A compound adaptive compliant control method for a spatial dual-arm robot to synchronously capture a target

Abstract

The application relates to a composite adaptive compliant control method for synchronously capturing a target by a space dual-arm robot, which comprises the following steps: firstly, a dynamic model of the space dual-arm robot, a target to be captured and a contact process is established; in order to ensure that the ends of the dual arms reach the surface of the target to be captured at the same time, an end path planning algorithm based on a B-spline curve is designed; subsequently, in order to reduce the impact on the capturing process of the dual-arm robot system, an impedance control strategy is designed according to the contact force on the ends of the dual arms; secondly, the resultant force on the target is decomposed into an internal force and an external force by using kinematics and geometric relations; finally, an adaptive internal force tracking impedance control strategy is designed to prevent the simultaneous capturing of the target by the dual arms from causing capturing failure or damage to the target. The application can solve the problems of excessive rigid impact on the space dual-arm robot system, excessive holding force or insufficient holding force leading to damage to the target or holding failure in the task scene of synchronously capturing a target by the space dual-arm robot.

Description

Technical Field

[0001] This invention belongs to the field of compliant control for space dual-arm robots, and specifically relates to a composite adaptive compliant control method for synchronous target acquisition by a space dual-arm robot. Background Technology

[0002] Space robots are capable of performing on-orbit operations such as satellite maintenance, space debris removal, and on-orbit assembly, serving as crucial tools and means to extend spacecraft lifespan, free up orbital resources, and enhance space safety. Among these, dual-arm robot systems, with their collaborative advantages and redundancy, overcome the limitations of traditional single-arm systems in terms of load capacity, working range, and operational flexibility, playing an irreplaceable role in future space missions. However, when dual-arm robots capture targets, they create a closed-chain constraint, causing the robot system to experience contact / collision forces while simultaneously generating capture internal forces on the target surface. This not only affects the safety of the dual-arm robot system but also threatens the safety of the target itself. Therefore, achieving synchronized movement of both arms while ensuring safe and compliant contact between the target and the robot system is a pressing and highly challenging task.

[0003] Existing research on target capture by dual-arm robots in space mostly focuses on single problems, such as synchronous motion planning for both arms (CN110104216A), cooperative motion control (CN109606753A), and constant-coefficient impedance control based on internal force decomposition (CN111268182A; CN109015658A), with few studies considering these problems simultaneously. Furthermore, considering the complexity of capture tasks, especially for non-cooperative target capture scenarios where the contact environment is often unknown and variable, adaptive variable impedance control schemes are needed. The literature (Jiao Chunting et al., “Adaptive Hybrid Impedance Control for Dual-Arm Cooperative Manipulation with Object Uncertainty” Automatica, Vol. 140, pp. 110232, 2022) considers both motion planning and internal force tracking control problems, proposing a master-slave motion planning and adaptive constant force control algorithm. However, the master-slave design leads to delays between the left and right arm movements, and this study does not control the impacts on the dual-arm robot system, introducing uncertainty risks to the robot system.

[0004] In summary, the current process of synchronous target acquisition by dual-arm robots in space faces the following three technical challenges that need to be further addressed: (1) the real-time problem of the movement trajectory of the two arms; (2) the unknown and changing contact environment may cause the performance of traditional controllers to degrade, resulting in damage to the target; and (3) the contact impact at the moment of target acquisition may cause the dual-arm robot system to become unstable. Summary of the Invention

[0005] For the operational scenario of a space dual-arm robot capturing an on-orbit target, considering issues such as synchronous movement of the two arms, unknown contact environment, and impacts and collisions to the robot body and target at the moment of operation, this invention provides a composite adaptive compliant control method for the synchronous target capture of a space dual-arm robot. This method can plan the end-effector pose of the dual-arm robot to synchronously reach the desired pose, avoid collision impacts on the robot system at the moment of contact, achieve constant internal force clamping of the target, and adapt to changing and unknown contact tasks. It can be used for the operation task of synchronously capturing an on-orbit target by a dual-arm robot under unknown contact conditions.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A composite adaptive compliant control method for synchronous target acquisition by a dual-arm space robot includes the following steps:

[0008] The first step is to establish a dynamic model of the space dual-arm robot, the contact process, and the target to be captured;

[0009] The second step is to design a path planning algorithm based on B-spline curves to ensure that the robot's end effector arrives at the target synchronously.

