Six-degree-of-freedom space pose measurement equipment calibration method, device and system

Abstract

The invention discloses a calibration method, device and system for six-degree-of-freedom space pose measurement equipment, and the method comprises the steps: selecting a control point based on the geometric parameters and motion range space of a six-degree-of-freedom parallel mechanism; based on the control point, generating a preliminary track by expanding a six-degree-of-freedom B spline curve; carrying out multi-objective optimization on the preliminary trajectory by utilizing an improved grey wolf optimization algorithm, enabling an objective function fusing operation space and joint space constraints to be minimum, generating an optimal motion trajectory, and enabling the motion trajectory to enhance smoothness and motion stability through optimization; inputting the optimal motion trail into a six-degree-of-freedom parallel mechanism, enabling the parallel mechanism to move according to the optimal motion trail, and enabling the to-be-calibrated measurement equipment to perform synchronous measurement; and taking the optimal motion trail as a standard motion trail, and performing decoupling equivalent calibration on the standard motion trail and a measurement result of the measurement equipment to obtain a calibration result. According to the invention, simultaneous calibration of six-degree-of-freedom complex motion of the spatial pose measurement equipment can be realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of geometric quantity calibration, and particularly relates to a six-degree-of-freedom space pose measurement device calibration method, device and system. BACKGROUND

[0002] The measurement device represented by a laser tracker is widely used in the digital assembly of large components in the fields of aerospace, high-speed rail and power generation due to its large measurement range and high accuracy. In the assembly process, the pose needs to be measured and adjusted in real time to ensure that the design requirements are met, and the assembly quality directly depends on the performance indicators of the pose measurement device.

[0003] The traditional method for calibrating the pose measurement device does not have the ability to simultaneously calibrate six degrees of freedom, and is difficult to cope with complex motion, resulting in reduced measurement accuracy in the assembly process and affecting the assembly quality. The traditional method can only decouple the six degrees of freedom and calibrate the length and attitude separately:

[0004] The length measurement error of the laser tracker is calibrated using a laser interferometer standard device as a standard device, and the difference between the length value measured by the laser tracker and the indicated value of the laser interferometer standard device is the length measurement indicated error. The attitude parameters of the verification platform use a multi-tooth indexing table as a standard device, which can generate a standard angle on one axis. The pose target can be fixed to the multi-tooth indexing table using a tool, and the attitude evaluation can be completed by comparing the angle values. In this process, the pose target needs to be converted in three directions to complete the evaluation of the rotation of the three coordinate axes.

[0005] The independent calibration of six degrees of freedom ignores the coupling effect of multiple degrees of freedom in actual motion, and cannot reflect the superposition and influence of errors in complex motion, resulting in deviations between the calibration results and actual application scenarios. The traditional method is usually completed on a static platform (such as a marble platform), but the dynamic motion (such as vibration and acceleration) of the components in the assembly process will introduce time-varying errors, and the static calibration results cannot effectively cover the dynamic scenarios. In addition, the traditional method has low spatial coverage, has a measurement blind area, takes a long time to calibrate, has low continuity, involves many manual intervention steps, and is low in efficiency. There is an urgent need to develop a six-degree-of-freedom dynamic parameter calibration method. SUMMARY

[0006] The purpose of the present application is to provide a six-degree-of-freedom space pose measurement device calibration method, device and system, which can simultaneously calibrate the six-degree-of-freedom complex motion of the space pose measurement device.

[0007] In order to achieve the above-mentioned purpose, one aspect of the present application provides a six-degree-of-freedom space pose measurement device calibration method, comprising:

[0008] Step S1, selecting control points based on the geometric parameters and motion range space of the six-degree-of-freedom parallel mechanism;

[0009] Step S2, generating a preliminary trajectory based on the control points by extending a six-degree-of-freedom B-spline curve;

[0010] Step S3, performing multi-objective optimization on the preliminary trajectory using an improved gray wolf optimization algorithm to minimize the objective function of the fusion operation space and joint space constraints, generate an optimal motion trajectory, and optimize the motion trajectory to enhance smoothness and motion stability;

[0011] Step S4, inputting the optimal motion trajectory into the six-degree-of-freedom parallel mechanism, causing the parallel mechanism to move according to the optimal motion trajectory, and causing the measurement device to be calibrated to perform synchronous measurement;

[0012] Step S5: Decoupling and equivalently calibrating the optimal motion trajectory as a standard motion trajectory with the measurement result of the measuring device to obtain a calibration result.

