Electrostatic Bellow Muscle—Multifunctional Transducer Based on Zipping Dielectric Liquids

The realization of high-performance robotic and mechatronic systems, that are able to operate autonomously in unstructured environment and to interact safely with humans, often requires advanced actuators that feature attributes like lightweight, high power density, high efficiency, fast/ease control, intrinsic reliability, low-cost and adaptability.<br/>The choice of actuation technology that maximizes these properties is strongly connected with the dimensional scale that is considered. For example, in the small scale range of 10^-3-10^-1 mm, electrostatic actuators represent often the best option, while in the larger scale range of 10¹-10³ mm, electromagnetic actuators usually provide better performance. However, if we look at actuation in the length-scale in the range of 10^-1-10 mm there we will find a lack a clear winning solution that is able to guarantee large energy densities and lifetime, finite strokes and fast response, shock insensitivity, low-cost and high efficiency.<br/><br/>To address these shortcomings, a ground-breaking new class of electrostatic transducers has been recently introduced and studied by different research groups under the name of HASEL [1], electro-ribbon actuators [2] and dielectric fluid transducers (DFT) [3]. Getting inspiration from the seminal work of Prof. Najafi [4], these new types of electrostatic devices share a common working principle that is based on the use of dielectric liquids that are combined with stretchable or flexible shell structures, made of polymeric dielectric/electrode composite films, to implement a novel class of soft electrically-driven fluidic transducers that deform according to a zipping kinematics.<br/><br/>In this context, we have recently introduced the concept of Electrostatic Bellow Muscle (EBM) [4], a novel electrostatic transducer that is capable of bidirectional operation and can be effectively employed as direct drive contractile actuator, as generator and eventually as a pump. EBM are made of thin films and liquid dielectrics combined with rigid polymeric stiffening elements to form actuation units capable of out-of-plane contraction. These units can be easily manufactured and can be arranged in arrays and stacks, which can be effectively used as a soft direct drive linear actuator.<br/><br/>This contribution illustrates the EBM working principle and provides an effective modelling approach to describe their response that is validated against experimental results. Different materials and manufacturing methods of EBM are explored to identify those that are suitable to achieve reliable devices for mass production. Additionally, several demonstrations are presented in order show that EBM can be effectively employed not only as a contractile actuator but it can also work as a pump for fluid-driven soft robots, or as an energy harvester with interesting performance.<br/><br/>[1] Acome, E., Mitchell, S.K., Morrissey, T.G., Emmett, M.B., Benjamin, C., King, M., Radakovitz, M. and Keplinger, C., 2018. Hydraulically amplified self-healing electrostatic actuators with muscle-like performance. Science, 359(6371), pp.61-65.<br/><br/>[2] Taghavi, M., Helps, T. and Rossiter, J., 2018. Electro-ribbon actuators and electro-origami robots. <i>Science Robotics</i>, <i>3</i>(25).<br/><br/>[3] A New Class of Variable Capacitance Generators Based on the Dielectric Fluid Transducer, Duranti M., Righi M, Vertechy R., Fontana M. Smart Materials and Structures, 26 (11), 2017.<br/><br/>[4] Sadeghi, Mahdi M., Hanseup S. Kim, Rebecca L. Becky Peterson, and Khalil Najafi. "Electrostatic micro-hydraulic systems." <i>Journal of Microelectromechanical Systems</i> 25, no. 3 (2016): 557-569.<br/><br/>[5] Sîrbu, I.D., Moretti, G., Bortolotti, G., Bolignari, M., Diré, S., Fambri, L., Vertechy, R. and Fontana, M., 2021. Electrostatic bellow muscle actuators and energy harvesters that stack up. Science Robotics, 6(51).