Tunable Anisotropic Stiffness with Square Fiber Jamming

Jamming is a phenomenon in which a collection of compliant elements is encased in an airtight envelope, and a vacuum-induced pressure enhances frictional and kinematic coupling, resulting in dramatic changes in stiffness. This paper introduces the jamming of square cross-sectioned fibers, which allow for tunable and programmable anisotropic stiffness. A theoretical model captures the effect of major geometric design parameters on the direction-variant bending stiffness of these long and slender jamming elements. The model is experimentally validated, and a 13-fold stiffening in one direction and a 22-fold stiffening in the orthogonal direction is achieved with a single jamming element. The performance of a square-fiber-jamming continuum robot structure is demonstrated in a steering task, with an average reduction of 74% in the measured insertion force when unjammed, and a direction-variant 53% or 100% increase in the measured tip stiffness when jammed.