This paper presents a hybrid controller that combines sliding-mode control (SMC) with a fuzzy strategy to regulate the vertical displacement of a bioinspired robotic dolphin. The structure of the robot and a simplified mathematical model for depth control are described. An SMC based on the line-of-sight guidance law and the sliding-mode observer is developed to overcome systematic uncertainties and environmental disturbances. The Lyapunov stability theory is utilized to analyze the stability and convergence properties of the closed-loop system. Depth control in the physical robot is realized by utilizing a fuzzy logic controller, which is represented as the mapping of the input propulsion forces/moments and output control parameters. Numerical and experimental results show that the proposed control strategy successfully steers the robot toward and along the desired depth.

This paper presents the mechatronic design and hydrodynamic analysis of a novel bioinspired robotic dolphin used for mobile water quality monitoring. A complementary configuration for mimicry of dolphin-like propulsion is first presented, involving a waist-fluke propulsive unit for dorsoventral oscillations and a pair of flippers with separate degree of freedom for three-dimensional (3-D) maneuvers. A host of onboard sensors is equipped to strengthen the capability of environment perception and mission execution on a near real-time basis. Considering the dynamic requirement for motion transition in water quality monitoring, a central pattern generator based controller is then built to govern the multimodal locomotion of the robotic dolphin. Moreover, a 3-D dynamic model based on the Lagrange method is employed to predict the propulsive performance, followed by simulations of continuous diving and surfacing motions. Finally, both laboratory and field experiments are conducted to demonstrate the effectiveness of the presented mechatronic design and control methods. The results further show that the robotic dolphin with 3-D maneuverability offers a feasible solution to aquatic mobile sensing.