Crack width measurement method and system considering the tilt angle of parallel laser beam

Abstract

The present application provides a crack width measurement method and system that takes into account the inclination angle of a parallel laser beam. The present application uses a laser beam emitting terminal to project a light spot on the measured plane, and calculates the imaging parameters of the camera when shooting the light spot and the gap on the measured plane by fitting the light spot and analyzing the images of the light spot at different rotation angles. As a result, the present application can directly calculate the corresponding gap width through the pixel position and number of pixels occupied by the gap on the measured plane obtained by the camera, thereby achieving accurate measurement of the gap size. The camera of the present application does not need to calibrate the installation position and installation angle of the laser equipment when shooting the gap and light spot image, and does not need to consider the influence of the inclination angle on the measurement accuracy, so the detection is simpler and the data obtained is more accurate.

Description

Technical Field

[0001] The present application relates to the technical field of bridge crack measurement, and in particular to a crack width measurement method and system taking into account the tilt angle of a parallel laser beam. Background Art

[0002] The measurement based on bridge inspection vehicles is costly and labor-intensive. Therefore, it is necessary to develop a portable non-contact measuring device that is small in size, low in cost, high in accuracy, and easy to use, so as to conveniently measure cracks during bridge maintenance.

[0003] Existing bridge gap measurement methods can use the center distance of parallel laser beams as the measurement reference, aim the parallel laser beam at the target to be measured and take a picture, extract the center of the laser spot in the image, use the center distance as the measurement reference, and use the image pixels as the measurement scale to achieve high-precision, portable crack measurement goals.

[0004] However, under the existing measurement methods, when using a portable crack measurement device to measure cracks, in order to obtain higher measurement accuracy, it is usually necessary to ensure that the target plane is parallel to the photographing plane. However, in actual measurement, due to the complex location of the crack, it is difficult to set up and adjust the installation position of the laser equipment, so it is difficult to ensure that the target plane is completely parallel to the photographing plane. In the prior art, once the inclination angle between the two is large, it is also necessary to consider the impact of the inclination angle on the measurement accuracy and correct the measurement deviation caused by the inclination angle. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present application provides a crack width measurement method and system that takes into account the tilt angle of a parallel laser beam. The present application obtains the ratio between the two axes of the spot ellipse by fitting the laser spot, and then obtains the angle between the laser center line and the measured plane, thereby calculating the shooting angle and object distance, and accurately calculating the actual width of the crack. The present application specifically adopts the following technical solutions.

[0006] Firstly, in order to achieve the above-mentioned purpose, a crack width measurement method considering the inclination angle of a parallel laser beam is proposed, and the steps include: respectively fitting the spots formed by the projection of several mutually parallel laser beams; determining the horizontal axis of the fitted spot ellipse and recording its axis length L1; keeping the distance between the laser beam emitting terminal and the measured plane, rotating the laser beam emitting terminal and photographing the spot images formed by the laser beam projection at different rotation angles; finding the shortest axis length L2 in the spot ellipse obtained by fitting all the laser spots according to the spot images formed by the laser beam projection at different rotation angles; calculating the angle β between the line connecting the laser centers at both ends of the laser beam emitting terminal and the plane where the measured crack is located according to the horizontal axis length L1 and the shortest axis length L2; determining the proximal micro-laser and its corresponding laser spot through the rotation angle; calculating the distance l2 between the center points of the laser spots at both ends on the measured plane according to the actual distance l1 between the centers of the lasers at both ends of the laser beam emitting terminal; determining the imaging parameters according to the pixel positions of the center points of the laser spots at both ends in the measured plane image, and thereby calculating the crack width corresponding to the pixel positions and number of cracks in the measured plane image.

[0007] Optionally, a crack width measurement method taking into account the inclination angle of a parallel laser beam as described above, wherein, when the laser beam emitting terminal is rotated and the spot image formed by the laser beam projection at different rotation angles is photographed, the rotation angle at least covers the state where the angle between the line connecting the laser centers at both ends of the laser beam emitting terminal and the plane where the crack to be measured is located is 0.

[0008] Optionally, in any of the above crack width measurement methods taking into account the inclination angle of the parallel laser beam, the angle β between the line connecting the laser centers at both ends of the laser beam emission terminal and the plane where the crack to be measured is located is arccos(L2 / L1).

