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

Abstract

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.

Collision Avoidance for Underactuated Marine Vehicles Using the Constant Avoidance Angle Algorithm

“…Remark 4. An alternative approach is to choose the turning direction to comply with the International regulations for preventing collisions at sea (COLREGS), as in [19], [24]. The vehicle would then turn to starboard when the obstacle comes from starboard, when the obstacle comes head on, or if the vehicle overtakes the obstacle from behind.…”

“…When the control system enters collision avoidance mode, there might thus be more than one obstacle in the current unsafe cone. The closest obstacle is then used to choose the turning direction according to (24).…”

“…The algorithm proposed by [24] uses circular path following to avoid moving obstacles, and the paper gives sufficient conditions for successful avoidance. By using set-based theory to switch between path following mode and collision avoidance mode, the algorithm is combined with the popular line-of-sight guidance law [25] for following of straight line path segments.…”

“…This path following algorithm is used as an example also in our paper, and is described in Section V-B. It is not, however, clear how to extend the algorithm of [24] to noncircular obstacles, nor is a minimum distance for when the vehicle should start the collision avoidance maneuver provided.…”

Path-Following Control Method for Surface Ships Based on a New Guidance Algorithm

“…Line of sight (LOS) is the most commonly used guidance algorithm. This algorithm was first applied to track control of surface ships by Mcgookin and Fossen and has been widely studied [6][7][8][9]. The advantage of the LOS guidance algorithm is that it controls the ship's motion by imitating the behavior of the helmsman to eliminate track deviation from the planned route.…”