Underwater concrete defect three-dimensional reconstruction system and reconstruction method thereof

Abstract

The invention discloses an underwater concrete defect three-dimensional reconstruction system and a reconstruction method thereof, and belongs to the technical field of underwater laser image shooting, the underwater concrete defect three-dimensional reconstruction system comprises a water tank, a stepping motor scanning system, an underwater image acquisition device, a system parameter calibration system and a three-dimensional laser point cloud reconstruction system, the stepping motor scanning system drives the underwater image acquisition equipment to do horizontal reciprocating rectilinear motion in the water tank, the underwater image acquisition equipment is used for shooting underwater concrete defect images with strong characteristic laser, and the system parameter calibration system is used for calibrating parameters of the underwater image acquisition equipment. According to the three-dimensional laser point cloud reconstruction system, three-dimensional reconstruction of underwater concrete defects is realized for underwater concrete defect images with strong characteristic laser, so that the detection efficiency and the detection precision of the underwater concrete defects are greatly improved, and the problem that the underwater three-dimensional reconstruction effect is limited by existing underwater camera equipment is solved; and the defect precision of the underwater concrete is low.

Description

Technical Field

[0001] The invention belongs to the technical field of underwater laser image shooting, and in particular relates to an underwater concrete defect three-dimensional reconstruction system and a reconstruction method thereof. Background Art

[0002] Infrastructure such as water conservancy projects, bridges, ports, and water tunnels bear the important responsibility of human development and utilization of water resources and the safety of life and property. However, for a long time, these underwater concrete structures often have various defects such as cracks, scouring, wear, and exposed steel bars when facing natural disasters such as earthquakes, geological disasters, and floods, which seriously threaten the safe operation of the project. Therefore, it is particularly urgent to conduct defect detection and hidden danger inspection in a timely and accurate manner. However, there is currently no underwater 3D reconstruction image acquisition device on the market that can fully utilize the fusion of binocular camera and line laser technology. Existing underwater camera equipment can usually only provide binocular camera or line laser functions, but cannot achieve the fusion of the two at the same time, which limits the effect and application scope of underwater 3D reconstruction. Summary of the invention

[0003] The present invention aims to provide a system and method for reconstructing underwater concrete defects in three-dimensional form, which solves the problem that the existing underwater camera equipment limits the effect of underwater three-dimensional reconstruction and leads to low accuracy of underwater concrete defects.

[0004] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is as follows:

[0005] Provided is an underwater concrete defect three-dimensional reconstruction system, which includes a water tank, a stepper motor scanning system, an underwater image acquisition device, a system parameter calibration system and a three-dimensional laser point cloud reconstruction system;

[0006] The top of the water tank has an opening, the bottom is a closed structure, and a shooting window is arranged on the bottom of the water tank; the underwater image acquisition device is arranged on the stepper motor scanning system, the underwater image acquisition device is located inside the water tank and the shooting direction is toward the shooting window, and the stepper motor scanning system drives the underwater image acquisition device to perform horizontal reciprocating linear motion inside the water tank;

[0007] The underwater image acquisition device includes two cameras and a laser transmitter, and the underwater image acquisition device is used to capture underwater concrete defect images with a strong characteristic laser;

[0008] The system parameter calibration system is used to calibrate the parameters of underwater image acquisition equipment;

[0009] The 3D laser point cloud reconstruction system is used to convert underwater concrete defect images with strong characteristic lasers into 3D point cloud data, and color the 3D point cloud data through a color camera to achieve 3D reconstruction.

[0010] The basic principle of the underwater concrete defect three-dimensional reconstruction system in the present invention is: a stepper motor scanning system drives the underwater image acquisition device to perform horizontal reciprocating linear motion inside the water tank, so as to obtain a wider range of shooting angles, and the underwater image acquisition device captures underwater concrete defect images with strong characteristic lasers, and the system parameter calibration system and the three-dimensional laser point cloud reconstruction system generate three-dimensional point cloud data according to the underwater concrete defect images with strong characteristic lasers, and color the three-dimensional point cloud data to realize three-dimensional reconstruction of underwater concrete defects, which greatly improves the detection efficiency and detection accuracy of underwater concrete defects, and solves the problem that the existing underwater camera equipment limits the effect of underwater three-dimensional reconstruction, resulting in low accuracy of underwater concrete defects.