[0010] The third step is to consider the synchronous capture of external forces by the dual-arm robot and design an impedance model to achieve compliant contact control.

[0011] The fourth step is to use kinematic and geometric relationships to decompose the synchronous contact force on the target into internal and external forces;

[0012] The fifth step is to consider the internal forces acting on the target when both arms capture it simultaneously and design an adaptive internal force tracking impedance control strategy.

[0013] Beneficial effects:

[0014] This invention simultaneously considers issues such as synchronous motion planning of dual arms, unknown contact environment, compliant operation of the robot system, and target holding force control, and proposes a composite adaptive compliant control scheme for a space dual-arm robot. The proposed capture control scheme avoids the time delay caused by traditional dual-arm master-slave operation, overcomes the limitation of a single control scheme in simultaneously ensuring safe contact between the target and the robot, and can adaptively adjust control parameters according to different target capture tasks. It can be used for compliant dual-arm capture control tasks of on-orbit targets in real-world scenarios.

[0015] The method of this invention can simultaneously achieve synchronous movement of both arms to the target point, adaptive constant force tracking of the target's internal force, and compliant contact control of the space dual-arm robot body, adapting to complex and unknown contact tasks, and providing theoretical and technical support for the synchronous capture of on-orbit targets by space dual-arm robots. Attached Figure Description

[0016] Figure 1 A flowchart of a composite adaptive compliant control method for synchronous target acquisition by a space dual-arm robot;

[0017] Figure 2 This invention presents a composite adaptive compliant control scheme for a space dual-arm robot.

[0018] Figure 3 This is the curve showing the change in internal force on the left side of the target to be captured according to the present invention;

[0019] Figure 4 This is the curve showing the change in internal force on the right side of the target to be captured according to the present invention;

[0020] Figure 5 The curve showing the change in contact force on the left arm of the space robot of the present invention;

[0021] Figure 6 The curve showing the change in contact force on the right arm of the space robot of the present invention;

[0022] Figure 7 The curve showing the damping coefficient variation during the internal force control of the left arm of the space robot in this invention;

[0023] Figure 8 The curve showing the change of damping coefficient in the internal force control of the right arm of the space robot of the present invention. Detailed Implementation

[0024] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0025] This invention provides a composite adaptive compliant control method for synchronous target acquisition by a space dual-arm robot. Addressing the problem of synchronous compliant acquisition control of a dual-arm robot where the target's pose and geometric characteristics are measurable, the method first establishes a dynamic model of the space dual-arm robot, the target to be acquired, and the contact process. Next, an end-effector path planning algorithm based on B-spline curves is designed to ensure that the ends of the dual-arm robots simultaneously and synchronously reach the target surface. Subsequently, to ensure the operational safety of the space dual-arm robot system, an impedance control strategy is designed to achieve compliant acquisition. Second, the resultant force on the target is decomposed into internal and external forces using kinematic and geometric relationships. Finally, considering the unknown and changing target contact characteristics, an impedance control strategy based on adaptive internal force tracking is designed.

