Field calibration system and method for calibrating a laser tracker

Abstract

The application provides a field calibration system for calibrating a laser tracker, and belongs to the technical field of laser measurement. The field calibration system comprises a truss reference device, a plurality of target ball seats and a plurality of connecting rods. Two adjacent target ball seats are fixedly connected by a connecting rod, so that the plurality of target ball seats form a truss structure through the plurality of connecting rods. A target ball is configured to be selectively fixed to any one of the plurality of target ball seats. The laser tracker is configured to measure a plurality of spatial position data of the target ball in a base coordinate system when the target ball is fixed to the plurality of target ball seats. The base coordinate system is established with the base of the laser tracker as the origin. A parameter calibration device is in communication connection with the laser tracker and is configured to determine a measurement distance value between two adjacent target ball seats based on the plurality of spatial position data, and calibrate the laser tracker based on the standard length of the plurality of connecting rods and the plurality of measurement distance values.

Description

Technical Field

[0001] This application relates to the field of laser measurement technology, and more specifically, to a field calibration system and method for calibrating a laser tracker. Background Technology

[0002] In the field of large-size spatial precision measurement, laser trackers have become the core equipment for high-precision geometric measurement in the field due to their technical advantages such as wide measurement range, excellent measurement accuracy, and outstanding dynamic target tracking performance. However, when laser trackers are in complex industrial environments and operate continuously under high loads, or are affected by external working conditions such as transportation, handling, and rapid fluctuations in ambient temperature, the precision mechanical components inside the equipment are prone to slight structural deformation, which can lead to drift in the parameters of the entire measurement system and cause a decrease in measurement accuracy.

[0003] Traditional calibration methods typically require transporting the laser tracker back to a metrology laboratory for separate calibration using large reference equipment such as a high-precision multi-tooth indexing table. However, this metrology laboratory-based calibration method has significant drawbacks: the calibration cycle is long and the cost is high. Furthermore, the ideal temperature and humidity environment of a metrology laboratory differs greatly from the actual industrial environment where the laser tracker operates, making it difficult to adapt the calibration parameters obtained from laboratory calibration to the actual field usage environment. Summary of the Invention

[0004] In view of this, this application provides a field calibration system and method for calibrating a laser tracker.

[0005] One aspect of this application provides a field calibration system for calibrating a laser tracker, comprising: a truss-type reference device including a plurality of target ball seats and a plurality of connecting rods, wherein two adjacent target ball seats are fixedly connected by the connecting rods, such that the plurality of target ball seats form a truss structure through the plurality of connecting rods; a target ball configured to be selectively fixed to any one of the plurality of target ball seats; wherein the laser tracker is configured to measure a plurality of spatial position data of the target ball in a base coordinate system when the target ball is fixed to the plurality of target ball seats, wherein the base coordinate system is established with the base of the laser tracker as the origin; and a parameter calibration device communicatively connected to the laser tracker, configured to determine a measured distance value between two adjacent target ball seats based on the plurality of spatial position data, and to calibrate the laser tracker based on the standard length of the plurality of connecting rods and the plurality of measured distance values.

[0006] According to an embodiment of this application, the above-mentioned field calibration system further includes: a plurality of temperature sensors, wherein the plurality of temperature sensors are fixedly fixed at intervals along the length direction of the connecting rod, and the temperature sensors are configured to acquire a measured temperature; a temperature compensation device, configured to determine a temperature compensation length of the connecting rod caused by temperature change based on the thermal expansion coefficient of the connecting rod and the plurality of measured temperatures, and to obtain a first actual length based on the temperature compensation length and the standard length of the connecting rod; wherein the parameter calibration device is configured to calibrate the laser tracker based on the plurality of the first actual lengths and the plurality of the measured distance values.

[0007] According to an embodiment of this application, the above-mentioned field calibration system further includes: a plurality of inclinometers, the inclinometers being fixedly mounted on the connecting rod, the inclinometers being configured to acquire attitude data of the connecting rod; an attitude compensation device, configured to determine, based on the attitude data and the material parameters of the connecting rod, the deformation compensation length of the connecting rod caused by gravity under the current attitude, and to obtain a second actual length based on the deformation compensation length and the standard length of the connecting rod; wherein, the parameter calibration device is configured to calibrate the laser tracker based on a plurality of the second actual lengths and a plurality of the measured distance values.

[0008] According to an embodiment of this application, the parameter calibration device is configured to: obtain a measurement error value based on the standard length of the connecting rod and the measured distance value; determine the initial pose transformation matrix of the base coordinate system relative to the first local coordinate system using the local exponential product method, wherein the first local coordinate system is established with the laser emission center of the laser tracker as the origin; and calibrate the laser tracker based on the initial pose transformation matrix and multiple measurement error values.

