Contact detection, isolation and estimation for orbital robots through an observer based on a centroid-joints dynamics

In this paper, the contact force detection, isolation and estimation problems for an orbital robot are addressed. First, an observer based on a base-joints dynamics is reviewed and analyzed considering the issues related to a space robotic application. Then, a new scheme is derived reformulating the dynamics in terms of the motion of the centroid of the whole robot and the joints. In both observers, three momentum-based residuals are defined, which can be used to reconstruct the external contact wrench. The reconstruction through the proposed observer turns out to provide superior performance with respect to the base-joints one thanks to the decoupling of the angular and joint momentum residuals from the spacecraft linear velocity, which is an inaccurate measurement in real space scenarios. The advantages of the proposed observer are shown through both simulative and hardware validation featuring a 7 degrees of freedom (DoF) arm mounted on a 6 DoF moving base.