Structured light-based multi-light-knife crack multi-point three-direction displacement measuring device and method

Abstract

The invention relates to a multi-light-knife crack multi-point three-way displacement measuring device and method based on structured light, the device comprises an illumination light source arranged above a crack, a laser, a camera and a light shield forming a whole closed environment, and the laser generates light knife projection to irradiate the surface of the crack by utilizing the measurement characteristics of the structured light; a camera shoots a light knife image irradiated on the surface of the building with the crack, and the deformation displacement of the two sides of the crack in the Y direction is calculated through light knife center extraction; image information is obtained through the illumination light source, the displacement of the crack in the X direction and the Z direction is calculated in an image feature point capturing and image comparison mode, and therefore three-direction displacement measurement is achieved, and the crack monitoring device has the advantages of being wide in range, high in environmental adaptability, high in reliability and the like and can meet the crack monitoring requirement in a complex engineering scene.

Description

Technical Field

[0001] This invention relates to the field of engineering measurement technology, and in particular to a device and method for measuring the multi-point triaxial displacement of cracks based on structured light multi-light knife. Background Technology

[0002] In the health monitoring system of modern large-scale civil engineering structures (such as bridges, dams, and tunnels), three-dimensional deformation monitoring of cracks is a key indicator for structural safety assessment. The core contradiction facing current measurement technologies lies in the trade-off between measurement range and accuracy: contact measurement devices typically only cover a range of 0-50 mm and are significantly affected by temperature and humidity (typical error ±0.5 mm); while non-contact optical measurement has the advantage of long-distance measurement, its three-dimensional measurement accuracy is generally limited to the millimeter level due to existing image recognition algorithms.

[0003] Structured light technology, with its excellent directionality and coherence, has high practical value in measuring multi-point triaxial changes in cracks. For example, patent CN223258886U utilizes structured light technology to achieve high-precision measurement of the 3D shape of an object's surface. However, a drawback is that it cannot be applied to monitoring and calculating crack feature points in scenarios such as building cracks. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention aims to provide a structured light multi-light blade crack multi-point triaxial displacement measurement device and method. This invention utilizes the measurement characteristics of structured light, setting a laser above the crack to generate a light blade, which is projected onto the crack surface. A camera captures an image of the light blade illuminating the cracked building surface. The deformation displacement in the Y direction on both sides of the crack is calculated by extracting the light blade center. Images are acquired through an illumination source, and the displacement in the X and Z directions of the crack is calculated based on feature point capture and image comparison, thereby achieving triaxial displacement measurement. This method features strong environmental adaptability and high reliability, and can meet the crack monitoring needs in complex engineering scenarios.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A structured light multi-light knife crack multi-point three-dimensional displacement measurement device includes a cantilever A that can be fixed to one side of the crack 6. The measuring end of the cantilever A is equipped with a light shield B that spans across the crack 6. The light shield B contains an illumination source 5, a laser 2, and a camera 3. The laser 2 emits a laser knife that vertically illuminates the surface of the crack 6. The camera 3 can receive the laser knife image 4 illuminating the crack 6 and the image illuminating the crack 6 by the illumination source 5. The images are processed and recognized by the main control circuit 1 itself or uploaded to the cloud to calculate the three-dimensional displacement data of the crack. The main control circuit 1 also provides power to the laser 2, the camera 3, and the illumination source 5.

[0007] The light shield B is opaque, and the bottom is made of soft material to form a simple dustproof seal with the cracked building surface. The bottom surface of the light shield B and the plane of the gap 6 are as close as possible.

[0008] The camera 3 is a CCD or CMOS camera or other image device.

[0009] The laser beam emitted by the laser 2 is generated by modulating the laser beam into multiple linear light sources with a width as narrow as possible, less than 1 mm.

[0010] Multiple lasers 2 are configured, and the resulting multiple light beams are projected onto different areas of the crack 6 to realize the displacement changes of the two sides of the crack in the Y direction at multiple coordinates on the crack, thereby enabling large-range measurement.

