A robotic arm compliant force tracking system and control method

Abstract

This invention relates to a compliant force tracking system and control method for a robotic arm. The system includes a robotic arm module, a robotic arm posture control module, a force acquisition module, and a dynamic adaptive hybrid impedance controller. The invention utilizes a dynamic adaptive hybrid impedance control algorithm within the dynamic adaptive hybrid impedance controller to achieve dynamic contact force tracking under uncertain environments, avoiding force overshoot during the contact phase while maintaining force tracking error during the dynamic tracking phase. This controller can adjust its update rate parameters online to track a reference force in uncertain environments.

Description

Technical Field

[0001] This invention belongs to the field of industrial robot technology, specifically relating to a robotic arm compliance force tracking system and control method. Background Technology

[0002] With the development of robotics technology, more advanced production demands are driving robots towards intelligence and diversification. In advanced manufacturing, robots are interacting more and more with their external environment, such as in the production of high-precision components, polishing and compliant assembly in industrial settings, and robot teaching and human-machine interaction. When performing these interactive tasks involving robot-environment contact, interaction forces are generated between the contact surfaces. When the end effector deviates from its planned trajectory, it may cause the actuator to detach from the contact surface or generate strong pressure. This not only significantly impacts the accuracy of the robot's control system but can also lead to destructive consequences due to the robot's high rigidity. Therefore, robots must possess a certain degree of environmental compliance to enable them to operate in unfamiliar environments.

[0003] To address the contact problem, a robot compliant control method is proposed, simultaneously solving position and force control. Compliant force control is mainly divided into active compliant control and passive compliant control. Passive compliant control primarily employs mechanical devices with environmental compliance, such as shock absorbers and springs, utilizing their elastic deformation to absorb vibration and impact energy, enabling the robot to exhibit compliant characteristics. Active compliant control, on the other hand, relies on intelligent control algorithms to process force / position information, causing the end effector to generate the required stiffness, damping, or force to achieve compliance. Due to the high force feedback capability of active compliant control, which results in higher control accuracy, active compliant control was chosen for this research.

[0004] Based on the relationship between position and force, active compliant control can be further divided into impedance control and position / force hybrid control. Position / force hybrid control, based on a formal model of the robotic arm and the task geometry, divides the task space into a position subspace and a force subspace. Since it is impossible to control position and force simultaneously along the same degree of freedom, it tracks force and position in different directions, which is the main drawback of this strategy.

[0005] To address this dynamic problem, a method based on controlling the relationship between position and force is proposed: classical impedance control. The principle of impedance control is to adjust the mechanical impedance of the robotic arm. Classical impedance control deals with the dynamic relationship between force and motion, thus allowing simultaneous control of motion and force in one direction. In many cases, impedance control outperforms position / force hybrid control in controlling the dynamic contact between the robotic arm and its environment, and exhibits stronger robustness in environments with unknown stiffness. However, while position / force hybrid control is easy to implement and has good dynamic force tracking performance, impedance control, although capable of precise force and position control, requires adjusting impedance parameters, which is cumbersome and unintuitive. Therefore, various studies combine the concepts of force / position control with impedance control schemes, i.e., hybrid impedance control schemes, to achieve better performance.

[0006] However, when there are significant uncertainties in the position and stiffness of the contact dynamic environment, hybrid impedance control suffers from substantial errors in force tracking accuracy. In such cases, an adaptive law that estimates impedance parameters in real time based on environmental parameters can expand the stability region of the impedance controller. Based on this, an improved adaptive hybrid impedance control strategy can both track the required force and compensate for uncertainties in the environmental position and stiffness. Furthermore, since most application robots are industrial robots, they can only be controlled in position mode. Therefore, to improve force tracking accuracy in unknown environments, a position-based adaptive hybrid impedance controller is proposed.

[0007] However, for certain types of machining, the parameters of the workpiece (such as ultra-thin parts, aircraft wings, or patient hearts) are time-varying during operations (such as polishing and cutting). While adaptive hybrid impedance control schemes offer superior performance in compensating for force tracking errors, they are prone to significant force overshoot. Relying on existing control strategies, it is difficult to maintain machining accuracy without damaging the parts, and simultaneously maintain a small force tracking error while avoiding force overshoot. To address these shortcomings, no simple and practical solution has yet been proposed for production practice in current industrial applications.

[0008] Therefore, the existing robotic arm compliant contact algorithms mainly have the following drawbacks:

[0009] (1) The position / force hybrid control strategy requires the design of separate control loops for force and position according to requirements, making it impossible to track force and position in the same direction, and requiring information about the interactive environment. However, in practical applications, it is difficult to obtain an accurate environmental model, resulting in many errors in the control effect;

[0010] (2) Although the hybrid impedance control scheme can achieve accurate force control and position control at the same time when the environmental model is known, it has a large error in force tracking accuracy when the environmental uncertainty is large, and cannot achieve effective tracking.

[0011] (3) The adaptive hybrid impedance control strategy has greatly improved the force tracking accuracy, but compared with the hybrid impedance control strategy, the force overshoot has also increased significantly, and the stability has deteriorated. When the robot transitions from the free motion space to the task space, it is easy to generate a large contact force with the environment in a very short time. The controller cannot react in time, which may damage the robot itself or the contact environment.

