A New Design of Multilayered String Jamming Mechanism with Three-Degree-of-Freedom

A robot must exhibit softness so as not to accidentally damage its environment. However, stiffness is also necessary, so that the robot can transmit forces and perform tasks. In soft robotics, it is desirable to be able to switch between two states, namely a flexible state for adapt ion to the environment and a rigid state for the transmission of forces. String jamming mechanisms, which comprise many units connected in a bead-like pattern, have received attention for their ability to switch between flexible and rigid states. In this study, we propose a new design of the string jamming mechanism that enhances the maximum stiffness in the rigid state while maintaining a high fitting performance for the environment in the flexible state. We evaluate the fitting of the mechanism to the environment in a qualitative geometric discussion and compare the performance of the mechanism with that of existing string jamming mechanisms. The results of experiments measuring the maximum stiffness show the usefulness of the proposed mechanism from a quantitative point of view.