  Displaying 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 on
the underlying contact mechanics is very limited. An experimental study was
conducted to investigate the contact evolution between the human finger and a
touchscreen 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, 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 real contact area and the
reduction in apparent area is due to stiffening of the finger skin in
tangential direction.
