Robot joint rigidity identification system and method based on standardized excitation flange

Abstract

The invention belongs to the technical field of robots, and provides a robot joint rigidity identification system and method based on a standardized excitation flange, and the system comprises a test flange which is installed at the tail end of a robot, and is provided with at least one excitation guide point location and at least two three-axis acceleration sensors. The excitation guide points are respectively fixed on preset fixed points of the test flange, and the data processing unit is configured to calculate linear acceleration signals of the different excitation guide points under the action of applying torque excitation to obtain three-axis acceleration signals of the test flange and angular acceleration signals of the axis of the test flange. Calculating an actual measurement frequency response function matrix under each test working condition based on the triaxial acceleration signal of the test flange and the angular acceleration signal of the axis of the test flange, and identifying and obtaining the rigidity value of each joint of the robot by combining the actual measurement frequency response function matrix and the theoretical frequency response function matrix under each test working condition. And the rigidity of all joints of the robot can be quickly, accurately and repeatedly identified.

Description

Technical Field

[0001] This invention belongs to the field of robotics technology, and in particular relates to a robot joint stiffness identification system and method based on a standardized excitation flange. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] The stiffness of robot joints is a key parameter determining their dynamic performance, positioning accuracy, and vibration characteristics. In high-speed, high-precision applications, accurate identification of robot joint stiffness is crucial for optimizing control algorithms and improving operational performance. Experimental Modal Analysis (EMA), particularly the impact test, is a commonly used method for obtaining structural dynamic characteristics due to its relatively simple equipment and high testing efficiency. However, applying the existing impact test method to robot joint stiffness identification suffers from several technical problems: insufficient and non-standard excitation; missing key joint information; incomplete response measurements; inability to capture rotational dynamics; the need for large-scale robot movement; complex testing processes with poor identification accuracy; and a lack of standardized testing procedures and poor repeatability. These issues necessitate improvements in both the efficiency and accuracy of robot joint stiffness identification. Summary of the Invention

[0004] To address at least one of the technical problems mentioned above, this invention provides a robot joint stiffness identification system and method based on a standardized excitation flange. It offers a complete end-to-end solution that enables rapid, accurate, and repeatable identification of the stiffness of all robot joints.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A first aspect of the present invention provides a robot joint stiffness identification system based on a standardized excitation flange, comprising: A test flange is installed at the end of the robot. The test flange has at least one excitation guide point. The excitation guide point and the central axis of the test flange have a preset lever arm distance, which is used to apply a quantifiable torque to stimulate the rotational dynamics of the robot's wrist joint. At least two triaxial accelerometers are fixed at preset fixed points on the test flange to acquire linear acceleration signals at different excitation guide points under applied torque excitation. The data processing unit is configured to: solve the linear acceleration signals of different excitation guide points under applied torque excitation to obtain the triaxial acceleration signal of the test flange and the angular acceleration signal of the test flange axis; calculate the measured frequency response function matrix under each test condition based on the triaxial acceleration signal of the test flange and the angular acceleration signal of the test flange axis; and identify the stiffness values ​​of each joint of the robot by combining the measured frequency response function matrix and the theoretical frequency response function matrix under each test condition.

[0006] Furthermore, the test flange is a cross-shaped test flange, which includes two orthogonally extending arms, defining a coordinate system for the cross-shaped test flange. The origin is located at the intersection of the center lines of the two arms on the bottom surface of the cross-shaped test flange. axis and Parallel to the center lines of the two arms respectively, The third axis Direction is determined by the right-hand rule. and The target has been determined.

[0007] Furthermore, the cross-shaped test flange has a reinforcing boss on its arm, the reinforcing boss comprising two orthogonal extended arms, the centerline of each extended arm being perpendicular to... and With axes parallel, the geometric center points of the two orthogonal extender centerlines lie on the axis. Above, the top and side surfaces of the extended arms are parallel and perpendicular to the bottom surface of the cross-shaped test flange, respectively. The ends of each extended arm of the reinforcing boss are located at... Axial distance The position is vertically cut to form four end planes that are simultaneously perpendicular to the bottom surface of the cross-shaped test flange and the center line of the reinforcing boss extension arm.

[0008] Furthermore, the excitation guide points include linear force excitation guide points and torque excitation guide points; wherein, the linear force excitation guide point is set at the geometric center point of the center lines of the two orthogonal extension arms of the reinforcing boss, and the torque excitation guide point is set at the end of the extension arm of the reinforcing boss of the cross-shaped test flange.

[0009] Furthermore, under all test conditions, the robot's main arm joints remained fixed, and only the relative geometric relationship between the robot's wrist joint axes was changed.

[0010] Furthermore, the calculation of the linear acceleration signals of different excitation guide points under applied torque excitation includes: The linear acceleration signals obtained from different excitation guide points under applied torque excitation are preprocessed; The preprocessed linear acceleration signal is transformed into the same coordinate system to obtain the corresponding time-domain signal; Based on the principles of rigid body kinematics, the triaxial acceleration signal and the angular acceleration signal of the test flange axis are obtained by solving the time-domain signal.

