Composite data acquisition device based on laser ultrasound and ultrasonic tomography method

Abstract

The invention relates to the fields of laser ultrasound and the like, in particular to a composite data acquisition device based on laser ultrasound and an ultrasonic tomography method. According to the invention, path planning of spiral scanning, linear scanning and fault scanning can be realized through the composite data acquisition device, and the problem of single scanning of a traditional scanning device is effectively solved. VMD decomposition is carried out on collected laser ultrasonic data to remove abrupt signals, and the signal-to-noise ratio of ultrasonic signals is increased. The noise-reduced signals pass through a signal mapping module, so that the slope and the amplitude difference of the ultrasonic one-dimensional signals are respectively mapped into a polar coordinate system as a polar angle and a polar radius, then a polar coordinate image is processed by adopting an image processing method, and a damaged area is highlighted. And finally, performing three-dimensional visualization of the defect on the acquired image by adopting a volume rendering method. According to the invention, data acquisition, signal noise reduction, signal mapping, image processing and three-dimensional visualization of the measured object are realized, and three-dimensional morphology characteristics of internal defects can be visually presented.

Description

Technical Field

[0001] The invention relates to the field of laser ultrasonic detection and laser ultrasonic imaging, and in particular to a composite data acquisition device based on laser ultrasound and an ultrasonic tomographic imaging method. Background Art

[0002] With the rapid development of my country's materials industry and manufacturing industry, further requirements have been put forward for the detection of internal damage of materials. At present, due to the relatively single scanning method of laser ultrasonic imaging and the high requirements of ultrasonic imaging algorithm on ultrasonic signal-to-noise ratio, problems such as poor laser ultrasonic signal and unclear imaging edge have been caused, which seriously restrict the development of laser ultrasonic imaging.

[0003] In terms of laser ultrasonic data acquisition, Xu Zhihui and others from Taiyuan University of Technology designed a rotary weld detection device in the patent "A laser ultrasonic detection device for drum wall ring weld" (authorization announcement number: CN220154261U) to detect drum wall ring welds, which can effectively scan the ring welds. The above detection device has problems such as few degrees of freedom and a single shape of the detected object. Chen Tao and others from Beijing Institute of Petrochemical Technology proposed a multi-degree-of-freedom detection device in the patent "A multi-degree-of-freedom metal crack laser ultrasonic detection device" (authorization announcement number: CN220120770U), which has a good detection effect, but the detection device is complex and the detection cost is high. Zhang Jun and others from Wuhan University proposed a laser ultrasonic imaging detection system and detection method in the patent "A laser ultrasonic imaging detection system and detection method for adaptive irregular surfaces" (authorization announcement number: CN111595949B), which maps the object to be measured through a surface profile measurement module to obtain its surface morphology characteristics, and scans irregular objects through a scanning galvanometer. This detection system has problems such as slow scanning speed, scanning accuracy being affected by the measurement module and high detection cost.

[0004] In terms of laser ultrasonic imaging, Ji Xuanrong and others from Guangdong University of Technology, in the invention patent "A full-field ultrasonic microscope imaging system without blind spots and its method" (authorization announcement number: CN111948147B), integrated ultrasonic imaging with laser ultrasonic imaging, used laser ultrasonic imaging in the near-field area, and used a phased focusing imaging algorithm to reconstruct the laser ultrasonic image of the near-field imaging point. The above-mentioned imaging in the form of full focusing has a large amount of calculation and high hardware requirements. At the same time, the use cost of phased array equipment is high. Zhang Jun and others from Wuhan University solved the impact of roughness on imaging in the invention patent "A method for accurately measuring the defect size of rough parts based on laser ultrasonic imaging" (authorization announcement number: CN111855801B), extracted the surface wave signal of the defect-free area as the reference signal; and drew a two-dimensional color map based on the time when the maximum amplitude position of the reference signal was located. The suitability of the selected reference will cause great interference to the imaging. In the invention patent "A High-Sensitivity Large-Area Laser Ultrasonic Imaging Method" (authorization announcement number: CN110596009B) by Zeng Lvming and others of Nanchang Yangshen Electronic Technology Co., Ltd., a microlens array made of piezoelectric material with high optical transmittance is selected as both a laser micro-focusing unit and an ultrasonic signal receiving unit, eliminating the optical or acoustic multiple reflection excitation or receiving structure, effectively improving the efficiency of laser ultrasonic excitation and the sensitivity and signal-to-noise ratio of reception. Reducing the noise of the imaging signal through hardware methods is costly and easily affected by the processing technology of the lens.

