Design and Application of High-Stretchability and Variable-Tensile-Stiffness Fiber via Crossing Layer Jamming Structure

Variable stiffness technology plays a key role in exploiting the advantages of soft robotics, however, few solutions can satisfy both large deformability and wide-range stiffness tunability. In this work, we present the variable tensile stiffness fiber (VTSF) based on crossing layer jamming, which enables both high stretchability and tensile stiffness tunability. By leveraging an X-shape crossing of layers and combining it with the outside silicone tube, the fiber can achieve fine stretchability and recovery. By applying a vacuum to the tube, friction between the layers generated by the atmosphere pressure allows for high tensile stiffness tunability. We establish the stretchability and mechanical models to illustrate the underlying principle of the VTSF and guide the design process. Our proposed fiber can achieve stretchability theoretically up to 300%, more than 100× tensile stiffness modulation, and a tunable maximum tensile force >25 N. We apply the VTSFs to the soft actuators and rigid-linkage joints to show the functionality. By combining the VTSFs with soft actuators, we verify their capability to achieve reprogrammable deformations and motions. Moreover, by applying the VTSFs to the rigid structures, we achieve both wide-range motion and high load capacity tunability of the soft-rigid coupled structures.