Research On Path Planning And Control Method For Free-floating Space Robot

With the development of space science and technology,the free-floating space robot is playing an increasingly important role in the field of space on-orbit service.Space robots substitute for astronauts in more and more tasks to perform dangerous extravehicular tasks,and also expand the working space of the task,thus achieve the purpose of improving the efficiency of task execution and reducing the cost of space task.Moreover,the free-floating space robot path planning and control method is the basis for successful completion of on-orbit service task,and is also the key technology to be solved.This paper whose background is the free-floating space robot does research on path planning,path tracking control and attitude control.The main research contents are as follows:Considering the problem of the large disturbance of the traditional path planning method to the attitude of the base satellite,a path planning method for the free-floating space robot based on control variable parameterization is proposed.And,a complete theoretical convergence proof is given,which solves the problem that the method of control variable parameterization is lack of theoretical convergence.First,the problem of point to point path planning in task space is described as an optimal control problem which meets the boundary constraints at the initial and terminal moments and the path constraints in the process of motion,and simultaneously minimizes the objective function of the disturbance of the base satellite.Then,the optimal control problem is discretized by the control variable parameterization method,and then transformed into the nonlinear programming problem and solved.Finally,the optimal path of the free floating space robot endeffector is obtained.Simulation results show that the proposed method effectively reduces the attitude disturbance of the base satellite and has higher accuracy.In order to improve the computing efficiency of path planning and meet the real-time requirement of path planning,the free-floating space robot path planning method based on Multiple-Phase Gauss pseudospectral method and hp-adaptive Gauss pseudospectral method is designed.The planning time is segmented by Multiple-Phase Gauss pseudospectral method,and the Jacobian matrix is transformed into a sparse array,thus the efficiency of the solution is improved,but it still can not achieve the purpose of real time.Therefore,the path planning method of space robot based on hp-adaptive Gauss pseudospectral method is further proposed,and the hp-adaptive decision variable is designed which can adaptively select the time unit subdivision or increase the number of matching points on the time unit without satisfying the precision requirement,thus the calculation efficiency is further improved.At the same time,the theoretical convergence proof of hp-adaptive Gauss pseudospectral method is given,And,a complete theoretical convergence proof is given,which solves the problem that hp-adaptive Gauss pseudospectral method is lack of theoretical convergence.The simulation results show that the algorithm can meet the real-time requirements.The trajectory tracking control method based on nonlinear model predictive control is proposed for the free-floating space robot system with obstacles in motion space,which solves the problem of avoiding real time obstacles in the trajectory tracking process.This method takes the minimum tracking error as the performance index at every moment,and satisfies the constraint conditions of the path constraint and obstacle constraint,and optimizes a set of finite time domain optimal control sequences.The first control variable of the control sequence is acted on the system as the actual control variable at the time,and the optimization is repeated at the next time.At the same time,an inequality constraint used to describe the obstacle avoidance in the task space is proposed,and it is considered as a constraint condition in the trajectory tracking control to achieve the purpose of avoiding the obstacles by the free-floating space robot.Simulation results show that the proposed method can effectively track the tasks and avoid obstacles.The attitude controller based on adaptive sliding mode variable structure control is designed for the free-floating space robot system with uncertain moment of inertia and external disturbance torque.The designed controller does not contain the moment of inertia matrix,and the real-time parameter updating strategy is introduced to estimate the disturbance torque,which overcomes the shortcomings of the traditional sliding mode controller which needs to obtain the moment of inertia and the upper bound of the disturbance moment.In addition,considering the input saturation of the system,another adaptive sliding mode variable structure controller is designed to ensure the stability of the closed loop system under the presence of input saturation.The simulation results verify the validity of the proposed method.