School of Mechanical Engineering and Automation, Harbin Institute of Technology, Shenzhen, PR China.
School of Mechanical Engineering and Automation, Harbin Institute of Technology, Shenzhen, PR China.
J Biomech. 2021 May 24;121:110417. doi: 10.1016/j.jbiomech.2021.110417. Epub 2021 Apr 5.
A frog can jump several times higher than its own height and then land smoothly on the ground. During the buffering phase, both forelimbs touch the ground and compact quickly to absorb most of the impact energy. However, the adjustment of the joint angles of the forelimb and the induced cushioning effect during the landing process have not been thoroughly investigated. In this study, we statistically summarized the angular displacements of forelimb joints with respect to landing velocities by using a high-speed motion capture system. It is found many joint angles were linearly influenced by landing velocity at both ground touching moment and maximum compression moment. Moreover, the double-peak pattern of ground reactive force was measured, which attributes to the forelimb landing and the followed abdomen/hindlimb landing. Before the appearance of the first peak, the compression of the forelimb and the reactive force revealed a linear relationship regardless of velocity, implying that the forelimbs act as a constant stiffness spring in landing. Accordingly, a simple spring-mass model was proposed and verified by simulation for forelimb cushioning of the frog. We anticipate our achievements to inspire the design of future landing mechanisms.
青蛙可以跳跃超过自身高度好几倍的距离，并且平稳地降落在地面上。在缓冲阶段，前肢同时接触地面并迅速压缩，以吸收大部分的冲击能量。然而，前肢关节角度的调整以及着陆过程中的诱导缓冲效应尚未得到彻底研究。在这项研究中，我们使用高速运动捕捉系统对前肢关节相对于着陆速度的角位移进行了统计总结。结果发现，在触地时刻和最大压缩时刻，许多关节角度都与着陆速度呈线性关系。此外，还测量到地面反作用力的双峰模式，这归因于前肢着陆和随后的腹部/后肢着陆。在第一个峰值出现之前，前肢的压缩和反作用力呈现出线性关系，与速度无关，这意味着前肢在着陆过程中充当一个恒定刚度的弹簧。因此，提出了一个简单的弹簧-质量模型，并通过模拟对青蛙的前肢缓冲进行了验证。我们期望我们的研究成果能够为未来的着陆机构设计提供启示。
