A variable structure control of a remotely operated vehicle

Designing a control system for an underwater remotely operated vehicle (ROV) presents various problems: the ROV dynamics is described by a strongly nonlinear model; this model is characterized by uncertain parameters; unmeasurable disturbances are present. In the paper, the robust technique known as variable (VSS) control or sliding mode control (SMC) has been used, in order to solve the above mentioned problems for a specific ROV model. The control problem that has been considered consists in tracking a given trajectory and the control variables chosen are the electrical currents that drive the four vehicle propellers: this choice, although it gives rise to a model that is nonlinear with respect to the control variables, is motivated by the fact that the resulting controller can take into account possible parametric variations in the relationship between thrusts and electrical currents. The performances of the controllers has been tested by means of suitable simulations, showing the effectiveness of the adopted control technique. Moreover, the possibility of obtaining the information necessary for synthesizing the control law by means of visual data is discussed