[0012] To address the aforementioned issues and improve the compliant contact control quality of robotic arms, there is an urgent need for a force tracking strategy that can accurately track contact forces while maintaining high stability. This force strategy can avoid force overshoot during the contact phase, maintain force error during the dynamic tracking phase, and exhibit high adaptability to time-varying dynamic environments, thus solving problems that traditional control algorithms cannot address. Summary of the Invention

[0013] In order to overcome the above-mentioned problems in the prior art, the present invention provides a robotic arm compliance force tracking system and control method to solve the above-mentioned problems in the prior art.

[0014] A robotic arm compliant force tracking system, the system comprising: a robotic arm module, a robotic arm posture control module, a force acquisition module, and a dynamic adaptive hybrid impedance controller;

[0015] The robotic arm posture control module is connected to the robotic arm module and is used to send control signals to the robotic arm module in real time and receive motion information from the robotic arm module in real time.

[0016] The force acquisition module is mounted on the robotic arm module and connected to the dynamic adaptive hybrid impedance controller, and is used to transmit the acquired force and torque of the robotic arm module to the dynamic adaptive hybrid impedance controller.

[0017] The dynamic adaptive hybrid impedance controller is connected to the robotic arm pose control module and the force acquisition module. It is used to receive motion information from the robotic arm module and force data from the force acquisition module in real time, and to perform kinematic calculations based on the dynamic adaptive hybrid impedance control strategy. The calculated desired pose control information is then output to the robotic arm pose control module, and the robotic arm pose control module outputs the calculated coordinate information to the robotic arm module according to the desired pose control information.

[0018] In addition to the aspects described above and any possible implementations, a further implementation is provided, which further includes a power supply module connected to the robotic arm module, the robotic arm pose control module, the force acquisition module, and the dynamic adaptive hybrid impedance controller.

[0019] In addition to the aspects described above and any possible implementations, a further implementation is provided in which the robotic arm module includes a robotic arm, a servo motor, and an end effector, wherein the end effector is disposed on the robotic arm and connected to the servo motor.

[0020] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the force acquisition module is implemented using a force sensor, which is disposed at the end of the robotic arm and is used to acquire the force and torque acting on the end effector.

[0021] In addition to the aspects described above and any possible implementation, a further implementation is provided, wherein the dynamic adaptive hybrid impedance controller includes a system and parameter initialization module, a robotic arm information processing module, a force information processing module, a dynamic update rate calculation module, an impedance function calculation module, an adaptive compensation rate calculation module, and a desired end-effector pose calculation module.

[0022] The robotic arm information processing module is used to process the robotic arm pose information transmitted from the robotic arm pose control module, and transmit the processed data information to the dynamic update rate calculation module.

[0023] The system and parameter initialization module is used to initialize the impedance parameters and desired contact force information, and transmit the initialized data information to the dynamic update rate calculation module.

[0024] The force information processing module is used to unpack the force data collected by the force acquisition module, convert the data format, and transmit the converted data information to the dynamic update rate calculation module.

[0025] The dynamic update rate calculation module is used to calculate the real-time update rate σ based on the processed force data information and the transformed data information, and transmit the real-time update rate σ to the adaptive compensation rate calculation module.

[0026] The adaptive compensation rate calculation module is used to calculate the real-time adaptive compensation rate ρ based on the transformed six-dimensional force information, the impedance parameters and the dynamic update rate σ, and transmit the real-time updated dynamic adaptive impedance parameters to the impedance function calculation module.

[0027] The impedance function calculation module is used to calculate the pose of the robotic arm at the next moment based on the transformed six-dimensional force information, the desired contact force information, the updated adaptive impedance parameters and the robotic arm pose information at the previous moment, and transmit the calculated pose information to the desired end pose calculation module.

[0028] The desired end-effector pose calculation module is used to output the Cartesian coordinates of the next moment's pose of the robotic arm based on the pose information, and transmit them to the robotic arm pose control module.

[0029] In addition to the aspects described above and any possible implementations, a further implementation is provided in which the robotic arm pose control module includes an inverse kinematics module that converts the received Cartesian coordinates into joint coordinates of the robotic arm.

[0030] In addition to the aspects described above and any possible implementations, a further implementation is provided in which the robotic arm is a six-degree-of-freedom robotic arm with joint coordinates.

[0031] In addition to the aspects described above and any possible implementations, a further implementation is provided in which the dynamic adaptive hybrid impedance controller is implemented on a PC and communication connections and data processing are performed in a C++ environment.

[0032] This invention also provides a control method for a robotic arm compliance force tracking system, the method being implemented using the aforementioned system; comprising the following steps:

[0033] S1. Start the system, start the robotic arm and robotic arm posture control module in the robotic arm module, and the end effector on the robotic arm moves under the drive of the servo motor;

[0034] S2. The force acquisition module acquires the force and torque information of the end effector during its movement at the current moment, and transmits this information to the dynamic adaptive hybrid impedance controller;

[0035] S3. The dynamic adaptive hybrid impedance controller calculates the Cartesian coordinates of the robot arm's pose at the next moment based on the force and torque information, the robot arm's pose information, the impedance parameters, and the desired contact force information, and transmits them to the robot arm pose control module.

[0036] S4. The robotic arm pose control module converts the Cartesian coordinates into joint coordinates of the robotic arm and sends them to the robotic arm, which then moves according to the received joint coordinates.

