Dynamics and control of large flexible space-robotic systems

Some of the proposed near-future space missions will require space robot technology. This dissertation studies the dynamics and control of two-dimensional, large, flexible, space-based, multi-link robotic systems. The dynamic equations of the systems are established by applying the Lagrangian approach with the finite element method. The system mass center offset, which is determined by the knowledge of the system mass distribution, is considered in the modeling of the dynamics of the multi-link robotic system. Four linear system control strategies are implemented utilizing (1) centralized control based on the linear quadratic regulator theory, (2) independent control based on the control designed independently for each of the physical subsystems, (3) reaction rejection control based on the control designed to reduce the effect of the reaction of the manipulator on the spacecraft, and (4) modal control based on the control designed for each of the modal coordinate subsystems. Two original tip position control techniques are proposed: (1) a linear and nonlinear compensation technique based on controlling a rigid link located at the manipulator tip for reducing the effect of the system flexibility on the manipulator tip position error; (2) a linear calibration technique based on adjusting the joint angles of the manipulator for reducing the effect of the system mass center offset on the manipulator tip position error. The dynamic models of the one-link and two-link flexible robotic manipulators mounted on a free-floating flexible spacecraft with two rigid payloads have been developed. The Lagrangian approach with the finite element method has been found quite useful for the modeling of the dynamics of flexible space-robotic systems. The space-robotic control problem has been examined within the framework of the four linear system control strategies. The compensation and calibration techniques have been used to control the robotic manipulator tip positions associated with the effects of the structural flexibility and the system mass center offset, respectively. The numerical results indicate that the system mass center offset causes increased coupling within the dynamic model and can result in the trajectory errors of the robotic manipulator tip position. The numerical simulations show that the real (actual) tip position of the robotic manipulator can immediately follow the desired (mission) trajectory with the tip position control techniques.