Methodology for control of a space robot with flexible links

A methodology of stable manipulation-variable feedback control of space rob ots with flexible links for positioning control to a static target and cont inuous path tracking control is discussed. The proposed methodology is effe ctive for base-fixed robots with flexible links on the ground, as well as f ree-flying space robots. To avoid instability of direct manipulation-variab le 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 c ontrols for rigid manipulators are extended to those for flexible manipulat ors, e.g. an extended local PD-control and a pseudo-resolved-acceleration c ontrol. They can be transformed into joint-variable feedback controls, and are robust stable. Combining those controls with a reduced-order modal cont rol yields a composite control. For the proposed controls, the asymptotic s tability of the static target is verified by Lyapunov's method. For the pat h tracking control, their orbital stability is discussed in terms of the si ngular perturbation method. Numerical simulations and hardware experiments of space flexible manipulators successfully demonstrate the effectiveness a nd feasibility of the proposed method.