We present a nonlinear adaptive path following controller that compensates for drift forces through vehicle sideslip. Vehicle sideslip arises during path following when the vehicle is subject to drift forces caused by ocean currents, wind, and waves. The proposed algorithm is motivated by a line-of-sight (LOS) guidance principle used by ancient navigators, which is here extended to path following of Dubins paths. The unknown sideslip angle is treated as a constant parameter, which is estimated using an adaptation law. The equilibrium points of the cross-track and parameter estimation errors are proven to be uniformly semiglobally exponentially stable. This guarantees that the estimated sideslip angle converges to its true value exponentially. The adaptive control law is in fact an integral LOS controller for path following since the parameter adaptation law provides integral action. The proposed guidance law is intended for maneuvering in the horizontal-plane at given speeds and typical applications are marine craft, autonomous underwater vehicles, unmanned aerial vehicles as well as other vehicles and crafts, where the goal is to follow a predefined parametrized curve without time constraints. Two vehicle cases studies are included to verify the theoretical results.

This paper presents an extensive analysis of the integral line-of-sight (ILOS) guidance method for path-following tasks of underactuated marine vehicles, operating on and below the sea surface. It is shown that due to the embedded integral action, the guidance law makes the vessels follow straight lines by compensating for the drift effect of environmental disturbances, such as currents, wind, and waves. The ILOS guidance is first applied to a 2-D model of surface vessels that includes the underactauted sway dynamics of the vehicle as well as disturbances in the form of constant irrotational ocean currents and constant dynamic, attitude dependent, and forces. The actuated dynamics are not considered at this point. A Lyapunov closed-loop analysis yields explicit bounds on the guidance law gains to guarantee uniform global asymptotic stability (UGAS) and uniform local exponential stability (ULES). The complete kinematic and dynamic closed-loop system of the 3-D ILOS guidance law is analyzed in the following and hence extending the analysis to underactuated autonomous underwater vehicles (AUVs) for the 3-D straight-line path-following applications in the presence of constant irrotational ocean currents. The actuated surge, pitch, and yaw dynamics are included in the analysis where the closed-loop system forms a cascade, and the properties of UGAS and ULES are shown. The 3-D ILOS control system is a generalization of the 2-D ILOS guidance. Finally, results from simulations and experiments are presented to validate and illustrate the theoretical results, where the 2-D ILOS guidance is applied to the cooperative autonomous robotics towing system vehicle and light AUV.

In this paper, we address the tracking problem for an underactuated ship using two controls, namely surge force and yaw moment. A simple state-feedback control law is developed and proved to render the tracking error dynamics globally K- exponentially stable. Experimental results are presented where the controller is implemented on a scale model of an offshore supply vessel.

In this paper, we consider the development of a control strategy for path following of underactuated marine surface vessels in the presence of ocean currents. The proposed control strategy is based on a modified Line-of-Sight (LOS) guidance law with integral action and a pair of adaptive feedback controllers. Traditional LOS guidance has several nice properties and is widely used in practice for path following of marine vehicles. However, it has the drawback of being susceptible to environmental disturbances. In this work, we propose a modified LOS guidance law with integral action for counteracting environmental disturbances. Paired with a set of adaptive feedback controllers, we show that this approach guarantees global asymptotic path following of straight-line paths in the presence constant and irrotational ocean currents.