JP7038399B2 - Calibrator for CT equipment - Google Patents

Description

The present invention relates to a calibrator used when performing dimensional measurement using a CT device.

A computer tomography device (hereinafter referred to as a CT (Computed Tomography) device) that captures a cross-sectional image of a subject irradiates the subject with radiation (for example, X-rays) generated from a radiation source, and X-rays the subject. One-dimensional or two-dimensional X-rays transmitted from the subject at each predetermined rotation position during one rotation by rotating the X-rays relative to the X-rays on the rotation axis that intersects the direction of the optical axis of the line. A tomographic image or volume data is generated by detecting with an X-ray detector having a plurality of detection channels, acquiring a fluoroscopic image of the subject from the detector output, and reconstructing the image.

The industrial X-ray CT apparatus is used as an inspection machine for determining the presence or absence of cracks or internal defects in industrial products by using the tomographic data and volume data.

Further, using X-ray CT data analysis software, the surface of the subject can be extracted from the volume data and the dimensional measurement of the subject can be performed, which is also used as a three-dimensional measurement related to dimensional accuracy.

In Patent Document 1, a calibrator (a plurality of spheres are arranged outside a cylinder) is placed on a turntable instead of an object to be measured, and a transmission image is transmitted from an X-ray detector while rotating the turntable 360 degrees. The information is acquired, and the volume data is reconstructed by the computer system based on the X-ray source, the X-ray detector, and the stage position information. After that, using X-ray CT data analysis software, the boundary surface (boundary surface between air and material) of each sphere can be surface-extracted, and the diameter value, center coordinates, distance between spheres, and the like of each sphere can be obtained. The X-ray CT apparatus is calibrated by comparing these values with the values previously obtained by a contact-type coordinate measuring machine such as CMM (Coordinate Measuring Machine).

That is, the scaling is calibrated using the distance between spheres, and the offset is calibrated using the diameter value. FCD (Focus to Rotation Center Threshold) and FDD (Focus to Detector Threshold), which indicate the geometrical positional relationship of the X-ray CT device itself, are set for scaling calibration, and gray value in surface extraction is set for offset calibration. A calibrator that sets a threshold is disclosed.

However, in this calibration method, the measurement object to be actually measured and the X-ray CT scan at the time of calibration are separate scans, and the X-ray CT conditions are different. Even if the X-ray CT conditions input to the device are the same, the conditions are not exactly the same when considering the stability of the X-rays, and the gray value threshold value in surface extraction fluctuates based on the object to be measured. It does not become a calibration.

There is also the problem that calibration is required each time the FCD or FDD changes.

Japanese Unexamined Patent Publication No. 2014-190933

The present invention has been diligently researched and completed by paying attention to such a problem, and an object of the present invention is to provide a calibrator for simultaneously performing dimensional measurement and calibration by a CT device.

In order to solve the above problems, the present invention has a support that supports the object to be measured, a calibration that is provided on the support, has known dimensions, and is CT-scanned at the same time as the object to be measured. It is equipped with a reference body for use.

According to the present invention, it is possible to provide a calibrator for simultaneously performing dimensional measurement and calibration by a CT device.

It is an overall schematic diagram of the X-ray CT apparatus which concerns on Example 1 of this invention. It is a side view of the calibrator for an X-ray CT apparatus which concerns on Example 1 of this invention. It is a perspective view of the calibrator for an X-ray CT apparatus which concerns on Example 1. FIG. It is a side view in the case where the measurement object is arranged on the calibrator for the X-ray CT apparatus which concerns on Example 1. FIG. It is a side view in the case where the measurement object is arranged on the calibrator for the X-ray CT apparatus which concerns on Example 1 with a spacer. It is a perspective view of the calibrator for an X-ray CT apparatus which concerns on Example 2. FIG. It is a perspective view of the calibrator for an X-ray CT apparatus which concerns on Example 3. FIG. It is a perspective view of the calibrator for an X-ray CT apparatus which concerns on Example 4. FIG. It is a perspective view of the calibrator for an X-ray CT apparatus which concerns on Example 5. FIG. It is a perspective view of the calibrator for an X-ray CT apparatus which concerns on Example 6. FIG. It is a perspective view of the reference body which concerns on Example 6. FIG. It is a perspective view of the calibrator for an X-ray CT apparatus which concerns on Example 7. FIG.

