Adaptive PD-controller for positioning of a remotely operated vehicle close to an underwater structure: Theory and experiments

The requirement for high accuracy in dynamic positioning of remotely operated vehicles (ROV), especially when tasks close to underwater structures have to be performed, demands high precision of sensor systems. Taut-wire and passive arm systems can satisfy this demand in measuring ROVs positions and orientations relative to a structure. However, the main drawback of these sensor systems is that additional forces act on ROVs due to the mechanical connection. In order to solve this problem, an adaptive PD controller is proposed and designed for dynamic positioning of ROVs working in close proximity of structures. Invoking the adaptation law, these additional forces caused by the passive arm and umbilical, and even by the uncertainties in gravity and buoyancy can be identified and compensated. By choosing an adequate Lyapunov candidate function, the system's stability is proven. The effectiveness of this design control method is demonstrated by means of numerical simulations and experiments.