Robotic Granular Jamming: Does the Membrane Matter?

Soft robotics for medical, endoscopic applications requires a dexterous and compliant mechanism to increase accessibility and decrease patient injury. However, soft structures do not offer the level of image and platform stability provided by rigid structures. Thus, a variable stiffness mechanism is an ideal solution to reconcile the two requirements of compliance and stability; the mechanism explored here is granular jamming. Granular jamming is a phenomenon in which particulate matter within a membrane can transition from a fluidlike to a solidlike state, based on the level of applied vacuum pressure. In the solidlike jammed state, the conventional assumption is made that granule-granule contacts dominantly contribute to the system's stiffness. Thus, many works have evaluated the effects of different granule types by experimentally varying the sizes, shapes, and material properties of the particles. However, the role of the membrane in determining the possible range of stiffness or the variability of granular jamming has not been well studied. This article investigates the effects and significance of membranes for a granular jamming system. Several membranes were experimentally tested and analyzed in order to find the amount of flexibility and stiffness they provide when the system is in an unjammed and jammed state, respectively. This article presents for the first time that the membrane plays a significant contributing factor in granular jamming stiffness.