[0026] Figure 1This is a flowchart of a composite adaptive compliant control method for synchronous target acquisition in a space dual-arm robot. See below for reference. Figure 1 Describe the control process of this method. For example... Figure 1 As shown, the method includes:

[0027] The first step is to establish a dynamic model of the space dual-arm robot, the contact process, and the target to be captured;

[0028] The general coupled dynamics model of the space dual-arm robot is established using the Kane equations as follows:

[0029] ,

[0030] in, The system inertia matrix includes the coupling effect of the base and the two arms. This is a nonlinear term in the dynamic model. To actively control force and torque, The resultant force of the collision or contact at the ends of the two arms. Indicates robotic arm The contact force received, The Jacobian matrix represents the spatial dual-arm robot system. Represents the generalized velocity of the space dual-arm robot system; the superscript "T" indicates the transpose of the matrix;

[0031] During implementation, a dual six-degree-of-freedom robotic arm system was used for simulation experiments. The two robotic arms had identical parameters; therefore, the system parameters for a single robotic arm are given below:

[0032]

[0033] The length of the base at the "#" mark should actually be the position vector of the connection point between arm 1 and the base within the base. .

[0034] robotic arm Contact force with the target to be captured The mathematical model expression is:

[0035] ,

[0036] in, Indicates environment The damping coefficient matrix, Indicates environment The stiffness coefficient matrix, , They represent robotic arms The pose and velocity vector of the end effector. , These represent the target to be captured and the robotic arm, respectively. The actual pose and velocity vector at the point of contact.

[0037] The damping coefficient and stiffness coefficient mentioned above are referred to as environmental parameters. In one embodiment, three sets of environmental parameters are set, with the left and right arms having the same contact environment. The system switches to one set of environmental parameters every 10 seconds.

[0038] ① Damping coefficient stiffness coefficient ;

[0039] ② Damping coefficient stiffness coefficient ;

[0040] ③ Damping coefficient stiffness coefficient .

[0041] The dynamic model of the target to be captured can be expressed as:

[0042] ,

[0043] in, The inertia matrix representing the target. The motion coupling matrix of the target is represented. , This indicates the velocity and acceleration of the target's motion. It is the resultant force of the contact forces between the arms and the target in the target's coordinate system, expressed as:

[0044] ,

[0045] in, It is a full-rank capture matrix that can be jointly determined by the robotic arm's motion state and the target's geometric information.

[0046] The second step is to design a motion planning algorithm so that the end arms of the dual-arm robot can simultaneously and synchronously reach the desired pose.

[0047] This step includes: [on a given robotic arm] After determining the initial pose, desired pose, and poses of several control points along the way, the end effector pose is planned in real-time using B-spline curves to achieve synchronous arrival of both arms at the desired pose within a specified time. Specifically, this process includes: robotic arms... exist Real-time motion trajectory on a certain degree of freedom at a given moment The expression is:

[0048] ,

[0049] in, No. One control point, Indicates the number of control points; express The B-spline basis functions can be solved recursively. , and The start and end times of the planning are defined. The planning time for all robotic arms is... and Simultaneously, the end effectors of the dual-arm robot can move synchronously to the target to be captured. In a specific simulation case, the following settings are configured... , Number of control points .

[0050] The third step is to consider the synchronous capture of external forces by the dual-arm robot and design an impedance model to achieve compliant contact control.

[0051] To ensure the safety of the dual-arm robot body system during the capture process, it is necessary to monitor the robotic arms. Apply compliance control algorithms to ensure It will not suddenly increase in size and damage the entire spacecraft system. The desired pose is achieved by modifying the following impedance control expression:

[0052] ,

[0053] in, , , These represent the matrices of the desired inertia coefficient, damping coefficient, and stiffness coefficient of the impedance controller i, respectively. , , This represents the pre-defined desired pose, velocity, and acceleration of robotic arm i. , , This represents the reference pose, velocity, and acceleration of robotic arm i during actual execution; assuming the robot has a perfect joint controller, then it is considered... , , In one embodiment, considering only motion control in the y-direction, the desired coefficient of inertia, damping coefficient, and stiffness coefficient are set as follows: , , .

[0054] The fourth step is to use kinematic and geometric relationships to decompose the synchronous contact force on the target to be captured into internal and external forces;

[0055] Contact force on the ends of both arms The same force will be applied to the target to be captured, and the force applied to the target to be captured can be divided into external forces. and internal strength Two components:

[0056] ,

[0057] in, Represents the capture matrix The false rebellion, It is the resultant force of the contact forces between the arms and the target in the target's coordinate system. It is a full-rank column matrix whose columns span 10 ... Zero space, It is the internal force acting on the center of mass of the target; It is the external force vector applied by the end effector, used to change the motion state of the target; It is an internal force acting on the contact point of the target, which does not change the target's motion state and is used to ensure that the target is safely and securely clamped.

