Research On Autonomous Control Strategy Of Space Robot For Target Capturing

In the past 40 years,space robots play a very important role in space exploration.On-orbit service technology is conducive to the maintenance of failed satellites' on-orbit life and the safe derailment of abandoned satellites.Based on this background,the autonomous control strategies of space robots at different capturing stages are studied in-depth in this paper.Furthermore,a ground verification system for space manipulator in the loop is established,and a series of target capturing experiments are conducted.The main research contents include the following aspects:Firstly,the base attitude maintenance control and end-effector orientation adjustment control for a space robot at the target observation stage are studied.The dynamic coupling between the manipulator and the base is utilized to achieve base related tasks.The motion control tasks at this stage include base attitude maintenance/adjustment,end-effector orientation adjustment,end-effector position stabilization related optimization task,constraint tasks.The task compensation in the joint space is utilited to derive the hybrid task priority motion planning algorithm in this article,which is designed to adjust the viewing angle of hand-eye-camera with multi-task.Besides,the algorithmic singularity can be avoided.Furthermore,the high priority task accuracy can be guaranteed by the implemation of the low-priority task in the weighted pesduinverse null-space of the high priority task,so that the safe operation ability under multi-constraint can be improved.The integrated numerical simulation platform is established to verify the effectiveness of the motion control algorithm.As for the satellite disturbance issue during the movement of space robots at the target approaching stage,the local optimization control law of reaction torque acted on the base's centroid is studied.The position and orientation of the end-effector should be controlled.Firstly,the analytical expression of the reaction torque is derived based on newton-euler equation,and the analytical expression shares the same formulation between space robots with different pedestal movements,the discretization solution is used to convert the acceleration-level reaction torque optimization into a control law that optimizes the reaction torque by tracking the desired joint angle.For a free-floating space manipulator,the analytical expression of the joint angular acceleration-free of the reaction torque can be obtained by using the six-dimensional space vector method,thus,the null-space based base disturbance algorithm for the free-floating space robot can be derived.Simulation results show that the proposed algorithm can optimize the reaction torque in the motion of the manipulator.As for the force control issue in the process of target capturing,the task priority impedance control is studied.For the nozzle capturing task,it is necessary to define that the impedance control in the position direction is a high priority task,the impedance control in the attitude direction is a low priority task,and the joint impedance control is performed in the null space of the main task to buffer the reaction force/torque between the manipulator and satellite base.Before the locking mechanism is locked,the capture device needs to keep track of the target trajectory while ensuring compliant contact,and the space manipulator is in the Cartesian impedance control mode.During the locking process,the locking mechanism moves in accordance with the target,the space manipulator is in the Cartesian zero-force control mode,and the adaptive force controller is studied to improve the force control performance in the capturing process due to inaccurate reference position.The effectiveness of the algorithm is verified by the actual simulation of the target capturing task.In order to verify the motion control and force control algorithms for target capturing,a space robot ground experiment system with nine degrees of freedom turntable and seven degrees of freedom space manipulator is built in this article.The characteristics of this system are: the system has good scalability,the ground verification can be applied to verify target capturing tasks under different conditions with appropriate modification,the space manipulator in the platform is a real manipulator hardware system,the simulator can realistically simulate data communication,the compliance control strategy can be verified.Furthermore,the ground verification experiments for target capturing show that: the hybrid task-priority motion control law can achieve base attitude mainteance control and end-effector orientation adjustment,discrete control law of space robot can realize the reaction torque optimization control,and task priority compliance control strategy can ensure safe and autonomous capturing.