Gripping, Catching, and Conveying With a Soft, Toroidal Hydrostat

This work demonstrates that a soft, toroidal hydrostat can be used to perform three functions found in both living and engineered systems: gripping, catching, and conveying. We first demonstrate a gripping mechanism that uses linear motion to drive the inversion of the toroid around objects, encapsulating them within a crumpled elastic membrane under hydrostatic pressure. This mechanism results in gripping forces ranging from 1–80 N, which depend predictably upon the geometric and material properties of the gripper and the object. We next demonstrate a catching mechanism akin to that of a chameleon’s tongue: the elasticity of the membrane is used to store mechanical energy and drive a rapid acceleration and inversion process (≈400 m/s2) to capture flying objects (e.g., a bouncing ball). Finally, we show how the soft topological structure can be implemented in a soft conveying mechanism which continuously inverts and passes objects through its center (~1 cm/s), serving a function like that of esophageal peristalsis (i.e., transporting objects through a tube), while eliminating the requirement of a lubricated interface and the coordinated actuation of a pressure wave. The hybrid hard-soft mechanisms presented here can be applied in the integration of soft functionality into conventional robotic systems for applications including the automation of agricultural and biological research processes. More generally, we show how inflatable structures comprising soft polymeric films arranged in complex topologies provide a promising approach to designing soft robotic systems with novel, bio-inspired functionality.