Multi-position splicing measurement calibration method and device based on guidance of laser tracker

Abstract

The invention discloses a multi-position splicing measurement calibration method based on guidance of a laser tracker. The method comprises the following steps: constructing a first transformation matrix for transformation between a laser tracker measurement coordinate system and a processing site coordinate system based on site ERS points; center point coordinates of the target ball seats are obtained through a laser tracer, and a second transformation matrix between the calibration plate coordinate system and the processing site coordinate system is constructed based on the first transformation matrix; a target splicing block is placed on the calibration plate, a second coordinate value of each feature point of the target splicing block in the calibration plate coordinate system is determined, and the second coordinate values are converted into the processing site coordinate system; acquiring a third coordinate value under the coordinate system of the laser contourgraph; and based on the second coordinate value and the third coordinate value, constructing a third transformation matrix between the laser contourgraph coordinate system and the processing site coordinate system. The invention further provides a multi-position splicing measurement calibration device. The method provided by the invention can effectively solve the problem that complex curved surfaces, large-area surfaces and gaps cannot be surveyed and mapped.

Description

Technical Field

[0001] The present invention belongs to the field of intelligent manufacturing, and particularly relates to a multi-position splicing measurement and calibration method and device guided by a laser tracker. Background Art

[0002] In the fields of aviation and shipbuilding engineering, a laser tracker is usually required to construct a large-scale measurement field during measurement. However, due to the high measurement accuracy of the laser tracker, it can only measure single-point coordinates and cannot measure continuous point clouds; a robot can carry a line laser profiler to measure complex curved surfaces and large-area surfaces to obtain continuous point cloud data, but due to the influence of the six degrees of freedom of the robot, the positioning accuracy is poor.

[0003] Patent document CN119334272A discloses a 3D laser profiler coordinate system conversion and calibration method. First, a calibration device is built; the calibration device has four calibration balls with adjustable spatial positions. By adjustment, all 4 calibration balls intersect with the laser plane emitted by the profiler, and the centers of the balls are not coplanar. Subsequently, a world coordinate system is established through the laser tracker, and the center coordinates of each calibration ball in the world coordinate system are obtained. Further, the center coordinates of the circle corresponding to the arc on the calibration ball surface and the arc radius are obtained by collecting pictures through the profiler, and then the center coordinates of each positioning ball under the profiler are obtained. Finally, the conversion matrix parameter solution is carried out according to the coordinates of the center of the ball obtained in the two coordinate systems to obtain the conversion matrix, and the optimal result is selected.

[0004] Patent document CN117989977A discloses a method and device for measuring the installation position of stator positioning ribs of a large hydro-generator, including: calibrating positioning marks for the positioning ribs to be measured; calibrating the transformation relationship between the positioning marks and the coordinate system of the laser profiler or laser scanner; measuring the spatial position of the positioning marks through the laser profiler or laser scanner; combining the profile or morphology of the positioning ribs to be measured to obtain the point cloud spatial coordinates of the profile or morphology of the positioning ribs to be measured relative to the coordinate system of the laser tracker or lidar; and obtaining the installation measurement parameters of the positioning ribs to be measured according to the point cloud spatial coordinates. Summary of the Invention

[0005] The purpose of the present invention is to provide a multi-position splicing measurement and calibration method and system guided by a laser tracker, which can effectively solve the problem that complex curved surfaces, large-area surfaces and gaps cannot be surveyed and mapped.

[0006] To achieve the first object of the present invention, the following technical solution is provided: A multi-position splicing measurement and calibration method guided by a laser tracker, including the following steps: Construct a first transformation matrix for converting the measurement coordinate system of the laser tracker and the processing site coordinate system based on the ERS points at the processing site; Set four target ball seats on the selected calibration plate and obtain the center point coordinates of each target ball seat through a laser tracker. Generate the first coordinate values corresponding to each target ball in the machining site coordinate system using the first transformation matrix; Construct a calibration plate coordinate system with a point on the calibration plate as the base point, and obtain the theoretical coordinate values of each target ball seat in the calibration plate coordinate system; Perform point set matching based on the first coordinate values and the theoretical coordinate values through singular value decomposition to construct the second transformation matrix between the calibration plate coordinate system and the machining site coordinate system; Place a target splicing block on the calibration plate, and calibrate feature points along the splicing seam of the target splicing block to determine the second coordinate values of each feature point of the target splicing block in the calibration plate coordinate system. Use the second transformation matrix to convert the second coordinate values to the machining site coordinate system; Collect the feature points of the splicing seam on the target splicing block through a laser profiler to obtain the third coordinate values in the laser profiler coordinate system; Perform point set matching based on the second coordinate values in the machining site coordinate system and the third coordinate values through singular value decomposition to construct the third transformation matrix between the laser profiler coordinate system and the machining site coordinate system.

