Augmented robust control of a free-floating flexible space robot

Abstract

The flexibility of the joints and links of space robots is considerable, arising from elasticity of the joints and links. Controlling such a robot is more complex than controlling rigid one due to the interactions of rigid and flexible motion. Only a single actuation signal could be applied at each joint, whilst it has to control the motion of the link joint, the flexure of both the joints itself, and the attached link for a flexible space robot. To investigate such an underactuated flexible-link flexible-joint space robot, a free-floating space manipulator with one flexible link and two flexible revolute joints was presented in this paper. The dynamical Lagrange equation was established, and a singularly perturbed model has been formulated. The model consisted of a rigid subsystem, a flexible-link fast subsystem, and a flexible-joint fast subsystem. Based on the two-time-scale separation of the manipulator dynamics, a reduced-order controller was designed. This controller consisted of a rigid control component and two fast control components. Based only on the possible bound of the uncertainty, an augmented robust control law was constructed for the rigid counterpart of the flexible-link flexible-joint robot. The flexible-joint fast subsystem controller would stabilize the elastic vibrations at the joints, and the flexible-link fast subsystem controller would damp out the vibration of the flexible link. Numerical simulations showed that the link and joint vibrations had been stabilized effectively with good tracking performance.