Researcher: Şirin, Ömer
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Şirin, Ömer
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Publication Metadata only Contact mechanics between the human finger and a touchscreen under electroadhesion(Natl Acad Sciences, 2018) Scaraggi, Michele; Persson, Bo N. J.; N/A; N/A; Department of Mechanical Engineering; Ayyıldız, Mehmet; Şirin, Ömer; Başdoğan, Çağatay; Researcher; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 125489The understanding and control of human skin contact against technological substrates is the key aspect behind the design of several electromechanical devices. Among these, surface haptic displays that modulate the friction between the human finger and touch surface are emerging as user interfaces. One such modulation can be achieved by applying an alternating voltage to the conducting layer of a capacitive touchscreen to control electroadhesion between its surface and the finger pad. However, the nature of the contact interactions between the fingertip and the touchscreen under electroadhesion and the effects of confined material properties, such as layering and inelastic deformation of the stratum corneum, on the friction force are not completely understood yet. Here, we use a mean field theory based on multiscale contact mechanics to investigate the effect of electroadhesion on sliding friction and the dependency of the finger-touchscreen interaction on the applied voltage and other physical parameters. We present experimental results on how the friction between a finger and a touchscreen depends on the electrostatic attraction between them. The proposed model is successfully validated against full-scale (but computationally demanding) contact mechanics simulations and the experimental data. Our study shows that electroadhesion causes an increase in the real contact area at the microscopic level, leading to an increase in the electrovibrating tangential frictional force. We find that it should be possible to further augment the friction force, and thus the human tactile sensing, by using a thinner insulating film on the touchscreen than used in current devices.Publication Metadata only Electroadhesion with application to touchscreens(Royal Soc Chemistry, 2019) Ayyıldız, Mehmet; Persson, Bo N. J.; N/A; Department of Mechanical Engineering; Şirin, Ömer; Başdoğan, Çağatay; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 125489There is growing interest in touchscreens displaying tactile feedback due to their tremendous potential in consumer electronics. In these systems, the friction between the user's fingerpad and the surface of the touchscreen is modulated to display tactile effects. One of the promising techniques used in this regard is electrostatic actuation. If, for example, an alternating voltage is applied to the conductive layer of a surface capacitive touchscreen, an attractive electrostatic force is generated between the finger and the surface, which results in an increase in frictional forces acting on the finger moving on the surface. By altering the amplitude, frequency, and waveform of this signal, a rich set of tactile effects can be generated on the touchscreen. Despite the ease of implementation and its powerful effect on our tactile sensation, the contact mechanics leading to an increase in friction due to electroadhesion has not been fully understood yet. In this paper, we present experimental results for how the friction between a finger and a touchscreen depends on the electrostatic attraction and the applied normal pressure. The dependency of the finger-touchscreen interaction on the applied voltage and on several other parameters is also investigated using a mean field theory based on multiscale contact mechanics. We present detailed theoretical analysis of how the area of real contact and the friction force depend on contact parameters, and show that it is possible to further augment the friction force, and hence the tactile feedback displayed to the user by carefully choosing those parameters.Publication Metadata only Fingerpad contact evolution under electrovibration(Royal Soc, 2019) Barrea, Allan; Lefevre, Philippe; Thonnard, Jean-Louis; N/A; Department of Mechanical Engineering; Şirin, Ömer; Başdoğan, Çağatay; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 125489Displaying tactile feedback through a touchscreen via electrovibration has many potential applications in mobile devices, consumer electronics, home appliances and automotive industry though our knowledge and understanding of the underlying contact mechanics are very limited. An experimental study was conducted to investigate the contact evolution between the human finger and a touch screen under electrovibration using a robotic set-up and an imaging system. The results show that the effect of electrovibration is only present during full slip but not before slip. Hence, the coefficient of friction increases under electrovibration as expected during full slip, but the apparent contact area is significantly smaller during full slip when compared to that of no electrovibration condition. It is suggested that the main cause of the increase in friction during full slip is due to an increase in the real contact area and the reduction in apparent area is due to stiffening of the finger skin in the tangential direction.Publication Metadata only Effect of finger velocity on frictional forces modulated by electrovibration(Institute of Electrical and Electronics Engineers (IEEE), 2018) Ayyıldız, Mehmet; N/A; Department of Mechanical Engineering; Şirin, Ömer; Başdoğan, Çağatay; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 125489We investigate the effect of sliding velocity on frictional forces between human finger and a touch screen actuated by electrostatic forces. For this purpose, we command a motorized slider to move human finger back and forth (one stroke) in horizontal direction at 9 different velocities (2, 5, 10, 20, 30, 40, 50, 60, 70 mm/s) while the finger is in contact with the touch screen and record the tangential forces for the normal forces varied in a controlled manner from 0.1 N to 0.9 N. During the experiments, the electrostatic forces were turned ON and OFF after every other stroke. The results of the experiments show that the data can be categorized into two groups: 1) stickslip and 2) sliding, which occurs at velocities higher than and equal to 30 mm/s. After grouping, we fit a nonlinear function in the form of Fτ = aFη b to the sliding data recorded for the OFF and ON conditions. Using the fit functions, we show that the magnitude of the electrostatic forces increases from 50 to 310 mN as the normal force is increased from 0.1 N to 0.9 N.Publication Metadata only Modeling sliding friction between human finger and touchscreen under electroadhesion(Ieee Computer Soc, 2020) Department of Mechanical Engineering; N/A; Başdoğan, Çağatay; Alipour, Mohammad; Şirin, Ömer; Faculty Member; PhD Student; PhD Student; Department of Mechanical Engineering; College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 125489; N/A; N/AWhen an alternating voltage is applied to the conductive layer of a capacitive touchscreen, an oscillating electroadhesive force (also known as electrovibration) is generated between the human finger and its surface in the normal direction. This electroadhesive force causes an increase in friction between the sliding finger and the touchscreen. Although the practical implementation of this technology is quite straightforward, the physics behind voltage-induced electroadhesion and the resulting contact interactions between human finger and the touchscreen are still under investigation. In this article, we first present the results of our experimental study conducted with a custom-made tribometer to investigate the effect of input voltage on the tangential forces acting on the finger due to electroadhesion during sliding. We then support our experimental results with a contact mechanics model developed for estimating voltage-induced frictional forces between human finger and a touchscreen as a function of the applied normal force. The unknown parameters of the model were estimated via optimization by minimizing the error between the measured tangential forces and the ones generated by the model. The estimated model parameters show a good agreement with the ones reported in the literature.