[0011] Furthermore, as a specific setting method of the stepper motor scanning system, the stepper motor scanning system includes a mounting frame arranged on the top of the water tank, a screw is rotatably arranged in the mounting frame, and a slider is threadedly connected to the screw; a stepper motor is arranged on one side of the mounting frame, and the output end of the stepper motor is fixedly connected to one end of the screw through a coupling; a mounting bracket is vertically arranged on the slider, the top of the mounting bracket is fixedly connected to the slider, and the bottom of the mounting bracket is located at the bottom of the water tank; the underwater image acquisition device is fixedly connected to the bottom of the mounting bracket.

[0012] The process of the stepper motor scanning system driving the underwater image acquisition device to move horizontally back and forth in a straight line inside the water tank is as follows: the stepper motor is started to drive the screw to rotate, and the rotating screw drives the slider to move back and forth in a straight line along the length direction of the screw, thereby driving the mounting bracket fixedly connected to the slider and the underwater image acquisition device fixedly connected to the mounting bracket to move horizontally back and forth in a straight line inside the water tank, so that the underwater image acquisition device has a wider shooting range, and the underwater image acquisition device can completely scan the target and obtain images corresponding to different positions.

[0013] Further, as a specific setting mode of the underwater image acquisition device, the underwater image acquisition device includes a binocular cabin and an aviation plug, the binocular cabin is fixedly connected to the bottom of the mounting bracket; the binocular cabin includes an intermediate cabin, two camera cabins are obliquely arranged on both sides of the intermediate cabin, and the two camera cabins are symmetrically arranged; a camera front glass is arranged at the front end of each camera cabin, a camera is arranged in each camera cabin, and a lens with a shooting direction facing the camera front glass is arranged at the front end of each camera cabin;

[0014] A laser front-view glass is arranged in the middle of the front of the middle cabin, and a laser emitter is arranged inside the middle cabin to emit laser lines in the direction of the laser front-view glass; the angle between the emission direction of the laser emitter and the shooting direction of each camera is an acute angle;

[0015] The aviation plug is sealed and connected to the wall of the intermediate cabin. The aviation plug inside the intermediate cabin is electrically connected to the laser transmitter and the camera. The aviation plug outside the intermediate cabin is electrically connected to the power supply, the system parameter calibration system and the three-dimensional laser point cloud reconstruction system.

[0016] The illumination directions of the two cameras and one laser transmitter are all toward the shooting window.

[0017] In the above technical scheme, by arranging two camera cabins on both sides of the middle cabin, arranging a laser transmitter in the middle cabin and arranging a camera in the camera cabin, the binocular camera and line laser technology are integrated into a set of equipment. The binocular camera integrates the line laser to realize the underwater image shooting function and realize high-precision and high-stability underwater three-dimensional reconstruction, thereby meeting the needs of marine engineering, marine science and other fields for underwater three-dimensional data acquisition, and solving the problem that the existing underwater camera equipment cannot realize the binocular camera and line laser functions at the same time, thereby limiting the effect and application scope of underwater three-dimensional reconstruction.

[0018] Furthermore, the middle cabin is connected to the two camera cabins, the back of the middle cabin is sealed and detachably provided with a rear cover plate, and the aviation plug is sealed and connected to the rear cover plate; the rear end of each camera cabin is sealed and detachably provided with a rear end sealing cover; the setting of the rear cover plate and the rear end sealing cover can facilitate the assembly and subsequent disassembly and maintenance of the laser emitter and the camera.

[0019] The camera front view glass and the laser front view glass are sealed and connected to the front end of the camera cabin and the front face of the middle cabin respectively through mounting parts. The mounting parts are in a circular ring structure, and a plurality of bolt connectors are evenly arranged on the mounting parts at annular intervals with their own axis as the center.

[0020] Furthermore, each camera cabin is provided with a camera fixing block, each camera fixing block is a hollow square column structure with an opening at one end and a sealed end at the other end, the end of the camera fixing block with the opening is arranged toward the camera front glass, and the other end of the camera fixing block is fixedly connected to the inner wall of the rear end sealing cover; the camera is fixedly arranged inside the camera fixing block;

[0021] The camera and the camera fixing block are movably matched, and a long hole is opened on the side wall of the camera fixing block. The long hole is arranged along the length direction of the camera cabin, and a bolt locking piece for locking the camera is arranged in the long hole.

