On the kinematics of multiple manipulator space free-flyers and their computation

In this paper, two basic approaches for kinematics modelling of multiple manipulator Space Free-Flying Robots (SFFRs) are developed. In the barycentric vector approach, the center of mass of the whole system is taken as a representative point for the system’s translational motion, and a set of body-fixed vectors which reflect both geometric configuration and mass distribution of the system are used. On the other hand, the direct path method relies on taking a point on the base body (preferably its center of mass) as the representative point for the system’s translational motion. The consequences of using each of the two approaches in deriving dynamics equations and in control design of SFFRs are discussed. It is revealed that the direct path method is a more appropriate approach for modelling multiple arm systems, in the presence of external forces/torques (i.e. free-flying mode). A fourteen degree-of-freedom space free-flying system is considered as a benchmark system and a quantitative comparison between the two approaches is presented. The results show that the direct path method requires significantly less computations for position and velocity analyses.