[0009] According to an embodiment of this application, the parameter calibration device is configured to: obtain an error screw corresponding to the initial pose transformation matrix based on the initial pose transformation matrix and multiple measurement error values; obtain a first pose transformation matrix based on the error screw and the initial pose transformation matrix; and calibrate the laser tracker using the first pose transformation matrix.

[0010] According to an embodiment of this application, the parameter calibration device is configured to: construct an error propagation equation between the measurement error parameter and the error screw parameter based on the initial pose transformation matrix; substitute multiple measurement error values ​​into the error propagation equation and solve for the error screw corresponding to the initial pose transformation matrix using the least squares method.

[0011] According to an embodiment of this application, the parameter calibration device is configured to: substitute multiple measurement error values ​​into the error propagation equation and use the Levenberg-Marquardt algorithm with damping factor to solve for the error spinter corresponding to the initial pose transformation matrix.

[0012] According to an embodiment of this application, the initial pose transformation matrix is ​​determined based on a plurality of indirect pose transformation matrices, wherein each of the indirect pose transformation matrices corresponds to a mechanical kinematic chain of the laser tracker.

[0013] According to an embodiment of this application, the parameter calibration device is configured to: obtain an indirect error screw corresponding to the indirect pose transformation matrix based on a plurality of the indirect pose transformation matrices and a plurality of the measurement error values; obtain a first indirect pose transformation matrix based on the indirect error screw and the indirect pose transformation matrix; and calibrate the laser tracker using a plurality of the first indirect pose transformation matrices.

[0014] Another aspect of this application provides a field calibration method for calibrating a laser tracker, comprising: sequentially fixing a target ball in multiple target ball seats of a truss-type reference device, wherein two adjacent target ball seats are fixedly connected by connecting rods of the truss-type reference device; measuring multiple spatial position data of the target ball in a base coordinate system when the target ball is fixed in the multiple target ball seats using a laser tracker; determining a measurement distance value between two adjacent target ball seats based on the multiple spatial position data; and calibrating the laser tracker based on the standard lengths of the multiple connecting rods and the multiple measurement distance values.

[0015] According to embodiments of this application, a truss structure is constructed using multiple target ball mounts and multiple connecting rods. A laser tracker measures multiple spatial position data of the target ball in the base coordinate system when the target ball is fixed to the multiple target ball mounts. Based on this multiple spatial position data, the measurement distance between two adjacent target ball mounts can be determined. Furthermore, by comparing and analyzing the known standard lengths of the multiple connecting rods with the multiple measurement distance values ​​measured by the laser tracker, multi-point, multi-directional, and multi-dimensional simultaneous calibration of the laser tracker can be achieved. This technical solution eliminates the need to move the laser tracker from the field to a laboratory; a truss-type reference device with stable geometric constraints can be directly constructed in the industrial production site, significantly improving the on-site adaptability and operational convenience of calibration. Simultaneously, through redundant comparison of multiple sets of distance data, the influence of environmental interference on a single measurement can be effectively suppressed, ultimately achieving high-efficiency and high-precision calibration of the laser tracker in actual industrial environments. Attached Figure Description

[0016] The above and other objects, features and advantages of this application will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0017] Figure 1 A schematic diagram of an on-site calibration system for calibrating a laser tracker according to an embodiment of this application is shown;

[0018] Figure 2 A schematic diagram of the structure of the truss-type reference device according to an embodiment of this application is shown;

[0019] Figure 3 A schematic diagram of a field calibration system for calibrating a laser tracker according to another embodiment of this application is shown;

[0020] Figure 4 A flowchart of an on-site calibration method for calibrating a laser tracker according to an embodiment of this application is shown. Detailed Implementation

[0021] The embodiments of this application will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of this application. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of this application for ease of explanation. However, it will be apparent that one or more embodiments may be implemented without these specific details. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this application.

[0022] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The terms “comprising,” “including,” etc., as used herein indicate the presence of features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0023] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0024] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0025] Figure 1A schematic diagram of an on-site calibration system for calibrating a laser tracker according to an embodiment of this application is shown.

[0026] like Figure 1 As shown, the field calibration system for calibrating the laser tracker includes a truss-type reference device 110, a target ball 120, and a parameter calibration device 130.

[0027] The truss-type reference device 110 serves as a physical reference carrier for on-site calibration of the laser tracker. It is constructed by combining several connecting rods and several target ball seats. For example, the truss-type reference device 110 includes a first target ball seat 1101 and a first connecting rod 1102. During the actual assembly process, two sets of target ball seats located close to each other are securely connected and fixed by connecting rods. Through this sequential assembly method, all target ball seats are interconnected and supported by multiple connecting rods, ultimately forming a stable and spatially regular truss-type overall structure.

[0028] Figure 2 A schematic diagram of the structure of a truss-type reference device according to an embodiment of this application is shown.

