Calibration method and calibration system for intrinsic parameters for workspace measurement and positioning system

Abstract

Disclosed in the present invention are a calibration method and calibration system for intrinsic parameters for a workspace measurement and positioning system, comprising: pre-calibrating initial intrinsic parameters of a transmitting station by means of a plurality of photoelectric receiving devices; fixing the transmitting station on a three-axis rotary table, and selecting a control point position for placing the photoelectric receiving device; adjusting the distance between the photoelectric receiving device and the three-axis rotary table multiple times, adjusting the pitch angle of the three-axis rotary table, and recording, by the photoelectric receiving device, a time interval after each rotation; on the basis of changes in distance and time, simulating the initial intrinsic parameters, and obtaining the deformation situations of light planes; and on the basis of the obtained deformation situations of the light planes, re-calibrating the transmitting station, calculating spatial geometric parameters of each light plane under a transmitting station coordinate system, and obtaining intrinsic parameters under a new model. In the present invention, the profile of a light plane mounted on the transmitting station is first calibrated by means of the high-precision three-axis rotary table, and then a proper light plane model is selected to fit an actual laser surface, thereby improving the angle measurement and coordinate measurement precision of the workspace measurement and positioning system.

Description

A method and system for calibrating intrinsic parameters of a workspace measurement and positioning system. Technical Field

[0001] This invention relates to a multi-base station workspace measurement and positioning system, specifically, to a workspace measurement and positioning system intrinsic parameter calibration method and calibration system. Background Technology

[0002] The workspace measurement and positioning system is a three-dimensional coordinate measurement and positioning system based on the principle of multi-station optical surface spatial intersection. Represented by iGPS and wMPS, this system is currently widely used in aerospace, large shipbuilding, and aircraft manufacturing. The system mainly consists of a transmitting station (comprised of a linear structured light beam, a uniformly rotating precision platform, and a synchronous light transmitter), an optoelectronic receiving device, and a signal processing device. Multiple transmitting stations are deployed in the positioning space, and the optoelectronic receiving device is mounted on a base at the point to be measured. The two work together to perform positioning measurements at the point. Each laser transmitter rotates and scans in space using two laser surfaces considered as ideal planes. The time elapsed between the starting position and the receiving device's position when the light surface reaches the receiving device is used for angular positioning. The spatial coordinates of the center of the optoelectronic receiving device are then determined by combining the spatial pose relationships between the multiple stations.

[0003] Traditional planar intrinsic parameter models treat the surface emitted by the structured light beam as an ideal plane and utilize this planar model in the coordinate calculation process. However, errors in laser manufacturing and assembly, such as the eccentricity or tilt of cylindrical mirrors, cause deformation of the laser surface, which becomes more pronounced in large-scale spaces. The laser surface serves as the sensing carrier for angle intersection measurements at both the transmitter and receiver in such systems. Therefore, the degree of fit between the actual laser surface and the plane directly affects the angular measurement accuracy of a single laser transmitter, thus impacting the point measurement accuracy of the constructed measurement system. In conclusion, replacing the planar model with a suitable model, such as a multi-faceted model or a curved surface model, has become a crucial direction for improving the positioning accuracy of workspace measurement and positioning systems. This, however, depends on the accurate calibration of the laser surface shape. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and propose an intrinsic parameter calibration method and system for a workspace measurement and positioning system. This method first calibrates the scanning optical surface pattern installed on the transmitting station using a high-precision three-axis turntable, and then selects a suitable optical surface model to fit the actual laser surface, thereby improving the angle measurement and coordinate measurement accuracy of the workspace measurement and positioning system. It also solves the problem that the linear structure optical surface pattern used by the transmitting station in the workspace measurement and positioning system cannot be accurately obtained, making it impossible to select a suitable intrinsic parameter model.

[0005] A method for calibrating intrinsic parameters of a workspace measurement and positioning system, comprising:

[0006] Preprocessing: Plan multiple control point locations in the workspace and obtain the coordinates of the control points in the world coordinate system; install the transmitter station and install photoelectric receiving devices at multiple control points;

[0007] The time elapsed from the starting position when the two optical planes of the transmitting station sweep across the photoelectric receiving device is obtained. Combined with the coordinates of the current control point, the spatial geometric parameters of each optical plane in the coordinate system of the transmitting station are calculated as the initial intrinsic parameters of the optical planes of the transmitting station.