[0011] Furthermore, when calculating the measured frequency response function matrix under each test condition, the final measured frequency response function matrix result is obtained by averaging the test results of multiple tests under the same test condition.

[0012] Furthermore, the method for determining the theoretical frequency response function matrix is ​​as follows: establish a simplified dynamic equation, convert the simplified dynamic equation into a state-space form, and based on the state-space model, calculate the theoretical frequency response function matrix corresponding to each working condition for any given joint stiffness vector.

[0013] Furthermore, when identifying the stiffness values ​​of each joint of the robot by combining the measured frequency response function matrix and the theoretical frequency response function matrix under each test condition, a cost function is defined based on the theoretical and experimental frequency response function matrices under all conditions, and the stiffness vector that minimizes the cost function is the final identification result.

[0014] A second aspect of the present invention provides a robot joint stiffness identification method based on a standardized excitation flange, which, based on the robot joint stiffness identification system based on a standardized excitation flange described in the first invention, includes the following steps: Obtain linear acceleration signals at different excitation guide points under applied torque excitation; The linear acceleration signals of the test flange and the angular acceleration signal of the test flange axis are obtained by solving the linear acceleration signals of different excitation guide points under applied torque excitation. The measured frequency response function matrix under each test condition is calculated based on the triaxial acceleration signal and the angular acceleration signal of the test flange axis. The stiffness values ​​of each joint of the robot are then identified by combining the measured frequency response function matrix and the theoretical frequency response function matrix under each test condition.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention addresses the problems of insufficient and non-standard excitation by transforming the experience-based and arbitrary hammering actions in traditional testing into standardized and repeatable engineering operations. This ensures the quality and consistency of excitation from the source, and through standardized and complete excitation, it ensures that all joint dynamics are effectively stimulated.

[0016] This invention addresses the problem of incomplete response measurement by using dual-sensor differential measurement and a corresponding calculation algorithm to achieve accurate measurement of four-degree-of-freedom response, breaking through the bottleneck of angular acceleration measurement. By combining the calculated angular acceleration with the averaged three-axis linear acceleration, this invention provides, for the first time, high-quality four-degree-of-freedom response data including three-dimensional translation and one-dimensional rotation for joint stiffness identification. It provides essential end-axis angular acceleration information for accurately decoupling and identifying the stiffness of wrist joints such as J4, J5, and J6.

[0017] This invention addresses the problems of complex testing processes and poor identification accuracy by employing a testing strategy of "fixing the main arm and traversing the wrist." Since wrist joint movement has minimal impact on the overall robot load, this method effectively avoids nonlinear changes in joint load and stiffness caused by large-scale movements. Furthermore, through systematic testing of three necessary poses and global optimization using multi-condition data, it ensures that the stiffness parameters of each joint can be accurately decoupled and identified under the linear model assumption.

[0018] This invention addresses the problems of lack of standardization and poor repeatability in testing processes. It integrates standardized hardware (cross-shaped flange), standardized processes (excitation point and test pose definition), and standardized algorithms (response calculation and parameter identification) into a complete end-to-end solution. From sensor installation and hammer excitation to data processing, each step has clear specifications, eliminating the human uncertainty introduced by temporary setups and arbitrary point placement in traditional methods. This ensures high consistency and reproducibility of test results, laying the foundation for the large-scale and engineering application of robot joint stiffness.

[0019] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0021] Figure 1 This is a schematic diagram of the installation of the cross-shaped test flange provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the cross-shaped test flange provided in an embodiment of the present invention; Figure 3 This is a flowchart of a robot joint stiffness identification method based on a standardized excitation flange provided in an embodiment of the present invention; Figure 4These are three sets of necessary test poses for the robot provided in this embodiment of the invention; wherein, (a) is necessary test pose 1, (b) is necessary test pose 2, and (c) is necessary test pose 3. Figure 5 These are schematic diagrams of three sets of necessary test pose axes provided in the embodiments of the present invention; wherein, (a) is a schematic diagram of the axis of necessary pose 1, (b) is a schematic diagram of the axis of necessary pose 2, and (c) is a schematic diagram of the axis of necessary pose 3. Among them, 1. Robot; 2. Test flange; 3. Triaxial accelerometer; 4. Reinforcing boss; 5. Base; 6. Center boss; 7. Center impact point; 8. Edge impact point. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0024] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0025] This invention discloses a robot joint stiffness identification system and method based on a standardized excitation flange, aiming to solve the problems of insufficient excitation, complex operation, poor repeatability, and inability to effectively decouple the dynamic characteristics of each joint in existing robot joint stiffness testing. Specifically, it addresses the following pain points: 1. Insufficient and non-standard excitation, resulting in missing information on key joints: Conventional testing typically involves hammering along the axial direction near the center of the robot's end flange. This method generates an excitation force whose line of action passes through or is close to the rotation center of the robot's J4 and J6 axes, failing to produce effective excitation torque. Consequently, the dynamic characteristics of these joints (especially torsional stiffness) cannot be fully excited and measured, leading to incomplete identification results. Furthermore, the lack of standardized guidance results in significant arbitrariness in the hammering point and direction, introducing human error that is difficult to quantify.