[0029] like Figure 2 As shown, the truss-type reference device 110 includes twelve connecting rods and eight target ball seats. Adjacent target ball seats are fixedly connected by connecting rods, so that the eight target ball seats form a cubic structure through the twelve connecting rods. For example, the first connecting rod 1102 is used to fixally connect the first target ball seat 1101 and the second target ball seat 1103. It should be noted that this embodiment uses an example of eight target ball seats and twelve connecting rods forming a cubic structure, but the specific number of target ball seats and connecting rods is not limited to this. In practical applications, the number of target ball seats constituting the truss-type reference device and the number of connecting rods connecting the corresponding target ball seats can be adaptively adjusted according to the required reference structure shape (such as a cuboid, other polyhedra, or more complex spatial trusses) and accuracy requirements.

[0030] The target ball 120 is configured to be selectively fixed to any one of a plurality of target ball seats. The laser tracker is configured to measure multiple spatial position data of the target ball in the base coordinate system when the target 120 is fixed to the plurality of target ball seats. The base coordinate system is established with the base of the laser tracker as the origin.

[0031] The target ball 120 features flexible assembly capabilities, allowing for independent installation and fixation on any target ball holder according to actual calibration needs. This enables flexible switching of the target ball's spatial position, facilitating the free selection of measurement points at different locations and meeting the requirements for multi-point and multi-directional data acquisition. Simultaneously, the truss-type reference device 110 can be located in any measurement space area, and can be set up in multiple spatial areas to acquire multiple sets of data for calibrating the laser tracker.

[0032] During the formal calibration data acquisition process, the laser tracker uses the base mounted on its bottom as the origin, establishing a dedicated base coordinate system. All related spatial position data are uniformly calculated and recorded based on this base coordinate system. Once the target ball 120 is sequentially fixed to its corresponding installation position on different target ball bases, the laser tracker can activate its spatial position measurement function. It accurately collects the actual spatial position information of the target ball 120 within the base coordinate system at each installation state, thereby summarizing multiple sets of complete spatial position data corresponding to different points, comprehensively covering the measurement point information of different areas on the truss structure.

[0033] The parameter calibration device 130 is communicatively connected to the laser tracker and is configured to determine the measurement distance between two adjacent target spheres based on multiple spatial position data, and to calibrate the laser tracker based on the standard length of multiple connecting rods and multiple measurement distance values.

[0034] The parameter calibration device 130 establishes a stable data interaction path with the laser tracker via wired or wireless communication, enabling it to receive all spatial position data collected and uploaded by the laser tracker in real time. Based on the acquired spatial position data, the parameter calibration device 130 can calculate the measured distance between any two sets of adjacent target spheres measured by the laser tracker. Simultaneously, the parameter calibration device 130 internally stores the standard length values ​​of each connecting rod verified under standard calibration conditions. These standard lengths are precise reference dimensions determined after rigorous verification and can serve as a reference for laser tracker calibration. The parameter calibration device 130 comprehensively compares the collected multiple measured distance values ​​with the corresponding standard lengths of the connections. By comparing the deviations between the two types of data, it analyzes the measurement deviations existing in the laser tracker's spatial ranging and spatial coordinate positioning processes. Based on these measurement deviations, it performs unified adjustments, corrections, and optimizations to the relevant parameters within the laser tracker, ultimately completing a comprehensive calibration of the overall measurement accuracy of the laser tracker.

[0035] Through the embodiments of this application, a truss structure is constructed using multiple target ball mounts and multiple connecting rods. A laser tracker measures multiple spatial position data of the target ball in the base coordinate system when the target ball is fixed to the multiple target ball mounts. Based on this multiple spatial position data, the measurement distance between two adjacent target ball mounts can be determined. Furthermore, by comparing and analyzing the known standard lengths of the multiple connecting rods with the multiple measurement distance values ​​measured by the laser tracker, multi-point, multi-directional, and multi-dimensional simultaneous calibration of the laser tracker can be achieved. This technical solution eliminates the need to move the laser tracker from the field to a laboratory; a truss-type reference device with stable geometric constraints can be constructed directly in the industrial production site, significantly improving the on-site adaptability and operational convenience of calibration. Simultaneously, through redundant comparison of multiple sets of distance data, the influence of on-site environmental interference on a single measurement can be effectively suppressed, ultimately achieving high-efficiency and high-precision calibration of the laser tracker in actual industrial environments.