[0022] In the above technical solution, the position of the camera in the camera fixing block can be adjusted, the distance between the lens on the camera and the camera front glass can be adjusted, and after the distance is adjusted, the current position of the camera and the lens can be fixed by tightening the bolt locking member to adapt to the use of different models of cameras and improve the flexibility of use of the entire underwater three-dimensional reconstruction image acquisition equipment.

[0023] Furthermore, a laser fixing block for fixing the laser transmitter is provided inside the intermediate cabin, and the rear end of the laser fixing block is sealed and connected to the rear cover plate, thereby improving the stability of laser installation and laser use; waterproof strips are provided on the connecting end surfaces of the rear cover plate and the rear end sealing cover, and the waterproof strips are used for waterproof treatment to prevent water from entering the interior of the device and causing malfunctions when the underwater image acquisition device is shooting underwater.

[0024] The present invention also provides a reconstruction method of an underwater concrete defect three-dimensional reconstruction system, which comprises:

[0025] Step 1: Acquire multiple underwater concrete defect images with different postures and strong characteristic lasers through underwater image acquisition equipment, eliminate noise of multiple images through Gaussian filtering, and then restore the field of view coordinates of multiple images in water according to the air and underwater light refraction model to obtain the field of view coordinates of multiple images in air;

[0026] Step 2: System parameter calibration: The system uses Zhang's calibration method to calibrate the internal reference table of the two cameras in the underwater image acquisition device;

[0027] Step 3, extracting the two-dimensional coordinates of the laser stripes from multiple underwater concrete defect images with different postures and strong characteristic lasers;

[0028] Step 4, system parameter calibration: the system photographs the chessboard calibration plate without laser stripes, extracts the intersection points of the laser line and the chessboard corner point connection line of the chessboard calibration plate image with laser, obtains the world coordinates of the intersection points based on the invariance of the cross ratio and brings it into the external parameter matrix, and fits these intersection points to obtain the laser plane equation;

[0029] Step 5: The 3D laser point cloud reconstruction system brings the laser stripes into the laser plane equation and selects the underwater concrete defect images with strong characteristic lasers from the left and right cameras for mirror-symmetric epipolar matching based on the field of view coordinates of the multiple images in the air, to obtain 3D point cloud data.

[0030] Step 6: Use a color camera to extract the color value corresponding to the laser line pixel coordinates and color the 3D point cloud data to achieve 3D reconstruction of underwater concrete defects.

[0031] The beneficial effects of the present invention are as follows: an underwater concrete defect three-dimensional reconstruction system and a reconstruction method thereof in the present invention, an underwater image acquisition device based on the binocular imaging principle and the principle of adding strong features to objects with laser lines, obtains underwater concrete defect images with strong feature lasers, and converts underwater concrete defect images with strong feature lasers into three-dimensional point cloud data through a system parameter calibration system and a three-dimensional laser point cloud reconstruction system, and colors the three-dimensional point cloud data through a color camera to achieve three-dimensional reconstruction, which greatly improves the detection efficiency and detection accuracy of underwater concrete defects, and solves the problem that the existing underwater camera equipment limits the effect of underwater three-dimensional reconstruction, resulting in low accuracy of underwater concrete defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the structure of an underwater concrete defect 3D reconstruction system.

[0033] Figure 2 This is a schematic diagram of the structure in which the stepper motor scanning system is connected and fixed to the underwater image acquisition device.

[0034] Figure 3 Schematic diagram of the underwater image acquisition device Figure 1 .

[0035] Figure 4 Schematic diagram of the underwater image acquisition device Figure 2 .

[0036] Figure 5 Flow chart of the reconstruction method of the underwater concrete defect 3D reconstruction system.

