A Soft Buoyancy Engine with Cascade Control for Small Autonomous Underwater Vehicles

This paper presents a flexible buoyancy engine designed for small autonomous underwater vehicles (AUVs), addressing limitations in existing buoyancy control technologies. The proposed system utilizes a constant-mass-variable-volume mechanism that inflates a bladder with an incompressible fluid, enabling precise depth control. A cascade feedback control loop is introduced, where the outer-loop uses a linear quadratic regulator (LQR) for depth stabilization and the innerloop uses feedback linearization for volume regulation. The findings demonstrate local stability of the closed-loop bladder dynamics and highlight practical limitations, such as max depth and speed. This research advances buoyancy engine design by integrating soft robotics principles with conventional actuation, paving the way for compact AUVs.