Composite self-adaptive compliance control method for synchronously capturing target by space double-arm robot

Abstract

The invention relates to a composite self-adaptive compliant control method for synchronously capturing a target by a space double-arm robot. The method comprises the following steps: firstly, establishing a dynamic model of the space double-arm robot, a target to be captured and a contact process; in order to ensure that the tail ends of the two arms simultaneously reach the surface of the to-be-captured target, a tail end path planning algorithm based on a B spline curve is designed; then, in order to reduce impact borne by the double-arm robot system in the capturing process, an impedance control strategy is designed according to contact force borne by the tail ends of the double mechanical arms; secondly, the resultant force borne by the target is decomposed into internal force and external force through the kinematics and geometrical relationship; and finally, designing a self-adaptive internal force tracking impedance control strategy in order to prevent capture failure or target damage caused by simultaneous target capture by two arms. Aiming at a task scene in which the space double-arm robot synchronously captures the target, the problem that the space double-arm robot system is subjected to too large rigid impact and too large / too small clamping force, so that the target is damaged or clamping fails can be solved.

Description

Technical Field

[0001] The present invention belongs to the field of compliant control of space dual-arm robots, and particularly relates to a composite adaptive compliant control method for synchronous target capture of a space dual-arm robot. Background Art

[0002] Space robots can perform on-orbit operation tasks such as satellite maintenance, space debris cleaning, and on-orbit assembly. They are important tools and means for extending the service life of spacecraft, releasing orbital resources, and enhancing space safety. Among them, the dual-arm robot system, due to its collaborative advantages and redundancy characteristics, can solve the limitations of traditional single-arm systems in terms of load, working range, and operation flexibility, and plays an irreplaceable role in future space missions. However, when the dual-arm robot captures a target, a closed-chain constraint is formed, causing the robot system to receive contact / collision forces and simultaneously generate capture internal forces on the target surface, which not only affects the safety of the dual-arm robot system but also threatens the safety of the target itself. Therefore, how to achieve synchronous motion of the two arms and ensure safe and compliant contact between the target and the robot system is an urgent and challenging task.

[0003] Regarding the process of a space dual-arm robot capturing a target, existing research mostly focuses on single issues, such as dual-arm synchronous motion planning (CN110104216A), cooperative motion control (CN109606753A), constant-coefficient impedance control based on internal force decomposition (CN111268182A; CN109015658A), etc. There are few studies that consider these issues simultaneously. In addition, considering the complexity of the capture task, especially for the non-cooperative target capture scenario, the contact environment is usually unknown and changing. Therefore, an adaptive variable impedance control scheme needs to be introduced. The literature (Jiao Chunting et al., "Adaptive Hybrid Impedance Control for Dual-Arm Cooperative Manipulation with Object Uncertainty" Automatica, Vol. 140, p. 110232, 2022) simultaneously considered the motion planning and internal force tracking control problems and proposed a master-slave-based motion planning and adaptive constant force control algorithm. However, the master-slave design will cause a delay between the left and right arm motions, and this study did not control the impact on the dual-arm robot system, which will bring uncertain risks to the robot system.

[0004] In summary, the current process of a space dual-arm robot synchronously capturing a target faces the following three technical problems to be further solved: (1) The real-time problem of the dual-arm motion trajectory; (2) The unknown and changing contact environment may degrade the performance of traditional controllers, resulting in target damage; (3) The contact impact at the moment of capturing the target may cause the dual-arm robot system to become unstable. Summary of the Invention

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

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

[0007] A composite adaptive compliant control method for a space dual-arm robot to synchronously capture a target, comprising the following steps:

[0008] The first step is to establish the dynamic models 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 end reaches the target to be captured synchronously;

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

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

[0012] The fifth step is to consider the internal forces received by the target during the simultaneous capture of the two arms and design an adaptive internal force tracking impedance control strategy.

[0013] Beneficial effects:

[0014] The present invention simultaneously considers issues such as the synchronous motion planning of the two arms, unknown contact environments, compliant operation of the robot system, and clamping force control of the target, and proposes a composite adaptive compliant control scheme for the space dual-arm robot. The capture control scheme proposed by the present invention avoids the time delay caused by the traditional master-slave operation of the two arms, overcomes the limitation that a single control scheme cannot ensure the safe contact of the target and the robot at the same time, and can adaptively adjust the control parameters according to different target capture tasks, and can be used for the dual-arm compliant capture control task of the on-orbit target in the actual scenario.

