This paper addresses the problem of robust bottom following control for a flight-style autonomous underwater vehicle (AUV) subject to system uncertainties, actuator dynamics, and input saturation. First, the actuator dynamics that is approximated by a first-order differential equation is inserted into the AUV dynamics model, which renders a high-order nonlinear dynamics analysis and design in the model-based backstepping controller by utilizing guidance errors. Second, to overcome the shaking control behavior resulted by the model-based high-order derivative calculation, a fuzzy approximator-based model-free controller is proposed, in order to online approximate the unknown part of the ideal backstepping architecture. In addition, the adaptive error estimation technology is resorted to compensate the system approximation error, ensuring that all the position and orientation errors of robust bottom following control tend to zero. Third, to further tackle the potential unstable control behavior from inherent saturation of control surfaces driven by rudders, an additional adaptive fuzzy compensator is introduced, in order to compensate control truncation between the unsaturated and saturation inputs. Subsequently, Lyapunov theory and Barbalat lemma are adopted to synthesize asymptotic stability of the entire bottom following control system. Finally, comparative numerical simulations with different controllers, environmental disturbances and initial states are provided to illustrate adaptability and robustness of the proposed bottom following controller for a flight-style AUV with saturated actuator dynamics.

This paper addresses the problem of coordinated path tracking for networked nonholonomic mobile vehicles, while building and keeping a desired formation. The control laws proposed are categorized into two envelopes by integrating individual path tracking and global virtual structure approaches. One is steering individual vehicles to track virtual vehicles moving along predefined paths, generated by a formation reference vehicle (FRV) of a time-varying desired virtual structure. The other is ensuring paths to be well tracked in order to build a geometric formation, through the distributed feedback law for path parameters related to the virtual vehicles, such that the physical vehicles are on the desired placements of the formation structure. Within this framework, geometric path tracking is achieved via nonlinear control theory, where an approaching angle is injected as a heading guidance design. The distributed feedback law is analyzed under communication constraints using algebraic graph theory. It is formally shown that the path tracking error of each vehicle is reduced to zero, and vehicles in the networked team globally asymptotically converge to a desired formation with equal path parameters. Simulation results illustrate the effectiveness of the proposed control design.