X-ray ct apparatus for measurement

Abstract

This invention provides a measurement X-ray CT apparatus. The measurement X-ray CT apparatus includes a rotating stage for mounting the object to be measured and a scanning mechanism between an X-ray source and an X-ray detector. The apparatus performs a CT scan by irradiating the object with X-rays based on pre-calibrated geometric positions of the X-ray source's focal point, the X-ray detector, and the rotating stage's center of rotation, thereby acquiring a projected image. A three-dimensional image of the object is generated by CT reconstruction of this projected image. The measurement X-ray CT apparatus includes: a reference frame having a material and structure resistant to environmental changes; and a sensor disposed on the reference frame for successively acquiring correction values ​​of the geometric positional relationship between the X-ray source's focal point and the X-ray detector during the CT scan. These correction values ​​are used as parameters for CT reconstruction.

Description

[0001] Cross-references to related applications

[0002] The disclosure of Japanese Application No. 2019-163422, filed on September 6, 2019, including the specification, drawings and claims, is incorporated herein by reference in its entirety. Technical Field

[0003] This invention relates to an X-ray CT apparatus for measuring industrial products, and more particularly to a measuring X-ray CT apparatus that can perform high-precision dimensional measurements of the entire internal structure of the object being measured, even if the geometrical positional relationship of the X-ray source focal point, X-ray detector, etc., changes from the time of calibration. Background Technology

[0004] Previously, X-ray CT scanners were used to observe and inspect defects in castings, welded parts, and electronic components that were difficult to detect visually. However, with the increasing prevalence of 3D printers in recent years, the demand for high-precision 3D dimensional measurement of processed parts has been growing. To address this need, a measurement X-ray CT scanner with length traceability was developed. This has led to ongoing research and development efforts to meet the requirements for high-precision dimensional measurement.

[0005] exist Figure 1 (Top view) and Figure 2 The side view shows a structural example of a conventional X-ray CT apparatus for measurement. This X-ray CT apparatus 1 primarily comprises the following components: an X-ray source 12, for example, an X-ray tube that irradiates X-rays; an X-ray detector 14, for example, a flat panel display that detects the X-ray beam 13 that passes through the workpiece 10 being measured after being irradiated by the X-ray source 12, and images the projected image of the workpiece 10 to obtain a projected image; a rotating stage 16, positioned between the X-ray source 12 and the X-ray detector 14, for mounting the workpiece 10; a scanning mechanism 18 that moves the rotating stage 16 to any position within the measurement space; and a computational control unit 20 (see reference 1). Figure 2 ).

[0006] In addition, Figure 1 In this model, the direction from the X-ray source 12 horizontally toward the X-ray detector 14 is set as the X-axis, the direction perpendicular to the X-axis is set as the Y-axis, and the direction perpendicular to the XY plane is set as the Z-axis.

[0007] The rotary table 16 can hold the workpiece 10 and move it along the XYZ axes via the scanning mechanism 18, and can also rotate the workpiece 10 along the θ axis. Through these adjustments, the position and magnification of the projected image of the workpiece 10 obtained by the X-ray detector 14 can be adjusted.

[0008] In order to obtain a three-dimensional image, i.e., volume data (CT image), of the workpiece 10, which is the final target of the X-ray CT apparatus 1 for measurement, a CT scan of the workpiece 10 is performed.

[0009] like Figure 3 As shown, the CT scan includes two processes: acquiring the projection image of the workpiece 10 and CT reconstruction. In the projection image acquisition process, during X-ray irradiation, the rotary table 16 carrying the workpiece 10 is rotated continuously at a fixed speed or intermittently at a fixed step size to acquire the projection image of the workpiece 10 in the whole circumference (fixed interval). CT reconstruction is performed on the obtained projection images in the whole circumference (fixed interval) using CT reconstruction algorithms such as back projection method and successive approximation method, thereby obtaining the volume data of the workpiece 10.

[0010] The obtained volume data can be used to perform various measurements such as size determination and defect analysis.

