Set-Based line-of-sight (LOS) path following with collision avoidance for underactuated unmanned surface vessels under the influence of ocean currents

Abstract

An essential ability of an autonomous unmanned surface vessel (USV) is to follow a predefined path in the presence of unknown ocean currents while avoiding collisions with both stationary and dynamic obstacles. This paper combines recent results for path following and collision avoidance for USVs, resulting in a switched guidance system with a designated path following and a collision avoidance mode. The closed-loop system relies on absolute velocity measurements only, and it is shown that a previously suggested guidance law for collision avoidance guarantees tracking of a safe radius about a dynamic obstacle also under the influence of unknown ocean currents. The guidance law is constructed to ensure collision avoidance while following the International Regulations for Preventing Collisions at Sea (COLREGs). Note that this set-based approach is highly generic and may be applied with any combination of methods for path following and collision avoidance. It is proven that the USV evades the obstacles in a COLREGs compliant manner and converges to the desired path in path following mode. Simulations results validate the theoretical results.