Flexible wiping method and system of flexible joint space robot based on dynamic adaptive impedance control

Abstract

The invention discloses a flexible wiping method and system of a flexible joint space robot based on dynamic adaptive impedance control, and the method comprises the steps: firstly, building a contact model between the flexible joint space robot and a wiped target; then, self-adaptive impedance control for dynamically updating impedance parameters is designed; and finally, performing comparison simulation on classical constant impedance, fixed update rate adaptive impedance control and dynamic update rate adaptive impedance control, and verifying the effectiveness of the method combining the dynamic update rate adaptive impedance control and singular perturbation control on friction force compliance control in the wiping process of the flexible joint space manipulator by a simulation result. The method is used for the field of on-orbit wiping of the flexible joint space robot, and accurate compliance force control can be conducted on the flexible joint space robot rapidly, efficiently and accurately; when the flexible joint space robot executes a task, necessary guarantee can be provided for the flexible joint space robot, and it is ensured that the space robot and a wiping target are not damaged, and meanwhile a good cleaning effect is obtained.

Description

Technical Field

[0001] This invention relates to the field of on-orbit wiping technology for space robots, and in particular to a compliant wiping method and system for flexible joint space robots based on dynamic adaptive impedance control. Background Technology

[0002] Molecular pollutants released from the smoke produced during satellite fuel combustion and collisions with high-speed debris easily adhere to the windows of space telescopes and observation towers, severely affecting their observation capabilities. To reduce extravehicular activity (EVA) for astronauts, there is an urgent need to develop on-orbit cleaning technology using space robots. To ensure good cleaning results without damaging the robot or the target being cleaned, contact force control is necessary. Impedance control approximates the contact point between the robot and the end-effector as a second-order "spring-damping-mass" system, establishing a relationship between the end-effector contact force and the robot's displacement. By adjusting the parameters of this second-order system, it is possible to adapt to environmental changes, thus achieving constant force control.

[0003] Traditional impedance control requires establishing a desired impedance model of the end contact force and trajectory tracking deviation to achieve compliant control. However, the environmental parameters of space wiping are often uncertain, making it difficult to obtain an accurate environmental contact model to achieve zero steady-state error in unknown or dynamic environments. While adaptive impedance control improves dynamic tracking performance, the magnitude of the adaptive update rate significantly impacts tracking capability and force overshoot, resulting in substantial overshoot.

[0004] Current research on force control algorithms for space robotic arms primarily focuses on purely rigid systems. However, real-world space robots commonly utilize harmonic reducers, resulting in significantly flexible joints. In this context, the motion of the space robotic arm no longer directly corresponds to the motion of the motor rotor. Furthermore, the presence of flexible joints inevitably leads to vibrations during high-speed and high-precision movements. Ignoring the existence of flexible joints in the modeling and control design of space robotic arm systems can severely impact both control accuracy and stability. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a compliant wiping method and system for flexible joint space robots based on dynamic adaptive impedance control. By dynamically adjusting the adaptive coefficient, it achieves both accurate force tracking and reduces the overshoot problem caused by the adaptive impedance during the contact phase. By introducing singular perturbation control, the system dynamic equations are approximately divided into two independent subsystems: "fast-changing" and "slow-changing," thereby achieving elastic vibration suppression and desired trajectory tracking of the flexible joint robot system. Furthermore, the hyperbolic tangent function is used to replace the sign function in the sliding mode control of the slow-changing subsystem to reduce system jitter.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a compliant wiping method for a flexible joint space robot based on dynamic adaptive impedance control, comprising the following steps:

[0007] Step 1: Construct the system dynamics equations for the three-degree-of-freedom flexible joint robotic arm;

[0008] Step 2: Establish a contact model between the flexible joint space robot and the target to be wiped;

[0009] Step 3: Design an adaptive impedance control with dynamically updated impedance parameters for the torque control outer loop of position-based impedance control;

[0010] Step 4: For the trajectory tracking inner loop based on position-based impedance control, singular perturbation control is introduced to approximately divide the system dynamic equations into fast-changing subsystems and slow-changing subsystems, which are independent of each other;

[0011] Step 5: For the fast-changing subsystem, design a speed difference feedback control to ensure system stability;

[0012] Step 6: For the slowly varying subsystem, design a hyperbolic tangent sliding mode control to ensure that the system achieves the desired trajectory tracking.

