Hyperbolic-tangent LOS guidance-based finite-time path following of underactuated marine vehicles

In this article, a novel hyperbolic-tangent line-of-sight (LOS) guidance-based finite-time path following (HLOS-FPF) framework is created to render an underactuated marine vehicle (UMV) rapidly and accurately follow the desired path, in the presence of complex unknowns including internal dynamics, external disturbances, and arbitrary sideslip. By defining a virtually desired sideslip angle of which the tangent-nonlinearity is exactly identified by a finite-time sideslip observer, the hyperbolic-tangent LOS (HLOS) guidance laws collaboratively governing heading, surge, and virtual ship velocity are devised in a finite-time manner such that cross-track error sensitively excites heading guidance. With the aid of nonsmooth auxiliary dynamics, guidance errors are finely dominated with finite-time convergence. Finite-time heading and surge controllers are further synthesized by integral and nonsingular terminal sliding-mode techniques, and ensure that HLOS guidance signals can be exactly tracked, whereby complex unknowns are exactly compensated by finite-time unknown observer. Eventually, nonsmooth analysis together with Lyapunov approach guarantees that the entire HLOS-FPF scheme is globally finite-time stable and contributes to exact path-following under heading-surge collaborative guidance. Simulation results and comprehensive comparisons with typical methods demonstrate remarkable superiority of the innovative HLOS-FPF scheme.