Industrial CT scanning geometric structure detection result evaluation and process parameter setting method

Abstract

The invention relates to an industrial CT scanning geometric structure detection result evaluation and process parameter setting method. The detection result evaluation method comprises the steps that a uniform blank is adopted to manufacture a test block with the diameter being D; the test block and the detected sample are both placed on a rotary table, the test block is located on the extension of the long edge of the scanning section face of the detected sample, an X-ray machine is started to conduct CT scanning on the detected sample and the test block, and a CT image is obtained; in a CT image, an image of an area where a test block is located is intercepted, a gray threshold is set, threshold segmentation processing is carried out on the intercepted image, edge contour lines of the threshold segmentation image of the test block are extracted, ellipse fitting is carried out on position information of all the contour lines, an optimal fitting result is calculated, and the lengths of a long axis and a short axis of an ellipse are obtained. Dividing the length of the long axis of the ellipse by the length of the short axis to obtain the shape degree value of the ellipse; if the shape degree value of the ellipse is smaller than a set shape degree threshold value, it is judged that the geometric structure precision of the current CT detection result meets the requirement.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial CT scanning, and particularly relates to a method for evaluating results of industrial CT scanning geometry detection and setting process parameters. BACKGROUND

[0002] Industrial CT detection technology is an electromagnetic non-destructive detection technology based on X-rays, which is widely used in the fields of industrial non-destructive testing, medical health and the like, and has the advantages of intuitive imaging, quantitative, positioning and qualitative accuracy. The traditional industrial CT imaging principle is that an X-ray source, a detected object and a detector are on an axis, the X-ray source emits X-rays of a certain energy, the detected object is penetrated by the X-rays, on the other side of the detected object, the detector receives the attenuation law and distribution of the X-rays after penetrating the detected object, the X-ray source and the detector are rotated (360°) around the detected object in a circumferential direction, a plurality of penetration images are collected in the circumferential direction, and the attenuation law and distribution of the X-rays are displayed in the form of images through computer information processing and image reconstruction technology.

[0003] Non-destructive inspection of structure is an important application of industrial CT technology, and in the detection, detection process setting is a very important link, and the detection process closely related to the CT scanning forming quality includes: magnification, detector parameters, sampling amplitude and spatial resolution, etc. How to develop a reasonable and efficient detection process is an important link in the application of industrial CT technology. BS ISO15708-3:2017 stipulates that in order to realize the ideal geometry, the projection sampling amplitude should be not less than π / 2×matrix size, the standard gives the upper limit of the sampling amplitude, which is difficult to implement in daily detection. In order to quickly respond to the process setting requirements of different structure sizes of detected objects, therefore, it is urgently needed to form a kind of industrial CT scanning geometry detection process parameter rapid setting and evaluation method for specific objects in engineering application.

[0004] Currently, relevant domestic and international standards provide rules for setting process parameters for industrial CT inspection. First, a ball or forest ball is scanned to measure the center-to-center distance, which is then compared with the true value (measured by a coordinate measuring machine) to determine the pixel size of the industrial CT inspection result. Furthermore, these standards provide upper limits for process parameter setting, but do not offer methods for rapid quantification. While some literature studies the impact of a single process parameter on CT image quality for a specific inspection object, the conclusions are that the analysis of the pattern does not provide quantitative setting formulas or methods. Other literature studies methods for quantitatively determining process parameters for defect detection capability, but does not address the quantification of process parameters for geometric structure inspection. Some studies use orthogonal experimental methods to determine the optimal inspection process, but this requires extensive data comparison and a long process exploration period. Therefore, the current research status quo demonstrates a lack of a method for evaluating inspection results and setting process parameters based on precise geometric structure requirements. Summary of the Invention

[0005] The first technical problem to be solved by the present invention is to provide a simple, fast and stable method for evaluating the detection results of industrial CT scan geometric structures, which is in contrast to the above-mentioned prior art.

[0006] The second technical problem to be solved by the present invention is to provide a method for setting process parameters for industrial CT scanning geometric structure detection, which is in contrast to the above-mentioned prior art, for determining the process parameters in the above-mentioned method for evaluating the results of industrial CT scanning geometric structure detection.

