Automated mobile station change measurement method based on mobile laser tracker

Abstract

An automated mobile station-changing measurement method based on a mobile laser tracker is proposed. First, a two-dimensional map coordinate system and a global coordinate system are established through scanning measurements using a mobile measurement system. Then, three-dimensional measurements are performed on the surfaces of each reflective column on the map. The two-dimensional equivalent center of the reflective column is reconstructed using the three-dimensional measurement data and defined as the equivalent reference point between the three-dimensional global coordinate system and the two-dimensional map coordinate system. The transformation relationship between the two is then solved. Next, the transformation relationship between the mobile platform coordinate system and the laser tracker coordinate system is calculated, and the movement path of the mobile measurement system between each target measurement station is planned. After reaching the designated station, coarse positioning based on radar scanning and fine positioning based on laser measurement are completed. Finally, based on the fine positioning data and the original calibration information, automated pointing measurement of the target point is achieved. This method solves the problems of low efficiency and low automation in traditional multi-person collaborative station-changing processes, achieving automated station-changing measurement without manual control.

Description

Technical Field

[0001] This invention belongs to the field of automated measurement and relates to an automated mobile station-changing measurement method based on a mobile laser tracker. Background Technology

[0002] Measurement-driven machining and assembly has become the mainstream mode of in-situ manufacturing of aerospace components. Improving measurement efficiency while ensuring measurement accuracy has become one of the key means to shorten the manufacturing cycle. Due to the large measurement range and severe obstruction of the measurement line of sight on the manufacturing site, multi-station network measurement with laser trackers has become the preferred large-scale measurement technology. Currently, multi-station network measurement on the manufacturing site mainly relies on manual replacement of measurement stations. In this process, manually dragging the laser tracker is time-consuming and laborious, and requires multiple people to work together to move the laser tracker and drag power and communication cables. Therefore, this station-changing mode has a very low degree of automation, making it difficult to improve station-changing efficiency and greatly extending the measurement cycle.

[0003] A highly flexible mobile platform integrated with a laser tracker forms a mobile laser measurement system, providing a solution to the aforementioned problem of inefficient station-changing measurement. However, to achieve fully automated mobile station-changing measurement, it is necessary to break down the information silos between the scene and the mobile laser tracker, and solve problems such as positioning and path planning of the mobile measurement system in complex large scenes. Therefore, this invention mainly focuses on the mobile station-changing measurement process, proposing a multi-coordinate system calibration-self-positioning in large scenes-path planning in complex scenes. Using this approach, the mobile measurement system is controlled to autonomously move to a pre-planned station, replacing the traditional manual station-changing process, avoiding the dragging of power and communication cables, and reducing the station-changing distance through path planning, ultimately achieving short-distance, high-efficiency, and automated mobile station-changing measurement.

[0004] The patent "AGV Positioning and Path Planning Method and Device" (patent number CN202410011939.1) discloses a method for planning AGV travel paths based on a multi-sensor data fusion algorithm. The patent "A Global Positioning Method for Laser-Navigate AGVs" (patent number CN201510082486.2) discloses a technique for determining AGV position information using lidar data combined with the Markov method. Both methods achieve autonomous navigation and positioning of AGVs through multi-sensor fusion and data processing. However, these patents only address the navigation and positioning of the AGV itself and do not cover large-scale measurement scenarios using mobile laser trackers, nor do they address multi-coordinate system calibration and modeling in such scenarios. Therefore, this invention proposes an automated mobile station-changing measurement method based on a mobile laser tracker, solving the problems of low efficiency and low automation in manual station changing during large-scale laser tracker network measurements in complex environments. Summary of the Invention

[0005] This invention addresses the low efficiency and low automation of multi-person collaboration and manual station-changing processes in multi-station network measurements using laser trackers. It proposes an automated mobile station-changing measurement method based on a mobile laser tracker. First, a two-dimensional map coordinate system is established through offline scanning measurements using a mobile measurement system. Then, the three-dimensional coordinates of a series of ground control points in the global coordinate system are acquired using the laser tracker. Next, three-dimensional measurements are performed on the surfaces of each reflector column on the map, and the two-dimensional equivalent center of the reflector column is reconstructed from the three-dimensional measurement data. This center is defined as the equivalent reference point between the three-dimensional global coordinate system and the two-dimensional map coordinate system, and the transformation relationship between the two is solved. Then, the transformation relationship between the mobile platform coordinate system and the laser tracker coordinate system is calculated. Using an improved A* algorithm, the mobile measurement system's movement path between each target measurement station is planned. After reaching the designated station, coarse positioning based on radar scanning and fine positioning based on laser measurement are performed sequentially. Finally, based on the fine positioning data and the original calibration information, automated pointing measurement of the target point is achieved. This method solves the problems of low efficiency and low automation in traditional multi-person collaborative station-changing processes. It can realize automated station-changing measurement without manual control, and is suitable for large-scale automated high-efficiency positioning in complex manufacturing sites. It has good versatility and scalability.

