connecting portion 30. The base 20 has through holes 26 formed therein, penetrating in the thickness direction. In the first embodiment, four through holes 26 are formed. The through holes 26 are arranged at intervals of approximately 90 degrees with respect to the center of the base 20. A rod-shaped member 32 (see FIG. 4) provided on the connecting portion 30 and fitted with a retaining mechanism is inserted into each of the through holes 26. The specific connection between the base 20 and the connecting portion 30 will be described later.

[0028] The base support legs 21 are configured to come into contact with the subject placement part 106 and support the base 20 when the measurement error evaluation instrument 10 is placed on the subject placement part 106 (see FIG. 6(b)). The base support legs 21 are provided on the back surface (lower surface) of the base 20. As an example, three base support legs 21 are provided. The base support legs 21 are formed of a semi-spherical member. The base support legs 21 are arranged at three points that are not on a straight line. As an example, the base support legs 21 are arranged at intervals of approximately 120 degrees (see FIG. 5) with respect to the center of the back surface of the base 20. Note that the base support legs 21 may be formed by embedding a spherical member on the back surface of the base 20 with a part of it exposed. Also, the arrangement interval of the base support legs 21 is not particularly limited.

[0029] The support 22 is configured to support the evaluation member 23. The support 22 supports the evaluation member 23 at one end, and is fitted into a fitting hole 25 formed in the surface of the base 20 at the other end. A plurality of support columns 22 are provided according to the number and positions of the fitting holes 25 formed in the surface of the base 20. In order to provide a plurality of levels of height positions of the evaluation member 23 relative to the base 20, the support columns 22 have a plurality of lengths. In FIG. 3, the support columns 22 are illustrated with two lengths for simplification. Note that the support columns 22 may have three or more lengths in order to provide three or more levels of height positions of the evaluation member 23 relative to the base 20. Examples of materials for the support columns 22 include CFRP (Carbon Fiber Reinforced Plastics), but the material for the support columns 22 is not particularly limited.

[0030] The evaluation member 23 has a spherical shape, for example. The evaluation member 23 is supported at one end of the support 22. A plurality of evaluation members 23 are provided according to the number and positions of the support 22 provided on the base 20. The evaluation members 23 are also disposed at a height position relative to the base 20 according to the length of the support 22. For example, a metal material such as aluminum or iron, a ceramic material such as silicon nitride, or a resin material is used as the evaluation member 23.

[0031] The cover 24 is disposed to cover the evaluation member 23 so as to prevent displacement of the spatial position of the evaluation member 23 after coordinate measurement by the three-dimensional coordinate measuring device 200. The cover 24 is removed before coordinate measurement by the three-dimensional coordinate measuring device 200 (see FIG. 2) and is attached after coordinate measurement by the three-dimensional coordinate measuring device 200. With the cover 24 attached to the measurement error evaluation instrument 10, X-ray CT imaging is performed on the measurement error evaluation instrument 10 by the X-ray CT device 100 (see FIG. 1).

[0032] The cover 24 covers the outer circumferential side surface of the base 20 and is connected to the connecting portion 30 so that the evaluation member 23 is located inside the cover 24. The cover 24 has a cylindrical shape, for example. The cover 24 includes a cylindrical body portion 24a, an opening portion 24b provided at one end of the body portion 24a, and a top surface 24c provided at the other end of the body portion 24a. The cover 24 is formed of an acrylic resin, for example. The cover 24 may be transparent or opaque. The shape and material of the cover 24 are not particularly limited.

[0033] The cover 24 is detachably connected to the connecting part 30. A cover hole is formed in the cover 24 near the opening 24b. In the first embodiment, three cover holes are formed. Each of the cover holes is disposed at an interval of approximately 120 degrees with respect to the central axis of the body 24a. The cover 24 is screwed to the cover opening engagement part 33 of the connecting part 30 via each of the cover holes. In addition, an end face of the opening 24b of the cover 24 is supported by the cover opening support part 34 of the connecting part 30. A specific connection between the cover 24 and the connecting part 30 will be described later.

[0034] The connecting portion 30 is configured to connect the base 20 and the cover 24. The connecting portion 30 connects the cover 24 and the base 20 in a detachable manner. The connecting portion 30 is engaged with the base 20 so that a relative position of the connecting portion 30 with respect to the base 20 changes. As shown in FIG. 4, the connecting portion 30 includes a first back surface support portion 31, a rod-shaped member 32, a cover opening engagement portion 33, and a cover opening support portion 34. The first back surface support portion 31 is an example of a "back surface support portion" in the claims.