[0007] The technical solution adopted by the present invention to solve the first technical problem mentioned above is: a method for evaluating the detection results of geometric structures in industrial CT scans, characterized by comprising the following steps:

[0008] Step 1: Use a uniform blank to manufacture a test block. The diameter of the test block is D, where D is the minimum structural dimension.

[0009] Step 2: The industrial CT system includes an X-ray machine, a turntable, and a detector arranged at intervals. The test block and the sample to be tested are placed on the turntable, with the test block located on the long side of the scanning slice of the sample to be tested. The X-ray machine is turned on to perform CT scanning on the sample to be tested and the test block to obtain CT images.

[0010] Step 3: In the CT image, the image of the area where the test block is located is cropped, and a grayscale threshold is set. Threshold segmentation is performed on the cropped image to extract the edge contour line of the threshold segmentation image of the test block. The position information of all contour lines is fitted to an ellipse. The optimal fitting result is calculated to obtain the length of the major axis and minor axis of the ellipse. The length of the major axis of the ellipse is divided by the length of the minor axis to obtain the shape value of the ellipse.

[0011] Step 4, judging whether the shape value of the ellipse is greater than or equal to the set shape threshold value, if yes, determining that the geometric structure accuracy of the current CT detection result does not meet the requirement; if no, determining that the geometric structure accuracy of the current CT detection result meets the requirement.

[0012] Preferably, the test block in the step 1 is a cylinder or a sphere.

[0013] The technical scheme adopted by the present application to solve the second technical problem is: a process parameter setting method for industrial CT scanning geometric structure detection, used for determining the process parameters in the above-mentioned industrial CT scanning geometric structure detection result evaluation method, characterized in that it comprises the following steps:

[0014] Step S1, the industrial CT system comprises an X-ray machine, a turntable and a detector arranged in sequence with intervals, the distance between the X-ray machine and the center of the turntable is set as SOD, and the distance between the X-ray machine and the detector is set as SDD;

[0015] The center of the turntable is taken as the image center position of the CT scanning simulation graph, the focal point position of the X-ray machine, the detector position and the circular test block position are plotted in the CT scanning simulation graph, the diameter of the circular test block is D, and the circular test block is located between the focal point of the X-ray machine and the image center;

[0016] Step S2, taking the focal point of the X-ray machine as the starting point, straight lines are drawn to each detection element on the detector in sequence, the length of each straight line passing through the circular test block is calculated, and a one-dimensional projection array is formed;

[0017] Step S3, the circular test block is rotated around the center of the turntable for one revolution, the one-dimensional projection array is calculated once every 360° / f, f sets of one-dimensional projection arrays are arranged in parallel, an nxf circumferential two-dimensional projection array is formed, the nxf circumferential two-dimensional projection array is subjected to CT reconstruction, and a reconstructed CT image is obtained; n is the resolution of the detector;

[0018] Step S4, in the reconstructed CT image, the image of the circular region is selected, and the circularity and the shape of the circular test block are calculated.

[0019] Step S5, judging whether the circularity of the circular test block is less than or equal to the set circularity threshold value and whether the shape degree of the circular test block is less than or equal to the set shape degree threshold value, if yes, it is determined that the current detection process parameter satisfies the requirement of the geometric structure precision, that is, the distance SOD between the current X-ray machine and the center of the turntable, the distance SDD between the X-ray machine and the detector and the sampling amplitude f in step S3 are determined as the process parameters in the above-mentioned evaluation method of the industrial CT scanning geometric structure detection result, and the process ends; if no, it is determined that the current detection process does not satisfy the requirement of the geometric structure precision, the distance SOD between the X-ray machine and the center of the turntable, the distance SDD between the X-ray machine and the detector and the sampling amplitude f in step S3 are adjusted, and the process goes back to step S1.

[0020] Preferably, the magnification M of the industrial CT system in step S1 satisfies

[0021] m is the size of a single detection element of the detector, and the units of D and m are millimeters.

