Polarity effect in electrovibration for tactile display

Abstract-Electrovibration is the tactile sensation of an alternating potential between the human body and a smooth conducing surface when the skin slides over the surface and where the current is too small to stimulate sensory nerves directly. It has been proposed as a high-density tactile display method, for example to display pictographic information to persons who are blind. Previous models for the electrovibration transduction mechanism are based on a parallel-plate capacitor in which the electrostatic force is insensitive to polarity. We present experimental data showing that electrovibratory perceptual sensitivity to positive pulses is less than that for negative or biphasic pulses and propose that this disparity may be due to the asymmetric electrical properties of human skin. We furthermore propose using negative pulses for insulated tactile displays based on electrovibration because their sensory thresholds were found to be more stable than for waveforms incorporating positive pulses

Electrostatic Friction Displays to Enhance Touchscreen Experience

Touchscreens are versatile devices that can display visual content and receive touch input, but they lack the ability to provide programmable tactile feedback. This limitation has been addressed by a few approaches generally called surface haptics technology. This technology modulates the friction between a user’s fingertip and a touchscreen surface to create different tactile sensations when the finger explores the touchscreen. This functionality enables the user to see and feel digital content simultaneously, leading to improved usability and user experiences. One major approach in surface haptics relies on the electrostatic force induced between the finger and an insulating surface on the touchscreen by supplying high AC voltage. The use of AC also induces a vibrational sensation called electrovibration to the user. Electrostatic friction displays require only electrical components and provide uniform friction over the screen. This tactile feedback technology not only allows easy and lightweight integration into touchscreen devices but also provides dynamic, rich, and satisfactory user interfaces. In this chapter, we review the fundamental operation of the electrovibration technology as well as applications have been built upon

Voltage-Induced Friction with Application to Electrovibration

Due to the growing interest in robotic and haptic applications, voltage-induced friction has rapidly gained in importance in recent years. However, despite extensive experimental investigations, the underlying principles are still not sufficiently understood, which complicates reliable modeling. We present a macroscopic model for solving electroadhesive frictional contacts which exploits the close analogy to classical adhesion theories, like Johnson-Kendall-Roberts (JKR) and Maugis, valid for electrically neutral bodies. For this purpose, we recalculate the adhesion force per unit area and the relative surface energy from electrostatics. Under the assumption of Coulomb friction in the contact interface, a closed form equation for the friction force is derived. As an application, we consider the frictional contact between the fingertip and touchscreen under electrovibration in more detail. The results obtained with the new model agree well with available experimental data of the recent literature. The strengths and limitations of the model are clearly discussed.TU Berlin, Open-Access-Mittel – 201

Multi-physics modelling and experimental validation of electrovibration based haptic devices

Electrovibration tactile displays exploit the polarisation of the finger pad, caused by an insulated high voltage supplied plate. This results in electrostatic attraction, which can be used to modulate the users' perception of an essentially flat surface and induce texture sensation. Two analytical models of electrovibration, based on parallel plate capacitor assumption, are demonstrably taken and assessed by comparisons with experimental results published in literature. In addition, an experimental setup was developed to measure the electrostatic force between the finger pad and a high voltage supplied plate in a static and out-of-contact state in order to support the use of parallel plate capacitor model. Development, validation, and application of a computational framework for modelling tactile scenarios on real and virtual surfaces rendered by electrovibration technique is presented. The framework incorporates fully parametric model in terms of materials and geometry of the finger pad, virtual and real surfaces, and can serve as a tool for virtual prototyping and haptic rendering in electrovibration tactile displays. This is achieved by controlling the applied voltage signal in order to guarantee similar lateral force cues in real and simulated surfaces

Modern Applications of Electrostatics and Dielectrics

Electrostatics and dielectric materials have important applications in modern society. As such, they require improved characteristics. More and more equipment needs to operate at high frequency, high voltage, high temperature, and other harsh conditions. This book presents an overview of modern applications of electrostatics and dielectrics as well as research progress in the field

Psychophysical Power Optimization of Friction Modulation for Tactile Interfaces

International audienceUltrasonic vibration and electrovibration can modulate the friction between a surface and a sliding finger. The power consumption of these devices is critical to their integration in modern mobile devices such as smartphones. This paper presents a simple control solution to reduce up to 68.8% this power consumption by taking advantage of the human perception limits

Electrovibration Modeling Analysis

International audienceElectrostatic attraction may be used to modulate the apparent friction coefficient between two surfaces. Applied to the human finger and a polarized interface, the principle can modify the user perception of the interface surface. In this paper, the different steps towards the modeling of the electrovibration phenomenon are developed. An investigation on the current modeling will be carried out, with a focus on the temporal evolution and frequency dependence of the stimulus. Thus, an improvement of the modeling will be proposed to take into account this major effect, and then, it will be checked with an experimental setup and compared with literature results. The last few years have seen an increasing interest for haptic stimulation and simulation. Different technologies are available to provide a tactile feedback to a user by modifying his perception of a surface. In particular, it is possible to control the friction between a surface and a finger thanks to squeeze film effect or to electrovibra-tion. This study is focused on the electrovibration effect: the modulation of the perceived friction coefficient due to the induced electrostatic force between a finger and a high voltage supplied plate [1]. The effect is known since the mid fifties [2], but the interest has raised only recently. Firstly, spatial division of electrode was developed to provide precise and complex stimulus pattern of conductive pads, but this solution suffered from its complexity and turned out difficult to apply [5]. Recently, electrovi-bration took advantage of technological improvements of fingertip's position sensor based on optical or resistive solutions. The possibility to track precisely the position of the finger leads to fine gratings simulation thanks to spatial-stimulus relation. With spatio-temporal transformation, the stimulator itself becomes easier to manufacture and it becomes possible to produce tactile feedback on transparent surfaces [1] or merge it with another tactile stimulation technique [3]. If the efficiency of the process to provide successful tactile feedback is clear, the physical modeling of the phenomenon involving the finger is not yet satisfactory. Th

Role of Fingerprint Mechanics and non-Coulombic Friction in Ultrasonic Devices

International audienceUltrasonic vibration of a plate can be used to modulate the friction of a finger pad sliding on a surface. This modulation can modify the user perception of the touched object and induce the perception of textured materials. In the current paper, an elastic model of finger print ridges is developed. A friction reduction phenomenon based on non-Coulombic friction is evaluated based on this model. Then, a comparison with experimental data is carried out to assess the validity of the proposed model and analysis