[0036] According to an embodiment of this application, the parameter calibration device is configured as follows: Based on the standard length of the connecting rod and the measured distance value, a measurement error value is obtained; using the local exponential product method, an initial pose transformation matrix of the base coordinate system relative to a first local coordinate system is determined, wherein the first local coordinate system is established with the laser emission center of the laser tracker as the origin; based on the initial pose transformation matrix, an error propagation equation is constructed between the measurement error parameter and the error screw parameter; multiple measurement error values ​​are substituted into the error propagation equation, and the error screw corresponding to the initial pose transformation matrix is ​​obtained using the least squares method; based on the error screw and the initial pose transformation matrix, a first pose transformation matrix is ​​obtained, and the laser tracker is calibrated using the first pose transformation matrix.

[0037] The local exponential product is a mathematical tool for describing the finite motion (especially rotation and translation) of a rigid body in space. It characterizes an object moving a certain distance along a helical axis from an initial pose to a new pose. "Local" means that the helical axis is defined relative to the object's current local coordinate system, rather than being fixed in the world coordinate system. Therefore, the local exponential product is suitable for expressing continuous, recursive motions, such as when robot joints sequentially drive links, each joint's motion is based on the current pose of the previous link. The essence of the local exponential product is to unify rotation and translation into a helical motion and express the result of the change from the initial pose to the current pose in exponential form.

[0038] The pose transformation matrix is ​​used to describe the positional changes (translation of the origin) and attitude changes (rotation of the coordinate axes) of one coordinate system relative to another. Using the pose transformation matrix, the coordinates of a point represented in one coordinate system can be transformed to another. The pose transformation matrix is ​​often used to represent the relative pose relationships between adjacent links, and by multiplying them together, the total pose of the end effector in the base coordinate system can be obtained.

[0039] The first local coordinate system is constructed with the laser emission center of the laser tracker itself as the origin, while the reference coordinate system is the standard reference coordinate system used uniformly in on-site calibration operations. By using the spatial pose derivation method corresponding to the local exponential product, the initial spatial position relationship and attitude deflection relationship between the reference coordinate system and the first local coordinate system can be accurately calculated and determined. This allows for the determination of the initial pose transformation matrices between the two systems, thus establishing the most basic spatial transformation relationship between the two different coordinate systems and laying the spatial coordinate foundation for subsequent error tracing.

[0040] The actual distance between the laser emission center and the target sphere of the laser tracker is determined based on the laser propagation time, and therefore this actual distance is not affected by deviations in the internal mechanical structure of the laser tracker. Spatial position data is obtained based on this actual distance and the pose transformation matrix. Deviations in the internal mechanical structure of the laser tracker will affect the pose transformation matrix, ultimately impacting the accuracy of the spatial position data. Therefore, to calibrate the laser tracker, it is necessary to analyze the error screw of the pose transformation matrix. Adding the initial pose transformation matrix to the error screw yields a first pose transformation matrix that reflects the actual mechanical conditions. Based on the actual distance between the laser emission center and the target sphere and the first pose transformation matrix, calibrated spatial position data is obtained, thus achieving the calibration of the laser tracker.

[0041] Error screw is an integrated error representation quantity used to uniformly characterize position and attitude deviations in the pose transformation matrix. It integrates translational offset errors and rotation angle errors between coordinate systems into a set of overall error representations, which can completely describe all systematic deviations existing in the spatial relative transformation process between two coordinate systems. It is the core error parameter for correcting pose transformation matrix deviations and eliminating equipment spatial positioning errors. The pose transformation matrix is ​​used to express the spatial correspondence between two different coordinate systems, including both spatial point translation relationships and spatial angle rotation relationships. It is the basic calculation basis for laser trackers to realize coordinate conversion, distance calculation, and spatial positioning. In an ideal state, the pose transformation matrix has no deviation and can accurately complete the mutual transformation of coordinate systems. However, due to factors such as equipment assembly and manufacturing tolerances, laser emission center installation offset, equipment base placement tilt, internal sensing element zero-point offset, and long-term structural micro-deformation, the pose transformation matrix in actual use will deviate from the theoretical standard state, resulting in two types of inherent deviations: position offset and angle deflection. This introduces systematic errors into the coordinate conversion process, ultimately causing inaccurate ranging and positioning measurement results. The error screw integrates the two types of deviations mentioned above: firstly, it includes a translational error component, corresponding to the spatial positional offsets along the three axes between coordinate systems, used to describe the positional deviations caused by the misalignment of the coordinate origins; secondly, it includes a rotational error component, corresponding to the attitude deflection angle deviations around the three axes between coordinate systems, used to describe the angular deviations caused by inconsistent spatial orientations. The overall parameter formed by the combination of these two components is the error screw, which can completely and without omission quantify all the spatial deviations of the current pose transformation matrix compared to the standard ideal matrix.

