A 7 cm-Scale Spherical Underwater Robot Using Piezoelectric Double-Jet Actuator for Deep-Sea Environment

Moving rapidly and agilely in high-pressure environment is a challenge for existing miniature underwater robots, which limits deeply the ocean exploitation. Here, we present a spherical underwater robot with diameter of 7 cm, and it has merits of miniature structure without bulky and antihydropressure devices, 3-DOFs agile motion, and good adaptability for 25 MPa environment simultaneously. Four designed piezoelectric double-jet actuators are embedded directly in the spherical shell without transmission mechanism, which enables the robot with relatively fast motion speed by compared with the published robots. Six motion modes are implemented by the cooperation of actuators, including rising, hovering, and sinking motions in the vertical direction and straight driving, turning, and in-situ turning motions in the horizontal plane. A robot prototype was fabricated, and its performance was tested. Experimental results indicated that the rising, straight driving, and in-situ turning speed reached up to 95.2 mm/s (1.36 BL/s), 99.6 mm/s (1.42 BL/s), and 5 rad/s, respectively. Besides, the robot could also rapidly turn at 1.3 rad/s with the turning radius of 22.1 mm. The speed deviation within 10% under different water pressures was obtained. The obstacle avoidance was successfully fulfilled by controlling the robot to pass through the narrow gap with width of only 1.5 body length of robot. There excellent characteristics demonstrate agile mobility and give the robot ability to move in the confined area of deep sea.