[0037] Among them, 1. water tank; 2. stepper motor scanning system; 201. mounting frame; 202. screw rod; 203. slider; 204. stepper motor; 205. mounting bracket; 3. underwater image acquisition equipment; 301. camera; 302. laser transmitter; 303. binocular cabin; 3031. middle cabin; 3032. camera cabin; 304. aviation plug; 305. lens; 306. laser front view glass; 307. rear cover; 308. rear end sealing cover; 309. mounting parts; 310. camera fixing block; 311. long strip hole; 312. laser fixing block; 313. camera front view glass. DETAILED DESCRIPTION

[0038] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0039] The present invention provides an underwater concrete defect three-dimensional reconstruction system, which includes a water tank 1, a stepper motor scanning system 2, an underwater image acquisition device 3, a system parameter calibration system and a three-dimensional laser point cloud reconstruction system;

[0040] like Figure 1 As shown, the top of the water tank 1 has an opening and the bottom is a closed structure, and a shooting window is arranged on the bottom of the water tank 1; the underwater image acquisition device 3 is arranged on the stepper motor scanning system 2, and the underwater image acquisition device 3 is located inside the water tank 1 and the shooting direction is toward the shooting window, and the stepper motor scanning system 2 drives the underwater image acquisition device 3 to perform horizontal reciprocating linear motion inside the water tank 1.

[0041] The underwater image acquisition device 3 includes two cameras 301 and a laser transmitter 302. The underwater image acquisition device 3 is used to capture underwater concrete defect images with strong characteristic lasers. The system parameter calibration system is used to calibrate the parameters of the underwater image acquisition device 3. The three-dimensional laser point cloud reconstruction system is used to convert underwater concrete defect images with strong characteristic lasers into three-dimensional point cloud data, and color the three-dimensional point cloud data through the color camera 301 to achieve three-dimensional reconstruction.

[0042] The basic principle of the underwater concrete defect three-dimensional reconstruction system in the present invention is: the stepper motor scanning system 2 drives the underwater image acquisition device 3 to perform horizontal reciprocating linear motion inside the water tank 1, so as to obtain a wider range of shooting angles, and the underwater image acquisition device 3 captures underwater concrete defect images with strong characteristic lasers, and the system parameter calibration system and the three-dimensional laser point cloud reconstruction system generate three-dimensional point cloud data according to the underwater concrete defect images with strong characteristic lasers, and color the three-dimensional point cloud data to realize three-dimensional reconstruction of underwater concrete defects, which greatly improves the detection efficiency and detection accuracy of underwater concrete defects, and solves the problem that the existing underwater camera equipment limits the effect of underwater three-dimensional reconstruction, resulting in low accuracy of underwater concrete defects.

[0043] Specifically, Figure 1 and Figure 2 As shown, as a specific setting method of the stepper motor scanning system 2, the stepper motor scanning system 2 includes a mounting frame 201 arranged on the top of the water tank 1, a screw rod 202 is rotatably arranged in the mounting frame 201, and a slider 203 is threadedly connected to the screw rod 202; a stepper motor 204 is arranged on one side of the mounting frame 201, and the output end of the stepper motor 204 is fixedly connected to one end of the screw rod 202 through a coupling; a mounting bracket 205 is vertically arranged on the slider 203, the top of the mounting bracket 205 is fixedly connected to the slider 203, and the bottom of the mounting bracket 205 is located at the bottom of the water tank 1; the underwater image acquisition device 3 is fixedly connected to the bottom of the mounting bracket 205.

[0044] The process of the stepper motor scanning system 2 driving the underwater image acquisition device 3 to move horizontally back and forth in a straight line inside the water tank 1 is as follows: by starting the stepper motor 204 to drive the screw rod 202 to rotate, the rotating screw rod 202 drives the slider 203 to move back and forth in a straight line along the length direction of the screw rod 202, thereby driving the mounting bracket 205 fixedly connected to the slider 203 and the underwater image acquisition device 3 fixedly connected to the mounting bracket 205 to move horizontally back and forth in a straight line inside the water tank 1, so that the underwater image acquisition device 3 has a wider shooting range, so that the underwater image acquisition device 3 can completely scan the target and obtain images corresponding to different positions.

[0045] like Figure 1~Figure 4 As shown, as a specific setting method of the underwater image acquisition device 3, the underwater image acquisition device 3 includes a binocular cabin 303 and an aviation plug 304, and the binocular cabin 303 is fixedly connected to the bottom of the mounting bracket 205; the binocular cabin 303 includes an intermediate cabin 3031, and two camera cabins 3032 are obliquely arranged on both sides of the intermediate cabin 3031, and the two camera cabins 3032 are symmetrically arranged; a camera front view glass 313 is arranged at the front end of each camera cabin 3032, a camera 301 is arranged in each camera cabin 3032, and a lens 305 with a shooting direction toward the camera front view glass 313 is arranged at the front end of each camera 301.

