Trajectory tracking control of an unmanned surface vessel (USV) based on feedback linearization and variable structure control (VSC) is developed. Feedback linearization transforms the nonlinear dynamics of the USV into a linear system. VSC rejects the effects of modeling imperfections and environmental disturbances. The position and orientation of the USV are measured by a visual motion capture system. The combination of accurate measurement and VSC allows trajectory tracking errors to be kept small as is verified in the experimental results. The influence of the sampling rate and the chattering phenomena are also addressed.

Describes the development and implementation of a dynamic positioning system for remotely operated underwater vehicles (ROVs) which is based on a mechanical passive arm (PA) for position measurement. The system, named DPSROV, is suited for tasks which require precise positioning within a limited range around a working site. The DPSROV was configured aiming at easy installation in most commercially available ROVs. The effectiveness of the DPSROV was tested on real ROVs. Two different control strategies were adopted: a conventional linear controller and a robust variable structure model-reference adaptive control. Experimental results are presented to illustrate the DPSROV performance.