Trajectory Tracking Control In Joint Space For Free-Floating Space Robot

Space robot will play an important role in development of human space activities. The research on space robot has become a research hotspot of aerospace technology in countries of the world. Working under the free-floating mode, space robot could save fuel and electricity, and then prolong the on-orbit life span. Therefore, free-floating space robot has wide application prospect compared with other categories. This paper studies on trajectory tracking control in joint space for free-floating space robot. The main work is as follows:The Jacobian Matrix of free-floating space robot system is derived, and the dynamic equation of system is derived with the Lagrange equation, and an example model of planar tow-link free-floating space robot is given as the foundation of control law design.Angular momentum of the free-floating space robot is conserved, which makes system dynamic equation under-actuated. The completely controllable system equation is obtained by making the equivalence change of the dynamic equation using the kinematic relation between the joint and base attitude. As the system inertia uncertainty and disturbances exists, the trajectory tracking control is a certain amount of bias. In order to improve the accuracy of tracking control, a robust controller is proposed considering the model uncertainty and disturbances of system. Simulation results show the feasibility of the proposed control scheme.An adaptive robust control algorithm is used aiming at the uncertainty of the system parameters. The adaptive law in the robust controller online estimates the unknown upper bound of the uncertainty, and robust control law assures the stability of whole system.Simulations illustrate the tracking performance obtained using the proposed controller.Considering the model uncertainty and disturbances of system, an Neural Network based robust control scheme is proposed. RBF neural network is used to approximate the unknown nonlinear function of robust controller, robust control law compresses the approximation error and external disturbance. Simulation results show the feasibility of the proposed control scheme.