We present a new technology for enhancing touch interfaces with tactile feedback. The proposed technology is based on the electrovibration principle, does not use any moving parts and provides a wide range of tactile feedback sensations to fingers moving across a touch surface. When combined with an interactive display and touch input, it enables the design of a wide variety of interfaces that allow the user to feel virtual elements through touch. We present the principles of operation and an implementation of the technology. We also report the results of three controlled psychophysical experiments and a subjective user evaluation that describe and characterize users' perception of this technology. We conclude with an exploration of the design space of tactile touch screens using two comparable setups, one based on electrovibration and another on mechanical vibrotactile actuation.

TeslaTouch: electrovibration for touch surfaces

An apparatus for producing an electrosensory sensation to a body member (120) The apparatus comprises one or more conducting electrodes (106), each of which is provided with an insulator (108) When the body member (120) is proximate to the conducting electrode, the insulator prevents flow of direct current from the conducting electrode to the body member A capacitive coupling over the insulator (108) is formed between the conducting electrode (106) and the body member (120) The conducting electrodes are driven by an electrical input which comprises a low-frequency component (114) in a frequency range between 10 Hz and 500 Hz The capacitive coupling and electrical input are dimensioned to produce an electrosensory sensation The apparatus is capable of producing the electrosensory sensation independently of any mechanical vibration of the one or more conducting electrodes (106) or insulators (108)

Method and apparatus for sensory stimulation

The tactual scanning of five naturalistic textures was recorded with an apparatus that is capable of measuring the tangential interaction force with a high degree of temporal and spatial resolution. The resulting signal showed that the transformation from the geometry of a surface to the force of traction and, hence, to the skin deformation experienced by a finger is a highly nonlinear process. Participants were asked to identify simulated textures reproduced by stimulating their fingers with rapid, imposed lateral skin displacements as a function of net position. They performed the identification task with a high degree of success, yet not perfectly. The fact that the experimental conditions eliminated many aspects of the interaction, including low-frequency finger deformation, distributed information, as well as normal skin movements, shows that the nervous system is able to rely on only two cues: amplitude and spectral information. The examination of the “spatial spectrograms” of the imposed lateral skin displacement revealed that texture could be represented spatially, despite being sensed through time and that these spectrograms were distinctively organized into what could be called “spatial formants.” This finding led us to speculate that the mechanical properties of the finger enables spatial information to be used for perceptual purposes in humans with no distributed sensing, which is a principle that could be applied to robots.

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The Spatial Spectrum of Tangential Skin Displacement Can Encode Tactual Texture

The sense of touch is one of the most informative senses humans possess, and tactation is the sensation perceived by the sense of touch. Tactation is resulted by the skin's receptors that are stimulated by modalities such as vibration, pressure, etc. The concept of tactile technologies is based on the skin's ability to communicate information through these modalities. Current advances include electrical stimulation, vibrotactile stimulation, thermal stimulation, etc. This paper is a comprehensive review of the technological enhancements of vibrotactile feedback systems in rehabilitation, sports and Information display domains used for motion improvement, motor learning, navigation, gaming, etc. The evolution of vibrotactile technology and its enhancements in the twenty first century for rehabilitation, sports and information display are presented.

Vibrotactile feedback systems: Current trends in rehabilitation, sports and information display

In this paper, we investigate the use of friction based tactile displays for the simulation of finely textured surfaces, as such displays offer a promising way for the development of devices with co-located vision and tactile feedback. The resolution of the textures rendered with such devices and their matching to real textures have never been investigated. The paper first contributes to the evaluation of the texture resolution of friction based tactile displays. In a controlled experiment, we investigate the differential thresholds for square gratings simulated with a friction based tactile device by dynamic touch. Then we compare them to the differential thresholds of real square wave gratings. We found that the Weber fraction remains constant across the different spatial period at 9%, which is close to the Weber fraction found for corresponding real square gratings. This study inclines us to conclude that friction based tactile displays offers a realistic alternative to pin based arrays and can be used for co-located vision and tactile rendering. From the results of the experiment, we also give the design guidelines to improve the perception of textures on friction based tactile displays.

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Discrimination of Virtual Square Gratings by Dynamic Touch on Friction Based Tactile Displays

A new electrostatic tactile display is proposed to realize compact tactile display devices that can be incorporated with virtual reality systems. The tactile display of this study consists of a thin conductive film slider with stator electrodes that excite electrostatic forces. Users of the device experience tactile texture sensations by moving the slider with their fingers. The display operates by applying two-phase cyclic voltage patterns to the electrodes. The display is incorporated into a tactile telepresentation system to realize explorations of remote surface textures with real-time tactile feedback. In the system, a PVDF tactile sensor and a DSP controller automatically generate voltage patterns to present surface texture sensations through the tactile display. A sensor, in synchronization with finger motion on the tactile display, scans a texture sample and outputs information about the sample surface. The information is processed by a DSP and fed back to the tactile display in real time. The tactile telepresentation system was evaluated in texture discrimination tests and demonstrated a 79 percent correct answer ratio. A transparent electrostatic tactile display is also reported in which the tactile display is combined with an LCD to realize a visual-tactile integrated display system.

T. Higuchi

Papers

Electrostatic tactile display with thin film slider and its application to tactile telepresentation systems