A three-dimensional reconstruction method based on B-scan images of dual phased array probes

Abstract

The present invention relates to the field of nondestructive testing, and provides a three-dimensional reconstruction method based on a dual-phased array probe B-scan image, comprising the following steps: using an ultrasonic phased array dual-probe device to detect a workpiece to be tested, and obtaining two groups of B-scan images of equal quantity and one-to-one correspondence; graying and filtering the two groups of images, respectively intercepting images equivalent to half the thickness of the workpiece, and performing splicing processing; screening images with defect echoes in the spliced ​​images, and filtering out noise through a two-dimensional trajectory judgment method; and performing three-dimensional reconstruction using the images with the noise filtered out. The present invention can be used in an actual strong noise factory to filter and remove noise through two-dimensional trajectory judgment, thereby increasing the recognition of small defects that are difficult to distinguish from noise. In addition, the three-dimensional model can accurately display the spatial information of the defect, such as the three-dimensional shape of the defect and its position in the workpiece, and has high visibility.

Description

Technical Field

[0001] The present invention relates to the field of nondestructive testing, and in particular to a three-dimensional reconstruction method of a dual-phased array probe B scanning image. Background Art

[0002] With the development of China's manufacturing industry, the demand for non-destructive testing technology for workpieces is increasing. Ultrasonic testing is one of the commonly used non-destructive testing technologies. Ultrasonic testing uses the reflection, transmission and other properties of ultrasound, and uses the time and amplitude of the echo to detect and locate defects. It has the advantages of safe operation, accurate defect location, high sensitivity, low cost and high speed.

[0003] Ultrasonic phased array detection technology uses multi-element transducers of different shapes to generate and receive ultrasonic beams. By controlling the different delay times of each element in the transducer array to transmit (or receive) pulses, the phase relationship when the sound wave arrives at (or comes from) a certain point in the object is changed, and the focus and direction of the sound beam are changed, thereby realizing the scanning, deflection and focusing of the ultrasonic beam. Then, a combination of mechanical scanning and electronic scanning is used to achieve imaging. Ultrasonic phased array detection can obtain a two-dimensional B-scan image, which can show the shape and size of defects on the cross section, and is a very intuitive ultrasonic detection result.

[0004] In theory, ultrasonic testing needs to be performed in an environment with less interference and less noise. However, in the factory testing environment of large ring parts, randomly generated noise is inevitable. Therefore, the B-scan images obtained by the phased array probe to detect such parts contain many clutters of unpredictable size and shape, which has a great impact on the judgment of defect location and shape, especially for defects with small size and unclear imaging. It is more difficult to identify.

[0005] When inspecting workpieces, due to the large reflection energy near the surface, a large blind area will exist in the near surface of the B-scan image obtained by inspection. If the B-scan image with a large blind area is used for three-dimensional reconstruction, the obtained three-dimensional model will have low restoration degree and poor three-dimensional imaging effect. Summary of the invention

[0006] Based on this, it is necessary to provide a three-dimensional reconstruction method for the B-scan image of a dual phased array probe to address the problems of poor anti-interference ability and insufficient small defect recognition ability of the B-scan image of large ring parts in a strong noise environment.

[0007] The present invention provides a three-dimensional reconstruction method based on a dual phased array probe B scanning image, the steps of which include:

[0008] S1. In an actual strong noise working environment, two phased array probes of an ultrasonic phased array instrument are used to simultaneously detect ring parts. After the detection is completed, two equal groups of B-scan images are obtained. The images of each group correspond to each other and are the results of phased array scanning on both sides of the same ring wall.

[0009] S2. After graying and filtering the two groups of images, the corresponding B-scan images are stitched together, the near-surface blind area parts of the two B-scan images are cut off, and the two far-surface images (each equivalent to half the thickness of the workpiece) are stitched into a B-scan image of the small blind area, thereby reducing the influence of the near-surface scanning blind area on the recognition of small defects.

[0010] S3, performing defect two-dimensional trajectory judgment on the continuous B-scan images after splicing processing, removing the reflected echo caused by noise, etc., to obtain a small blind area B-scan image with noise removed.

[0011] S4. Using the B-scan image processed by S3, the original rotating part is reconstructed in three dimensions to obtain a three-dimensional model of the original rotating part. The three-dimensional model can accurately display the spatial information of the defect, such as the three-dimensional shape of the defect and the position in the workpiece, and has high visibility.

