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

Abstract

Recent studies have shown that a button click sensation could be simulated thanks to ultrasonic vibrations. In this context, a travelling wave may enhance the simulation because it creates internal lateral stresses that are released during the stimulation. However, this solution is difficult to integrate on plates. We present 2MoTac, a method which superpose a longitudinal and a bending mode simultaneously on a plate, in order to create a pseudo-travelling wave. We present the design, and a psychophysical study to deduce the optimal ratio between the bending and longitudinal mode amplitudes, in terms of detection threshold and robustness.

Control of an ultrasonic haptic interface for button simulation

“…When the stimulation is created only from normal displacement of the surface, the success rate is only 30% with a large Standard deviation (19%). This confirms the study in [8] in which this stimulation principle was found to be very variable from one participant to the other. But interestingly, when introducing the elliptical motion of particles, the participants could distinguish the simulated button with a success rate of 95%.…”

“…In order to simplify this model, we consider that ω is close to the value at resonance, and we introduce then δω i the deviation from ω i0 to ω, ω = ω i0 + δω i with δω i ω i0 . We can then consider M i + Ki ω 2 ≈ 2M i and Ki ω − M i ω = 2M i δω i , leading the simplified equations (8):…”

“…The device presented in this paper derives from [8]. It consists in a beam which dimension is precisely adjusted in order to have one bending mode and one longitudinal mode at the same frequency, and energized by piezoelectric patches.…”

“…When the two vibration modes are excited simultaneously at the same frequency, but with a phase shift of ±π/2 an elliptical motion occurs, producing the net lateral force, as described figure 1. Previous research has shown that optimal haptic feedback is produced when the displacements along the two directions are equal [8]. However, fulfilling the conditions for an elliptical motion of the particles is not an easy task.…”