[0009] Optionally, a crack width measurement method taking into account the inclination angle of a parallel laser beam as described above, wherein the step of determining the proximal micro-laser and its corresponding laser spot by the rotation angle comprises: establishing a coordinate system with the measured plane as the plane where the origin is located, with the horizontal direction from left to right along the screen of the laser beam emitting terminal as the x-axis, with the horizontal direction from bottom to top along the screen of the laser beam emitting terminal as the z-axis, and with the direction pointing to the measured plane as the y-axis; calculating the rotation angle values[3] of the laser beam emitting terminal around the z-axis according to the distance between different micro-lasers and the measured plane; and determining the proximal micro-laser and its corresponding laser spot by the rotation angle.

[0010] Optionally, in any of the above crack width measurement methods taking into account the inclination angle of the parallel laser beam, the distance between the center points of the laser spots at both ends of the measured plane is l2 = l1 / cosβ.

[0011] Optionally, a crack width measurement method considering the inclination angle of a parallel laser beam as described above, wherein the imaging parameters are determined according to the pixel positions of the center points of the laser spots at both ends in the measured plane image, and the specific steps of calculating the crack width corresponding to the pixel positions and number of cracks in the measured plane image include: calculating the distance L from the measured plane to the imaging center and the angle β between the line connecting the laser centers at both ends of the laser beam emitting terminal and the plane where the measured crack is located according to the pixel positions of the center points of the laser spots at both ends in the measured plane image and the total number of loudnesses 2n within the imaging angle of view, and thereby calculating the actual width of the crack as:

[0012]

[0013] Optionally, in any of the above-mentioned crack width measurement methods taking into account the tilt angle of the parallel laser beam, the specific steps of calculating the distance L from the measured plane to the imaging center and the angle β between the line connecting the laser centers at both ends of the laser beam emission terminal and the plane where the measured crack is located according to the pixel positions of the center points of the laser spots at both ends in the measured plane image and the total number of loudness 2n within the imaging angle of view include: Calculate the distance L from the measured plane to the imaging center, and the angle β between the line connecting the laser centers at both ends of the laser beam emission terminal and the plane where the measured crack is located;

[0014] Among them, l2 = AB represents the actual position of the laser center at both ends of the laser beam emission terminal on the measured plane, and α represents the imaging angle. Determine, where d is the diagonal length of the film, f is the imaging focal length, w is the imaging width of the object, and W=l2 is the actual width of the object being measured.

[0015] At the same time, in order to achieve the above-mentioned purpose, the present application also provides a crack width measurement system that takes into account the inclination angle of the parallel laser beam based on any of the above methods, which includes: a laser beam emitting terminal, on which a micro laser is installed, for projecting a number of mutually parallel laser beams to the measured plane; a rotating mechanism, which is connected to the laser beam emitting terminal, and is used to drive the laser beam emitting terminal to rotate while keeping the distance between the laser beam emitting terminal and the measured plane unchanged; a camera, which actually collects the light spot formed by the laser beam of the laser beam emitting terminal projected on the measured plane in real time; and a computing unit, which is used to perform ellipse fitting on the light spot formed by the projection of each laser beam, determine the horizontal axis of the fitted light spot ellipse, record its axis length L1, and adjust the rotation speed according to different rotation speeds. The spot image formed by the laser beam projection under the rotation angle finds the shortest axis length L2 in the spot ellipse obtained by fitting all the laser spots, and calculates the angle β between the line connecting the laser centers at both ends of the laser beam emitting terminal and the plane where the crack to be measured is located according to the horizontal axis length L1 and the shortest axis length L2. The proximal micro-laser and its corresponding laser spot are determined by the rotation angle, and the distance l2 between the center points of the laser spots at both ends of the laser beam emitting terminal on the measured plane is calculated according to the actual distance l1 between the centers of the lasers at both ends of the laser beam emitting terminal. Then, the imaging parameters are determined according to the pixel positions of the center points of the laser spots at both ends in the measured plane image, and the crack width corresponding to the pixel position and number of cracks in the measured plane image is calculated.

[0016] Optionally, in the system as described in any of the above, the laser beam emitting terminal is provided with at least three micro-lasers with mutually parallel projection angles, and the light spots formed by the three micro-lasers projected on the measured plane do not cross or overlap.

