Path Following Using Rendezvous Dubins Curves and Integral Line-of-Sight for Unmanned Marine Systems

Accurately following a prescribed path is critical for safe and efficient operation of autonomous systems in the field, especially for marine robots that typically operate away from human support and with sporadic communication abilities. Traditionally, variations of a lookahead control strategy have been employed for unmanned marine systems; however, these strategies can encounter problems when faced with disturbances and discontinuities in localization. In underwater applications, intermittent global localization updates are common due to constraints imposed by the lack of external updates from GPS. This paper examines the application of an online replanning tool based on Dubins curves to a path follower based on integral line-of-sight (ILOS) control. The fundamental idea is to drive the vehicle towards the prescribed path along a Dubins path. The proposed guidance strategy enables the path following controller to be tuned to aggressively track the path, improving disturbance rejection of an ILOS implementation without rendezvous ability by twofold in the simulated scenarios. The proposed method is experimentally validated on both an autonomous underwater vehicle and an autonomous surface vehicle with extended testing in a pond environment. Results indicate that the guidance strategy is able to track paths through disturbances and intermittent localization discontinuities in both surface and underwater use. This work has broad applications to field deployments of marine robots as a means to efficiently link mission level plans to vehicle level control signals considering realistic constraints on localization and control. Specific near-term applications focus on mobile underwater docking for undersea persistence.