Multi-morph pneu-net systems with a single input

A variety of shape-morphing actuators are adopted as an essential element of soft robots. While most of the existing actuators morph in a single mode, e.g., bending, twisting, or stretching, under a single stimulus, here we report a soft actuation technology that can achieve multiple morphing modes under a single stimulus with different intensities. A pneu-net system with soft chambers of different cross-sectional areas or wall materials is actuated at a relatively softer region first, but increasing the actuation pressure does not bulge the chamber indefinitely. Rather, the strain-hardening effects of hyperelastic elastomers stop the initially actuated chamber from swelling. The increased pressure actuates the remaining chambers that have not gone through strain-hardening. Hence, we can achieve multiple morphing sequentially by elaborate arrangements of the chambers of different stiffnesses. We experimentally demonstrate pneu-net systems that can sequentially exhibit 'bending and stretching', 'bending and twisting', and 'bending of opposite curvature' using a single air port. Our theoretical model combined with strain-hardening measurement data allows us to predict the transient and steady-state shapes of our soft robotic systems.