Viola seed capsules inspired high-contraction rhombic electrohydraulic actuators

Inspired by the geometry-mediated deformation mechanism of Viola seed capsules, this study proposes a high-contraction actuator composed of rhombic framework and stacked actuation units. The expansion of the stacked hydraulically amplified self-healing electrostatic (HASEL) units is mechanically converted by the rhombic frame into large axial contraction, enabling the local deformation of individual units to accumulate into a high overall contraction strain. Then, an analytical model based on geometric constraints and the minimum potential energy principle is developed to quantitatively predict the actuator output and validated through prototype experiments. Furthermore, the effects of key design parameters and driving signals on the static response are systematically investigated. The proposed high-contraction rhombic electrohydraulic actuators demonstrate pronounced contraction capability, with an unloaded maximum steady-state contraction ratio approximately 100 % and achieve a 42 % linear contraction with 5 g load.These findings provide a new strategy for the design and application of compact and high-performance bioinspired soft actuators.