[0011] A method for measuring multi-point triaxial displacement of cracks based on structured light multi-light scalpel, using the aforementioned measuring device, includes the following steps:

[0012] Step 1: Set up the measuring device, use camera 3 to capture image 4 of the laser beam illuminating the gap 6 after laser 2 is emitted, and extract the center of the laser beam using the centroid algorithm:

[0013]

[0014] Where i represents the row cell coordinate variable of the image;

[0015] I i (i,j) represents the light intensity of the image in the i-th row and j-th column;

[0016] Based on the structured light principle, the coordinates (Xi, Zi) of the light scalpel irradiation point are extracted, and the number of misaligned pixels ΔU at the center of the light scalpel at the left and right ends of the crack is calculated. i ,like Figure 5 As shown, the coordinates (Xi, Zi) of the laser scalpel irradiation point can be calculated, along with the displacement ΔY in the depth Y direction on both sides of the crack. i ΔY i With ΔU i The relationship follows the structured light measurement formula (2):

[0017]

[0018] Where S is the object distance between slit 6 and camera 3, S' is the image distance, and α i The angle between the laser scalpel i and the optical axis of camera 3 is given by the angle between their axes. Therefore, the camera obtains the number of misaligned pixels ΔU at the centers of the laser scalpels at the left and right ends of the crack. i The displacement ΔY in the Y direction of the crack can then be obtained. i The Y direction is perpendicular to the surface of crack 6, the crack width direction is the X direction, and the vertical direction of the crack is the Z direction.

[0019] Step 2: Measure the displacement change ΔY in the Y direction. i Afterwards, all lasers 2 are turned off, illumination source 5 is turned on, and camera 3 acquires images of the surface of the slit 6 that have undergone displacement changes in the X or Z direction. The main control circuit 1 directly processes the image signal or uploads it to the cloud. The position changes of feature points with coordinates (Xi, Zi) in the X and Z directions on both sides of the slit 6 can be calculated through image feature recognition algorithms. The change in the number of rows and columns of pixels with the coordinates (Ui, Vj) of the feature point image is then calculated. j ΔU i Directly calculate the crack width ΔX in the X direction of coordinates (Xi, Yi). i Changes and displacement changes in the Z direction ΔZ i That is, to obtain the transverse X and longitudinal Z displacements of the crack.

[0020] The principle of step 1 is as follows: Assuming that the crack 6 undergoes a displacement change in the Y direction, the image of the laser beam emitted by the laser 2 projected onto the crack 6 will also change. Assuming that the building surfaces on both sides of the crack are on the same plane, the laser beam image 4 obtained by the camera 3 shows a straight line on both sides of the crack. When one side of the crack changes by ΔY in the Y direction... i The light slash image 4 obtained by camera 3 shows a broken line on both sides of the crack, and the number of pixels jumping on the broken line is related to ΔY. i A functional relationship based on the structured light measurement formula (2) is formed. Conversely, the corresponding projection image of the light blade as a polygonal line is acquired by the camera 3. The application program in the main control circuit 1, based on the structured light principle, calculates the displacement change ΔY in the Y direction according to the change of the polygonal line in the light blade image based on the structured light measurement formula (2). i .

[0021] Multiple lasers 2 are arranged to ensure that all laser beams are projected onto the surface of the slit 6. The camera 3 must be able to simultaneously capture images of all laser beams, and the laser beams must not intersect in the images. Multiple laser beams are projected onto different areas of the slit 6, and the coordinates (Xi, Yi) of the intersection point of each laser beam with the slit are measured, along with the displacement ΔY in the Y direction on both sides of the slit. i This allows for the measurement of displacement data at multiple points (Xi, Yi) on the crack, thus realizing the displacement change ΔY of the crack's coordinates (Xi, Yi) in the Y direction on both sides of the crack. i .

[0022] Compared with the prior art, the advantages of the present invention are:

[0023] (1) This invention employs the structured light measurement principle in the Y direction, fully utilizing the characteristics of high coherence and directionality of lasers. It uses lasers to generate multiple optical blades and extracts the center of the optical blades based on the centroid algorithm, thereby realizing the multi-point Y-direction displacement change ΔY of the crack.i High-precision measurement; achieving high-precision measurement of the displacement change ΔY in the Y direction of the crack.

[0024] (2) This invention uses illumination sources in the X and Z directions, and relies on image comparison algorithms to calculate the displacement of the crack in the X and Z directions by capturing image feature points and comparing images. This can realize the ΔX displacement of multiple points on the crack. i ΔZ i High-precision displacement measurement.

