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AUV Tool Manipulation With Hard and Soft Actuators

Autonomous underwater vehicles (AUVs) outfitted with manipulators are useful for performing various tasks. As the AUVs manipulate tools, they deviate from neutral buoyancy, and must constantly actuate to maintain depth and orientation. This results in large energy consumption. Furthermore, AUVs continuously oscillate when thrusters are unable to fix minor motion discrepancies. This letter investigates the use of reversible fuel cells–enabled buoyancy control devices (BCDs, soft actuators) with existing thrusters (hard actuators) to correct the heave and tilt motion during tool manipulation. A state-space model that describes an AUV equippped with a manipulator and actuated with thrusters and BCDs is derived. A set of control laws are proposed to allow for a novel collaboration between the two actuators (thrusters and BCDs) for station keeping. Different scenarios are simulated using the model with experimentally identified parameters to analyze the motion and energy performance of the control law. Simulation results show that synergizing the two forms of actuation (soft/hard) improves performance and energy efficiency with the thrusters providing quick depth and orientation correction while BCDs adjust buoyancy and small maneuvering.