[0035] The first back surface support part 31 is formed of an annular plate-like member. As shown in Fig. 6(a), the first back surface support part 31 supports the back surface of the base 20 when the base 20 is lifted up from the subject placement part 106. Also, as shown in Fig. 6(b), when the base 20 is placed on the subject placement part 106 via the base support legs 21, the first back surface support part 31 is separated from the back surface of the base 20 and comes into contact with the subject placement part 106.

[0036] As shown in FIG. 4, the rod-shaped member 32 is provided so as to extend upward from the first back surface support portion 31. Four rod-shaped members 32 are provided. Each of the rod-shaped members 32 is arranged at intervals of approximately 90 degrees (see FIG. 5) with respect to the center of the annular first back surface support portion 31. Each of the rod-shaped members 32 is inserted into the through hole 26 (see FIG. 3) of the base 20. The end of the rod-shaped member 32 opposite to the first back surface support portion 31 is provided with a retaining member to prevent it from coming off. The rod-shaped member 32 is inserted into the through hole 26 of the base 20 with a play such that the relative position of the cover 24 with respect to the base 20 changes in both the vertical and horizontal directions. Specifically, as shown in FIG. 6, the diameter d1 of the rod-shaped member 32 is smaller than the hole diameter d2 of the through hole 26 of the base 20, and the length h1 of the rod-shaped member 32 is formed to be longer than the depth h2 of the through hole 26 of the base 20.

[0037] As shown in Fig. 4, the cover opening engagement parts 33 are provided so as to protrude upward from the outer periphery side of the first back surface support part 31. In the first embodiment, three cover opening engagement parts 33 are provided. Each of the cover opening engagement parts 33 is disposed at an interval of approximately 120 degrees (see Fig. 5) with respect to the center of the annular first back surface support part 31. The cover opening engagement parts 33 are configured to support the cover 24 by, for example, screwing the cover 24 through the through holes 26 of the cover 24.

[0038] The cover opening support portion 34 is provided so as to extend from the lower portion of the cover opening engagement portion 33 toward the outside of the cover opening engagement portion 33. The cover opening support portion 34 is configured to support the cover 24 by contacting, at its upper surface, with the end surface of the opening 24b of the cover 24.

[0039] As described above, the rod-shaped member 32 is inserted through the through-hole 26 of the base 20 with a play so that the relative position of the cover 24 with respect to the base 20 can change, and thus the connecting portion 30 and the cover 24 supported by the connecting portion 30 can move vertically with respect to the base 20 by the play. As shown in FIG. 6(a), when the base 20 is lifted from the subject placement portion 106, the first back surface support portion 31 moves vertically upward with respect to the base 20 by the play to support the back surface of the base 20. Also, as shown in FIG. 6(b), when the base 20 is placed on the subject placement portion 106 via the base support leg portion 21, the first back surface support portion 31 moves vertically downward with respect to the base 20 by the play to separate from the back surface of the base 20 and come into contact with the subject placement portion 106. As a result, the cover 24 is not supported by the base 20, but is supported by the subject placement portion 106 together with the connecting portion 30.

[0040] In the measurement error evaluation instrument 10 in the first embodiment, as shown in Fig. 2, the cover 24 is removed from the measurement error evaluation instrument 10 when performing coordinate measurement by the three-dimensional coordinate measuring device 200. Furthermore, when performing CT imaging by the X-ray CT device 100, the cover 24 is attached to the measurement error evaluation instrument 10 as shown in Fig. 1, but as shown in Fig. 6(b), the cover 24 attached to the measurement error evaluation instrument 10 is not supported by the base 20, but is supported by the subject placement part 106 together with the connecting part 30. Therefore, in the measurement error evaluation instrument 10 in the first embodiment, the state (distortion) of the base 20 when the cover 24 is removed during coordinate measurement by the three-dimensional coordinate measuring device 200 is substantially the same as the state (distortion) of the base 20 when the cover 24 is attached during X-ray CT imaging by the X-ray CT device 100. Therefore, the spatial position (three-dimensional position) of the evaluation member 23 remains substantially unchanged between a state in which the cover 24 is removed and a state in which the cover 24 is attached.

[0041] In contrast, Fig. 7 is a schematic diagram for explaining distortion of the base 301 in the measurement error evaluation tool 300 in the comparative example. Fig. 7(a) shows the measurement error evaluation tool 300 in the comparative example 1, and the cover 303 is placed on the peripheral portion of the base 301 when CT imaging is performed by the X-ray CT device. In the measurement error evaluation tool 300 in the comparative example 1, the cover 303 is also removed from the measurement error evaluation tool 300 when coordinate measurement is performed by the three-dimensional coordinate measuring device. In addition, the cover 303 is placed on the peripheral portion of the base 301 in the measurement error evaluation tool 300 when CT imaging is performed by the X-ray CT device. In a state where the cover 303 is attached and the load of the cover 303 is applied to the peripheral portion of the base 301, the base 301 may be distorted due to the load of the cover 303, compared to a state where the cover 303 is removed.