[0025] In summary, this invention, through the application of structured light, image feature point recognition methods, and image comparison calculation methods, can measure the changes in length, width, and depth of cracks, and has broad engineering application prospects. Attached Figure Description

[0026] Figure 1 This is the front view of the present invention.

[0027] Figure 2 This is the left view of the present invention.

[0028] Figure 3 This is a top view of the present invention.

[0029] Figure 4 This is a schematic diagram of the coordinate direction during measurement according to the present invention.

[0030] Figure 5 This is a schematic diagram of the crack scalpel effect of the present invention.

[0031] In the diagram: 1-Main control circuit; 2-Laser; 3-Camera; 4-Light blade image; 5-Illumination source; 6-Gap; A-Cantilever; B-Light shield. Detailed Implementation

[0032] The present invention will now be described in detail with reference to the accompanying drawings.

[0033] Reference Figure 1 , Figure 2 A structured light multi-scalar crack multi-point three-dimensional displacement measurement device includes a cantilever A fixed to one side of the crack 6. The measuring end of the cantilever A is equipped with a light shield B that spans across the crack 6. The light shield B contains an illumination source 5, a laser 2, and a camera 3. The laser scalar emitted by the laser 2 vertically illuminates the surface of the crack 6. The camera 3 can receive the laser scalar image 4 illuminating the crack 6 and the image illuminating the crack 6 by the illumination source 5. The images are processed and recognized by the main control circuit 1 itself or uploaded to the cloud to calculate the three-dimensional displacement data of the crack. The main control circuit 1 also provides power to the laser 2, the camera 3, and the illumination source 5.

[0034] The light shield B is opaque, and the bottom is made of soft material to form a simple dustproof seal with the cracked building surface, which can also achieve opacity and prevent stray light. The bottom surface of the light shield B and the plane of the gap 6 are as close as possible.

[0035] The camera 3 is a CCD or CMOS camera or other image device.

[0036] The laser beam emitted by the laser 2 is generated by modulating the laser beam into multiple linear light sources with a width as narrow as possible, less than 1 mm.

[0037] Multiple lasers 2 are configured, and the resulting multiple light blades are projected onto different areas of the crack 6. This refines the measurement range of the crack, allowing for the measurement of the displacement changes of the crack at the coordinates Xi and Zi of each light blade intersection point with the crack. The entire device can then provide displacement data for multiple points of the crack, enabling high-precision measurement over a large range.

[0038] A method for measuring multi-point triaxial displacement of cracks based on structured light multi-light scalpel, using the aforementioned measuring device, with reference to... Figure 3 This includes the following steps:

[0039] Step 1: Set up the measuring device and use camera 3 to capture image 4 of the laser beam illuminating the gap 6 after laser 2 is emitted. Extract the center of the laser beam using the following centroid algorithm:

[0040]

[0041] Where i represents the row cell coordinate variable of the image;

[0042] I i (i,j) represents the light intensity of the image in the i-th row and j-th column;

[0043] Based on the structured light principle, the coordinates (Xi, Zi) of the light scalpel irradiation point are extracted, and the number of misaligned pixels ΔU at the center of the light scalpel at the left and right ends of the crack is calculated. i ,like Figure 5 As shown, the coordinates (Xi, Zi) of the laser scalpel irradiation point can be calculated, along with the displacement ΔY in the depth Y direction on both sides of the crack. i ΔY i With ΔU i The relationship follows the structured light measurement formula (2):

[0044]

[0045] Where S is the object distance between slit 6 and camera 3, S' is the image distance, and α i The angle between the laser scalpel i and the optical axis of camera 3 is given by the angle between their axes. Therefore, the camera obtains the number of misaligned pixels ΔU at the centers of the laser scalpels at the left and right ends of the crack. i The displacement ΔY in the Y direction of the crack can then be obtained.i The Y direction is perpendicular to the surface of crack 6, the X direction is the crack width direction, and the Z direction is the vertical direction of the crack. See details in the [reference needed] section. Figure 4 As shown.