[0037] In addition to the aspects described above and any possible implementations, a further implementation is provided in which the dynamic adaptive hybrid impedance controller performs calculations using a dynamic adaptive hybrid impedance control strategy, the strategy comprising:

[0038] H1. Establish the adaptive hybrid impedance control algorithm formula, and calculate the real-time position error e(t) based on the force tracking error ΔF:

[0039]

[0040] in,

[0041] m d : The desired inertial parameters of the controller;

[0042] b d : The desired damping parameters of the controller;

[0043] ΔF: The error between the actual contact force and the expected force;

[0044] e(t): The current position tracking error of the robotic arm's end effector, correspondingly, This is the current speed tracking error. This is the current acceleration tracking error;

[0045] ρ: The adaptive compensation law for force tracking error, which can be dynamically adjusted based on the force tracking error, is calculated by the following formula:

[0046]

[0047] The meanings of each variable are as follows:

[0048] T: Sampling period;

[0049] b: Initial value of environmental stiffness;

[0050] σ: Update rate;

[0051] f d (tT): Expectation force at the previous moment;

[0052] f e (tT): The actual contact force at the previous moment;

[0053] ρ(tT): The adaptive compensation rate at the previous time step;

[0054] ρ(t): The adaptive compensation rate at the current moment.

[0055] H2. The position command for the next moment is calculated using the following formula:

[0056] P c (t)=P d (t)+e(t).

[0057] in:

[0058] e(t): Current position tracking error of the robotic arm's end effector;

[0059] P d (t): Desired position;

[0060] P c (t): The position of the instruction being output at the current moment.

[0061] Based on the position error e(t), the desired position P d (t) performs real-time updates to obtain the instruction position P. c (t) is tracked by a position-based robot servo control system, which adjusts the position of the end effector of the robotic arm to ensure that the contact force continuously tracks the desired force.

[0062] Beneficial effects of the present invention

[0063] In the compliant contact force tracking system for robotic arms of this invention, a dynamic adaptive hybrid impedance control algorithm is used in the dynamic adaptive hybrid impedance controller to achieve dynamic contact force tracking in uncertain environments (such as grinding, polishing, assembly, and other production scenarios). This avoids force overshoot during the contact phase while maintaining force tracking error during the dynamic tracking phase. The controller can adjust its update rate parameter online to track the reference force in uncertain environments.

[0064] This invention addresses the problem that traditional robot compliant control cannot simultaneously consider transient contact force overshoot and steady-state force tracking error. It designs a dynamic adaptive hybrid impedance controller to handle dynamic contact force tracking under uncertain environments. The transient response and steady-state error of traditional impedance control and the improved adaptive hybrid impedance control are analyzed, and experiments and performance comparisons are conducted in Simulink simulation and industrial robot experimental environments. Improvements are made to the traditional impedance algorithm, enhancing the stability and accuracy of compliant control. Attached Figure Description

[0065] Figure 1 This is a schematic diagram of the principle of the robotic arm compliance force tracking system of the present invention;

[0066] Figure 2 This is a schematic diagram illustrating the algorithm implementation of the dynamic adaptive hybrid impedance control method in this embodiment of the invention;

[0067] Figure 3 This is a flowchart of the robotic arm compliance force tracking system in this invention. Detailed Implementation

[0068] To better understand the technical solution of this invention, the content of this invention includes, but is not limited to, the specific embodiments described below. Similar technologies and methods should be considered within the scope of protection of this invention. To make the technical problems to be solved, the technical solutions, and advantages of this invention clearer, a detailed description will be provided below in conjunction with the accompanying drawings and specific embodiments.

[0069] It should be understood that the embodiments described in this invention are merely some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0070] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0071] This invention provides a robotic arm compliant force tracking system, the system comprising: a robotic arm module, a robotic arm posture control module, a force acquisition module, and a dynamic adaptive hybrid impedance controller;

[0072] The robotic arm posture control module is connected to the robotic arm module and is used to send control signals to the robotic arm module in real time and receive motion information from the robotic arm module in real time.

[0073] The force acquisition module is mounted on the robotic arm module and connected to the dynamic adaptive hybrid impedance controller, and is used to transmit the acquired force and torque of the robotic arm module to the dynamic adaptive hybrid impedance controller.

[0074] The dynamic adaptive hybrid impedance controller is connected to the robotic arm pose control module and the force acquisition module. It is used to receive motion information from the robotic arm module and force data from the force acquisition module in real time, and to perform kinematic calculations based on the dynamic adaptive hybrid impedance control strategy. The calculated desired pose control information is then output to the robotic arm pose control module, and the robotic arm pose control module outputs the calculated coordinate information to the robotic arm module according to the desired pose control information.

[0075] Furthermore, it also includes a power supply module connected to the robotic arm module, robotic arm posture control module, force acquisition module, and dynamic adaptive hybrid impedance controller.

[0076] Furthermore, the robotic arm module includes a robotic arm, a servo motor, and an end effector, wherein the end effector is mounted on the robotic arm and connected to the servo motor.

[0077] Furthermore, the force acquisition module is implemented using a force sensor, which is located at the end of the robotic arm to collect the force and torque acting on the end effector.

[0078] Furthermore, the dynamic adaptive hybrid impedance controller includes a system and parameter initialization module, a robotic arm information processing module, a force information processing module, a dynamic update rate calculation module, an impedance function calculation module, an adaptive compensation rate calculation module, and a desired end-effector pose calculation module.

[0079] The robotic arm information processing module is used to process the robotic arm pose information transmitted from the robotic arm pose control module, and transmit the processed data information to the dynamic update rate calculation module.

[0080] The system and parameter initialization module is used to initialize the impedance parameters and desired contact force information, and transmit the initialized data information to the dynamic update rate calculation module.

[0081] The force information processing module is used to unpack the force data collected by the force acquisition module, convert the data format, and transmit the converted data information to the dynamic update rate calculation module.