[0005] In summary, in order to solve the problems of single scanning mode, low signal-to-noise ratio of collected signals, ultrasonic signal feature extraction and ultrasonic signal noise reduction, it is necessary to design a new composite data acquisition device and ultrasonic tomography method based on laser ultrasound. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects of the prior art and provide a composite data acquisition device based on laser ultrasound and an ultrasonic tomography method. The present application can realize multi-path scanning of the object to be measured.

[0007] In a first aspect, the present application provides a composite data acquisition device based on laser ultrasound, comprising:

[0008] A first drive motor, a lifting guide rail, a lifting block, a lifting platform, a rotating fixed platform, a second drive motor, a ring drive gear, an interferometer and a laser;

[0009] The first driving motor is connected to the lifting guide rail, the lifting guide rail is connected to the lifting block, and the lifting block is connected to the lifting platform;

[0010] A fixed annular gear is arranged on the lifting platform to provide a circular motion path for the annular driving gear; a first annular groove is processed on the lifting platform to constrain the annular driving gear to make circular motion; the annular driving gear supports the rotating fixed platform; and the second driving motor is connected to the annular driving gear;

[0011] The interferometer and the laser are arranged on a rotating fixed table;

[0012] The first driving motor is used to drive the lifting guide rail to rotate, thereby driving the lifting block to move up and down along the lifting guide rail, and then driving the lifting platform and the rotating fixed platform to move up and down;

[0013] The second driving motor is used to drive the annular driving gear to rotate, thereby driving the rotating fixed platform to rotate, and further driving the interferometer and the laser to rotate; the rotating path surrounds the object to be measured.

[0014] In a possible implementation, the lifting platform and the rotating fixed platform are both annular.

[0015] In a possible implementation, the data acquisition device further includes: a third drive motor and a rotating workbench;

[0016] The third driving motor is connected to the rotating worktable, and the rotating worktable is used to place the object to be measured; the third driving motor is used to drive the rotating worktable to rotate, and then drive the object to be measured to rotate.

[0017] In a possible implementation, the data acquisition device further includes: a motor support plate and four support columns; the four support columns are fixed under the motor support plate at intervals of 90°; the first drive motor and the third drive motor are both fixed on the motor support plate.

[0018] In a possible implementation, four of the first drive motors, lifting guide rails and lifting blocks are provided; the four first drive motors are respectively used to drive the four lifting guide rails to rotate, thereby driving the four lifting blocks to move up and down along the four lifting guide rails.

[0019] In a possible implementation, the data acquisition device further includes: a balancing block;

[0020] A second annular groove is machined on the lifting platform to constrain the balancing block to make circular motion;

[0021] The first annular groove and the second annular groove are respectively arranged on the inner side and the outer side of the fixed annular gear; the annular driving gear and the balancing block jointly support the rotating fixed platform.

[0022] In some embodiments, the lifting block may be a triangular lifting block.

[0023] In a second aspect, the present application provides a composite data acquisition method based on laser ultrasound, which completes path scanning and data acquisition based on the composite data acquisition device based on laser ultrasound;

[0024] Among them, path scanning and data collection include: spiral path scanning and data collection;

[0025] Wherein, the spiral path scanning includes spiral rough scanning;

[0026] The spiral rough scanning and data collection includes: the first drive motor rotates a certain angle to lift the lifting platform a certain distance; when the first drive motor stops, the second drive motor rotates a certain angle to rotate the annular drive gear, driving the rotating fixed platform to make a circular motion, and then driving the interferometer and the laser to make a circular motion around the object to be measured; after the second drive motor stops moving, the first drive motor starts to rotate; and so on, repeating the above movement steps until the entire spiral rough scanning is completed according to the set parameter values; at the same time, the laser is always excited and the interferometer is always receiving ultrasonic signals; thereby, the spiral rough scanning and data collection are completed;

[0027] In a possible implementation, the spiral path scanning further includes spiral fine scanning;

[0028] The spiral fine scanning and data collection include: the first drive motor rotates a certain angle to lift the lifting platform a certain distance; when the first drive motor stops, the third drive motor rotates a certain angle, thereby driving the rotating worktable to rotate, and then driving the object to be measured to rotate, so that the interferometer and the laser move relative to the object to be measured; after the third drive motor stops moving, the first drive motor starts to rotate; and so on, repeating the above movement steps until the entire spiral fine scanning is completed according to the set parameter values; at the same time, the laser is always energized and the interferometer is always receiving ultrasonic signals; thereby, the spiral path scanning and data collection of the object to be measured are completed.