[0007] The present invention constructs the conversion relationship between the laser profiler coordinate system and the machining site coordinate system in the current machining site through the target ball seats and splicing blocks on the calibration plate, effectively improving the accuracy of data collection, thereby solving the problems of poor positioning accuracy of the robot carrying the laser profiler and the inability of the laser tracker to measure complex curved surfaces, large-area surfaces and gaps.

[0008] Specifically, the feature points are extracted and obtained from the vertices at the turning points of the splicing seam on the target splicing block.

[0009] Specifically, the four target ball seats are arranged in an array on the calibration plate, and the center point of the closed area formed by connecting the four target ball seats is used as the base point of the calibration plate coordinate system.

[0010] Specifically, the first transformation matrix, the second transformation matrix, and the third transformation matrix all include a rotation matrix and a translation matrix.

[0011] Specifically, the projection point of the center point of the target splicing block on the calibration plate coincides with the base point in the calibration plate coordinate system.

[0012] Specifically, the conversion formula between the two coordinate systems is as follows: ; where represents the rotation matrix in the transformation matrix, and represent the coordinate values of the same point in the two coordinate systems.

[0013] Specifically, it further includes the calibration process of the third transformation matrix. In the calibration process, after rotating the calibration plate by a predetermined angle along a fixed direction, the feature points of the current target splicing block are re-acquired through a laser profiler, and a corresponding first correction matrix is generated based on the re-acquired feature points. The third transformation matrix before rotation is compared with the generated first correction matrix. If the two are inconsistent, the operation needs to be repeated after rotating by the predetermined angle again, and the second correction matrix obtained after the second rotation is used. If the second correction matrix is consistent with the third transformation matrix before rotation, no correction is performed. If the second correction matrix is consistent with the first correction matrix, the first correction matrix or the second correction matrix is output as the corrected third transformation matrix.

[0014] To achieve the second object of the present invention, the following technical solutions are provided: A multi-position splicing measurement calibration device includes: A robot system, including a fixed base, a multi-degree-of-freedom robotic arm provided on the fixed base, and a motion controller. The end of the multi-degree-of-freedom robotic arm is provided with a line laser profiler interface; A line laser profiler, used to collect the contour data of the splicing block surface, is fixed on the end effector of the robot to emit a linear laser beam and receive the reflected light; A calibration plate, including a substrate, and a target ball seat and a splicing block provided on the substrate; A laser tracker, used to collect the position coordinate information of the target ball seat, is placed at the processing site to emit a dot laser beam and receive the reflected light.

[0015] Specifically, the splicing block is a triangular splicing block with bottom angles of 60°. The bottom side of the triangular splicing block is parallel to the two sides of the calibration plate, and the other two sides are perpendicular.

[0016] Specifically, the triangular splicing block is arranged at the central position of a square flat plate, and the end face where the bottom side of the triangular splicing block is located is used as the fixed surface to be fixed to the square flat plate.

[0017] Compared with the prior art, the beneficial effects of the present invention are: It can realize the conversion between the coordinate systems of the line laser profiler and the laser tracker by using a simple calibration plate, which is convenient for multi-position data splicing; different from the traditional hand-eye calibration method, it avoids the errors caused by the six degrees of freedom of the robot and greatly improves the accuracy; there is no need to rely on external detection equipment for auxiliary measurement; it provides a new measurement method for splicing the measurement data of the laser profiler in a large-size measurement field and realizing the measurement of parameters such as large-size flatness, roundness, and perpendicularity based on the line laser profiler, and has engineering application value. Description of the Drawings

[0018] Figure 1Flowchart of the multi-position stitching measurement and calibration method guided by a laser tracker provided in this embodiment; Figure 2 Schematic diagram of the calibration board provided in this embodiment; Figure 3 Schematic diagram of the multi-position stitching measurement and calibration device provided in this embodiment; In the figure, 1 is a line laser profiler; 2 is a laser tracker; 3 is a calibration board; 4 is the coordinate system of the line laser profiler; 5 is the coordinate system of the calibration board; 6 is the coordinate system of the laser tracker. Detailed implementation manners

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are only some, rather than all, of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and illustrated in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0020] As Figure 1 shown, a multi-position stitching measurement and calibration method guided by a laser tracker provided in this embodiment includes the following steps: The laser tracker measures the ERS points on site. Through station transfer calculation, the measurement coordinate system of the tracker is made consistent with the on-site coordinate system, mainly to provide a larger coverage range, higher accuracy, and more complete data during the measurement process.

