Constant depth control for a novel underwater robot with four vectored water-jet thrusts

Due to the disadvantages of the traditional AUV such as inefficiency of attitude control and poor maneuverability at low speed, a novel vectored water-jet-based underwater robot was proposed. Based on the characteristics of the structure of the robot and its movement features, a reliable method was presented with the adaptive sliding mode control technology for longitudinal depth control and the corresponding robust controller was built. A smooth saturation function, which forces the system to maintain stable condition, was used to reduce chatter and to improve transient performance. With presented adaptive sliding mode controller, the underwater robot can be steered under the condition with modeling error due to the multiple-dimension, multiple-inputs and highly coupled nonlinearity of the dynamic model. The simulations results show that the depth and the pitching angle of the robot can be stabilized around the expected point.