[0015] The method of the present invention can simultaneously achieve the synchronous movement of the two arms to the target point, the adaptive constant force tracking of the target internal force, and the compliant contact control of the space dual-arm robot body, adapt to complex and unknown contact tasks, and provides theoretical and technical support for the space dual-arm robot to synchronously capture the on-orbit target. Description of the Drawings

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

[0017] Figure 2 It is the composite adaptive compliant control scheme of the space dual-arm robot designed by the present invention;

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

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

[0020] Figure 5 It is the contact force change curve of the left arm of the space robot in the present invention;

[0021] Figure 6 It is the contact force change curve of the right arm of the space robot in the present invention;

[0022] Figure 7 It is the damping coefficient change curve in the internal force control of the left arm of the space robot in the present invention;

[0023] Figure 8 It is the damping coefficient change curve in the internal force control of the right arm of the space robot in the present invention. Detailed implementation manners

[0024] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present disclosure can be more thoroughly understood and the scope of the present disclosure can be fully conveyed to those skilled in the art.

[0025] The present invention provides a composite adaptive compliant control method for synchronous capture of a target by a space dual-arm robot. For the problem of synchronous compliant capture control of a dual-arm robot with measurable target pose and geometric characteristics, first, a dynamic model of the space dual-arm robot, the target to be captured, and the contact process is established; next, a terminal path planning algorithm based on B-spline curves is designed to enable the terminals of the dual-arm robot to reach the target surface simultaneously and synchronously; subsequently, to ensure the operation safety of the space dual-arm robot system, an impedance control strategy is designed to achieve compliant capture; secondly, the resultant force received by the target is decomposed into internal force and external force by 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 1It is a flow chart of a composite adaptive compliant control method for synchronous capture of a target by a space dual-arm robot. The following will refer to Figure 1 to describe the control process of this method. As Figure 1 shown, this method includes:

[0027] In the first step, establish the dynamic models of the space dual-arm robot, the contact process, and the target to be captured;

[0028] Use Kane's equation to establish the general coupled dynamic model of the space dual-arm robot as:

[0029] ,

[0030] where, is the system inertia matrix including the coupling effect of the base and the two arms, is the non-linear term in the dynamic model, is the active control force and torque, is the resultant force of collision or contact at the end of the two arms, represents the mechanical arm subjected to the contact force, represents the Jacobian matrix of the space dual-arm robot system, represents the generalized velocity of the space dual-arm robot system; the superscript "T" represents the transpose of the matrix;

[0031] During the implementation process, a double six-degree-of-freedom robotic arm system is used for simulation experiments. The parameters of the two robotic arms are the same. Therefore, only the system parameters of a single robotic arm are given below:

[0032] where the length of the matrix at the "#" position should actually be the position vector of the connection point between the first arm and the matrix in the matrix, which is .

[0033] The mathematical model expression of the contact force between the robotic arm and the target to be captured is:

[0034] ,

[0035] where, represents the damping coefficient matrix of the environment , represents the stiffness coefficient matrix of the environment , , respectively represent the pose and velocity vectors of the end effector of the robotic arm , , respectively represent the target to be captured and the robotic arm The actual pose and velocity vector at the contact point.

[0036] The above damping coefficient and stiffness coefficient are called environmental parameters. In one embodiment, three sets of environmental parameters are set. The contact environments of the left arm / right arm are the same, and one set of environmental parameters is switched to every 10 seconds:

[0037] ① Damping coefficient , stiffness coefficient ;

[0038] ② Damping coefficient , stiffness coefficient ;

[0039] ③ Damping coefficient , stiffness coefficient .

[0040] The dynamic model of the target to be captured can be expressed as:

[0041] ,

[0042] where, represents the inertia matrix of the target, represents the motion coupling matrix of the target, 、 represent the velocity and acceleration of the target's motion, is the resultant force of the contact forces between the two arms and the target in the target body coordinate system, and the expression is:

[0043] ,

[0044] where, is a full row rank capture matrix, which can be jointly determined by the motion state of the robotic arm and the geometric information of the target.

[0045] Second, design a motion planning algorithm to make the ends of the two-arm robot reach the desired pose simultaneously and synchronously.

[0046] This step includes: After the initial pose, desired pose, and several control point poses that need to be passed through in the given robotic arm , the end pose is subjected to real-time path planning using a B-spline curve to achieve synchronous arrival of the two arms at the desired pose within the specified time. Specifically, this process includes: The robotic arm at the real-time motion trajectory of a certain degree of freedom of motion at a moment is

[0047] ,

[0048] where, the A control point, indicating the number of control points; indicating the \(k\)th B-spline basis function, which can be solved recursively; , and define the start time and end time of the plan. When the planning times of all manipulators and are the same, the end effectors of the dual-arm robot can be synchronously moved to the target to be captured. In a specific simulation case, set , , the number of control points .

