Ring origami spring capable of eversion morphing

Abstract Origami structures have been widely used in soft robots, mechanical metamaterials, architectural engineering and biomedical engineering in recent years, benefiting from their reconfigurable shape morphing and tunable mechanical properties through folding and unfolding. In this work, we construct a new origami structure named ring origami spring (ROS) by alternately folding two perpendicularly arranged paper ribbons with the same size and connecting two ends of them. ROS can achieve an eversion morphing with four stable states, based on which both underwater locomotion and traversing water-air interface have been implemented. Theoretical models for characterizing the eversion morphing during the transition of stable states and the induced locomotion performance of ROS have been developed, and the theoretical predictions are in good agreement with the experimental results. The current work provides a new strategy for the design of origami robots, which is potentially applied in exploring complex environments.