[0026] 2. Incomplete response measurement and inability to capture rotational dynamics: Most testing methods only directly measure the three-dimensional linear acceleration of the robot's end effector, failing to directly obtain angular acceleration information. This makes it difficult to decouple the deformation dynamics of the J4, J5, and J6 joints in the robot's wrist from the interaction with other joints, leading to a systematic bias in the stiffness identification of the robot's wrist.

[0027] 3. The robot requires a wide range of motion, leading to complex testing and poor identification accuracy: In existing identification methods, to decouple the influence of each axis on the end effector response as much as possible, the robot needs to perform a wide range of motion within the workspace. However, the site may not allow for such a wide range of movements, and the test sensors are also easily limited by cables, requiring frequent disassembly and reassembly, which brings difficulties to on-site testing. In addition, the robot's wide range of motion will cause significant changes in joint load, introducing additional influencing factors into joint stiffness identification and reducing the accuracy of joint stiffness identification.

[0028] 4. Lack of standardized testing procedures and poor repeatability: Due to the lack of standardized testing equipment and procedures, existing methods rely heavily on the professional experience of test engineers. Uncertainties exist in aspects such as the temporary setup of excitation devices, the arbitrary placement of sensors, and the selection of hammer impact points, making it difficult to guarantee the repeatability and reliability of test results, thus hindering the engineering and large-scale application of this technology.

[0029] This invention includes a cross-shaped test flange, two triaxial accelerometers positioned at predetermined points on the flange, and a matching testing and stiffness calculation method. The cross-shaped flange provides standardized linear force and torque application guide points for hammer impact excitation. The dual-sensor arrangement can calculate the dynamic response of the end flange in three-dimensional translation and torsion around its axis. The calculation method utilizes high-quality excitation and response data with known geometric relationships to accurately identify the stiffness of each joint of the robot. Through hardware and software co-design, this invention provides a complete end-to-end solution capable of rapid, accurate, and repeatable identification of the stiffness of all robot joints.

[0030] As one embodiment of the present invention, this embodiment provides a robot joint stiffness identification system based on a standardized excitation flange, comprising: A test flange is installed at the end of the robot. The test flange has at least one excitation guide point. The excitation guide point and the central axis of the test flange have a preset lever arm distance, which is used to apply a quantifiable torque to stimulate the rotational dynamics of the robot's wrist joint. At least two triaxial accelerometers are fixed at preset fixed points on the test flange to acquire linear acceleration signals at different excitation guide points under applied torque excitation. The data processing unit is configured to: solve the linear acceleration signals of different excitation guide points under applied torque excitation to obtain the triaxial acceleration signal of the test flange and the angular acceleration signal of the test flange axis; calculate the measured frequency response function matrix under each test condition based on the triaxial acceleration signal of the test flange and the angular acceleration signal of the test flange axis; and identify the stiffness values ​​of each joint of the robot by combining the measured frequency response function matrix and the theoretical frequency response function matrix under each test condition.

[0031] This invention solves the problems of insufficient excitation, complex operation, poor repeatability, and inability to effectively decouple the dynamic characteristics of each joint in existing robot joint stiffness testing. It provides a complete end-to-end solution that can achieve rapid, accurate, and repeatable identification of the stiffness of all robot joints.

[0032] like Figure 1 As shown, a test flange 2 is installed at the end of robot 1. The test flange 2 is a cross-shaped test flange, and at least two three-axis accelerometers 3 are installed at preset fixed points on the cross-shaped test flange in a specified coordinate alignment manner. An excitation guide point is set on the cross-shaped test flange. In this embodiment, robot 1 is a six-axis robot. like Figure 2 As shown, the cross-shaped test flange is a preset structure. In this embodiment, two triaxial accelerometers 3 are arranged on the cross-shaped test flange. In this embodiment, IEPE type triaxial accelerometers are used, and they are respectively referred to as triaxial accelerometer A and triaxial accelerometer B. Specifically, the triaxial accelerometer A is mounted along... The triaxial accelerometer B is mounted on the arm end mounting base along the positive axis. The arm end is mounted on the base in the negative axis direction. Both sensors are aligned using reference surfaces on the base, and their respective local coordinate systems... and With flange coordinate system The relative attitude relationship is a known fixed value, stored in the end-effector response signal calculation program, where, , , Flange coordinate system The three orthogonal directions.

[0033] The cross-shaped test flange is designed as a lightweight, high-rigidity structure to avoid the impact of "mass loading effect" on the robot system under test. Specifically, the cross-shaped test flange has two orthogonally extending arms, defining the cross-shaped flange coordinate system. The origin is located at the intersection of the center lines of the two arms on the bottom surface of the cross flange. axis and Parallel to the center lines of the two arms respectively, The third axis Direction is determined by the right-hand rule. and The target has been determined.