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is an overall schematic view of an X-ray CT apparatus according to a first embodiment of the present invention. Here, an X-ray CT apparatus will be described as an example of the CT apparatus. The object 1 to be measured is placed on the support 2, and X-rays generated from the X-ray source 3 which is a radiation source are irradiated toward the object 1 to be measured. The support 2 is rotated relative to the X-ray by the rotation axis 5 of the support 2 that intersects the direction of the optical axis 4 of the X-ray source 3, and the object to be measured is measured at each predetermined rotation position during one rotation. The X-rays transmitted from 1 are detected by an X-ray detector 6 having a plurality of one-dimensional or two-dimensional detection channels, and a fluoroscopic image of the measurement object 1 is acquired from the output of the detector 6. Then, the volume data (or three-dimensional data) is reconstructed.

Further, the X-ray CT apparatus can change the distance from the X-ray focal point F by moving the support 2 and the detector 6 closer to or further from the X-ray focal point F of the X-ray source 3, and the focal point F and the rotation axis 5 can be changed. The shooting distance between FCD (Focus to rotation Center Distance) and the detection distance FDD (Focus to Detector Distance) between the focal point F and the detection surface of the detector 6 are changed, and the shooting magnification (=) according to the purpose is changed. FDD / FCD) can be changed.

In the case of FIG. 1, the measurement object 1 is two spheres at both ends, and it is possible to obtain the center coordinates of the spheres.

That is, the distance between the two balls has already been measured in advance by a three-dimensional coordinate measuring device such as CMM (Coordinate Measurement Machine). Then, surface extraction is performed to determine the boundary surface between the air and the material of the sphere from the volume data reconstructed from the X-ray CT apparatus, the sphere is recognized, the center coordinates of the sphere are obtained, and the distance between the two spheres is calibrated.

Here, when the center coordinates of the sphere are obtained, the measured value of the boundary surface, that is, the diameter fluctuates depending on the threshold value of the gray value in the surface extraction, but when the center coordinates of the sphere are obtained, the influence of the magnitude of the threshold value is small.

However, the dimensional measurement of the object to be measured is not limited to the measurement using the center coordinates.

That is, surface extraction for determining the boundary surface is very important because it is necessary to measure the distance between planes, the wall thickness, and the geometrical tolerance using the boundary surface instead of the center coordinates. In addition, a calibrator and calibration method based on surface extraction is needed.

In the present embodiment, a calibrator and a calibration method capable of performing dimensional measurement more accurately are provided. By simultaneously performing an X-ray CT scan of the calibrator and the object to be measured, more precise surface extraction is performed. In addition, since the X-ray CT scan of the calibrator and the object to be measured is performed at the same time, it is troublesome to perform the calibration and the dimensional measurement separately, and the X-ray CT scan for calibration is performed again because the FCD or FDD is changed. It is not necessary to carry out separately.

<Construction of calibrator>
First, the configuration of the calibrator for the X-ray CT apparatus according to the first embodiment will be described with reference to FIGS. 2, 3, 4, and 5.

FIG. 2 is a side view of the calibrator for an X-ray CT apparatus according to the first embodiment of the present invention. FIG. 3 is a perspective view of the calibrator for the X-ray CT apparatus according to the first embodiment.

The calibrator consists of a circular support 100, a plurality of stanchions (210, 220, 230), and a reference body (310, 320, 330) of known dimensions resting on each stanchion. .. The material of the support 100 may be any metal such as iron. The support is not limited to a circular shape, but may be a non-circular shape. The support may have a shape that can be easily held by a fixed chuck device or the like on the rotary table of the X-ray CT device.

