Rendering tactile effects on a touch screen via electrovibration has many potential applications. However, our knowledge on tactile perception of change in friction and the underlying contact mechanics are both very limited. In this article, we investigate the tactile perception and the contact mechanics for a step change in friction under electrovibration during a relative sliding between a finger and the surface of a capacitive touch screen. First, we conduct magnitude estimation experiments to investigate the role of normal force and sliding velocity on the perceived tactile intensity for a step increase and decrease in friction, called rising friction (RF) and falling friction (FF). To investigate the contact mechanics involved in RF and FF, we then measure the frictional force, the apparent contact area, and the strains acting on the fingerpad during sliding at a constant velocity under three different normal loads using a custom-made experimental set-up. The results show that the participants perceived RF stronger than FF, and both the normal force and sliding velocity significantly influenced their perception. These results are supported by our mechanical measurements; the relative change in friction, the apparent contact area, and the strain in the sliding direction were all higher for RF than those for FF, especially for low normal forces. Taken together, our results suggest that different contact mechanics take place during RF and FF due to the viscoelastic behavior of fingerpad skin, and those differences influence our tactile perception of a step change in friction.

中文翻译：

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电振动下摩擦的阶跃变化

通过电振动在触摸屏上呈现触觉效果具有许多潜在的应用。然而，我们对摩擦变化的触觉感知和潜在接触力学的了解都非常有限。在本文中，我们研究了在手指与电容式触摸屏表面之间相对滑动期间电振动下摩擦力阶跃变化的触觉感知和接触力学。首先，我们进行幅度估计实验，以研究法向力和滑动速度对感知触觉强度的作用，以增加和减少摩擦，称为上升摩擦 (RF) 和下降摩擦 (FF)。为了研究 RF 和 FF 中涉及的接触力学，我们然后测量摩擦力、表观接触面积、以及使用定制的实验装置在三种不同的法向载荷下以恒定速度滑动期间作用在指垫上的应变。结果表明，参与者对 RF 的感知强于 FF，并且法向力和滑动速度都显着影响了他们的感知。这些结果得到了我们的机械测量的支持；RF 的摩擦相对变化、表观接触面积和滑动方向的应变都高于 FF，尤其是对于低法向力。总之，我们的结果表明，由于指垫皮肤的粘弹性行为，在 RF 和 FF 期间会发生不同的接触力学，这些差异会影响我们对摩擦阶跃变化的触觉感知。