IEEE Trans Haptics. 2021 Apr-Jun;14(2):235-241. doi: 10.1109/TOH.2021.3073747. Epub 2021 Jun 17.
The contact between the fingertip and an object is formed by a collection of micro-scale junctions, which collectively constitute the real contact area. This real area of contact is only a fraction of the apparent area of contact and is directly linked to the frictional strength of the contact (i.e., the lateral force at which the finger starts sliding). As a consequence, a measure of this area of real contact can help probe into the mechanism behind the friction of skin on glass. In this article, we present two methods to measure the variations of contact area; one that improves upon a tried-and-true fingertip imaging technique to provide ground truth, and the other that relies on the absorption and reflection of acoustic energy. To achieve precise measurements, the ultrasonic method exploits a recently developed model of the interaction that incorporates the non-linearity of squeeze film levitation. The two methods are in good agreement ($\rho =0.94$) over a large range of normal forces and vibration amplitudes. Since the real area of contact fundamentally underlies fingertip friction, the methods described in the article have importance for studying human grasping, understanding friction perception, and controlling surface-haptic devices.
指尖与物体的接触是由一系列微观尺度的接触点组成的，这些接触点共同构成了实际接触面积。这个实际接触面积只是表观接触面积的一小部分，与接触的摩擦力（即手指开始滑动时的侧向力）直接相关。因此，测量实际接触面积的大小可以帮助探究皮肤与玻璃之间摩擦的机理。在本文中，我们提出了两种测量接触面积变化的方法：一种方法改进了经过验证的指尖成像技术，提供了真实的接触面积；另一种方法则依赖于声能的吸收和反射。为了实现精确的测量，超声方法利用了最近开发的挤压膜悬浮非线性相互作用模型。这两种方法在很大的法向力和振动幅度范围内具有很好的一致性（$\rho=0.94$）。由于实际接触面积是指尖摩擦力的基础，本文描述的方法对于研究人类抓握、理解摩擦感知和控制表面触觉设备具有重要意义。