[0082] The dynamic update rate calculation module is used to calculate the real-time update rate σ based on the processed force data information and the transformed data information, and transmit the real-time update rate σ to the adaptive compensation rate calculation module.

[0083] The adaptive compensation rate calculation module is used to calculate the real-time adaptive compensation rate ρ based on the transformed six-dimensional force information, the impedance parameters and the dynamic update rate σ, and transmit the real-time updated dynamic adaptive impedance parameters to the impedance function calculation module.

[0084] The impedance function calculation module is used to calculate the pose of the robotic arm at the next moment based on the transformed six-dimensional force information, the desired contact force information, the updated adaptive impedance parameters and the robotic arm pose information at the previous moment, and transmit the calculated pose information to the desired end pose calculation module.

[0085] The desired end-effector pose calculation module is used to output the Cartesian coordinates of the next moment's pose of the robotic arm based on the pose information, and transmit them to the robotic arm pose control module.

[0086] Furthermore, the robotic arm pose control module includes an inverse kinematics module, which converts the received Cartesian coordinates into the joint coordinates of the robotic arm.

[0087] Furthermore, the robotic arm is a six-degree-of-freedom robotic arm with joint coordinates.

[0088] Furthermore, the dynamic adaptive hybrid impedance controller is implemented on a PC, and communication and data processing are performed in a C++ environment.

[0089] Furthermore, the dynamic adaptive hybrid impedance controller employs a dynamic adaptive hybrid impedance control strategy for calculation, the strategy including:

[0090] H1. Establish the adaptive hybrid impedance control algorithm formula, which can calculate the real-time position error e(t) based on the force tracking error ΔF:

[0091]

[0092] The meanings of each variable are as follows:

[0093] m d : The desired inertial parameters of the controller;

[0094] b d : The desired damping parameters of the controller;

[0095] ΔF: The error between the actual contact force and the expected force;

[0096] e(t): The current position tracking error of the robotic arm's end effector, correspondingly, This is the current speed tracking error. This is the current acceleration tracking error;

[0097] ρ: The adaptive compensation law for force tracking error, which can be dynamically adjusted based on the force tracking error, is calculated by the following formula:

[0098]

[0099] The meanings of each variable are as follows:

[0100] T: The system's sampling period;

[0101] b: Initial value of environmental stiffness;

[0102] σ: Update rate;

[0103] f d (tT): The expected force at the previous moment, a known quantity;

[0104] f e (tT): The actual contact force at the previous moment, a known quantity;

[0105] ρ(tT): The adaptive compensation rate at the previous moment, a known quantity;

[0106] ρ(t): The adaptive compensation rate at the current moment.

[0107] H2. The position command for the next moment is calculated using the following formula:

[0108] P c (t)=Pd (t)+e(t).

[0109] The meanings of each variable are as follows:

[0110] e(t): Current position tracking error of the robotic arm's end effector;

[0111] P d (t): Desired position;

[0112] P c (t): The position of the instruction being output at the current moment.

[0113] The above formula can be used to determine the desired position P based on the position error e(t). d By performing real-time updates, the instruction location P can be obtained. c The tracking is performed by a position-based robot servo control system. By adjusting the position of the robotic arm's end effector, the contact force continuously tracks the desired force.

[0114] Specifically Figure 1 This invention illustrates a robotic arm compliant force tracking system for detecting dynamic contact forces under uncertain environments. A dynamic adaptive hybrid impedance controller is designed to achieve constant force compliant tracking of the contact forces. Without generating large overshoot, the system solves the force tracking error caused by position uncertainty and environmental stiffness uncertainty under unknown environments, and realizes the deployment of a dynamic adaptive hybrid impedance control algorithm on a six-degree-of-freedom robotic arm.

[0115] The robotic arm compliant force tracking system in this embodiment of the invention includes a power module, a robotic arm pose control module, a robotic arm, a servo motor, an end effector, a force acquisition module, and a dynamic adaptive hybrid impedance controller. The power module provides power to the system. The robotic arm, mounted on the robot and implemented with six degrees of freedom, moves under the control of the robotic arm pose control module and feeds back motion information to the same module. The robotic arm pose control module sends control signals to the six-degree-of-freedom robotic arm in real time and receives motion information from the robotic arm in real time. The servo motor is mounted at the end of the robotic arm and follows the robotic arm to a designated position, driving the end effector located at the end of the robotic arm to complete specific tasks. The end effector, driven by the servo motor, is used to complete a series of production tasks such as grinding, polishing, and assembly.

[0116] The force acquisition module, mounted on the end effector of the six-degree-of-freedom robotic arm, is used to acquire the six-dimensional force and six-dimensional torque acting on the end effector.

[0117] The power module can be in the form of common wired or battery-powered devices; there are no specific restrictions here, as long as it can provide power.

[0118] The dynamic adaptive hybrid impedance controller is connected to the robotic arm pose control module and the force acquisition module, and is used to receive the motion information of the robotic arm pose control module and the force data of the force acquisition module in real time, and perform robotic kinematic calculations based on a dynamic adaptive hybrid impedance control strategy to obtain the desired pose control information of the robotic arm, and output it to the inverse kinematics module of the robotic arm pose control module. The inverse kinematics module of the robotic arm outputs the calculated joint coordinate information of the robotic arm to the six-degree-of-freedom robotic arm, and updates the motion state of the robotic arm in real time. The robotic arm drives the end effector to move to the calculated desired position, and adjusts the end contact force to be constant by controlling the position of the end effector.

