Ultrasonic Friction Modulation While Pressing Induces a Tactile Feedback

Current touchscreen technology makes for intuitive human-computer interactions but often lacks haptic feedback offered by conventional input methods. Typing text on a virtual keyboard is arguably the task in which the absence of tactile cues imparts performance and comfort the most. Here we investigated the feasibility of modulating friction via ultrasonic vibration as a function of the pressing force to simulate a tactile feedback similar to a keystroke. Ultrasonic vibration is generally used to modulate the sliding friction which occurs when a finger moves laterally on a surface. We found that this method is also effective when the exploratory motion is normal to the surface. Psychophysical experiments show that a mechanical detent is unambiguously perceived in the case of signals starting with a high level of friction and ending to a low friction level. A weaker effect is experienced when friction is increasing with the pressure exerted by the finger, which suggests that the mechanism involved is a release of the skin stretch accumulated during the high-friction state.