[0022] In order to obtain the optimal process parameters through simulation, in the CT scanning simulation diagram, the distance between the circular test block and the image center is L' pixels, the distance between the detector and the image center is SDD' pixels, the distance between the focus of the X-ray machine and the image center is SOD' pixels, and the diameter of the circular test block is D' pixels.

[0023] L is the distance between the center of the circular test block and the center of the turntable. The units of L, SDD and SOD are millimeters.

[0024] In order to facilitate simulation, in the CT scanning simulation diagram, the positions of the focus, the image center and the center of the circular test block are on the same straight line.

[0025] Preferably, the circularity calculation method of the circular test block in step S4 is: performing threshold segmentation processing on the selected circular region image, counting the number s of pixels occupied by the circle in the threshold segmentation image, extracting the edge contour line of the circle in the threshold segmentation image, fitting the position information of all contour lines into a circle, and obtaining the optimal radius value r according to the optimal fitting result, and then

[0026] Preferably, the shape degree calculation method of the circular test block in step S4 is: performing threshold segmentation processing on the selected circular region image, extracting the edge contour line of the circle in the threshold segmentation image, fitting the position information of all contour lines into an ellipse, obtaining the lengths of the major axis and the minor axis of the ellipse according to the optimal fitting result, and obtaining the shape degree value of the ellipse by dividing the length of the major axis by the length of the minor axis.

[0027] Compared with the prior art, the method has the advantages that the method can evaluate the structural reconstruction clarity of the specific object of the current detection process by using a simple test block, and the method can calculate the optimal detection process suitable for clear geometric structure without processing a specific test block. Therefore, the method is easy to realize automatic measurement, and the measurement result is fast and stable. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 Fig. 1 is a position image of a cylindrical test block and a sample to be detected in the embodiment one of the present application;

[0029] Figure 2 Fig. 2 is a processing process diagram of a CT image in the embodiment one of the present application; wherein Figure 2 (a) in Fig. 2 is a two-dimensional CT image of a cylindrical test block, Figure 2 (b) in Fig. 2 is an image after threshold segmentation, Figure 2 (c) in Fig. 2 is an edge contour line image;

[0030] Figure 3 Fig. 3 is a CT scanning simulation diagram in the embodiment one of the present application;

[0031] Figure 4 Fig. 4 is an image in which a straight line is drawn from the focus of an X-ray machine to each detection element on the detector in the embodiment one of the present application;

[0032] Figure 5 Fig. 5 is a nxf circumferential two-dimensional projection array in the embodiment one of the present application;

[0033] Figure 6 Fig. 6 is a reconstructed CT image in the embodiment one of the present application;

[0034] Figure 7 Fig. 7 is a circular region image selected in the embodiment one of the present application;

[0035] Figure 8 Fig. 8 is a circle fitting image in the embodiment one of the present application;

[0036] Figure 9 Fig. 9 is a processing process diagram of a CT image in the embodiment two of the present application; wherein Figure 9 (a) in Fig. 9 is a CT image of a spherical test block, Figure 9 (b) in Fig. 9 is an image after threshold segmentation, Figure 9 (c) in Fig. 9 is an edge contour line image. DETAILED DESCRIPTION

[0037] The present application will be further described in detail below with reference to the embodiments of the drawings.

[0038] Embodiment one:

[0039] The evaluation method for industrial CT scan geometric structure detection results in this embodiment includes the following steps:

[0040] Step 1: Use a uniform blank to manufacture a test block. The diameter of the test block is D, where D is the minimum structural dimension.

[0041] In this embodiment, the test block is a cylinder made of aluminum alloy. The maximum penetration thickness of the sample is calculated, and the structural diameter D that needs to be clearly characterized is set according to the maximum penetration thickness. In this embodiment, D = 5.0 mm. The value of D is calibrated by a high-precision coordinate measuring machine.

[0042] Step 2: The industrial CT system includes an X-ray machine, a turntable, and a detector arranged at intervals. The test block and the sample to be tested are placed on the turntable, with the test block located on the long side of the scanning slice of the sample to be tested. The X-ray machine is turned on to perform CT scanning on the sample to be tested and the test block to obtain CT images.