[0013] Another aspect of the present invention provides a six-degree-of-freedom spatial posture measurement device calibration device, comprising:

[0014] A control point selection unit selects control points based on the geometric parameters and motion range space of the six-degree-of-freedom parallel mechanism;

[0015] A preliminary trajectory generating unit generates a preliminary trajectory based on the control points by extending a six-degree-of-freedom B-spline curve;

[0016] a trajectory optimization unit, which performs multi-objective optimization on the preliminary trajectory using an improved gray wolf optimization algorithm to minimize an objective function of the fusion operation space and joint space constraints, thereby generating an optimal motion trajectory, and optimizing the motion trajectory to enhance smoothness and motion stability;

[0017] A measurement execution unit inputs the optimal motion trajectory into the six-degree-of-freedom parallel mechanism, causes the parallel mechanism to move according to the optimal motion trajectory, and causes the measurement device to be calibrated to measure synchronously;

[0018] The calibration unit uses the optimal motion trajectory as a standard motion trajectory to perform decoupling equivalent calibration with the measurement result of the measuring device to obtain a calibration result.

[0019] Another aspect of the present invention provides a six-degree-of-freedom spatial posture measurement device calibration system, including a basic structure module, a motion execution module, a perception and feedback module, an intelligent control module, a calibration auxiliary system, a software and interaction module, a self-calibration and maintenance module, and the above-mentioned six-degree-of-freedom spatial posture measurement device calibration device.

[0020] The base structure module comprises a fixed base for providing stable support for the system and a moving platform for mounting the target; the motion execution module is used for controlling the spatial pose of the moving platform relative to the fixed base to realize complex six-degree-of-freedom motion; the perception and feedback module is used for monitoring and dynamically adjusting the motion state and stress state of the system in real time; the intelligent control module is used for real-time solving, dynamic compensation and environment optimization; the calibration auxiliary system is used for providing a stable and controllable calibration environment for the measuring device; the software and interaction module is used for designing the six-degree-of-freedom motion trajectory and analyzing data; and the self-calibration and maintenance module is used for real-time self-checking, redundant checking and predictive maintenance.

[0021] According to the six-degree-of-freedom spatial pose measuring device calibration method, device and system of the above aspect of the present application, the six-degree-of-freedom complex motion of the spatial pose measuring device can be calibrated at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings used in the description of the embodiments of the present application. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings:

[0023] Figure 1 is a flow chart of the six-degree-of-freedom spatial pose measuring device calibration method of an embodiment of the present application;

[0024] Figure 2 is a structural schematic diagram of a six-degree-of-freedom parallel mechanism of an embodiment of the present application;

[0025] Figure 3 is a control point position distribution and attitude angle selection schematic diagram of the selection of the spatial position and attitude of an embodiment of the present application; (a) is a control point position coordinate top view, (b) is a control point position coordinate perspective view, and (c) is a control point sequence and angle selection relationship;

[0026] Figure 4 is a flow chart of the improved grey wolf optimization and six-degree-of-freedom B-spline trajectory optimization method of an embodiment of the present application;

[0027] Figure 5 is a coordinate system relationship schematic diagram of an embodiment of the present application;

[0028] Figure 6 is a structural schematic diagram of a six-degree-of-freedom spatial pose measuring device system of an embodiment of the present application. DETAILED DESCRIPTION

[0029] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below in conjunction with the drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0030] An embodiment of the present application provides a six-degree-of-freedom space pose measurement device calibration method, which calibrates a pose measurement device based on improved grey wolf optimization and B-spline trajectory. As shown in Figure 1 , the method of the embodiment of the present application comprises steps S1-S5.

[0031] In step S1, a control point is selected based on the geometric parameters and the motion range space of a six-degree-of-freedom parallel mechanism.

[0032] In an exemplary embodiment, as shown in Figure 2 , the six-degree-of-freedom parallel mechanism comprises a fixed base, a moving platform and six legs, and the length of each leg is L i (i=1, 2,..., 6). One end of each leg is connected to the fixed base through a hook joint b i , and the other end is connected to the moving platform through a spherical joint p i . Since the six legs can independently extend and retract through servo motors, the moving platform can move and rotate along the x, y and z axes. A coordinate system {O p} is established with the motion center of the moving platform as the origin, and γ p is the minimum included angle between adjacent joints. A coordinate system {O b} is established with the motion center of the fixed base as the origin, and γ b is the minimum included angle between adjacent joints. The joints b i and p i of the fixed base and the moving platform are distributed on circles with radii R b and R p , respectively:

[0033]

[0034] wherein,

[0035] The kinematic description of the six-degree-of-freedom parallel mechanism includes a forward kinematics model (FKM) and an inverse kinematics model (IKM). IKM uses the known position and direction of the moving platform to solve the lengths L i of the six legs. The lengths L i are calculated using p i and b i .

[0036] L i = t + h + R x p i -b i

[0037] h is the distance from the upper surface of the fixed base to the upper surface of the moving platform in the reference state, where the position and orientation matrix is:

[0038]

[0039] where c and s represent cos and sin, respectively, and ψ, θ, and φ are the direction angles of the x, y, and z axes, respectively.

[0040] In contrast, FKM uses the known lengths of the six legs to solve the position and orientation of the moving platform. Compared with IKM, FKM solves a nonlinear equation without an analytical solution, and is usually solved by numerical methods. The FKM calculation formula is:

[0041]

[0042] In an exemplary embodiment, as shown in FIG. 1, the control points are selected as follows: Figure 3

[0043] For the workspace Ω of the parallel mechanism, under the premise of being able to guarantee more effective space coverage, the initial control point position coordinate set is generated by presetting the spatial feature points with the condition number of the Jacobian matrix as the observation index, and the same spatial coordinates are used for the first and last points to form a closed curve.