[0013] In a preferred embodiment, the system dynamics equations of the three-degree-of-freedom flexible joint manipulator constructed in step 1 are specifically as follows:

[0014]

[0015]

[0016] In the formula: Let be the system's inertia matrix. It is a column vector that includes centrifugal force and Coriolis force. Here is the inertia matrix of the joint actuator. Let be the moment of inertia of each joint actuator. This is the stiffness matrix of the flexible joint; ,, The system's rigid generalized coordinate matrix; for Figure 2 The base angle indicated in the text, Center of mass Coordinates in an inertial coordinate system , Represents the joint coordinate matrix. They represent Figure 2 The coordinate angles of the robot arm joints are indicated in the diagram. , Represents a flexible generalized coordinate matrix. , express Figure 2 The generalized coordinate matrix of the joint actuators as indicated in the figure. They are respectively Figure 2 The generalized coordinates of the joint actuators are indicated in the figure; Input torque to the robotic arm joints, This represents the total torque matrix element of the joint actuator.

[0017] In a preferred embodiment, the contact model between the flexible joint space robot and the target being wiped established in step 2 specifically includes: simplifying the end effector and the environment in the normal direction into a spring model, wherein... The desired contact force between the end effector and the environment. for The corresponding actuator end reference position is at middle The coordinates of the axis; thus the contact force of the robot's end effector with the normal environment. for

[0018]

[0019] In the formula: x represents the actual position of the robot's end effector. Indicates environmental stiffness. Indicates the location of the environment.

[0020] In a preferred embodiment, step 3, which involves designing an adaptive impedance control system for dynamically updating impedance parameters in the outer loop of the position-based impedance control torque control, specifically includes: the impedance equation for the normal contact force is a second-order differential equation.

[0021]

[0022] In the formula: , , For the desired inertia, desired damping, and desired stiffness of the environment; further...

[0023]

[0024] In the formula: , , x represents the position, velocity, and acceleration corrections at the end effector of the robot actuator, respectively. d Desired acceleration, velocity, and position of the robot's end effector; Desired normal contact force , Let be the desired frictional force.

[0025] In a preferred embodiment, in a real working environment, when the environmental stiffness is variable or unknown:

[0026] Therefore, environmental location is used. Replace the unavailable accurate reference trajectory Let the position correction amount , Furthermore, because the position tracker stably tracks the desired trajectory, there is Therefore,

[0027]

[0028] By selection and ensure The above formula still holds true even under unknown circumstances, thus ensuring stable force tracking error. ;

[0029] Similarly, when the environmental location changes dynamically, To compensate for the steady-state error in force tracking, an adaptive compensation term is introduced. Design an adaptive impedance control algorithm

[0030]

[0031] Where: at the initial time ; The sampling period; For the update rate; design the following dynamic update rate.

[0032]

[0033] Update rate According to force error With force error change rate Feedback is updated in real time; and Selecting positive numbers, respectively and Update rate weights; to ensure system stability, The range of values ​​is ,make .

[0034] In a preferred embodiment, the overall control law of the system in step 4 Represented as To ensure system stability, is the control law of the slowly varying subsystem, used to achieve the desired trajectory tracking control; For the control law of the fast variable subsystem.

[0035] In a preferred embodiment, step 5 involves applying the normal environmental contact force to the robot's end effector. Substituting into the dynamic equation, we get For the fast-changing subsystem, the speed difference feedback control method is selected for control. ; It is a diagonal matrix containing positive numbers.

[0036] In a preferred embodiment, step 6 involves designing a hyperbolic tangent sliding mode control based on the slow-varying subsystem to ensure the system achieves the desired trajectory tracking; the following hyperbolic tangent sliding mode control law for the slow-varying subsystem is designed:

[0037]

[0038] In the formula: All are greater than 0, by setting different Value adjustment Steepness of the function; As a third-order column vector compensation term, it ensures that the input control torque on the right is always 0; , , for The corresponding matrix or vector, Defined as , , , for Expected quantity; For positive numbers, a function for switching sliding surfaces is introduced.

[0039] This invention provides a compliant wiping system for a flexible joint space robot based on dynamic adaptive impedance control, comprising a processor, a memory, and a bus, wherein the memory stores machine-readable instructions executed by the processor;

[0040] When the system is running, the processor and the memory communicate via a bus, and the machine-readable instructions are executed by the processor as described in the compliant wiping method for a flexible joint space robot based on dynamic adaptive impedance control.

[0041] Compared with existing technologies, this invention has the following advantages: When the external environment is unknown or dynamically changing, it solves the problem of inaccurate force tracking caused by traditional impedance control, and also addresses the issues of larger bias, larger oscillation amplitude, and longer system stabilization time caused by fixed update rate adaptive impedance control. Comparative simulation experiments were conducted in MATLAB using traditional impedance (IC), adaptive impedance (AIC), and dynamic update rate adaptive impedance (DAIC), demonstrating that the proposed algorithm remains effective under the three task requirements of constant friction force, slope variation, and sinusoidal variation during the wiping process, even when environmental stiffness and friction coefficient change abruptly. Attached Figure Description

[0042] Figure 1 This is a flowchart illustrating the steps of the flexible joint space robot based on the dynamic adaptive impedance control method of the present invention.