[0029] In a possible implementation, the path scanning and data collection further includes linear path scanning and data collection;

[0030] The linear path scanning and data collection includes: the first driving motor rotates at a certain speed, so that the lifting platform, the rotating worktable, the laser and the interferometer are constantly raised and lowered until the linear path scanning is completed according to the set parameter values; at the same time, the laser is constantly excited and the interferometer is constantly receiving ultrasonic signals; thereby, the linear scanning and data collection of the object to be measured are completed;

[0031] In a possible implementation, the path scanning and data acquisition further includes fault-type path scanning and data acquisition;

[0032] The fault-type path scanning and data collection includes: the first drive motor rotates a certain angle to lift the lifting platform a certain distance; when the first drive motor stops, the second drive motor rotates until the entire object to be measured is scanned, and the second drive motor stops moving; repeating the above movement steps until the fault-type path scanning is completed according to the set parameter values; at the same time, the laser is always excited and the interferometer is always receiving ultrasonic signals; thereby, the fault-type path scanning and data collection of the object to be measured are completed.

[0033] The parameter values ​​that are set include the scanning height and the rotation angle.

[0034] In a third aspect, the present application provides an ultrasonic tomographic imaging method, which firstly performs a spiral path scanning and data acquisition or a tomographic path scanning and data acquisition on the object to be measured based on the above-mentioned composite data acquisition method based on laser ultrasound to obtain an original laser ultrasonic signal;

[0035] Then, the original laser ultrasonic signal is subjected to polar coordinate mapping and image processing to obtain a tomographic image; and the tomographic image is then three-dimensionally reconstructed to obtain a three-dimensional model of the object being measured.

[0036] In a possible implementation, the performing polar coordinate mapping and image processing on the original laser ultrasonic signal includes: performing one-dimensional signal denoising, polar coordinate mapping and two-dimensional signal denoising on the original laser ultrasonic signal.

[0037] In a possible implementation, performing one-dimensional signal denoising on the original laser ultrasonic signal includes: performing denoising on the original laser ultrasonic signal through VMD mode decomposition.

[0038] In a possible implementation, the polar coordinate mapping includes: for the laser ultrasonic signal that has completed one-dimensional signal noise reduction, the coordinate values ​​of adjacent points are acquired in sequence according to the time sequence of signal acquisition; whether the amplitudes of adjacent points are equal, if they are equal, the ordinate value of the coordinate value of the point acquired later is set to zero; and the slope and amplitude difference of two adjacent points are calculated; the inclination angle corresponding to the calculated slope is calculated. The polar angle of the midpoint in the polar coordinate system is taken as the calculated amplitude difference, and the polar diameter of the midpoint in the polar coordinate system is taken as the polar angle of the midpoint in the polar coordinate system; the information of the entire laser ultrasonic signal is extracted in sequence according to the time sequence of signal acquisition, and all slopes and amplitude differences are mapped to the polar coordinate system; thereby, the one-dimensional laser ultrasonic signal is converted into a two-dimensional image signal.

[0039] In a possible implementation, the two-dimensional signal noise reduction includes image enhancement on the two-dimensional image signal, selecting the ROI area therein, performing mean filtering on the ROI area, performing contrast-limited adaptive histogram equalization, image morphological processing and edge extraction to obtain a tomographic imaging image.

[0040] The composite data acquisition device based on laser ultrasound and the ultrasonic tomography method provided by the present application can realize multi-path planning and scanning, and can effectively solve the problem of single scanning mode of traditional scanning devices. The laser ultrasonic data collected from the object to be measured is subjected to VMD decomposition to remove abrupt signals, which can improve the signal-to-noise ratio of the ultrasonic signal. The de-noised signal is mapped to the polar coordinate system through polar coordinate mapping, and the slope and amplitude difference of the one-dimensional laser ultrasonic signal can be mapped to the polar coordinate system as the polar angle and polar diameter respectively, and then the two-dimensional image signal image is processed by the image processing method to highlight the damaged area. Finally, the acquired image can be used to realize the three-dimensional visualization of the defects of the object to be measured by the volume rendering method. The present application can realize data acquisition, signal noise reduction, polar coordinate mapping, image processing and three-dimensional visualization of the object to be measured, and can intuitively present the three-dimensional morphological characteristics of the internal defects of the object to be measured.

