Effect of Finger Velocity on Frictional Forces Modulated by Electrovibration

We investigate the effect of sliding velocity on frictional forces between human finger and a touch screen actuated by electrostatic forces. For this purpose, we command a motorized slider to move human finger back and forth (one stroke) in horizontal direction at 9 different velocities (2, 5, 10, 20, 30, 40, 50, 60, 70 mm/s) while the finger is in contact with the touch screen and record the tangential forces for the normal forces varied in a controlled manner from 0.1 N to 0.9 N. During the experiments, the electrostatic forces were turned “ON” and “OFF” after every other stroke. The results of the experiments show that the data can be categorized into two groups: 1) stickslip and 2) sliding, which occurs at velocities higher than and equal to 30 mm/s. After grouping, we fit a nonlinear function in the form of F
_τ
= aF
_η
^b
to the sliding data recorded for the “OFF” and “ON” conditions. Using the fit functions, we show that the magnitude of the electrostatic forces increases from 50 to 310 mN as the normal force is increased from 0.1 N to 0.9 N.