[0043] Figure 2 This is a schematic diagram of the floating-based flexible joint space robot system of the present invention and the target being wiped;

[0044] Figure 3 This is a schematic diagram of the forces acting on the end effector when it comes into contact with the environment.

[0045] Figure 4 This is a schematic diagram of the impedance control model in this invention;

[0046] Figure 5 This is a schematic diagram of position-based impedance control in this invention;

[0047] Figure 6 This is a schematic diagram of the control of the singular perturbation method in this invention;

[0048] Figure 7 , 8 This is a schematic diagram illustrating the change in frictional force and frictional force error tracking when the desired frictional force is constant.

[0049] Figure 9 , 10 This is a schematic diagram illustrating the changes in friction force and friction force error tracking when the desired friction force slope changes.

[0050] Figure 11 , 12 This is a schematic diagram illustrating the change in friction force and friction force error tracking when the desired sinusoidal change in friction force is achieved. Detailed Implementation

[0051] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0052] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. 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 application pertains.

[0053] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application; 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.

[0054] A compliant wiping method for flexible joint space robots based on dynamic adaptive impedance control, referenced Figure 1-12 This includes the following steps:

[0055] Step 1: Construct the system dynamics equations for the three-degree-of-freedom flexible joint robotic arm;

[0056] Step 2: A contact model between the flexible joint space robot and the target being wiped was established;

[0057] Step 3: An adaptive impedance control capable of dynamically updating impedance parameters was designed for the torque control outer loop of position-based impedance control.

[0058] Step 4: For the trajectory tracking inner loop based on position-based impedance control, singular perturbation control is introduced to approximately divide the system dynamic equations into two independent subsystems: "fast-changing" and "slow-changing".

[0059] Step 5: For the fast-changing subsystem, design a speed difference feedback control to ensure system stability;

[0060] Step Six: For the slowly varying subsystem, design a hyperbolic tangent sliding mode control to ensure that the system achieves the desired trajectory tracking;

[0061] Further: The system dynamic equations for constructing the three-degree-of-freedom flexible joint robotic arm in step one are as follows:

[0062]

[0063]

[0064] In the formula: Let be the system's inertia matrix. It is a column vector that includes centrifugal force and Coriolis force. Here is the inertia matrix of the joint actuator. Let be the moment of inertia of each joint actuator. This is the stiffness matrix of the flexible joint; , The system's rigid generalized coordinate matrix; The included angle of the base, Center of mass Coordinates in an inertial coordinate system , Represents the joint coordinate matrix. These represent the included angles of the robot arm joint coordinates. , Represents a flexible generalized coordinate matrix. , Represents the generalized coordinate matrix of the joint actuator. These are the generalized coordinates of the joint actuators; Input torque to the robotic arm joints, This represents the total torque matrix element of the joint actuator.

[0065] Further, in step two, a contact model was established between the flexible joint space robot and the target being wiped. The end effector and the environment were simplified into a "spring" model along the normal direction. The desired contact force between the end effector and the environment. for The corresponding actuator end reference position is at middle The coordinates of the axis. Therefore, the contact force of the robot's end effector with the environment. for

[0066]

[0067] In the formula: x represents the actual position of the robot's end effector. Indicates environmental stiffness. Indicates the location of the environment.

[0068] Further: In step three, an adaptive impedance control capable of dynamically updating impedance parameters was designed for the torque control outer loop of the position-based impedance control. The impedance equation for the normal contact force is a second-order differential equation.

[0069]

[0070] In the formula: , , For the desired inertia, desired damping, and desired stiffness of the environment. Further...

[0071]

[0072] In the formula: , , , , and x represent the position, velocity, and acceleration corrections of the robot actuator end effector, respectively. d Desired acceleration, velocity, and position of the robot's end effector; Desired normal contact force , Let be the desired frictional force.

[0073] In a real work environment, and It is often unknown or time-varying, so it needs to be discussed on a case-by-case basis.

[0074] (1) Variable environmental stiffness or unknown environmental stiffness

[0075] Because the environmental stiffness is unknown, an accurate reference trajectory cannot be obtained. Therefore, use environmental location Instead, let the position correction amount , Furthermore, because the position tracker stably tracks the desired trajectory, there is... Therefore, there is

[0076]

[0077] Through reasonable selection and Guaranteed The above formula still holds true even under unknown circumstances, thus ensuring stable force tracking error. .