[0034] The cross-shaped test flange has a reinforcing boss 4 on its arm. The reinforcing boss 4 is a cross-shaped reinforcing boss, which includes two orthogonal protruding arms. The geometric center of the reinforcing boss 4 is located on the axis. Above, the center lines of each extended arm and and The axes are parallel, and the top and side surfaces of the extended arms of the reinforcing boss 4 are parallel and perpendicular to the bottom surface of the cross-shaped test flange 2, respectively. The ends of each extended arm of the reinforcing boss 4 are at... Axial distance The position is vertically cut to form four end planes that are simultaneously perpendicular to the bottom surface of the cross-shaped test flange and the center line of the extended arm of the reinforcing boss. Each extended arm of the reinforcing boss 4 is provided with a base 5 for mounting the accelerometer. Each base 5 uses the end plane and the bottom surface of the cross-shaped test flange as two orthogonal mounting reference surfaces to achieve precise positioning of the sensor.

[0035] Of course, in practical applications, corresponding triaxial accelerometers can be placed at the mounting bases of any two adjacent orthogonal arms. The mounting position and orientation of the sensors can be determined in the coordinate system. The precise representation ensures the consistency and repeatability of sensor position during each test.

[0036] Preferably, the cross-shaped test flange is made of 7075 aerospace aluminum alloy to ensure high rigidity and lightweight, and its cross arm extension length is [not specified]. It is 150mm; As a further implementation, the excitation guide points include linear force excitation guide points and torque excitation guide points; Specifically, the linear force excitation guide point is located at the center of the cross flange, where there is an axis... The shaft has a high-rigidity central boss 6, and the top surface of the central boss 6 is perpendicular to... The shaft, with each side respectively... and The axis is parallel or perpendicular. In the hammering experiment, the center point of the top surface of the central boss 6 is taken as the central striking point 7, and is numbered as follows. Guide the operator along , , Align the shaft with the center striking point 7 and strike the top surface and sides of the center boss to apply pressure along the cross test flange. , , Purely linear force excitation on the axis.

[0037] Torque excitation guide points: The center points of the two end planes of the cross-shaped test flange without the accelerometer installed are designated as the edge tapping points 8 of the cross-shaped flange, and are numbered as follows: , These two points are the torque excitation guide points, guiding the operator along the coordinate system. Axis direction aligned , Tapping the end of the extended arm of the reinforcing boss can apply a lever arm to the end flange based on the generated linear force excitation. The torque excitation, whose size can be accurately calculated, effectively stimulates the rotational dynamics of the J4 and J6 joints in the robot's wrist.

[0038] Existing methods typically involve randomly hammering the center of the end flange, with the force line passing through or near the axis of the wrist joints such as J4 and J6, failing to generate effective torque and thus making it impossible to identify the torsional stiffness of these critical joints. This invention solves this problem through an innovative design of a cross-shaped test flange: Standardization of torque excitation: Dedicated torque excitation guide points (P1, P2) are provided at the ends of the flange arm. The operator can apply a calculable and directional torque to the end by hammering along the guide points. This directly solves the core problem of insufficient excitation of the wrist rotation joint, ensuring that the dynamic characteristics of the J4 and J6 joints can be fully excited and measured, thereby obtaining complete stiffness information of the six joints.

[0039] Standardization of linear force excitation: The linear force excitation guide point (P0) at the center of the flange provides a clear reference for the application of pure linear force along the three axes, and the specially designed vertical surfaces of the central boss provide clear landing points for hammering in the axial direction, so that the hammering is as close as possible to the desired axial direction, greatly reducing the generation of additional torque.

[0040] Through the above design, this invention transforms the experience-based and arbitrary hammering action in traditional testing into a standardized and repeatable engineering operation, ensuring the quality and consistency of the excitation from the source.

[0041] As one implementation method, the robot's main arm joints remain fixed under all test conditions, and only the relative geometric relationship between the robot's wrist joint axes is changed.

[0042] As one implementation method, the calculation of linear acceleration signals at different excitation guide points under applied torque excitation includes: The linear acceleration signals obtained from different excitation guide points under applied torque excitation are preprocessed; The preprocessed linear acceleration signal is transformed into the same coordinate system to obtain the corresponding time-domain signal; Based on the principles of rigid body kinematics, the triaxial acceleration signal and the angular acceleration signal of the test flange axis are obtained by solving the time-domain signal.

[0043] As one implementation method, when calculating the measured frequency response function matrix under each test condition, the final measured frequency response function matrix result is obtained by averaging the test results of multiple tests under the same test condition.

[0044] As one implementation method, the theoretical frequency response function matrix is ​​determined as follows: a simplified dynamic equation is established, the simplified dynamic equation is converted into a state-space form, and based on the state-space model, the theoretical frequency response function matrix corresponding to each working condition is calculated for any given joint stiffness vector.

[0045] As one implementation method, when identifying the stiffness values ​​of each joint of the robot by combining the measured frequency response function matrix and the theoretical frequency response function matrix under each test condition, a cost function is defined based on the theoretical and experimental frequency response function matrices under all conditions, and the stiffness vector that minimizes the cost function is the final identification result.