[0041] Beneficial effects:

[0042] The composite data acquisition device based on laser ultrasound and the ultrasonic tomography method provided in the present application can realize spiral, linear and tomographic path planning scanning and data acquisition, and can realize multiple path scanning, effectively solving the problem of single scanning of traditional scanning devices. By performing polar coordinate mapping and noise reduction on the one-dimensional time-domain ultrasonic signal data collected by the laser ultrasonic acquisition device, the ultrasonic signal-to-noise ratio and signal feature extraction are effectively improved, and the quality of laser ultrasonic signal imaging is effectively improved. The ultrasonic tomography method provided in the present application can also realize three-dimensional reconstruction of internal defects of the object being measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a three-dimensional schematic diagram of a laser scanning device in one embodiment of the present application;

[0044] Figure 2 This is a front view schematic diagram of a laser scanning device in one embodiment of the present application;

[0045] Figure 3 This is a structural schematic diagram of the circular motion of a ring gear in one embodiment of the present application;

[0046] Figure 4 This is a scanning flow chart of a laser scanning device in one embodiment of the present application;

[0047] Figure 5 This is a schematic diagram of the spiral motion trajectory in one embodiment of the present application;

[0048] Figure 6 This is a flow chart of polar coordinate mapping and image processing of signals in one embodiment of the present application;

[0049] Figure 7This is a schematic diagram of polar coordinate mapping in one embodiment of the present application;

[0050] Figure 8 This is a schematic diagram of three-dimensional reconstruction of internal damage of an object under test in one embodiment of the present application.

[0051] Explanation of the accompanying drawings: 1-second drive motor; 2-rotating fixed table; 3-workbench; 4-first drive motor; 5-support column; 6-motor support plate; 7-rotating workbench; 8-interferometer; 9-lifting guide rail; 10-laser; 11-fixed ring gear; 12-lifting block; 13-third drive motor; 14-measured object; 15-limit block; 16-balance block; 17-ring drive gear; 18-lifting platform. DETAILED DESCRIPTION

[0052] In order to enable those skilled in the art to better understand the present application, the application will be further described below in conjunction with the drawings and specific implementation methods in the embodiments of the present application.

[0053] Embodiment 1:

[0054] The present application provides a composite data acquisition device based on laser ultrasound, comprising:

[0055] A first drive motor, a lifting guide rail, a lifting block, a lifting platform, a rotating fixed platform, a second drive motor, a ring drive gear, an interferometer and a laser;

[0056] The first driving motor is connected to the lifting guide rail, the lifting guide rail is connected to the lifting block, and the lifting block is connected to the lifting platform;

[0057] A fixed annular gear is arranged on the lifting platform to provide a circular motion path for the annular driving gear; a first annular groove is processed on the lifting platform to constrain the annular driving gear to make circular motion; the annular driving gear supports the rotating fixed platform; and the second driving motor is connected to the annular driving gear;

[0058] The interferometer and the laser are arranged on a rotating fixed table;

[0059] The first driving motor is used to drive the lifting guide rail to rotate, thereby driving the lifting block to move up and down along the lifting guide rail, and then driving the lifting platform and the rotating fixed platform to move up and down;

[0060] The second driving motor is used to drive the annular driving gear to rotate, thereby driving the rotating fixed platform to rotate, and further driving the interferometer and the laser to rotate; the rotating path surrounds the object to be measured.

[0061] In some embodiments, the lifting platform and the rotating fixed platform are both annular.

[0062] In some embodiments, the data acquisition device further includes: a third drive motor and a rotating workbench;

[0063] The third driving motor is connected to the rotating worktable, and the rotating worktable is used to place the object to be measured; the third driving motor is used to drive the rotating worktable to rotate, and then drive the object to be measured to rotate.

[0064] In some embodiments, the data acquisition device further includes: a motor support plate and four support columns; the four support columns are fixed under the motor support plate at intervals of 90°; the first drive motor and the third drive motor are both fixed on the motor support plate.

[0065] In some embodiments, four of the first drive motors, lifting guide rails and lifting blocks are provided; the four first drive motors are respectively used to drive the four lifting guide rails to rotate, thereby driving the four lifting blocks to move up and down along the four lifting guide rails.

[0066] In some embodiments, the data acquisition device further includes: a balancing block;

[0067] A second annular groove is machined on the lifting platform to constrain the balancing block to make circular motion;

[0068] The first annular groove and the second annular groove are respectively arranged on the inner side and the outer side of the fixed annular gear; the annular driving gear and the balancing block jointly support the rotating fixed platform.

[0069] In some embodiments, the lifting block may be a triangular lifting block.