[0043] When placing the cylindrical test block, ensure that its central axis is perpendicular to the turntable plane. The scanning parameters of the industrial CT system are: integration time of 0.5s, tube voltage of 90kV, tube current of 160mA, and sampling amplitude of 600pic, etc. The relative position of the cylindrical test block to the sample being tested is as follows: Figure 1 As shown, Figure 1 The scanning slice of the sample being tested is basically rectangular. The reason for placing the test block on the long side of the scanning slice of the sample being tested is that the accuracy decreases as the test block is placed further away. If the result calculated at the farthest position meets the requirements, then the accuracy inside will meet the testing requirements.

[0044] Step 3: In the CT image, the image of the area where the test block is located is cropped, and a grayscale threshold is set. Threshold segmentation is performed on the cropped image to extract the edge contour line of the threshold segmentation image of the test block. The position information of all contour lines is fitted to an ellipse. The optimal fitting result is calculated to obtain the length of the major axis and minor axis of the ellipse. The length of the major axis of the ellipse is divided by the length of the minor axis to obtain the shape value of the ellipse.

[0045] The specific processes of threshold segmentation, edge contour extraction, and ellipse fitting described above are all existing technologies and will not be elaborated here.

[0046] like Figure 2 As shown, Figure 2 Image (a) in the image is a two-dimensional CT image of the cylindrical specimen. Figure 2 Image (b) in the image is the image after thresholding. Figure 2 (c) in the image represents the edge contour line.

[0047] Step 4: Determine whether the shape accuracy value of the ellipse is greater than or equal to the set shape accuracy threshold. If yes, it is determined that the geometric structure accuracy of the current CT detection result does not meet the requirements; otherwise, it is determined that the geometric structure accuracy of the current CT detection result meets the requirements.

[0048] The above-mentioned shape threshold can be confirmed based on experiments or experience. In this embodiment, the shape threshold is set to 1.02.

[0049] To obtain the optimal process parameters in the above-mentioned evaluation method for industrial CT scan geometric structure inspection results, the process parameters in the evaluation method for industrial CT scan geometric structure inspection results are determined by the following process parameter setting method. The process parameter setting method for industrial CT scan geometric structure inspection in this embodiment includes the following steps:

[0050] Step S1: The industrial CT system includes an X-ray machine, a turntable, and a detector arranged sequentially at intervals. The distance between the X-ray machine and the center of the turntable is set as SOD, and the distance between the X-ray machine and the detector is set as SDD.

[0051] The center of the turntable is used as the image center of the CT scan simulation. The focal point, detector, and circular test block of the X-ray machine are drawn in the CT scan simulation. The diameter of the circular test block is D, and the circular test block is located between the focal point of the X-ray machine and the image center.

[0052] The magnification M of the industrial CT system satisfies M = SDD / SOD, where m is the size of a single detector element, and both D and m are in millimeters.

[0053] like Figure 3 As shown, in the CT scan simulation, the focal point, the image center, and the center of the circular test block are on the same straight line. In addition, in the CT scan simulation, the distance between the circular test block and the image center is L′ pixels, the distance between the detector and the image center is SDD′ pixels, the distance between the X-ray machine's focal point and the image center is SOD′ pixels, and the diameter of the circular test block is D′ pixels.

[0054] L is the distance between the center of the circular test block and the center of the turntable; The units for L, SDD, and SOD are all millimeters;

[0055] In this embodiment, M = 2, SOD = 200mm, and SDD = 400mm; taking the size of a single detector element m = 0.2mm as the unit, the cylinder diameter D is converted to pixels D′ = 25, SOD is converted to pixels SOD′ = 1000, SDD is converted to pixels SDD′ = 2000, and L = 40mm is converted to pixels L′ = 200.