[0008] Calibration phase: The transmitting station is fixed on a precision three-axis turntable, and an optoelectronic receiving device is placed in the workspace;

[0009] Adjust the pitch angle of the three-axis turntable, and the photoelectric receiver records the time interval after each rotation;

[0010] The distance between the transmitting station and the three-axis turntable was adjusted multiple times, and the pitch angle of the three-axis turntable was repeatedly adjusted. The photoelectric receiver recorded the time interval after each rotation.

[0011] Based on the obtained distance and corresponding time interval, the initial intrinsic parameters of the light plane are simulated to obtain the deformation of the light plane;

[0012] Based on the obtained optical surface deformation, the transmitting station is recalibrated, and the spatial geometric parameters of each optical plane in the transmitting station coordinate system are calculated to obtain the intrinsic parameters under the new model.

[0013] Furthermore, during the calibration phase, the center height of the photoelectric receiving device is equal to the laser center of the transmitting station.

[0014] Furthermore, in the preprocessing stage, the number of photoelectric receiving devices is not less than 20; in the formal calibration stage, a photoelectric receiving device is set in the workspace, and the distance L between the photoelectric receiving device and the precision three-axis turntable 1 is adjusted by moving the position of the photoelectric receiving device.

[0015] Furthermore, during the calibration phase, when the launch station is fixed on a precision three-axis turntable, it is necessary to ensure that the rotation axis of the launch station is perpendicular to the horizontal plane.

[0016] Furthermore, the calibration phase specifically includes:

[0017] S1: A photoelectric receiving device is fixed on a bracket located in the workspace, and the photoelectric receiving device is capable of receiving laser emitted by the transmitting station;

[0018] S2: Use a precision three-axis turntable to adjust the transmitter station to the preset initial position, and calibrate the time interval t between the light plane emitted by the transmitter station scanning from the starting point to the photoelectric receiving device;

[0019] S3: Adjust the pitch angle of the three-axis turntable within a certain range at certain angular intervals, and record the time interval t' after each adjustment;

[0020] S4: Adjust the distance between the photoelectric receiver and the three-axis turntable, then return to S3 to adjust the pitch angle of the three-axis turntable. The photoelectric receiver records the time interval after each rotation.

[0021] Repeat steps S3 to S4 one to three times to obtain the time interval t' for different distances between the launch station and the three-axis turntable;

[0022] S5: Based on the distance and time interval t' obtained in S4, the distance h from the center of the optical plane to the rotation center of the turntable, and the initial intrinsic parameters of the optical plane obtained in the preprocessing stage, simulation is performed to obtain the theoretical scanning time interval t at each pitch angle when the optical plane is an ideal plane. ideal By subtracting the time interval t' obtained from S4 and combining it with the rotational speed of the transmitting station, the deformation Δd of the optical plane at various angles can be obtained:

[0023] Where n is the rotational speed of the launching station, L is the distance, and t is the distance. ideal t' is the theoretical scan time interval, and t' is the time interval after rotation.

[0024] S6: Based on the optical surface deformation obtained from the S5 simulation, determine the intrinsic parameter model, recalibrate the transmitting station, and calculate the time elapsed from the starting position when each optical plane of the transmitting station sweeps across the photoelectric receiving device.

[0025] Based on the selected intrinsic parameter model, the spatial geometric parameters of each optical plane in the transmitter coordinate system are recalculated to obtain the intrinsic parameter parameters under the new model, which are used for subsequent measurement of the workspace measurement and positioning system.

[0026] Furthermore, the intrinsic parameter model is selected from a folded surface model or a curved surface model.

[0027] The present invention also discloses a calibration system, including a three-axis turntable 1, a photoelectric receiving device 4, and a signal processing unit arranged in a workspace; the three-axis turntable is fixedly mounted with a transmitting station to be calibrated via a connector, and the photoelectric receiving device is electrically connected to the signal processing unit;

[0028] The signal processing unit is used to receive data from the photoelectric receiving device, simulate the initial intrinsic parameters of the optical plane based on the obtained distance and corresponding time interval, and obtain the deformation of the optical plane; based on the obtained optical plane deformation, the transmitting station is recalibrated, and the spatial geometric parameters of each optical plane in the transmitting station coordinate system are calculated to obtain the intrinsic parameters under the new model.