[0021] The laser tracker measures the four target ball seats on the calibration board, and obtains the coordinates of the center points of the four target ball seats (hereinafter referred to as target ball points) in the on-site coordinate system. The coordinates are matched with the theoretical coordinate values of the center points of the four target ball seats (i.e., the coordinate values of the four target ball points in the calibration board coordinate system) by the singular value decomposition (SVD) method to obtain the rotation matrix r and translation matrix t from the calibration board coordinate system to the on-site coordinate system; through the rotation matrix r and translation matrix t, the coordinates of three feature points in the calibration board coordinate system are converted to the on-site coordinate system. Among them, point set matching means and By the singular value decomposition (SVD) method, the rotation matrix r and translation matrix t from the calibration board coordinate system to the on-site coordinate system are obtained, that is, there is , and the data of the three feature points in the on-site coordinate system are denoted as , and the coordinate values in the calibration board coordinate system are denoted as , the value can be obtained through the formula , and can be obtained.

[0022] As Figure 2 shown, the calibration plate is mainly composed of two parts. The first part is a square surface with through holes at the four corners for installing the target base and target ball. The center of the target ball is the target ball point to be measured. The second part is composed of two identical triangular blocks closely joined at the center of the square surface. The three vertices of the closely joined blocks are the feature points. The calibration plate is centrosymmetric as a whole. In this embodiment, the joining block selected is a triangular joining block with base angles of 60°.

[0023] Keep the position of the calibration plate unchanged, and guide the robot by the position of the target ball measured by the tracker. The robot holds the line laser profiler to align the line laser with the three feature points of the triangular joining block, and extracts the coordinate values of the feature points in the coordinate system of the line laser profiler.

[0024] Through the singular value decomposition (SVD) method, point set matching is performed on the coordinates of the three feature points in the coordinate system of the line laser profiler and the coordinates of the three feature points in the field coordinate system, and the rotation matrix R and translation matrix T from the coordinate system of the line laser profiler to the field coordinate system can be obtained.

[0025] In addition, during the measurement and calibration process, there is also an inspection process, that is, the calibration plate is rotated by a certain angle around the center of gravity, the line laser profiler is aligned with the gap, and the data of the three feature points are scanned. Through the pose transformation matrix R and T obtained above, the coordinates of the three feature points in the coordinate system of the laser tracker are obtained, and they are compared with the coordinates of the three feature points obtained by inversely solving the target ball point measured by the laser tracker, so as to perform calibration inspection.

[0026] This embodiment also provides a multi-position splicing measurement and calibration device, as Figure 3 shown, including: A robot system, including a fixed base, a multi-degree-of-freedom robotic arm provided on the fixed base, and a motion controller. The end of the multi-degree-of-freedom robotic arm is provided with a line laser profiler interface; A line laser profiler 1, used to collect the contour data of the surface of the joining block, which is fixed on the end effector of the robot, used to emit a linear laser beam and receive the reflected light. The collected contour data is located in the coordinate system 4 of the line laser profiler; A calibration plate 3, including a substrate, and a target ball base and a joining block provided on the substrate. The objects on its substrate are all in the calibration plate coordinate system 5; A laser tracker 2, used to collect the position coordinate information of the target ball base, placed at the processing site, used to emit a dot-like laser beam and receive the reflected light. The collected position coordinate information is located in the laser tracker coordinate system 6.

[0027] More specifically, the robot is guided by the position of the target ball measured by the laser tracker 2. The robot holds the line laser profiler 1 and aligns the line laser with three feature points of the triangular splicing block, and extracts the coordinate values of the feature points in the coordinate system 4 of the line laser profiler.

[0028] The line laser profiler 1 is installed at the end of the robot flange, enabling the robot to carry the line laser profiler 1 to align with the tight splicing position of the triangular splicing block, ensuring that the laser line coincides with the splicing seam gap.

[0029] The scan data of the line laser profiler 1 needs to be processed. The point cloud data needs to be linearly fitted to extract feature points, that is, to find three intersection points corresponding to the connections of four consecutive lines. The point set is denoted as .

[0030] By using the singular value decomposition (SVD) method, point set matching is performed between the coordinates of the three feature points in the coordinate system 4 of the line laser profiler and the coordinates of the three feature points in the on-site coordinate system, that is, and Performing point set matching can obtain the rotation matrix R and the translation matrix T, which are used to achieve the conversion between the coordinate system of the line laser profiler and the on-site coordinate system. After measuring multiple positions, the data converted in the on-site coordinate system can be stitched.

[0031] In the inspection step, based on the design of the calibration plate triangular block, it can be rotated by a certain angle around the centroid. The line laser profiler 1 is aligned with the gap, and the data of three feature points are scanned. Through the obtained pose transformation matrices R and T, the coordinates of the three feature points in the coordinate system 6 of the laser tracker are obtained, and they are compared with the coordinates of the three feature points obtained by inverse calculation of the target ball points measured by the laser tracker 2, so as to perform calibration inspection.