[0119] The robotic arm pose control module is connected to the power supply module. The present invention uses a robotic arm control cabinet supporting an industrial robotic arm, which is used to send control signals to the six-degree-of-freedom robotic arm in real time, receive the motion information of the robotic arm in real time, and connect to the dynamic adaptive hybrid impedance controller installed on the PC-side host computer to complete the transmission of control signals and feedback signals. The system uses a wired method to complete the data interaction between the robotic arm pose control module and the impedance controller, based on the Ethernet communication protocol defined by the IEEE 802.3 standard. Connect one end of the network cable to the LAN network port of the robotic arm control cabinet, and the other end to the PC side, that is, the dynamic adaptive hybrid impedance controller, and modify the IP address of the PC side to make it in the same network segment as the IP address of the control cabinet. It can be understood that the data transmission method can also be in the form of serial port, Ethernet, SPI, etc., and no specific limitation is made here as long as the function of data transmission can be achieved.

[0120] Combined with Figure 1 As shown, the six-degree-of-freedom robotic arm is connected to the robotic arm pose control module, receives the control signal of the control module and feeds back the motion information to the control module. It can be understood that the robotic arm can be an ordinary industrial six-degree-of-freedom robotic arm, and no specific limitation is made here as long as the function can be achieved.

[0121] Again, Figure 1 As shown, the servo motor is installed at the end of the robotic arm and moves to the specified position following the robotic arm. By precisely controlling the position, speed and torque of the end effector, high-precision grinding, assembly and other operations can be achieved. It can be understood that the servo motor can be a stepper servo motor, an AC servo motor, a linear servo motor, etc., and no specific limitation is made here as long as the function can be achieved.

[0122] The end effector is connected to the servo motor and completes a series of production tasks such as grinding, polishing, and assembly under the drive of the motor. It can be understood that different end effectors can be selected according to specific uses. For example, a grinding head needs to be installed to complete the grinding task, and a servo gripper needs to be installed for the assembly task, etc. No specific limitation is made here as long as the function can be achieved.

[0123] The force acquisition module is mounted on the end effector of a six-DOF robotic arm to acquire six-dimensional forces and torques acting on the end effector. This module can employ a six-dimensional force sensor based on the resistance strain gauge principle. The electrical and physical layers use the RS-485 communication protocol, while the application layer uses the Modbus-RTU protocol. The six-dimensional force sensor is installed on the end effector and connected to a dynamic adaptive hybrid impedance controller (PC) via a network cable. The dynamic adaptive hybrid impedance controller unpacks the force data received by the six-dimensional force sensor according to the Modbus-RTU protocol. The data format is a 32-bit floating-point number in the IEEE-754 standard and needs to be converted to decimal data. It is understood that the force acquisition module can use force sensors with other measurement principles and transmission protocols; no specific restrictions are imposed here, as long as the functionality of six-dimensional force measurement and data transmission can be achieved.

[0124] The dynamic adaptive hybrid impedance controller is connected to the robotic arm pose control module and the force acquisition module. It receives real-time motion information from the robotic arm and force data from the force acquisition module, and performs robot kinematics calculations based on a dynamic adaptive hybrid impedance control strategy, outputting the desired pose control information for the robotic arm. This module is implemented on a PC, with communication and data processing handled in a C++ environment. It is understood that other programming languages ​​such as C and C# can be used for control implementation; no specific restrictions are imposed here, as long as the functionality is achieved.

[0125] The transfer function of the interaction model of the entire compliant force tracking system is shown below:

[0126]

[0127] The above block diagram represents a simple closed-loop control circuit for the controller, robot, and environment system. The controller is implemented on a computer, the robot motion controller is implemented using the robot's built-in position-based servo control system, and the environment is the force space at the end effector of the robotic arm, where the contact force acting on the end effector is measured using a force sensor. c P is the position command issued by the impedance controller. e F represents the actual moving position of the robotic arm. d For the desired contact force, F e The force sensor measures the actual contact force. G(s) and H(s) are the transfer functions of the controller and feedback loop, respectively, where G(s) = C(s) / E(s) and E(s) = F. d -F e Because robot motion controllers have superior position tracking capabilities, PID control or other compensation techniques can suppress model uncertainties (including inertia, friction, etc.) and some external disturbances. This means that P... c =Pe (Position tracking capability), so the gain of the motion controller can be simplified to 1.

[0128] The aforementioned dynamic adaptive hybrid impedance control strategy first selects the impedance model of a linear second-order system, and expresses the dynamic relationship between the force tracking error ΔF and the position error e(t), i.e., the impedance function relationship, as follows:

[0129]

[0130] In the formula, e(t) = P d -P e P e P represents the actual end position of the workpiece. d Let e(t) be the desired end position, and e(t) be the position tracking error. Accordingly, For speed tracking error, For acceleration tracking error; F e F represents the actual contact force on the workpiece. d Let ΔF be the desired force, and ΔF be the force tracking error. d b d k d The parameters are the desired inertia, damping, and stiffness gains of the controller. In equation (1), when the force tracking error ΔF is known, the position error e(t) can be calculated using a second-order differential equation. Based on the position error e(t), the desired position P is determined. d By performing real-time updates, the instruction location P can be obtained. c (t)=P d The contact force (t) + e(t) is tracked by a position-based robot servo control system. By adjusting the position of the robotic arm's end effector, the contact force continuously tracks the desired force.

