Research On Trajectory Planning And Trajectory Tracking Of Free-floating Space Robot

With the deepening of human exploration for space,the outer space mission needed to be performed have become more complex and diverse.Using space robot instead of aerospace workers in some space tasks can significantly reduce the risk of astronauts working in unknown environment and protect their life safety.Also,the reasonable use of space robot can greatly improve the efficiency and quality of the tasks.Therefore,with the development of aerospace industry,space robot will play an important role in reducing the maintenance cost of space equipment,ensuring the safety of astronauts,and promoting the industrialization of space technology.Free-Floating Space Robot is a special type of space robot.Its distinctive feature is the underactuation of the base compared with fixed-base robot.That is,the base of Free-Floating Space Robot has no driving force and stay in a free-floating state during the movement process.Therefore,it's difficult to control the position and posture of the base,thereby affecting the accuracy of end-effector.The trajectory planning is firstly carried out based on above considerations,and the controller will be designed to track the planned trajectory in this paper.The rigid body dynamic model of Free-Floating Space Robot is firstly studied.In order to modeling the system,equations describing the relationship between the velocity,angular velocity and the corresponding joint angle is derived firstly by using the conservation of momentum and angular momentum of Free-Floating Space Robot.Then the kinetic energy of the system was calculated,and the dynamic model was established using Lagrange Equation.Secondly,the Pseudospectral method is used to solve the trajectory planning problem in joint space.Pseudospectral method is a numerical calculation method for optimal control problem,which can significantly improve calculation speed when solving trajectory planning problem.According to the difference of discrete nodes,Gauss Pseudospectral method and adaptive Radau Pseudospectral method are applied to deal with the problem,and the calculation error of adaptive Radau Pseudospectral is analyzed.Finally,the Terminal Sliding Mode Controller is designed to track the planned trajectory in this paper.The stability is proved using Lyapunov method and the effect of the designed controller on the trajectory tracking problem is verified in the process of controller design.