[0032] In addition, the terms "upper", "lower", "inner", "outer", "front", and "rear" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. Unless otherwise specifically stated, the relative steps, numerical expressions, and numerical values of the components and steps described in these embodiments do not limit the scope of the present invention.

[0033] Of course, the above are only specific embodiments of the present invention and are not intended to limit the scope of the present invention. Any equivalent changes or modifications made according to the structure, features, and principles described in the scope of the patent application of the present invention should be included in the scope of the patent application of the present invention.

[0034] Finally, it should be noted that the above-described embodiments are only specific embodiments of the present invention, used to illustrate the technical solutions of the present invention, rather than limiting it. The protection scope of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that any person skilled in the technical field of the present invention can still modify the technical solutions described in the foregoing embodiments, or can easily think of changes, or perform equivalent replacements on some of the technical features; and these modifications, changes or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A multi-position stitching measurement and calibration method guided by a laser tracker, characterized in that Including the following steps: Based on the ERS points at the processing site to construct a first transformation matrix for the conversion between the coordinate system measured by the laser tracker and the processing site coordinate system; Set four target ball seats on the selected calibration plate and obtain the center point coordinates of each target ball seat through laser tracker measurement. Use the first transformation matrix to generate the corresponding first coordinate values of each target ball seat in the processing site coordinate system; Take a point on the calibration plate as the base point to construct a calibration plate coordinate system, and obtain the theoretical coordinate values of each target ball in the calibration plate coordinate system; Based on the first coordinate values and the theoretical coordinate values, perform point set matching through the singular value decomposition method to construct a second transformation matrix between the calibration plate coordinate system and the processing site coordinate system; Place the target splicing block on the calibration plate, and calibrate the feature points along the splicing seam of the target splicing block to determine the second coordinate values of each feature point of the target splicing block in the calibration plate coordinate system. Use the second transformation matrix to convert the second coordinate values into the processing site coordinate system; Collect the feature points of the splicing seam on the target splicing block through a laser profiler to obtain the third coordinate values in the laser profiler coordinate system; Based on the second coordinate values in the processing site coordinate system and the third coordinate values, perform point set matching through the singular value decomposition method to construct a third transformation matrix between the laser profiler coordinate system and the processing site coordinate system.

2. The multi-position stitching measurement and calibration method based on laser tracker guidance according to claim 1, wherein The feature points are extracted and obtained from the vertices at the turning points of the splicing seam on the target splicing block.

3. The multi-position stitching measurement and calibration method guided by a laser tracker according to claim 1, characterized in that Four target ball seats are arranged in an array on the calibration plate, and the center point of the closed area formed by connecting the four target ball seats is used as the base point of the calibration plate coordinate system.

4. The multi-position stitching measurement and calibration method guided by a laser tracker according to claim 1, wherein, The first transformation matrix, the second transformation matrix, and the third transformation matrix all include a rotation matrix and a translation matrix.

5. The multi-position stitching measurement and calibration method based on laser tracker guidance according to claim 1, characterized in that The projection point of the center point of the target splicing block on the calibration plate coincides with the base point in the calibration plate coordinate system.

6. The multi-position stitching measurement and calibration method based on laser tracker guidance according to claim 1, wherein The conversion formula between two coordinate systems is as follows: ; where represents the rotation matrix in the transformation matrix, and represent the coordinate values of the same point in two coordinate systems.

7. The multi-position stitching measurement and calibration method based on laser tracker guidance according to claim 1, characterized in that It also includes a calibration process for the third transformation matrix. The calibration process is to rotate the calibration plate by a predetermined angle along a fixed direction, and then re-collect the feature points of the current target splicing block through a laser profiler, and generate a corresponding first correction matrix with the re-collected feature points. Compare the third transformation matrix before rotation with the generated first correction matrix. If the two are inconsistent, it is necessary to rotate by a predetermined angle again and repeat the operation, and the second correction matrix obtained after the second rotation. If the second correction matrix is consistent with the third transformation matrix before rotation, no correction is performed. If the second correction matrix is consistent with the first correction matrix, the first correction matrix or the second correction matrix is used as the corrected third transformation matrix for output.

8. A multi-position splicing measurement and calibration device, characterized in that, For performing the steps of the multi-position splicing measurement and calibration guided by a laser tracker according to any one of claims 1 to 7, including: A robot system, including a fixed base, a multi-degree-of-freedom robotic arm provided on the fixed base, and a motion controller. The end of the multi-degree-of-freedom robotic arm is provided with a line laser profiler interface; A line laser profiler for collecting the contour data of the surface of the splicing block; A calibration plate, including a substrate, and target ball seats and splicing blocks provided on the substrate; A laser tracker for collecting the position coordinate information of the target ball seats.

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