[0042] FIG. 7(b) shows the measurement error evaluation tool 300 of Comparative Example 2. When CT imaging is performed by the X-ray CT device, the cover 303 is fixed to the base via a clamping member 304 that clamps the periphery of the base 301. The clamping member 304 tightens the base 301 and is fixed to the base 301. In the measurement error evaluation tool 300 of Comparative Example 2, the cover 303 is also removed from the measurement error evaluation tool 300 when coordinate measurement is performed by the three-dimensional coordinate measuring device. When CT imaging is performed by the X-ray CT device, the cover 303 is fixed to the base via the clamping member 304 in the measurement error evaluation tool 300. When the cover 303 is fixed to the periphery of the base 301 via the clamping member 304, the base 301 may be distorted due to the tightening of the clamping member 304 compared to when the cover 303 is removed.

[0043] Therefore, in the measurement error evaluation tools 300 in Comparative Examples 1 and 2, the state (distortion) of the base 301 when the cover 303 is removed during coordinate measurement by the three-dimensional coordinate measuring device is different from the state (distortion) of the base 301 when the cover 303 is attached during X-ray CT imaging by the X-ray CT device. Therefore, the spatial position (three-dimensional position) of the evaluation member 302 may change between the state when the cover 303 is removed and the state when the cover 303 is attached. For convenience of explanation, the distortion is illustrated in an exaggerated manner.

[0044] (Effects of the first embodiment) In the first embodiment, the following effects can be obtained.

[0045] In the first embodiment, as described above, there is provided a cover 24 arranged to cover the evaluation member 23, the cover 24 and the base 20 being detachable from each other, and a connecting portion 30 connecting the base 20 and the cover 24, the connecting portion 30 being engaged with the base 20 so that its relative position changes, and when the base 20 is placed on the subject placement portion 106, the cover 24 is not supported by the base 20, but is supported by the subject placement portion 106 together with the connecting portion 30.

[0046] As a result, when the base 20 is placed on the subject placement part 106, the relative position of the connecting part 30 to the base 20 changes, so that the cover 24 can be supported by the subject placement part 106 without being supported by the base 20. Therefore, when the measurement error evaluation instrument 10 on which the cover 24 is placed is subjected to X-ray CT imaging by the CT device, when the base 20 is placed on the subject placement part 106, the load of the cover 24 is applied to the subject placement part 106, not to the base 20. Also, when the measurement error evaluation instrument 10 is used to measure the coordinates of the evaluation member 23 by the three-dimensional coordinate measuring device 200, the cover 24 is removed from the measurement error evaluation instrument 10, so the load of the cover 24 is naturally not applied to the base 20. Therefore, it is possible to suppress a change in the state (distortion) of the base 20 caused by the load of the cover 24 between a state in which the cover 24 is removed and a state in which the cover 24 is attached. As a result, it is possible to suppress a change in the spatial position (three-dimensional position) of the evaluation member 23 between a state in which the cover 24 is removed and a state in which the cover 24 is attached.

[0047] Moreover, in the first embodiment, by being configured as follows, the following further effects can be obtained.

[0048] That is, in the first embodiment, as described above, the connecting unit 30 is connected to the base 20 with a play such that the relative position of the cover 24 with respect to the base 20 changes in both the vertical and horizontal directions. This allows the connecting unit 30 to connect the cover 24 to the base 20 in a state in which the cover 24 can move with respect to the base 20 by the play. Therefore, when the base 20 is placed on the subject placement unit 106, the cover 24 moves with respect to the base 20 in the vertical direction by the play, so that the cover 24 can be easily supported by the subject placement unit 106 without being supported by the base 20. In addition, since the connecting unit 30 and the base 20 are connected with a play in the horizontal direction, it is possible to prevent the connecting unit 30 and the base 20 from coming into contact with each other in the horizontal direction and causing distortion.

[0049] Moreover, in the first embodiment, the connecting part 30 includes a first back surface support part 31 that supports the back surface of the base 20 when the base 20 is lifted from the subject placement part 106. As a result, when the base 20 placed on the subject placement part 106 is lifted from the subject placement part 106, the cover 24 is lifted, and the connecting part 30 moves in the vertical direction relative to the base 20 by an amount corresponding to play, so that the back surface of the base 20 can be supported by the first back surface support part 31 of the connecting part 30. Therefore, since the base 20 can be supported by the first back surface support part 31, the base 20 can be easily moved together with the cover 24.

