Electrovibration has become one of the promising approaches for adding tactile feedback on touchscreen. Previous studies revealed that the normal force applied on the touchscreen by the finger affects significantly the electrostatic force. It is obvious that the normal force affects the electrostatic force if it changes the contact area between the finger and the touchscreen. However, it is unclear whether the normal force affects the electrostatic force when the apparent contact area is constant. In this paper, we estimated the electrostatic force via measuring the tangential force of the finger sliding on a 3M touchscreen at different normal forces under the constant apparent contact area. We found that the electrostatic force increases significantly as the normal force increases from 0.5 to 4.5N. We explained the experimental results using the most recently proposed electrostatic force model, which considers the effect of air gap. We estimated the averaged air gap thickness using the electrostatic force model. The results showed that the relationship between the air gap thickness and the normal force follows a power function. Our experiment suggests that the normal force has a significant effect on the air gap thickness, thus require consideration in the design of tactile feedback.

中文翻译：

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外加法向力对电振动的影响

电振动已成为在触摸屏上添加触觉反馈的有前途的方法之一。先前的研究表明，手指施加在触摸屏上的法向力会显着影响静电力。很明显，如果法向力改变了手指和触摸屏之间的接触面积，就会影响静电力。然而，当表观接触面积恒定时，法向力是否影响静电力尚不清楚。在本文中，我们通过测量手指在 3M 触摸屏上以不同的法向力在恒定的表观接触面积下滑动的切向力来估计静电力。我们发现随着法向力从 0.5 增加到 4.5N，静电力显着增加。我们使用最近提出的静电力模型解释了实验结果，该模型考虑了气隙的影响。我们使用静电力模型估计了平均气隙厚度。结果表明，气隙厚度与法向力之间的关系服从幂函数。我们的实验表明，法向力对气隙厚度有显着影响，因此需要在触觉反馈设计中加以考虑。