Fundamental Acoustical Finger Force Calculation for Out-of-Plane Ultrasonic Vibration and its Correlation with Friction Reduction

When a finger touches an ultrasonic vibrating plate, non-sinusoidal contact force appears, named acoustical finger force. In this paper, we present a method to observe its fundamental in the case of a friction reduction haptic interface. The capability of the method to be achieved on-line, in a small micro-controller, is established. We show a correlation between this measurement and the friction when sliding the finger. A model that predicts the friction coefficient and the friction contrast is laid down; it gives consistent output for 10 participants out of 12 having different biomechanical skin parameters of the skin.