[0050] Furthermore, in the first embodiment, when the base 20 is placed on the subject placement section 106, the first back surface support section 31 moves away from the back surface of the base 20, and the connecting section 30 comes into contact with the subject placement section 106. As a result, when the base 20 is placed on the subject placement section 106, the cover 24 moves vertically with respect to the base 20 by an amount of play, so that the first back surface support section 31 moves away from the back surface of the base 20, thereby making it possible to suppress the application of force to the back surface of the base 20 via the connecting section 30. Therefore, it is possible to further suppress the change in the spatial position of the evaluation member 23 between a state in which the cover 24 is removed and a state in which the cover 24 is attached.

[0051] In the first embodiment, the base 20 includes a through hole 26 penetrating in the thickness direction, and the connecting part 30 includes a rod-shaped member 32 that is inserted into the through hole 26 of the base 20 and has a diameter smaller than the hole diameter of the through hole 26 and is longer than the depth of the through hole 26. This allows the connecting part 30 and the cover 24 to move in the vertical direction while being guided by the through hole 26 of the base 20 via the rod-shaped member 32 of the connecting part 30. Therefore, when the base 20 placed on the subject placement part 106 via the through hole 26 is lifted from the subject placement part 106, the connecting part 30 can be easily moved upward relative to the base 20 by the amount of play, and when the base 20 is placed on the subject placement part 106, the connecting part 30 can be easily moved downward relative to the base 20 by the amount of play.

[0052] [Second embodiment] Next, a second embodiment of the present invention will be described with reference to Figs. 8 to 11. In the second embodiment, unlike the first embodiment in which the cover 24 is not supported by the base 20 but is supported by the subject placement section 106 together with the connecting section 30 when the base 20 is placed on the subject placement section 106, the connecting section 40 includes a base contact section 45 that contacts the base 20 at a corresponding position on the surface of the base 20 corresponding to the base support leg 21 or in the vicinity of the corresponding position, and when the base 20 is placed on the subject placement section 106, the cover 24 is supported by the base 20 via the base contact section 45 of the connecting section 40. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

[0053] (Instrument for evaluating measurement error) As shown in FIG. 8, the measurement error evaluation instrument 10 includes a base 20, a base support leg 21, a support 22, an evaluation member 23, a cover 24, and a connecting portion 40.

[0054] In the second embodiment, recesses 20a (see FIG. 11) into which base contact portions 45 of connecting portions 40 described later fit are formed on the surface of the base 20. Each recess 20a is provided at a corresponding position on the surface of the base 20 corresponding to a base support leg 21 or in the vicinity of the corresponding position. Three base support legs 21 are provided at intervals of approximately 120 degrees relative to the center of the back surface of the base 20. Therefore, three recesses 20a are provided.

[0055] Here, in this specification, "near the corresponding position on the surface of the base 20 corresponding to the base support leg 21" means within a cylindrical region whose radius with the vertical direction of the center of the base support leg 21 as its central axis is 10% or less of the distance between adjacent base support legs 21.

[0056] In the second embodiment, the coupling part 40 is also configured to couple the base 20 and the cover 24. The coupling part 40 is engaged with the base 20 so that the relative position with respect to the base 20 changes. The coupling part 40 includes an annular member 41, a connection member 42, a second back surface support part 43 (see FIG. 10), and a cover opening engagement part 44. The second back surface support part 43 is an example of a "back surface support part" in the claims.

[0057] The annular member 41 is formed of a circular plate-like member. The annular member 41 is disposed on the outer periphery of the base 20.

[0058] The connection members 42 are configured to connect the base 20 and the annular member 41. Three connection members 42 are provided. Each of the connection members 42 is disposed at an interval of approximately 120 degrees (see FIG. 9) with respect to the center of the annular member 41. The connection members 42 are provided with a base contact portion 45 (see FIG. 11) on one end side. The connection members 42 are connected to the annular member 41 on the other end side, for example, by screwing. The method of connecting the connection members 42 and the annular member 41 is not particularly limited.

[0059] 11(a), the base contact portion 45 is formed of a semispherical member. The base contact portion 45 may be a spherical member embedded in the rear surface of the connection member 42 with a portion exposed. The base contact portion 45 is configured to contact the base 20 at a corresponding position on the surface of the base 20 corresponding to the base support leg 21 or in the vicinity of the corresponding position. Specifically, the base contact portion 45 is configured to fit into the base 20 in a recess 20a provided at a corresponding position on the surface of the base 20 corresponding to the base support leg 21 or in the vicinity of the corresponding position.

[0060] The base contact portion 45 fits into the recess 20a of the base 20 with some play such that the relative position of the cover 24 with respect to the base 20 changes in both the vertical and horizontal directions. Specifically, the vertical distance t1 from the lower surface P1 of the connection member 42 to the upper surface P2 of the second back surface support portion 43 is greater than the thickness t2 of the base 20, and the lower end of the base contact portion 45 is located below the surface along the front surface of the base 20 when the back surface (lower surface) of the base 20 and the upper surface P2 of the second back surface support portion 43 are in contact with each other.

