Underwater docking approach of an under-actuated AUV in the presence of constant ocean current

Underwater docking of an AUV (Autonomous Underwater Vehicle) provides a means of data transmit and battery recharge to extend the endurance capability of the vehicle. In this paper, we consider a torpedo-shaped under-***actuated vehicle and a funnel-shaped unidirectional docking station. The problem is that the desired heading to approach to the docking station compensating the effect of ocean current is different from the desired heading to be aligned to the direction of the dock entrance. We propose final approaching and guidance scheme in the terminal phase of underwater docking considering the effect of ocean current. A conventional PID controller for path following and a bang-bang controller for the final alignment are adopted. Switching criterion between two controllers is proposed. Simulation was carried out to validate the proposed scheme and results are included.