Methodology for control of a space robot with flexible links

A methodology of stable manipulation-variable feedback control of space robots with flexible links for positioning control to a static target and continuous path tracking control is discussed. The proposed methodology is effective for base-fixed robots with flexible links on the ground, as well as free-flying space robots. To avoid instability of direct manipulation-variable feedback, a virtual rigid manipulator (VRM) concept is introduced and a pseudo-resolved-motion-rate control (pseudo-RMRC) for flexible manipulators is derived from the RMRC for rigid manipulators. By using the VRM, other controls for rigid manipulators are extended to those for flexible manipulators, e.g. an extended local PD-control and a pseudo-resolved-acceleration control. They can be transformed into joint-variable feedback controls, and are robust stable. Combining those controls with a reduced-order modal control yields a composite control. For the proposed controls, the asymptotic stability of the static target is verified by Lyapunov's method. For the path tracking control, their orbital stability is discussed in terms of the singular perturbation method. Numerical simulations and hardware experiments of space flexible manipulators successfully demonstrate the effectiveness and feasibility of the proposed method.