Sea Shell Bioinspired Variable Stiffness Mechanism Enabled by Hybrid Jamming Transition

Layer jamming and positive pressure jamming demonstrated great potential in soft robotic applications. The combination of these technologies can increase the performance of variable stiffness-oriented designs. Inspired by the shape of sea shell radial ribs, we introduce a planar lightweight device that can be easily adapted to different application scenarios, providing both significant stiffness variation and high load-bearing capabilities. Exploiting the ease of the system in terms of design and manufacturing, we tested the device with a different number of layers. It shows higher performances than standard layer jamming systems: in particular, the 1 layer per side version (7.5g) shows a variable stiffness ratio of 64:1 and a force required to reach a 10 mm deflection equal to 19N. The same values for the 5 layers per side version (17.2g) are 42.5:1 and 62N. These values are in line with the most promising innovative approaches reported in the literature on layer jamming. In addition, the presented results allow making a comparison between the introduced device and the biological counterpart in terms of performance, showing the validity of sea shells as a bioinspiration source for variable stiffness systems.