[0131] By analyzing the steady-state force tracking error of ΔF, it can be seen that when the stiffness gain k d When k is zero, the system can satisfy the ideal steady-state condition, that is, the steady-state force error is zero. At this time, when k... d When =0, the impedance function in equation (1) can be rewritten as:

[0132]

[0133] In real-world systems, environmental stiffness is a continuous, time-varying variable. Due to the change in environmental stiffness, even if k... dSetting it to zero cannot avoid force tracking error. Furthermore, robot servo systems or force sensors suffer from transmission delays, measurement noise, and model uncertainties, resulting in an infinite steady-state force tracking error. Therefore, the aforementioned ordinary hybrid impedance control is inadequate for accurate force tracking control. To reduce force tracking error, an improvement is made to equation (2), and the improved adaptive hybrid impedance control algorithm is shown in equation (3):

[0134]

[0135] Where ρ is the adaptive compensation law for force tracking error, which can be adjusted online according to the force error and can be calculated by equation (4):

[0136]

[0137] ρ(t) is the adaptive compensation rate at the current time, ρ(tT) is the adaptive compensation rate at the previous time, and t is a known quantity. In the initial state, ρ(0) = 0, T is the sampling period of the system, b is the initial value of the environmental stiffness, and f is a known quantity. d (tT) represents the expected force at the previous moment, and f is a known quantity. e (tT) represents the actual contact force at the previous moment, which is a known quantity; σ is the update rate, which is a time-varying parameter related to the stability of the system.

[0138] According to the impedance control law in equation (3), for By performing a double integral, the real-time position error to be compensated, e(t), can be calculated, as shown in equation (5):

[0139]

[0140] By correcting this error based on the position at the previous moment, the position command for the next moment can be obtained, as shown in equation (6):

[0141] P c (t)=P d (t)+e(t) (6)

[0142] Where P d (t) represents the desired position at the previous moment, from which the position command P is obtained. c After (t), update the expected position at this time and set P. d (t)=P c (t). and the position instruction P c (t) is sent to the robot servo controller to drive the robot to the commanded position.

[0143] This robust adaptive control scheme allows for real-time adjustment of impedance parameters based on environmental contact force, compensating for uncertainties in the environment. Based on the error of the desired force and the adaptive law, adaptive hybrid impedance control can maintain a constant desired force.

[0144] At this point, analysis of the compensation law reveals that when the update rate σ is large, the compensation effect is more significant (better force tracking capability), but the contact force jitter range is larger (larger force overshoot). Conversely, when the update rate σ is small, the compensation effect is not significant (poor force tracking capability), and the contact force change trend is slower (smaller force overshoot). That is, if σ is too large, oscillation will occur; if σ is too small, the force error will be relatively large. Therefore, in order to simultaneously reduce force tracking error and avoid force overshoot, maintaining a stable desired contact force, it is inappropriate to keep the update rate σ constant throughout the control process. To improve the controller's performance, the update rate σ needs to be adjusted online. Therefore, an algorithm for dynamically calculating the update rate is added to the controller, using feedback information from the force error Δf and the force error change Δf' to correct the update rate σ online.

[0145]

[0146] Where α and β are the gains used to adjust the weight of the force error and the change in force error. limt This is the upper limit to ensure the system remains in a stable state. In practical applications, to ensure the asymptotic stability of the system, the update rate σ needs to be set within a small range, and the upper limit must be large enough, thus sacrificing some force tracking accuracy.

[0147] The update rate can be dynamically adjusted based on the force error using equation (7). When the robot transitions from the free motion space to the task space, the contact force error is relatively large, and the update rate σ is relatively small. When the robot enters the stable contact stage, the force error is small, and the update rate σ gradually increases as the force error decreases. By dynamically adjusting σ, the controller can achieve small force overshoot and high-precision force tracking.

[0148] Deploying the aforementioned dynamic adaptive hybrid control strategy onto the dynamic adaptive hybrid impedance controller can compensate for force tracking errors caused by changes in environmental stiffness, and ensure that the system does not have large force overshoot by adjusting σ. In the contact state, small steps are taken to avoid overshoot, while in the steady state, large steps are taken to achieve force tracking.

[0149] The dynamic adaptive hybrid impedance controller includes a robotic arm information processing module, which processes the robotic arm posture information transmitted from the robotic arm posture control module and transmits the data information to the dynamic update rate calculation module.

[0150] The dynamic adaptive hybrid impedance controller includes a system and parameter initialization module, which is used to initialize information such as impedance parameters and desired contact force, and transmit the data information to the dynamic update rate calculation module.

[0151] The dynamic adaptive hybrid impedance controller includes a force information processing module, which is used to unpack the force data collected by the force acquisition module, convert the data format, and transmit the data information to the dynamic update rate calculation module.

[0152] The dynamic adaptive hybrid impedance controller includes a dynamic update rate calculation module, which is used to calculate the real-time update rate σ based on the six-dimensional force information and the impedance parameters, and transmit the real-time update rate to the adaptive compensation rate calculation module.

[0153] The dynamic adaptive hybrid impedance controller includes an adaptive compensation rate calculation module, which is used to calculate the real-time adaptive compensation rate ρ based on the six-dimensional force information, the impedance parameters and the dynamic update rate σ, and transmit the real-time updated dynamic adaptive impedance parameters to the impedance function calculation module.

[0154] The dynamic adaptive hybrid impedance controller includes an impedance function calculation module, which is used to calculate the pose of the robotic arm at the next moment based on the six-dimensional force information, the desired contact force information, the updated adaptive impedance parameters and the pose information of the robotic arm at the previous moment, using the operation relationship of the impedance control algorithm shown in Equation (5), and transmit the calculated pose information to the desired end pose calculation module.

