Series joint mechanism error correction method, actuator and storage medium

Abstract

The application discloses a kind of series joint mechanism error correction method, actuator and storage medium, it is related to robot kinematics precision and reliability analysis technical field, it is difficult to correct when the end pose deflection of multiple joint series mechanism in the existence of machining and assembly error is solved Technical problems.The method includes establishing series joint mechanism coordinate system according to the degree of freedom of series joint mechanism on three-dimensional space section, and calibrating joint center, bar length and joint kinematic pair;Effective length parameter is obtained by effective rod length theory;The joint local coordinate pose correction amount is obtained by vector sum method;D-H conversion matrix is corrected by effective length parameter and joint local coordinate pose correction amount, and error transmission chain is formed based on motion transmission sequence, end pose uncertain position vector is obtained by combining D-H conversion matrix, and the joint error of series joint mechanism is corrected according to the end pose uncertain position vector.

Description

Technical Field

[0001] This invention relates to the field of robot kinematics accuracy and reliability analysis technology, and in particular to a method for error correction of a series joint mechanism, an actuator and a storage medium. Background Technology

[0002] Serial joint mechanisms are widely used in industrial robots, collaborative robotic arms, bionic mechanisms, and various multi-degree-of-freedom actuators. They typically consist of multiple rotary or prismatic joints connected in series according to a predetermined motion sequence to achieve the position and attitude output of the end effector in space. Due to the inherent characteristic of serial structures where errors accumulate and can be amplified at each stage, internal structural uncertainties such as geometrical errors of links, joint axis installation deviations, and clearances between joint kinematic pairs inevitably exist during manufacturing, assembly, and long-term operation. These factors couple and superimpose during coordinate transformation and motion transmission, and are transmitted to the end effector, causing end effector pose and trajectory deviations, which in turn affect trajectory tracking accuracy, operational stability, and system reliability. Therefore, establishing a kinematic model that can describe internal structural uncertainties and calculate and predict end effector pose deviations is of great significance for the accuracy assessment, assembly tolerance design, and error compensation of serial joint mechanisms.

[0003] In existing technologies, methods for end-effector error analysis and modeling of tandem joint mechanisms mainly include: parametric error linearization methods based on nominal kinematic models. These methods assume small perturbations in errors such as link length and joint parameters and estimate error propagation using the Jacobian matrix. While applicable when errors are small and the model is simplified, these methods typically rely on small perturbation approximations, making it difficult to uniformly handle nonlinear pose drift caused by joint clearances and its coupling effect with link errors. Furthermore, they lack an intuitive representation of the transmission mechanism of "rotational amplification and directional coupling" in multi-stage tandem joints. Other techniques equate joint clearances or assembly deviations to single-joint additional displacements or empirical compensation terms, or reduce errors by experimentally calibrating and fitting end-effector compensation parameters. However, these methods are often sensitive to changes in attitude, load, and wear, limiting parameter universality and transferability, and lack interpretable modeling of error sources and propagation paths. Some technologies only consider the geometric error of the connecting rod or only the clearance factor of the kinematic pair when modeling, or they treat the two separately and then simply superimpose them on the end. This can easily lead to omission of error terms, double counting, or inconsistent coordinate system definitions. This is not conducive to quantitatively revealing the law of error transmission from the base joint to the end, nor is it conducive to carrying out tolerance allocation and structural optimization for engineering applications.

[0004] In the process of realizing this invention, the inventors discovered at least the following problems in the prior art: 1. It is difficult to simultaneously characterize the uncertainty of link error and the uncertainty of joint kinematic pair clearance under a unified coordinate transformation framework; 2. It is difficult to accurately reveal the pattern of error transmission from the base joint to the end joint and the resulting end-point trajectory deviation, thus making it difficult to calculate the joint correction amount; 3. It is difficult to form a calculable representation of the end-effector pose offset, making it difficult to quantify the joint correction amount. Summary of the Invention

[0005] The purpose of this invention is to provide a method, actuator, and storage medium for correcting errors in a series joint mechanism, thereby solving the technical problem in the prior art where end-effector pose shifts due to machining and assembly errors, making it difficult to quantify the joint correction amount. The numerous technical effects of the preferred solutions among the many technical solutions provided by this invention are detailed below.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for correcting errors in a series joint mechanism, comprising: Based on the degrees of freedom of the tandem joint mechanism on the three-dimensional sectional plane, a coordinate system for the tandem joint mechanism is established, and the centers of each joint, the lengths of the links, and the kinematic pairs of the joints are calibrated. Based on the length of the rod, the effective rod length parameters are obtained through the effective rod length theory. Based on the displacement of the joint kinematic pair, the local coordinate pose correction amount of the joint is obtained through the vector sum method; The DH transformation matrix is ​​corrected using the effective rod length parameter and the joint local coordinate pose correction amount; An error propagation chain is formed according to the motion propagation sequence, and the end pose uncertainty position vector is obtained by combining it with the corrected DH transformation matrix. The joint correction amount is obtained based on the deviation between the uncertain position vector of the end effector and the theoretical position vector of the end effector, thereby completing the correction of the joint error of the series joint mechanism.