[0061] As shown in FIG. 10, the second back surface support portion 43 is configured to protrude downward from the annular member 41 and extend toward the inside of the annular member 41 to support the back surface of the base 20. Three second back surface support portions 43 are provided. Each of the second back surface support portions 43 is disposed at an interval of approximately 120 degrees with respect to the center of the annular member 41. As shown in FIG. 11(a), when the base 20 is disposed on the subject placement portion 106 via the base support leg portion 21, the second back surface support portion 43 is separated from the back surface of the base 20 with play from the base 20. Also, as shown in FIG. 11(b), when the base 20 is lifted from the subject placement portion 106, the second back surface support portion 43 supports the back surface of the base 20.

[0062] As shown in Fig. 8, the cover opening engagement parts 44 are provided so as to protrude upward from the annular member 41. In the second embodiment, three cover opening engagement parts 44 are provided. Each of the cover opening engagement parts 44 is disposed at an interval of approximately 120 degrees with respect to the center of the annular member 41 (see Fig. 9). The cover opening engagement parts 44 are configured to support the cover 24, for example, by screwing the cover 24 through the through holes 26 of the cover 24. When the base 20 is placed on the subject placement part 106, the cover 24 is supported by the base 20 through the base contact parts 45.

[0063] As described above, the base contact portion 45 is fitted into the recess 20a of the base 20 with a play so that the relative position of the cover 24 with respect to the base 20 changes, and thus the connecting portion 40 and the cover 24 supported by the connecting portion 40 can move vertically with respect to the base 20 by the play. As shown in FIG. 11(a), when the base 20 is placed on the subject placement portion 106 via the base support leg 21, the second back surface support portion 43 moves vertically downward with respect to the base 20 by the play and separates from the back surface of the base 20. The cover 24 is supported by the base 20 via the base contact portion 45 located directly or substantially directly above the base support leg 21. Also, as shown in FIG. 11(b), when the base 20 is lifted from the subject placement portion 106, the second back surface support portion 43 moves vertically upward with respect to the base 20 by the play and supports the back surface of the base 20.

[0064] The other configurations of the second embodiment are similar to those of the first embodiment.

[0065] (Effects of the second embodiment) In the second embodiment, the following effects can be obtained.

[0066] In the second embodiment, as described above, the connecting portion 40 includes a base contact portion 45 that contacts the base 20 at a corresponding position on the surface of the base 20 corresponding to the base support leg 21 or near the corresponding position, and when the base 20 is placed on the subject placement portion 106, the cover 24 is supported on the base 20 via the base contact portion 45 of the connecting portion 40.

[0067] This allows the load of the cover 24 to be received by the base support leg 21 from approximately directly above via the base contact portion 45 of the connecting portion 40, and therefore, unlike a case where the position where the base contact portion 45 of the connecting portion 40 contacts the base 20 is far away from the position of the base support leg 21 in a plan view, it is possible to suppress distortion of the base 20 due to the load of the cover 24. As a result, it is possible to suppress a change in the state (distortion) of the base 20 due to the load of the cover 24 between a state where the cover 24 is removed and a state where the cover 24 is attached. Therefore, it is possible to suppress a change in the spatial position (three-dimensional position) of the evaluation member 23 between a state where the cover 24 is removed and a state where the cover 24 is attached.

[0068] Moreover, in the second embodiment, by being configured as follows, the following further effects can be obtained.

[0069] That is, in the second embodiment, as described above, three base support legs 21 are provided on the back surface of the base 20, and the connecting portion 40 further includes an annular ring member 41 arranged on the outside of the outer periphery of the base 20, and three connecting members 42 having base contact portions 45 and connecting the base 20 and the ring member 41. As a result, since three base support legs 21 are provided on the back surface of the base 20, a surface is determined by three points, and the base 20 can be placed on the subject placement portion 106 without rattling. In addition, the three base support legs 21 can be easily supported from almost directly above via the three base contact portions 45 of the connecting portion 40, and since the ring member 41 supporting the cover 24 is arranged on the outside of the outer periphery of the base 20, it is possible to prevent the arrangement area of ​​the evaluation member 23 arranged on the base 20 from becoming narrower than when the ring member 41 supporting the cover 24 is arranged on the inside of the outer periphery of the base 20.

[0070] Other effects of the second embodiment are similar to those of the first embodiment.

[0071] [Third embodiment] Next, a third embodiment of the present invention will be described with reference to Fig. 12. In the third embodiment, unlike the second embodiment in which the coupling portion 40 includes an annular member 41 that is disposed outside the outer periphery of the base 20 and supports the cover 24, and a connecting member 42 that has a base contact portion 45 and connects the base 20 and the annular member 41, an example will be described in which the coupling portion 50 is configured of three coupling portions 50. Note that the same components as those in the second embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

[0072] (Instrument for evaluating measurement error) As shown in FIG. 12, the measurement error evaluation instrument 10 includes a base 20, a base support leg 21, a support 22, an evaluation member 23, a cover 24, and a connecting portion 50.