[0155] The dynamic adaptive hybrid impedance controller includes a desired end-effector pose calculation module, which outputs the Cartesian coordinates of the next moment pose of the robotic arm based on the calculation results of the impedance function calculation module, and transmits them to the robot inverse kinematics module of the robotic arm pose control module for inverse kinematics calculation to convert them into the movement of each joint, thereby controlling the movement of the robotic arm.

[0156] As an embodiment of the present invention, the present invention also provides a control method for a robotic arm compliance force tracking system, the method being implemented using the aforementioned system; comprising the following steps:

[0157] S1. Start the system, start the robotic arm and robotic arm posture control module in the robotic arm module, and the end effector on the robotic arm moves under the drive of the servo motor;

[0158] S2. The force acquisition module acquires the force and torque information of the end effector during its movement at the current moment, and transmits this information to the dynamic adaptive hybrid impedance controller;

[0159] S3. The dynamic adaptive hybrid impedance controller calculates the Cartesian coordinates of the robot arm's pose at the next moment based on the force and torque information, the robot arm's pose information, the impedance parameters, and the desired contact force information, and transmits them to the robot arm pose control module.

[0160] S4. The robotic arm pose control module converts the Cartesian coordinates into joint coordinates of the robotic arm and sends them to the robotic arm, which then moves according to the received joint coordinates.

[0161] Combination Figure 2 The diagram shows the algorithm implementation of the dynamic adaptive impedance control method for the impedance controller, which consists of the following six steps. Steps 2 to 6 form a loop with a period of 4ms.

[0162] (1) System and parameter initialization module: The control algorithm first performs system initialization and parameter setting. System initialization includes enabling and posing the robot arm, establishing Modbus communication connection with the force sensor, clearing the force sensor data, and performing initialization work such as gravity compensation between the sensor and the end effector; parameter setting includes setting impedance parameters, desired tracking force, and upper limit of update rate.

[0163] (2) Force Information Processing Module: This module acquires the actual contact force in real time through a force sensor and performs coordinate system transformation on the sensor's force information, converting the force information from the sensor's own coordinate system to the robot arm's base coordinate system. It calculates the force error Δf based on the actual and expected contact forces, and then calculates the gradient Δf' of the force error using the difference.

[0164] (3) Dynamic update rate calculation module: Based on the force error and force error gradient at this time, the dynamic parameter update rate σ is calculated by equation (7).

[0165] (4) Adaptive compensation rate calculation module: Based on the error between the actual contact force and the expected force and the dynamic update rate σ at this time, the adaptive compensation rate ρ is calculated by equation (4).

[0166] (5) Impedance Function Calculation Module: Based on the above information, impedance is calculated. A double integral is used to solve the second-order differential equation, and the required position error is calculated step-by-step based on the force error. To facilitate application in industrial robots, the control algorithm is discretized through sampling time. Figure 2 The formulas in the text are in discretized form.

[0167] (6) Expected end-effector pose calculation module: Finally, calculate the Cartesian position coordinates P of the robotic arm at the next moment. c The position command is sent to the robot servo system. Once the entire loop is complete, it returns to step 2 and loops indefinitely. The entire control cycle is 4ms.

[0168] Combination Figure 3 As shown, in some embodiments, the designed compliant force tracking system for the robotic arm can be simulated using Simulink. Figure 3 The flowchart in the middle is the simulation implementation. In Simulink, the control system block diagram is built. First, the desired tracking force is set at the input signal, and the difference between the desired tracking force and the actual tracking force fed back by the three-dimensional model of the robot arm is obtained to obtain the force tracking error. The force tracking error is input into the dynamic update rate calculation module, and the dynamic parameter update rate σ is calculated by equation (7) and input into the adaptive compensation rate calculation module. The adaptive compensation rate calculation module calculates the adaptive compensation rate ρ by equation (4) based on the force tracking error and the update rate σ, and inputs it into the impedance function calculation module. The impedance function calculation module performs impedance calculation, calculates the position error of the next moment by the force tracking error and the robot arm pose of the previous moment, and inputs it into the desired pose calculation module. The desired pose calculation module calculates the desired Cartesian pose and converts it into the six joint coordinates of the robot inverse solution module. The joint coordinates are input into the three-dimensional model of the robot, so that the three-dimensional model moves to the given coordinates. By continuously detecting the actual contact force at the end of the robot arm, the entire process is repeated, and the position of the end of the robot arm is continuously adjusted to achieve the control effect of contact force tracking the desired force.

[0169] The dynamic adaptive hybrid impedance control strategy used in this embodiment of the invention is the same as that in the previous embodiment, and the implementation principles of modules such as the dynamic update rate calculation module, the adaptive compensation rate calculation module, and the impedance function calculation module are the same as those in the previous embodiment.

[0170] Unlike the previous embodiments' control strategies deployed on actual industrial robots, this invention analyzes the transient response and steady-state error characteristics of traditional impedance control and the improved dynamic adaptive hybrid impedance control strategy in a simulation environment, highlighting the necessity of dynamic adaptation of the update rate. For the dynamic contact force tracking problem under uncertain environments, an improved dynamic adaptive hybrid impedance control method is proposed. Using this method, a compliant force tracking system for a robotic arm is built in a simulation environment, achieving compliant force tracking of planar forces, curved surface forces, and irregular planar forces.

