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Traditional robots – made from electric motors and gears – are noncompliant, complex, and bulky, which limits their ability to perform in unstructured environments and increases risk during human-robot interactions. As a result, there have been efforts to design actuators from soft, compliant materials for use in versatile and adaptable robots. Electrohydraulic Peano-HASEL (Hydraulically Amplified Self-healing ELectrostatic) actuators have shown promise as linearly contracting soft actuators with high-speed operation, scalability, and simple design. Coupled with their versatility in fabrication and material systems, Peano-HASEL actuators have broad potential in robotics.
In this presentation, we derive an analytical model that accurately predicts the quasi-static stress-strain behavior and scaling laws of Peano-HASEL actuators without using fitting parameters. We provide extensive experimental validation of this model using actuators constructed from heat-sealable biaxially-oriented polypropylene shells, vegetable-based transformer oil, and ionically-conductive hydrogel electrodes. Despite using a simple set of geometric assumptions, we find robust agreement between model and experiment. From these results, we identify several straightforward methods for tuning and improving the performance of Peano-HASELs – including the creation of actuators optimized for maximum strain or maximum force, and a strategy for improving the specific energy of these devices from 6 J/kg currently to > 1000 J/kg. The basic principles of these methods are applicable to a wide range of HASEL actuators. Further, we experimentally demonstrate actuators with increased specific energies following the predictions of these modeling results. Moving forward, these results will serve as a roadmap for the development of high-performance Peano-HASEL actuators, opening new applications in robotics.
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