Liquid-based electroactive polymers (LEAP) for a new class of soft actuators and generators

Future robotic systems will be pervasive technologies operating autonomously in unknown spaces that are shared with humans. Such complex interactions make it compulsory for them to be lightweight, soft, and efficient in a way to guarantee safety, robustness and long-term operation. This set of qualities can be achieved using soft multipurpose systems that combine, integrate and commute between conventional electromechanical and fluidic drives, as well as harvest energy during inactive actuation phases for increased energy efficiency. Recent research work has shown that dielectric fluids with specific properties, can be combined with stretchable or flexible shell structures made of polymeric dielectric/electrode composite films, to implement a novel type of soft electrically-driven fluidic transducers with self-healing and self-sensing capabilities that take the name of Liquid-based Electro-Active Polymer transducers (LEAPs). These devices are similar to dielectric elastomer transducers in regards to their electrostatic working principle, but they can potentially produce larger displacements due to their lower mechanical stiffness. In this thesis a novel electrostatic transducer is presented; the transducer is made of thin polymer films and liquid dielectrics, combined with rigid stiffening elements to form a circular electrostatic bellow muscle (EBM) unit capable of out-of-plane contraction. These units are easy to manufacture and can be arranged in arrays and stacks that can be employed as contractile artificial muscles, pumps for fluid-driven soft robots, or as energy harvesters. As artificial muscles, EBMs of 20 - 40 millimeters in diameter can exert forces of up to 6 newtons, lift loads over a hundred times their own weight, and reach contractions of over 40 per cent with strain rates over 1200 per cents per second, with a bandwidth over 10 Hz. As pump drivers, EBMs produce flow rates of up 0.63 liters per minute and maximum pressure head of 6 kilopascals, whereas as generators, they reach a conversion efficiency close to 20 per cent. The compact shape, low cost, simple assembling procedure, high reliability and large contractions make the EBM a promising technology for high-performance robotic systems.