Research On Trajectory Tracking Control For Free-Floating Flexible Space Robot

With the development of the robot technology and the deepening of space exploration, more and more space robots have been applied in the exploitation of space resource. As a result of the complexity of space missions and the particularity and risk of the space environment, the space robots should have the characters of light weight, high speed and efficiency, and have robustness to the external disturbance. Moreover, due to physical limitation, the actuator outputs are constantly bounded or constrained, and the light manipulator have the flexible vibration. These practical problems have to be taken into the system controller design. This thesis mainly focuses on a kind of free-floating flexible space robot and deeply studies on trajectory tracking and active vibration control strategies of the space robot system.First, based on the flexible multi-body dynamics, the dynamic equations of the space robot are derived by means of Lagrange's equations and the assumed modes method. And then, the coupling relationship between rigid motion and flexible vibration is analyzed. The decoupling equations are presented, in which the flexible vibration is regarded as the disturbance of the rigid motion and the rigid motion is regarded as excitation of the flexible vibration.Second, a robust control approach using adaptive terminal sliding mode is developed for the trajectory tracking control. In the approach, the terminal sliding mode control law is designed based on equivalence principle of sliding mode and the adaptive law is presented to real-timely adjust disturbance parameters and assure robustness of the control law. Complete finite time stability and performance analysis are presented using Lyapunov theory. And a modified controller with the modified adaptive control law is intruduct for the the upper bound on the distrubance to improve the adaptive performances. Moreover, an adaptive non-singular terminal sliding mode control scheme is proposed to solve the singular problem of terminal sliding mode control, in which the saturation function replaces the sign function to weaken the chattering phenomenon of sliding mode control. Meanwhile, the conditional integral is introduced to modify the non-singular terminal sliding mode to reducing the stable error causing by the spacecraft attitude disturbance and the robust effect of the weakening chattering. Simulation results show the effectiveness and feasibility of these control schemes.Last but not the least, the trajectory tracking control and vibration eliminating control problems with the actuators saturation are deeply studied. A hybrid control scheme of an adaptive state feedback strategy and the input shaping technology is proposed. The proposed control scheme includes the robust input shapers designed for active vibration suppression, and the adaptive state feedback trajectory tracking controller designed with an adaptive law to real-timely adjust the disturbance parameters and the bounded hyperbolic tangent functions to promiss the bounded of the control law. And the complete stability and performance analysis are presented using Lyapunov theory and illustrative simulation results show the effectiveness to the trajectory tracking and vibration elimination in the present of actuators saturation.