[0017] Beneficial Effects

[0018] The crack width measurement method and system that considers the inclination angle of the parallel laser beam provided in the present application utilizes a laser beam emitting terminal to project a light spot on the measured plane, and calculates the imaging parameters of the camera when shooting the light spot and the gap on the measured plane by fitting the light spot and analyzing the images of the light spot at different rotation angles. Therefore, the present application can directly calculate the corresponding gap width through the pixel position and number of pixels occupied by the gap on the measured plane obtained by the camera, so as to achieve accurate measurement of the gap size. The camera of the present application does not need to calibrate the installation position and installation angle of the laser equipment when shooting the gap and light spot image, and does not need to consider the influence of the inclination angle on the measurement accuracy, so the detection is simpler and the obtained data is more accurate.

[0019] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent from the description, or may be understood by practicing the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings are used to provide a further understanding of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation of the present application. In the accompanying drawings:

[0021] Figure 1 It is a schematic flow chart of the steps of the crack width measurement method considering the tilt angle of the parallel laser beam of the present application;

[0022] Figure 2 It is a structural schematic diagram of the laser beam emission terminal and the light spot projection method on the measured plane in the crack width measurement system of the present application;

[0023] Figure 3 It is a schematic diagram of the camera imaging principle in the system of the present application; DETAILED DESCRIPTION

[0024] In order to make the purpose and technical solution of the embodiment of the present application clearer, the technical solution of the embodiment of the present application will be clearly and completely described in conjunction with the drawings of the embodiment of the present application. Obviously, the described embodiment is a part of the embodiment of the present application, not all of the embodiments. Based on the described embodiment of the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0025] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0026] The term “connection” as used in this application may mean a direct connection between components or an indirect connection between components via other components.

[0027] Figure 1 A flow chart of the steps of a crack width measurement method considering the tilt angle of a parallel laser beam provided in this application, which uses Figure 2 , the laser beam emitting terminal shown in the figure projects several mutually parallel laser beams to the measured plane, and then analyzes and calculates the light spot formed by the laser beam of the laser beam emitting terminal projected on the measured plane collected by the camera, and calculates the actual width of the crack in the measured plane image through the following steps:

[0028] Ellipse fitting is performed on the light spots formed by the projection of several mutually parallel laser beams respectively;

[0029] Determine the horizontal axis of the fitted spot ellipse and record its axis length L1;

[0030] Keep the distance between the laser beam emitting terminal and the measured plane, rotate the laser beam emitting terminal and take pictures of the light spot images formed by the laser beam projection at different rotation angles;

[0031] According to the spot images formed by the laser beam projection at different rotation angles, find out the shortest axis length L2 among the spot ellipses obtained by fitting all the laser spots;

[0032] According to the horizontal axis length L1 and the shortest axis length L2, the angle β between the line connecting the laser centers at both ends of the laser beam emission terminal and the plane where the crack to be measured is located is calculated;

[0033] The proximal micro-laser and its corresponding laser spot are determined by the rotation angle;

[0034] According to the actual distance l1 between the laser centers at both ends of the laser beam emission terminal, calculate the distance l2 between the center points of the laser spots at both ends of the measured plane;

[0035] The imaging parameters are determined according to the pixel positions of the center points of the laser spots at both ends in the measured plane image, and the crack width corresponding to the pixel positions and number of cracks in the measured plane image is calculated accordingly.

[0036] The specific calculation principle is described as follows:

[0037] (1) In the process of ellipse fitting of the light spots irradiated by two parallel laser beams on the detection terminal onto the measured plane:

[0038] Assuming that the two laser beams are in an ideal parallel state and the irradiated area is the same plane, since the short-distance divergence of the laser is low, it can be seen that when there is an inclination angle that affects the crack measurement accuracy, the light spots of the two laser beams on the measured plane can be fitted into an ellipse. The major axis, minor axis and major axis inclination angle of the ellipse of the two laser beams can be considered to be close to the same. Therefore, the mean of the sum of squares of the corresponding errors of the data of each point of the two fitted ellipses and the original data of the light spot edge are calculated respectively. The calculation formula is as follows:

[0039]

[0040] From the calculation results, find the one with the smallest MSE among the two ellipses, set it as m, then set:

[0041]

[0042] Because A m , B m ,θ m If it is known, then for another ellipse outside m, we only need to recalculate a i ,bi ,c i ,d i ,e i Among them, A i is the length of the major semi-axis of the ellipse, B i is the length of the minor semi-axis of the ellipse, θ i is the major axis inclination, a i ,b i ,c i ,d i ,e i is the ellipse ax 2 +bxy+cy 2 +dx+ey+1=0 is the coefficient in the equation.

