Guidance law for docking of an underactuated autonomous underwater vehicle

Abstract

This dissertation presents guidance law of final approach for unidirectional docking of an underactuated AUV (Autonomous Underwater Vehicle) with drift. The AUVs have been in the spotlight as devices to survey oceanography. The vehicle gets around without any physical connections in deep-sea and accomplish the tasks autonomously. Operation range is restricted by battery capability while amount of data is limited by mass storage device. To overcome these restrictions, underwater docking for battery recharge and communication technology have come to the fore. For safety docking, precise and robust guidance is demanded. In this dissertation, guidance for unidirectional approach docking of an underactuated underwater vehicle with drift wii be considered and investigated. Number of actuators of the vehicle are less than degrees of freedom to increase dynamic efficiency and to decrease weight and cost in many cases. Configuration of a slender body with two rudders and two elevators in the buttock including one propeller thruster is most typical. In this case, drift angle exists when there are ocean currents and the vehicle’s heading and course become different. Unidirectional docking is analogous with landing of airplanes having constraints with respect to position, attitude and motion. But, if there is drift, control inputs to satisfying the constraint attitude and motion are in conflict with each other. Guidance laws considering this conflict and satisfying all contraints are proposed. First, mathematical modeling of the underactuated AUV and ocean currents are introduced. Dynamic characteristics of the vehicle are shown. Second, modeling of a docking station that permits only unidirectional approach is also introduced. By referring actual well-made docking stations, a funnel-shape entry section is modeled by using a sector. And constraints are also specified with respect to position, attitude and motion. This sector-form model of the docking station becomes a regi...