Multiple Impedance Control for Space Free-Flying Robots Abstract Assistant Professor j PhD Student k Associate Professor Member AIAA

Abstract:  To increase the mobility of on-orbit robotic systems, Space Free-Flying Robots (SFFR) in which one or more manipulators are mounted on a thruster-equipped base, have been proposed. Unlike fixed-based manipulators, the robotic arms of SFFR are dynamically coupled with each other and the free-flying-base, hence the control problem becomes more challenging. In this paper, the Multiple Impedance Control (MIC) is developed to manipulate space objects by multiple arms of SFFR. The MIC law is based on the concept of designated impedances and enforces them at various system levels, i.e., the free-flying base, all cooperating manipulators, and the manipulated object itself. The object may include an internal angular momentum source, as is the case in most satellite manipulation tasks. The disturbance rejection characteristic of this algorithm is also studied. The result of this analysis reveals that the effect of disturbances substantially reduces through appropriate tuning of the controller mass matrix gain. A system of three manipulators mounted on a free-flying base is simulated in which force and torque disturbances are exerted at several points. The system dynamics is developed symbolically and the controlled system is simulated. The simulation results reveal the merits of the MIC algorithm in terms of smooth performance, i.e. negligible small tracking errors in the presence of impacts due to contact with the obstacles and