Hydraulically amplified self-healing electrostatic (HASEL) actuators offer mechanical performance suitable for soft robotics and wearable devices. Strain decrease associated with sustained DC voltage application (DCV), however, remains a challenge. Here we discuss the role of charge retention (CR) in the actuation behavior of linearly contracting Peano HASELs under different voltage conditions and material compositions. We then discuss techniques for measuring dielectric absorption of different material combinations used to fabricate HASELs and discuss their relationship to CR. Selection of material combinations significantly impacts CR and is crucial to consider for HASELs and other devices driven by electrostatic forces.
Recently developed hydraulically amplified self-healing electrostatic (HASEL) actuators can utilize diverse material systems to create high-performance, muscle-mimetic actuators that can be tailored to specific applications. Initial versions of HASEL required cumbersome high voltage driving electronics and utilized a manual fabrication technique which was not easily adjusted to iterate designs. This presentation will describe a versatile and accessible fabrication technique using a computer numerically controlled (CNC) heat sealing machine to rapidly prototype complex designs of HASEL actuators. With this simple fabrication technique, we can create high performance HASELs which offer a variety of actuation modes. These actuators harness electrostatic zipping mechanisms to reduce operating voltages and facilitate a smooth actuation response to input voltage. Moreover, these HASELs feature linear strains over 100%, specific power of 816 W/kg, and cut-off frequencies of 125 Hz; these metrics enable actuators which are fast and powerful enough to jump. Using these devices, we create a continuum actuator capable of three-dimensional articulation and an active surface with programmable morphology. Additionally, we develop a portable electronics package for untethered operation of these soft robotic devices. This presentation will highlight the diverse design freedom inherent to HASEL actuators in terms of material selection and actuator design.
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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