[0029] The beneficial effects of this invention are as follows:

[0030] The intrinsic parameter calibration method and system for workspace measurement and positioning systems proposed in this invention overcome the problems of traditional scanning optical surface calibration methods being cumbersome, having multiple sources of error, and only allowing measurements before the laser is installed at the transmitting station. Furthermore, it comprehensively reflects the influence of scanning light intensity, optical surface thickness, and deformation of the light stripe energy centerline on the scanning optical surface shape. It offers good feasibility, simplicity, low cost, and more accurate evaluation results, effectively solving the problem of accurately obtaining laser surface shapes. It provides an accurate reference for selecting intrinsic parameter models, thereby improving the fitting effect of the intrinsic parameter model on the scanning optical surface, and is of great significance for improving the angular measurement accuracy and coordinate measurement accuracy of workspace measurement and positioning systems. Attached Figure Description

[0031] Figure 1 is a schematic diagram of the internal parameter calibration system of the workspace measurement and positioning system of the present invention;

[0032] Figure 2 is a flowchart of the calibration method.

[0033] Among them: 1: Precision three-axis rotary table; 2: Precision tooling; 3: Transmitting station; 4: Optoelectronic receiving device; 5: Support frame; 6: Signal processing unit. Detailed Implementation

[0034] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The specific embodiments described are only for explanation and illustration of the present invention and are not intended to limit the present invention.

[0035] As shown in Figure 1, a workspace measurement and positioning system internal parameter calibration system includes a precision three-axis turntable 1, a photoelectric receiving device 4, and a signal processing unit 6, all disposed in the workspace. The precision three-axis turntable 1 is a commercially available three-axis turntable, on which a transmitting station 3 to be calibrated is fixedly mounted via a precision fixture 2. The precision fixture 2 is a connector threadedly connected to the three-axis turntable 1 and the transmitting station 3. A tripod 5 is disposed within the workspace, on which the photoelectric receiving device 4, corresponding to the transmitting station 3, is fixedly mounted. The photoelectric receiving device 4 is capable of receiving the laser emitted by the transmitting station 3, and the center of the photoelectric receiving device 4 is at the same height as the center of the linear scanning light of the transmitting station 3. The photoelectric receiving device 4 is electrically connected to the signal processing unit 6.

[0036] As shown in Figure 2, the calibration method of the intrinsic parameter calibration device of the workspace measurement and positioning system includes the following steps:

[0037] Step 1: Set up control points in the workspace according to a certain pattern. Use a laser tracker to determine the coordinates of each control point in the world coordinate system.

[0038] Step 2: Select a fixed point in space for pre-calibration of the transmitting station 3, and arrange one of the photoelectric receiving devices 4 at each of the multiple control points, wherein the position of the transmitting station 3 enables the photoelectric receiving device 4 to receive the emitted light plane.

[0039] Acquire and record the time taken for the two optical planes of transmitter station 3 to sweep across each photoelectric receiver from their starting positions. Combine this with the coordinates of the current control point obtained in step one in the world coordinate system, and calculate the spatial geometric parameters of each optical plane in the coordinate system of transmitter station 3. These parameters serve as the initial intrinsic parameters of the emitted optical plane of transmitter station 3. The spatial geometric parameters refer to the parameters of the spatial geometric equation of the optical plane. The general form of the spatial plane equation is ax + by + cz + d = 0, where a, b, c, and d are the spatial geometric parameters.

[0040] Step 3: Fix the launch station 3 onto the precision three-axis turntable 1 using the precision tooling 2 (this is not the original launch station location determined in Step 1), ensuring that the rotation axis of the launch station 3 is perpendicular to the horizontal plane of the workspace.

[0041] Step 4: Fix one of the photoelectric receiving devices 4 from Step 2 onto the tripod 5. The tripod 5 is placed in the workspace. The distance between the center point of the photoelectric receiving device on the tripod 5 and the center point of the precision three-axis turntable 1 is L. Make the center height of the photoelectric receiving device 4 equal to the laser center of the transmitting station 3. Connect the photoelectric receiving device to the signal processing unit 6.

[0042] Step 5: Use a precision three-axis turntable to adjust the transmitter station 3 to the preset initial position, that is: set the roll angle of the precision three-axis turntable to 0°, the horizontal angle to 0°, and the pitch angle to -21°. Use the signal processing unit 6 to measure the time interval t between the scanning light emitted by the transmitter station 3 from the starting point to the photoelectric receiving device 4.

