This work presents robust path following controllers with disturbance rejection terms for autonomous surface vehicles in the presence of unknown bounded disturbances. The objective is to steer the vehicle to the desired path while its temporal evolution on the path is defined via a path parameter. The disturbance rejection terms are based on sliding mode control utilizing either constant or time-varying gains. To mitigate the chattering effect in the sliding mode controllers, a continuous adaptive control law based on a normalization technique is subsequently developed. Since the control protocols are proposed as control forces based on the nonlinear dynamics of the surface vehicle, Lyapunov stability theory and backstepping control technique are adopted for the control system design and the global stability analysis. Under the proposed controllers, the vehicle is shown to converge to the desired path asymptotically. Simulation results are also provided to support the theoretical analysis.
