Autonomous Surface Vehicle based docking for an Autonomous Underwater Vehicle

Abstract

Autonomous underwater vehicles have been used as tools for underwater operations. Autonomy means the capability to perform deliberative planning on-board without any human interaction. The levels of autonomy of underwater vehicles have been increasing over the years. One essential enabler for autonomous operation concerns docking. Autonomous docking will allow vehicles to operate independently of human interaction in remote areas. Docking concepts range from underwater docking stations to launch and recovery from autonomous surface vessels. The Underwater Systems and Technologies Laboratory (LSTS) has been developing and using this type of vehicles for more than twenty years and therefore the need of automatic docking of vehicles has emerged. This dissertation aims to develop an approach for docking between two existing vehicles from the LSTS fleet. The vehicles would be an Autonomous Surface Vehicle (ASV) \textit{Caravela} and a Light Autonomous Underwater Vehicle (LAUV). For this reason, we study and discuss the derivation and simplification of motion equations for sub-aquatic and surface vehicles and known approaches for docking, between a fixed or a moving dock. We studied a way to have localization between the two vehicles using Global Positioning System (GPS) and/or Ultra-Short Baseline (USBL) and the internal Inertial Measurement Unit (IMU), currently available on the systems. Several state machines where implemented in order to have an optimized and fail-safe docking maneuver even having external disturbances like sea-currents on the docking approach. The whole approach was implemented using the tool-chain developed in LSTS (Dune, IMC and Neptus).