[0046] Step 2: Measure the displacement change ΔY in the Y direction. i Afterwards, all lasers 2 are turned off, the illumination source 5 is turned on, and the camera 3 acquires images of the surface of the slit 6 that have undergone displacement changes in the X or Z direction. The main control circuit 1 directly processes the image signal or uploads it to the cloud. The position changes of the feature points with coordinates (Xi, Zi) in the X and Z directions on both sides of the slit 6 can be calculated through the image feature recognition algorithm. The change in the number of rows and columns of the feature point image pixel coordinates (Ui, Vj) ΔV is then used to calculate the position changes of the feature points. j ΔU i The crack width ΔX in the X direction at coordinate (Xi, Yi) can be directly calculated. i Changes and displacement changes in the Z direction ΔZ i That is, to find the transverse X and longitudinal Z displacements of the crack, with the crack width direction as the X direction and the crack vertical direction as the Z direction.

[0047] The principle of step 1 is as follows: Using the plane containing the crack 6 as a reference, the emission direction of laser 2 is adjusted to focus the laser into a very narrow beam, called a structural beam. This beam is projected perpendicularly onto both sides of the crack 6, thus forming two broken beams. Assuming the building surfaces on both sides of the crack are on the same plane, the beam image 4 obtained by the camera shows the broken beams on both sides of the crack as a straight line. Assuming the crack 6 undergoes a displacement in the Y direction, the image of the beam emitted by laser 2 projected onto the crack 6 will also change. Assuming the building surfaces on both sides of the crack are on the same plane, the beam image 4 obtained by camera 3 shows the beams on both sides of the crack as a straight line. When one side of the crack changes by ΔY in the Y direction... i The light slash image 4 obtained by camera 3 shows a broken line on both sides of the crack, and the number of pixels jumping on the broken line is related to ΔY. i A functional relationship based on the structured light measurement formula (2) is formed. Conversely, the corresponding projection image of the light blade as a polygonal line is acquired by the camera 3. The application program in the main control circuit 1, based on the structured light principle, calculates the displacement change ΔY in the Y direction according to the change of the polygonal line in the light blade image and the structured light measurement formula (2). i ;

[0048] Step 2 specifically involves: Assuming that the crack 6 to be tested undergoes a displacement change in the X direction, the image of crack 6 will also change. Laser 2 is turned off, illumination source 5 is turned on, and camera 3, positioned within the device, directly acquires images of the cracks on the building surface. The application program in the main control circuit, based on the image comparison and change algorithm, calculates the change in the number of column pixels ΔV based on the feature point image pixel coordinates (Ui, Vj).j The crack width direction ΔX at coordinate (Xi, Yi) can be directly calculated. i By changing the displacement value, the change in displacement ΔX in the X direction can be calculated. i ;

[0049] Similarly, assuming the crack under test undergoes displacement in the Z direction, the crack image will also change. A camera positioned within the device captures the changed image of the crack. The application program in the main control circuit, based on an image contrast algorithm, determines the change by adjusting the row pixel number change ΔU at the image pixel coordinates (Ui, Vj). i The displacement change ΔZ in the Z direction can then be calculated. i ;

[0050] Steps one and two together achieve the ΔX in the three directions (X, Y, Z) of the crack coordinate point (Xi, Yi). i ΔY i ΔZ i The three-dimensional changes.

[0051] In the actual environment, the change in gap 6 occurs simultaneously in three directions. The measurement is performed in two steps. First, laser 2 is activated to generate a laser beam, which projects a change onto the crack image. A camera positioned inside the device captures the corresponding changed projection image. The application program in the main control circuit, based on the laser beam image change algorithm, first calculates the displacement change ΔY in the Y direction. i The second step is to turn off laser 2, turn on illumination source 5, and then calculate the displacement ΔX in the X and Z directions using an image comparison algorithm. i ΔZ i .

[0052] The camera 3 captures images of the gap 6. The method for finding image feature points is to use the image coordinates (Ui, Vj) of each intersection point between the light blade and the gap as the coarse coordinates for selecting image recognition feature points. At least three feature coordinate points are selected around these coarse coordinates as feature point data. Selecting at least three coordinate points serves as backup (in case a feature point is damaged). On both sides of the gap 6, each light blade has an intersection point, and the feature point coordinates are determined using the same method. When calculating the X and Z displacement changes, three sets of data points from both sides, totaling six points, are used for overall calculation to determine three sets of X and Z displacement data ΔX. i ΔZ i The final data is obtained by averaging the three sets of data, or by finding the minimum value among the three sets of data as the final change value ΔX. i ΔZ i .

