The tactile information about object surfaces isobtained through perceived contact stresses and frictioninducedvibrations generated by the relative motionbetween the fingertip and the touched object. The frictionforces affect the skin stress-state distribution during surfacescanning, while the sliding contact generates vibrations thatpropagate in the finger skin activating the receptors (mechanoreceptors)and allowing the brain to identify objectsand perceive information about their properties. In thisarticle, the friction coefficient between a real human fingerand both rigid surfaces and fabrics is retrieved as a functionof the contact parameters (load and scanning speed). Then,the analysis of the vibration spectra is carried out toinvestigate the features of the induced vibrations, measuredon the fingernail, as a function of surface textures andcontact parameters. While the friction coefficient measurementson rigid surfaces agree with empirical lawsfound in literature, the behaviour of the friction coefficientwhen touching a fabric is more complex, and is mainly thefunction of the textile constructional properties. Resultsshow that frequency spectrum distribution, when touchinga rigid surface, is mainly determined by the relativegeometry of the two contact surfaces and by the contactparameters. On the contrary, when scanning a fabric, thestructure and the deformation of the textile itself largelyaffect the spectrum of the induced vibration. Finally, somemajor features of the measured vibrations (frequency distributionand amplitude) are found to be representative oftactile perception compared to psychophysical and neurophysiologicworks in literature.
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