[0044] The control point attitude angle is generated according to the zero point synchronization rule, and each of the x, y, and z axes is rotated by a fixed angle in the forward direction and a fixed angle in the reverse direction by ensuring that the control points are separated, and the remaining two axes remain at zero.

[0045] The position coordinates and attitude angles of the control points are used to construct the initial control point set.

[0046] In step S2, based on the control points, a preliminary trajectory is generated by extending a six-degree-of-freedom B-spline curve.

[0047] ​​In an exemplary embodiment, the traditional 5th order non-uniform B-spline interpolation spatial position is adopted, and the end-to-end repeated configuration of the node vector is adopted to realize the accurate interpolation of the curve end point control point. In the attitude interpolation, the "double domain mapping" method is adopted to convert the Euler angle into a quaternion, and further mapped to the tangent space for B-spline interpolation, and finally mapped back to the three-dimensional space, and the traditional B-spline method is extended from three-dimensional position coordinate points to attitude angles, so as to complete the six-degree-of-freedom pose interpolation, realize the coordination of motion trajectory uniformity, singularity resistance and high efficiency of calculation, and meet the demand of six-degree-of-freedom measurement equipment calibration for accurate pose interpolation.

[0048] In step S3, the improved grey wolf optimization algorithm is used to optimize the trajectory, so that the target function of the fusion operation space and joint space constraint is minimized, the optimal calibration motion trajectory is generated, and the motion trajectory is enhanced in the optimization process. Smoothness and motion stability.

[0049] In an exemplary embodiment, the design of the target function comprehensively considers the operation space and the joint space, constructs a multi-dimensional weighted target function F, and fuses the operation space position tracking error T error , the acceleration term A, the jerk term J, the control point penalty P and the joint space change rate O. The weight mechanism is introduced:

[0050] F=w1*T error +w2*A+w3*J+w4*P++w5*O

[0051] w1, w2, w3, w4, w5 are the weights corresponding to the position tracking error T error , the acceleration term A, the jerk term J, the control point penalty P and the joint space change rate O.

[0052] The position tracking error ensures that the trajectory fits the expected path; the acceleration / jerk term suppresses the high-frequency vibration and impact of the mechanical system, so that the trajectory runs smoothly; the control point penalty limits the adjustment amplitude of the B-spline control point, avoiding the distortion of the trajectory due to excessive optimization; and the joint space change rate constrains the motion amplitude of the mechanical arm end, prevents the mutation of force / torque, and ensures the operation stability. The multi-objective dynamic balance mechanism fully considers the motion stability of the operation space, and innovatively introduces the joint space change rate term, solves the problem that most trajectory optimization only pays attention to the operation space and ignores the real-time constraints of the task related joint space, and causes the task to fail.

[0053] In an exemplary embodiment, step S3 further comprises steps S31-S34.

[0054] S31: Using a hybrid coding scheme, decouple the three-dimensional position offset of the B-spline control points and the sequence characteristics of the attitude motion axis, and encode them as gray wolf positions for optimization algorithm. For position offset, real number coding is used to accurately search in continuous position space, ensuring effective optimization of trajectory position accuracy; for sequence characteristics of attitude motion axis, discrete coding is used to accurately represent the sequence order information of attitude motion, preventing coupling caused by simultaneous movement of multiple axes with large angles. Based on the initial position, a gray wolf population of size N is randomly generated, with each gray wolf representing a potential solution. Through the hybrid coding, the optimization variables are decomposed into position perturbation (i.e., position offset of all control points) and angle sequence parameters (including execution order and direction mode of angle change).

[0055] S32: According to the objective function, the top 10% elite individuals of the gray wolf population are retained and directly participate in the position update of the leader wolf; the second-order difference mutation is performed on the non-elite individuals, and for each non-elite individual, different individuals are randomly selected to generate a trial position solution vector through an adaptive scaling factor, and a new position solution vector is generated from the trial position solution vector and the original position solution vector through second-order crossover;

[0056] S33: In terms of dynamic search strategy, the entire wolf pack gradually approaches the optimal solution through cooperation and competition. The gray wolf position is updated based on an adaptive convergence factor and a periodic disturbance mechanism, where the convergence factor decays exponentially and is superimposed with random disturbance. The exponential decay part makes the convergence factor gradually decrease with the increase of iteration number, ensuring the algorithm gradually transitions from global exploration to local fine search. The periodic micro-disturbance periodically increases the disturbance during the convergence factor decay process, allowing the algorithm to jump out of the local optimal trap during local search, balancing global exploration ability and local fine search;

[0057] S34: Repeat the above two steps until the iteration process is completed or the objective function remains unchanged for a certain number of iterations, improving the running efficiency of the algorithm and avoiding unnecessary computational overhead.