[0007] Preferably, establishing the coordinate system of the tandem joint mechanism based on its degrees of freedom in the three-dimensional sectional plane includes: Based on the degrees of freedom of the tandem joint mechanism in the sagittal, horizontal, and coronal planes, determine the direction of the motion axis of each joint; A global coordinate system for the series joint mechanism is constructed with the direction of the motion axis as a reference. The motion axis direction of each joint is used as the reference axis of the corresponding local coordinate system, and a local coordinate system is constructed at each joint based on the DH rule.

[0008] Preferably, the calibration of the joint centers, link lengths, and joint kinematic pairs includes: In the global coordinate system, the joint center, the length of the link, and the initial position of the joint kinematic pair are calibrated by locating the joint center, determining the length of the link, and marking the initial position of the joint kinematic pair.

[0009] Preferably, obtaining the effective rod length parameter based on the rod length using the effective rod length theory includes: The effective link length parameter is obtained by superimposing the theoretical link length of the series joint mechanism with the geometric errors caused by link manufacturing errors and link assembly errors. Among them, the two ends of the rod and the joint connection are taken as the measurement objects to determine the spatial position of the reference point at the end of the rod, and then the actual length of the rod is obtained. The deviation between the actual length of the rod and the theoretical length of the rod is taken as the manufacturing error of the rod. The deviation of the spatial distance between the centers of two adjacent joints in the actual assembly state from the theoretical distance is taken as the assembly error of the rod.

[0010] Preferably, the step of obtaining the joint local coordinate pose correction amount based on the displacement of the joint kinematic pair using a vector sum method includes: Based on the displacement deviation vector generated in the local coordinate system by the joint gap formed by the envelope and the supported member of the joint kinematic pair, the local coordinate pose correction amount of the joint is determined by vector summation.

[0011] Preferably, the step of correcting the DH transformation matrix using the effective rod length parameter and the joint local coordinate pose correction amount includes: performing segmented independent correction on the DH transformation matrix corresponding to each adjacent coordinate transformation unit.

[0012] Preferably, the step of forming an error propagation chain according to the motion propagation sequence and obtaining the end-effector pose uncertainty position vector by combining the corrected DH transformation matrix includes: According to the motion transmission sequence, a superimposed transmission chain is formed in which the uncertainty intervals of the link error and joint clearance are transmitted sequentially from the global coordinate system to each joint. Based on the uncertain interval superimposed with the transfer chain and the corrected DH transformation matrix, the uncertain position vector of the end pose is obtained.

[0013] Preferably, the step of obtaining the joint correction amount based on the deviation between the uncertain end-effector pose vector and the theoretical end-effector pose vector, and thus completing the correction of the joint error of the tandem joint mechanism, includes: Based on the deviation between the uncertain position vector of the end effector pose and the theoretical pose vector of the end effector, the comprehensive pose deviation vector of the end effector plane is obtained. Construct a compensation gain matrix and a planar Jacobian matrix, and obtain the joint correction amount based on the end-plane integrated pose deviation vector, the compensation gain matrix, and the planar Jacobian matrix; The joint correction amount is applied to the joint control vector to obtain the corrected joint control vector, and joint error correction is performed.

[0014] In a second aspect, the present invention also provides a multi-degree-of-freedom actuator, comprising: a controller and a series joint mechanism, the series joint mechanism being connected to the controller, the controller being used to implement the series joint mechanism error correction method as described in the first aspect during execution.

[0015] In a third aspect, the present invention also provides a computer-readable storage medium storing a computer program that, when executed, implements the error correction method for the tandem joint mechanism as described in the first aspect.

