Robots made of soft materials are demonstrating to be well suited in applications where dexterity and intrinsic safety are necessary. However, one of the most challenging goals of soft robotics remains the ability to change the stiffness of body parts to guarantee stability and to produce significant forces. Among soft actuation technologies reported in literature, the jamming phenomenon is now achieving resounding interest. The jamming transition was observed and studied both with granular and laminar material; however, there is a third possibility that is not gaining the attention that probably would deserve: the fiber jamming. The aim of this study was an attempt to analyze the main parameters influencing the fiber jamming transition as promising stiffening solution for soft robotics. A preliminary analysis to choose the most suitable filling material and the external membrane that compose the system was performed and three possible configurations were designed. The prototypes thus assembled were experimentally investigated by using two different setups: one for conducting comparative bending tests on the systems and another for assessing the mechanical properties of single filling fibers. The results of the tests are used to feature the correlation between the arrangement and the material properties of the fibers and the stiffening capability of the fiber jamming systems. The investigation has shown performances comparable with those obtained with granular and layer jamming, demonstrating that fiber jamming is a good candidate for integration in soft robotic devices.
Keywords: compliant materials; fiber jamming transition; flexible mechanisms; soft robotics; variable stiffness mechanisms.