[0006] The technical solution of the present invention:

[0007] An automated mobile station-changing measurement method based on a mobile laser tracker includes the following steps:

[0008] The first step is to construct a two-dimensional map coordinate system and conduct global measurement of control point coordinates.

[0009] First, using the initial position of the vehicle-mounted LiDAR as the origin of the two-dimensional map coordinate system, with the 0° scanning direction as the +X direction, and the counterclockwise direction relative to the X-axis as the positive rotation direction, a two-dimensional map coordinate system is drawn. The vehicle-mounted LiDAR on the moving platform scans the reflective pillars of the surrounding environment to obtain the coordinates T of all reflective pillars in the two-dimensional map coordinate system. w :

[0010]

[0011] Among them, (x Ti w y Ti w ) represents the coordinates of the i-th reflector in the map coordinate system, and m represents the number of reflectors;

[0012] Then, a vehicle-mounted laser tracker was used to measure all control points in the measurement field, and a global coordinate system was established. The three-dimensional coordinates P of all control points in the global coordinate system were then determined. g for:

[0013]

[0014] Among them, (x pj g y pj g z pj g (j) represents the coordinates of the j-th control point in the global coordinate system, and n represents the number of control points.

[0015] Based on the installation relationship between the lidar and the mobile platform, the ground normal is defined as the Z-axis direction of the lidar, and the Z-coordinate value of the lidar is supplemented according to the structural dimensions. If the Z-axis of the global coordinate system is not parallel to the Z-axis direction of the lidar, the global coordinate system needs to be rotated using equation (3) to make the Z-axis of the two parallel.

[0016]

[0017] Among them, R x R y R z These are rotation matrices about the X, Y, and Z axes, respectively. P is the set of three-dimensional coordinate points measured by the vehicle-mounted laser tracker, and P is the rotated set of three-dimensional coordinate points.

[0018] The second step is to calibrate the coordinate system of the laser tracker and the coordinate system of the moving platform based on the equivalent reference point.

[0019] First, the vehicle-mounted laser tracker measures and fits the cylindrical axis vector of each reflector, where the cylindrical surface equation of the reflector is shown in equation (4):

[0020]

[0021] Wherein, the axis of the cylindrical surface is The radius of the circular tangent is r, and any point on the axis of the cylindrical surface is [x0 y0 z0]. T ;

[0022] Then, multiple points are measured on the upper surface of the cylinder and a plane is fitted. The intersection of this plane with the axis of the cylinder is calculated. Only the horizontal and vertical coordinates of the intersection points are extracted and used as the two-dimensional equivalent center of the cylindrical surface of the reflector. The coordinates of the two-dimensional equivalent center of all reflectors, also known as equivalent reference points, are obtained in sequence to obtain the equivalent reference point sequence set Q. c :

[0023] Q c =[q c,1 q c,2 ...q c,n ] T (5)

[0024] Where, q c,i =[xc,i y c,i ] T Let be the coordinates of the i-th equivalent reference point;

[0025] Furthermore, the rotation matrix R between the two-dimensional map coordinate system and the global coordinate system is solved based on multiple sets of equivalent reference points. w_g Translation vector T w_g , which is the transformation matrix between the current station laser tracker coordinate system and the two-dimensional map coordinate system, as shown in equation (6):

[0026]

[0027] Where, q c,i and p w,i These are the coordinates of the equivalent center of the i-th reflector in the laser tracker coordinate system and the two-dimensional map coordinate system, respectively.

[0028] Finally, based on the pose of the mobile platform in the two-dimensional map coordinate system [x w a y w a ρ w a ] T The transformation relationship between the two-dimensional map coordinate system and the current station laser tracker coordinate system is used to calculate the coordinates of the mobile platform in the vehicle-mounted laser tracker coordinate system and the pose relationship R between the mobile platform and the laser tracker using equation (7). c_a T c_a ;

[0029]

[0030] Among them, [x c a y c a ] T R represents the coordinates of the moving platform within the laser tracker's coordinate system. c_w T c_w R is the transformation matrix between the laser tracker coordinate system and the 2D map coordinate system. a_w T a_w This describes the transformation relationship between the mobile platform coordinate system and the two-dimensional map coordinate system.

