Dynamic modelling of finger-surface contacts

The tactile perception, originated from the scanning of the fingertip on object surfaces, is related to the contact stresses and to the vibrations induced by the sliding contact that activate the mechanoreceptors located in the skin, allowing the brain to identify objects and to perceive information about their surfaces [1-3]. The relationship between the friction induced vibration and the tactile sensation is rarely investigated, while a clear understanding of the mechanisms of the tactile sense is basilar for manifold applications, like the development of artificial tactile sensors for intelligent prostheses or robotic assistants, and for the ergonomics. In this context, it is necessary to perform appropriate experiments to find out the frequency characteristics of the vibrations induced by the surface scanning. The aim is to analyze the induced vibrations highlighting their dependence on contact and scanning conditions. The study of a finger that moves on a surface involves different difficulties that are related to the material characteristics and to the measurements themselves. In fact, the goal is the measurement and the analysis of the vibrations induced by the scanning, which are very low in magnitude; thus, it is complicated to isolate them from the vibration noise coming out from the experimental set-up and to detect them without significant alteration. For these reasons, an experimental set-up named TRIBOTOUCH was developed to recover the contact forces and the induced vibrations [4]. While the experimental tests, describing how the spectra of the vibrations measured on finger nail can be related to surface characteristics, to scanning speed and to contact force, are presented in the previous works [5-6], in this paper a numerical model reproducing the finger-surface scanning is introduced. The model takes into account finger and surface geometries, their material properties, normal contact force and scanning speed.