Tatsuma Sakurai

Sharp tactile sensation using superposition of vibrotactile stimuli in different phases

The overlapping of vibrations that are in different phases and in close proximity to each other produces a tactile image that is more localized than one produced by pin vibrators. The mechanism behind the former is still unclear; it may be attributed to the fact that the resultant vibration is highly localized and of a high frequency, making the tactile sensations more perceptible by the human hand. In this study, a finite element (FE) model of a human finger is analyzed to investigate the reason for the difference in the sizes of tactile images produced under different mechanical conditions. In the dynamic analysis, we observed the spatial distribution of the strain energy density (SED) in the model and estimated the perceptual area of the mechanical stimuli. To determine the perceptual area, the threshold SED for perceiving the vibratory stimuli was determined by analyzing the FE finger model on a flat vibratory surface. In the deformation analysis results, we observed that the spatial distribution of SED was more localized by the overlapped vibrations than in a pin vibrator. Moreover, spectral analysis revealed that a higher-frequency vibration was generated locally between the two vibrations. A psychophysical experiment was conducted to determine the effect of the high frequency component on detection thresholds.

Presenting sharp surface shapes using overlapped vibrotactile stimuli

Previous surface shape presenting methods had difficulties in generating high-density tactile information owing to blurriness in tactile images caused by lateral skin deformations. In this study, a new surface shape presenting method is proposed, and it employs overlapping small-amplitude vibrations instead of a single vibration. This method represents the mechanism of stationary boundary contacts (SBCs), a vibrotactile sensitivity enhancement method proposed in a previous research. A series of psychophysical experiments showed that the vibrations overlapping method can significantly enhance the human vibrotactile sensitivity and lead to the production of sharp tactile images. Moreover, the stimuli intensity can be controlled not only by changing the vibration amplitudes but also by changing the phase deviations between vibrations; this enables the presentation of various surface shape patterns that cannot be presented by using the previous SBC method alone.

Enhancement of vibrotactile sensitivity: Effects of stationary boundary contacts

Tactile sensations experienced by humans, such as roughness and softness, require not only high-frequency (200 Hz) but also lower-frequency vibrations (< 50 Hz). However, such low frequencies are difficult to achieve with small actuators that can be integrated into mobile devices. Therefore, it is necessary to develop methods for enhancing human vibrotactile sensitivity. We focused on a phenomenon whereby simultaneous contact with vibratory and stationary surfaces enhances human vibrotactile sensitivity, which we call stationary-boundary-contact (SBC) enhancement. SBC produces a line sensation along the gap between the vibratory and stationary surfaces. In this study, we determined the detection thresholds for SBC-enhanced sensitivity under several conditions. Psychophysical experiments showed that the detection thresholds of SBC were reduced by more than three times at low frequencies as compared to those under normal conditions. We then investigated the mechanism behind SBC enhancement by using a finite element model for the skin. Static and dynamic deformation analyses indicated that the dynamic impact of skin against the edge of a stationary surface contributes to an increase in the vibration frequency of the skin. This hypothesis was also supported by the psychophysical experiment, which showed that an edge-rounded stationary surface had less effect on sensitivity enhancement. Finally, we investigated possible SBC arrangements for practical applications on the basis of line sensation.

Research of conditions of stimulus for inducing grasping force control reflex

Humans can change their grasping force before the grasped object unconsciously slips off their fingers. This reflex is called the grasping force control reflex. This paper describes the methods used to induce reflective grasping force control and presents the observed results. To clarify the stimulus conditions needed to induce reflective grasping force control, we developed an observation device with piezoelectric actuators and a force sensor. Vibration stimuli and force senses were presented to a human finger, and a change in the grasp force was observed by the force sensor. In this study, we changed the parameters of the vibration stimuli and force senses and detected the difference in the grasp force.

Sharp tactile line presentation array using edge stimulation method

We report on a tactile shape presentation display that has a rigid plane for a surface and can present highly localized tactile stimuli using small vibrotactile stimuli. We have proposed an edge stimulation (ES) method that can present sharp tactile sensation along the boundary edge of vibratory surfaces. The basic concept is to use the ES method for shape presentation. The ES method allows the tactile display surface to be a flat plane; it can be mounted on a flat surface of any devices and can project images on this surface. The ES method uses low-frequency and small-amplitude vibrations that achieves low power actuation. Previously, we have developed an edge stimulation device (ES device) with voice coil actuators in 2×2 array and examined the concept of the ES method for shape presentation, though it was low rigidity (display surface was easy to be bent) and not capable for various shape presentation. In this study, we developed 3×3 array shape presentation display with rigid piezo-vibrators taking advantage of ES method. Psychophysical experiment on detection thresholds for vibratory stimuli demonstrated the display can make 5 μm at 30 Hz vibration perceivable, even though they normally require a 30 μm amplitude for simple vibrations. In the shape recognition test results, users correctly scored of 96 % for 8 patterns discrimination tasks.

Character Reading via Stylus Reproducing Normal Handwriting Motion

In this paper, we report a method of intuitively transmitting symbolic information to untrained users via only their hands, without using any visual or auditory cues. In this simple concept, three-dimensional letter trajectories are presented to the users hand via a stylus which is mechanically manipulated. In experiments, participants were able to read 14 mm-high lower-case letters displayed at a rate of one letter per second with an accuracy rate of 71.9 percent in their first trials, which improved to 91.3 percent after a 5-minute training period. These results showed small individual differences among participants (standard deviation of 12.7 percent in the first trials and 6.7 percent after training). We also found that this accuracy was still retained to a high level (85.1 percent, with SD of 8.2 percent) even when the letters were reduced to a height of 7 mm. Thus, we revealed that sighted adults potentially possess the ability to read small letters accurately at normal writing speed using their hands.

[D02] Sharp tactile lines by edge stimulation method

Summary form only given, as follows. Demonstration includes an experiment of presenting sharp line-shape vibrotactile sensations produced by Edge Stimulation (ES) method. A 3×3 vibrator array tactile display with small amplitudes present various tactile line sensations between the vibrators rather than on the vibrators themselves. The display can make 5 um vibration at 30 Hz perceivable, even though they normally require a 30 um amplitude for simple vibrations. The ES method allows the tactile display surface to be a flat plane; it can be mounted on a flat surface of any devices and can project images on this surface.