[0016] Implementing one of the above-described technical solutions of the present invention has the following advantages or beneficial effects: 1. This invention uses the effective rod length theory to equivalently apply the length error generated during rod manufacturing and assembly to the link geometry parameters, so that the rod error directly enters the kinematic link in the form of DH parameters; 2. The joint kinematic pair clearance is equivalent to the position deviation vector in the joint local coordinate system, and is injected into the pose correction matrix of the joint local coordinate system in a vector sum manner, so that the joint clearance enters the coordinate system transformation process in the form of homogeneous pose perturbation. 3. Based on link error and joint clearance correction, consistent modeling of "link error - joint clearance - coordinate system mapping - end pose" is achieved under a unified DH homogeneous transformation framework. This realizes the quantification of end pose offset, avoids the problem of omission and double counting of error terms caused by using errors only as end experience compensation or only local analysis of single joints, improves the completeness and consistency of end pose offset calculation, and thus improves the accuracy of joint correction calculation. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a flowchart of the error correction method for the serial joint mechanism according to an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the uncertainty modeling principle of interval superposition in an embodiment of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the present invention clearer, various exemplary embodiments described below will be referenced to the accompanying drawings, which form part of the exemplary embodiments, illustrating various exemplary embodiments that may be used to implement the present invention. Unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. It should be understood that they are merely examples of processes, methods, and apparatuses consistent with some aspects of the present invention disclosed as detailed in the appended claims, and other embodiments may be used, or structural and functional modifications may be made to the embodiments listed herein without departing from the scope and spirit of the present invention.

[0019] In the embodiments of the present invention, the effective rod length theory refers to the theoretical method of equating the dimensional errors of rods caused by factors such as processing, assembly, and deformation to changes in the geometric length of the rods, and participating in kinematic transformations in the form of equivalent lengths. Whether it is based on the direct superposition of rod length errors, the correction based on the equivalent geometric model, or the calculation method based on the equivalent rod length obtained by parameter identification, all are within the protection scope of the effective rod length theory described in the present invention.

[0020] Those skilled in the art can understand the specific meaning of the above terms in this invention based on their understanding.

[0021] To illustrate the technical solution described in this invention, specific embodiments are described below, showing only the parts related to the embodiments of this invention.

[0022] Example 1: like Figure 1 As shown, the present invention provides a method for correcting errors in a series joint mechanism, comprising: Based on the degrees of freedom of the tandem joint mechanism on the three-dimensional sectional plane, a coordinate system for the tandem joint mechanism is established, and the centers of each joint, the lengths of the links, and the kinematic pairs of the joints are calibrated. Based on the length of the rod, the effective rod length parameters are obtained through the effective rod length theory. Based on the displacement of the joint kinematic pair, the local coordinate pose correction amount of the joint is obtained through the vector sum method; The DH transformation matrix is ​​corrected using the effective rod length parameter and the joint local coordinate pose correction amount; An error propagation chain is formed according to the motion propagation sequence, and the end pose uncertainty position vector is obtained by combining it with the corrected DH transformation matrix. The joint correction amount is obtained based on the deviation between the uncertain position vector of the end effector and the theoretical position vector of the end effector, thereby completing the correction of the joint error of the series joint mechanism.

[0023] This invention utilizes the effective link length theory to apply length errors generated during link manufacturing and assembly to the link geometry parameters, allowing link errors to directly enter the kinematic link in the form of DH parameters. Simultaneously, it equates joint kinematic pair clearances to position deviation vectors in the joint local coordinate system and injects them into the joint local coordinate system pose correction matrix using a vector sum approach. This allows joint clearances to enter the coordinate system transformation process as homogeneous pose perturbations, thereby achieving consistent modeling of "link error—joint clearance—coordinate system mapping—end-effector pose" within a unified DH homogeneous transformation framework. This avoids the problems of omission and duplication of error terms caused by treating errors only as end-effector empirical compensation or only performing local analysis at a single joint, improving the completeness and consistency of end-effector pose offset calculations, and ultimately enhancing the accuracy of joint error correction.

[0024] As an optional implementation, establishing the coordinate system of the series joint mechanism based on the degrees of freedom of the series joint mechanism in the three-dimensional spatial sectional plane includes: Based on the degrees of freedom of the tandem joint mechanism in the sagittal, horizontal, and coronal planes, determine the direction of the motion axis of each joint; A global coordinate system for the series joint mechanism is constructed with the direction of the motion axis as a reference. The motion axis direction of each joint is used as the reference axis of the corresponding local coordinate system, and a local coordinate system is constructed at each joint based on the DH rule.