[0070] In some embodiments, the structure of the laser ultrasound-based composite data acquisition device is as follows: Figures 1 to 3 As shown. Four support columns 5 are distributed below the motor support plate 6 at intervals of 90°, and the support columns 5 are connected to the motor support plate through threads. Five motors are fixed above the motor support plate 6, including four first drive motors 4 and one third drive motor 13. Among them, the third drive motor 13 is connected to the rotating worktable 7 through a coupling, and the rotation of the third drive motor 13 drives the rotating worktable 7 to rotate. The first drive motor 4 is connected to the lifting guide rail 9 through a coupling, and the lifting guide rail 9 is connected to the lifting block 12 through threads. The limit block 15 is fixed above the lifting guide rail 9 to prevent the lifting block 12 from detaching from the lifting guide rail 9. The rotation of the first drive motor 4 will drive the lifting guide rail 9 to rotate, thereby driving the lifting block 12 to move up and down along the lifting guide rail 9, and then driving the rotating fixed table 2 to move up and down.

[0071] The second drive motor 1 is connected to the annular drive gear 17 through a coupling, and the rotation of the second drive motor 1 will drive the annular drive gear 17 to rotate; the fixed annular gear 11 is fixed to the lifting platform 18 by screws, providing a circular motion path for the annular drive gear 17; the annular drive gear 17 and the balancing block 16 are constrained to make circular motion by the annular groove processed on the lifting platform 18; the annular drive gear 17 and the balancing block 16 jointly support the rotating fixed platform 2; the rotation of the annular drive gear 17 drives the rotating fixed platform 2 to rotate; the interferometer 8 and the laser 10 are fixed above the rotating fixed platform by screws, and the rotating fixed platform 2 drives the interferometer 8 and the laser 10 to rotate.

[0072] Embodiment 2:

[0073] The embodiment of the present application provides a composite data acquisition method based on laser ultrasound, which completes path scanning and data acquisition based on the composite data acquisition device based on laser ultrasound described in the first embodiment;

[0074] Among them, path scanning and data collection include: spiral path scanning and data collection;

[0075] Wherein, the spiral path scanning includes spiral rough scanning;

[0076] In order to achieve spiral rough scanning, the second drive motor 1 and the first drive motor 4 need to cooperate with each other. The first drive motor 4 rotates a certain angle so that the lifting platform 18 is lifted a certain distance. When the first drive motor 4 stops, the second drive motor 1 rotates a certain angle so that the annular drive gear 17 rotates and the balance block 16 moves in a circular motion, driving the rotating fixed table 2 to make a circular motion, and then driving the interferometer 8 and the laser 10 to make a circular motion around the object to be measured 14. After the second drive motor 1 stops moving, the first drive motor 4 starts to rotate. And so on, repeat the above movement steps until the entire spiral rough scanning is completed according to the set parameter values. At the same time, the laser 10 is always energized and the interferometer 8 is always receiving ultrasonic signals. In this way, the spiral path scanning and data collection can be completed. Subsequently, each motor can return to the starting position.

[0077] In some embodiments, the spiral path scanning further comprises a spiral fine scanning;

[0078] In order to achieve spiral fine scanning, the third drive motor 13 and the first drive motor 4 need to cooperate with each other. The first drive motor 4 rotates a certain angle to lift the lifting platform 18 a certain distance. When the first drive motor 4 stops, the third drive motor 13 rotates a certain angle, thereby driving the rotating workbench 7 to rotate, and then driving the object to be measured 14 to rotate, so that the interferometer 8 and the laser 10 move relative to the object to be measured 14. After the third drive motor 13 stops moving, the first drive motor 4 starts to rotate. And so on, repeat the above movement steps until the entire spiral fine scanning is completed according to the set parameter values. At the same time, the laser 10 is always energized, and the interferometer 8 is always receiving ultrasonic signals. In this way, the spiral path scanning and data collection of the object to be measured can be completed. Subsequently, each motor can return to the starting position.

[0079] In some embodiments, the flowchart of the spiral path scanning is as follows Figure 4 As shown in the figure, it includes circular scanning and lifting scanning. Figure 5 Shown

[0080] In some embodiments, the path scanning and data collection further includes linear path scanning and data collection;

[0081] In order to achieve linear path scanning, the first drive motor 4 rotates at a certain speed, so that the lifting platform 18, the rotating table 7, the laser 10 and the interferometer 8 are constantly lifted and lowered until the linear path scanning is completed according to the set parameter values; at the same time, the laser 10 is constantly excited and the interferometer 8 is constantly receiving ultrasonic signals. In this way, the linear scanning and data collection of the object to be measured can be completed.