[0042] Error screws lead to measurement errors. Therefore, in the embodiments of this application, an error propagation equation can be constructed to characterize the quantitative impact of error screws on measurement errors. This error propagation equation is obtained based on the pose transformation matrix. During spatial pose calculation and measurement error analysis, the translational deviation component and rotational attitude deviation component included in the error screw can be considered as independent influencing variables. Based on the functional relationship corresponding to the pose transformation matrix, partial derivatives are calculated for each screw error component to obtain the magnitude and trend of measurement error changes caused by individual changes in each error component. By successively calculating partial derivatives, each minute spatial deviation in the error screw is decomposed and mapped into the corresponding error influence quantity in the measurement dimension. The influence relationships derived from all partial derivatives are then integrated and summarized to finally form a complete error propagation equation. This equation can accurately quantify the magnitude of the impact of each screw error on the final measurement result, clearly establishing a quantitative relationship between the source error and the measured error. In the embodiments of this application, based on multiple specific measurement error values, the relevant parameters of the error propagation equation can be determined by the least squares method, so that the error propagation equation can be adapted to the actual measurement error variation law. Then, by combining the relevant parameters and multiple measurement error values, the specific value of the error spinor can be obtained.

[0043] In the embodiments of this application, the Levenberg-Marquardt algorithm with damping factor can be used to iteratively optimize and solve the above-mentioned least squares problem.

[0044] The Levenberg-Marquardt algorithm with damping factor is an iterative numerical method for nonlinear least squares optimization. Its core is to introduce a dynamically adjustable damping factor on the basis of the Gauss-Newton method, combining the stability of gradient descent with the fast convergence of Gauss-Newton.

[0045] Conventional least squares methods are often used for data fitting and parameter solving in linear relationships. While their computational logic is simple, they are prone to problems such as slow iterative convergence, oscillating divergence during the solution process, getting trapped in local optima, and sensitivity to initial values ​​when dealing with the nonlinear mapping relationship presented by the error propagation equation in this embodiment. These issues make it difficult to consistently obtain accurate results. The Levenberg-Marquardt algorithm with a damping factor, while retaining the core objective of minimizing the overall sum of squared residuals in least squares methods, introduces a dedicated damping factor for computational control, combining the advantages of gradient descent and Gauss-Newton methods. During the iterative solution of error-related parameters and the specific values ​​of the error spinor, the damping factor allows for flexible adjustment of the iteration step size and search direction. This accelerates the overall convergence speed in the early stages of the solution process and slows down the adjustment as the iteration approaches the optimal solution, effectively preventing numerical divergence and deviations from the true values. It also significantly reduces the adverse effects of initial value deviations on the final solution. Applying this algorithm to the embodiments of this application, after substituting multiple sets of measurement error values, it can solve the parameters of the error propagation equation more smoothly and accurately, and on this basis, it can stably invert and calculate the specific value of the error screw with higher accuracy and better fit to the actual working conditions. This effectively improves the stability, accuracy and practicality of the entire laser tracker's pose error solution and equipment calibration work, and is more suitable for solving nonlinear parameters such as spatial pose error.

[0046] In the embodiments of this application, the initial pose transformation matrix is ​​determined based on multiple indirect pose transformation matrices, wherein each indirect pose transformation matrix corresponds to a mechanical kinematic chain of the laser tracker. When the initial pose transformation matrix is ​​determined based on multiple indirect pose transformation matrices, the parameter calibration device is configured to: obtain an indirect error screw corresponding to the indirect pose transformation matrix based on the multiple indirect pose transformation matrices and multiple measurement error values; obtain a first indirect pose transformation matrix based on the indirect error screw and the indirect pose transformation matrix; and calibrate the laser tracker using multiple first indirect pose transformation matrices.

[0047] The base, azimuth axis, pitch axis, and laser emission center of the laser tracker are connected in series to form a complete mechanical kinematic chain. The rotational motion transmission and spatial pose transformation of the laser tracker are all carried out along this kinematic chain. The geometric errors of the laser tracker (such as axis misalignment, perpendicularity error between axes, zero-position error, etc.) are essentially pose deviations between adjacent components in the kinematic chain. Therefore, the sources of error can be systematically characterized, modeled, and calibrated through a mechanical kinematic chain model.

[0048] First, based on the instrument's mechanical kinematic chain, multiple adjacent local coordinate systems can be constructed sequentially. This kinematic chain consists of the laser tracker's base, azimuth axis, pitch axis, and laser emission center connected in series. Specifically, a local coordinate system {0} is established on the base, a local coordinate system {1} is established at the end of the azimuth axis, a local coordinate system {2} is established at the end of the pitch axis, and a local coordinate system {3} is established at the laser emission center. These coordinate systems move synchronously with the instrument's mechanical components, intuitively reflecting the position and attitude relationships between the various mechanical components. Subsequently, the theory of local exponential products is introduced to mathematically describe the ideal motion of each motion axis. The ideal motion of the azimuth and pitch axes in their respective local coordinate systems is abstracted into corresponding local motion spinors, used to characterize the axis direction, position, and rotation direction of the axis. Based on this, a forward kinematic model of the laser tracker is constructed. For example, the actual spatial coordinates of the target point in the base coordinate system are measured. The positive kinematic model can be expressed as:

