Design and Evaluation of a Spherical Multi-Layered Unit for String Jamming Mechanisms

Abstract

In soft robotics, it is desirable to be able to switch between two states, namely a soft state for adaptation to the environment and a rigid state for the transmission of forces. String jamming mechanisms, composed of bead-like connected units, have gained attention for their ability to switch between these states. This paper presents the design and evaluation of a new multi-layered unit for string jamming mechanisms aimed at enhancing holding torque while maintaining high flexibility. The proposed spherical-layered unit addresses the dual-state challenge by introducing a spherical multi-layer structure that enhances frictional forces and improves holding torque in the rigid state without compromising flexibility in the soft state. Through theoretical analysis and experimental validation, we demonstrate that the proposed unit achieves an improvement in each fitting performance and holding torque compared to existing designs. This study provides guidelines for future applications of variable stiffness technologies, particularly in soft robotics, manipulators, and haptic devices.