[0073] In the third embodiment, the connecting portion 50 is also configured to connect the base 20 and the cover 24. The connecting portion 50 has an L-shape. The connecting portion 50 is provided on the surface of the base 20 and includes a base contact portion 51 extending along the surface of the base 20, and a vertical portion 52 extending vertically upward from the base contact portion 51. The shape of the connecting portion 50 is not limited to an L-shape, and may be a step shape having two or more steps, or may be another shape.

[0074] The base contact portion 51 contacts the base 20 at a corresponding position on the surface of the base 20 corresponding to the base support leg 21 or in the vicinity of the corresponding position. As an example, the base contact portion 51 is fixed by screwing at the corresponding position or in the vicinity of the corresponding position. In the third embodiment, three base support legs 21 are provided at intervals of approximately 120 degrees relative to the center of the back surface of the base 20. Three connecting portions 50 are provided, the same number as the base support legs 21. Note that the method of fixing the base contact portion 51 to the base 20 is not particularly limited.

[0075] The vertical portion 52 is configured to support the cover 24, for example, by screwing the cover 24 through the through-hole 26 of the cover 24. The end face of the opening 24b of the cover 24 is not in contact with the base 20. When the base 20 is placed on the subject placement portion 106, the cover 24 is supported by the base 20 via the base contact portion 51 located directly or substantially directly above the base support leg 21.

[0076] The other configurations of the third embodiment are similar to those of the second embodiment.

[0077] (Effects of the third embodiment) In the third embodiment, the following effects can be obtained.

[0078] In the third embodiment, as described above, three base support legs 21 are provided on the back surface of the base 20, the connecting portion 50 is configured by the three connecting portions 50, and the cover 24 is supported on the base 20 via the base contact portions 51 of the three connecting portions 50. As a result, since three base support legs 21 are provided on the back surface of the base 20, a plane is determined by three points, so that the base 20 can be placed on the subject placement portion 106 without rattling. Furthermore, by supporting the cover 24 via the base contact portions 51 of the three connecting portions 50, it is possible to prevent the structure of the connecting portion 50 from becoming complicated as compared to a configuration in which the connecting portion 50 includes a plurality of members.

[0079] Other effects of the third embodiment are similar to those of the second embodiment.

[0080] [Fourth embodiment] Next, a fourth embodiment of the present invention will be described with reference to Fig. 13 and Fig. 14. In the fourth embodiment, unlike the second embodiment in which the connecting portion 40 includes an annular ring-shaped member 41 that is disposed outside the outer periphery of the base 20 and supports the cover 24, and a connecting member 42 that has a base contact portion 45 and connects the base 20 and the ring-shaped member 41, an example will be described in which the connecting portion 60 is provided with a base contact portion 61 at one end and is configured by three rod-shaped connecting portions 60 that engage with the top surface 24c at the other end. Note that the same components as those in the second embodiment are denoted by the same reference numerals, and their description will be omitted.

[0081] (Instrument for evaluating measurement error) As shown in FIG. 13, the measurement error evaluation instrument 10 includes a base 20, a base support leg 21, a support 22, an evaluation member 23, a cover 24, and a connecting portion 60.

[0082] In the fourth embodiment, the connecting part 60 is also configured to connect the base 20 and the cover 24. The connecting part 60 is configured of a rod-shaped member having a base contact part 61 at one end and engaging at the other end via an engaging member 62 in an engaging hole 24d provided in the top surface 24c of the cover 24. The rod-shaped member of the connecting part 60 is formed of a material with high X-ray transmittance, such as CFRP (Carbon Fiber Reinforced Plastics).

[0083] The base contact portion 61 contacts the base 20 at a corresponding position on the surface of the base 20 corresponding to the base support leg 21 or in the vicinity of the corresponding position. As an example, the base contact portion 61 is fixed by fitting into a fitting hole 25 provided in the base 20 at the corresponding position or in the vicinity of the corresponding position. As shown in FIG. 14, in the fourth embodiment, three base support legs 21 are provided at intervals of approximately 120 degrees relative to the center of the back surface of the base 20. Three connecting portions 60 are provided, the same number as the base support legs 21. Note that a method for fixing the base contact portion 61 to the base 20 is not particularly limited.

[0084] 13, the other end of the connecting portion 60 is engaged with the top surface 24c of the cover 24 by, for example, screwing, and supports the cover 24 in a non-detachable state. The method of engaging the other end of the connecting portion 60 with the top surface 24c of the cover 24 is not particularly limited.