[0058] In an exemplary embodiment, a six-degree-of-freedom motion trajectory optimization method is built using Python language, as shown in Figure 4 , which specifically includes:

[0059] According to the given six-degree-of-freedom parallel mechanism model parameters modeling, select the initial control point as the initialization gray wolf population; in each round of iterative search, according to the order of the curve and the node distribution mode, the base function is calculated by using the recursive relationship, the curve is generated by the weighted combination of the control point and the corresponding base function, and the position and attitude joint interpolation is realized. For the six-degree-of-freedom trajectory optimization problem, the improved gray wolf optimization algorithm is adopted, and a hybrid coding scheme and a dynamic search strategy are designed. In the coding strategy design, the real number coding mode is adopted for the control point position offset, so that the algorithm can accurately search in the continuous three-dimensional position space, and the effective optimization of the trajectory position accuracy is ensured; the discrete coding mode is adopted for the control point attitude motion axis sequence characteristics, and the time sequence information and axis constraint of the attitude motion are accurately represented. In terms of dynamic search, according to the objective function, the population is divided into elite individuals and non-elite individuals, and the reserved and second-order difference operations are performed as the population of this iteration. The current gray wolf population is divided into leader wolves and candidate wolves according to the objective function again, and the position of the leader wolf is used to guide the population to approach the prey (optimal solution). Specifically, the first three high-quality solutions are selected from N gray wolf populations as leader wolves, named Alpha wolf (global optimal), Beta wolf (suboptimal search), Delta wolf (third optimal exploration), and the remaining N-3 individual solutions are candidate wolves. According to the dynamically adjusted search range, the prey is surrounded by the three high-quality individual solutions of Alpha wolf, Beta wolf and Delta wolf, and the position of all populations is updated. When the change of the objective function is less than a specified threshold (0.001) within a certain number of iterations or the maximum number of iterations is reached, otherwise, the iteration number and the search range are updated, and a new round of iteration is started for the current control point. Through the differential cooperation strategy, the balance between breadth and depth search is realized, and finally the smooth and physically feasible motion trajectory is output. Through the cooperation of parameter space decoupling, dynamic convergence control and intelligent termination strategy, the convergence efficiency of complex trajectory in position accuracy, attitude smoothness and multi-objective constraint is significantly improved, and an efficient and reliable solution is provided for the six-degree-of-freedom trajectory optimization problem.

[0060] In an exemplary embodiment, the control points are selected within the workspace of the standard parallel mechanism device, the initial trajectory is generated by using the extended B-spline, and the improved gray wolf optimization algorithm is used for optimization. The results show that the smoothness and stability of the optimized curve are greatly improved.

[0061] In step S4, the target is fixed on the parallel mechanism, the optimized motion trajectory is input into the six-degree-of-freedom parallel mechanism, and the parallel mechanism moves according to the motion trajectory, and the to-be-calibrated measurement device measures synchronously.

[0062] In step S5, the standard motion trajectory and the measurement results of the measurement device are determined by decoupling equivalent calibration method to determine the calibration results.

[0063] In an exemplary embodiment, the decoupling equivalent calibration method in step S5 specifically comprises:

[0064] Based on the rigid body kinematics decomposition theorem, the pose transformation is decoupled into rotation and translation components. The rotation reference coordinate system coincides with the moving platform coordinate system of the parallel mechanism, and the translation reference coordinate system coincides with the base coordinate system of the parallel mechanism.

[0065] In the aspect of attitude calibration, in the trajectory design stage, the multi-axis rotation is decoupled, and the rotation is sequentially performed in the same trajectory, so that in the case that there is a registration error between the target coordinate system and the rotation coordinate system, an equivalent rotation axis / angle is established based on the trace of the rotation matrix, a joint parameterization error model containing unregistered Euler angles and a second-order parameter Jacobian matrix is established, the model parameters are solved by the least square method, and finally the rotation matrix is corrected through error back compensation.

[0066] In the aspect of position calibration, an initialization method based on spatial coordinate conversion is adopted. In combination with the relationship between the target coordinate system and the base coordinate system, i.e. the translation coordinate system, an error model is established, the model parameters are solved by the least square method, and finally the error back compensation is realized.

[0067] In actual application, the relationship of the coordinate systems is as shown in Figure 5 The rotation coordinate system coincides with the moving coordinate system, and the moving coordinate system coincides with the moving platform coordinate system of the parallel mechanism. The laser tracker and the target coordinate system are registered, but there is a small installation error between the target coordinate system and the moving coordinate system. The present application jointly models the same in the process of establishing the joint parameterization error model by the rotation decoupling equivalent method, thereby solving the problem.

[0068] The embodiment of the present application also provides a six-degree-of-freedom space pose measurement device calibration device, which comprises an intelligent control module, and the intelligent control module comprises:

[0069] A control point selection unit selects a control point based on the geometric parameters and the motion range space of the six-degree-of-freedom parallel mechanism.

