Electrically Driven Robotic Pistons Exploiting Liquid-Vapor Phase Transition for Underwater Applications

Soft actuators have shown great potential in underwater applications due to diverse deformations, silent actuation mode, and waterproof features. To accomplish a versatile actuation approach with no environmental disturbances, this study demonstrates an electrically driven robotic piston that combines the advantages of soft robots with those of rigid mechanisms to provide adaptive and robust actuation. The robotic piston was actuated by multiple linearly stacked liquid pouch motors based on the liquid-vapor phase transition. The liquid pouch actuator is filled with low boiling fluid, which is capable of inflating several folds of its initial thickness by Joule heating to a temperature above the boiling point and contracting to the initial state by cooling. Based on the reversible liquid-vapor phase transition of the filled fluid, a series of linearly stacked pouch actuators can inflate and contract, which results in the reciprocating forward and backward movement of the piston rod in contact with them. The performance of liquid pouch actuators and soft robotic pistons was evaluated. The proposed soft robotic piston can be adapted as an electrical machine integrated with other different mechanisms, which was eventually demonstrated in robotic gripper systems and a legged walking robot in the underwater environment.