Optimal skin impedance promotes perception of ultrasonic switches

Abstract

International audienceUltrasonic friction reduction is one potential technology for bringing tangibility to flat touchscreens. We previously established that this approach can be used to create an artificial sensation of pressing a mechanical switch by varying the coefficient of friction, which depends on the force applied by the user. This sensation proves effective majority of, but a non-negligible fraction reported feeling only weak sensations or none at all. In the present study, we examined the factors possibly involved in producing a vivid perception of a stimulus by measuring the mechanical impedance of the fingertip as an index to the frictional behavior, and performing psychophysical experiments. Subjects who experienced weaker sensations were found to have a weaker susceptibility to friction modulation, which may in turn be attributable to either a larger or a smaller than average/normal impedance; whereas those with a mechanical impedance of around 55 N.s/m clearly perceived the ultrasonic switch. Measuring and factoring the users impedance in real time could therefore provide a useful means of improving the rendering of ultrasonic surface haptic devices

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

“…Although, the earlier studies have investigated the contact mechanics of friction [5], [10]- [17] and our perceptual ability to discriminate two different surfaces based on friction [18]- [20], the number of studies investigating the intermittent contact mechanics during a change in friction on a touch surface is very limited [21]- [24]. Furthermore, the factors affecting our tactile perception of this change have not been investigated in depth yet [22]- [26].…”

“…Apart from the studies on sliding-finger, it has been shown that a click effect, as in key press, can be created by reducing the friction as the user presses on an ultrasonically actuated touch surface [23], [26], [30], [31]. Tashiro et al [30] have rendered the feeling of buckling and restitution of mechanical buttons using Langevin-type ultrasonic transducer.…”

“…Unlike [30], Monnoyer et al [31] argued that the feeling of click occurs due to a sudden release of stress at the fingertip, which is accumulated when the friction of surface is high. Recently, it has been shown that there is an optimal value of finger impedance that leads to a stronger perception of haptic click effect [26]. Moreover, the rate of change in normal force has been reported to play an important role in perception of click effect [23].…”

Detection of Friction-Modulated Textures is Limited by Vibrotactile Sensitivity

“…10.b) when compared to the vibratory transfer function V . The variability between plate vibration and friction reduction efficiency reflects differences in the bio-mechanical properties of the finger skin, which were also observed in [45] and have been shown to significantly affect subjects' perception [46]. Therefore, stimuli generation on surface haptics should focus on controlling the frictional force and friction coefficient rather than the ultrasonic amplitudes, as proposed in [47], [48].…”

Travelling Ultrasonic Wave Enhances Keyclick Sensation

“…Users detected more easily the falling friction than the rising friction and reported to feel it as a convincing keyclick sensation. The proposed method relies on sudden changes in the impedance of the finger [13], which are provoked by the influence of the ultrasonic lubrication [19,16] on the compression of the fingerpad. Lateral motion of the finger is generally necessary to the occurrence of friction modulation by ultrasonic lubrication.…”