[0070] A preliminary trajectory generation unit generates a preliminary trajectory by extending a six-degree-of-freedom B-spline curve based on the control point.

[0071] A trajectory optimization unit performs multi-objective optimization on the preliminary trajectory by using an improved grey wolf optimization algorithm, so that a target function fused with the operation space and the joint space constraint is minimized, an optimal motion trajectory is generated, and the motion trajectory is enhanced in smoothness and motion stability through optimization.

[0072] A measurement execution unit inputs the optimal motion trajectory into the six-degree-of-freedom parallel mechanism, so that the parallel mechanism moves according to the optimal motion trajectory, and a measurement device to be calibrated is synchronously measured.

[0073] The calibration unit decouples the optimal motion trajectory as a standard motion trajectory from the measurement result of the measurement device for equivalent calibration to obtain a calibration result.

[0074] The embodiment of the present application also provides a six-degree-of-freedom space pose measurement device calibration system, as shown in the figure. Figure 6 The six-degree-of-freedom space pose measurement device calibration system of the embodiment of the present application includes a basic structure module, a motion execution module, a perception and feedback module, an intelligent control module, a calibration auxiliary system, a software and interaction module, a self-calibration and maintenance module, and the six-degree-of-freedom space pose measurement device calibration device of the above-mentioned embodiment of the present application, which work cooperatively to realize the motion control, perception, calibration and other core functions of the parallel mechanism.

[0075] The basic structure module serves to provide stable mechanical support and ensure the accurate pose adjustment of the moving platform.

[0076] In actual application, the basic structure module includes a fixed base and a moving platform. The fixed base is fixed at a reference position to provide stable support for the whole device; the moving platform can be installed with a target, and the accurate adjustment of the position and attitude of the target is crucial to the calibration work.

[0077] The motion execution module accurately controls the space pose of the moving platform relative to the fixed base through the cooperative motion of six groups of adjustable support chains (six legs) to realize complex six-degree-of-freedom motion.

[0078] In actual application, the motion execution module includes six groups of adjustable support chains, each of which covers a driving unit, a transmission mechanism and a flexible hinge / spherical hinge. One end of each leg is connected with the fixed base through the hinge, and the other end is connected with the moving platform through the spherical hinge to realize the six-degree-of-freedom space pose transformation of the moving platform relative to the fixed base.

[0079] The perception and feedback module realizes real-time monitoring and dynamic adjustment of the motion state and force state of the system to ensure the high precision, stability and safety of the device.

[0080] In actual application, the perception and feedback module includes built-in sensors and an external reference system. In the built-in sensors, a grating encoder measures the length change of the support chain in real time; a six-dimensional force sensor monitors the force state of the moving platform for dynamic compensation. The external reference system performs external calibration on the parallel mechanism to effectively verify the accuracy of the platform pose.

[0081] The intelligent control module ensures the realization of ultra-high precision control of the system under complex working conditions through real-time calculation, dynamic compensation and environment optimization.

[0082] The intelligent control module includes a multi-axis motion controller and an adaptive algorithm part; the multi-axis motion controller realizes real-time kinematics calculation based on FPGA, ensuring six-degree-of-freedom synchronous control. The adaptive algorithm dynamically corrects pose deviation by fusing data such as temperature and gravity deformation, improving control accuracy.

[0083] The auxiliary calibration system provides a stable and controllable calibration environment for high-precision measurement equipment, ensuring the accuracy and reliability of the calibration results.

[0084] The calibration auxiliary system includes a target and an environment control unit. The corresponding target is selected according to the measurement equipment to be calibrated to complete the adaptation. The environment control unit has an active vibration isolation platform to suppress ground vibration; a constant temperature cavity to maintain temperature control and reduce the influence of thermal deformation.

[0085] The software and interaction module completes the design and data analysis of six-degree-of-freedom motion trajectory, realizes the real-time presentation of operation instruction analysis execution and interactive feedback, and provides efficient operation experience for the operator;

[0086] In actual application, the software and interaction module intuitively displays the process of parallel mechanism motion after inputting six-degree-of-freedom trajectory parameters through a three-dimensional visual simulation system, realizes real-time mapping of platform pose, branch stretching state and coordinate system transformation, and achieves spatial coupling visualization of kinematics parameters; the data analysis module displays three-dimensional trajectory comparison before and after optimization and attitude angle curve; a "simulation-warning-evaluation" closed-loop mechanism is designed, a leg stroke safety threshold monitoring algorithm is built in the automatically generated motion simulation video, real-time over-limit warning is triggered and abnormal frames are marked; an optimization effect quantitative evaluation system is established, multi-dimensional comparison of characteristic indexes such as acceleration change rate is performed, and visual optimization situation analysis results are generated. The entire interface adopts an interactive design concept, integrates one-key simulation start, dynamic parameter adjustment, video progress control and other function modules, so that the evaluation process of complex motion planning effect has real-time, intuitiveness and traceability.

[0087] The self-calibration and maintenance module ensures long-term high precision and reliability of the system through real-time self-checking, redundancy checking and predictive maintenance, and reduces sudden failure and manual intervention cost.

