Travelling Ultrasonic Wave Enhances Keyclick Sensation

Abstract

A realistic keyclick sensation is a serious challenge for haptic feedback since vibrotactile rendering faces the limitation of the absence of contact force as experienced on physical buttons. It has been shown that creating a keyclick sensation is possible with stepwise ultrasonic friction modulation. However, the intensity of the sensation is limited by the impedance of the fingertip and by the absence of a lateral force component external to the finger. In our study, we compare this technique to rendering with an ultrasonic travelling wave, which exerts a lateral force on the fingertip. For both techniques, participants were asked to report the detection (or not) of a keyclick during a forced choice one interval procedure. In experiment 1, participants could press the surface as many time as they wanted for a given trial. In experiment 2, they were constrained to press only once. The results show a lower perceptual threshold for travelling waves. Moreover, participants pressed less times per trial and exerted smaller normal force on the surface. The subjective quality of the sensation was found similar for both techniques. In general, haptic feedback based on travelling ultrasonic waves is promising for applications without lateral motion of the finger.

2MoTac: Simulation of Button Click by Superposition of Two Ultrasonic Plate Waves

“…However, the detection thresholds of this click are higher compared with those measured to detect a friction change in presence of a lateral motion of the fingertip [12]. Therefore, [6] suggests to use a travelling wave instead of a standing wave. Indeed, the results show a lower perceptual threshold for travelling waves, and participants press less times per trial and exert smaller normal force on the surface in order to perceive click effect.…”

“…As in [6], two force levels f 1 = [0.1N, 0.4N ] are interleaved in order to avoid the prediction of the next stimulation intensity. Five different values for Λ = [0.5 2/3 1 1.5 2 ∞] were tested.…”

“…2a). The keyclick rendering was performed as in [6]; two normal force thresholds were defined f 1 and f 2 = f 1 + 0.3N . When the user reaches f 1 , we turn on the two modes, with specific vibration speeds U L and U B leading to a value for Λ.…”

“…To cope with this issue, [10] uses the rapid vibration of a standing wave at ultrasonic frequency, to reduce the internal stresses inside the finger pulp due to the friction that appears when pressing the touchscreen. More robust results are obtained if a net tangential force is produced, by using electroadhesion force synchronized on ultrasonic lateral displacement [15] or by using a travelling wave [6]. These solutions however seem difficult to be integrated on plates, without obstructing the view by actuators.…”

The Perception of Ultrasonic Square Reductions of Friction With Variable Sharpness and Duration

“…Beyond the rendering of textures and shapes, the applications for controlled friction modulation are becoming more diverse including new techniques for button-click rendering [36], [37] or haptic enrichment of musical experiences [38]. It is therefore essential to continue extending our understanding of the parameters mediating subjective perception of frictional signals in order to develop novel and more realistic types of haptic feedback.…”