[0031] The third step is the autonomous planning of the mobile laser tracker's station-changing path.

[0032] First, a complex 3D measurement scene is reconstructed. By projecting the measurement scene into two dimensions, a two-dimensional map containing obstacles is obtained. Then, the two-dimensional map is binarized and rasterized. One grid is added outside the boundary of the grid containing obstacles as a safe area. The size of the grid is the same as the area of ​​the mobile platform.

[0033] Then, iterative optimization of the movement path nodes is performed based on the evaluation function to obtain all nodes of the entire movement path, and then the movement path is obtained by reverse tracing. Considering that the measurement site often focuses more on the movement time, the A* algorithm is improved by using the running time as the evaluation function and taking into account the turning time penalty term to construct the optimization objective of the shortest running time. The expression of its evaluation function is as follows:

[0034] f(k)=g(k)+w(k)h(k)+c(k) (8)

[0035] Where f(k) is the estimated time for the initial node to reach the target node via node k, g(k) is the actual time from the initial node to node k, h(k) is the estimated time for the optimal path from node k to the target node, w(k) is the weight factor of the estimated time, and c(k) is the additional time (turning penalty term).

[0036] Finally, all nodes are simplified according to the path order of start-end point, that is, multiple nodes on the same straight-line movement path are simplified into the first and last nodes.

[0037] The fourth step involves global precise positioning and autonomous search measurement based on a coarse-fine composite mobile measurement system.

[0038] After the mobile platform moves to the target measurement station according to the planned path, it combines the already calibrated information with the mobile platform's positioning information in the two-dimensional map coordinate system [x w a ,y w a ,ρ w a ] T Solve for the pose matrix R of the current vehicle-mounted laser tracker in the two-dimensional map coordinate system. c_w With T c_w :

[0039]

[0040] Among them, R cu a_w T cu a_w R represents the transformation relationship between the current mobile platform coordinate system and the two-dimensional map coordinate system. c_a T c_a These represent the transformation relationship between the laser tracker coordinate system and the moving platform coordinate system;

[0041] By combining the calibration results between the 2D map coordinate system and the global coordinate system, the pose matrix of the laser tracker in the global coordinate system is calculated:

[0042]

[0043] The two-dimensional transformation matrix is ​​upgraded to a three-dimensional transformation matrix, as shown in equation (11):

[0044]

[0045] in, These are the three-dimensional rotation matrix and translation vector, d c The height between the origin of the laser tracker's coordinate system and the XOY plane of the global coordinate system;

[0046]

[0047] Among them, [x c p y c p z c p ] T 、[x g p y g p z g p ] T These are the coordinates of the corresponding measurement points in the current laser tracker coordinate system and the global coordinate system, respectively.

[0048] Based on the transformation relationship between the global coordinate system and the vehicle-mounted laser tracker coordinate system R c_g T c_g The pose of the moving platform in the global coordinate system is obtained by matrix multi-level transfer.

[0049]

[0050] Among them, [x g a y g a ] T R represents the coordinates of the moving platform within the global coordinate system. g_c T g_c This represents the pose matrix of the laser tracker in the global coordinate system.

[0051] Finally, based on the accurate calculation results of the current laser tracker pose in the global coordinate system, the laser tracker's pointing search measurement technology and vision-assisted guidance measurement technology are used to achieve autonomous search and measurement of all test points.

[0052] The beneficial effects of this invention are as follows: This invention proposes a multi-coordinate system calibration-self-positioning in a large scene-path planning in a complex scene approach. By using the above approach, the mobile measurement system is controlled to move autonomously to the pre-planned station, which solves the problems of low efficiency and low automation in the process of multiple people coordinating station switching when laser trackers are networked and measured in a large area of ​​complex sites. It is suitable for large-scale automated and efficient positioning in complex manufacturing sites, and realizes high-efficiency automated measurement in the manufacturing site of large components, which has broad application prospects. Attached Figure Description

[0053] Figure 1 This is a flowchart of an automated mobile station-changing measurement method based on a mobile measurement system.

[0054] Figure 2 This is a schematic diagram of the automated mobile station-changing measurement layout of a mobile measurement system.

[0055] Figure 3 This is a flowchart of the path planning for a mobile measurement system.

[0056] In the diagram: 1-Laser tracker; 2-LiDAR; 3-Mobile platform; 4-Mobile measurement system; p1~p24-Control points; q1~q12-Target points to be measured; T1~T9-Reflecting columns. Detailed Implementation

[0057] The specific embodiments of the present invention will be described in detail below with reference to the technical solutions and accompanying drawings.