[0046] A laser front-view glass 306 is arranged in the middle of the front of the middle cabin 3031, and a laser emitter 302 emitting laser lines in the direction of the laser front-view glass 306 is arranged inside the middle cabin 3031; the angle between the emission direction of the laser emitter 302 and the shooting direction of each camera 301 is an acute angle.

[0047] The aviation plug 304 is sealed and connected to the wall of the intermediate cabin 3031. The aviation plug 304 inside the intermediate cabin 3031 is electrically connected to the laser emitter 302 and the camera 301. The aviation plug 304 outside the intermediate cabin 3031 is electrically connected to the power supply, the system parameter calibration system and the three-dimensional laser point cloud reconstruction system.

[0048] The irradiation directions of the two cameras 301 and the one laser emitter 302 are both toward the shooting window.

[0049] In the above technical scheme, by arranging two camera cabins 3032 on both sides of the middle cabin 3031, arranging a laser transmitter 302 on the middle cabin 3031 and arranging a camera 301 in the camera cabin 3032, the binocular camera 301 and the line laser technology are integrated into a set of equipment. The binocular camera 301 integrates the line laser to realize the underwater image shooting function and realizes high-precision and high-stability underwater three-dimensional reconstruction, thereby meeting the needs of marine engineering, marine science and other fields for underwater three-dimensional data acquisition, and solving the problem that the existing underwater camera 301 equipment cannot realize the binocular camera 301 and line laser functions at the same time, thereby limiting the effect and application scope of underwater three-dimensional reconstruction.

[0050] Preferably, but not limited to, the middle cabin 3031 is connected to the two camera cabins 3032, the back of the middle cabin 3031 is sealed and detachably provided with a rear cover plate 307, and the aviation plug 304 is sealed and connected to the rear cover plate 307; the rear end of each camera cabin 3032 is sealed and detachably provided with a rear end sealing cover 308; the setting of the rear cover plate 307 and the rear end sealing cover 308 can facilitate the assembly and subsequent disassembly and maintenance of the laser emitter 302 and the camera 301.

[0051] The camera front view glass 313 and the laser front view glass 306 are sealedly connected to the front end of the camera cabin 3032 and the front face of the middle cabin 3031 respectively through the mounting parts 309. The mounting parts 309 are in a circular ring structure, and a plurality of bolt connectors are evenly arranged on the mounting parts 309 at annular intervals with their own axis as the center.

[0052] Each camera cabin 3032 is provided with a camera fixing block 310. Each camera fixing block 310 has an opening at one end and a sealed hollow square column structure at the other end. The open end of the camera fixing block 310 is arranged toward the camera front view glass 313, and the other end of the camera fixing block 310 is fixedly connected to the inner wall of the rear end sealing cover 308; the camera 301 is fixedly arranged inside the camera fixing block 310.

[0053] The camera 301 is movably matched with the camera fixing block 310 . A long hole 311 is provided on the side wall of the camera fixing block 310 . The long hole 311 is arranged along the length direction of the camera cabin 3032 . A bolt locking member for locking the camera 301 is arranged in the long hole 311 .

[0054] In the above technical solution, the position of the camera 301 in the camera fixing block 310 can be adjusted, the distance between the lens 305 on the camera 301 and the camera front view glass 313 can be adjusted, and after the distance is adjusted, the current position of the camera 301 and the lens 305 can be fixed by tightening the bolt locking member to adapt to the use of different models of cameras 301 and improve the flexibility of use of the entire underwater three-dimensional reconstruction image acquisition equipment.

[0055] Specifically, a laser fixing block 312 for fixing the laser emitter 302 is provided inside the middle cabin 3031, and the rear end of the laser fixing block 312 is sealed and connected to the rear cover plate 307, thereby improving the stability of laser installation and laser use; waterproof strips are provided on the connecting end surfaces of the rear cover plate 307 and the rear end sealing cover 308, and the waterproof strips are used for waterproof treatment to prevent water from entering the interior of the device and causing malfunctions when the underwater image acquisition device 3 is shooting underwater.

