Jamming Mechanism with Constrictional Chainmail Structures for Robotic Leg Mechanisms Under Uneven Terrain Contact

Legged robots exhibit high mobility on uneven terrain but face challenges in stability, complex control systems, and energy efficiency. This study proposes a leg mechanism that significantly alters its stiffness by inducing jamming in a chainmail structure through only gravity-induced compression. To evaluate the fundamental characteristics of the proposed mechanism, experiments were conducted to identify the jamming point and to assess stiffness in the jammed state. The results confirmed that the force required to trigger jamming increases proportionally with the mass applied from above, which demonstrates properties similar to friction between solid materials. Furthermore, the stiffness in the jammed state is strongly correlated with the contact points within the structure. These results prove the effectiveness of the proposed passive leg mechanism for stiffness switching. In a case study assuming landing on uneven terrain, the mechanism could be fixed in any orientation based on the designed compressive force.