A lightweight, simple-structured, and fast-response buoyancy adjustment actuator is essential for underwater vehicles. This article presents the design of an electro-hydraulic actuator that can adjust buoyancy by electric stimuli. The buoyancy adjustment approach of the actuator resembles that of the swim bladder, but the electrostatic force, instead of the muscle tension, is applied to expand the volume of the actuator so that the buoyancy changes with the volume when the entire weight of the actuator is fixed. We propose the structural design guidelines and the operating constraints of the actuator by investigating its mechanical model via the minimum energy principle. In the experiment, the actuator shows a maximum 8.58 g buoyancy adjustment ability with a self-weight of 58.6 g. The experimental results also demonstrate that the depth of the actuator in water can be controlled by applying different voltage signals. The electro-hydraulic actuator presents promising potential for future underwater intelligent vehicles in adjusting buoyancy and depth control.
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