Soft actuators promise to expand the capabilities of conventional robots, allowing them to navigate unstructured terrain and to safely interact with humans. HASEL (hydraulically amplified, self-healing, electrostatic) actuators are a class of soft actuators that feature direct electrical activation via Maxwell stress, electrical self-healing, and fast actuation. Planar HASEL actuators, a subset of HASELs that expand in-plane upon activation, comprise a stretchable dielectric shell that is coated with compliant electrodes and filled with a liquid dielectric. While planar HASEL actuators have demonstrated strong experimental performance, the details of the underlying electromechanics are yet to be explored. In experiments, two mechanisms of deformation are observed: elastic stretching and electrohydraulic “zipping”. This letter analyzes these mechanisms using two examples: a circular planar HASEL actuator that stretches equibiaxially, and a linear actuator that both stretches and zips. We use an energy minimization approach to derive nonlinear electromechanical models for their quasistatic actuation behavior. The analysis shows that the actuation behavior of circular HASEL actuators is similar to that of dielectric elastomer actuators (DEAs), and reveals how the added liquid layer in planar HASELs reduces their stiffness, allowing them to achieve greater strains than DEAs of the same dimensions. For the linear actuator, the model displays how the actuator only stretches until it reaches a critical voltage at which it starts to zip, drastically increasing strain. This work lays the foundation for the theoretical analysis of planar HASEL actuators, which consist of stretchable materials.

软执行器有望扩展传统机器人的能力，使它们能够在非结构化地形中导航并安全地与人类互动。HASEL（液压放大、自愈、静电）致动器是一类软致动器，具有通过麦克斯韦应力直接电激活、电自愈和快速致动的特点。平面 HASEL 致动器是 HASEL 的一个子集，在激活时会在平面内扩展，包括一个可拉伸的介电外壳，该外壳涂有柔顺电极并填充有液体电介质。虽然平面 HASEL 执行器已表现出强大的实验性能，但潜在的机电细节仍有待探索。在实验中，观察到两种变形机制：弹性拉伸和电动液压“拉链”。这封信使用两个示例分析了这些机制：等双轴拉伸的圆形平面 HASEL 致动器，以及同时拉伸和拉动的线性致动器。我们使用能量最小化方法为其准静态驱动行为推导非线性机电模型。分析表明，圆形 HASEL 致动器的致动行为与介电弹性体致动器 (DEA) 的致动行为相似，并揭示了平面 HASEL 中添加的液体层如何降低其刚度，从而使其获得比相同尺寸的 DEA 更大的应变。对于线性致动器，模型显示致动器如何仅在达到临界电压时才开始拉伸，从而开始拉动，从而显着增加应变。这项工作为平面HASEL执行器的理论分析奠定了基础，