[0056] Step S2, taking the focal point of the X-ray machine as the starting point, draw a straight line to each detector element on the detector in turn, calculate the length of each straight line passing through the circular test block, the length unit is pixel, form a one-dimensional projection array;

[0057] As shown in Figure 4 , the image of drawing a straight line to each detector element on the detector in turn, taking the focal point of the X-ray machine as the starting point;

[0058] Step S3, rotate the circular test block around the center of the turntable for one revolution, calculate the one-dimensional projection array once every 360° / f, and arrange f groups of one-dimensional projection arrays in parallel to form an nxf circumferential two-dimensional projection array, perform CT reconstruction on the nxf circumferential two-dimensional projection array to obtain the reconstructed CT image; n is the resolution of the detector; f is the sampling amplitude; f=400 in this embodiment;

[0059] As shown in Figure 5 , the nxf circumferential two-dimensional projection array, and the reconstructed CT image is shown in Figure 6 ;

[0060] Step S4, select the image of the circular region in the reconstructed CT image, and calculate the circularity and shape of the circular test block;

[0061] The circularity calculation method of the circular test block is: threshold segmentation processing is performed on the selected circular region image, the number of pixels s occupied by the circle in the threshold segmentation image is counted, and the edge contour line of the circle in the threshold segmentation image is extracted. The position information of all contour lines is fitted into a circle, and the optimal radius value r is obtained according to the optimal fitting result. The unit of r is also pixel, then As shown in Figure 7 , the selected circular region image; as shown in Figure 8 , the circle fitting image;

[0062] The shape calculation method of the circular test block is: threshold segmentation processing is performed on the selected circular region image, the edge contour line of the circle in the threshold segmentation image is extracted, the position information of all contour lines is fitted into an ellipse, and the length of the major axis and the minor axis of the ellipse is obtained according to the optimal fitting result. The shape value of the ellipse is obtained by dividing the length of the major axis by the length of the minor axis;

[0063] Step S5: Determine whether the roundness of the circular test block is less than or equal to the set roundness threshold, and whether the shape of the circular test block is less than or equal to the set shape threshold. If yes, it is determined that the current detection process parameters meet the geometric accuracy requirements, that is: determine the current distance SOD between the X-ray machine and the turntable center, the distance SDD between the X-ray machine and the detector, and the number of sampling amplitudes f in step S3 as the process parameters in the above-mentioned industrial CT scan geometric structure detection result evaluation method, and end; if no, it is determined that the current detection process does not meet the geometric accuracy requirements, adjust the distance SOD between the X-ray machine and the turntable center, the distance SDD between the X-ray machine and the detector, and the number of sampling amplitudes f in step S3, and proceed to step S1.

[0064] Example 2:

[0065] Unlike Example 1, the test block in this example is a sphere made of aluminum alloy with a diameter of D = 5.0 mm; Figure 9 As shown, Figure 9 (a) in the image is a CT image of the spherical specimen. Figure 9 Image (b) in the image is the image after thresholding. Figure 9 (c) in the figure represents the edge contour image. In this embodiment, the CT scan is a cone-beam scanning method to acquire a three-dimensional CT image.

[0066] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for evaluating the results of industrial CT scan geometric structure inspection, characterized in that... Includes the following steps: Step 1: Use a uniform blank to manufacture a test block. The diameter of the test block is D, where D is the minimum structural dimension. Step 2: The industrial CT system includes an X-ray machine, a turntable, and a detector arranged at intervals. The test block and the sample to be tested are placed on the turntable, with the test block located on the long side of the scanning slice of the sample to be tested. The X-ray machine is turned on to perform CT scanning on the sample to be tested and the test block to obtain CT images. Step 3: In the CT image, the image of the area where the test block is located is cropped, and a grayscale threshold is set. Threshold segmentation is performed on the cropped image to extract the edge contour line of the threshold segmentation image of the test block. The position information of all contour lines is fitted to an ellipse. The optimal fitting result is calculated to obtain the length of the major axis and minor axis of the ellipse. The length of the major axis of the ellipse is divided by the length of the minor axis to obtain the shape value of the ellipse. Step 4: Determine whether the shape accuracy value of the ellipse is greater than or equal to the set shape accuracy threshold. If so, it is determined that the geometric accuracy of the current CT detection result does not meet the requirements. If not, then the geometric accuracy of the current CT scan result is determined to meet the requirements.

2. The method for evaluating the results of industrial CT scan geometric structure detection according to claim 1, characterized in that: The test block in step 1 is a cylinder or a sphere.