[0088] In actual application, the self-calibration and maintenance module includes an in-situ self-checking program and a predictive maintenance system, checks the pose of the parallel mechanism through redundant sensors, monitors motor current fluctuation, bearing vibration and potential problems such as mechanical wear, and timely warns to ensure stable operation of the device.

[0089] In one exemplary embodiment, the six-degree-of-freedom spatial pose measurement equipment calibration system is as shown in Figure 6As shown, before calibrating the measuring device, the perception and feedback module uses the method of laser tracker multi-edge optimization networking to calibrate the six-degree-of-freedom parallel mechanism itself with high precision. In this process, the grating encoder monitors the length of the branch chain in real time, the six-dimensional force sensor and the external multiple laser trackers network collect pose data, and after the adaptive algorithm fuses the temperature and vibration compensation factors, the feedback is fed back to the control layer to correct the driving parameters.

[0090] During calibration, the user inputs the control points through the software and interaction module, sets a reasonable weight to optimize the six-degree-of-freedom motion trajectory, and transmits the motion trajectory parameters to the intelligent control module; the multi-axis motion controller calculates the inverse kinematics solution in real time based on FPGA to generate 6 sets of coordinated driving signals for the branch chain, drives the servo motor to adjust the length of the branch chain through the ball screw, and makes the moving platform accurately reach the target pose. In this process, the grating encoder detects the length of the branch chain in real time; the environmental control unit suppresses external disturbances through active vibration isolation and constant temperature systems. At the same time, the target fixed on the moving platform provides a traceable spatial reference for the measured device, transmits the standard motion trajectory and the measuring result of the measuring device back to the software and interaction module, calibrates through the decoupling equivalent calibration method, and determines the calibration result. When the device runs to the preset maintenance period, the six-degree-of-freedom parallel mechanism installs redundant sensors on the key joints, uses forward and reverse measurement residuals to build an error model, estimates the kinematic parameters by combining an optimization algorithm to realize self-calibration, and maintains through regular parameter updates and sensor state monitoring. The whole process realizes the whole chain closed loop of "instruction-execution-perception-compensation-verification", ensuring high calibration accuracy and long-term stability.

[0091] In summary, the six-degree-of-freedom spatial pose measurement device calibration method, device and system of the embodiment of the application adopts a six-degree-of-freedom parallel mechanism to develop a passive attitude calibration device. Compared with other mechanisms, the parallel mechanism has obvious advantages as an attitude calibration device. Its inherent design can minimize structural deformation, thereby ensuring the robustness of the device and enhancing the resistance to external interference. In addition, the mechanism can effectively avoid singular points in the specified workspace, thereby improving the overall performance and reliability of the calibration tool. The application uses a high-repetition parallel mechanism standard device as a six-degree-of-freedom motion pose generator, designs an improved grey wolf optimization and a six-degree-of-freedom B-spline motion trajectory to realize the six-degree-of-freedom dynamic calibration of the measurement device. The application specifies the control points, uses an extended B-spline curve for joint interpolation of the pose, and optimizes a smooth and stable six-degree-of-freedom motion trajectory. Compared with the traditional calibration method, the high-repetition parallel mechanism synchronously generates a six-degree-of-freedom continuous motion trajectory, which can realize real-time calibration of multi-degree-of-freedom coupling errors under dynamic conditions, overcome the static limitations of traditional decoupling calibration, and significantly improve the calibration accuracy and efficiency in complex motion scenarios. The specific advantages of the application are analyzed from the adopted parallel mechanism and the measurement device calibration method based on the improved grey wolf optimization and the six-degree-of-freedom B-spline trajectory:

[0092] I. Adopting a parallel mechanism as a calibration device for six-degree-of-freedom spatial pose measurement device calibration

[0093] Unlike traditional one-by-one dimensional calibration methods, the application adopts a six-degree-of-freedom motion trajectory of a parallel mechanism to calibrate the measurement device. By designing and optimizing a standard path, all degrees of freedom are calibrated simultaneously in a six-degree-of-freedom motion space. The trajectory parameters are input into the parallel mechanism standard device to real-time adjust the pose of the parallel mechanism platform as a standard trajectory, thereby realizing high-precision pose measurement device calibration in a complex working environment.

[0094] (I) High calibration accuracy and reliability

[0095] By externally calibrating the parallel mechanism, the accuracy of the parallel mechanism itself is guaranteed. Compared with traditional dimension reduction calibration methods, the application simultaneously calibrates in a full-dimensional space, thereby avoiding error accumulation and inaccuracy caused by one-by-one calibration.

[0096] (II) Processing complex six-degree-of-freedom motion

[0097] The parallel mechanism standard device adopted by the application can move in six degrees of freedom in the workspace. Through the design of a six-degree-of-freedom parallel trajectory, the motion of the parallel mechanism solves the problem of failure in calibrating the measurement device in complex six-degree-of-freedom space motion.

