Contact of a Finger on Rigid Surfaces and Textiles: Friction Coefficient and Induced Vibrations

Abstract

The tactile information about object surfaces is obtained through perceived contact stresses and friction-induced vibrations generated by the relative motion between the fingertip and the touched object. The friction forces affect the skin stress-state distribution during surface scanning, while the sliding contact generates vibrations that propagate in the finger skin activating the receptors (mechanoreceptors) and allowing the brain to identify objects and perceive information about their properties. In this article, the friction coefficient between a real human finger and both rigid surfaces and fabrics is retrieved as a function of the contact parameters (load and scanning speed). Then, the analysis of the vibration spectra is carried out to investigate the features of the induced vibrations, measured on the fingernail, as a function of surface textures and contact parameters. While the friction coefficient measurements on rigid surfaces agree with empirical laws found in literature, the behaviour of the friction coefficient when touching a fabric is more complex, and is mainly the function of the textile constructional properties. Results show that frequency spectrum distribution, when touching a rigid surface, is mainly determined by the relative geometry of the two contact surfaces and by the contact parameters. On the contrary, when scanning a fabric, the structure and the deformation of the textile itself largely affect the spectrum of the induced vibration. Finally, some major features of the measured vibrations (frequency distribution and amplitude) are found to be representative of tactile perception compared to psychophysical and neurophysiologic works in literature

Natural scenes in tactile texture

“…Studies with biomimetic devices have led to the proposition that the spatial period of fingerprints would be reflected in the frequency spectrum of vibrations elicited by nonperiodic textures ). However, other studies have suggested that fingerprints merely enhance the magnitude of the elicited vibrations indiscriminately (Oddo et al 2011) or that their frequency composition depends on the ratio between the spatial period of the texture and that of the fingerprints (Fagiani et al 2011(Fagiani et al , 2012.…”

“…Previous studies examining texture-elicited vibrations have focused on small sets of (mainly artificial) textures and have used techniques requiring direct skin contact Hollins 2003, 2005;Fagiani et al 2012), which might alter or impede the signal. Furthermore, the factors that shape the vibrations remain unclear.…”

“…Some studies found that scanning periodic textures elicits vibrations whose frequency is determined by their spatial period (Bensmaia and Hollins 2003;Delhaye et al 2012;Wiertlewski et al 2011a). However, experiments using biomimetic fingertips suggest that it is the spatial period of the fingerprints that determines the frequency of the elicited vibrations , although the precise role of fingerprints in texture perception remains controversial (Dahiya and Gori 2010;Fagiani et al 2012;Fishel and Loeb 2012;Oddo et al 2011). Here we use a noncontact measurement technique to measure vibrations as they travel across the fingertip skin.…”

The role of the sliding direction against a grooved channel texture on tool steel: An experimental study on tactile friction

“…In most cases, the exploratory procedure to detect the surface features of various objects consists of a sliding movement of our finger(s) at a moderate load and relatively low sliding velocity (Klatzky and Pawluk, 2013;Barnes et al, 2004). Surface recognition is deciphered by the cutaneous sensory neurons from the specific movement made by our finger during active touch (Fagiani et al, 2012). The touch perception is greatly influenced by the friction generated between the fingertip and counter-surfaces (Darden and Schwartz, 2013;Klatzky and Pawluk, 2013;Skedung et al, 2011).…”

Texture design for skin friction and touch perception of stainless steel surfaces

“…In most cases, the exploratory procedure to detect the surface features of various objects consists of a sliding movement of our finger(s) at a moderate load and relatively low sliding velocity . Surface recognition is deciphered by the cutaneous sensory neurons from the specific movement made by our finger during active touch (Fagiani et al, 2012). The touch perception is greatly influenced by the friction generated between the fingertip and countersurfaces (Darden and Schwartz, 2013;Liu et al, 2008;.…”