The ultrafast snap of a finger is mediated by skin friction.

IF 3.7 2区 综合性期刊 Q1 MULTIDISCIPLINARY SCIENCES Journal of The Royal Society Interface Pub Date : 2021-11-01 DOI:10.1098/rsif.2021.0672
Raghav Acharya, Elio J Challita, Mark Ilton, M Saad Bhamla
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引用次数: 7

Abstract

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 × 106° 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.

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手指的超快啪啪声是由皮肤摩擦引起的。
几千年来,在人类文化中,打响指一直被用作一种交流和音乐的形式。然而,对这种快速运动的动力学还没有进行系统的分析。利用高速成像和力传感器,我们分析了指扣的动力学。我们发现,在7毫秒内,手指的咔嚓声达到了1.6 × 106°s-2的峰值角加速度,使其成为人体产生的最快角加速度记录之一(超过职业棒球投球)。我们的分析揭示了皮肤摩擦在调节弹跳动力学中的核心作用,通过充当锁存器来控制由此产生的高速度和加速度。我们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率,通过实验来评估这种摩擦锁的作用。在这样做的过程中,我们揭示了手指垫的可压缩、摩擦锁闩可能在摩擦和压缩的最佳状态下运行。我们还开发了一个软的、可压缩的基于闭锁的摩擦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的闭锁相互作用。我们的数学模型表明,摩擦在指扣中起着双重作用,既有助于力的加载和能量的储存,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,并为许多机器人和超快速能量释放结构中的摩擦复杂性提供了设计见解。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Journal of The Royal Society Interface
Journal of The Royal Society Interface 综合性期刊-综合性期刊
CiteScore
7.10
自引率
2.60%
发文量
234
审稿时长
2.5 months
期刊介绍: J. R. Soc. Interface welcomes articles of high quality research at the interface of the physical and life sciences. It provides a high-quality forum to publish rapidly and interact across this boundary in two main ways: J. R. Soc. Interface publishes research applying chemistry, engineering, materials science, mathematics and physics to the biological and medical sciences; it also highlights discoveries in the life sciences of relevance to the physical sciences. Both sides of the interface are considered equally and it is one of the only journals to cover this exciting new territory. J. R. Soc. Interface welcomes contributions on a diverse range of topics, including but not limited to; biocomplexity, bioengineering, bioinformatics, biomaterials, biomechanics, bionanoscience, biophysics, chemical biology, computer science (as applied to the life sciences), medical physics, synthetic biology, systems biology, theoretical biology and tissue engineering.
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