[0049] (1);

[0050] in, 01 Let be the initial nominal pose transformation matrix between local coordinate system {0} and local coordinate system {1}. 12 Let be the initial nominal pose transformation matrix between local coordinate system {1} and local coordinate system {2}. 23 Let be the initial nominal pose transformation matrix between local coordinate system {2} and local coordinate system {3}. Let be the nominal local spinor of the azimuth axis in the local coordinate system {1}. Let $\frac{ ... It is the azimuth angle. The pitch angle, To measure the homogeneous coordinates of the target point in the local coordinate system {3}, D is the distance between the target point and the laser emission center.

[0051] Subsequently, a multi-constraint calibration model for the laser tracker can be constructed as follows:

[0052] (2);

[0053] in, This represents the nth measurement error value. This represents the error spinor of the i-th indirect pose transformation matrix. Let be the Jacobian matrix in the nth pose state.

[0054] Since the number of distance constraints acquired in the field is much greater than the error spinor of the indirect pose transformation matrix to be determined, multiple sets of distance constraint deviations can be obtained. The optimization objective is to minimize the sum of squares. A Levenberg-Marquardt algorithm with a damping factor is used for global iterative solution at the data processing end. In each iteration, the algorithm directly calculates the error spinor of the indirect pose transformation matrix between adjacent local coordinate systems and compensates for it in the following way:

[0055] (3);

[0056] Once the conditions for terminating the iteration are met, the optimized local coordinate system transformation parameters, i.e., the first indirect pose transformation matrix, are output.

[0057] The on-site calibration system can use multiple first-stage indirect pose transformation matrices as new compensation coefficients, directly feeding them back through the communication interface and embedding them into the internal control system of the laser tracker, or reconstructing the data in the host computer software. In subsequent measurements, the laser tracker directly calls the updated local coordinate system model to achieve high-precision on-site tracing under real-world conditions.

[0058] According to an embodiment of this application, the on-site calibration system further includes: multiple temperature sensors, which are fixed at intervals along the length of the connecting rod, and the temperature sensors are configured to acquire a measured temperature; a temperature compensation device, configured to determine a temperature compensation length of the connecting rod caused by temperature changes based on the thermal expansion coefficient of the connecting rod and the multiple measured temperatures, and to obtain a first actual length based on the temperature compensation length and the standard length of the connecting rod; wherein, the parameter calibration device is configured to calibrate the laser tracker based on the multiple first actual lengths and multiple measured distance values.

[0059] Real-world industrial environments are not constant; ambient temperatures fluctuate. The connecting rod itself, being made of a material with corresponding thermal expansion properties, will naturally stretch or contract when the ambient temperature rises or falls, causing its actual length to deviate from the pre-calibrated standard length. Using the length of this temperature-deformation-error connecting rod as the calibration benchmark will lead to discrepancies in subsequent laser tracker distance measurements, ultimately resulting in distorted calibration results and failing to meet the requirements for high-precision on-site calibration.

[0060] To address this, multiple temperature sensors can be installed and fixed on the surface of the connecting rod at even intervals. This dispersed arrangement of multiple temperature sensors allows for comprehensive collection of real-time ambient temperatures across different sections of the connecting rod. This avoids the problem of a single temperature measurement point only obtaining localized temperature data and failing to reflect the actual heating conditions of the entire connecting rod. It accurately acquires the real-time measured temperature at each location on the connecting rod, completely reconstructing the true temperature conditions of the entire connecting rod.

[0061] Taking a connecting rod C, which is fixedly connected to target ball seat A and target ball seat B, as an example, k temperature sensors are installed on connecting rod C. Each temperature sensor corresponds to a pre-known local micro-segment length of the connecting rod, and the sum of the k local micro-segment lengths is the standard length of connecting rod C. The temperature compensation device can receive the field-measured temperature data transmitted from all temperature sensors in real time, and simultaneously retrieve pre-stored relevant attribute parameters such as the thermal expansion coefficient of the connecting rod. Based on the collected real-time temperature data, the device comprehensively calculates the overall length deformation difference of the entire connecting rod caused by the change in the actual ambient temperature compared to the calibration temperature. This deformation difference is the temperature compensation length of the connecting rod caused by the temperature change. The temperature compensation length of connecting rod C caused by temperature change. It can be represented as:

[0062] (4);

[0063] Where α is the coefficient of thermal expansion of the connecting rod, and T0 is the initial calibration temperature. Let j be the temperature measured by the j-th temperature sensor. For the first The length of a local micro-segment represented by a temperature sensor.