The plurality of columns (210, 220, 230) need to be placed at a position (for example, an outer edge) away from the central axis of the support 100. This is to place the object to be measured on the central axis. The shape of the support column is a cylinder, but the shape is not limited to this, and any shape may be used as long as the reference body can be mounted. The columns are preferably made of a material having the same or lower X-ray absorption rate than the object to be measured (for example, CFRP (Carbon Fiber Reinforced Plastics)). Further, since the support column does not have to move from the support 100 during measurement, it may be attached to the support with an adhesive or the like.

The reference body (310, 320, 330) is a hexahedron, and it is required that the width, height, and depth length (dimensions) are known. The hexahedron is not limited to the hexahedron, and any polyhedron may be used.

Further, it is desirable that the dimensions of each reference body are different. This is because it becomes possible to measure objects of various sizes. Further, it is desirable that the heights of the columns on which the reference bodies are placed are different so that the transmitted images of the reference bodies do not overlap during the X-ray CT scan. Further, it is preferable that the material of the reference body is made of a material having the same or lower X-ray absorption rate than the object to be measured, like the support column. For example, if the object to be measured is aluminum, the reference body may be aluminum, alumina, silicon carbide, silicon nitride, ceramics such as NEXCERA (TM) (ultra-low thermal expansion ceramics), ruby, or the like.

In this embodiment, a plurality of columns (210, 220, 230) and reference bodies (310, 320, 330) are provided, but the number of columns and the reference body may be one or more.

FIG. 4 is a side view when the measurement object is arranged on the calibrator for the X-ray CT apparatus according to the first embodiment. In the object to be measured 400, the white central portion is hollow and the black outer portion is covered with a predetermined material.

FIG. 5 is a side view when an object to be measured is placed on the calibrator for the X-ray CT apparatus according to the first embodiment via a spacer. The spacer 500 is arranged to provide an inclination between the support 100 and the object to be measured 400. Further, the spacer 500 is preferably made of a material having a low X-ray absorption rate (for example, plastic or styrofoam) with respect to the object to be measured.

<Operation of X-ray CT device using calibrator>
First, the X-ray CT apparatus performs a CT scan of the measurement object 400 and the calibrator at the same time. By performing at the same time, the CT environment for calibration and the CT environment for dimension measurement become the same. That is, the X-ray conditions are the same for calibration and dimensional measurement. In addition, no pre-scan for calibration is required, and only one CT scan is required, which saves time and effort. In addition, calibration can be done using a reference body of known length.

The CT scan data acquired by the FDK (Feldkamp) method is reconstructed to generate volume data.

Next, the surface of each reference body and the object to be measured is extracted using the analysis software. Here, "VGStudio MAX" of Volume Graphics Co., Ltd. is used as general analysis software.

When reconstructed by the FDK (Feldkamp) method, the perspective image output from the detector 6 in FIG. 1 is a horizontal plane away from the optical axis 4 in FIG. 1 (for example, the upper surface and the lower surface of the measurement object 400 in FIG. 4). ) Is difficult to extract. Therefore, when the object to be measured 400 is placed diagonally on the spacer 500 as shown in FIG. 5, the horizontal plane disappears, and the surface can be extracted with higher accuracy than in the case of FIG.

In this embodiment, the reference bodies (310, 320, 330) are hexahedrons, not spheres. This is because in the case of a calibrator using a sphere as a reference body, horizontal planes (upper surface and lower surface) inevitably exist even if the calibrator is tilted.

FIG. 6 is a perspective view of the calibrator for the X-ray CT apparatus according to the second embodiment. In Example 1, the column was placed on the outer edge of the support 100 (210', 220', 230' in FIG. 6).

<Structure>
In the second embodiment, the support column is closer to the center of the support 100 than the 210', 220', and 230'. The stanchions (211, 221 and 231) and the reference bodies (311 and 321 and 331) resting on them are closer to the center of the support 100 than the positions of 210', 220' and 230'.

<Operation>
If the object to be measured placed in the center of the support 100 is small, the fluoroscopic image of the object to be measured may be magnified to the detector (6 in FIG. 1). In such a case, a CT scan for calibration using the support (211, 221, 231) centered on the outer edge of the support 100 and the reference body (311, 321, 331) on the support is used. CT scans for measuring the dimensions of the object to be measured can be performed at the same time. That is, only one CT scan is required.

