Constrained Visual Servoing for Capturing Adapter Rings on Tumbling Satellites With a Free-Floating Robot

This article proposes a constrained visual servoing method for the safe and reliable capture of noncooperative tumbling satellites using a free-floating space robot. The adapter ring serves as both the capture interface and the visual feature. However, during the close-range fine servoing phase, only a limited portion of the adapter ring is visible within the hand–eye camera's field of view due to its large size, leading to reduced servoing accuracy. To address this issue, a three-line structured light system is introduced in this phase to augment visual features and complement the long-range guidance provided by the monocular camera. This scheme enables visual servoing from long to close range. Moreover, the target's tumbling motion, the ring's geometric properties, and the coupled dynamics between the manipulator and the base pose significant challenges to the reliability and safety of the servoing process. To mitigate these issues, a set of constraints is formulated, including hard constraints to ensure that visual features remain within the camera's field of view and to avoid obstacles, as well as soft constraints to maintain continuous communication with the ground station and minimize impact forces at the moment of capture. To manage these constraints and regulate the system in real time, a motion planner employing nonlinear model-predictive control is developed, supported by differential models of visual features. Furthermore, a low-level joint controller based on quadratic programming ensures accurate tracking of planned trajectories while adhering to torque limits. Simulation results validate the effectiveness of the proposed method.