Safe breakwater-following control of an autonomous underwater vehicle with non-zero forward velocity

Periodic inspection is essential for the maintenance and security of port facilities. This paper discusses safe path-following control of an autonomous underwater vehicle (AUV) for port area inspection. An AUV usually has a non-holonomic constraint and cannot be stabilized by continuous linear feedback control. In this paper, we derive the error dynamics with respect to a straight line path and show that its linear form is controllable. We then propose a tuning method of linear feedback control gains, which considers the turn point, safety during navigation, and the physical limitations of the vehicle. A critical damped response to a given path is commonly regarded as an ideal one. However, in some cases underdamped and overdamped responses are better for safe navigation. The tuning method can select the suitable damping degree of the control response. Our method is first described for horizontal motion control and then is generalized to vertical motion and 3-D motion controls. Simulations were done to verify the effectiveness of the proposed tuning method and the results are discussed.