[0078] (2) Dynamic changes in environmental location

[0079] Similarly, let's assume To compensate for the steady-state error in force tracking, an adaptive compensation term is introduced. Design an adaptive impedance control algorithm

[0080]

[0081] Where: at the initial time ; The sampling period; Let the update rate be [value]. Design the following dynamic update rate.

[0082]

[0083] Update rate According to force error With force error change rate Feedback is updated in real time. and Selecting positive numbers, respectively and The update rate weight. To ensure system stability, The range of values ​​is ,make .

[0084] Further: In step four, singular perturbation control is introduced into the inner loop of the position-based impedance control trajectory tracking, approximating the system dynamics equations as two independent subsystems: a "fast-changing" subsystem and a "slow-changing" subsystem. The overall control law of the system... It can be represented as

[0085]

[0086] in, This is the control law for the slowly varying subsystem, used to achieve desired trajectory tracking control; For the control law of the fast variable subsystem.

[0087] Further: In step five, for the rapidly changing subsystem, a speed difference feedback control is designed to ensure system stability. This involves controlling the contact force of the robot's end effector with the normal environment. Substituting into the dynamic equations, we can obtain For the fast-changing subsystem, the speed difference feedback control method is selected for control. . It is a diagonal matrix containing positive numbers.

[0088] Further: In step six, for the slowly varying subsystem, a hyperbolic tangent sliding mode control is designed to ensure the system achieves the desired trajectory tracking. The following control law for the hyperbolic tangent sliding mode slowly varying subsystem is designed.

[0089]

[0090] In the formula: All are greater than 0, by setting different The value can be adjusted Steepness of the function. As a third-order column vector compensation term, it ensures that the input control torque on the right is always 0; , , for The corresponding matrix or vector, Defined as , , , for Expected quantity; For positive numbers, a function for switching sliding surfaces is introduced.

[0091] Figures 7 to 12The MATLAB results of this invention are given, with the following conditions:

[0092] right Figure 1 The floating-based three-link flexible joint space robot shown is simulated. The masses of each component are as follows: , , , The moments of inertia are respectively , , , Length of each member , , , , , , .

[0093] Assume the end effector posture during the wiping process Angle with target wiping surface Always maintain The desired trajectory of the end effector in the direction parallel to the rubbed surface is: Suppose that the environmental stiffness and friction coefficient undergo abrupt changes at 8s and 4s, respectively. The changing patterns of the environmental stiffness and friction coefficient are as follows:

[0094]

[0095] Let the initial attitude angle of the carrier be... Initial value of joint angle 1 Initial value of joint angle 2 Initial value of joint angle 3 The coordinates of the robot's end effector in inertial space are... , Take sliding mode parameters , , , Impedance parameters , , The adaptive impedance control method sets the update rate. An adaptive impedance control method based on dynamic update rate sets the dynamic update rate weight. , , .

[0096] in Figure 7 and Figure 8 Let the desired friction force be =5 N; Figure 9 and Figure 10 Set the desired friction force =5 + 0.1t N; Figure 11 and Figure 12 Set the desired friction force N. The results show that the method of this invention can effectively achieve precise and compliant wiping of flexible joint space robots. Compared with IC, DAIC can achieve precise tracking of friction force. When there are sudden changes in environmental stiffness and friction coefficient, DAIC significantly reduces the maximum bias, oscillation amplitude, and system stabilization time compared with AIC in terms of friction force tracking.

[0097] use:

[0098] This invention is used in the field of on-orbit wiping of flexible joint space robots. It can quickly, efficiently and accurately perform precise compliant force control on flexible joint space robots. It can provide necessary safety and reliability for flexible joint space robots when performing tasks, and ensure that the space robot and the wiping target achieve good cleaning results without damage.

Claims

1. A compliant wiping method based on dynamic adaptive impedance control for a flexible joint space robot, characterized in that, The method comprises the following steps: Step 1: constructing a system dynamics equation of a three-degree-of-freedom flexible joint robot arm; Step 2: establishing a contact model between the flexible joint space robot and the wiped target; Step 3: designing an adaptive impedance control with dynamically updated impedance parameters for the torque control outer loop based on position-based impedance control; Step 4: introducing singular perturbation control to approximately divide the system dynamics equation into a fast-varying subsystem and a slow-varying subsystem for the trajectory tracking inner loop based on position-based impedance control, wherein the fast-varying subsystem and the slow-varying subsystem are independent of each other; Step 5: designing a velocity difference feedback control based on the fast-varying subsystem to ensure the stability of the system; Step 6: designing a hyperbolic tangent sliding mode control based on the slow-varying subsystem to ensure that the system achieves desired trajectory tracking.