[0058] In this embodiment, the measurement range is approximately 24m × 5m, including 24 control points, 12 target points, and 9 reflective columns.

[0059] The first step is to construct a two-dimensional map coordinate system and conduct global measurement of control point coordinates.

[0060] As attached Figure 2 As shown, 24 control points and 12 target points were arranged within a 24m × 5m area, spaced 2m apart, along with 9 reflective pillars. The coordinates T of the reflective pillars in the map coordinate system were obtained using lidar measurement. w The coordinates P of the control point in the global coordinate system were measured using a laser tracker. g And rotate it to the direction defined by the Z-axis of the lidar according to equation (3):

[0061]

[0062]

[0063] The second step is to calibrate the coordinate system of the laser tracker and the coordinate system of the moving platform based on the equivalent reference point.

[0064] First, construct the two-dimensional equivalent center of all reflective columns according to equations (4) and (5), and measure the coordinates Q of the equivalent center of some reflective columns. c for:

[0065]

[0066] Then, the transformation relationship R between the laser tracker coordinate system and the map coordinate system is determined by equation (6). w_g T w_g :

[0067]

[0068] Then, the transformation matrix R between the mobile platform and the map coordinate system is calculated based on the mobile platform's pose in the map coordinate system. a_w T a_w :

[0069]

[0070] The pose of the mobile platform in the laser tracker coordinate system is calculated using equation (7), which is the transformation relationship between the mobile platform and the vehicle-mounted laser tracker:

[0071]

[0072] The third step is the autonomous planning of the mobile laser tracker's station-changing path.

[0073] according to Figure 3 The steps involve planning the movement of the mobile platform to the designated position using an improved A* algorithm. Since there are no obstacles in this embodiment, a straight path from the starting position to the target position is planned.

[0074] The fourth step involves global precise positioning and autonomous search measurement based on a coarse-fine composite mobile measurement system.

[0075] Once the mobile surveying system reaches the designated location, it completes the coarse positioning of the mobile surveying system within the map coordinate system based on the calibrated information and the position of the mobile platform within the map coordinate system.

[0076] Then, a laser tracker is used to measure some control points, and the transformation matrix R between the laser tracker coordinate system and the global coordinate system is calculated using equation (10). c_g T c_g Complete the precise positioning of the measurement system in the global coordinate system:

[0077]

[0078] Then, the pose of the laser tracker in the global coordinate system is calculated by inverse equation (13):

[0079]

[0080] Finally, all test points were measured using laser tracker pointing search measurement technology and vision-assisted guidance measurement technology.

[0081] This invention proposes a multi-coordinate system calibration-self-localization in large scenes-path planning for complex scenes approach. By using the above approach, the mobile measurement system is controlled to move autonomously to the pre-planned station, which solves the problems of low efficiency and low automation in the process of multiple people working together to switch stations when laser trackers are networked in complex sites. It is suitable for large-scale automated and efficient positioning in complex manufacturing sites, and realizes high-efficiency automated measurement in the manufacturing site of large components, with broad application prospects.

