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A hybrid natural/artificial electrostatic actuator for tactile stimulation

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Abstract

Two modes of tactile communication have been previously explored-electrocutaneous and electrostatic. The electrostatic mode has the significant advantage of not passing electrical current into tissue to effect stimulation of afferent touch nerves. In previous research, we microfabricated electrostatic tactile displays on a 4-inch wafer using standard clean room processing. Tactile perception studies performed on those showed that subjects could discriminate simple spatial geometric patterns. The focus of the current work is to develop a better understanding of the basic mechanism of perception (activation of receptors) during electrostatic stimulation at the skin-display interface. Three displays were constructed with polyimide (PI) dielectric layers of varying thickness. Studies were performed on human subjects to determine the dependence of threshold of sensation on the PI thickness using both the method of limits and two-alternate forced-choice techniques. The theoretical model for the behavior of the interface (a parallel-plate capacitor) suggests a linear relationship between voltage and dielectric thickness. However, our results indicate that the thickness has little or no effect on the threshold. The results are promising in that they may provide an indirect estimate of the depth of the subcutaneous conductive layer of the skin, and a better understanding of the interface
... Two main techniques fall into this category: electro-vibration (EV) and vibro-tactile (VT) devices. Electro-vibration uses electrostatic force to attract the skin [5,6]or a slider [7] on a surface submitted to a high voltage. Since the normal force at the contact area is modified [8,9], the friction force is modulated simultaneously. ...
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In the field of tactile feedback, researchers try to generate localized stimulations on screens. Some solutions such as time reversal or phased array use vibration induced in the screen equipped with piezoelectric ceramics. We propose to use the modal basis to reproduce a specified velocity field on such devices. We explain the theory and propose a methodology to practically synthesize the voltages to achieved a controlled focusing in a given time. Experiments on a simple demonstrator are in good agreement with the theory for various velocity fields and a reduced number of modes.
... However, since the moving distance and the generated force are very small, it was difficult to functionalize a system with a single electrostatic actuator [23]. Therefore, an actuator using electrostatic force was fabricated through various hybrid techniques to compensate for the disadvantages [24][25][26][27]. In this study, gravity was used as an additional power source. ...
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In this study, we propose a new ‘V’-shaped actuator with two panels and experimentally and theoretically investigate its actuation to find the most efficient structure. The V-shaped actuator operates like a seesaw. Specifically, when a high voltage input is applied between the V-shaped actuator and metal plate at the bottom substrate, another panel rises due to electrostatic attraction. Both gravity and electrostatic attraction forces are utilized for the operation of the actuator. We made a model of the actuation mechanism considering torque, gravity, and electrostatic forces. Theoretical values were compared with experimental results considering all factors of force applied to actuators. Additionally, we added torque by restoring force to compensate for the experimental conditions. The theoretical value almost coincided with the experimental value with R2 = 0.9.
... Insulator Properties [Agarwal et al., 2002] investigated the effect of dielectric thickness on haptic perception during electrostatic stimulation. Their results showed that variations in dielectric thickness had little effect on the threshold voltage. ...
... Agarwal et. al [12] investigated the effect of dielectric thickness on haptic perception during electrostatic stimulation. Their results showed that variations in dielectric thickness had little effect on the threshold voltage. ...
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In this study, we investigated the effect of input voltage waveform on our haptic perception of electrovibration on touch screens. Through psychophysical experiments performed with eight subjects, we first measured the detection thresholds of electrovibration stimuli generated by sinusoidal and square voltages at various fundamental frequencies. We observed that the subjects were more sensitive to stimuli generated by square wave voltage than sinusoidal one for frequencies lower than 60 Hz. Using Matlab simulations, we showed that the sensation difference of waveforms in low fundamental frequencies occurred due to the frequency-dependent electrical properties of human skin and human tactile sensitivity. To validate our simulations, we conducted a second experiment with another group of eight subjects. We first actuated the touch screen at the threshold voltages estimated in the first experiment and then measured the contact force and acceleration acting on the index fingers of the subjects moving on the screen with a constant speed. We analyzed the collected data in the frequency domain using the human vibrotactile sensitivity curve. The results suggested that Pacinian channel was the primary psychophysical channel in the detection of the electrovibration stimuli caused by all the square-wave inputs tested in this study. We also observed that the measured force and acceleration data were affected by finger speed in a complex manner suggesting that it may also affect our haptic perception accordingly.
Chapter
Understanding the characteristics of human tactile sensing is essential to design effective tactile displays. Hence, this chapter first reviews the current literature about the human touch, which falls into the scope of this monograph. It gives a brief introduction of the fingerpad and skin anatomy, sensory receptors, and human tactile perception. Afterward, it presents an overview of surface haptics displays explaining different actuator types. Finally, it summarizes the state of the art research on electrovibration for surface haptic displays.