[0064] After accurately determining the temperature compensation length, the temperature compensation device adds the temperature compensation length to the standard length to obtain the first actual length of the connecting rod under the current field environment after eliminating the influence of temperature error. This length can truly reflect the actual physical size of the connecting rod without temperature error on site.

[0065] According to an embodiment of this application, the on-site calibration system further includes: multiple inclinometers, each inclinometer being fixedly mounted on a connecting rod, the inclinometers being configured to acquire attitude data of the connecting rod; an attitude compensation device, configured to determine, based on the attitude data and the material parameters of the connecting rod, the deformation compensation length of the connecting rod caused by gravity under the current attitude, and to obtain a second actual length based on the deformation compensation length and the standard length of the connecting rod; wherein, the parameter calibration device is configured to calibrate the laser tracker based on multiple second actual lengths and multiple measured distance values.

[0066] In actual field calibration conditions, when a truss-type reference device is erected solely by a fixed installation structure, it cannot maintain an absolutely horizontal and vertical standard ideal posture at all times. Affected by factors such as the installation location, erection angle, and differences in support points, the connecting rods of the truss-type reference device are prone to tilting, bending, and swaying. When the connecting rod is in a non-standard placement posture, it will undergo natural bending and sagging deformations under its own weight and the forces at both ends, changing the actual effective length of the connecting rod. If a preset standard length is directly used as the calibration benchmark, the dimensional deviation caused by gravitational deformation will be ignored, thus affecting the distance calibration results of the laser tracker and reducing the overall calibration reliability.

[0067] Therefore, an inclinometer can be fixedly installed on each connecting rod. The inclinometer is securely assembled with the connecting rod as a single unit, allowing it to synchronously rotate and change attitude with the connecting rod. This enables real-time and accurate acquisition of comprehensive attitude data, including the current tilt angle, spatial orientation, and overall deflection state of the connecting rod, providing complete and reliable raw attitude data for subsequent deformation compensation. The current tilt angle of the connecting rod can include both pitch and roll angles.

[0068] The attitude compensation device can receive real-time attitude data of the connecting rod from all inclinometers, and simultaneously retrieve pre-stored basic material parameters such as the material hardness, bending resistance, and self-weight of the connecting rod. Combined with the rigid body space transformation matrix, it comprehensively analyzes and calculates the length deviation corresponding to the bending and sagging deformation of the connecting rod under its current tilted position due to the continuous action of its own gravity. This length deviation is the compensation length for the deformation of the connecting rod caused by gravity.

[0069] After accurately determining the deformation compensation length, the attitude compensation device adds the deformation compensation length and the standard length to obtain the second actual length of the connecting rod in the current actual placement posture after eliminating the gravity deformation error. The second actual length can truly reflect the effective actual distance of the connecting rod under the on-site attitude conditions.

[0070] Figure 3 A schematic diagram of a field calibration system for calibrating a laser tracker according to another embodiment of this application is shown.

[0071] like Figure 3As shown, the field calibration system for calibrating a laser tracker includes a truss-type reference device, a first target ball 320, a first parameter calibration device 330, multiple temperature sensors, and multiple inclinometers. The truss-type reference device includes multiple connecting rods and multiple target ball seats. Taking a specific second connecting rod 3103 as an example, the second connecting rod 3103 is used to fixally connect the third target ball seat 3101 and the fourth target ball seat 3102. The first temperature sensor 3401 and the second temperature sensor 3401 are respectively fixed on the second connecting rod 3103, and the first inclinometer 350 is fixed at the midpoint of the second connecting rod 3103. The first target ball 320 can be fixed in any one of the target ball seats in the truss-type reference device. The specific functions of the above components have been described in detail in the preceding sections of this document and will not be repeated here.

[0072] Figure 4 A flowchart of an on-site calibration method for calibrating a laser tracker according to an embodiment of this application is shown.

[0073] like Figure 4 As shown, the field calibration method for calibrating the laser tracker includes operations S410~S440.

[0074] In operation S410, the target ball is fixed in sequence in multiple target ball seats of the truss-type reference device, and two adjacent target ball seats are fixedly connected by the connecting rod of the truss-type reference device.

[0075] In operating the S420, a laser tracker is used to measure the spatial position data of the target ball in the base coordinate system when the target ball is fixed on multiple target ball seats.

[0076] In operation S430, the measured distance between two adjacent target balls is determined based on multiple spatial location data.

[0077] In operation of S440, the laser tracker is calibrated based on the standard lengths of multiple connecting rods and multiple measured distance values.

[0078] Those skilled in the art will understand that the features described in the various embodiments of this application can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in this application. In particular, the features described in the various embodiments of this application can be combined and / or combined in various ways without departing from the spirit and teachings of this application. All such combinations and / or combinations fall within the scope of this application.

