Attitude Control System of a Highly Maneuverable Hybrid ROV for Ship-Hull Inspection

Usually, ROVs are operated at small pitch and roll angles. However, tasks appear that require their operation at a whole range of orientation angles. Such operating modes are necessary for the ROV "Iznos" with a hybrid propulsion system (includes both thrusters and wheels) developed in Bauman Moscow State Technical University for ship hull inspection. The control system is required to operate in whole range of orientation angles in two modes: tracking of reference yaw, pitch and roll angles (YPR - mode) set by operator and tracking desired rotations relative to the axis associated with the ROV. A traditional approach to a ROV attitude control implies the usage of Euler angles and has singularity and nonuniqueness problems at pitch +/- 90 degrees. To avoid these problems attitude control using error quaternion feedback is used. The quality of the obtained control law is verified by field tests on the ROV "Iznos". Performance of the system in YPR - mode was compared to the traditional approach based on Euler angles and traditional approach with decomposition algorithm. All approaches have the problem of perturbations between yaw, pitch, roll control channels. In turn, control system based on quaternions has a simple structure and acceptable quality for ROV for the ship-hull inspection.