[0043] Step 6: Adjust the pitch angle of the precision three-axis turntable within a certain range at certain angular intervals. After each adjustment, the photoelectric receiving device 4 records the time interval t'. For example, starting from -21°, adjust to 21° at 0.7° intervals each time, and a total of 61 t's and corresponding pitch angles can be recorded.

[0044] Step 7: Move the bracket 5 to change the distance L between the photoelectric receiving device 4 on the bracket 5 and the precision three-axis turntable 1. Return to step 4 and repeat steps 4-7 1-3 times to obtain data under different evaluation distances L.

[0045] Step 8: Based on the distance L obtained in Step 7, the time interval t' after each rotation, the height h of the optical plane center from the turntable rotation center, and the initial intrinsic parameters of the optical plane obtained in Step 2, perform simulation to calculate the theoretical scanning time interval t at each pitch angle when the optical plane is an ideal plane. ideal The difference between the time interval t' obtained in step six and the time interval t' obtained in step six, combined with the rotational speed of the transmitting station 3, can be used to obtain the deformation of the light plane at each angle Δd.

[0046] Where n is the rotational speed of the launching station, L is the distance, and t is the distance. ideal t' is the theoretical scan time interval, and t' is the time interval after rotation.

[0047] Step Nine:

[0048] Select an intrinsic parameter model: Based on the smooth surface deformation obtained from the simulation in step eight, and in combination with actual needs, select an appropriate intrinsic parameter model from the folded surface model and curved surface model with 2-6 folded surfaces;

[0049] Recalibrate the system: Repeat step two, that is, recalibrate the transmitting station and calculate the time elapsed from the starting position when each optical plane of the transmitting station 3 sweeps across the photoelectric receiving device;

[0050] Based on the selected intrinsic parameter model, the spatial geometric parameters of each optical plane in the 3-coordinate system of the transmitting station are recalculated to obtain the intrinsic parameter parameters under the new model.

[0051] The newly obtained intrinsic parameters are imported into the workspace measurement and positioning system, thereby improving the accuracy of angle and coordinate measurement in the workspace measurement and positioning system.

[0052] In this invention, multiple photoelectric receiving devices 4 are arranged in the workspace during the pre-calibration process to perform pre-calibration of the transmitting station. After the pre-calibration is completed, the transmitting station is fixed on the turntable for formal calibration. At this time, only one photoelectric receiving device 4 needs to be placed on the tripod. After each execution of steps five and six, the tripod is moved to adjust the distance L between the support 5 and the precision three-axis turntable 1.

[0053] The specific application of the intrinsic parameter calibration method of the workspace measurement and positioning system is as follows:

[0054] In the docking of large ship sections, the methods for measuring and positioning the two sections of the ship to be docked using a workspace measurement and positioning system (wMPS) include:

[0055] First, a laser emitting station, photoelectric receiving devices, and a signal processing unit are set up in the workspace. Multiple photoelectric receiving devices are installed around the laser emitting station to receive the light signals emitted by the station. A signal processor connected to these photoelectric receiving devices is also installed to process the signals received and determine the precise coordinates of the receiver within the laser emitting station's coordinate system in the measurement space.

[0056] Then, the signal processor imports the new intrinsic parameters (i.e., the spatial geometric parameters of each optical plane in the transmitter coordinate system) obtained in step nine of the workspace measurement and positioning system intrinsic parameter calibration method as the transmitter intrinsic parameters, and then calculates the spatial coordinates through the angle intersection positioning principle.

[0057] Although preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art, under the guidance of the present invention, can make many other modifications without departing from the spirit and scope of the claims, all of which fall within the scope of protection of the present invention.

Claims

1. A method for calibrating intrinsic parameters of a workspace measurement and positioning system, characterized in that, include: Preprocessing: Plan multiple control point locations in the workspace and obtain the coordinates of the control points in the world coordinate system; install the transmitter station (3) and install photoelectric receiving devices (4) at multiple control points; The time elapsed from the starting position when the two optical planes of the transmitting station (3) sweep across the photoelectric receiving device is obtained. Combined with the coordinates of the current control point, the spatial geometric parameters of each optical plane in the coordinate system of the transmitting station (3) are calculated and used as the initial intrinsic parameters of the optical planes of the transmitting station (3). Calibration stage: The transmitting station is fixed on a precision three-axis turntable (1), and an optoelectronic receiving device (4) is placed in the workspace; Adjust the pitch angle of the three-axis turntable, and the photoelectric receiver records the time interval after each rotation; The distance between the transmitting station and the three-axis turntable was adjusted multiple times, and the pitch angle of the three-axis turntable was repeatedly adjusted. The photoelectric receiver recorded the time interval after each rotation. Based on the obtained distance and corresponding time interval, the initial intrinsic parameters of the light plane are simulated to obtain the deformation of the light plane; Based on the obtained optical surface deformation, the transmitting station is recalibrated, and the spatial geometric parameters of each optical plane in the transmitting station coordinate system are calculated to obtain the intrinsic parameters of the new model.

