Our setups for investigating the haptic rendering technique of electrovibration. We measure the smallest electrovibration forces that participants can reliably feel (left) while interacting with a display using diverse contact conditions, along with the finger-pad deformations caused by these forces (right).
Researchers worldwide want to discover how to generate compelling tactile sensations on touchscreens to increase the usability of mobile devices and other interactive computer systems. One technique for generating such sensations is to control the friction force between the screen and the finger-pad of the user via electrostatic actuation; this haptic rendering approach is commonly called electrovibration. When an alternating voltage is applied to the conductive layer of a touch screen, an attractive force is generated between its surface and the user's finger. Systematic modulation of the voltage creates various haptic effects.
This project aims to shed light on our limited knowledge of how finger motion (stationary or moving), finger pressing force, and contact by multiple fingers affect electrovibration perception and the underlying physical mechanisms of these perceptions.
In our first study [ ], by conducting psychophysical experiments and simultaneously measuring contact forces, we proved for the first time that both the finger’s motion and contact by a second finger significantly affect what the user feels. At a given voltage, a single moving finger experiences much larger fluctuating electrovibration forces than a single stationary finger, making electrovibration much easier to feel during interactions involving finger movement. Indeed, only about 30% of participants could detect the stimulus without motion. Part of this difference comes from the fact that relative motion greatly increases the electrical impedance between a finger and the screen. In contrast to some theories, we found that threshold-level electrovibration did not significantly affect the coefficient of kinetic friction in any conditions.
Currently, we are investigating the effects of electrovibration on the contact evolution of finger-pad area. Our preliminary results indicate that the real contact area increases as a function of the alternating electrovibration force, again suggesting that electrovibration perception is mediated by temporal neural mechanisms rather than an overall increase in friction.