[0011] Furthermore, in order to perform dimensional measurements with higher accuracy using the aforementioned X-ray CT apparatus, it is important to perform various inherent calibrations of the apparatus before starting the measurement. For example, Japanese Patent Application Publication No. 2012-189517 discloses a calibration method and an evaluation method for an X-ray CT apparatus that utilizes standard instruments for calibration and evaluation.

[0012] The X-ray CT apparatus 1 for measurement acquires a projected image by irradiating the workpiece 10 with an X-ray beam 13 to perform CT scanning based on the pre-calibrated geometric positional relationship between the focal point of the X-ray source 12, the X-ray detector 14, and the rotation center of the rotary stage 16. The volume data of the workpiece 10 is generated by CT reconstruction of the projected image. Summary of the Invention

[0013] The problem the invention aims to solve

[0014] In addition, it is known that the geometric positional relationship of the focal point of the X-ray source 12, the X-ray detector 14, etc. is affected by the heating of various devices and changes in the surrounding environment. When correction is performed, the geometric positional relationship undergoes a slight change, which has an adverse effect on the quality of the volume data (image quality, geometric accuracy).

[0015] Furthermore, Japanese Patent Application Publication No. 2012-112790 describes a method of photographing a mark attached to a rotating stage using an optical camera and correcting deviations in the position and angle of the projected data caused by rotational accuracy. However, this method can only correct deviations caused by rotational accuracy and does not use a reference frame, thus failing to adequately improve the effect.

[0016] The present invention was made in view of the above-mentioned problems, and its objective is to enable high-precision X-ray CT measurement of the entire body, including the internal structure of the object being measured, even if the geometric positional relationship of the X-ray source focal point, X-ray detector, etc. changes from the time of calibration.

[0017] Solution for solving the problem

[0018] This invention relates to a measurement X-ray CT apparatus, which includes a rotating stage for mounting the object to be measured and a scanning mechanism capable of moving the rotating stage to any position within the measurement space between an X-ray source and an X-ray detector. The measurement X-ray CT apparatus performs a CT scan by irradiating the object with X-rays based on pre-calibrated geometrical relationships between the focal point of the X-ray source, the X-ray detector, and the rotation center of the rotating stage, thereby acquiring a projected image. A three-dimensional image of the object is generated by CT reconstruction of the projected image. The measurement X-ray CT apparatus includes: a reference frame having a material and structure resistant to environmental changes; and a sensor disposed on the reference frame for successively acquiring correction values ​​of the geometrical relationships between the focal point of the X-ray source and the X-ray detector during the CT scan. These correction values ​​are used as parameters for CT reconstruction. Thus, the measurement X-ray CT apparatus solves the aforementioned problems.

[0019] Here, the reference frame can be positioned at the location of the X-ray source and X-ray detector separated by the rotating stage.

[0020] In addition, the reference frame can be set as a cuboid-shaped measurement frame.

[0021] In addition, the reference frame can be positioned at the location of the rotary table and the X-ray source, and the mark on the X-ray detector can be detected by a camera mounted on the reference frame.

[0022] In addition, the reference frame can be set as a cubic measuring frame.

[0023] Alternatively, the mark can be set as a light-emitting diode.

[0024] In addition, the reference frame can be positioned at the location of the X-ray source, and a laser interferometer positioned on the reference frame can be used to detect the corner prism (Japanese: コーナーキューブ) positioned on the X-ray detector.

[0025] In addition, an eccentricity measuring device can be installed on the rotary table, and a sensor for detecting the position of the eccentricity measuring device can be installed on the reference frame.

[0026] In addition, a reference surface for eccentricity measurement can be formed on the outer periphery of the rotary table.

[0027] Additionally, a sensor for detecting the position of the rotary table can be installed on the reference frame.

[0028] In addition, the sensor can be configured as a laser tracker for detecting the cat's eye stone attached to the measuring object fixing fixture on the rotary table.

[0029] The effects of the invention

[0030] According to the present invention, even if the geometrical positional relationship of the X-ray source focal point, X-ray detector, etc., changes from the time of calibration, it is possible to perform high-precision X-ray CT measurements of the entire body, including the internal structure of the object being measured. Therefore, high-resolution analysis can be performed by improving the quality of volume data, and high-precision measurements can be achieved through X-ray CT applications.