[0082] In some embodiments, the path scanning and data collection further include tomographic path scanning and data collection;

[0083] In order to realize the fault path scanning, the first drive motor 4 rotates a certain angle so that the lifting platform 18 is lifted a certain distance. When the first drive motor 4 stops, the second drive motor 1 rotates until the entire object 14 is scanned, and the second drive motor 1 stops moving. At the same time, the first drive motor 4 continues to rotate a certain angle, and the second drive motor 1 continues to move. By analogy, the above movement steps are repeated until the fault path scanning is completed according to the set parameter values; at the same time, the laser 10 is always excited, and the interferometer 8 is always receiving ultrasonic signals. In this way, the fault path scanning and data collection of the object to be measured can be completed.

[0084] Among them, users can perform spiral path scanning, linear path scanning or tomographic path scanning on the physical object to be measured according to their needs and collect corresponding laser ultrasonic signals.

[0085] Embodiment three:

[0086] In a third aspect, the present application provides an ultrasonic tomography method, which firstly performs a spiral path scanning and data acquisition or a tomographic path scanning and data acquisition on the object to be measured based on the composite data acquisition method based on laser ultrasound described in Example 2 to obtain an original laser ultrasonic signal;

[0087] Then, the original laser ultrasonic signal is subjected to polar coordinate mapping and image processing to obtain a tomographic image; and the tomographic image is then three-dimensionally reconstructed to obtain a three-dimensional model of the object being measured.

[0088] Among them, the tomographic imaging image is all the original laser ultrasonic signals (laser ultrasonic A-scan signals) obtained by rotating around the object to be measured in the spiral scanning and tomographic scanning methods. The image data is obtained after one-dimensional signal noise reduction, polar coordinate mapping and two-dimensional signal noise reduction processing of all the original laser ultrasonic signals.

[0089] like Figure 6 As shown, in some embodiments, the polar coordinate mapping and image processing of the original laser ultrasonic signal includes: performing one-dimensional signal denoising, polar coordinate mapping and two-dimensional signal denoising on the original laser ultrasonic signal.

[0090] In some embodiments, performing one-dimensional signal noise reduction on the original laser ultrasonic signal includes: performing noise reduction on the original laser ultrasonic signal by VMD mode decomposition.

[0091] In this step, the original laser ultrasonic signal (laser ultrasonic A-scan signal) is used as the input of the one-dimensional signal denoising module, and the one-dimensional signal denoising module decomposes and denoises the original laser ultrasonic signal through the VMD (Variational Mode Decomposition) mode, including decomposing the original laser ultrasonic signal through the VMD mode, filtering and denoising the decomposed signal, and reconstructing the laser ultrasonic signal using the filtered signal; the reconstructed laser ultrasonic signal is template matched with the original laser ultrasonic signal, that is, the reconstructed laser ultrasonic signal is compared with the original laser ultrasonic signal to observe whether the abrupt signal in the original laser ultrasonic signal is removed; if it is not removed, the reconstructed laser ultrasonic signal is continuously decomposed and denoised through the VMD mode, and then the corresponding reconstructed laser ultrasonic signal is compared with the original laser ultrasonic signal until the abrupt signal of the original laser ultrasonic signal is removed. In this way, the one-dimensional denoising of the original laser ultrasonic signal is completed.

[0092] In some embodiments, the polar coordinate mapping includes: for the laser ultrasonic signal that has completed one-dimensional signal noise reduction, sequentially acquiring coordinate values ​​of adjacent points in the order of signal acquisition time; determining whether the amplitudes of adjacent points are equal, and if they are equal, setting the ordinate value of the coordinate value of the point acquired later to zero; and calculating the slope and amplitude difference between two adjacent points;

[0093] Assuming that the first point obtained is A (x1, y1) and the second point obtained is B (x2, y2), the slope of two adjacent points can be obtained by the following formula:

[0094] (1)

[0095] The formula for calculating the amplitude difference is:

[0096] (2)

[0097] The calculated slope corresponds to the inclination angle The polar angle of the midpoint in the polar coordinate system is used, and the calculated amplitude difference is used as the polar diameter of the midpoint in the polar coordinate system; the information of the entire laser ultrasonic signal is extracted in sequence according to the time sequence of signal acquisition, and all slopes and amplitude differences are mapped to the polar coordinate system to form a polar coordinate view.

[0098] In this step, the laser ultrasonic signal with one-dimensional signal denoising is used as the input of the signal mapping module. The signal mapping module performs the above processing to complete the polar coordinate mapping of the ultrasonic signal. The schematic diagram of the mapping is as follows: Figure 7 The one-dimensional laser ultrasonic signal is converted into a two-dimensional image signal (i.e., polar coordinate view), thereby realizing the extraction of damage features in the laser ultrasonic signal and improving the subsequent reconstruction accuracy of three-dimensional reconstruction.