[0025] As an optional implementation, the calibration of the joint centers, link lengths, and joint kinematic pairs includes: In the global coordinate system, the joint center, the length of the link, and the initial position of the joint kinematic pair are calibrated by locating the joint center, determining the length of the link, and marking the initial position of the joint kinematic pair.

[0026] Unified calibration is performed in a global coordinate system to ensure that the calibration data of joint center, link length, and joint kinematic pairs are in the same coordinate system, avoiding parameter deviations caused by inconsistent calibration benchmarks. At the same time, a unified calibration benchmark can achieve precise matching of various parameters, providing accurate basic data for subsequent acquisition of effective link length parameters and calculation of joint pose correction, further improving the accuracy of error propagation analysis, and ensuring the accuracy of calculation of the uncertain position vector of the end effector pose.

[0027] As an optional implementation, obtaining the effective rod length parameter based on the rod length using the effective rod length theory includes: The effective link length parameter is obtained by superimposing the theoretical link length of the series joint mechanism with the geometric errors caused by link manufacturing errors and link assembly errors. Among them, the two ends of the rod and the joint connection are taken as the measurement objects to determine the spatial position of the reference point at the end of the rod, and then the actual length of the rod is obtained. The deviation between the actual length of the rod and the theoretical length of the rod is taken as the manufacturing error of the rod. The deviation of the spatial distance between the centers of two adjacent joints in the actual assembly state from the theoretical distance is taken as the assembly error of the rod.

[0028] By superimposing the theoretical rod length with manufacturing and assembly geometric errors using the effective rod length theory, explicit modeling of rod geometric errors is achieved. Compared with existing technologies that do not consider rod errors or only calculate errors separately, this method can convert rod errors into effective rod length parameters that can be directly used in calculations, facilitating subsequent integration into the DH transformation matrix for unified correction.

[0029] As an optional implementation, the step of obtaining the joint local coordinate pose correction amount based on the displacement of the joint kinematic pair using a vector sum method includes: Based on the displacement deviation vector generated in the local coordinate system by the joint gap formed by the envelope and the supported member of the joint kinematic pair, the local coordinate pose correction amount of the joint is determined by vector summation.

[0030] By combining the joint gap formed by the envelope of the joint kinematic pair and the supported member, the correction amount is determined by the displacement deviation vector sum method, which accurately quantifies the pose deviation caused by the joint gap. Compared with the existing technology that ignores the joint gap or simplifies the gap modeling, the present invention can truly reflect the influence of the joint gap.

[0031] As an optional implementation, the step of correcting the DH transformation matrix using the effective rod length parameter and the joint local coordinate pose correction amount includes: performing segmented independent correction on the DH transformation matrix corresponding to each adjacent coordinate transformation unit.

[0032] By segmenting and independently correcting the DH matrix between adjacent coordinate systems, hierarchical error propagation modeling is achieved. Compared with the existing method of correcting the DH matrix as a whole, segmented and independent correction can accurately locate the error source of each joint and link, which is convenient for forming an uncertainty interval superposition and propagation chain, thereby improving the pertinence and accuracy of error propagation analysis.

[0033] As an optional implementation, the step of forming an error propagation chain according to the motion propagation sequence and obtaining the end-effector pose uncertainty position vector by combining the corrected DH transformation matrix includes: According to the motion transmission sequence, a superimposed transmission chain is formed in which the uncertainty intervals of the link error and joint clearance are transmitted sequentially from the global coordinate system to each joint. Based on the uncertain interval superimposed with the transfer chain and the corrected DH transformation matrix, the uncertain position vector of the end pose is obtained.

[0034] By forming a superimposed transmission chain of uncertainty intervals, the step-by-step transmission quantification of link errors and joint clearances is realized; it can clearly present the transmission process of errors from the global coordinate system to each joint and even to the end point. Through the transmission chain, the uncertainty range of the end point pose is accurately calculated, providing a clear quantitative basis for the precision optimization, error compensation and correction of serial joint mechanisms.

[0035] As an optional implementation, the step of obtaining the joint correction amount based on the deviation between the uncertain position vector of the end effector and the theoretical position vector of the end effector, and thus completing the correction of the joint error of the tandem joint mechanism, includes: Based on the deviation between the uncertain position vector of the end effector pose and the theoretical pose vector of the end effector, the comprehensive pose deviation vector of the end effector plane is obtained. Construct a compensation gain matrix and a planar Jacobian matrix, and obtain the joint correction amount based on the end-plane integrated pose deviation vector, the compensation gain matrix, and the planar Jacobian matrix; The joint correction amount is applied to the joint control vector to obtain the corrected joint control vector, and joint error correction is performed.