[0053] The laser 2 uses galvanometer or projection technology to adjust the spacing of the scanning light blades as needed, and collects image feature points on the surface of the slit 6, which can increase the measurement range and adjust the spatial resolution.

[0054] This invention transforms the three-dimensional displacement changes of a crack into changes in a laser beam projection image. Based on the principle of structured light measurement, it measures the relative displacement changes in the Y-direction (out-of-plane direction) on both sides of the crack. Its measurement accuracy can reach 0.1 millimeters or even down to the micrometer level.

[0055] The present invention also employs image processing algorithms such as image feature point extraction. By collecting the pixel number changes of feature points on both sides of the crack, the displacement changes of the feature point crack in the X (crack width direction) and Z (crack vertical direction) directions are extracted and calculated, thereby improving the measurement accuracy by an order of magnitude, with an accuracy of 0.01 mm or even 1 micrometer.

[0056] This invention allows for adjustment of the spatial resolution of crack measurement by adjusting the number and spatial spacing of the laser blades 2. The spatial resolution can be adjusted from 0.1 mm to millimeters or a specified number of spatial resolution crack measurements. The crack measurement accuracy can be adjusted by adjusting the number of laser blades and the focal length of the camera lens, achieving crack measurement accuracy from micrometers to millimeters or higher.

Claims

1. A multi-point triaxial displacement measurement device for cracks based on structured light multi-light knife, characterized in that, The system includes a cantilever (A) fixed to one side of the gap (6). The measuring end of the cantilever (A) is equipped with a light shield (B) and spans across the gap (6). Inside the light shield (B) are an illumination source (5), a laser (2), and a camera (3). The laser beam emitted by the laser (2) vertically illuminates the surface of the gap (6). The camera (3) can receive the image (4) of the laser beam illuminating the gap (6) and the image of the illumination source (5) illuminating the gap (6). The main control circuit (1) processes and recognizes the images or uploads them to the cloud to calculate the three-dimensional displacement data of the crack. The main control circuit (1) also provides power to the laser (2), the camera (3), and the illumination source (5).

2. The structured light multi-light knife crack multi-point triaxial displacement measurement device according to claim 1, characterized in that, The light shield (B) is opaque, and the bottom is made of soft material to form a simple dustproof seal with the cracked building surface. The bottom surface of the light shield (B) and the plane of the gap (6) are as close as possible.

3. The structured light multi-light knife crack multi-point triaxial displacement measurement device according to claim 1, characterized in that, The camera (3) is a CCD or CMOS camera or other image device.

4. The structured light multi-light knife crack multi-point triaxial displacement measurement device according to claim 1, characterized in that, The laser beam emitted by the laser (2) is generated by modulating the laser beam into multiple linear light sources with a width as narrow as possible, and the line width is less than 1 mm.

5. The structured light multi-light knife crack multi-point triaxial displacement measurement device according to claim 1, characterized in that, Multiple lasers (2) are set up, and the resulting multiple light blades are projected onto different areas of the crack (6) to realize the displacement change of the two sides of the crack in the Y direction of multiple coordinates on the crack, and to realize a large range measurement.