[0099] In some embodiments, the two-dimensional signal noise reduction includes image enhancement of the two-dimensional image signal, selecting the ROI area therein, performing mean filtering on the ROI area, performing contrast-limited adaptive histogram equalization, image morphological processing and edge extraction to obtain a tomographic imaging image.

[0100] In this step, the two-dimensional image signal is used as the signal input of the two-dimensional signal noise reduction module. The two-dimensional image signal is enhanced to improve the image quality, make the image clearer, highlight the target area and rich information in the image, and make the image target information more prominent. The ROI area (Region of Interest) is obtained, and the ROI area of ​​the two-dimensional image signal is framed to provide an area for subsequent image processing and image enhancement. The ROI area is mean filtered to remove the influence of Gaussian noise on the image. Then, the limited contrast adaptive histogram equalization is performed, and the distribution of the image histogram is limited by setting a threshold before calculating the cumulative distribution function of the image pixels, thereby changing the shape of the histogram. The image is subjected to image morphological processing (including dilation) to expand the boundary of the target outward. It can be used to fill the holes or boundary depressions in the ROI area and eliminate the small particle noise therein. Finally, the ROI area is subjected to Canny edge extraction to extract the edge area of ​​the ROI area to improve the accuracy of subsequent three-dimensional reconstruction.

[0101] In the application of damage detection on the object under test, the ROI area is the damage area.

[0102] In some embodiments, the three-dimensional reconstruction of the tomographic image may be performed by using a volume rendering method to reconstruct the tomographic image in three dimensions. The volume rendering method can directly view the volume image without segmenting the surface or object, and retains the relationship between the volume data values ​​of the original image. It abandons the constraints of constructing the body by the surface in traditional graphics, and uses the volume rendering illumination model to directly draw the distribution of various physical quantities from the three-dimensional data field.

[0103] The reconstruction method of volume rendering retains the information of the original two-dimensional image, and can also use the features between adjacent images to generate a two-dimensional image that did not exist originally. The defect-based three-dimensional visualization process is: 1) Project the pre-processed image and put the tomographic image into the Cartesian coordinate system, such as Figure 8 As shown; 2) The tomographic image is reduced, interpolated and smoothed; 3) The isosurface data of the tomographic image is extracted from the three-dimensional volume data, and the normal vectors of the isosurface vertices are calculated; 4) The color of the reconstructed model is set and lighting conditions are added to achieve a three-dimensional visualization effect of the defects of the object being measured.

[0104] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A composite data acquisition device based on laser ultrasound, characterized in that: include: A first drive motor, a lifting guide rail, a lifting block, a lifting platform, a rotating fixed platform, a second drive motor, a ring drive gear, an interferometer and a laser; The first driving motor is connected to the lifting guide rail, the lifting guide rail is connected to the lifting block, and the lifting block is connected to the lifting platform; A fixed annular gear is arranged on the lifting platform to provide a circular motion path for the annular driving gear; a first annular groove is processed on the lifting platform to constrain the annular driving gear to make a circular motion; The annular drive gear supports the rotating station; The second drive motor is connected to the annular drive gear; The interferometer and the laser are arranged on a rotating fixed table; The first driving motor is used to drive the lifting guide rail to rotate, thereby driving the lifting block to move up and down along the lifting guide rail, and then driving the lifting platform and the rotating fixed platform to move up and down; The second driving motor is used to drive the annular driving gear to rotate, thereby driving the rotating fixed platform to rotate, and further driving the interferometer and the laser to rotate; the rotating path surrounds the object to be measured.

2. The laser-ultrasound-based composite data acquisition device according to claim 1, characterized in that: Also includes: a third drive motor and a rotating worktable; The third driving motor is connected to the rotating worktable, and the rotating worktable is used to place the object to be measured; the third driving motor is used to drive the rotating worktable to rotate, and then drive the object to be measured to rotate.

3. The laser-ultrasound-based composite data acquisition device according to claim 1, characterized in that: Also includes: A motor support plate and four support columns; the four support columns are fixed below the motor support plate at intervals of 90 degrees; the first drive motor and the third drive motor are both fixed on the motor support plate.

4. The laser-ultrasound-based composite data acquisition device according to claim 1, characterized in that: There are four of the first drive motors, lifting guide rails and lifting blocks; the four first drive motors are used to drive the four lifting guide rails to rotate, thereby driving the four lifting blocks to move up and down along the four lifting guide rails.

5. The laser-ultrasound-based composite data acquisition device according to claim 1, characterized in that: Also includes: Balance weight; A second annular groove is machined on the lifting platform to constrain the balancing block to make circular motion; The first annular groove and the second annular groove are respectively arranged on the inner side and the outer side of the fixed annular gear; the annular driving gear and the balancing block jointly support the rotating fixed platform.