[0049] Step 3: Considering the external forces received by the dual-arm robot during synchronous capture, design an impedance model to achieve compliant contact control;

[0050] To ensure the safety of the on-orbit dual-arm robot body system during the capture process, it is necessary to apply a compliant control algorithm to the manipulator to ensure that will not suddenly increase and damage the entire spacecraft system. The following impedance control expression is used to modify the desired pose:

[0051] ,

[0052] where , , respectively represent the desired inertia coefficient, damping coefficient, and stiffness coefficient matrix of impedance controller \(i\); , , represent the desired pose, velocity, and acceleration of manipulator \(i\) set in advance, , , represent the reference pose, velocity, and acceleration actually executed by manipulator \(i\); assuming that the robot has a perfect joint controller inside, then it is considered that , , . In an embodiment, only the motion control in the \(y\)-direction is considered, and the set desired inertia coefficient, damping coefficient, and stiffness coefficient are , , .

[0053] Step 4: Use kinematic and geometric relationships to decompose the synchronous contact force received by the target to be captured into internal forces and external forces;

[0054] The contact force received by the end effectors of the dual arms will also be applied to the target to be captured. The force applied to the target to be captured can be divided into external forces and internal forces into two components:

[0055] ,

[0056] wherein, represents the pseudo-inverse of the capture matrix , is the resultant force of the contact forces between the two arms and the target in the target body coordinate system, is a full column rank matrix, and its columns span the null space of is the internal force acting on the centroid of the target; is the external force vector applied by the end effector to change the motion state of the target; is the internal force acting on the contact point of the target, which will not change the motion state of the target and is used to ensure that the target is securely clamped;

[0057] Using the resultant contact force received at the ends of the two arms, the analytical expressions of the internal and external forces can be obtained:

[0058] ,

[0059] wherein, represents the identity matrix of appropriate dimension;

[0060] Step 5: Consider the internal force received by the target to be captured when the two arms capture simultaneously, and design an adaptive internal force tracking impedance control strategy.

[0061] Without loss of generality, only the design of the adaptive internal force tracking controller in a certain y direction will be considered next, and the design methods of the controllers in other directions are the same. The adopted adaptive variable damping impedance control law is as follows:

[0062] ,

[0063] wherein, represents the internal force received by the target to be captured, represents the desired clamping force of the target to be captured, that is, the desired contact internal force, represents the internal force tracking error, , represent the preset desired mass coefficient and damping coefficient, , respectively represent the correction amounts of the impedance model to the acceleration and velocity of the robot end, represents the correction amount of the damping coefficient at time

[0064] ,

[0065] Among them, and respectively represent the moment and the auxiliary variable at the moment, represents the simulation step size, represents the corrected speed at the moment, represents the internal force tracking error at the moment, is an adjustment coefficient. The expected mass coefficient , the initial damping coefficient , the expected internal force on the left side of the target is , the expected internal force on the right side is , the adjustment coefficient , the simulation step size .

[0066] The designed composite adaptive compliant control scheme for the space dual-arm robot to synchronously capture the target is simulated and verified according to Figure 2 . According to Figure 3 and Figure 4 , it can be seen that after the two arms reach the target capture point simultaneously, although the environmental parameters change, the absolute values of the clamping forces on the left and right sides of the target always remain at the level of 5N; from Figure 5 and Figure 6 , it can be seen that the contact forces of the left and right arms will change with the change of environmental parameters and always remain within 80N; according to Figure 7 and Figure 8 , it can be seen that the damping parameters can be adaptively adjusted during the task execution to ensure the constant tracking of the internal force.

[0067] The content not described in detail in the specification of the present invention belongs to the prior art well-known to those skilled in the art. It is easy for those skilled in the art to understand that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A compound adaptive compliant control method for synchronous target capture of a spatial dual-arm robot, characterized in that Including the following steps: First step, establish the dynamic models of the space dual-arm robot, the contact process, and the target to be captured; Second step, to ensure that the end of the robot reaches the target to be captured synchronously, design a path planning algorithm based on B-spline curves; Third step, considering the external forces received during the synchronous capture of the dual-arm robot, design an impedance model to achieve compliant contact control; Fourth step, use kinematic and geometric relationships to decompose the synchronous contact force received by the target into internal and external forces; Fifth step, considering the internal forces received by the target during the simultaneous capture of the two arms, design an adaptive internal force tracking impedance control strategy.

