Control strategies for underwater vehicle autopilots

The Remotely Operated Vehicle (ROV) is used in many underwater applications where the cost or risk associated with human divers would be unacceptable. There is no doubt than an experienced diver can undertake tasks of far greater complexity than the present generation of ROV, but the unmanned vehicle can operate at greater depths without the need for decompression and related support facilities. In attempting to cover the full range of requirements, ROVs have been developed in many forms. The authors describe the test vehicle built at the University of Liverpool which has six identical thrusters mounted in pairs aligned with the three orthogonal axes. The thrusters are attached to the inside of a cellular spherical frame. The instrumentation, drive and control systems are mounted inside the frame. The Aquasphere is ballasted to have slight positive buoyancy and with the centre of buoyancy just above the centre of mass. It therefore floats in the event of loss of power, and is self righting, but can be rotated along the pitch and roll axes if necessary to improve the reach of the five joint manipulator arm. All systems are electrical