[0036] By solving for joint corrections using the compensation gain matrix and the planar Jacobian matrix, a mapping relationship between end-effector pose deviation and joint motion can be established. This provides a quantitative basis and dynamic constraints for the error correction process, improving the accuracy and rationality of the joint correction solution. The solved joint correction is then superimposed on the original joint target vector to form a corrected joint control vector, which is then used for correction. This approach can specifically compensate for motion deviations caused by factors such as component manufacturing errors and joint clearances, effectively suppressing end-effector pose shifts caused by the cascading propagation of errors, stabilizing the motion accuracy of the cascaded joint mechanism, and improving the stability and control precision of the mechanism's operation.

[0037] The embodiments described herein are merely specific examples and do not imply that this is the only possible implementation of the invention. Those skilled in the art will understand that the serial joint mechanisms described in this invention include, but are not limited to, lower limb exoskeletons, upper limb exoskeletons, lumbar exoskeletons, full-body exoskeletons, industrial serial robotic arms, collaborative robots, and bionic motion mechanisms. Any open-chain motion mechanism possessing two or more motion joints connected sequentially by rigid links in a predetermined motion transmission sequence, regardless of whether its joint type is a rotary or translating joint, the number of joint degrees of freedom, link configuration parameters, drive type, or application scenario, falls within the scope of the serial joint mechanisms described in this invention.

[0038] Example 2: Example 2 is a specific example of the method described in Example 1.

[0039] This embodiment uses a lower limb exoskeleton leg module as the object of the serial joint mechanism. This module includes three rotational joints, namely the hip joint, knee joint and ankle joint, as well as three connecting rods (thigh, calf and foot segments) for more detailed explanation.

[0040] This embodiment includes the following steps: S1. Construct the geometric and kinematic framework of the lower limb exoskeleton, and establish a global coordinate system based on the degree of freedom distribution of the lower limb exoskeleton on the three-dimensional spatial plane. Local coordinate system of each joint And complete the calibration of key positions (i.e., the coordinates of each joint center, the length of the link and the initial position of the joint kinematic pair); S2. Establish an internal structural uncertainty model: For rods and joint kinematic pairs, the effective rod length theory and vector sum method are used respectively to construct and obtain the effective rod length parameters and the joint local coordinate pose correction amount; S3. Construct a kinematic transmission model containing internal uncertainties: Use the DH matrix to describe the coordinate system transformation relationship, incorporate the link error and joint clearance into the transformation process, correct the DH transformation matrix through the effective link length parameter and the joint local coordinate pose correction amount, form an error transmission chain according to the transmission law from the hip joint to the end, construct the pose model of the three joints and the end under the condition of internal uncertainty, and then obtain the uncertain position vector of the end pose. S4. Based on the joint and end-effector pose equations under internal uncertainty conditions, calculate the deviation between the theoretical end-effector pose vector and the uncertain end-effector pose position vector, and perform feedback correction based on the generated joint correction amount.

[0041] Step S1 includes: S11. Based on the degrees of freedom of the lower limb exoskeleton in the sagittal, horizontal and coronal planes, determine the direction of the motion axis of each joint. Since each joint is a revolute joint, the direction of its motion axis is the direction of the rotation axis of the corresponding joint, and is used as the reference axis direction of the corresponding local coordinate system. S12. Construct a global coordinate system for the lower limb exoskeleton based on the defined axes of motion. Local coordinate systems were constructed at the hip, knee, and ankle joints according to the DH rule. In this system, the z-axis of each local coordinate system coincides with the corresponding joint rotation axis, the x-axis is determined by the common normal direction between adjacent rotation axes, and the y-axis is determined by the right-hand rule.

[0042] S13. In the global coordinate system, calibrate the joint centers, link lengths, and initial positions of the joint kinematic pairs of the lower limb exoskeleton, i.e., the joint centers are respectively... .