[0098] II. Pose measurement device calibration method based on improved grey wolf optimization and B-spline trajectory

[0099] The improved grey wolf optimization algorithm is used to optimize the extended B-spline curve to obtain a six-degree-of-freedom motion trajectory, which has the following advantages:

[0100] (1) Anti-singularity

[0101] In the position selection aspect, the condition number of the Jacobian matrix is used as an observation index to ensure that the initial trajectory is located in an area with high flexibility of the mechanism; in the attitude design aspect, the axes are alternately rotated in the forward and reverse directions to avoid motion coupling caused by large-angle transformation of multiple axes at the same time. The avoidance rate of singularity is improved through the selection of the initial attitude.

[0102] The singularity of three-dimensional rotation is avoided by converting Euler angles to quaternions, and the cut space linear interpolation can ensure the continuity of the attitude change. Compared with the traditional Euler angle interpolation algorithm, the attitude interpolation strategy can effectively reduce the gimbal phenomenon and avoid sudden changes in attitude angles.

[0103] (2) Smoothness

[0104] On the basis of ensuring the tracking error, the dynamics optimization of the operation space and the joint space is considered in the objective function. Compared with the position acceleration and angular acceleration before optimization, the high-frequency vibration is suppressed, the position jerk and angular jerk are greatly reduced, the high-frequency impact is suppressed, and the control point penalty is introduced to prevent trajectory distortion. Finally, the joint space penalty term is introduced to optimize the operation space, solving the problem of task failure in traditional single-objective optimization.

[0105] (3) Short time consumption

[0106] The time consumption of attitude interpolation is shortened, the quaternion is projected into the cut space for operation, and the computational complexity O(n 3 ) is reduced to O(n); the reverse mapping process only requires quaternion normalization operation without iterative calculation requirement.

[0107] (4) Optimization efficiency and convergence

[0108] The convergence degree of the grey wolf optimization algorithm is improved. A hybrid coding scheme is adopted to decouple the position offset and attitude axis sequence coding, and the search space dimension is reduced; the double-decay convergence factor is exponentially decayed to ensure the global search ability, the periodic micro-disturbance avoids local optimum, the threshold is set to stop early, the invalid iteration is reduced, the optimization efficiency is improved; the elite strategy is adopted, the elite individuals are reserved in each generation and directly participate in the leader wolf position update, preventing high-quality solutions from being damaged by random disturbance in the iteration process, improving search accuracy and convergence speed; at the same time, the selection of the initial control point makes the condition number of the corresponding Jacobian matrix small, so that the solution obtained by the optimization algorithm is more accurate, the convergence is faster, and the stability is better.

[0109] (5) Calibration results

[0110] By decoupling the equivalent calibration method, an error model is established, and high-precision calibration of six degrees of freedom is realized in a motion trajectory.

[0111] The present application solves the high-precision field calibration problem of six-degree-of-freedom measuring equipment under complex working conditions by constructing a complete technical chain from trajectory generation, optimization algorithm to verification calibration based on improved grey wolf optimization and B-spline trajectory pose measurement equipment calibration, has the technical advantages of intelligent trajectory planning, multi-constraint collaborative optimization and adaptive dynamic adjustment, significantly improves the calibration efficiency and precision, and is suitable for six-degree-of-freedom dynamic precise calibration of pose measurement equipment such as laser tracker. In addition, the present application can also be applied to the fields of aerospace, high-speed rail, power generation large component assembly measurement and other fields with high requirements for multi-degree-of-freedom motion accuracy, and by real-time correction of the position and attitude error of the equipment in space motion, the dynamic measurement accuracy is significantly improved.

[0112] The above only describes certain exemplary embodiments of the present application by way of illustration, and it is needless to say that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present application. Therefore, the above figures and description are illustrative in nature and should not be understood as limiting the scope of protection of the claims of the present application.

Claims

1. A six-degree-of-freedom spatial posture measurement device calibration method, characterized in that: include: Step S1, selecting control points based on the geometric parameters and motion range space of the six-degree-of-freedom parallel mechanism; Step S2, generating a preliminary trajectory based on the control points by extending a six-degree-of-freedom B-spline curve; Step S3, performing multi-objective optimization on the preliminary trajectory using an improved gray wolf optimization algorithm to minimize the objective function of the fusion operation space and joint space constraints, generate an optimal motion trajectory, and optimize the motion trajectory to enhance smoothness and motion stability; Step S4, inputting the optimal motion trajectory into the six-degree-of-freedom parallel mechanism, causing the parallel mechanism to move according to the optimal motion trajectory, and causing the measurement device to be calibrated to perform synchronous measurement; Step S5: Decoupling and equivalently calibrating the optimal motion trajectory as a standard motion trajectory with the measurement result of the measuring device to obtain a calibration result.

2. The method according to claim 1, characterized in that The six-degree-of-freedom parallel mechanism includes a fixed base, a mobile platform and six legs. One end of each leg is connected to the fixed base through a hinge, and the other end is connected to the mobile platform through a ball joint. The six legs can independently perform telescopic movements, so that the mobile platform can achieve six-degree-of-freedom spatial posture transformation relative to the fixed base.