3. A method for setting process parameters for industrial CT scanning geometric structure inspection, used to determine the process parameters in the industrial CT scanning geometric structure inspection result evaluation method as described in any one of claims 1 or 2, characterized in that... Includes the following steps: Step S1: The industrial CT system includes an X-ray machine, a turntable, and a detector arranged sequentially at intervals. The distance between the X-ray machine and the center of the turntable is set as SOD, and the distance between the X-ray machine and the detector is set as SDD. The center of the turntable is used as the image center of the CT scan simulation. The focal point, detector, and circular test block of the X-ray machine are drawn in the CT scan simulation. The diameter of the circular test block is D, and the circular test block is located between the focal point of the X-ray machine and the image center. Step S2: Starting from the focal point of the X-ray machine, draw straight lines sequentially to each element on the detector, calculate the length of each line passing through the circular test block, and form a one-dimensional projection array. Step S3: Rotate the circular test block around the center of the turntable for one revolution. Every 360° / f revolutions, calculate the one-dimensional projection array once. Arrange the f sets of one-dimensional projection arrays in parallel to form an n×f circumferential two-dimensional projection array. Perform CT reconstruction on the n×f circumferential two-dimensional projection array to obtain the reconstructed CT image; n is the resolution of the detector. Step S4: In the reconstructed CT image, select the image of the circular region and calculate the roundness and shape of the circular test block; Step S5: Determine whether the roundness of the circular test block is less than or equal to the set roundness threshold, and whether the shape of the circular test block is less than or equal to the set shape threshold. If yes, it is determined that the current detection process parameters meet the geometric accuracy requirements, that is: determine the current distance SOD between the X-ray machine and the turntable center, the distance SDD between the X-ray machine and the detector, and the number of sampling amplitudes f in step S3 as the process parameters in the industrial CT scanning geometric structure detection result evaluation method as described in any one of claims 1 or 2 above, and end; if no, it is determined that the current detection process does not meet the geometric accuracy requirements, adjust the distance SOD between the X-ray machine and the turntable center, the distance SDD between the X-ray machine and the detector, and the number of sampling amplitudes f in step S3, and proceed to step S1.

4. The method for setting process parameters for industrial CT scanning geometric structure detection according to claim 3, characterized in that: The magnification M of the industrial CT system in step S1 satisfies m represents the size of a single detector element; both D and m are in millimeters.

5. The method for setting process parameters for industrial CT scanning geometric structure detection according to claim 4, characterized in that: In the CT scan simulation, the distance between the circular specimen and the image center is L. ′ The distance between the detector and the center of the image is SDD′ pixels, the distance between the focal point of the X-ray machine and the center of the image is SOD′ pixels, and the diameter of the circular test block is D′ pixels; L is the distance between the center of the circular test block and the center of the turntable; The units for L, SDD, and SOD are all millimeters.

6. The method for setting process parameters for industrial CT scanning geometric structure inspection according to any one of claims 3 to 5, characterized in that: In the CT scan simulation, the focal point, the image center, and the center of the circular test block are on the same straight line.

7. The method for setting process parameters for industrial CT scanning geometric structure inspection according to any one of claims 3 to 5, characterized in that: The method for calculating the roundness of the circular test block in step S4 is as follows: Threshold segmentation is performed on the selected circular region image; the number of pixels 's' occupied by the circle in the threshold segmented image is counted; the edge contour lines of the circle in the threshold segmented image are extracted; the position information of all contour lines is fitted to a circle; and the optimal radius value 'r' is obtained based on the optimal fitting result.

8. The method for setting process parameters for industrial CT scanning geometric structure detection according to claim 7, characterized in that: The method for calculating the shape of the circular test block in step S4 is as follows: perform threshold segmentation on the selected circular region image, extract the edge contour lines of the circle in the threshold segmentation image, perform ellipse fitting on the position information of all contour lines, obtain the lengths of the major axis and minor axis of the ellipse according to the optimal fitting result, and obtain the shape value of the ellipse by dividing the length of the major axis by the length of the minor axis.

Images