[0043] Step S2 includes: S21. Analyze the dimensional errors generated during the manufacturing and assembly of the rods. Apply the effective rod length theory to apply the uncertainty of the rod error to the geometric length of the rod, and obtain the effective rod length parameters that include the error: in, For the first The effective length of the segment member For the first The theoretical length of a segment member For the first The length error of the segment member; the first The length error of a member is composed of both manufacturing error and assembly error. in, Indicates the first Manufacturing errors of segment members, Indicates the first Assembly errors of segment members; Furthermore, The method of obtaining it is: based on the first The connection points at both ends of the member with the joint are the measurement objects. The actual spatial positions of the reference points or reference hole centers at both ends of the member are determined, and their actual lengths are calculated and compared with the theoretical lengths to obtain the manufacturing error. Let the first... The theoretical reference points at both ends of the segment member are respectively and The corresponding actual measurement reference points are as follows: and The actual manufacturing length of the rod for: Theoretical manufacturing length for: Manufacturing error can be represented for: Wherein, the actual reference point , The reference point can be obtained through a coordinate measuring machine, laser tracker, vision measurement system, calipers, micrometer, or special inspection tool; when the end of the rod is connected by a hole-shaft fit, the reference point is preferably taken as the center of the connection hole, the center of the pin, or a feature point on the mounting reference surface; Furthermore, the assembly error The method for obtaining the value is as follows: After the joint and rod assembly is completed, the assembly error is characterized by the deviation of the spatial distance between the centers of two adjacent joints in the actual assembly state relative to the theoretical distance: Let the first joint be the... The actual positions of the joint centers at both ends of the segment connection after assembly are as follows: and The corresponding theoretical positions are respectively and The actual equivalent length after assembly for: Theoretical assembly length for: Assembly error It can be represented as: S22. Analyze the fit clearance of the joint kinematic pairs, treating it as a positional deviation vector. Apply the kinematic pair clearance to the pose of the joint local coordinate system using a vector sum method to obtain the joint local coordinate pose correction amount including the clearance: in, For the first The gap between each joint is equivalent to the displacement in the local coordinate system, and , The radius of the enclosing component (such as holes in joint housings, bearing outer ring seat holes, bushing inner holes, hinge seat holes, and circular holes in joint seats, etc., which have accommodating space and are used to enclose and support the corresponding moving parts). Let the radius of the supported component (such as the journal of a joint pivot / pin / journal, the journal corresponding to the inner ring of a bearing, the outer circle of a bushing, a hinge pin, a ball joint pin, etc., which are enclosed by the envelope and can generate relative motion within the envelope) be such that the origin of the local coordinate system is... From offset to , O 2 and O The same applies to all three.

[0044] Step S3 includes: S31. Based on the motion sequence characteristics of the three joints (hip, knee, and ankle) of the lower limb exoskeleton, define the DH parameters between each link as follows: ,in The length of the link. For the connecting rod torsion angle, For joint displacement, Joint angle; Preferably, in this embodiment, let ; S32. Using the DH matrix to describe the transformation relationship between the global coordinate system and the local coordinate system, as well as between adjacent local coordinate systems, we can obtain the theoretical transformation from the global coordinate system to the end point and the theoretical pose vector of the end point. The DH transformation matrix from the global coordinate system to the local coordinate system of the hip joint is: The DH transformation matrix from the hip joint to the knee joint is: The DH transformation matrix from the knee joint to the ankle joint is: The theoretical transformation from global to terminal is as follows: in, , , These are all intermediate parameters; Therefore, the theoretical pose vector of the end effector can be determined as: in, for elements, i, j All are counting identifiers; S33. Substitute the effective rod length parameters and joint local coordinate pose corrections into the DH transformation matrix. The modeling principle is as follows: Figure 2 As shown, the corrected DH transformation matrix from the global coordinate system to the local coordinate system of the hip joint is: The corrected DH transformation matrix from the hip joint to the knee joint is: The corrected DH transformation matrix from the knee joint to the ankle joint is: S34. Following the sequence of motion transmission, derive and reveal the transmission law of link errors and joint clearances from the hip joint to the end-effector trajectory, thereby forming a superimposed transmission chain containing uncertainties: in, ; These are all intermediate parameters; Therefore, joint and end-effector pose equations are established under internal uncertainty conditions, and the uncertain end-effector position vector is: in, for elements, i, j All are counting identifiers.