Article
Electrovibration has become one of the promising approaches for adding tactile feedback on touchscreen. Previous studies revealed that the normal force applied on the touchscreen by the finger affects significantly the electrostatic force. It is obvious that the normal force affects the electrostatic force if it changes the contact area between the finger and the touchscreen. However, it is unclear whether the normal force affects the electrostatic force when the apparent contact area is constant. In this paper, we estimated the electrostatic force via measuring the tangential force of the finger sliding on a 3M touchscreen at different normal forces under the constant apparent contact area. We found that the electrostatic force increases significantly as the normal force increases from 0.5N to 4.5N. We explained the experimental results using the most recently proposed electrostatic force model, which considers the effect of air gap. We estimated the averaged air gap thickness using the electrostatic force model. The results showed that the relationship between the air gap thickness and the normal force follows a power function. Our experiment suggests that the normal force has a significant effect on the air gap thickness, thus require consideration in the design of tactile feedback.
Article
Designing algorithms for rendering haptic texture on electrostatic tactile displays requires a quantitative understanding of human perception. In this paper, we report detection and discrimination thresholds for haptic gratings rendered on such displays based on the waveform and amplitude of the applied voltage. The haptic gratings consist of functions that describe the variation in voltage amplitude as a function of the position of finger on the display. Four types of virtual haptic gratings are considered in two experiments. In Experiment I, we estimate the absolute detection thresholds of haptic gratings for four different voltage amplitude functions, consisting of spatial waveforms with sinusoidal, square, triangle, or sawtooth shape. In Experiment II, we report discrimination thresholds for haptic gratings at five reference values of the voltage amplitude (80, 120, 160, 200, and 240 Vpp) for each of the voltage amplitude functions used in Experiment I. The results indicate that the detection thresholds for the four virtual haptic gratings are between 30 and 36 Vpp, and that the JND increases with the increase of voltage amplitudes. In addition, the JNDs of the four virtual gratings differ significantly, with the lowest and highest values being given by the triangle and sawtooth waveform, respectively.
Chapter
Electrovibration has been used to render the surface texture on tactile devices. To understand how the rendering performance is related to the normal force applied to the surface of the device by a finger, we investigated the influence of the applied normal force on electrovibration perception magnitude. We conducted a magnitude estimation experiment to observe how the electrovibration perception relates to the applied normal force ranging from 0.5 to 5 N. We measured the frictional force on a finger together with the normal force and calculated the friction induced by the electrostatic force. We found that the electrovibration perception magnitude increased with the increased applied normal force. Similarly, the friction induced by the electrostatic force increased with the applied normal force. This study demonstrates that the applied normal force has a large influence on the electrovibration perception, which needs to be considered in virtual texture rendering on electrovibration-based tactile devices.
Article
Electrovibration is one of promising methods for tactile feedback in mobile devices because of its simplicity of the structure and principle. In order to increase the capability of tactile presentation with the electrovibration, we developed an electrovibration tactile display with 1 mm electrode resolution. Voltage to each electrode is controlled separately and the tactile display can present electrovibration stimulus distribution. We designed the tactile display and optimized the voltage waveform to avoid destruction of an insulator. We fabricated the proposed tactile display with micro-fabrication process. We experimentally evaluated the relationships between stimulation condition and perception in subjects. The obtained results indicated that the multi- electrode design had a potential to enhance tactile rendering performance of electrovibration stimulation.
Article
WE describe here a vision substitution system which is being developed as a practical aid for the blind and as a means of studying the processing of afferent information in the central nervous system. The theoretical neurophysiological basis1 and the physical concept of the instrumentation2 have been discussed previously, and results obtained with preliminary models have been briefly reported3. A detailed description of the apparatus will appear elsewhere (manuscript in preparation).
Article
The human threshold of sensation of 50 Hz current has hitherto been considered to be around 1 mA. A new sensing mechanism is reported which lowers the threshold about 3 decades. It is elicited when the skin slides on the current carrying conductor, and the sensation disappears when the skin is wet. The sensation is a feeling of vibration or increased surface roughness. The sensing mechanism has been shown to be due to electrostatic forces in the skin caused by the electric field in a poorly conducting stratum corneum. The mechanism is primarily potential dependent, and the absolute threshold of sensation has been found to be about 1.5 volt or 0.15 mu A rms at 50 Hz. In practical daily-life situations it is shown that 82% of 40 test subjects were able to sense a current of 2 mu A rms, 50 Hz.
This paper describes two optical-to-tactile imageconversion systems being developed for the blind. The first is a reading aid in which an area on the printed page about the size of a letterspace is translated into a corresponding vibratory tactile image. The tactile image is produced by a 24-by-6 array of pins driven by piezoelectric bimorphs. The array of 144 pins fits on the distal and a portion of the middle phalanges of one finger. The piezoelectric bimorphs cause the pins to impact the skin in a nonlinear manner. Precise measurements on this bimorph-finger system are given. These measurements also show that shades of "grey" can be displayed by sequentially varying the threshold level. Three experiments conducted with the reading aid involved measurement of legibility, reading rate, and the effect of field of view. Legibility in the 92-98 percent range was obtained at the design magnification. A reading rate of 50 words per minute was achieved with one subject after roughly 160 hours of practice. Three other subjects achieved reading rates of over 10 words per minute after about 40 hours of practice. Reading rate increased markedly as the number of columns in the array was varied from one to six. The second optical-to-tactile image-conversion system is merely an extension of the first to permit information to be acquired from the environment. In fact, ultimately only one system with two sets of optics, one appropriate for the printed page and one appropriate for environment sensing, would be used.