Claims

1. An automated mobile station-changing measurement method based on a mobile laser tracker, characterized in that, The steps are as follows: The first step is to construct a two-dimensional map coordinate system and conduct global measurement of control point coordinates. First, using the initial position of the vehicle-mounted LiDAR as the origin of the two-dimensional map coordinate system, with the 0° scanning direction as the +X direction, and the counterclockwise direction relative to the X-axis as the positive rotation direction, the two-dimensional map coordinate system is drawn. The vehicle-mounted LiDAR on the moving platform scans the reflective pillars of the surrounding environment to obtain the coordinates of all reflective pillars within the two-dimensional map coordinate system. : (1) in, For the first in the map coordinate system The coordinates of the reflector pillars The number of reflective columns; Then, a vehicle-mounted laser tracker is used to measure all control points in the measurement field, establishing a global coordinate system. The three-dimensional coordinates of all control points within the global coordinate system are then determined. for: (2) in, For the first in the global coordinate system The coordinates of the control points To control the number of points; Based on the installation relationship between the lidar and the mobile platform, the ground normal is defined as the Z-axis direction of the lidar, and the Z-coordinate value of the lidar is supplemented according to the structural dimensions. If the Z-axis of the global coordinate system is not parallel to the Z-axis direction of the lidar, the global coordinate system needs to be rotated using equation (3) to make the Z-axis of the two parallel. (3) in, These are rotation matrices about the X, Y, and Z axes, respectively. The set of three-dimensional coordinate points measured by the vehicle-mounted laser tracker. The set of three-dimensional coordinate points after rotation; The second step is to calibrate the coordinate system of the laser tracker and the coordinate system of the moving platform based on the equivalent reference point. First, the vehicle-mounted laser tracker measures and fits the cylindrical axis vector of each reflector, where the cylindrical surface equation of the reflector is shown in equation (4): (4) Wherein, the axis of the cylindrical surface is The radius of the circular tangent is Any point on the axis of the cylindrical surface is ; Then, multiple points are measured on the upper surface of the cylinder and a plane is fitted. The intersection of this plane with the axis of the cylinder is calculated. Only the horizontal and vertical coordinates of the intersection points are extracted and used as the two-dimensional equivalent center of the cylindrical surface of the reflector. The coordinates of the two-dimensional equivalent center of all reflectors, also known as equivalent reference points, are obtained in sequence to obtain the equivalent reference point sequence set. : (5) in, For the first The coordinates of one equivalent reference point; Furthermore, the rotation matrix between the two-dimensional map coordinate system and the global coordinate system is solved based on multiple sets of equivalent reference points. Translation vector , which is the transformation matrix between the current station laser tracker coordinate system and the two-dimensional map coordinate system, as shown in equation (6): (6) in, and The coordinates of the laser tracker and the coordinates of the two-dimensional map are respectively the first... Equivalent center coordinates of each reflector column; Finally, based on the pose of the mobile platform in the two-dimensional map coordinate system The transformation relationship between the two-dimensional map coordinate system and the current station laser tracker coordinate system is used to calculate the coordinates of the mobile platform in the vehicle-mounted laser tracker coordinate system and the pose relationship between the mobile platform and the laser tracker using Equation (7). , ; (7) in, This represents the coordinates of the moving platform within the laser tracker's coordinate system. , This is the transformation matrix between the laser tracker coordinate system and the 2D map coordinate system. , This describes the transformation relationship between the mobile platform coordinate system and the two-dimensional map coordinate system. The third step is the autonomous planning of the mobile laser tracker's station-changing path. First, a complex 3D measurement scene is reconstructed. By projecting the measurement scene into two dimensions, a two-dimensional map containing obstacles is obtained. Then, the two-dimensional map is binarized and rasterized. One grid is added outside the boundary of the grid containing obstacles as a safe area. The size of the grid is the same as the area of ​​the mobile platform. Then, iterative optimization of the movement path nodes is performed based on the evaluation function to obtain each node of the entire movement path, and then the movement path is obtained by reverse tracing; considering that the measurement site often focuses more on the movement time, for A The algorithm is improved by using running time as the evaluation function and considering the turning time penalty term, constructing an optimization objective that minimizes running time. The evaluation function expression is as follows: (8) in, For the initial node through the node The estimated time to reach the target node. From the initial node to the node The actual time For nodes The estimated time for the optimal path to the target node. To estimate the weighting factors for time, Additional time (turning penalty item); Finally, all nodes are simplified according to the path order of start-end point, that is, multiple nodes on the same straight-line movement path are simplified into the first and last nodes. The fourth step involves global precise positioning and autonomous search measurement based on a coarse-fine composite mobile measurement system. After the mobile platform moves to the target measurement station according to the planned path, it combines the already calibrated information with the mobile platform's positioning information in the two-dimensional map coordinate system. Solve for the pose matrix of the current vehicle-mounted laser tracker in the two-dimensional map coordinate system. and : (9) in, This defines the transformation relationship between the current mobile platform coordinate system and the 2D map coordinate system. These represent the transformation relationship between the laser tracker coordinate system and the moving platform coordinate system; By combining the calibration results between the 2D map coordinate system and the global coordinate system, the pose matrix of the laser tracker in the global coordinate system is calculated: (10) The two-dimensional transformation matrix is ​​upgraded to a three-dimensional transformation matrix, as shown in equation (11): (11) in, , These are the three-dimensional rotation matrix and translation vector, respectively. The height between the origin of the laser tracker's coordinate system and the XOY plane of the global coordinate system; (12) in, , These are the coordinates of the corresponding measurement points in the current laser tracker coordinate system and the global coordinate system, respectively. Based on the transformation relationship between the global coordinate system and the vehicle-mounted laser tracker coordinate system , The pose of the moving platform in the global coordinate system is obtained by matrix multi-level transfer. (13) in, This represents the coordinates of the moving platform within the global coordinate system. This represents the pose matrix of the laser tracker in the global coordinate system. Finally, based on the accurate calculation results of the current laser tracker pose in the global coordinate system, the laser tracker's pointing search measurement technology and vision-assisted guidance measurement technology are used to achieve autonomous search and measurement of all test points.

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