2. The composite adaptive compliant control method for synchronous capture of targets by the spatial dual-arm robot according to claim 1, wherein: The first step includes: Adopt Kane's equation to establish the general coupled dynamic model of the space dual-arm robot as: ， Among them, the system inertia matrix including the base and the coupled action of the two arms, is the non-linear term in the dynamic model, is the active control force and torque, is the resultant collision or contact force at the end of the two arms, represents the manipulator subjected to the contact force, represents the Jacobian matrix of the space dual-arm robot system, represents the generalized velocity of the space dual-arm robot system; the superscript "T" represents the transpose of the matrix; Robotic arm Contact force with the target to be captured The mathematical model expression is as follows: ， Among them, represents the damping coefficient matrix of the environment , represents the stiffness coefficient matrix of the environment , , and respectively represent the pose and velocity vector of the end effector of the robotic arm , and respectively represent the actual pose and velocity vector at the contact point between the target to be captured and the robotic arm 3. The compound adaptive compliant control method for synchronous target capture of the spatial dual-arm robot according to claim 2, wherein The damping coefficient and stiffness coefficient are called environmental parameters. A total of three groups of environmental parameters are set. The contact environments of the left arm and the right arm are the same, and switch to one of the groups of 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 capture of the spatial dual-arm robot according to claim 2, characterized in that: The first step also includes: Establish the dynamic model of the target to be captured as follows: ， Among them, represents the inertia matrix of the target, represents the motion coupling matrix of the target, , represent the velocity and acceleration of the target motion, is the resultant force of the contact forces between the two arms and the target in the target body coordinate system, and the expression is: ， Among them, is a full row rank capture matrix, which is jointly determined by the manipulator motion state and the target geometric information.

5. The composite adaptive compliant control method for synchronous target capture of the spatial dual-arm robot according to claim 1, characterized in that: The second step includes: After the initial pose, desired pose, and several control point poses that need to be passed through in the middle of a given robotic arm are given, the end pose performs real-time path planning using a B-spline curve 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 capture of the spatial dual-arm robot according to claim 5, characterized in that: The second step includes: the robotic arm At the real-time motion trajectory on a certain degree of freedom of motion at a moment The expression is: ， Among them, represents the th control point, represents the number of control points; represents times the B-spline basis function, which is solved recursively; , and define the start time and end time of the plan. When the planning times of all manipulators and are the same, the end points of the dual-arm robot can move synchronously to the target to be captured.

7. The compound adaptive compliance control method for synchronous target capture of the spatial dual-arm robot according to claim 2, wherein: The third step includes: For the robotic arm Apply a compliance control algorithm and modify the desired pose using the following impedance control expression to achieve it: ， Among them, , , respectively represent the desired inertia coefficient, damping coefficient, and stiffness coefficient matrix of the impedance controller i; , , represent the desired pose, velocity, and acceleration of the robotic arm i set in advance, , , represent the reference pose, velocity, and acceleration actually executed by the robotic arm i.

8. The compound adaptive compliant control method for synchronous target capture of the spatial dual-arm robot according to claim 7, characterized in that: The fourth step includes: Contact forces received at the ends of the two arms will also be applied to the target to be captured. The forces applied to the target to be captured are divided into external forces and internal forces with two components: ， wherein, represents the pseudo-inverse of the capture matrix , is the resultant force of the contact forces of the two arms and the target in the target body coordinate system, is a full column rank matrix, and its columns span the null space of is the internal force acting on the centroid of the target; is the external force vector applied by the end effector to change the motion state of the target; is the internal force acting on the contact point of the target, which does not change the motion state of the target and is used to ensure that the target is securely clamped. Using the contact resultant force received at the ends of the two arms , the analytical expressions of the internal and external forces are obtained: ， Among them, represents an identity matrix of an appropriate dimension.

9. The composite adaptive compliant control method for synchronous target capture of the spatial dual-arm robot according to claim 1, characterized in that: The fifth step includes: The adaptive internal force tracking impedance control strategy is as follows: ， Among them, represents the internal force received by the target to be captured, represents the desired clamping force of the target to be captured, that is, the desired contact internal force, represents the internal force tracking error, 、 represent the preset desired mass and damping coefficient, 、 respectively represent the correction amounts of the impedance model to the acceleration and velocity of the robot end, represents the correction amount of the damping coefficient at time which is calculated by the following adaptive law: ， Among them, and respectively represent time and the auxiliary variable at time, represents the simulation step size, represents the corrected speed at time, represents the internal force tracking error at time, is a regulation coefficient.

10. The composite adaptive compliant control method for synchronous capture of a target by a spatial dual-arm robot according to claim 9, characterized in that: Expected quality coefficient , initial damping coefficient , expected internal force on the left side of the target is , expected internal force on the right side is , adjustment coefficient , simulation step size .

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