[0079] The embodiments of this application have been described above. However, these embodiments are merely illustrative and not intended to limit the scope of this application. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. Without departing from the scope of this application, those skilled in the art can make various substitutions and modifications, all of which should fall within the scope of this application.

Claims

1. A field calibration system for calibrating a laser tracker, comprising: A truss-type reference device includes multiple target ball seats and multiple connecting rods. Two adjacent target ball seats are fixedly connected by the connecting rods, so that the multiple target ball seats form a truss structure through the multiple connecting rods. The target ball is configured to be selectively fixed to any one of the plurality of target ball seats; The laser tracker is configured to measure multiple spatial position data of the target ball in the base coordinate system when the target ball is fixed on multiple target ball seats, wherein the base coordinate system is established with the base of the laser tracker as the origin; A parameter calibration device, communicatively connected to the laser tracker, is configured to determine the measurement distance between two adjacent target spheres based on multiple spatial position data, and to calibrate the laser tracker based on the standard lengths of multiple connecting rods and the multiple measurement distance values.

2. The field calibration system according to claim 1, characterized in that, The field calibration system also includes: Multiple temperature sensors are fixedly mounted on the connecting rod at intervals along the length of the connecting rod, and the temperature sensors are configured to acquire the measured temperature. A temperature compensation device is configured to determine the temperature compensation length of the connecting rod caused by temperature changes based on the thermal expansion coefficient of the connecting rod and a plurality of the measured temperatures, and to obtain a first actual length based on the temperature compensation length and the standard length of the connecting rod; The parameter calibration device is configured to calibrate the laser tracker based on multiple first actual lengths and multiple measured distance values.

3. The field calibration system according to claim 1, characterized in that, The field calibration system also includes: Multiple inclinometers are fixedly mounted on the connecting rod, and the inclinometers are configured to acquire the attitude data of the connecting rod. An attitude compensation device is configured to determine, based on the attitude data and the material parameters of the connecting rod, the deformation compensation length of the connecting rod caused by gravity under the current attitude, and to obtain a second actual length based on the deformation compensation length and the standard length of the connecting rod; The parameter calibration device is configured to calibrate the laser tracker based on a plurality of second actual lengths and a plurality of measured distance values.

4. The field calibration system according to claim 1, characterized in that, The parameter calibration device is configured as follows: Based on the standard length of the connecting rod and the measured distance value, the measurement error value is obtained; The initial pose transformation matrix of the base coordinate system relative to the first local coordinate system is determined using the local exponential product method, wherein the first local coordinate system is established with the laser emission center of the laser tracker as the origin; The laser tracker is calibrated based on the initial pose transformation matrix and multiple measurement error values.

5. The field calibration system according to claim 4, characterized in that, The parameter calibration device is configured as follows: Based on the initial pose transformation matrix and the multiple measurement error values, the error screw corresponding to the initial pose transformation matrix is ​​obtained; Based on the error screw and the initial pose transformation matrix, the first pose transformation matrix is ​​obtained, and the laser tracker is calibrated using the first pose transformation matrix.

6. The field calibration system according to claim 5, characterized in that, The parameter calibration device is configured as follows: Based on the initial pose transformation matrix, an error propagation equation is constructed between the measurement error parameters and the error screw parameters; Substitute multiple measurement error values ​​into the error propagation equation and use the least squares method to obtain the error spinor corresponding to the initial pose transformation matrix.

7. The field calibration system according to claim 6, characterized in that, The parameter calibration device is configured as follows: Substituting multiple measurement error values ​​into the error propagation equation, the error spinor corresponding to the initial pose transformation matrix is ​​obtained by using the Levenberg-Marquardt algorithm with damping factor.

8. The field calibration system according to claim 4, characterized in that, The initial pose transformation matrix is ​​determined based on multiple indirect pose transformation matrices, wherein each indirect pose transformation matrix corresponds to a mechanical kinematic chain of the laser tracker.

9. The field calibration system according to claim 8, characterized in that, The parameter calibration device is configured as follows: Based on the multiple indirect pose transformation matrices and the multiple measurement error values, the indirect error screw corresponding to the indirect pose transformation matrix is ​​obtained; Based on the indirect error screw and the indirect pose transformation matrix, a first indirect pose transformation matrix is ​​obtained, and the laser tracker is calibrated using multiple first indirect pose transformation matrices.

10. A field calibration method for calibrating a laser tracker, comprising: The target ball is fixed in sequence in multiple target ball seats of the truss-type reference device, and two adjacent target ball seats are fixedly connected by the connecting rod of the truss-type reference device; The laser tracker is used to measure the spatial position data of the target ball in the base coordinate system when the target ball is fixed to multiple target ball seats; The measured distance between two adjacent target balls is determined based on multiple spatial location data. The laser tracker is calibrated based on the standard lengths of the multiple connecting rods and the multiple measured distance values.

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