[0085] The other configurations of the fourth embodiment are similar to those of the second embodiment.

[0086] (Effects of the fourth embodiment) In the fourth embodiment, the following effects can be obtained.

[0087] In the fourth embodiment, as described above, the cover 24 includes a top surface 24c provided on the opposite side to the base 20, three base support legs 21 are provided on the back surface of the base 20, the connecting portion 60 is configured by three rod-shaped connecting portions 60 each having a base contact portion 61 at one end and engaging with the top surface 24c at the other end, and the cover 24 is supported on the base 20 via the base contact portion 61 of each of the three connecting portions 60. As a result, since three base support legs 21 are provided on the back surface of the base 20, a surface is determined by three points, so that the base 20 can be placed on the subject placement portion 106 without rattling. Also, by supporting the cover 24 via the base contact portion 61 of each of the three rod-shaped connecting portions 60, the cover 24 can be more easily received on the base support legs 21 from approximately directly above via the base contact portion 61 of the connecting portion 60.

[0088] [Variations] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not by the description of the embodiments above, and further includes all modifications (variations) within the meaning and scope of the claims.

[0089] For example, in the first to fourth embodiments, an example in which three support base legs are provided is shown, but the present invention is not limited to this. For example, four or more support base legs may be provided.

[0090] In the first embodiment, the connecting portion includes four rod-shaped members, but the present invention is not limited to this. For example, the connecting portion may include two, three, five or more rod-shaped members.

[0091] In the above first embodiment, the cover opening support portion supports the cover, but the present invention is not limited to this. For example, the cover may be simply screwed to the cover opening engagement portion without providing the cover opening support portion.

[0092] In the first embodiment, the first back surface support part is formed of a circular plate-like member, but the present invention is not limited to this. For example, the first back surface support part may have a shape other than a circular shape as long as it can support the back surface of the base when the base is lifted up from the subject placement part.

[0093] In addition, in the second to fourth embodiments, the number of connecting parts is three, but the present invention is not limited to this. For example, the number of connecting parts may be four or more depending on the number of legs of the support base.

[0094] In the first embodiment, the support base legs are provided, but the present invention is not limited to this. For example, the support base legs do not have to be provided.

[0095] [Aspects] It will be appreciated by those skilled in the art that the exemplary embodiments described above are examples of the following aspects.

[0096] (Item 1) A measurement error evaluation tool for a CT apparatus for measuring three-dimensional shapes, which is disposed on a subject placement section for placing a subject between an X-ray source and an X-ray detector, and used, comprising: The base and An evaluation member provided on the base; A cover disposed so as to cover the evaluation member; The cover and the base are detachable from each other, and a connecting portion is provided to connect the base and the cover, The coupling portion is engaged with the base so that a relative position of the coupling portion changes with respect to the base, A measurement error evaluation tool for a CT scanner, wherein when the base is placed on the subject placement part, the cover is not supported by the base but is supported by the subject placement part together with the connecting part.

[0097] (Item 2) A measurement error evaluation tool for a CT apparatus for measuring three-dimensional shapes, which is disposed on a subject placement section for placing a subject between an X-ray source and an X-ray detector, and used, comprising: The base and a base support leg provided on a rear surface of the base and supporting the base; An evaluation member provided on the base; A cover disposed so as to cover the evaluation member; The cover and the base are detachable from each other, and a connecting portion is provided to connect the base and the cover, the coupling portion includes a base contact portion that contacts the base at a corresponding position on a surface of the base that corresponds to the base support leg or in the vicinity of the corresponding position, A measurement error evaluation tool for a CT scanner, wherein when the base is placed on the subject placement section, the cover is supported on the base via the base contact portion of the connecting portion.

[0098] (Item 3) 3. The measurement error evaluation tool for a CT apparatus according to item 1 or 2, wherein the connecting portion is connected to the base with play such that the relative position of the cover with respect to the base changes in both the vertical and horizontal directions.

[0099] (Item 4) 3. The measurement error evaluation tool for a CT apparatus according to item 1 or 2, wherein the connecting portion includes a back surface support portion that supports a back surface of the base when the base is lifted up from the subject placement portion.

[0100] (Item 5) the connecting portion includes a back surface support portion that supports a back surface of the base when the base is lifted up from the subject placement portion, 2. The measurement error evaluation tool for a CT apparatus according to item 1, wherein, when the base is placed on the subject placement portion, the back surface support portion is spaced apart from the back surface of the base and the connecting portion is in contact with the subject placement portion.

[0101] (Item 6) The base includes a through hole extending in a thickness direction, 2. The measurement error evaluation tool for a CT apparatus according to claim 1, wherein the connecting portion includes a rod-shaped member that is inserted into the through hole of the base, has a diameter smaller than the diameter of the through hole, and is longer than the depth of the through hole.