[0171] The foregoing description illustrates and describes several preferred embodiments of the present invention. However, as previously stated, it should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A robotic arm compliant force tracking system, characterized in that, The system includes: a robotic arm module, a robotic arm posture control module, a force acquisition module, and a dynamic adaptive hybrid impedance controller; The robotic arm posture control module is connected to the robotic arm module and is used to send control signals to the robotic arm module in real time and receive motion information from the robotic arm module in real time. The force acquisition module is mounted on the robotic arm module and connected to the dynamic adaptive hybrid impedance controller, and is used to transmit the acquired force and torque of the robotic arm module to the dynamic adaptive hybrid impedance controller. The dynamic adaptive hybrid impedance controller is connected to the robotic arm pose control module and the force acquisition module. It receives motion information from the robotic arm module and force data from the force acquisition module in real time, performs kinematic calculations based on the dynamic adaptive hybrid impedance control strategy, and outputs the calculated desired pose control information to the robotic arm pose control module. The robotic arm pose control module then outputs the calculated coordinate information to the robotic arm module based on the desired pose control information. The dynamic adaptive hybrid impedance control strategy includes: H1. Establish the adaptive hybrid impedance control algorithm formula, based on the force tracking error. Calculate real-time position error : in, : The desired inertial parameters of the controller; : The desired damping parameters of the controller; The error between the actual contact force and the expected force; The current position tracking error of the robotic arm's end effector, correspondingly, This is the current speed tracking error. This is the current acceleration tracking error. ; ρ: Adaptive compensation law for force tracking error, dynamically adjusted based on force tracking error, calculated by the following formula: in, Sampling period; Initial value of environmental stiffness; Update rate: Where α and β are the gains used to adjust the weight of the force error and the change in force error. It is the upper limit to ensure the system remains in a stable state; Δf is the force error and Δf ’ For force error variation; : The expectation of the previous moment; : The actual contact force at the previous moment; : The adaptive compensation rate of the previous moment; : The adaptive compensation rate at the current moment; H2. The position command for the next moment is calculated using the following formula: ； in: : Expected location; : The current position of the output instruction; According to position error For desired position Perform real-time updates to obtain the command location. The tracking is performed by a position-based robot servo control system, which adjusts the position of the end effector of the robotic arm to ensure that the contact force continuously tracks the desired force.

2. The system according to claim 1, characterized in that, It also includes a power supply module connected to the robotic arm module, robotic arm posture control module, force acquisition module and dynamic adaptive hybrid impedance controller.

3. The system according to claim 1 or 2, characterized in that, The robotic arm module includes a robotic arm, a servo motor, and an end effector, wherein the end effector is mounted on the robotic arm and connected to the servo motor.

4. The system according to claim 3, characterized in that, The force acquisition module is implemented using a force sensor, which is located at the end of the robotic arm and is used to acquire the force and torque acting on the end effector.

5. The system according to claim 4, characterized in that, The dynamic adaptive hybrid impedance controller includes a system and parameter initialization module, a robotic arm information processing module, a force information processing module, a dynamic update rate calculation module, an impedance function calculation module, an adaptive compensation rate calculation module, and a desired end-effector pose calculation module. The robotic arm information processing module is used to process the robotic arm pose information transmitted from the robotic arm pose control module, and transmit the processed data information to the dynamic update rate calculation module. The system and parameter initialization module is used to initialize the impedance parameters and desired contact force information, and transmit the initialized data information to the dynamic update rate calculation module. The force information processing module is used to unpack the force data collected by the force acquisition module, convert the data format, and transmit the converted data information to the dynamic update rate calculation module. The dynamic update rate calculation module is used to calculate the real-time update rate σ based on the processed data information and the converted force data information, and transmit the real-time update rate σ to the adaptive compensation rate calculation module. The adaptive compensation rate calculation module is used to calculate the real-time adaptive compensation rate ρ based on the transformed six-dimensional force information, the impedance parameters and the dynamic update rate σ, and transmit the real-time updated dynamic adaptive impedance parameters to the impedance function calculation module. The impedance function calculation module is used to calculate the pose of the robotic arm at the next moment based on the transformed six-dimensional force information, the desired contact force information, the updated adaptive impedance parameters and the robotic arm pose information at the previous moment, and transmit the calculated pose information to the desired end pose calculation module. The desired end-effector pose calculation module is used to output the Cartesian coordinates of the next moment's pose of the robotic arm based on the pose information, and transmit them to the robotic arm pose control module.

6. The system according to claim 5, characterized in that, The robotic arm pose control module includes an inverse kinematics module, which converts the received Cartesian coordinates into the joint coordinates of the robotic arm.

7. The system according to claim 3, characterized in that, The robotic arm uses joint coordinates of a six-degree-of-freedom robotic arm.

8. The system according to claim 1, characterized in that, The dynamic adaptive hybrid impedance controller is implemented on a PC, and communication and data processing are performed in a C++ environment.

9. A control method for a compliant force tracking system for a robotic arm, characterized in that, The method is implemented using the system described in any one of claims 1-8; and includes the following steps: S1. Start the system, start the robotic arm and robotic arm posture control module in the robotic arm module, and the end effector on the robotic arm moves under the drive of the servo motor; S2. The force acquisition module acquires the force and torque information of the end effector during its movement at the current moment and transmits this information to the dynamic adaptive hybrid impedance controller; S3. The dynamic adaptive hybrid impedance controller calculates the Cartesian coordinates of the robot arm's pose at the next moment based on the force and torque information, the robot arm's pose information, the impedance parameters, and the desired contact force information, and transmits them to the robot arm pose control module. S4. The robotic arm pose control module converts the Cartesian coordinates into joint coordinates of the robotic arm and sends them to the robotic arm, which then moves according to the received joint coordinates.

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