Fingertip scanning on a surface: friction coefficients and induced vibrations

Tactile perception happens when scanning the fingertip on object surfaces (haptic sensing), by activating the receptors that are located in the skin. The skin deformation due to the contact stresses and the vibrations induced by the sliding contact activate the mechanoreceptors which generate electric impulses and allow the brain to identify objects and perceive information about their surfaces. In this paper, the friction coefficient between a real human finger and both rigid surfaces and fabrics is recovered, as a function of the contact parameters (load and scanning speed). Then, the analysis of the vibration spectra is carried out to investigate the characteristics of the induced vibrations, measured on the fingernail, as a function of surface features and contact parameters. Different behaviour of the friction coefficient is recovered scanning rigid surfaces or textiles, with respect to the contact parameters. Results show that frequency spectrum distribution when touching a rigid surface is mainly determinate by the relative geometry of the two contact surfaces, while, when scanning a fabric, the structure and the deformation of the textile itself affect largely the spectrum of the induced vibration. Some main characteristics of the measured vibrations are found to be representative of tactile perception, by comparison with psychophysical and neurophysiologic works in literature.