FIG. 7 is a perspective view of the calibrator for the X-ray CT apparatus according to the third embodiment. In Example 1, the strut and the reference body were separate objects.

<Structure>
In the third embodiment, each reference body (2310, 2320, 2330) of the cylinder is integrated with the support. And the dimensions (diameter and height) of the cylinder are known.

<Operation>
Since the diameter and height of each reference body (2310, 2320, 2330) integrated with the column are known, a CT scan for measuring the dimensions of the object to be measured and an integrated column are used as in the first embodiment. CT scans for calibration using the reference body can be performed at the same time at one time.

FIG. 8 is a perspective view of the calibrator for the X-ray CT apparatus according to the fourth embodiment.

<Structure>
The fourth embodiment is also a reference body (2311, 2321, 2331) integrated with the support. Unlike Example 3, the reference body is a prism. And the dimensions (width, depth and height) of the prism are known.

<Operation>
Since the width, depth and height of each reference body (2311, 2321, 2331) integrated with the support column are known, the CT scan for measuring the dimensions of the object to be measured and the support column are as in the third embodiment. CT scans for calibration using an integrated reference can be performed simultaneously at one time.

FIG. 9 is a perspective view of the calibrator for the X-ray CT apparatus according to the fifth embodiment.

<Structure>
The fifth embodiment is also a reference body (2312, 2321, 2331) integrated with the support. Unlike the third embodiment, the support column has a cylindrical shape such as a cylinder. And the dimensions of the cylinder (outer diameter, inner diameter and height) are known.

<Operation>
Since the outer diameter, inner diameter, and height of each reference body (2312, 2321, 2331) integrated with the support are known, a CT scan for measuring the dimensions of the object to be measured and a reference are performed as in the third embodiment. A CT scan for calibration using a body-integrated strut can be performed simultaneously at one time.

FIG. 10 is a perspective view of the calibrator for the X-ray CT apparatus according to the sixth embodiment.

<Structure>
The reference body 3000 of the sixth embodiment has a concave shape having a recess in the center, and unlike the first to fifth embodiments, at least one is sufficient. The dimensions (height, width, depth) of this reference body 3000 are known. Further, it is preferable that the reference body 3000 is placed at a position (for example, an outer edge) away from the central axis (corresponding to the rotation axis 5 in FIG. 1) of the support 100. Although the object to be measured is placed on the central axis, the object to be measured is omitted in FIG. 10 for convenience of explanation.

FIG. 11 is a perspective view of the reference body 3000 according to the sixth embodiment. The reference body 3000 has a concave shape with a recess in the center in the width direction.

The reference body 3000 is provided with a first cube portion 3200 on the left side and a second cube portion 3300 on the right side at predetermined intervals in the width direction on the base 3100. The base 3100, the first cube portion 3200, and the second cube portion 3300 are integrally formed of Nexera as a material. In addition, you may assemble after forming separately.

<Operation>
First, the X-ray CT apparatus simultaneously performs a CT scan of a calibrator composed of a disk-shaped support 100 and a reference body 3000 having known dimensions, and an object to be measured (not shown). By performing at the same time, the CT environment for calibration and the CT environment for dimension measurement become the same. That is, the X-ray conditions are the same for calibration and dimensional measurement. In addition, no pre-scan for calibration is required, and only one CT scan is required, which saves time and effort. In addition, calibration can be done using a reference body of known length.

The present embodiment is characterized in that the cross section of the reference body has a concave shape, and one reference body has two types of measurement directions (the same direction and the opposite direction). That is, it is characterized in that it has two types of reference lengths. Here, the first cube portion 3200 and the second cube portion 3300 face each other, and the facing surfaces are the inner surfaces (3200a, 3300a), and the opposite surfaces are the outer surfaces (3200b, 3300b). Call.

The first reference length 3010 is the length between the surfaces in the same direction, and is a distance of 20 mm from the outer surface 3200b of the first cube portion to the inner surface 3300a of the second cube portion. The second reference length 3020 is the length between the facing surfaces, and is the width (thickness) of 10 mm of the first cube or the width (thickness) of 5 mm of the second cube. In this embodiment, the wall thickness of the first cube portion and the wall thickness of the second cube portion are made different, but they may be the same.

