The concept of multiple Autonomous Underwater Vehicles (AUVs) cooperatively performing a mission offers several advantages over single vehicles working in a non-cooperative manner such as increased efficiency, performance, reconfigurability, robustness and the emergence of new capabilities. This paper introduces the concept of coordinated path-following control of multiple AUVs. The vehicles are required to follow pre-specified spatial paths while keeping a desired inter-vehicle formation pattern in time. We show how Lyapunov-based techniques and graph theory can be brought together to yield a decentralized control structure where the dynamics of the cooperating vehicles and the constraints imposed by the topology of the inter-vehicle communications network are explicitly taken into account. Path-following for each vehicle amounts to reducing an appropriately defined geometric error to a small neighborhood of the origin. Vehicle coordination is achieved by adjusting the speed command of each vehicle along its path according to information on the positions of a subset of the other vehicles, as determined by the communications topology adopted. We illustrate our design procedure for underwater vehicles moving in three-dimensional space. Simulations results are presented and discussed.

INTRODUCTION

The ever increasing sophistication of autonomous underwater vehicles (AUVs) is steadily paving the way for the execution of complex missions without direct supervision of human operator. A key enabling element for the execution of such missions is the availability of advance systems for motion control of AUVs. The past few decades have witnessed considerable interest in this area (Fossen, 1994; Leonard, 1995; Encarnaçãao and Pascoal, 2000; Alonge et al., 2001; Jiang, 2002; Pettersen and Nijmeijer, 2003; Aguiar and Hespanha, 2004; Aguiar and Hespanha, 2007; Aguiar and Pascoal, 2007b). The problems of motion control can be roughly classified into three groups: point stabilization, where the goal is to stabilize a vehicle at a given target point with a desired orientation;

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