[0045] Step S4 includes: S41. Based on the uncertain position vector at the end With end-point theoretical pose vector Calculate the end-plane position deviation vector ; S42. Based on the theoretical attitude angle at the end point. With the terminal uncertain attitude angle Determine the end attitude deviation ; S43. Construct the end-plane composite pose deviation vector based on the end-plane position deviation vector and the end-plane attitude deviation vector. ; S44. Construct the compensation gain matrix and the plane Jacobian matrix; Specifically, the compensation gain matrix Represented as: in, , The ends are on the plane respectively direction and Position compensation gain in the direction, End-plane attitude angle compensation gain; Planar Jacobian Matrix of a Three-Joint Serial Mechanism for: S45. Obtain the joint correction amount based on the end-plane integrated pose deviation vector, the compensation gain matrix, and the plane Jacobian matrix. , is represented as: Right now S46. Apply the joint correction amount to the joint control vector to obtain the corrected joint control vector, and perform joint error correction. Let the joint control vector be The corrected joint control vector is then: The corrected joint control vectors are sent to the corresponding drive units of the hip, knee, and ankle joints to drive the tandem joint mechanism to perform end-effector position and orientation correction actions. By controlling the joints using the corrected joint control vectors, multi-source inherent errors such as component manufacturing and assembly errors and joint clearances obtained from the initial modeling can be feedforward compensated in the form of joint control quantities. This directly offsets the pose offset caused by errors along the motion transmission chain, solving the core pain point that traditional theoretical model open-loop control cannot adapt to the actual physical errors of the mechanism. This significantly improves the absolute positioning accuracy, repeatability, and trajectory tracking accuracy of the end-effector of the tandem joint mechanism.

[0046] In some embodiments, step S47 is further included: after the mechanism performs the correction action, the actual planar position and actual planar orientation of the end effector are obtained through the position detection device, and the actual pose vector of the end effector is set as: in, Let x be the coordinate component of the actual position of the end point in the x-direction. Let be the coordinate components of the actual position of the end point in the y-direction. This refers to the actual attitude angle at the end point; The corrected target end pose vector is: in, The corrected target end position is represented by the coordinate components in the x-direction. The corrected target end position is represented by the coordinate components in the y-direction. The corrected target end attitude angle; The actual feedback error vector at the end is: when If necessary, repeat steps S41 to S46 until the deviation between the actual end-effector pose and the target pose meets the preset threshold. Requirements.

[0047] It should be emphasized that this embodiment is merely an exemplary illustration of the present invention and is not intended to limit its scope of protection. Similarly, the error correction method for the serial joint mechanism described in this invention can be applied not only to the lower limb exoskeleton described in this embodiment, but also to upper limb exoskeletons, lumbar exoskeletons, and full-body exoskeletons. All of these exoskeletons include rotary joints and rigid links. The upper limb exoskeleton has shoulder joints, elbow joints, wrist joints, and corresponding links; the lumbar exoskeleton has lumbar rotary joints, hip joints, and corresponding links; and the full-body exoskeleton integrates all of the above joints and links. The basic principles of error transmission and pose solving are exactly the same as those of the lower limb exoskeleton mechanism. The method described in this invention can also be applied to various multi-degree-of-freedom serial robotic arms, humanoid robots, rehabilitation robots, industrial linkage mechanisms, and other mechanisms with rotary joints and serial links, which will not be elaborated upon here.

[0048] Example 3: This embodiment provides a multi-degree-of-freedom actuator, including: a controller and a series joint mechanism, wherein the series joint mechanism is connected to the controller, and the controller is used to implement the method described in Embodiment 1 or Embodiment 2 during execution.

[0049] Those skilled in the art will understand that the multi-degree-of-freedom actuators described in this invention include, but are not limited to, industrial robots, collaborative robotic arms, and bionic motion mechanisms. Any multi-degree-of-freedom motion execution device that has multiple rotary joints and / or movable joints connected in series according to a predetermined motion transmission sequence, regardless of its application scenario, drive form, number of joint degrees of freedom, or linkage structure parameters, falls within the scope of the multi-degree-of-freedom actuators described in this invention.

[0050] Example 4: Those skilled in the art will understand that all or part of the features / steps of the above-described method embodiments can be implemented by methods, data processing systems, or computer programs. These features may be implemented without hardware, entirely in software, or in a combination of hardware and software. The aforementioned computer program may be stored in one or more computer-readable storage media. When the computer program is executed (e.g., by a processor), it performs the steps of the above-described embodiments of the series joint mechanism error correction method.

[0051] The aforementioned storage media capable of storing program code include: static hard disks, solid-state hard disks, random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), optical storage devices, magnetic storage devices, flash memory, magnetic disks or optical disks, and / or combinations of the above devices, that is, they can be implemented by any type of volatile or non-volatile storage devices or combinations thereof.