[0046] like Figure 3 As shown, as another embodiment of the present invention, a method for identifying robot joint stiffness based on a standardized excitation flange is provided, specifically including the following steps: Step 1: Obtain the linear acceleration signals at different excitation guide points under applied torque excitation; In this embodiment, following the excitation guide points provided by the cross-shaped flange, a hammer is used to sequentially strike multiple points and in multiple directions to apply standardized force and torque excitation. Simultaneously, the force signal from the hammer and the triaxial acceleration signals from all acceleration sensors are recorded.

[0047] Based on a standardized testing process, high-quality dynamic data was collected to decouple and identify the stiffness of all six joints by changing only the wrist joint posture. In this embodiment, the base and main arm joints (J1, J2, J3) are fixed, and the posture of the wrist joints (J4, J5, J6) is systematically changed only. Sufficient and diverse end-effector stimulation information is provided by tapping different stimulation points. This testing method not only avoids the testing complexity caused by large-scale robot movements and the nonlinear interference introduced by load changes, but also fully stimulates the dynamic characteristics of all six joints, improving identification accuracy.

[0048] Specifically, the steps include the following: Step 101: Test preparation and main arm positioning; The cross-shaped test flange and sensor system are installed on the end effector of the robot under test. The robot is controlled to move the main arm joints J1, J2, and J3 to a selected test position (e.g., a working pose near the center of the workspace) and keep them locked throughout the test.

[0049] Specifically, the robot is controlled to move the main arm joints J1, J2, and J3 to a fixed test pose (e.g., ), and remain locked during subsequent wrist posture traversal and hammering tests; Step 102: With the main arm joint locked, adjust the robot wrist joint to a preset pose, and perform the excitation and acquisition process in each pose. In this embodiment, with the main arm joint locked, the robot wrist joints J4, J5, and J6 are controlled to move sequentially, so that the robot end effector reaches the set target test pose and executes the excitation and acquisition process. Specifically, to fully stimulate the dynamics of each axis and effectively decouple the stiffness parameters of each joint, this embodiment defines three sets of essential typical wrist poses, such as... Figure 4 and Figure 5 As shown, these poses are constructed by changing the relative geometric relationship of the axes of joints J4, J5, and J6, ensuring that the contribution of each joint can be clearly distinguished under different excitations.

[0050] Among them, the required pose 1 is that the axes J4 and J6 are parallel, and the axis J5 is perpendicular to both the axes J4 and J6 and parallel to the axis J3.

[0051] Required pose 2: The axes J4 and J6 are perpendicular, and the axis J5 is perpendicular to both the axes J4 and J6 and parallel to the axis J3.

[0052] Required pose 3: The axes J4 and J6 are perpendicular, and the axis J5 is perpendicular to both the axes J4 and J6 and also perpendicular to the J3 axis.

[0053] The J6 joint angle for the above three sets of required poses is fixed at 0 degrees to reduce unnecessary complexity.

[0054] In this embodiment, the following excitation and acquisition process is performed for each pose, including: The operator holds a hammer with a built-in force sensor and sequentially applies force to three excitation guide points (center point P0, edge points P1 and P2) on the cross flange along the flange coordinate system. of , , The hammering was performed in three orthogonal directions. To ensure data quality, each hammering direction at each excitation point was repeated 5 times.

[0055] Using a data acquisition system, at a sampling rate of 10240 Hz, the system simultaneously records one force signal output from the hammer and a total of six acceleration signals output from two triaxial accelerometers. Integrating all postures, motivation points, and motivation directions, a total test was conducted. The final force input and final acceleration output response of the group working condition are measured, and no less than [number] are performed. In the end-impact excitation experiment, taking three groups as an example, after completing the tests of all three poses, a total of [data missing] were obtained. This is the first effective hammer impact excitation and response data.

[0056] In addition to the required poses mentioned above, other optional poses can be added (e.g., the joint angles of J4, J5, and J6 are all 45 degrees) to further enhance the diversity of data and improve the robustness of the identification model.

[0057] Existing methods for decoupling the effects of individual joints often require the robot to perform large-scale movements. This is not only complex but also introduces nonlinear errors due to drastic changes in joint load, reducing recognition accuracy. This invention effectively avoids this problem through a testing strategy of "fixing the main arm and traversing the wrist." The testing process is simplified: the entire test only requires changing the posture of the wrist joints J4, J5, and J6, while the main arm joints (J1, J2, J3) remain fixed. This greatly simplifies on-site operations and avoids problems such as cable tangling and insufficient space.

[0058] Improved identification accuracy: Since wrist joint movement has a minimal impact on the overall robot load, this method effectively avoids nonlinear changes in joint load and stiffness caused by large-scale movements. Furthermore, through systematic testing of three necessary poses and global optimization using multi-condition data, it is ensured that the stiffness parameters of each joint can be accurately decoupled and identified under the linear model assumption.

