The ultrafast snap of a finger is mediated by skin friction
The ultrafast snap of a finger is mediated by skin friction
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DOI：
10.1098/rsif.2021.0672
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发表时间：
2021-11-17
影响因子：
3.9
通讯作者：
Bhamla, M. Saad
中科院分区：
文献类型：
--
作者：
Acharya, Raghav;Challita, Elio J.;Bhamla, M. Saad
在人类文化中，弹指一挥间被用作交流和音乐的形式已有数千年。然而，尚未对这种快速运动的动力学进行系统的分析。使用高速成像和力传感器，我们分析了手指弹动的动力学。我们发现，手指在7 ms内实现了1.6 x 10（6）度s（-2）的峰值角加速度，使其成为人体产生的最快记录角加速度之一（超过职业棒球投球）。我们的分析揭示了中心作用的皮肤摩擦调解的卡扣动力学作为一个闩锁，以控制由此产生的高速度和加速度。我们通过实验评估这种摩擦闩锁的作用，用不同的材料覆盖拇指和中指，以产生不同的摩擦系数和不同的压缩性。在这样做时，我们揭示了指垫的可压缩的摩擦闩锁可能在摩擦和压缩的最佳调整的状态下操作。我们还开发了一个软的，可压缩的摩擦为基础的闩介导的弹簧驱动模型，以进一步阐明摩擦的关键作用，以及它如何与可压缩闩相互作用。我们的数学模型表明，摩擦力在手指扣动中起着双重作用，既有助于力的加载和能量的存储，同时又阻碍能量的释放。我们的工作揭示了如何利用表面之间的摩擦作为可调闩锁系统，并提供了对许多机器人和超快速能量释放结构中摩擦复杂性的设计见解。
The snap of a finger has been used as a form of communication and music for millennia across human cultures. However, a systematic analysis of the dynamics of this rapid motion has not yet been performed. Using high-speed imaging and force sensors, we analyse the dynamics of the finger snap. We discover that the finger snap achieves peak angular accelerations of 1.6 x 10(6)degrees s(-2) in 7 ms, making it one of the fastest recorded angular accelerations the human body produces (exceeding professional baseball pitches). Our analysis reveals the central role of skin friction in mediating the snap dynamics by acting as a latch to control the resulting high velocities and accelerations. We evaluate the role of this frictional latch experimentally, by covering the thumb and middle finger with different materials to produce different friction coefficients and varying compressibility. In doing so, we reveal that the compressible, frictional latch of the finger pads likely operates in a regime optimally tuned for both friction and compression. We also develop a soft, compressible friction-based latch-mediated spring actuated model to further elucidate the key role of friction and how it interacts with a compressible latch. Our mathematical model reveals that friction plays a dual role in the finger snap, both aiding in force loading and energy storage while hindering energy release. Our work reveals how friction between surfaces can be harnessed as a tunable latch system and provides design insight towards the frictional complexity in many robotic and ultra-fast energy-release structures.