6. A method for measuring multi-point triaxial displacement of cracks based on structured light multi-light scalpel, characterized in that, Based on the measuring device according to any one of claims 1-5, the method includes the following steps: Step 1: Set up the measuring device, use camera (3) to acquire the image (4) of the laser blade illuminating the gap (6) after the laser (2) is emitted, and extract the center of the laser blade using the centroid algorithm: Light knife centroid image coordinates Where i represents the row cell coordinate variable of the image; I i (i,j) represents the light intensity of the image in the i-th row and j-th column; Based on the structured light principle, the coordinates (Xi, Zi) of the light scalpel irradiation point are extracted, and the number of misaligned pixels ΔU at the center of the light scalpel at the left and right ends of the crack is calculated. i As shown in Figure 5, the coordinates (Xi, Zi) of the laser irradiation point can be obtained, along with the displacement ΔY in the depth Y direction on both sides of the crack. i ΔY i With ΔU i The relationship follows the structured light measurement formula (2): Where S is the object distance between slit 6 and camera 3, S' is the image distance, and α i The angle between the laser scalpel i and the optical axis of camera 3 is given by the angle between their axes. Therefore, the camera obtains the number of misaligned pixels ΔU at the centers of the laser scalpels at the left and right ends of the crack. i The displacement ΔY in the Y direction of the crack can then be obtained. i The Y direction is perpendicular to the surface of crack 6, the crack width direction is the X direction, and the vertical direction of the crack is the Z direction. Step 2: Measure the displacement change ΔY in the Y direction. i Afterwards, all lasers (2) are turned off, the illumination source (5) is turned on, and the camera (3) acquires images of the surface of the gap (6) where displacement changes in the X or Z direction. The main control circuit (1) directly processes the image signal or uploads it to the cloud. The position changes of the feature points on both sides of the gap (6) in the X and Z directions can be calculated by the image feature recognition algorithm. The change in the number of rows and columns of the feature point image element coordinates (Ui, Vj) is calculated by the change in the number of rows and columns of the feature point image element coordinates (Ui, Vj). j ΔU i Directly calculate the crack width ΔX in the X direction of coordinates (Xi, Yi). i Changes and displacement changes in the Z direction ΔZ i That is, to obtain the transverse X and longitudinal Z displacements of the crack.

7. The method for measuring multi-point triaxial displacement of cracks based on structured light multi-light scalpel as described in claim 6, characterized in that, Step one assumes that after the crack (6) undergoes a displacement change in the Y direction, the image of the laser beam emitted by the laser (2) projected onto the crack (6) will also change. Assuming that the building surfaces on both sides of the crack are on the same plane, the laser beam image (4) obtained by the camera (3) shows a straight line on both sides of the crack. When one side of the crack changes ΔY in the Y direction... i The light knife image (4) obtained by camera (3) shows a broken line on both sides of the crack, and the number of pixels jumping on the broken line is related to ΔY. i A functional relationship based on the structured light measurement formula (2) is formed. Conversely, the corresponding projection image of the light blade forming a polygonal line is acquired by the camera (3). The application program in the main control circuit (1), based on the structured light principle, can calculate the displacement change ΔY in the Y direction according to the change of the polygonal line in the light blade image based on the structured light measurement formula (2). i .

8. The method for measuring multi-point triaxial displacement of cracks based on structured light multi-light scalpel as described in claim 6, characterized in that, Multiple lasers (2) are arranged to ensure that all laser blades are projected onto the surface of the slit (6). The camera (3) must be able to simultaneously capture images of all laser blades, and the laser blades must not intersect in the images. Multiple laser blades are projected onto different areas of the slit (6), and the coordinates (Xi, Yi) of the intersection point of each laser blade and the crack are measured, along with the displacement ΔY in the Y direction on both sides of the crack. i This allows for the measurement of displacement data at multiple points (Xi, Yi) on the crack, thus realizing the displacement change ΔY of the crack's coordinates (Xi, Yi) in the Y direction on both sides of the crack. i .

9. The method for measuring multi-point triaxial displacement of cracks based on structured light multi-light scalpel as described in claim 6, characterized in that, The camera (3) acquires images of the gap (6). The method for finding image feature points is to use the image coordinates (Ui, Vj) of each intersection point of the light blade and the gap as the coarse coordinates for selecting image recognition feature points. At least three feature coordinate points are selected around these coarse coordinates as feature point data. On both sides of the gap (6), each light blade will have an intersection point. The feature point coordinates are determined according to the method for finding image feature points. When calculating the displacement changes in the X and Z directions, at least three sets of data from the left and right sides, a total of six points, will be used for overall calculation to calculate at least three sets of X and Z displacement data ΔX. i ΔZ i The final data is obtained by averaging these at least three sets of data, or by finding the minimum value among these at least three sets of data as the final change value ΔX. i ΔZ i .

10. The method for measuring multi-point triaxial displacement of cracks based on structured light multi-light scalpel as described in claim 6, characterized in that, The laser (2) uses galvanometer or projection technology to adjust the spacing of the scanning light blade as needed, and collects image feature points on the surface of the slit (6) to increase the measurement range and spatial resolution adjustment.

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