Localized Tactile Feedback on a Transparent Surface through Time-Reversal Wave Focusing

Abstract

This article addresses the problem of producing independent tactile stimuli to multiple fingers exploring a transparent solid surface without the need to track their positions. To this end, wave time-reversal was applied to re-focus displacement impulses in time and in space at one or several locations in a thin glass plate. This result was achieved using ultrasonic bending waves produced by a set of lamellar piezoelectric actuators bonded at the periphery of the plate. Starting from first principles, the relations linking implementation parameters to the performance of the display are developed. The mechanical design of the display, signal processing, and driving electronics are described. A set of engineering tradeoffs are made explicit and used for the design of a mock up device comprising a glass plate 148 × 210 × 0.5 mm (3). Tests indicate that a peak amplitude of 7 &#956m confined to a 20 mm (2) region could be obtained for an average power consumption of 45 mW. Simultaneous focusing at several locations was successfully achieved. We showed that a lumped-mass model for the fingertip can effectively describe the effect of an actual fingertip load at the focus point. Lastly, we elucidated a likely stimulation mechanism that involves the transient decoupling of the finger skin from the plate surface. This phenomenon explains the observed tactile effect.

Differentiated haptic stimulation by modal synthesis of vibration field

“…The idea is to evaluate the impact of the gradient of the velocity field for multi-finger interaction by contrast with a located interaction with a single finger as in [7]. The point is that, at this stage, the rise time of the two lowest frequencies modes are prominent as can be seen from the spectrogram of fig.…”

“…Time reversal on the other hand uses more complicated signals which are recording by transducers of the propagated vibration due to an initial deformation at some location. Each transducer then plays backward the recorded signal, in a synchronous manner, to "replay" the original deformation [7]. Therefore, an identification procedure, is required.…”

Generating controlled localized stimulations on haptic displays by modal superimposition

“…To do so, the transducers composing phased arrays produce the same vibration delayed by a time interval proportional to the distance separating them from the focus target. Time reversal allows to improve the focusing accuracy and resolution [22,23]. This implies an additional knowledge resulting from an identification procedure.…”

Control and evaluation of a 2-D multimodal controlled-friction display

“…To cope with this issue, and propose multi-finger interactions, several authors have proposed solutions. For example the time reversal wave focusing [7] allows to create different tactile stimulation on two positions independently. However, the sensation felt is vibrotactile and simulation of fine gratings have not been confirmed yet.…”