3. The method according to claim 2, characterized in that Step S1 includes: In the working space of the parallel mechanism, the Jacobian matrix condition number is used as an observation index, and an initial control point position coordinate set is constructed through preset three-dimensional space points, and the first and last points use the same spatial coordinates to form a closed curve; The control point attitude angle is generated according to the zero point synchronization rule. By separating the control points, each axis is guaranteed to rotate forward by a fixed angle and reversely by a fixed angle, while the other two axes remain at zero position. The position coordinates and posture angles of the control points are used to construct an initial control point set.

4. The method according to any one of claims 1 to 3, characterized in that Step S2 includes: According to the position coordinates of the control points, a coordinate trajectory is generated by a B-spline method; Converting the attitude angle of the control point from Euler angle to quaternion, and further mapping it to tangent space, performing B-spline interpolation on the attitude to generate an attitude trajectory; The coordinate trajectory and the posture form a six-degree-of-freedom motion trajectory as the preliminary trajectory.

5. The method according to any one of claims 1 to 3, characterized in that Step S3 includes: A hybrid coding scheme is used to decouple the B-spline control point position offset and the posture motion axis sequence features and encode them separately. The position of the gray wolf population is generated based on the coding of the control points. Based on the objective function, the top several elite individuals in the gray wolf population are retained to directly participate in the position update of the leader wolf, and second-order differential mutation is performed on non-elite individuals; The position of the gray wolf is updated based on the adaptive convergence factor and the periodic perturbation mechanism. The iteration is terminated according to the rate of change of the objective function to achieve the optimal search of the gray wolf population. The control point solution set with the optimal objective function is output as the optimal motion trajectory.

6. The method according to claim 5, characterized in that In the hybrid coding scheme, real number coding is used for position offset, which can accurately search in the continuous position space and ensure the effective optimization of trajectory position accuracy; for the posture motion axis sequence characteristics, discrete coding is used to accurately characterize the sequence order information of the posture motion and prevent the coupling phenomenon caused by simultaneous large-angle motion of multiple axes.

7. The method according to claim 5, characterized in that The objective function F is: F=w1*T error +w2*A+w3*J+w4*P++w5*O Among them, T error is the position tracking error, A is the acceleration term, J is the jerk term, P is the control point penalty, O is the rate of change of joint space, w1, w2, w3, w4 and w5 are the position tracking error T error , the weights corresponding to the acceleration term A, the jerk term J, the control point penalty P and the joint space change rate O.

8. The method according to claim 2 or 3, characterized in that In step S5, the decoupling equivalent calibration includes: establishing the calibration of the motion trajectory in different coordinate systems according to translation and rotation, establishing an error model, and realizing calibration; the translation coordinate system of the calibration coincides with the fixed base of the parallel mechanism, and the rotation coordinate system coincides with the mobile platform of the parallel mechanism.

9. A six-degree-of-freedom spatial posture measurement equipment calibration device, characterized in that: include: A control point selection unit selects control points based on the geometric parameters and motion range space of the six-degree-of-freedom parallel mechanism; A preliminary trajectory generating unit generates a preliminary trajectory based on the control points by extending a six-degree-of-freedom B-spline curve; a trajectory optimization unit, which performs multi-objective optimization on the preliminary trajectory using an improved gray wolf optimization algorithm to minimize an objective function of the fusion operation space and joint space constraints, thereby generating an optimal motion trajectory, and optimizing the motion trajectory to enhance smoothness and motion stability; A measurement execution unit inputs the optimal motion trajectory into the six-degree-of-freedom parallel mechanism, causes the parallel mechanism to move according to the optimal motion trajectory, and causes the measurement device to be calibrated to measure synchronously; The calibration unit uses the optimal motion trajectory as a standard motion trajectory to perform decoupling equivalent calibration with the measurement result of the measuring device to obtain a calibration result.

10. A six-degree-of-freedom spatial posture measurement equipment calibration system, characterized in that: It includes a basic structure module, a motion execution module, a perception and feedback module, an intelligent control module, a calibration auxiliary system, a software and interaction module, a self-calibration and maintenance module, and the six-degree-of-freedom spatial posture measurement equipment calibration device according to claim 9, The basic structure module includes a fixed base and a mobile platform, the fixed base is used to provide stable support for the system, and the mobile platform is used to install the target; the motion execution module is used to control the spatial position of the mobile platform relative to the fixed base to achieve complex six-degree-of-freedom motion; the perception and feedback module is used to monitor and dynamically adjust the motion state and force state of the system in real time; the intelligent control module is used to optimize the environment through real-time solution, dynamic compensation and environment; the calibration auxiliary system is used to provide a stable and controllable calibration environment for the measuring equipment; the software and interaction module is used to design the six-degree-of-freedom motion trajectory and perform data analysis; the self-calibration and maintenance module is used to perform real-time self-test, redundancy verification and predictive maintenance.

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