[0058] Utilizing the resultant contact force at the ends of both arms We can obtain the analytical expressions for the internal and external forces:

[0059] ,

[0060] in, Represents an identity matrix of appropriate dimension;

[0061] The fifth step is to consider the internal forces acting on the target when both arms capture it simultaneously, and design an adaptive internal force tracking impedance control strategy.

[0062] Without loss of generality, we will now consider only the design of the adaptive internal force tracking controller in the y-direction; the design method for controllers in other directions is the same. The adaptive variable damping impedance control law used is as follows:

[0063] ,

[0064] in, This represents the internal force acting on the target to be captured. This represents the desired clamping force on the target to be captured, which is also the desired contact internal force. Indicates the internal force tracking error. , This represents the pre-set desired mass coefficient and damping coefficient. , These represent the corrections made by the impedance model to the robot's end effector acceleration and velocity, respectively. express The correction for the damping coefficient at time step is calculated using the following adaptive law:

[0065] ,

[0066] in, and They represent Time and Auxiliary variables at time, Indicates the simulation step size. express Adjust speed constantly express The internal force tracking error at any given moment It is an adjustment coefficient. Expected quality coefficient. The initial damping coefficient The expected internal force on the left side of the target is The expected internal force on the right is adjustment coefficient Simulation step size .

[0067] The designed composite adaptive compliant control scheme for synchronous target acquisition of a dual-arm space robot is based on... Figure 2 Simulation verification was performed, based on Figure 3 and Figure 4 It can be seen that after both arms reach the target acquisition point simultaneously, despite changes in environmental parameters, the absolute value of the bearing force on both sides of the target remains at 5N; Figure 5 and Figure 6 It can be seen that the contact force of the left and right arms changes with environmental parameters, but always remains within 80N; according to Figure 7 and Figure 8 It can be seen that the damping parameters can be adaptively adjusted as the task is executed to ensure constant tracking of internal forces.

[0068] The contents not described in detail in this specification are prior art known to those skilled in the art. Those skilled in the art will readily understand that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the invention. Any modifications, equivalent substitutions, and improvements 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 composite adaptive compliant control method for synchronous target acquisition by a space dual-arm robot, characterized in that, Includes the following steps: The first step is to establish a dynamic model of the space dual-arm robot, the contact process, and the target to be captured; The second step, to ensure the robot's end effector arrives at the target synchronously, involves designing a path planning algorithm based on B-spline curves; this second step includes: the robotic arm exist Real-time motion trajectory on a certain degree of freedom at a given moment The expression is: in, Indicates the first One control point, Indicates the number of control points; express The B-spline basis functions are solved recursively. , and The start and end times of the planning are defined, and the planning time for all robotic arms is... and At the same time, it can achieve synchronous movement of the end effector of the dual-arm robot to the target to be captured; The third step is to consider the synchronous capture of external forces by the dual-arm robot and design an impedance model to achieve compliant contact control. The fourth step is to use kinematic and geometric relationships to decompose the synchronous contact force on the target into internal and external forces; Fifth, considering the internal forces acting on the target when both arms capture it simultaneously, an adaptive internal force tracking impedance control strategy is designed. The adaptive internal force tracking impedance control strategy is as follows: in, This represents the internal force acting on the target to be captured. This represents the desired clamping force on the target to be captured, which is also the desired contact internal force. Indicates the internal force tracking error. , This represents the pre-set desired mass and damping coefficient. , These represent the corrections made by the impedance model to the robot's end effector acceleration and velocity, respectively. express The correction for the damping coefficient at time step is calculated using the following adaptive law: in, and They represent Time and Auxiliary variables at time, Indicates the simulation step size. express Adjust speed constantly express The internal force tracking error at any given moment It is an adjustment coefficient.

