Moving-Base Space Robots—Applying Eigen-Dynamics of a Reduced System to Synthesize Controls

Abstract

A review of trends in space robotics identifies a promising class of assembly and service robotic space modules (ASRSM). This paper considers the topical problem of automating the assembly of large space objects. For certain ASRSM operations that are of practical interest, engineers can apply a design model comprising a moving base, a handler, and a payload. A massless single-DoF handler is an important special case. It is shown that in the absence of forces external to the system, the payload displacement with respect to the base can be described by an independent differential equation derived by Routhian formalism. In the common case where the angular momentum of the original system is non-zero, this equation is the dynamics equation for some non-linear oscillatory system, which, using the traditional terminology of analytical mechanics, we referred to as a reduced system and is seen as a controllable object. The proposed approach is convenient for studying the Eigen movement of a system by the internal degree of freedom, which movement is caused by the non-zero values both on the (neglected) cyclic axis, and on the hinged positional axis. Using these movements to synthesize the controls makes sense from the point of view of an important principle applicable to robotic movement arrangements; the principle consists in harmonizing the free and forced movements of the handler. The paper considers a modeling problem, which is of practical interest in its own right. The results can be generalized to apply to a general case of spatial motion of a system.