Bidirectional bending of soft actuators with elliptical cavities and arched sidewalls under dual pressure actuation

Soft pneumatic actuators offer remarkable flexibility and adaptability for interacting with complex environments. Owing to their low cost, lightweight construction, rapid responsiveness, and ease of fabrication, pneumatic actuation has become a dominant technology in soft robotics. However, most existing soft pneumatic bending actuators function exclusively under either positive or negative pressure, and designs that can effectively exploit both regimes remain scarce. In this work, we present a novel soft actuator architecture that integrates perforated elliptical holes with arched sidewalls to generate asymmetric bending under positive and negative pressure, thereby enabling a diverse range of motions. Finite element analysis is employed to systematically examine how the geometry and spatial distribution of the elliptical holes, together with the structural parameters of the arched sidewalls, influence bending performance. Guided by these insights, we design an actuator capable of bending in opposite directions when subjected to positive and negative pressure, respectively. Experimental characterization further elucidates the relationship between input pressure and deformation magnitude, showing close agreement with finite element simulations and validating the proposed design. Extending this minimal functional unit concept, we demonstrate a multi-directionally bendable actuator capable of reliable deformation toward any quadrant through the coordinated application of positive and negative pressure via two independent pneumatic interfaces. This design significantly broadens the functional repertoire of soft pneumatic actuators and opens new avenues for soft robotic systems with enhanced versatility, with potential applications in robotics, wearable devices, and medical assistive technologies.