[0059] Step 2: Solve the linear acceleration signals of different excitation guide points under applied torque excitation to obtain the triaxial acceleration signal of the test flange and the angular acceleration signal of the test flange axis; In this embodiment, using the known and fixed geometric position relationship of the sensors, the collected multiple sets of linear acceleration signals are solved in real time and converted into triaxial acceleration signals of the robot end flange and angular acceleration signals of the cross flange axis through a preset algorithm.

[0060] Specifically, the steps include the following: Step 201: Preprocess the acquired raw acceleration signal; In this embodiment, the preprocessing specifically includes filtering and windowing the force signal and six acceleration signals of each group of data; Specifically, filtering involves applying a bandpass filter, such as a 2-2000Hz bandpass filter, to filter out high-frequency noise that is independent of the structural modes and low-frequency drift caused by sensor zero bias.

[0061] Windowing involves applying an appropriate window function (such as an exponential window) to the effective signal segment of each hammer strike to reduce spectral leakage caused by signal truncation.

[0062] After processing, the force signal of the hammer blow was obtained. And two sets of clear acceleration signals , .

[0063] Step 202: Convert the preprocessed acceleration signal to the same coordinate system to obtain the corresponding time domain signal; In this embodiment, a pre-stored rotation matrix is ​​used. and The acceleration signals from sensors A and B , Unified transformation to flange coordinate system Below, get and .

[0064] Since the measurements from sensors A and B are based on their respective local coordinate systems and To perform kinematic calculations, they must be unified to the common coordinate system of the cross flange. .

[0065] Based on the precise installation relationship defined in step 1, sensors A and B are relative to the coordinate system. The attitude is determined by the rotation matrix , Precise description.

[0066] Therefore, the two sets of acceleration signals can be converted to the following formula: In coordinate system: (1), (2), in, and Indicates that sensors A and B are in Acceleration time-domain signal in coordinate system; Step 203: Based on the principle of rigid body kinematics, the time-domain signal is solved to obtain the triaxial translational acceleration and angular acceleration about the axis of the end test flange; In this embodiment, the triaxial translational acceleration of the entire rigid body (cross flange) is solved using the known accelerations at two points. With respect to the axis angular acceleration of rotation .

[0067] Among them, the triaxial translational acceleration of the end cross flange The solution includes: Origin of the cross flange coordinate system Translational acceleration By measuring acceleration and The averaging method is used to obtain the result, which effectively suppresses acceleration measurement noise, and is expressed as: (3), Flange angular acceleration about axis The solution includes: Cross flange around axis angular acceleration The solution can be obtained by analyzing the acceleration difference vector between the two sensors. Assume the overall arrangement of the acceleration sensors is as follows: Figure 2 As shown, A is located The sensor mounting base is located in the positive axis direction, and the accelerometer B is positioned there. Sensor mounting base in the negative direction of the axis. Then around... angular acceleration of the axis It can be represented as: (4), in, , They are respectively exist , directional components, , They are respectively exist , directional components, The distance from the sensor mounting base to the center axis of the flange.

[0068] Step 204: Calculate the triaxial linear acceleration of the cross flange. and around angular acceleration of the axis As the final response signal of this hammer strike, and the corresponding force signal They are stored together to provide complete input data for stiffness identification in step 4.

[0069] Existing methods only measure three-dimensional linear acceleration and cannot capture rotational dynamics, leading to difficulties in decoupling wrist joint stiffness and inaccurate identification. This invention completely changes this situation through a dual-sensor differential measurement scheme and supporting algorithms: (a) Direct calculation of angular acceleration: By arranging two triaxial accelerometers with known precise relative positions on the flange, this invention utilizes the principles of rigid body kinematics to successfully calculate the end-effector angular acceleration about the axis, which cannot be obtained by traditional methods, by analyzing the difference between the two sets of acceleration signals. ).

[0070] (b) Complete response data: Combining the calculated angular acceleration with the average calculated three-axis linear acceleration, this invention provides for the first time high-quality response data of four degrees of freedom, including three-dimensional translation and one-dimensional rotation, for joint stiffness identification. It provides essential end-axis angular acceleration information for accurately decoupling and identifying the stiffness of wrist joints such as J4, J5, and J6.

[0071] Step 3: Calculate the measured frequency response function matrix under each test condition based on the triaxial acceleration signal of the test flange and the angular acceleration signal of the test flange axis; In this embodiment, the end-effector four-degree-of-freedom response signal and the corresponding excitation force signal are utilized. Calculate the measured frequency response function (FRF) matrix; In this embodiment, the calculated excitation force is utilized. and four-degree-of-freedom response ( , ), calculate the following for each test condition (pose and excitation point combination) Experimental Frequency Response Function (FRF) Matrix The signal-to-noise ratio is improved by averaging the results of multiple tests, such as five, under the same operating condition.

[0072] The single-impact FRF calculation involves the following: for a single impact, the excitation is a three-dimensional force vector, and the response is a four-dimensional acceleration vector. The calculation yields a... The FRF matrix, where each column represents an excitation direction ( , , Each line represents a response direction ( , , , ).

