Reconfigurable Soft Flexure Hinges via Pinched Tubes

Tuning the stiffness of soft robots is essential in order to extend usability and control the maneuverability of soft robots. In this paper, we propose a novel mechanism that can reconfigure the stiffness of tubular structures, using pinching to induce highly directional changes in stiffness. When pinched, these tubes can be then utilized as flexure hinges to create virtual joints on demand; the orientation of the hinge axis can additionally be selected via control of the distribution of pinch forces on the surface of the tube. Through proper material and geometry selection, passive shape recovery is observed when pinching forces are removed; a proposed active shape recovery technique can further assist the tube to recover its initial shape in order to re-configure the hinge in a new orientation. The proposed mechanism has been validated in FEA as well as experimentally, looking specifically at the relation between pinching force and curvature change, as well as comparing tube stiffness between pinched and unpinched configurations. The experimental prototype detailed in this paper - and demonstrated in the associated video - is capable of controlling the generation and recovery of flexure hinges at multiple orientations around the radial axis of tubes on demand.