Browsing by Subject "Contact forces"

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Open Access
Tactile perception by friction induced vibrations
(2011) Fagiani, R.; Massi, F.; Chatelet, E.; Berthier, Y.; Akay, A.
When a finger moves to scan the surface of an object (haptic sensing), the sliding contact generates vibrations that propagate in the finger skin activating the receptors (mechanoreceptors) located in the skin, allowing the brain to identify objects and perceive information about their properties. The information about the surface of the object is transmitted through vibrations induced by friction between the skin and the object scanned by the fingertip. The mechanoreceptors transduce the stress state into electrical impulses that are conveyed to the brain. A clear understanding of the mechanisms of the tactile sensing is fundamental to numerous applications, like the development of artificial tactile sensors for intelligent prostheses or robotic assistants, and in ergonomics. While the correlation between surface roughness and tactile sensation has already been reported in literature, the vibration spectra induced by the finger-surface scanning and the consequent activation of the mechanoreceptors on the skin have received less attention. In this paper, frequency analysis of signals characterizing surface scanning is carried out to investigate the vibration spectrum measured on the finger and to highlight the changes shown in the vibration spectra as a function of characteristic contact parameters such as scanning speed, roughness and surface texture. An experimental set-up is developed to recover the vibration dynamics by detecting the contact force and the induced vibrations; the bench test has been designed to guarantee reproducibility of measurements at the low amplitude of the vibrations of interest, and to perform measurements without introducing external noise. Two different perception mechanisms, as a function of the roughness wavelength, have been pointed out. The spectrum of vibration obtained by scanning textiles has been investigated. © 2011 Elsevier Ltd. All rights reserved.
Open Access
Three-dimensional mortar-based frictional contact treatment in isogeometric analysis with NURBS
(2012) Temizer, I.; Wriggers, P.; Hughes, T. J. R.
A three-dimensional mortar-based frictional contact treatment in isogeometric analysis with NURBS is presented in the finite deformation regime. Within a setting where the NURBS discretization of the contact surface is inherited directly from the NURBS discretization of the volume, the contact integrals are evaluated through a mortar approach where the geometrical and frictional contact constraints are treated through a projection to control point quantities. The formulation delivers a non-negative pressure distribution and minimally oscillatory local contact interactions with respect to alternative Lagrange discretizations independent of the discretization order. These enable the achievement of improved smoothness in global contact forces and moments through higher-order geometrical descriptions. It is concluded that the presented mortar-based approach serves as a common basis for treating isogeometric contact problems with varying orders of discretization throughout the contact surface and the volume. © 2011 Elsevier B.V.