Tactile Perception of Virtual Edges and Gratings Displayed by Friction Modulation via Ultrasonic Actuation

Abstract

To render tactile cues on a touchscreen by friction modulation, it is important to understand how human perceive a change in friction. In this study, we investigate the relations between perceived change in friction on an ultrasonically actuated touchscreen and parameters involved in contact between finger and its surface. We first estimate the perceptual thresholds to detect rising and falling friction while finger is sliding on the touch surface. Then, we conduct intensity scaling experiments and investigate the effect of finger sliding velocity, normal force, and rise/fall time of vibration amplitude (transition time) on the perceived intensity of change in friction. In order to better understand the role of contact mechanics, we also look into the correlations between the perceived intensities of subjects and several parameters involved in contact. The results of our experiments show that the contrast and rate of change in tangential force were best correlated with the perceived intensity. The subjects perceived rising friction more strongly than falling friction, particularly at higher tangential force contrast. We argue that this is due to hysteresis and viscoelastic behavior of fingertip under tangential loading. The results also showed that transition time and normal force have significant effect on our tactile perception.

Understanding the Effects of Tactile Grating Patterns on Perceived Roughness Over Ultrasonic Friction Modulation Surfaces

“…This explains why low- and high-friction zones resulted in similar perceived roughness. Such a result is in line with Saleem et al (Saleem et al, 2020), which showed that period gratings displayed by consecutive sequences of FF followed by RF were perceived with the same acuity as compared to vice versa.…”

“…(2017) are different (ultrasonic vs. electrostatic), the perceived roughness in both studies exhibited inverted U-shape trends with varying widths of low-friction and high-friction zones. This may be because the perceived roughness over virtual gratings depends on gratings’ edges (Saleem et al, 2020) and the two device types could generate similar gratings’ edges (E. Vezzoli et al, 2015).…”

“…In their study, the participants distinguished a difference of 8.96% in the spatial periods (SPs) of the two patterns presented to them. Saleem et al (2020) studied step changes in frictional gratings on an ultrasonic friction surface. Their results showed a step fall in friction followed by a step rise in friction could be identified more easily than the reverse order.…”

Step-Change in Friction Under Electrovibration

“…The dynamics of multiple step changes in friction is different from the single one since the interval between the steps is a factor affecting the tactile perception. This topic (multiple step changes in friction) has been already investigated by Vardar et al [18] for electrovibration and Gueorguiev et al [19] Saleem et al [20] for ultrasonic actuation.…”

Surface haptic rendering of virtual shapes through change in surface temperature

“…Ultrasonic vibration decreases friction force by creating a lubricating squeeze film using surface vibration, whereas electroadhesion increases friction forces using high-voltage electrostatic interaction (typically 100 to 500 V) between fingertips and screens (16,17). The current commercially available devices can achieve 15 to 30% increase over the base friction force with typical voltages of 100 to 200 V (18)(19)(20)(21)(22)(23)(24)(25). Higher friction modulation of up to 43% has also been demonstrated with higher driving voltages of 200 to 500 V (26)(27)(28).…”