[0043] (2) Determine the horizontal axis of the fitted ellipse: First, connect the centers of the two ellipses, and determine which of the two axes is the horizontal axis based on the angle between the connecting line and the two axes. Select the axis with the smaller angle with the connecting line as the horizontal axis, and record its axis length L1.

[0044] (3) On the premise that the distance between the mobile terminal and the measuring plane remains basically unchanged, the mobile terminal is rotated so that the angle between the plane where the laser beam on the mobile terminal is located and the measured plane changes, and the change process at least covers the state when the angle is 0, and pictures of the measured plane (including the laser spot) at various angles are taken during the rotation.

[0045] (4) Perform image processing and analysis on each of the photographs of the measured plane, use ellipse fitting and other methods to fit the laser spot in the image, calculate the major and minor axis lengths of the ellipse fitted by each laser spot, and find the shortest axis length L2 among the ellipses fitted by all the laser spots.

[0046] (5) Using the two values ​​of L1 and L2, calculate the angle β between the laser center line at both ends of the mobile terminal and the measured plane. The calculation principle is as follows: Figure 2 As shown;

[0047] (6) According to the distance between the two laser beams on the mobile terminal, calculate the distance between the center points of the laser spots on the measured plane. First, determine the laser spot emitted by the laser that is closer to the measured plane. The determination method is as follows: Set the coordinate system as shown in the figure below. Assume that the paper is used as the measured plane, the mobile terminal is parallel to the measured plane, and the micro-laser connection line remains horizontal. Then the direction of the x-axis is from left to right along the horizontal direction of the mobile terminal screen, the direction of the z-axis is from bottom to top along the horizontal direction of the mobile terminal screen, and the direction of the y-axis is from the mobile phone vertically to the measured plane. Then the y-axis in the coordinate system is the coordinate axis that represents the distance between different micro-lasers in the mobile terminal and the measured plane. If the distances between the two micro-lasers and the measured plane are different, the mobile terminal should have a rotation angle around the z-axis. Therefore, the direction sensor in the mobile terminal is used to obtain the rotation angle values ​​of the mobile terminal along the z-axis [3]. The near-end micro-laser and its corresponding laser spot can be determined by the rotation angle.

[0048] (7) If the actual distance between the center points of the two micro-lasers is known to be l1, the distance between the center points of the laser spots at both ends of the measured plane is calculated as follows:

[0049] l2=l1 / cosβ (4)

[0050] (8) The crack width is calculated based on the position and number of pixels occupied by the crack as follows:

[0051] refer to Figure 3 , let A and B be the actual positions of the centers of the laser spots at both ends on the measured plane, then AB=l2, P a , P b is the imaging position of the laser spot center A and B on the image. Assuming the total number of pixels in the viewing angle is 2n, we have:

[0052]

[0053] In the above formula, l2, α, P a , P b It is known that the centers of two light spots are a , P b The corresponding relationship of step (6) is determined, L and β are unknown, so they are further calculated by combining the following formula:

[0054]

[0055] Where d is the diagonal length of the film, f is the focal length, w is the imaging width of the object, and W is the actual width of the object being measured. In this method, W = l2, w = w1*(P a -P b ) can be calculated. Combining formulas (5) and (6), L and β can be calculated.

[0056] Assume that CD is the actual crack width, P c , P d is the imaging width of the crack, then: 8

[0057]

[0058] The actual crack width can be calculated using formula (7).

[0059] The above is only an implementation method of the present application, and its description is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present application. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present application, which all belong to the protection scope of the present application.

