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Flexoskeleton Fingers: 3D Printed Reconfigurable Ridges Enabling Multi-Functional and Low-Cost Underactuated Grasping

In this letter, we present a design and fabrication framework for soft, underactuated grippers that utilize reconfigurable laminate layers for finger stiffness modulation. The grippers consist of internal flexoskeleton layers, which are hybrid soft-rigid structures composed of a flexible thermoplastic sheet with rigid structures 3D printed directly onto the flexible layer. The flexoskeleton structures are encased in an external silicone skin, which enables smooth and soft contact surfaces between the gripper and objects. We designed the flexoskeleton layers to be reconfigurable through layer sliding, which enables finger stiffness modulation by two methods: 1) continuum stiffness modulation through layer sliding to enable strong overlap gripping, and 2) locking and unlocking of flexoskeleton ridge structures that enable stable grasps without actuation. The gripper designs presented here are extremely easy to design and fabricate and present a template for future soft grippers.