[0031] These features, advantages, and other features and advantages of the present invention will become clear from the following detailed description of preferred embodiments. Attached Figure Description

[0032] Preferred embodiments will be described with reference to the accompanying drawings, in which the same elements are labeled with the same reference numerals, wherein,

[0033] Figure 1 This is a top view showing the main structural components of a conventional X-ray CT measuring device.

[0034] Figure 2 This is a side view showing the main structural components of a conventional X-ray CT measuring device.

[0035] Figure 3 This is a diagram illustrating the general outline of CT reconstruction using an existing X-ray CT apparatus.

[0036] Figure 4 This is a diagram illustrating the basic concept of the present invention.

[0037] Figure 5 This is a perspective view illustrating the first embodiment of the present invention.

[0038] Figure 6 This is a flowchart illustrating an example of the processing procedure of the present invention.

[0039] Figure 7 This is a perspective view illustrating the second embodiment of the present invention.

[0040] Figure 8 This is a perspective view illustrating the third embodiment of the present invention.

[0041] Figure 9 This is a perspective view illustrating the fourth embodiment of the present invention.

[0042] Figure 10 This is a top view showing the eccentricity measuring device used in the fourth embodiment.

[0043] Figure 11 This is a side view showing the eccentricity measuring device used in the fourth embodiment.

[0044] Figure 12 This is a perspective view illustrating the fifth embodiment of the present invention. Detailed Implementation

[0045] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Furthermore, the present invention is not limited to the contents described in the following embodiments and examples. Additionally, the constituent elements in the embodiments and examples described below include constituent elements readily conceived by those skilled in the art, substantially the same constituent elements, and constituent elements of the same scope. Moreover, the constituent elements disclosed in the embodiments and examples described below can be appropriately combined or selected for use.

[0046] exist Figure 4 The figure shows the geometric model of the X-ray CT apparatus used for measurement.

[0047] As parameters that change during CT scanning, the rotation (3) and translation (3) are related to the posture of the rotary stage 16, and the focal length f (2), skew (1), and center position (2) are related to the X-ray detector (camera model) 14 (the numbers in parentheses indicate the number of parameters corresponding to the degrees of freedom). Therefore, in this invention, the parameter changes during CT scanning are constantly checked, and high-precision X-ray CT measurement is achieved.

[0048] exist Figure 5 The first embodiment of the present invention is shown in the figure.

[0049] In this embodiment, a reference frame (referred to as a metrology frame) 20, which is not easily affected by the environment, has two faces (the right and left faces in the figure) positioned between the X-ray source 12 and the X-ray detector 14, separated by a rotary table 16. A displacement meter 22 for detecting the displacement of the target 12A of the X-ray source 12 in the X-axis direction, and three displacement meters 24A, 24B, and 24C for detecting the displacement of various parts (the upper part and the left and right ends) of the X-ray detector 14 are fixed on the metrology frame 20. This allows the position and orientation of the X-ray source 12 and the X-ray detector 14 to be detected with reference to the metrology frame 20. Furthermore, additional displacement meters can be added to detect the displacement of the target 12A in the Y-axis and Z-axis directions.

[0050] By utilizing positional and pose data that change during CT scanning detected by the displacement gauges 22, 24A, 24B, and 24C during CT reconstruction processing, the effects of these changes can be suppressed.

[0051] Specifically, such as Figure 6 As shown, in step 100, after correcting the values ​​of the parameters representing the geometrical positional relationship between the focal point of the X-ray source 12, the X-ray detector 14, and the rotary stage 16 of the X-ray CT apparatus 1 for measurement, the values ​​are saved as initial correction values.

[0052] Meanwhile, in step 110, the displacement values ​​of the sensors of the metering frame 20, namely displacement gauges 22, 24A, 24B, and 24C, are acquired and saved as initial displacement values.

[0053] Next, in step 120, the workpiece 10 is placed on the rotary table 16 and then irradiated with an X-ray beam 13 to perform a CT scan, acquiring multiple (e.g., 800) projection images.

[0054] At this time, in step 130, the displacement value (e.g., 800 data) of the sensor of the metering frame 20 during the acquisition of each projection image is obtained.

