Full-Scale Sea Trials of a Motion Control System for ROVs Based on a High-Gain State Observer

Abstract

This paper reports selected results from full-scale sea trials, along with the description of the digital version implemented in practice, of a Motion Control System (MCS) previously proposed by the authors in the continuous-time domain, which has station keeping, i.e. dynamic positioning, and trajectory tracking capabilities for navigating observation class Remotely Operated Vehicles (ROV) used to carry out automated high-resolution image capturing missions, e.g. assessments, inspections, mappings, and surveys. Such capabilities are a key feature to enable the end-users of the ROV technology to acquire sequential high-quality images at proper pace to construct consistent representations of the objects or of the environments of interest. Four degrees-of-freedom are controlled, namely surge, sway, heave, and yaw. The MCS consists of an output feedback control system based on a high-gain state observer and a MIMO PID controller aided by reference feedforward. Feedback linearisation of the plant dynamics is also performed by the MCS. Satisfactory performance for suitable and sufficiently smooth reference trajectories are attained despite the presence of unmodelled dynamics, plant parameter variations, measurement noise, and environmental disturbances.