[0012] Specifically, the workpiece to be measured is a circular workpiece.

[0013] Specifically, the detection method in step S1 is: the workpiece to be tested is placed flat, and the two probes of the ultrasonic phased array dual-probe device are placed opposite to each other, respectively located at the upper and lower sides of the workpiece to be tested; the probes are fixed, the workpiece is rotated, and the probes are turned on for detection.

[0014] Specifically, in step S2, the filtering is median filtering.

[0015] Specifically, in step S2, the specific operation of intercepting and stitching images is: intercepting the image of the lower half of the workpiece taken by the upper probe and the image of the upper half of the workpiece taken by the lower probe, and stitching them together.

[0016] Specifically, in step S3, the two-dimensional trajectory judgment method is used to filter out noise. The specific principle of the two-dimensional trajectory judgment is: the theoretical two-dimensional trajectory of the defect echo in the adjacent B-scan image is a sine curve. When a suspected defect is detected, the theoretical coordinate values ​​of the suspected defect echo in the adjacent image are calculated respectively, and compared with the actual detected coordinate values, and the correlation coefficient between the theoretical value and the actual value is calculated. If the correlation coefficient exceeds the threshold, it means that the reflection is caused by the defect, otherwise it is filtered out as noise. The specific threshold is set according to the detection environment. If the detection equipment has high accuracy, the threshold is set to about 0.8, and if the accuracy is low, it can be set to about 0.5.

[0017] Assuming that the radius of the copper ring is R, the angular velocity of rotation is w, the B-scan image acquisition interval is t, and a total of m consecutive B-scan images containing a defect are acquired, then theoretically the coordinate x of the defect in the nth image in the X direction is (the m / 2 term in the formula is rounded up, the center of the workpiece is the origin, and the radial direction is the X direction):

[0018]

[0019] That is, x and the number of B-scan images satisfy the sinusoidal function relationship, and the two-dimensional trajectory of the defect is presented as a sinusoidal curve after the images are arranged in order. The actual coordinate values ​​of the suspected defects in the m images are analyzed, and the theoretical coordinate values ​​x of the defects are calculated. The correlation coefficient is calculated based on the m theoretical values ​​and the actual values. If the correlation coefficient exceeds the threshold, it means that the reflection is caused by the defect, otherwise it is filtered out as noise. The specific threshold is set according to the detection environment. If the detection equipment has high accuracy, the threshold is set to about 0.8, and if the accuracy is low, it can be set to about 0.5.

[0020] By adopting the above technical solution, the beneficial effects of the present invention are:

[0021] (1) The present invention uses the images obtained by splicing the double-sided phased array B-scan images for three-dimensional reconstruction, which can effectively reduce the detection blind area and improve the visibility of ultrasonic detection.

[0022] (2) The present invention adopts a two-dimensional trajectory judgment method to eliminate the influence of noise, which can enhance the display effect of ultrasonic three-dimensional images and prevent false detection.

[0023] (3) The present invention can remove noise through two-dimensional trajectory judgment and screening in an actual high-noise factory, thereby increasing the recognition of small defects that are difficult to distinguish from noise. In addition, the three-dimensional model can accurately display the spatial information of the defect, such as the three-dimensional shape of the defect and its position in the workpiece, and has high visibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the process of three-dimensional reconstruction method of dual phased array probe B scanning image.

[0025] Figure 2 Schematic diagram of the splicing process.

[0026] Figure 3 The 3D reconstruction result of B-scan image.

[0027] Figure 4 Schematic diagram of the principle of the defect two-dimensional trajectory judgment method. DETAILED DESCRIPTION

[0028] Taking a large ring-like part as an example of the inspection workpiece, the three-dimensional reconstruction method of the dual-phased array probe B scanning image is explained in detail.

[0029] like Figure 1 As shown, the three-dimensional reconstruction method of the scanning image of the dual phased array probe B includes the following steps in sequence:

[0030] S1. In an actual strong noise working environment, two phased array probes of a phased array instrument are used to simultaneously detect ring parts. The specific detection orientation is: the relative phased array probes sandwich the ring wall for detection, and the probes are located on the upper and lower sides of the ring wall. During the detection, the dual phased array probes are fixed and the ring parts rotate to complete the detection of the entire part. After the detection is completed, two sets of B-scan images are obtained.

