School of Chemical Engineering, University of Birmingham, Birmingham B15 2TT, UK.
J R Soc Interface. 2012 Dec 19;10(80):20120467. doi: 10.1098/rsif.2012.0467. Print 2013 Mar 6.
Many aspects of both grip function and tactile perception depend on complex frictional interactions occurring in the contact zone of the finger pad, which is the subject of the current review. While it is well established that friction plays a crucial role in grip function, its exact contribution for discriminatory touch involving the sliding of a finger pad is more elusive. For texture discrimination, it is clear that vibrotaction plays an important role in the discriminatory mechanisms. Among other factors, friction impacts the nature of the vibrations generated by the relative movement of the fingertip skin against a probed object. Friction also has a major influence on the perceived tactile pleasantness of a surface. The contact mechanics of a finger pad is governed by the fingerprint ridges and the sweat that is exuded from pores located on these ridges. Counterintuitively, the coefficient of friction can increase by an order of magnitude in a period of tens of seconds when in contact with an impermeably smooth surface, such as glass. In contrast, the value will decrease for a porous surface, such as paper. The increase in friction is attributed to an occlusion mechanism and can be described by first-order kinetics. Surprisingly, the sensitivity of the coefficient of friction to the normal load and sliding velocity is comparatively of second order, yet these dependencies provide the main basis of theoretical models which, to-date, largely ignore the time evolution of the frictional dynamics. One well-known effect on taction is the possibility of inducing stick-slip if the friction decreases with increasing sliding velocity. Moreover, the initial slip of a finger pad occurs by the propagation of an annulus of failure from the perimeter of the contact zone and this phenomenon could be important in tactile perception and grip function.
手指垫的接触区域存在复杂的摩擦相互作用，这影响了抓握功能和触觉感知的多个方面，这正是当前研究的主题。虽然摩擦力在抓握功能中起着至关重要的作用，但它对涉及手指垫滑动的辨别触摸的确切贡献却更加难以捉摸。对于纹理辨别，很明显振动触觉在辨别机制中起着重要作用。除其他因素外，摩擦力会影响由于指尖皮肤相对于探测物体的相对运动而产生的振动的性质。摩擦力还会对表面的触觉愉悦感产生重大影响。手指垫的接触力学受指纹脊和从这些脊上的毛孔分泌的汗液控制。反直觉的是，当与不透气的光滑表面（如玻璃）接触时，摩擦力在几十秒的时间内可以增加一个数量级。相比之下，对于多孔表面（如纸张），摩擦力会降低。摩擦力的增加归因于阻塞机制，可以用一级动力学来描述。令人惊讶的是，摩擦力对法向载荷和滑动速度的敏感性相对来说是二阶的，而这些依赖性为理论模型提供了主要依据，这些模型迄今为止在很大程度上忽略了摩擦动力学的时间演变。对触觉的一个显著影响是，如果摩擦力随滑动速度的增加而减小，则可能会产生粘滑现象。此外，手指垫的初始滑动是通过从接触区域的周边传播失效环来实现的，这种现象在触觉感知和抓握功能中可能很重要。
