Perception of Ultrasonic Switches Involves Large Discontinuity of the Mechanical Impedance

Abstract

The distinct tactile feedback provided by mechanical keyboards notifies users that their actions have been successfully recorded. The presence of these subtle yet informative tactile cues is one of the reasons why mechanical keyboards are still preferred to their virtual counterparts. An artificial sensation of pressing a mechanical switch can be produced by varying the coefficient of friction as the user is pressing down on a glass surface using ultrasonic vibration. We examined the factors involved in producing a vivid sensation of a stimulus by measuring the mechanical impedance, the frictional behavior of the fingertip and the perceptual thresholds. Subjects who experienced weaker sensations also showed a weaker sensitivity to friction modulation, which may in turn be attributable to the presence of a larger or a smaller than average impedance. In the second experiment, the user's finger impedance was measured during the click, and it was observed that the successful detection of the stimulus was correlated with the presence of considerable discontinuity in the mechanical impedance added to the plate by the finger. This discontinuity in the evolution of the impedance supports the idea that the skin is being reconfigured towards a new equilibrium state after the change in friction.

Fundamental Acoustical Finger Force Calculation for Out-of-Plane Ultrasonic Vibration and its Correlation with Friction Reduction

“…Therefore, to obtain a same perceptual intensity of a tactile stimuli, the vibration amplitude should be adapted according to the scanning speed and pressing force, which can be measured with sensors, but also to the biomechanical properties of the finger pad, which change from one user to the other. In [8], the measured acoustical impedance is correlated to the perception of simulated keyclick, since this measure is directly correlated to the biomechanical properties of the finger pad. The authors propose to use this *This work has been carried out within the framework of the Mint Project of IRCICA (Service and Research unit from CNRS) 1,2 The authors are with Univ.…”

Initial contact shapes the perception of friction

“…This metric is used to control the force applied by robotic grippers to soft and fragile objects (19)(20)(21). In haptic rendering, it is possible to produce tactile sensations by releasing the accumulated stress using ultrasonic friction modulation (22). However, the perception of the frictional strength with a single normal motion is not as salient.…”

Detection of Friction-Modulated Textures is Limited by Vibrotactile Sensitivity

“…A higher finger velocity was found to increase the intensity of the perception [32]. Interestingly, it has been shown that transient changes in friction could also be perceived with static touch [33] to recreate the illusion of pressing a button. Other studies have shown that the perception of two superimposed friction modulated sinusoidal gratings presents masking effects [34], [35].…”