Tactile displays have been widely studied for many decades. Although multiple tactile stimuli are more effective to improve the quality of the presented tactile sensation, most tactile displays provide a single tactile stimulus. An integrated tactile display with electrovibration and electrical stimuli is proposed herein. It is expected that vibrational friction, pressure and vibration can be presented at the same time through the tactile display. Also, these stimuli only require electrodes for stimulation. Therefore, the tactile display can be easily miniaturized and densely arrayed on a substrate. In this study, a tactile display is designed and fabricated using the micro-fabrication process. Furthermore, the display is evaluated. First, the relationship between a single stimulus and the perception is investigated. The electrovibration and electrical stimuli have a frequency dependence on perception. Second, whether the multiple stimuli with the electrovibration and electrical stimuli are perceivable by the subjects is also evaluated. The results indicate that the multiple tactile stimuli are perceivable by the subjects. Also, the possibility that the electrovibration and electrical stimuli affect each other is confirmed.

Recently, electrovibration tactile displays were studied and applied to several use cases by researchers. The high-resolution electrode for electrovibration stimulus will contribute to the presentation of a more realistic tactile sensation. However, the sizes of the electrodes that have been used thus far are of the millimeter-order. In this study, we evaluated whether a single narrow electrode was able to provide the electrovibration stimulus adequately. The widths of the prepared electrodes were 10, 20, 50, 100, 200, and 500 μm. We conducted a sensory experiment to characterize each electrode. The electrodes with widths of 50 μm or less were not durable or suitable for the applied signal, although the subjects perceived the stimulus. Therefore, we conducted the experiment without using these non-durable electrodes. The voltage waveform condition affected perception, and the subjects were not sensitive to the electrovibration stimulus at low frequencies. In addition, the stroke direction of the fingertip had a significant effect on perception under certain conditions. The results indicate that electrovibration stimulation requires an electrode with a width of only a few hundred micrometers for stimulation.

Unlike tactile displays that use mechanical actuators, electrode-type tactile displays can be easily integrated and miniaturized because they consist of electrodes and insulators. Electrical tactile displays only require electrodes and use an electric current to stimulate vibration or pressure. Likewise, electrostatic friction tactile displays also only require electrodes and an insulator and can induce changes in friction between the display and a fingerpad. We have developed a tactile display that integrates electrical and electrostatic friction stimulation owing to their affinity to microfabrication techniques. This tactile display can provide both pressure and friction at the same time. In this study, we presented an elongated bar shape via the tactile display to experimental participants. The experimental results showed that a tactile display employing multiple stimuli as opposed to a single stimulus can induce the perception of larger shapes.