COOPERATIVE PATH-FOLLOWING OF MULTIPLE SURFACE VESSELS.pdf

COOPERATIVE PATH-FOLLOWING OF MULTIPLE SURFACE VESSELS WITH PARAMETRIC MODEL UNCERTAINTY AND IN THE PRESENCE OF OCEAN CURRENTS Joa?o Almeida ? Carlos Silvestre ? Anto?nio Pascoal ? ? Institute for Systems and Robotics, Instituto Superior Te?cnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal E-mails: {jalmeida,cjs,antonio}@isr.ist.utl.pt Abstract: This paper addresses the problem of cooperative path-following of multiple autonomous vehicles. Stated briefly, the problem consists in steering a group of vehicles along specified paths, while keeping a desired spatial formation arrangement. For a given class of autonomous surface vessels, it is shown how Lyapunov based techniques and graph theory can be brought together to design a decentralised control structure where the vehicle dynamics and the constraints imposed by the topology of the inter-vehicle communication network are explicitly taken into account. Path-following for each vehicle amounts to reducing an appropriately defined geometric error to zero, in the presence of ocean currents and parametric model uncertainty. Vehicle cooperation is achieved by adjusting the speed of each vehicle along its path according to information exchanged on the positions of a subset of the other vehicles, as determined by the communication topology adopted. Global stability and convergence of the closed-loop system are guaranteed. Keywords: Cooperative motion control, Path-following, Autonomous surface vehicles, Graph theory, Nonlinear control, Adaptive control. 1. INTRODUCTION The topic of multi-agent system cooperation is of great interest in a wide range of scientific and technological areas such as mobile robotics, biology, and artificial intelligence, among others. Using a group of simple, and possibly inexpensive robots, not only allows for the execution of tasks too complex for a single robot, but also increases 1 Research supported in part by project GREX / CEC- IST (Contract No. 035223), project MAYA-Sub of the AdI (PT), t