Set-based Line-of-Sight (LOS) path following with collision avoidance for underactuated unmanned surface vessel

Abstract

Abstract-A cornerstone ability of an autonomous unmanned surface vessel (USV) is to avoid collisions with stationary obstacles and other moving vehicles while following a predefined path. USVs are typically underactuated, and this paper extends recent results in set-based guidance theory to an underactuated surface vessel, resulting in a switched guidance system with a path following mode and a collision avoidance mode. This system can be used with any combination of path following and collision avoidance guidance laws. Furthermore, a specific guidance law for collision avoidance is suggested that ensures tracking of a safe radius about a moving obstacle. The guidance law is specifically designed to assure collision avoidance while abiding by the International Regulations for Preventing Collisions at Sea (COLREGs). It is proven that the USV successfully circumvents the obstacles in a COLREGs compliant manner and that path following is achieved in path following mode. Simulations results confirm the effectiveness of the proposed approach.

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

“…The first contribution of this paper is extending recent results for collision avoidance of a USV [14] by proving that a previously suggested LOS-based guidance law for collision avoidance is applicable also when unknown ocean currents are present. In [14], a path following and collision avoidance method is presented that guarantees collision avoidance of both moving and static obstacles while ensuring path following of a straight line path when no ocean currents are present.…”

“…In [14], a specific guidance law for USVs is presented to safely avoid obstacles while abiding by COLREGs when no ocean currents are present. This guidance law is given below, and it is proven that it is suitable also for collision avoidance in combination with ocean current compensation.…”

“…In this paper, λ is chosen according to [14], where the COLREGs situation is determined based on the angle between the fore of the obstacle and the USV. Note that this parameter does not change as the USV circumvents the obstacle and thereby the before-mentioned angle changes.…”

“…Furthermore, it is designed specifically to achieve collision avoidance while abiding by the COLREGs. The preliminary results [14] did not suggest a specific guidance law for path following, and only simulations of a straight line path with no influence of currents were presented. The second contribution of this paper is a complete guidance and control system which is applicable to both straight line and curved paths, and is suitable whether ocean currents are present or not.…”

“…In [14], a path following and collision avoidance method is presented that guarantees collision avoidance of both moving and static obstacles while ensuring path following of a straight line path when no ocean currents are present. The results are based on recent work [15], [16] that integrates set-based tasks into the widely used prioritized task kinematic control framework [17], which are then adapted to the underactuation of USVs.…”