Fingerpad Skin Stretch Increases the Perception of Virtual Friction

This research focuses on the relative importance of fingerpad skin stretch on the perception of friction. It is hypothesized that the perceived magnitude of friction rendered by traditional force feedback can be increased through the addition of fingertip skin stretch. Perceptual data are presented from two separate tests performed on nine male subjects. The first experiment determines the perceptual thresholds for friction based on a modified Karnopp friction model where friction is rendered as purely a kinesthetic resistance via a PHANToM force feedback device. JNDs of 0.056-50.150 corresponding to static coefficients for friction of mu_s = 0.2-0.8 were established. The second experiment evaluates possible changes in the perceived friction magnitude due to imposing small amounts of tangential skin stretch (0.25-0.75 mm) to the fingerpad in combination with force feedback (kinesthetic resistance). Our results show that even these small amounts of skin stretch lead to a statistically significant increase in perceived friction (p < 0.01). This significant finding will enable the hapticians to more realistically and accurately render friction via a combination of kinesthetic resistance and tactile feedback.