2. The compliant wiping method based on dynamic adaptive impedance control for a flexible joint space robot according to claim 1, wherein, The system dynamics equation of the three-degree-of-freedom flexible joint robot arm constructed in step 1 is specifically: wherein: is the inertia matrix of the system, is the column vector including centrifugal force and Coriolis force, is the inertia matrix of the joint actuator, is the moment of inertia of each joint actuator, is the flexible joint stiffness matrix; , is the rigid generalized coordinate matrix of the system; is the base angle, is the center of mass coordinates in the inertial coordinate system, , denotes the joint coordinate matrix, denotes the robot arm link joint coordinate angles, , denotes the flexible generalized coordinate matrix, , denotes the joint actuator generalized coordinate matrix, are the joint actuator generalized coordinates, respectively; is the mechanical arm joint input torque, is the total torque matrix element of the joint actuator.

3. The compliant wiping method based on dynamic adaptive impedance control for a flexible joint space robot according to claim 1, wherein, The contact model between the flexible joint space robot and the target being wiped established in step 2 specifically includes: simplifying the end effector and the environment in the normal direction as a spring model, wherein... The desired contact force between the end effector and the environment. for The corresponding actuator end reference position is at middle The coordinates of the axis; thus the contact force of the robot's end effector with the normal environment. for In the formula: x represents the actual position of the robot end, represents the environmental stiffness, represents the environmental position.

4. The compliant wiping method based on dynamic adaptive impedance control for a flexible joint space robot according to claim 1, wherein, The adaptive impedance control with dynamically updated impedance parameters for the torque control outer loop based on position-based impedance control in step 3 specifically includes that the impedance equation of the normal contact force is a second-order differential equation wherein: , , are the desired inertia, desired damping and desired stiffness of the environment; further have wherein: , , denote the position, velocity, acceleration correction of the robot effector tip, x d robot tip desired acceleration, velocity, position; , desired normal contact force , desired friction force.

5. The compliant wiping method based on dynamic adaptive impedance control for a flexible joint space robot according to claim 4, wherein, In the actual working environment, when the environmental stiffness changes or the environmental stiffness is unknown: So instead of an accurate reference trajectory which is not available, an environmental position is used to correct the position , ; and since the position tracker is stable in tracking the desired trajectory, there is a small error in the position By choosing with guarantee The above equation still holds without knowing the situation, thus ensuring the force tracking stability error ; When the environmental position dynamically changes, the same reason is set To compensate for force tracking steady-state error, an adaptive compensation term is introduced An adaptive impedance control algorithm is designed where: at initial time ; is the sampling period; is the update rate; a dynamic update rate is designed as follows update rate according to force error with force error change rate feedback is updated in real time; with selected as positive numbers, respectively with update rate weight; to meet system stability, the value range of , let .

6. The compliant wiping method based on dynamic adaptive impedance control for a flexible joint space robot according to claim 1, wherein, Total control law of the system in step 4 is expressed as wherein, is a slow subsystem control law for achieving desired trajectory tracking control; is a fast subsystem control law.

7. The compliant wiping method based on dynamic adaptive impedance control for a flexible joint space robot according to claim 1, wherein, The normal environmental contact force at the end of the robot in step 5 Bringing into the dynamic equation ; the fast-changing subsystem is controlled by using the velocity difference feedback control method ; is a diagonal matrix, which contains positive numbers.

8. The compliant wiping method based on dynamic adaptive impedance control for a flexible joint space robot according to claim 1, wherein, In step 6, the hyperbolic tangent sliding mode control is designed for the slow-varying subsystem to ensure that the system achieves desired trajectory tracking; the hyperbolic tangent-based sliding mode slow-varying subsystem control law is designed as follows In the formula: All greater than 0, by setting different The value adjusts The steepness of the function; As a three-order column vector compensation term, it is guaranteed that the right input control torque is 0; , , When The corresponding matrix or vector, ; defined as , , , The expected amount of ; Is a normal number, which introduces a switching sliding mode surface function.

9. A compliant wiping system based on dynamic adaptive impedance control of a flexible joint space robot, comprising a processor, a memory and a bus, wherein the memory stores machine readable instructions executed by the processor; characterized in that, When the system is running, the processor and the memory communicate through the bus, and the machine readable instructions are executed by the processor to implement the compliant wiping method based on dynamic adaptive impedance control of a flexible joint space robot as claimed in any one of claims 1 to 8.

Images