Comprehensive framework for tracking control and thrust allocation for a highly overactuated autonomous surface vessel

In this paper, we present a comprehensive trajectory tracking framework for cooperative manipulation scenarios involving marine surface ships. Our experimental platform is a small boat equipped with six thrusters, but the technique presented here can be applied to a multi-ship manipulation scenario such as a group of autonomous tugboats transporting a disabled ship or unactuated barge. The primary challenges of this undertaking are: (1) the actuators are unidirectional and experience saturation; (2) the hydrodynamics of the system are difficult to characterize; and (3) obtaining acceptable performance under field conditions (i.e., GPS errors, wind, waves, etc) is arduous. To address these issues, we present a frame work that includes trajectory generation, tracking control, and force allocation that, despite actuator limitations, results in asymptotically convergent trajectory tracking. In addition, the controller employs an adaptive feedback law to compensate for unknown – difficult to measure – hydrodynamic parameters. Field trials are conducted utilizing a 3 meter vessel in a nearby creek.