[0073] Among them, data averaging and integration: the results of multiple hammer blows under the same working condition (same pose, excitation point, excitation direction) are averaged to improve the signal-to-noise ratio of FRF.

[0074] By integrating the FRF matrices for all operating conditions, a matrix containing... Dataset of the FRF matrix of the group experiment As a benchmark for subsequent parameter identification, among which These are the input frequency values ​​for the FRF matrix.

[0075] Step 4: Identify the stiffness values ​​of each joint of the robot by combining the measured frequency response function matrix and the theoretical frequency response function matrix under each test condition; Specifically, the steps include the following: Step 401: Simplify the dynamic equations. Convert the simplified dynamic equations into state-space form. Based on the state-space model, for any given joint stiffness vector, calculate the theoretical frequency response function matrix corresponding to each working condition. In this embodiment, a simplified, linear robot dynamics model is established to describe the dynamic response of the system under hammering excitation. Specifically, it includes: Step 4011, Simplify the dynamic equations: Considering that the robot's joints are locked during the hammer impact test (rigid joint angular velocity and acceleration are zero) and the joint deformation is small, the complex nonlinear dynamic equations can be simplified into the following linear differential equations: (5), In the formula, Let be the rigid joint angle vector of the robot. This is the joint dynamic deformation vector. and The first Rigid joint rotation and dynamic torsional deformation of each joint For the quality matrix, Here is the joint stiffness matrix. Here is the joint deformation damping matrix. , These are the joint stiffness vector and the deformation damping vector, respectively. and The first Torsional stiffness and deformation structural damping of each joint, Represents diagonal matrix operators. From the base coordinate system to a specific excitation point The velocity Jacobian matrix, the excitation point The center tapping point can be predefined on the cross flange. Edge tapping point and , This is the end-effector vector acting on the excitation point.

[0076] Compared to the complete dynamic equation, this equation is reasonably simplified based on the specific working conditions of the hammer impact test. It ignores the second-order effects of Coriolis force, centrifugal force, and small deformations at the joints on the mass and Jacobian matrix, enabling efficient linearization analysis while maintaining accuracy. Due to the rigid joint angle locking, and All A defined constant matrix can be obtained through calculations using the robot's forward kinematics and dynamics models. Joint stiffness matrix. and joint deformation damping matrix These are the parameters to be identified.

[0077] Step 4012: Convert the simplified dynamic equations into state-space form; To facilitate the calculation of the FRF, the simplified dynamic equations are converted into state-space form.

[0078] First, adopting the Rayleigh damping assumption, let ,in This is an empirical coefficient that can be estimated based on material properties. The system's state vector is defined as follows: The system output is the terminal four-degree-of-freedom acceleration. , operator This represents the vertical stacking of elements. The state-space equation of the system can be expressed as: (6), (7), The independent variables of each dynamic matrix Omitted expression, and let and Let the zero matrix and the identity matrix be respectively, and the system matrix in the state space can be specifically represented as: (8), Among them, the output Jacobian matrix It is an important component of the state space, mapping the deformation velocity in the joint space to the four-degree-of-freedom motion velocity of the end flange. This matrix is... The matrix consists of three rows, the top three being the standard velocity Jacobian matrix, and the fourth row... The angular velocity Jacobian of the axis is defined as follows: ,in and From the robot base coordinate system to the cross flange coordinate system The speed Jacobian and the angular velocity Jacobian, for Selection matrix for axial angular acceleration.

[0079] Step 4013: Based on the state-space model, for any given joint stiffness vector, calculate the theoretical frequency response function matrix corresponding to each working condition, expressed as: (9), in, The imaginary unit; For the definition For each test condition, the corresponding robot pose and excitation point Jacobian can be substituted to calculate the results. Group corresponding The theoretical FRF matrix, denoted as .

[0080] Step 402: Define the cost function based on the theoretical and experimental frequency response function matrix under all working conditions, and find the stiffness vector that minimizes the cost function; Specifically, the steps include the following: Step 4021: Accumulate the differences between the theoretical and experimental FRF matrices for all operating conditions, and define the global cost function. for: (10) in, Let be the Frobenius norm of the matrix, which incorporates the errors across all frequency points and all excitation and response channels. Number of test cases For the first i The measured frequency response function matrix under the group test conditions. For the first i Theoretical frequency response function matrix under test conditions; Step 4032: Use mature nonlinear optimization algorithms (such as Levenberg-Marquardt or sequential quadratic programming) to find the cost function that makes the cost function... Minimize the stiffness vector : (11), After optimization and convergence, the final identified torsional stiffness values ​​of robot joints J1 to J6 are output. .

