Sliding Speed Influences Electrovibration-Induced Finger Friction Dynamics on Touchscreens

Electrovibration technology enables tactile texture rendering on capacitive touchscreens by modulating friction between the finger and the screen through electrostatic attraction forces, generated by applying an alternating voltage signal to the screen. Accurate signal calibration is essential for robust texture rendering but remains challenging due to variations in sliding speed, applied force, and individual skin mechanics, all of which unpredictably affect frictional behavior. Here, we investigate how exploration conditions affect electrovibration-induced finger friction on touchscreens and the role of skin mechanics in this process. Ten participants slid their index fingers across an electrovibration-enabled touchscreen at five sliding speeds ($20\sim100$ mm/s) and applied force levels ($0.2\sim0.6$ N). Contact forces and skin accelerations were measured while amplitude modulated voltage signals spanning the tactile frequency range were applied to the screen. We modeled the finger-touchscreen friction response as a first-order system and the skin mechanics as a mass-spring-damper system. Results showed that sliding speed influenced the friction response's cutoff frequency, along with the estimated finger moving mass and stiffness. For every $1$ mm/s increase in speed, the cutoff frequency, the finger moving mass, and stiffness increased by $13.8$ Hz, $3.23\times 10^{-5}$ kg, and $4.04$ N/m, respectively. Correlation analysis revealed that finger stiffness had a greater impact on the cutoff frequency than moving mass. Notably, we observed a substantial inter-participant variability in both finger-display interaction and skin mechanics parameters. Finally, we developed a speed-dependent friction model to support consistent and perceptually stable electrovibration-based haptic feedback across varying user conditions.