Guidance and control of a reconfigurable unmanned underwater vehicle

The problem of designing, implementing and testing a general-purpose guidance and control system for unmanned underwater vehicles for scientific applications is addressed in this paper. A three-level hierarchical architecture is proposed in order to uncouple the execution of user-defined motion-task functions with respect to the operating environment (guidance), from linear and angular speed control and mapping of the required control actions onto the actuation system. The introduction of PI-type task functions enables a conventional Lyapunov-based guidance system to counteract the effects both of unmodelled, i.e. unmeasured kinematic interactions between the vehicle and the environment, and of bias in velocity measurements. The vehicle dynamics are managed by conventional gain scheduling regulators performing velocity control, while an advanced actuator model, which considers propeller-hull interactions, improves the precision of the thrust to propeller rate mapping. Preliminary tests, carried out in a high-diving pool with an over-actuated prototype ROV, proved the system's functionality and showed high performances in terms of its precision in accomplishing near bottom slow motion tasks, e.g. altitude and hovering control and trajectory tracking, even when the mapping of the required control actions onto the actuation system is reconfigured to face any type of thruster fault. (C) 2000 Elsevier Science Ltd. All rights reserved.