Elektrotitreşim için kontak mekaniği

The understanding and control of human skin contact against technological substrates is the key aspect behind the design of several electro-mechanical devices. Among these, surface haptic displays that modulate the friction between the human finger and touch surface are emerging as new user interfaces. One such modulation can be achieved by applying an alternating voltage to the conducting layer of a capacitive touchscreen, in order to control electroadhesion between its surface and the finger-pad. However, our knowledge and understanding on the underlying contact mechanics is very limited. We conducted an experimental study to investigate the contact mechanics between the human finger and a touchscreen under electrovibration using a robotic set-up and an imaging system. The results show that the coefficient of friction increases under electrovibration as expected, but the apparent contact area is significantly smaller during full slip when compared to that of no electrovibration condition. We speculate that the main cause of the increase in friction is an increase in real contact area and the reduction in apparent area is due to stiffening of the finger skin in tangential direction. We also present the adverse effect of fingertip skin moisture on electrovibration. We speculate that high moisture decreases the electrical impedance of the interfacial gap between the finger and the touchscreen, leading to a smaller increase in frictional force under electrovibration. Finally, 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.