Docking Method for Hovering-Type AUVs Based on Acoustic and Optical Landmarks

Abstract

Autonomous underwater vehicles (AUVs) have the advantage of not requiring tether cables or human control; however, they have limited energy, and must be recovered before their batteries drain completely. To charge AUV batteries efficiently, in-situ charging systems have attracted much attention. This study proposes a method for hovering-type AUVs to dock at a seafloor station, for long-term deployment of the system with minimum human intervention. In the proposed method, an AUV docks at a seafloor station autonomously, based on both acoustic and optical landmarks attached to the station. The AUV stochastically estimates its position and orientation with regard to the station, and controls itself to land on the exact docking spot at the station. When docking is completed, the station begins electric power transmission via non-contact charging devices. The proposed method was evaluated on the AUV Tri-TON 2, and a seafloor station testbed. The vehicle succeeded in autonomous docking at the station in both the tank and sea trials. Non-contact charging during docking was also verified during the tank experiments, using the non-contact charging devices developed by our group.