Claims

1. A crack width measurement method considering the tilt angle of a parallel laser beam, characterized in that the steps include: Ellipse fitting is performed on the light spots formed by the projection of several mutually parallel laser beams respectively; Determine the horizontal axis of the fitted spot ellipse and record its axis length ; Keep the distance between the laser beam emitting terminal and the measured plane, rotate the laser beam emitting terminal and take pictures of the light spot images formed by the laser beam projection at different rotation angles; According to the spot image formed by the laser beam projection at different rotation angles, find the shortest axis length among all the spot ellipses fitted by the laser spot ; According to the horizontal axis length and the shortest axis length Calculate the angle between the line connecting the laser centers at both ends of the laser beam emission terminal and the plane where the crack to be measured is located ; The proximal micro-laser and its corresponding laser spot are determined by the rotation angle; According to the actual distance between the laser centers at both ends of the laser beam emission terminal , calculate the distance between the center points of the laser spots at both ends of the measured plane ; According to the pixel positions of the center points of the laser spots at both ends in the measured plane image, the imaging parameters are determined, and the pixel positions and number of cracks in the measured plane image and the corresponding crack widths are calculated accordingly; The specific steps of determining the imaging parameters according to the pixel positions of the center points of the laser spots at both ends in the measured plane image, and calculating the pixel positions and the crack widths corresponding to the number of cracks in the measured plane image include: According to the pixel position of the center point of the laser spot at both ends in the measured plane image and the total loudness within the imaging angle of view is 2n, the distance from the measured plane to the imaging center is calculated. , and the angle between the line connecting the laser centers at both ends of the laser beam emission terminal and the plane where the crack to be measured is located , and the actual width of the crack is calculated as ; according to Calculate the distance from the measured plane to the imaging center , and the angle between the line connecting the laser centers at both ends of the laser beam emission terminal and the plane where the crack to be measured is located ; in, is the imaging position of the laser spot center A and B on the image, is the imaging width of the crack, Indicates the actual position of the laser center at both ends of the laser beam emission terminal on the measured plane. The imaging angle is represented by Determine, among which, is the diagonal length of the film, is the imaging focal length, is the imaging width of the object, is the actual width of the object being measured.

2. The crack width measurement method considering the tilt angle of the parallel laser beam according to claim 1, characterized in that: When rotating the laser beam emitting terminal and photographing the spot images formed by the laser beam projection at different rotation angles, the rotation angle at least covers the state where the angle between the line connecting the laser centers at both ends of the laser beam emitting terminal and the plane where the crack to be measured is located is 0.

3. The crack width measurement method considering the tilt angle of the parallel laser beam according to claim 1, characterized in that: The angle between the line connecting the centers of the lasers at both ends of the laser beam emission terminal and the plane where the crack to be measured is located .

4. The crack width measurement method considering the tilt angle of the parallel laser beam according to claim 1, characterized in that: The steps of determining the proximal micro-laser and its corresponding laser spot by the rotation angle include: The measured plane is the plane where the origin is, and the horizontal direction along the laser beam emission terminal screen from left to right is The axis is from bottom to top along the horizontal direction of the laser beam emission terminal screen. Axis, with the direction pointing to the measured plane as The coordinate system is established by the axis, and the distance between the laser beam emission terminal and the measured plane is calculated according to the distance between the different micro lasers and the measured plane. Axis rotation angle , the proximal micro-laser and its corresponding laser spot are determined by the rotation angle.

5. The crack width measurement method considering the tilt angle of the parallel laser beam according to claim 1, characterized in that: The distance between the center points of the laser spots at both ends of the measured plane .

6. A crack width measurement system taking into account the tilt angle of a parallel laser beam based on the method according to any one of claims 1 to 5, characterized in that: include: A laser beam emitting terminal, on which a micro laser is mounted, for projecting a plurality of mutually parallel laser beams toward the plane to be measured; A rotating mechanism connected to the laser beam emitting terminal and used to drive the laser beam emitting terminal to rotate while keeping the distance between the laser beam emitting terminal and the measured plane unchanged; The camera collects the light spot formed by the laser beam of the laser beam transmitting terminal projected on the measured plane in real time; The calculation unit is used to perform ellipse fitting on the light spot formed by each laser beam projection, determine the horizontal axis of the fitted light spot ellipse, and record its axis length According to the spot image formed by the laser beam projection at different rotation angles, find the shortest axis length in the spot ellipse obtained by fitting all laser spots , according to the horizontal axis length and the shortest axis length Calculate the angle between the line connecting the laser centers at both ends of the laser beam emission terminal and the plane where the crack to be measured is located The near-end micro-laser and its corresponding laser spot are determined by the rotation angle, and the actual distance between the laser centers at both ends of the laser beam emission terminal is determined by the rotation angle. , calculate the distance between the center points of the laser spots at both ends of the measured plane Then, the imaging parameters are determined according to the pixel positions of the center points of the laser spots at both ends in the measured plane image, and the crack width corresponding to the pixel positions and numbers of cracks in the measured plane image is calculated.

7. The system according to claim 6, characterized in that The laser beam emission terminal is provided with at least three micro lasers with mutually parallel projection angles, and the light spots formed by the three micro lasers projected on the measured plane have no intersection or overlap.

Images