Autonomous Control for a Differential Thrust ROV

Smaller autonomous underwater vehicles that use differential thrust for surge and yaw motion control has the advantage of low cost and, at the same time, increased ma­ neuverability in yaw direction. However, since such vehicles are underactuated vehicles, design of an autonomous control system that enables the vehicle to autonomously track a predefined trajectory is challenging. In this paper, we presented such an autonomous control system and implemented it on a small underactuated ROV with the use of unscented Kalman filter for vehicle localization, a underwater acoustic positioning system as the position sensor and a compass as the direction sensor. In designing the control law, the integrator backstep technique is used to achieve Lyapunov stability. Computer simulation and field tests have shown that the autonomous control system works well for the vehicle to track a predefined trajectory and the the tracking error converged to a certain small value.