By using the first reference length 3010, it is possible to calibrate the voxel size deviation of the volume data reconstructed from the X-ray CT apparatus (see FIG. 1) and calibrate the scaling. This is structurally characterized in that the outer surface 3200b of the first cube and the inner surface 3300a of the second cube face in the same direction. Even if the outer surface 3200b of the first cube is displaced, the inner surface 3300a of the second cube is also displaced in the same direction, canceling each other out and not affecting the voxel size, so that scaling with high accuracy is possible. It has the effect of being able to calibrate.

The deviation in voxel size is due to the deviation in the detection distance of FCD and FDD.

Further, by using the second reference length 3020, the surface boundary (the boundary surface between air and the material) can be calibrated, that is, the offset can be calibrated. This is structurally characterized in that, for example, when a wall thickness of 10 mm of the first cube portion 3200 is used, the inner surface 3200a and the outer surface 3200b facing each other sandwich the first cube portion 3200. The sandwiching has the effect of calibrating the deviation of the surface boundaries of the inner surface 3200a and the outer surface 3200b of the first cube portion 3200.

When the wall thickness of the second cube portion 3300 is 5 mm, there is a structural feature in that the inner surface 3300a and the outer surface 3300b that face each other sandwich the second cube portion 3300. The sandwiching has the effect of calibrating the deviation of the surface boundaries of the inner surface 3300a and the outer surface 3300b of the second cube portion 3300.

In the first to fifth embodiments, the CT environment for calibration and the CT environment for dimension measurement can be made the same, but the calibration is performed in a mixture of scaling calibration and offset calibration. On the other hand, in this embodiment, the CT environment for calibration and the CT environment for dimension measurement can be made the same, and scaling calibration is performed, then offset calibration, and so on. Since the calibration of the offset and the calibration are performed separately, there is an effect that more accurate calibration can be performed as a whole.

FIG. 12 is a perspective view of the calibrator for the X-ray CT apparatus according to the seventh embodiment.

<Structure>
In Example 7, the reference body 4000 has a rotationally symmetric cylindrical shape, and the thick portion of the cylinder is along the outer edge of the support 100, and the measurement target is in the hollow portion of the reference body 4000 (see 400 in FIG. 4). Can be installed.

A spacer 5000 for the reference body is provided between the support body 100 and the reference body 4000. The spacer 5000 for the reference body is made of a material (for example, plastic, styrofoam) having a low X-ray absorption rate with respect to the object to be measured.

If the spacer 5000 for the reference body is disk-shaped and the support 100 cannot be seen from the hollow portion of the reference body 4000, the object to be measured (see 400 in FIG. 4) is placed on the spacer 5000 for the reference body. Become. On the other hand, when the spacer 5000 for the reference body is cylindrical and the support 100 can be seen from the hollow portion of the reference body 4000, the measurement object 400 is placed on the support 100 via the spacer 500 as shown in FIG. It will be.

<Operation>
Similar to Example 6, this embodiment is also characterized in that one reference body has two types of measurement directions (same direction and opposite directions) when considered in terms of a cross section in the radial direction of the reference body. That is, it is characterized in that it has two types of reference lengths. The first reference length 4010 in the case of this embodiment is a distance of 115 mm from one end point (point A) of the outer peripheral surface 4000b of the reference body to the other end point (point B) of the inner peripheral surface 4000a of the reference body. .. Further, the second reference length 4020 is a thickness of 5 mm (distance from the point B to the point C) of the thick portion 4020 of the reference body 4000.

By using the first reference length 4010, it is possible to calibrate the voxel size deviation of the volume data reconstructed from the X-ray CT apparatus (see FIG. 1) and calibrate the scaling. This is structurally characterized in that one end point (point A) of the outer peripheral surface 4000b of the reference body and the other end point (point B) of the inner peripheral surface 4000a of the reference body face in the same direction. Even if the point A shifts, the point B also shifts in the same direction, cancels each other out, and does not affect the voxel size. Therefore, it has the effect of enabling highly accurate scaling calibration. ..