[0031] S2. Use LabVIEW software to stitch the B-scan images obtained by the two probes. The process is as follows: Figure 2 As shown, the process includes image segmentation, mean filtering, graying, image rotation and segmentation to obtain a small blind area B-scan composite image.

[0032] S3. Use Python software to perform two-dimensional trajectory judgment on the spliced ​​continuous small blind area B-scan images, retain the grayscale value of the defect, and filter out the reflection area generated by clutter to complete the filtering of clutter.

[0033] S4. The B-scan grayscale image processed in the previous step is reconstructed in three dimensions on the VTK platform. The volume reconstruction method used is the nearest neighbor interpolation voxel method. The voxels in the space are traversed to find the closest corresponding pixel point, and the grayscale value of the pixel point is inserted into the voxel. Figure 3 The results shown show that the reconstructed model can view defects from any angle. It can be seen that compared with single-sided image reconstruction, three-dimensional reconstruction after splicing of dual phased array B-scan images can effectively reduce the surface blind area.

[0034] The principle of two-dimensional trajectory judgment in step S3 is as follows Figure 4 As shown in the figure. Since the probe has a certain width, the same defect will be detected multiple times. There is a flat bottom hole defect in the ring. Its motion trajectory during the rotation of the ring is as follows Figure 4 As shown, there are defect echoes in five consecutive B-scan images, and the position of the defect echo signal in the X-axis direction will change to a certain extent. The five B-scan images in the figure correspond to the images when the defect is at positions a, b, c, d, and e. The radius of the copper ring is 300mm, the rotation speed of the copper ring during detection is 0.05rad / s, and the acquisition interval is 0.1s. The angle between the two images is 0.005rad. Since there are a total of 5 images to capture the defect, for the nth B-scan image, the theoretical defect horizontal coordinate x is:

[0035]

[0036] That is, the coordinates of the defect in the x direction and the image page number where the defect is located conform to the sinusoidal function relationship. The coordinates of the defects actually collected are calculated, and a set of theoretical values ​​and a set of actual values ​​are obtained from 5 images. The correlation coefficient of the two sets of numbers is calculated. If the correlation coefficient exceeds the threshold, the echo is judged as a defect, otherwise the echo is filtered out as noise. In this embodiment, the threshold is set to 0.6.

[0037] The above-described embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A three-dimensional reconstruction method based on a dual phased array probe B scan image, characterized in that: The following steps are involved: S1. Use an ultrasonic phased array dual-probe device to detect the workpiece to be tested, and obtain two sets of B-scan images of equal quantity and one-to-one correspondence; S2, after graying and filtering the two sets of images, respectively intercept images equivalent to half the thickness of the workpiece and perform stitching processing; S3, screening images with suspected defect echoes from the spliced ​​images, and filtering out noise by using a two-dimensional trajectory judgment method; S4, performing three-dimensional reconstruction using the image with noise removed; The detection method in step S1 is as follows: the workpiece to be tested is placed flat, and the two probes of the ultrasonic phased array dual-probe device are placed opposite to each other, respectively located at the upper and lower sides of the workpiece to be tested; the probes are fixed, the workpiece is rotated, and the probes are turned on for detection; In step S2, the specific operation of intercepting and stitching images is: intercepting the image of the lower half of the workpiece taken by the upper probe and the image of the upper half of the workpiece taken by the lower probe, and stitching them together; In step S3, the two-dimensional trajectory determination method is specifically as follows: The theoretical coordinate x of the defect in the nth image in the X direction is: R is the radius of the copper ring, w is the angular velocity of the workpiece, t is the B-scan image acquisition interval, a total of m consecutive B-scan images containing suspected defects are acquired, and x is the theoretical coordinate value of the defect in the X direction; Read the actual coordinate values ​​of the suspected defects in the X direction from m images containing suspected defects, and calculate the correlation coefficient between the actual coordinate values ​​and the theoretical coordinate values. If the correlation coefficient exceeds the threshold, it means that the echo is caused by the defect, otherwise the echo is screened out as noise.

2. The three-dimensional reconstruction method based on the dual phased array probe B scan image according to claim 1, characterized in that: The workpiece to be measured is a circular ring workpiece.

3. The three-dimensional reconstruction method based on the dual phased array probe B scan image according to claim 1, characterized in that: In step S2, the filtering is median filtering.

4. The three-dimensional reconstruction method based on the dual phased array probe B scan image according to claim 1, characterized in that: The threshold is set to 0.5-0.8.

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