[0052] The above description is merely a preferred embodiment of the present invention. Those skilled in the art will understand that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the present invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A method for correcting errors in a series joint mechanism, characterized in that, include: Based on the degrees of freedom of the tandem joint mechanism on the three-dimensional sectional plane, a coordinate system for the tandem joint mechanism is established, and the centers of each joint, the lengths of the links, and the kinematic pairs of the joints are calibrated. Based on the length of the rod, the effective rod length parameters are obtained through the effective rod length theory. The process of obtaining the effective rod length parameters based on the rod length using the effective rod length theory includes: The effective link length parameter is obtained by superimposing the theoretical link length of the series joint mechanism with the geometric errors caused by link manufacturing errors and link assembly errors. Among them, the two ends of the rod and the joint connection are taken as the measurement objects to determine the spatial position of the reference point at the end of the rod, and then the actual length of the rod is obtained. The deviation between the actual length of the rod and the theoretical length of the rod is taken as the manufacturing error of the rod. The deviation of the spatial distance between the centers of two adjacent joints in the actual assembly state from the theoretical distance is taken as the assembly error of the rod. Based on the displacement of the joint kinematic pair, the local coordinate pose correction amount of the joint is obtained through the vector sum method; The DH transformation matrix is ​​corrected using the effective rod length parameter and the joint local coordinate pose correction amount; The step of correcting the DH transformation matrix using the effective rod length parameter and the joint local coordinate pose correction amount includes: performing piecewise independent correction on the DH transformation matrix corresponding to each adjacent coordinate transformation unit; An error propagation chain is formed according to the motion propagation sequence, and the end pose uncertainty position vector is obtained by combining it with the corrected DH transformation matrix. The step of forming an error propagation chain according to the motion propagation sequence, and combining it with the corrected DH transformation matrix to obtain the end-effector pose uncertainty position vector includes: According to the motion transmission sequence, a superimposed transmission chain is formed in which the uncertainty intervals of the link error and joint clearance are transmitted sequentially from the global coordinate system to each joint. Based on the uncertain interval superimposed transfer chain and the corrected DH transformation matrix, the uncertain position vector of the end pose is obtained; The joint correction amount is obtained based on the deviation between the uncertain position vector of the end effector and the theoretical position vector of the end effector, thereby completing the correction of the joint error of the series joint mechanism.

2. The error correction method for a tandem joint mechanism according to claim 1, characterized in that, The step of establishing a coordinate system for the series joint mechanism based on its degrees of freedom in a three-dimensional sectional plane includes: Based on the degrees of freedom of the tandem joint mechanism in the sagittal, horizontal, and coronal planes, determine the direction of the motion axis of each joint; A global coordinate system for the series joint mechanism is constructed with the direction of the motion axis as a reference. The motion axis direction of each joint is used as the reference axis of the corresponding local coordinate system, and a local coordinate system is constructed at each joint based on the DH rule.

3. The error correction method for a tandem joint mechanism according to claim 2, characterized in that, The calibration of the joint centers, link lengths, and joint kinematic pairs includes: In the global coordinate system, the joint center, the length of the link, and the initial position of the joint kinematic pair are calibrated by locating the joint center, determining the length of the link, and marking the initial position of the joint kinematic pair.

4. The error correction method for a tandem joint mechanism according to claim 2, characterized in that, The method of obtaining the joint local coordinate pose correction amount based on the displacement of the joint kinematic pair through a vector sum method includes: Based on the displacement deviation vector generated in the local coordinate system by the joint gap formed by the envelope and the supported member of the joint kinematic pair, the local coordinate pose correction amount of the joint is determined by vector summation.

5. The error correction method for a tandem joint mechanism according to claim 1, characterized in that, The step of obtaining the joint correction amount based on the deviation between the uncertain position vector of the end effector and the theoretical position vector of the end effector, and thus completing the correction of the joint error of the cascaded joint mechanism, includes: Based on the deviation between the uncertain position vector of the end effector pose and the theoretical pose vector of the end effector, the comprehensive pose deviation vector of the end effector plane is obtained. Construct a compensation gain matrix and a planar Jacobian matrix, and obtain the joint correction amount based on the end-plane integrated pose deviation vector, the compensation gain matrix, and the planar Jacobian matrix; The joint correction amount is applied to the joint control vector to obtain the corrected joint control vector, and joint error correction is performed.

6. A multi-degree-of-freedom actuator, characterized in that, include: A controller and a series joint mechanism, wherein the series joint mechanism is connected to the controller, and the controller is used to implement the series joint mechanism error correction method according to any one of claims 1-5 when executing.

7. A computer-readable storage medium, characterized in that, The storage medium stores a computer program, which, when executed, implements the error correction method for the tandem joint mechanism according to any one of claims 1-5.

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