2. The composite adaptive compliant control method for synchronous target acquisition by a dual-arm space robot according to claim 1, characterized in that: The first step includes: The general coupled dynamics model of the space dual-arm robot is established using the Kane equations as follows: in, The system inertia matrix includes the coupling effect of the base and the two arms. This is a nonlinear term in the dynamic model. To actively control force and torque, The resultant force of the collision or contact at the ends of the two arms. Indicates robotic arm The contact force received, The Jacobian matrix represents the spatial dual-arm robot system. Represents the generalized velocity of the space dual-arm robot system; the superscript "T" indicates the transpose of the matrix; robotic arm Contact force with the target to be captured The mathematical model expression is: in, Indicates environment The damping coefficient matrix, Indicates environment The stiffness coefficient matrix, , They represent robotic arms The pose and velocity vector of the end effector. , These represent the target to be captured and the robotic arm, respectively. The actual pose and velocity vector at the point of contact.

3. The composite adaptive compliant control method for synchronous target acquisition by a dual-arm space robot according to claim 2, characterized in that, The damping coefficient and stiffness coefficient are called environmental parameters. Three sets of environmental parameters are set. The contact environment of the left and right arms is the same. The system switches to one of the environmental parameters every 10 seconds. ① Damping coefficient stiffness coefficient ; ② Damping coefficient stiffness coefficient ; ③ Damping coefficient stiffness coefficient .

4. The composite adaptive compliant control method for synchronous target acquisition by a dual-arm space robot according to claim 2, characterized in that: The first step also includes: The dynamic model of the target to be captured is established as follows: in, The inertia matrix representing the target. The motion coupling matrix of the target is represented. , This indicates the velocity and acceleration of the target's motion. It is the resultant force of the contact forces between the arms and the target in the target's coordinate system, expressed as: in, It is a full-rank capture matrix, determined jointly by the robotic arm's motion state and the target's geometric information.

5. The composite adaptive compliant control method for synchronous target acquisition by a dual-arm space robot according to claim 1, characterized in that: The second step includes: In a given robotic arm After determining the initial pose, desired pose, and poses of several control points that need to be passed through, the end pose is planned in real time using B-spline curves to achieve synchronous arrival of both arms at the desired pose within a specified time.

6. The composite adaptive compliant control method for synchronous target acquisition by a dual-arm space robot according to claim 2, characterized in that: The third step includes: For robotic arm A compliant control algorithm is applied, and the desired pose is modified using the following impedance control expression: in, , , These represent the matrices of the desired inertia coefficient, damping coefficient, and stiffness coefficient of the impedance controller i, respectively. , , This represents the pre-defined desired pose, velocity, and acceleration of robotic arm i. , , This represents the reference pose, velocity, and acceleration of the robotic arm i during its actual execution.

7. The composite adaptive compliant control method for synchronous target acquisition by a dual-arm space robot according to claim 6, characterized in that: The fourth step includes: Contact force on the ends of both arms The same force will be applied to the target to be captured, and the force applied to the target to be captured is divided into external forces. and internal strength Two components: in, Represents the capture matrix The false rebellion, It is the resultant force of the contact forces between the arms and the target in the target's coordinate system. It is a full-rank column matrix whose columns span 10 ... Zero space, It is the internal force acting on the center of mass of the target; It is the external force vector applied by the end effector, used to change the motion state of the target; It is an internal force acting on the contact point of the target, which does not change the target's motion state and is used to ensure that the target is safely and securely clamped. Utilizing the resultant contact force at the ends of both arms The analytical expressions for the internal and external forces are obtained as follows: in, Represents an identity matrix of appropriate dimensions.

8. The composite adaptive compliant control method for synchronous target acquisition by a dual-arm space robot according to claim 1, characterized in that: Expected quality coefficient The initial damping coefficient The expected internal force on the left side of the target is The expected internal force on the right is adjustment coefficient Simulation step size .

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