Design and Control of a Free-Floating Robot for Ground Microgravity Experiment

In this paper, a cube shaped free-floating robot that is composed of air-bearing, high-pressure gas tank, pressure reducing valve, solenoid valve, and nozzle is designed for ground microgravity experiment of on-orbit servicing missions. The attitude of the robot is controlled by a reaction wheel and the position of the robot is controlled by eight nozzles symmetrically distributed around itself. Their thrust is calibrated using the ballistic pendulum method and verified by a pressure sensor. To be able to control the robot accurately, the moment of inertia and the position of the mass center of the robot are obtained by experiments. To control the robot tracking an arbitrary trajectory, a trajectory planning method based on quintic polynomial curve interpolation and the hysteresis control law are applied in this paper. Simulation and experimental results show that the designed free-floating robot can achieve high precision using the presented trajectory planning method and control strategy.