2. The method for calibrating the intrinsic parameters of a workspace measurement and positioning system according to claim 1, characterized in that, In the preprocessing stage, the number of photoelectric receiving devices (4) is not less than 20; in the formal calibration stage, a photoelectric receiving device (4) is set in the workspace, and the distance between the photoelectric receiving device (4) and the precision three-axis turntable (1) is adjusted by moving the position of the photoelectric receiving device (4), and the center height of the photoelectric receiving device (4) is the same as the laser center of the transmitting station (3).

3. The method for calibrating the intrinsic parameters of a workspace measurement and positioning system according to claim 1, characterized in that... During the calibration phase, when the launch station (3) is fixed on the precision three-axis turntable, it is necessary to ensure that the rotation axis of the launch station (3) is perpendicular to the horizontal plane.

4. The method for calibrating the intrinsic parameters of a workspace measurement and positioning system according to claim 3, characterized in that, The calibration phase specifically includes: S1: A photoelectric receiving device (4) is fixed on a bracket (5) located in the workspace, and the photoelectric receiving device (4) is able to receive the laser emitted by the transmitting station (3); S2: Use the three-axis turntable (1) to adjust the transmitting station (3) to the preset initial position, and calibrate the time interval t from the starting point to the photoelectric receiving device (4) when the light plane emitted by the transmitting station (3) is scanned. S3: Adjust the pitch angle of the three-axis turntable within a certain range at certain angular intervals. After each adjustment, the photoelectric receiving device (4) records the time interval t' at this time. S4: Adjust the distance between the photoelectric receiver (4) and the three-axis turntable, then return to S3 to adjust the pitch angle of the three-axis turntable. The photoelectric receiver records the time interval after each rotation. Repeat steps S3 to S4 one to three times to obtain the time interval t' for different distances between the launch station and the three-axis turntable; S5: Based on the distance and time interval t' obtained in S4, the distance h from the center of the optical plane to the rotation center of the turntable, and the initial intrinsic parameters of the optical plane obtained in the preprocessing stage, simulation is performed to obtain the theoretical scanning time interval t at each pitch angle when the optical plane is an ideal plane. ideal By subtracting the time interval t' obtained from S4 and combining it with the rotational speed of the transmitting station (3), the deformation of the light plane at each angle Δd can be obtained: Where n is the rotational speed of the launching station, L is the distance, and t is the distance. ideal t' is the theoretical scanning time interval, and t' is the time interval after rotation; S6: Based on the optical surface deformation obtained from the S5 simulation, determine the intrinsic parameter model, recalibrate the transmitting station, and calculate the time elapsed from the starting position when each optical plane of the transmitting station (3) sweeps across the photoelectric receiving device. Based on the selected intrinsic parameter model, the spatial geometric parameters of each optical plane in the coordinate system of the transmitting station (3) are recalculated to obtain the intrinsic parameter parameters under the new model, which are used for subsequent measurement of the workspace measurement and positioning system.

5. The method for calibrating the intrinsic parameters of a workspace measurement and positioning system according to claim 4, characterized in that, The intrinsic parameter model is selected from either a folded surface model or a curved surface model.

6. A calibration system for intrinsic parameters of a workspace measurement and positioning system, characterized in that, It includes a three-axis turntable (1), an optoelectronic receiving device (4), and a signal processing unit (6) set in the workspace; the three-axis turntable (1) is fixedly installed with the transmitting station (3) to be calibrated through a connector, and the optoelectronic receiving device (4) is electrically connected to the signal processing unit (6); The signal processing unit (6) is used to receive data from the photoelectric receiving device (4), simulate the initial intrinsic parameters of the light plane according to the obtained distance and the corresponding time interval, and obtain the deformation of the light plane; according to the obtained light plane deformation, recalibrate the transmitting station, solve the spatial geometric parameters of each light plane in the transmitting station coordinate system, and obtain the intrinsic parameters under the new model.

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