6. A composite data acquisition method based on laser ultrasound, characterized in that: The laser-ultrasound-based composite data acquisition device according to any one of claims 1 to 5 completes path scanning and data acquisition; Among them, path scanning and data collection include: spiral path scanning and data collection, linear path scanning and data collection, fault path scanning and data collection; Wherein, the spiral path scanning includes spiral rough scanning; The spiral rough scanning and data collection includes: the first drive motor rotates a certain angle to lift the lifting platform a certain distance; when the first drive motor stops, the second drive motor rotates a certain angle to rotate the annular drive gear, driving the rotating fixed platform to make a circular motion, and then driving the interferometer and the laser to make a circular motion around the object to be measured; after the second drive motor stops moving, the first drive motor starts to rotate; and so on, repeating the above movement steps until the entire spiral rough scanning is completed according to the set parameter values; at the same time, the laser is always excited and the interferometer is always receiving ultrasonic signals; thereby, the spiral rough scanning and data collection are completed; The linear path scanning and data collection includes: the first driving motor rotates at a certain speed, so that the lifting platform, the rotating worktable, the laser and the interferometer are constantly raised and lowered until the linear path scanning is completed according to the set parameter values; at the same time, the laser is constantly excited and the interferometer is constantly receiving ultrasonic signals; thereby, the linear scanning and data collection of the object to be measured are completed; The fault-type path scanning and data collection includes: the first drive motor rotates a certain angle to lift the lifting platform a certain distance; when the first drive motor stops, the second drive motor rotates until the entire object to be measured is scanned, and the second drive motor stops moving; repeating the above movement steps until the fault-type path scanning is completed according to the set parameter values; at the same time, the laser is always excited and the interferometer is always receiving ultrasonic signals; thereby, the fault-type path scanning and data collection of the object to be measured are completed.

7. The laser-ultrasound-based composite data acquisition method according to claim 5, characterized in that: The laser-ultrasound-based composite data acquisition device according to any one of claims 2 to 5 completes path scanning and data acquisition; The spiral path scanning also includes spiral fine scanning; The spiral fine scanning and data collection includes: the first driving motor rotates a certain angle so that the lifting platform is lifted a certain distance; When the first drive motor stops, the third drive motor rotates a certain angle, thereby driving the rotary table to rotate, and then driving the object to be measured to rotate, so that the interferometer and the laser move relative to the object to be measured; after the third drive motor stops moving, the first drive motor starts to rotate; and so on, repeating the above movement steps until the entire spiral fine scanning is completed according to the set parameter values; at the same time, the laser is always energized and the interferometer is always receiving ultrasonic signals; thereby, the spiral path scanning and data collection of the object to be measured are completed.

8. An ultrasonic tomography method, firstly based on the composite data acquisition method based on laser ultrasound according to any one of claims 6 to 7, a spiral path scanning and data acquisition or a tomographic path scanning and data acquisition is performed on the object to be measured to obtain an original laser ultrasonic signal; Then, the original laser ultrasonic signal is subjected to polar coordinate mapping and image processing to obtain a tomographic image; and the tomographic image is then three-dimensionally reconstructed to obtain a three-dimensional model of the object being measured.

9. The ultrasonic tomography method according to claim 9, characterized in that: The polar coordinate mapping and image processing of the original laser ultrasonic signal includes: performing one-dimensional signal noise reduction, polar coordinate mapping and two-dimensional signal noise reduction on the original laser ultrasonic signal.

10. The ultrasonic tomography method according to claim 9, characterized in that: The polar coordinate mapping includes: for the laser ultrasonic signal that has completed one-dimensional signal noise reduction, the coordinate values ​​of adjacent points are obtained in sequence according to the time sequence of signal acquisition; judging whether the amplitudes of adjacent points are equal, and if they are equal, setting the ordinate value of the coordinate value of the point obtained later to zero; and calculating the slope and amplitude difference of two adjacent points; and calculating the inclination angle corresponding to the calculated slope. The polar angle of the midpoint in the polar coordinate system is taken as the calculated amplitude difference, and the polar diameter of the midpoint in the polar coordinate system is taken as the polar angle of the midpoint in the polar coordinate system; the information of the entire laser ultrasonic signal is extracted in sequence according to the time sequence of signal acquisition, and all slopes and amplitude differences are mapped to the polar coordinate system; thereby, the one-dimensional laser ultrasonic signal is converted into a two-dimensional image signal.

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