[0056] like Figure 5 As shown, the present invention also provides a reconstruction method of an underwater concrete defect three-dimensional reconstruction system, which comprises:

[0057] Step 1: Acquire multiple underwater concrete defect images with different postures and strong characteristic lasers through underwater image acquisition equipment 3, eliminate noise of multiple images through Gaussian filtering, and then restore the field of view coordinates of multiple images in water according to the air and underwater light refraction model to obtain the field of view coordinates of multiple images in air;

[0058] Step 2: System parameter calibration: The system uses Zhang's calibration method to calibrate the internal reference table of the two cameras in the underwater image acquisition device;

[0059] Step 3, extracting the two-dimensional coordinates of the laser stripes from multiple underwater concrete defect images with different postures and strong characteristic lasers;

[0060] Step 4, system parameter calibration: the system photographs the chessboard calibration plate without laser stripes, extracts the intersection points of the laser line and the chessboard corner point connection line of the chessboard calibration plate image with laser, obtains the world coordinates of the intersection points based on the invariance of the cross ratio and brings it into the external parameter matrix, and fits these intersection points to obtain the laser plane equation;

[0061] Step 5: The 3D laser point cloud reconstruction system brings the laser stripes into the laser plane equation and selects the underwater concrete defect images with strong characteristic lasers from the left and right cameras 301 for mirror-symmetric epipolar line matching according to the field of view coordinates of the multiple images in the air, thereby obtaining 3D point cloud data.

[0062] Step 6: Use a color camera to extract the color value corresponding to the laser line pixel coordinates and color the 3D point cloud data to achieve 3D reconstruction of underwater concrete defects. The specific modeling software can be CloudCompare software.

[0063] Furthermore, in step 1, the calculation formula for obtaining the field of view coordinates of multiple images in the air is:

[0064]

[0065] in, is the field of view coordinate in air of a certain point in the image; is the underwater field coordinate of a certain point in the image; is the affine transformation matrix, The 8 position parameters of the affine transformation matrix.

[0066] In summary, the present invention provides a three-dimensional reconstruction system and reconstruction method for underwater concrete defects. The underwater image acquisition device 3 obtains underwater concrete defect images with strong characteristic lasers based on the binocular imaging principle and the principle of adding strong features to objects with laser lines. The underwater concrete defect images with strong characteristic lasers are converted into three-dimensional point cloud data through the system parameter calibration system and the three-dimensional laser point cloud reconstruction system, and the three-dimensional point cloud data are colored by the color camera 301 to achieve three-dimensional reconstruction, which greatly improves the detection efficiency and detection accuracy of underwater concrete defects and solves the problem that the existing underwater camera equipment limits the effect of underwater three-dimensional reconstruction, resulting in low accuracy of underwater concrete defects.

Claims

1. A 3D reconstruction system for underwater concrete defects, characterized in that: It includes a water tank, a stepper motor scanning system, an underwater image acquisition device, a system parameter calibration system and a 3D laser point cloud reconstruction system; The water tank has an opening at the top and a closed structure at the bottom, and a shooting window is arranged on the bottom of the water tank; the underwater image acquisition device is arranged on the stepper motor scanning system, the underwater image acquisition device is located inside the water tank and the shooting direction is toward the shooting window, and the stepper motor scanning system drives the underwater image acquisition device to perform horizontal reciprocating linear motion inside the water tank; The underwater image acquisition device includes two cameras and a laser transmitter, and the underwater image acquisition device is used to capture underwater concrete defect images with a strong characteristic laser; The system parameter calibration system is used to calibrate the parameters of the underwater image acquisition equipment; The three-dimensional laser point cloud reconstruction system is used to convert underwater concrete defect images with strong characteristic lasers into three-dimensional point cloud data, and color the three-dimensional point cloud data through a color camera to achieve three-dimensional reconstruction.

2. The underwater concrete defect 3D reconstruction system according to claim 1, characterized in that: The stepper motor scanning system includes a mounting frame arranged on the top of the water tank, a screw rod is rotatably arranged in the mounting frame, and a slider is threadedly connected to the screw rod; a stepper motor is arranged on one side of the mounting frame, and the output end of the stepper motor is fixedly connected to one end of the screw rod through a coupling; a mounting bracket is vertically arranged on the slider, the top of the mounting bracket is fixedly connected to the slider, and the bottom of the mounting bracket is located at the bottom of the water tank; the underwater image acquisition device is fixedly connected to the bottom of the mounting bracket.

