Design and Experimental Validation of a Shock-Absorption Mechanism Inspired From the Frog's Forelimbs

Frogs reveal superior shock-absorption ability, which is mainly brought by the forelimbs. Frogs touch the ground with their forelimbs first in landing, followed by the elbow joints’ compression. In this process, the muscles and tendons of the forelimbs are pulled to store energy. However, muscles and tendons reveal different characteristics in the buffering process. The shock-absorption principle of the frog's forelimbs should be discussed explicitly and systematically on the coordination of muscles and tendons. In this study, we compared the EMG signals of m. anconeus, a primary muscle of frog's forelimb for landing, with the dynamic motions of the forelimb in the landing process. A short muscle potential resting was found around the time of ground touching. Meanwhile, we found that after the frog's toes touched the ground, the movement of the frog went into a buffer stage to absorb impact energy, and the buffering process exhibited different stages, revealing linear and nonlinear characteristics. These results revealed that the forelimb muscles and tendons worked at different times in landing, which formed the different stages. Inspired by the buffering principle of the frog, a bionic shock-absorption mechanism was designed using the torsion springs and dampers. The newly designed mechanism revealed improved buffering performances than the traditional spring-damper devices.