Robust control of a dual-arm space robot for in-orbit screw-driving operation

As large-scale spacecraft like Hubble Space Telescope need in-orbit assembly, there is an increasing need for the in-orbit assembly automatically carried out by space robots. This paper proposes a potential in-orbit screw-driving strategy carried out by a dual-arm space robot. Unlike single-arm space robots, a dual-arm space robot can avoid the translation and rotation of the target during the screw-driving process. For explanation, one arm can be set as the mission arm in the screw-driving process. The other arm can simultaneously provide the opposite contact forces and torques applied to the target. The hybrid position/force control strategy is developed for a dual-arm space robot to precisely deliver the desired contact forces by the end-effectors. Moreover, the base attitude of the space robot is controlled by reaction wheels to reduce the coupled movement between the base and the manipulators. According to a typical screw-driving procedure for automatic assembly, a desired fastening torque–angle curve is designed to ensure that the screw is firmly tightened. A robust Sliding Mode Controller (SMC) is designed to perform well against the uncertainties and disturbances applied to the space robot system. The simulation results show the feasibility of the potential dual-arm in-orbit screw-driving strategy.