The Coordinated Compliance Control Of Dual-arm Space Robot For Capturing Tumbling Target

With the deepening of space exploration,the number of failed or decommissioned spacecraft has increased year by year.Those spacecraft do not have a functioning attitude control,so in many cases they will be tumbling due to the transfer of residual angular momentum from their control systems.The tumbling spacecraft not only waste valuable orbital space resources,but also threaten the safety of on-orbit spacecraft.Therefore,the demand for the capturing tumbling spacecraft is increasingly urgent.Using dual-arm space robot can precisely control and operate the spacecraft,which is conducive to the spacecraft recycling.However,physical contact happens during the target capture phase.The excessive contact force caused by the collision may lead to the damage of the contact interface,and may also disturb the target,causing the target to escape.In addition,the key to successful capture is to use contact force to reduce the angular velocity of the tumbling target,which helps the space robot to track the target's pose in the capturing task.Therefore,the coordinated force compliance must be achieved in the process of capturing tumbling target.This research comes from the project of CASC named"Development of Space Manipulator Control System for Capturing the Hovering Aerocraft".In this paper,the free-floating dual-arm space robot is taken as the research object.Aiming at the tumbling target capture task,the key technologies including the dynamic modeling method,the coordinated compliance control strategy under different contact states,and the control optimization of base attitude adjustment are studied.The simulation and experiments are further designed to verify the effectiveness of the proposed technologies.The main research includes:Firstly,for the case of fixed contact between the end-effector and the tumbling target,the coordinated compliant control method of the dual-arm space robot is studied.The dual-arm space robot dynamics model is established at first.The base acceleration term in the dynamics model is eliminated and the decoupling of joint motion and base motion is completed.Combined with the tumbling target dynamic equation,the unified dynamic model is constructed,which lays the foundation for the control strategy design.Based on the unified dynamic model,the impedance control algorithm is designed to achieve a precise friction control,which can reduce the target angular velocity steadily.Then,for the case of sliding contact between the end-effector and the tumbling target,the coordinated compliant control method of the dual-arm space robot is studied.Based on the LuGre model,the contact dynamic model between the arm and the tumbling target is established.The mathematical expression of the contact force is obtained.In addition,the relationship between contact force and relative motion is analyzed.Based on the unified dynamic model and the contact dynamic model,the hybrid impedance control algorithm is designed to achieve the decoupling of the normal pressure and the tangential friction force,thus ensuring the compliance between the dual-arm space robot and the target.Considering the uncertainties of the capture system parameters,an adaptive control algorithm based on RBF network is designed to compensate the control errors caused by the system parameters errors and ensure the control accuracy.After that,aiming at the target capture task under microgravity,the control optimization of base attitude adjustment is studied.The angular momentum and the linear momentum of the free-floating system(with the target)are conservative without the influence of external forces.The target motion term is eliminated and the mapping relationship between base motion and joint motion is obtained.The system's extended Jacobian matrix is obtained by combining the base motion equation and the generalized Jacobian matrix.In this way,coordinated planning of the base and the arms during the tumbling target capture process can be realized.The zero-space Jacobian matrix of the dual-arm space robot is established,and particle swarm optimization(PSO)algorithm is used to optimize the joint torque without affecting the target capture task.Finally,the experiment of the coordinated compliance control of dual-arm space robot for capturing tumbling target is discussed.Reconstructing the ground microgravity air flotation experimental platform,and the experiment of the dual-arm space robot capturing tumbling target in sliding contact mode is designed.The effectiveness and practicability of the proposed algorithms are verified by analyzing experimental data.