An explorable electrotactile display has been constructed and tested. A thus far neglected sensation was identified and has been shown to be more useful than the more common electrotactile sensations. Exploration of the surface of the electrotactile display elicits a sensation describable as texture. Experiments have indicated that the intensity of this texture sensation is due primarily to the peak applied voltage rather than to current density as is the case for the classical electrotactile sensation. For subjects employing the texture sensation, experimental results are given for approximate thresholds and for the effect of electrode area on these thresholds. A boundary-localization measurement is offered as a measure of the usefulness of the display for textured-area presentation, and form-separation measurements are given as a measure of usefulness for line-drawing presentations. A proposed model for the mechanism producing the texture sensation is offered as a guide for future experimentation and display-engineering development.
The feasibility of communicating pictorial information through the skin has been demonstrated. A tactile television system has permitted blind subjects to determine the position, size, shape, and orientation of visible objects and to track moving targets. The system comprises 1) a vidicon camera utilizing a zoom lens, 2) a digital switching matrix to sequentially connect each element of the photocathode surface through a single video amplifier and signal conditioner to each of the 3) 400 tactile stimulators in a 20 × 20 matrix in contact with a 10-inch square of skin. This image-projector matrix impresses on the skin a two-dimensional vibrating facsimile of either the silhouette or the outline of a visible object. The single-channel swept system exhibits inherent economies when a great number of picture elements is to be processed. Since the fovea of the human eye subserving the central two degrees of detailed vision is comprised of cone cells in a matrix about 200 receptors across, the present 20-line system permits picture transmission with a linear resolution about one-tenth that of the fovea, and has proved adequate for the recognition of human faces. Calculations indicate that the input capacity of the skin of the trunk should compare favorably with that of the fovea. We have determined the electrical-stimulus parameters for painless stimulation of the sensation of mechanical vibration with small electrodes in a closely spaced matrix.
The instrumentation produced and the results obtained with the tactile vision-substitution system (TVSS) developed in our laboratories have been described by Collins [1] and White [2]. With the TVSS, the information from a TV camera is carried to the brain by means of the tactile receptors in the skin of the back and their neural pathways. Such information produces subjective impressions in blind subjects that are analogous to the subjective impressions produced by the visual input in normal sighted people. Some of the neural mechanisms underlying the systems design and the results obtained with the TVSS are noted.
Article
An electrostatic haptic display with three 7×7 electrode arrays of three different sizes was fabricated on a 4-in wafer using lithographic microfabrication techniques. The display utilizes electrostatic stimulation to generate a tactile sensation of texture on a scanning finger. The tactile sensation appeared to be a result of increased friction and vibration due to the electrostatic forces between the finger skin and the electrodes. Various spatial tactile patterns (lines, circles, squares, and triangles, etc.) can be presented on the display. Experiments of threshold, line separation, and pattern recognition were performed on subjects with visual impairments to study the spatial resolution and information transmission on arrays of variant electrode size and spacing. Two columns with two-column spacing can be resolved with 80% accuracy on the small array, for a spatial resolution of 5.8 mm in terms of edge-to-edge electrode distance. The overall percentages of correct recognition for the patterns were 68.3, 72.1, and 71.3% on the small, medium, and large arrays, respectively. While subject is an important factor for both threshold and pattern recognition, electrode size was statistically significant for threshold only. Frequency and duty cycle of the stimulation waveform did not show statistical significance
Article
From February 1992 until the end of 1993, the authors ((IPO) Institute for Perception Research) participated in a European ((TIDE) Technology Initiative for Disabled and Elderly) project which addressed the problem arising for visually disabled computer-users from the growing use of Graphical User Interfaces (GUIs). With the authors' project partners (Frank Audiodata, the Nottingham Polytechnic, and Sensory Visionaid), they developed and evaluated a system which allows visually disabled users of computers to continue using computers, despite the fact that the workplace must, for reasons of uniformity, service, system management, etc., adapt to the use of GUI's. In principle, two approaches to dealing with the aforementioned problem are possible. Firstly, a software bridge can be made to transfer system information to and from a user-specific I/O device (e.g., a Braille line and keyboard). Secondly, a hardware solution can be created, consisting of a second computer which taps the video output and feeds back information via the keyboard and/or mouse connection. Each solution has its own advantages and disadvantages. However, both approaches require modeling of the GUI information in order to transfer data efficiently between the GUI and the user-specific I/O device. In the authors' project, the hardware approach was chosen, the pros and cons of which are discussed here. The GUI modeling proved feasible and is incorporated in the VISA-comp system. The authors' usability evaluation showed that visually disabled users can have access to a GUI, although it takes them about three times longer than sighted users
Goldstein Sensation and Perception
  • E Bruce