[0055] Next, in step 140, the initial correction value, initial displacement value, and sensor displacement value during the acquisition of the projection image are input to the calculation control unit as parameters for CT reconstruction processing. The acquired projection image is then subjected to CT reconstruction processing to generate volume data.

[0056] In this CT reconstruction process, the displacement values ​​of the sensors during the acquisition of projected images are used to generate high-quality volume data that suppresses the effects of geometric position changes during CT scanning.

[0057] exist Figure 7 The second embodiment of the present invention is shown in the figure.

[0058] In this embodiment, a cubic reference frame, namely the metrology frame 30, is positioned with two faces (the right and left faces in the figure) at the positions of the X-ray source 12 and the rotary stage 16. Cameras 32A and 32B, located at the upper ends of the left face of the metrology frame 30, detect the mark 34 at the position of the target 12A of the X-ray source 12. Cameras 32C and 32D, located at the upper ends of the right face of the metrology frame 30, detect, for example, three marks 36A, 36B, and 36C located at the X-ray detector 14.

[0059] The markings 34, 36A, 36B, and 36C can be, for example, set as light-emitting diodes (LEDs).

[0060] Other aspects are the same as in the first embodiment, so the description is omitted.

[0061] Furthermore, the mounting positions of cameras 32A, 32B, 32C, and 32D on the measuring frame 30 are not limited to this.

[0062] Alternatively, the same displacement meter 22 as in the first embodiment can be used to replace the combination of cameras 32A, 32B and marker 34.

[0063] Next, refer to Figure 8 The third embodiment of the present invention will be described below.

[0064] In this embodiment, a square-shaped reference frame, namely a metrology frame 40, is disposed at the position of the X-ray source 12. The same three corner prisms 50A, 50B, and 50C disposed on the X-ray detector 14 are detected by, for example, three laser interferometer emission sections 48A, 48B, and 48C disposed on the metrology frame 40.

[0065] The laser interferometer 42 consists of a light source unit 44, optical fibers 46A, 46B, 46C, and laser interferometer emission parts 48A, 48B, 48C mounted on the metering frame 40.

[0066] Furthermore, the position of the target 12A of the X-ray source 12 is detected, for example, by a displacement meter 22, which is the same as that in the first embodiment.

[0067] Other points are the same as in the described implementation, so the description is omitted.

[0068] Next, refer to Figure 9 The fourth embodiment of the present invention will now be described.

[0069] This embodiment is a method obtained by adding an eccentricity measuring device 60 for measuring the position and eccentricity of the rotary table 16 to the third embodiment.

[0070] like Figure 10 (Top view) and Figure 11 As shown in the side view, the eccentricity measuring device 60 includes an eccentricity measuring frame 62 and displacement gauges 64A, 64B, 64C, 64D, 64E, and 64F (not shown) disposed thereon. A reference surface 16A (desiring small roundness) is provided on the outer periphery of the rotary table 16. The eccentricity measuring frame 62 disposed on this outer periphery is radially ( Figure 10 ) and axial ( Figure 11 One or more sensitive displacement gauges 64A, 64B, 64C, 64D, 64E, and 64F (not shown) are installed in each direction to measure the radial and axial displacement of the rotary table 16.

[0071] In addition, the distance between the eccentricity measuring device 60 and the measuring frame 40 is determined by detecting the corner prism 50D set on the eccentricity measuring device 60 by using a laser emitted from the laser interferometer emission section 48D set on the measuring frame 40.

[0072] This embodiment can be converted into a measurement X-ray CT by retrofitting a non-measurement X-ray CT device.

[0073] Next, refer to Figure 12 The fifth embodiment of the present invention will now be described.

[0074] This embodiment is obtained by changing the position and eccentricity measuring component of the rotary table 16 in the fourth embodiment to a laser tracker 70 installed on the measuring frame 40.

[0075] The laser tracker 70 measures the position and eccentricity of the rotary table 16, for example, by using a cat's eye stone 74 provided with a cylindrical measuring object fixing fixture 72.

[0076] Other points are the same as in the described implementation, so the description is omitted.