[0102] (Item 7) The base support legs are provided in three on the back surface of the base, 3. The measurement error evaluation device for a CT scanner according to item 2, wherein the connecting portion further includes a circular ring-shaped member that is arranged outside the outer periphery of the base, and three connecting members that have the base contact portion and connect the base and the ring-shaped member.

[0103] (Item 8) The base support legs are provided in three on the back surface of the base, The connecting portion is composed of three connecting portions, 3. The measurement error evaluation device for a CT apparatus according to claim 2, wherein the cover is supported on the base via the base contact portions of each of the three connecting portions.

[0104] (Item 9) The cover includes a top surface provided on the opposite side to the base, The base support legs are provided in three on the back surface of the base, The connecting portion is configured by three rod-shaped connecting portions each having the base contact portion at one end and engaging with the top surface at the other end, 3. The measurement error evaluation device for a CT apparatus according to claim 2, wherein the cover is supported on the base via the base contact portions of each of the three connecting portions. [Explanation of symbols]

[0105] 10. Instruments for evaluating measurement errors 20 Foundations 21 Base support legs 23 Evaluation materials 24 Cover 24c Top 26 Through hole 30, 40, 50, 60 connection part 31, 43 Back support 32 Rod-shaped member 41 Annular member 42 Connection parts 45, 51, 61 Base contact part 100 X-ray CT device 101 X-ray source 102 X-ray detector 106 Subject placement section

Claims

1. A measurement error evaluation tool for a CT apparatus for three-dimensional shape measurement, the tool being disposed on a subject placement section for placing a subject between an X-ray source and an X-ray detector, the tool comprising: The base and An evaluation member provided on the base; A cover disposed so as to cover the evaluation member; The cover and the base are detachable from each other, and a connecting portion is provided to connect the base and the cover, The coupling portion is engaged with the base so that a relative position of the coupling portion changes with respect to the base, A measurement error evaluation tool for a CT apparatus, wherein when the base is placed on the subject placement section, the cover is not supported by the base but is supported by the subject placement section together with the connecting section.

2. A measurement error evaluation tool for a CT apparatus for three-dimensional shape measurement, the tool being disposed on a subject placement section for placing a subject between an X-ray source and an X-ray detector, the tool comprising: The base and a base support leg provided on a rear surface of the base and supporting the base; An evaluation member provided on the base; A cover disposed so as to cover the evaluation member; The cover and the base are detachable from each other, and a connecting portion is provided to connect the base and the cover, the coupling portion includes a base contact portion that contacts the base at a corresponding position on a surface of the base that corresponds to the base support leg or in the vicinity of the corresponding position, A measurement error evaluation tool for a CT apparatus, wherein, when the base is placed on the subject placement section, the cover is supported on the base via the base contact portion of the connecting portion.

3. 3. The measurement error evaluation device for a CT apparatus as described in claim 1 or 2, wherein the connecting portion is connected to the base with some play such that the relative position of the cover with respect to the base changes in both the vertical and horizontal directions.

4. 3. The measurement error evaluation tool for a CT apparatus according to claim 1, wherein the connecting portion includes a back surface support portion that supports a back surface of the base when the base is lifted up from the subject placement portion.

5. the connecting portion includes a back surface support portion that supports a back surface of the base when the base is lifted up from the subject placement portion, 2. The measurement error evaluation device for a CT apparatus according to claim 1, wherein, when the base is placed on the subject placement portion, the back surface support portion is spaced apart from the back surface of the base and the connecting portion is in contact with the subject placement portion.

6. The base includes a through hole extending in a thickness direction, 2. The measurement error evaluation tool for a CT apparatus as described in claim 1, wherein the connecting portion includes a rod-shaped member that is inserted into the through hole of the base, has a diameter smaller than the hole diameter of the through hole, and is longer than the depth of the through hole.

7. The base support legs are provided in three on the back surface of the base, The measurement error evaluation device for a CT apparatus as described in claim 2, wherein the connecting portion further includes a circular ring-shaped member arranged outside the outer periphery of the base, and three connecting members having the base contact portion and connecting the base and the ring-shaped member.

8. The base support legs are provided in three on the back surface of the base, The connecting portion is composed of three connecting portions, 3. The measurement error evaluation tool for a CT apparatus according to claim 2, wherein the cover is supported on the base via the base contact portions of the three connecting portions.

9. The cover includes a top surface provided on the opposite side to the base, The base support legs are provided in three on the back surface of the base, the connecting portion is configured by three rod-shaped connecting portions each having the base contact portion at one end and engaging with the top surface at the other end; 3. The measurement error evaluation tool for a CT apparatus according to claim 2, wherein the cover is supported on the base via the base contact portions of the three connecting portions.

Images