Sandwich Jamming-Based Variable Stiffness Structures With User-Defined Degrees of Freedom for Soft Wearable Devices

Abstract

Variable stiffness structures are essential in soft wearable robotics, where both flexibility and load-bearing capacity are required within a single design. However, achieving stiffness profiles with user-defined degrees of freedom (DoFs) remains a major challenge. This paper presents a systematic, simulation-based method for designing sandwich jamming structures achieving variable stiffness with the targeted DoFs. The approach begins with DoF selection and uses topology optimization to generate unit cell geometries tailored to the desired mechanical behavior. These designs are then refined through geometric preprocessing and scaled into full-sized cores. Parametric optimization, using the Taguchi Design of Experiments and finite element simulations, fine-tunes the stiffness response under both jammed and unjammed conditions. Two designs, 1D-Flex and 2D-Flex Core, are developed to mimic the interphalangeal (IP) and metacarpophalangeal (MCP) finger joints, respectively. Experimental results confirm directional stiffness contrasts aligned with the design intent, and integration into a glove -type wearable device demonstrates the structure's ability to support external load without finger contact. These results validate the proposed method as a versatile tool for designing soft wearable systems with customizable variable stiffness with user-defined DoFs.