Abstract-In this paper, a robust controller is designed to achieve accurate positioning of an unactuated surface vessel by using multiple unidirectional tugboats. After initially locating opposing tugboats to specific configurations, the control problem is transformed into a second order system with an uncertain non-symmetric input gain matrix. Upon applying a matrix decomposition, a robust controller is proposed. Detailed stability analysis ensured asymptotic tracking. Numerical simulation results demonstrate the efficiency of the proposed controller.
I. INTRODUCTIONThe positioning of large surface vessels like barges, platforms and unactuated ships is considered as the marine example of the swarm robotic applications. Since these types of large vessels can not generate necessary position and orientation control effort due to their low speed operation, they are in need of assistance of multiple tugboats. As a result of this, this objective is realized via a group of tugboats that are strategically positioned along the vessel's hull. Manipulation with multiple tugboats can be seen as a feasible solution for these type of applications. However, the radio communication between all involved tugboats, especially in human manipulated tugboats, affects the control performance dramatically. Although, the communication performance is increased with advanced global positioning systems, control of these type of systems is still a challenging problem because of possible problems that may arise in communication system during manipulation. As a natural result of these, above mentioned marine control problem has attracted attention of the control community.In the last decade, different types of controller designs have been proposed for these type of applications. In [1], orientation tracking control of a unactuated vessel through the utilization of a swarm of vehicles operating in a decentralized fashion was achieved via presented robust control strategy. In order to design this robust controller, the influence of the other swarm vehicle was treated as a force disturbance into the model dynamics. In [2], an exact model knowledge position and orientation tracking controller was proposed for an unactuated surface vessel. In [3], an adaptive position