Further, by using the second reference length 4020, the surface boundary (the boundary surface between air and the material) can be calibrated, that is, the offset can be calibrated. This is structurally characterized in that when a reference body 4000 having a wall thickness of 5 mm is used, the opposing points B and C sandwich the wall thickness. Then, this sandwiching has the effect of calibrating the deviation of the surface boundaries of points B and C.

In this embodiment as in the sixth embodiment, the CT environment for calibration and the CT environment for dimension measurement can be made the same, scaling calibration is performed, and then offset calibration is performed. Since the scaling calibration and the offset calibration are performed separately, there is an effect that more accurate calibration can be performed as a whole.

Although the examples (including modified examples) of the present invention have been described above, two or more of these examples may be combined and carried out. Alternatively, one of these examples may be partially implemented. Furthermore, among these, two or more examples may be partially combined and carried out.

For example, even if a cylinder (third embodiment), a prism (fourth embodiment), and a cylinder (fifth embodiment) are combined as a reference body integrated with a column having known dimensions and different heights. good. In this case, it is necessary that the dimensions of each reference body are known, and it is preferable that the dimensions of each reference body are different. Further, the lower portion of the reference body 4000 may be closed so that the support 100 cannot be seen from the hollow portion of the reference body 4000.

The present invention is not limited to the description of the embodiments of the above invention. Various modifications are also included in the present invention to the extent that those skilled in the art can easily conceive without departing from the description of the scope of claims.

For example, a hexahedron (first embodiment) is used as a reference body, but the present invention is not limited to this, and a sphere may be used.

1,400 Object to be measured 3 X-ray source 4 Optical axis 5 Rotating axis 6 Detector 2,100 Support 210, 220, 230 Strut 310, 320, 330, 2310, 2311, 2312, 2320, 2321, 2322, 2330, 2331, 2332, 3000, 4000 Reference body 500 Spacer 3100 Base 3200 First cube part 3300 Second cube part 3010, 4010 First reference length 3020, 4020 Second reference length 5000 Spacer for reference body

Claims (7)

A support that supports the object to be measured and
A reference body of a polyhedron for calibration, which is provided on the support, has known dimensions, and is CT-scanned at the same time as the object to be measured.
Equipped with
The reference body is a calibrator for a CT device provided around the object to be measured . A support provided between the support and the reference body is provided .
The calibrator for a CT device according to claim 1 , wherein the reference body and the support column are present, and the dimensions of each reference body and each support column are different . A support that supports the object to be measured and
A reference body for calibration, which is provided on the support, has known dimensions, and is CT-scanned at the same time as the object to be measured.
It is a calibrator for CT equipment equipped with
The reference body has a base and a first cube portion and a second cube portion provided on the base at predetermined intervals.
In the first cube portion and the second cube portion, the facing surfaces are the inner surfaces thereof, and the opposite surfaces are the outer surfaces thereof.
The distance from the outer surface of the first cube to the inner surface of the second cube is defined as the first reference length.
A calibrator for a CT device having the thickness of the first cube or the thickness of the second cube as the second reference length. The calibrator for a CT device according to claim 3 , wherein the base, the first cube portion, and the second cube portion are integrally formed. A support that supports the object to be measured and
A reference body for calibration, which is provided on the support, has known dimensions, and is CT-scanned at the same time as the object to be measured.
It is a calibrator for CT equipment equipped with
The reference body has a rotationally symmetric cylindrical shape.
The distance from one end point of the outer peripheral surface of the reference body to the other end point of the inner peripheral surface of the reference body is defined as the first reference length.
A calibrator for a CT device whose second reference length is the thickness of the thick portion of the reference body. The thick portion of the reference body is along the outer edge of the support.
The calibrator for a CT device according to claim 5 , wherein the object to be measured can be installed in a hollow portion of the reference body. The calibrator for a CT device according to claim 5 or 6 , wherein a spacer for the reference body is provided between the reference body and the support.

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