[0077] Furthermore, while the embodiment shown presents an example of a combination of a measuring frame and a sensor, the combination of the measuring frame and sensor is not limited thereto and can be any combination as needed. The type of marking is also not limited to LEDs.

[0078] It will be apparent to those skilled in the art that the embodiments described above are merely illustrative, representing the application of the principles of the invention. Those skilled in the art can readily devise various other embodiments without departing from the spirit and scope of the invention.

Claims

1. A measurement X-ray CT apparatus having a rotary table for mounting a measurement object and a scanning mechanism capable of moving the rotary table to an arbitrary position in a measurement space region between an X-ray source and an X-ray detector, and the measurement X-ray CT apparatus performs CT scanning by irradiating an X-ray to the measurement object on the basis of previously correcting a geometric positional relationship of a focal point of the X-ray source, the X-ray detector, and a rotation center of the rotary table, thereby acquiring a projection image, and generates a three-dimensional image of the measurement object by performing CT reconstruction on the projection image, the measurement X-ray CT apparatus characterized by comprising: a metrology frame provided at positions of the X-ray source and the X-ray detector across the rotary table; and a position sensor configured to the metrology frame for sequentially acquiring a correction value of the geometric positional relationship of the focal point of the X-ray source and the X-ray detector in CT scanning, wherein the measurement X-ray CT apparatus using the correction value as a parameter for CT reconstruction.

2. The measurement X-ray CT apparatus according to claim 1, characterized in that the metrology frame is a cuboid.

3. A measurement X-ray CT apparatus having a rotary table for mounting a measurement object and a scanning mechanism capable of moving the rotary table to an arbitrary position in a measurement space region between an X-ray source and an X-ray detector, and the measurement X-ray CT apparatus performs CT scanning by irradiating an X-ray to the measurement object on the basis of previously correcting a geometric positional relationship of a focal point of the X-ray source, the X-ray detector, and a rotation center of the rotary table, thereby acquiring a projection image, and generates a three-dimensional image of the measurement object by performing CT reconstruction on the projection image, the measurement X-ray CT apparatus characterized by comprising: a metrology frame provided at positions of the rotary table and the X-ray source; and a camera provided to the metrology frame, the measurement X-ray CT apparatus detecting a marker provided to the X-ray detector by the camera, and sequentially acquiring a correction value of the geometric positional relationship of the focal point of the X-ray source and the X-ray detector in CT scanning, the measurement X-ray CT apparatus using the correction value as a parameter for CT reconstruction.

4. The measurement X-ray CT apparatus according to claim 3, characterized in that the metrology frame is a cube.

5. A measurement X-ray CT apparatus having a rotary table for mounting a measurement object and a scanning mechanism capable of moving the rotary table to an arbitrary position in a measurement space region between an X-ray source and an X-ray detector, and the measurement X-ray CT apparatus performs CT scanning by irradiating an X-ray to the measurement object on the basis of previously correcting a geometric positional relationship of a focal point of the X-ray source, the X-ray detector, and a rotation center of the rotary table, thereby acquiring a projection image, and generates a three-dimensional image of the measurement object by performing CT reconstruction on the projection image, the measurement X-ray CT apparatus characterized by comprising: a metrology frame provided at a position of the X-ray source; and a laser interferometer provided to the metrology frame, The measurement X-ray CT device detects a corner cube prism provided to an X-ray detector by the laser interferometer, and sequentially acquires a correction value of a geometric positional relationship between a focal point of an X-ray source and the X-ray detector in CT scanning, The measurement X-ray CT device uses the correction value as a parameter for CT reconstruction.

6. The measurement X-ray CT device according to claim 1, wherein An eccentricity measurer is provided to the rotary table, and a sensor for detecting a position of the eccentricity measurer is provided to the metrology frame.

7. The measurement X-ray CT device according to claim 6, wherein A reference surface for eccentricity measurement is formed on an outer periphery of the rotary table.

8. The measurement X-ray CT device according to claim 1, wherein A sensor for detecting a position of the rotary table is provided to the metrology frame.

9. The measurement X-ray CT device according to claim 8, wherein The sensor is a laser tracker that detects an alexandrite provided to a measurement object fixing jig on the rotary table.

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