Safe COLREGs-aware finite-time guidance and control of marine vehicles

We establish a new guidance, navigation and control strategy for uninhabited marine vehicles, equipped with finite-time convergence characteristics while obeying collision regulations (COLREGs) stipulated by the International Maritime Organisation. Mathematical guarantees are provided by deriving conditions under which (i) convergence to the waypoint and (ii) safe obstacle avoidance is guaranteed while (iii) input constraints are satisfied. First, we propose a prescribed-time heading control to enforce ship heading convergence to a Line-of-Sight (LOS) convergence in finite time. Using the above as a building block, we develop a provably safe algorithm for waypoint navigation by strategically and automatically introducing intermediate virtual waypoints to avoid obstacles while adhering to COLREGs. The proposed evasive strategy is based on creating a dynamic virtual unsafe set around obstacles using the commonly employed closest point of approach (CPA). Our approach provides analytical validation of avoidance of the unsafe set while converging to a target waypoint in finite time, thus guaranteeing safety. Extensive simulations demonstrate safe obstacle avoidance in a range of scenarios. Comparison with existing well-known strategies such as Velocity Obstacles and biased LOS methods demonstrate the efficacy of the proposed approach in terms of the distance between the ship and the obstacle, cross track error and control effort.