[0081] This invention integrates standardized hardware (cross-shaped flange), standardized processes (excitation point and test pose definition), and standardized algorithms (response calculation and parameter identification) into a complete end-to-end solution. From sensor installation and hammer excitation to data processing, each step has clear specifications, eliminating the human uncertainty introduced by temporary setups and arbitrary point placement in traditional methods. This ensures high consistency and reproducibility of test results, laying the foundation for the large-scale and engineering application of robot joint stiffness.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A robot joint stiffness identification system based on a standardized excitation flange, characterized in that, include: A test flange is installed at the end of the robot. The test flange has at least one excitation guide point. The excitation guide point and the central axis of the test flange have a preset lever arm distance, which is used to apply a quantifiable torque to stimulate the rotational dynamics of the robot's wrist joint. At least two triaxial accelerometers are fixed at preset fixed points on the test flange to acquire linear acceleration signals at different excitation guide points under applied torque excitation. The data processing unit is configured to: solve the linear acceleration signals of different excitation guide points under applied torque excitation to obtain the triaxial acceleration signal of the test flange and the angular acceleration signal of the test flange axis; calculate the measured frequency response function matrix under each test condition based on the triaxial acceleration signal of the test flange and the angular acceleration signal of the test flange axis; and identify the stiffness values ​​of each joint of the robot by combining the measured frequency response function matrix and the theoretical frequency response function matrix under each test condition.

2. The robot joint stiffness identification system based on standardized excitation flange as described in claim 1, characterized in that, The test flange is a cross-shaped test flange, which includes two orthogonally extending arms. A coordinate system for the cross-shaped test flange is defined. The origin is located at the intersection of the center lines of the two arms on the bottom surface of the cross-shaped test flange. axis and Parallel to the center lines of the two arms respectively, The third axis Direction is determined by the right-hand rule. and The target has been determined.

3. The robot joint stiffness identification system based on standardized excitation flange as described in claim 2, characterized in that, The cross-shaped test flange has a reinforcing boss on its arm. The reinforcing boss includes two orthogonal extended arms, the centerline of which is perpendicular to the centerline of the extended arm. and With axes parallel, the geometric center points of the two orthogonal extender centerlines lie on the axis. Above, the top and side surfaces of the extended arms are parallel and perpendicular to the bottom surface of the cross-shaped test flange, respectively. The ends of each extended arm of the reinforcing boss are located at... Axial distance The position is vertically cut to form four end planes that are simultaneously perpendicular to the bottom surface of the cross-shaped test flange and the center line of the reinforcing boss extension arm.

4. The robot joint stiffness identification system based on standardized excitation flange as described in claim 3, characterized in that, The excitation guide points include linear force excitation guide points and torque excitation guide points; wherein, the linear force excitation guide point is set at the geometric center point of the center line of the two orthogonal extension arms of the reinforcing boss, and the torque excitation guide point is set at the end of the extension arm of the reinforcing boss of the cross-shaped test flange.

5. The robot joint stiffness identification system based on standardized excitation flange as described in claim 1, characterized in that, Under all test conditions, the robot's main arm joints remained fixed, and only the relative geometric relationship between the robot's wrist joint axes was changed.

6. The robot joint stiffness identification system based on standardized excitation flange as described in claim 1, characterized in that, The calculation of the linear acceleration signals of different excitation guide points under applied torque excitation includes: The linear acceleration signals obtained from different excitation guide points under applied torque excitation are preprocessed; The preprocessed linear acceleration signal is transformed into the same coordinate system to obtain the corresponding time-domain signal; Based on the principles of rigid body kinematics, the triaxial acceleration signal and the angular acceleration signal of the test flange axis are obtained by solving the time-domain signal.

7. The robot joint stiffness identification system based on standardized excitation flange as described in claim 1, characterized in that, When calculating the measured frequency response function matrix under each test condition, the final measured frequency response function matrix result is obtained by averaging the test results of multiple tests under the same test condition.

8. The robot joint stiffness identification system based on standardized excitation flange as described in claim 1, characterized in that, The method for determining the theoretical frequency response function matrix is ​​as follows: establish a simplified dynamic equation, convert the simplified dynamic equation into a state-space form, and based on the state-space model, calculate the theoretical frequency response function matrix corresponding to each working condition for any given joint stiffness vector.

9. The robot joint stiffness identification system based on standardized excitation flange as described in claim 1, characterized in that, When identifying the stiffness values ​​of each joint of the robot by combining the measured frequency response function matrix and the theoretical frequency response function matrix under each test condition, a cost function is defined based on the theoretical and experimental frequency response function matrices under all conditions, and the stiffness vector that minimizes the cost function is the final identification result.

10. A method for identifying robot joint stiffness based on standardized excitation flanges, characterized in that, The robot joint stiffness identification system based on a standardized excitation flange according to any one of claims 1-9 includes the following steps: Obtain linear acceleration signals at different excitation guide points under applied torque excitation; The linear acceleration signals of the test flange and the angular acceleration signal of the test flange axis are obtained by solving the linear acceleration signals of different excitation guide points under applied torque excitation. The measured frequency response function matrix under each test condition is calculated based on the triaxial acceleration signal and the angular acceleration signal of the test flange axis. The stiffness values ​​of each joint of the robot are then identified by combining the measured frequency response function matrix and the theoretical frequency response function matrix under each test condition.

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