Design and Experimental Characterization of a Vacuum-Actuated Granular-Jamming Actuator for Stiffness Modulation

Variable-stiffness tactile interfaces are of interest for applications including medical simulation, rehabilitation, and human–machine interaction, where controllable mechanical resistance is required during physical contact. Granular jamming provides a mechanically simple approach for modulating stiffness by transitioning a particle-filled compliant structure from a deformable to a load-bearing state through vacuum-induced confinement. This study presents the design, fabrication, and quasi-static mechanical characterization of a 25 mm diameter vacuum-controlled granular-jamming tactile nodule. The device consisted of a compliant membrane chamber containing 8 g of 0.6–0.8 mm plastic microbeads and was actuated using a syringe-based vacuum circuit. Compression testing was performed using a finger-like rubber indenter across eleven vacuum levels from 0 to −68.9 kPa. Global and depth-dependent local stiffness were calculated from repeated force-displacement measurements. Vacuum actuation increased effective global stiffness from 1.168 N/mm at atmospheric pressure to a maximum of 9.808 N/mm at −62.1 kPa, representing an approximately 8.4-fold increase. Local stiffness exhibited nonlinear pressure- and depth-dependent behavior, reaching 15.06 N/mm at 2.00 mm indentation and −68.9 kPa. These results provide quantitative design guidance for future granular-jamming tactile interfaces requiring controllable compliance and realistic mechanical feedback.