3. The underwater concrete defect 3D reconstruction system according to claim 2, characterized in that: The underwater image acquisition device comprises a binocular cabin and an aviation plug, wherein the binocular cabin is fixedly connected to the bottom of the mounting bracket; the binocular cabin comprises an intermediate cabin, and two camera cabins are obliquely arranged on both sides of the intermediate cabin, and the two camera cabins are symmetrically arranged; a camera front glass is arranged at the front end of each camera cabin, a camera is arranged in each camera cabin, and a lens with a shooting direction facing the camera front glass is arranged at the front end of each camera cabin; A laser front-view glass is arranged in the middle of the front of the intermediate cabin, and a laser emitter is arranged inside the intermediate cabin for emitting laser lines in the direction of the laser front-view glass; the angle between the emission direction of the laser emitter and the shooting direction of each camera is an acute angle; The aviation plug is sealed and connected to the wall of the intermediate cabin, the aviation plug inside the intermediate cabin is electrically connected to the laser transmitter and the camera, and the aviation plug outside the intermediate cabin is electrically connected to the power supply, the system parameter calibration system and the three-dimensional laser point cloud reconstruction system; The irradiation directions of the two cameras and the one laser transmitter are all toward the shooting window.

4. The underwater concrete defect 3D reconstruction system according to claim 3, characterized in that: The middle cabin is connected to the two camera cabins, and the back of the middle cabin is sealed and detachably provided with a rear cover plate, and the aviation plug is sealed and connected to the rear cover plate; the rear end of each camera cabin is sealed and detachably provided with a rear end sealing cover; the camera front view glass and the laser front view glass are sealed and connected to the front end of the camera cabin and the front of the middle cabin respectively through mounting parts, and the mounting parts are in a circular ring structure, and a plurality of bolt connectors are evenly arranged on the mounting parts in an circumferential direction with their own axis as the center.

5. The underwater concrete defect 3D reconstruction system according to claim 4, characterized in that: Each of the camera cabins is provided with a camera fixing block, each of the camera fixing blocks is a hollow square column structure with an opening at one end and a sealed end at the other end, the end of the camera fixing block with the opening is arranged toward the camera front glass, and the other end of the camera fixing block is fixedly connected to the inner wall of the rear end sealing cover; the camera is fixedly arranged inside the camera fixing block; The camera is movably matched with the camera fixing block. A long hole is provided on the side wall of the camera fixing block. The long hole is arranged along the length direction of the camera cabin. A bolt locking piece for locking the camera is arranged in the long hole.

6. The underwater concrete defect 3D reconstruction system according to claim 5, characterized in that: A laser fixing block for fixing the laser transmitter is arranged inside the intermediate cabin, and the rear end of the laser fixing block is sealed and connected to the rear cover plate; waterproof rubber strips are arranged on the connecting end surfaces of the rear cover plate and the rear end sealing cover.

7. A reconstruction method of the underwater concrete defect 3D reconstruction system according to any one of claims 1 to 6, characterized in that: include: Step 1: Acquire multiple underwater concrete defect images with different postures and strong characteristic lasers through underwater image acquisition equipment, eliminate noise of multiple images through Gaussian filtering, and then restore the field of view coordinates of multiple images in water according to the air and underwater light refraction model to obtain the field of view coordinates of multiple images in air; Step 2: System parameter calibration: The system uses Zhang's calibration method to calibrate the internal reference table of the two cameras in the underwater image acquisition device; Step 3, extracting the two-dimensional coordinates of the laser stripes from multiple underwater concrete defect images with different postures and strong characteristic lasers; Step 4, system parameter calibration: the system photographs the chessboard calibration plate without laser stripes, extracts the intersection points of the laser line and the chessboard corner point connection line of the chessboard calibration plate image with laser, obtains the world coordinates of the intersection points based on the invariance of the cross ratio and brings it into the external parameter matrix, and fits these intersection points to obtain the laser plane equation; Step 5: The 3D laser point cloud reconstruction system brings the laser stripes into the laser plane equation and selects the underwater concrete defect images with strong characteristic lasers from the left and right cameras for mirror-symmetric epipolar matching based on the field of view coordinates of the multiple images in the air, to obtain 3D point cloud data. Step 6: Use a color camera to extract the color value corresponding to the laser line pixel coordinates and color the 3D point cloud data to achieve 3D reconstruction of underwater concrete defects.

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