Quantitative assessment of friction perception for fingertip touching with different roughness surface

摘要

Abstract There are many mechanical stimulation receptors and sensory nerve endings in human skin, which are the important tools in tactile perception. It is a complex process for human to perceive objects and friction relative motion plays an important role during this process. When human’s fingertips friction against objects, they will produce compression and tensile mechanical deformation, which can stimulate the mechanical stimulation receptors in fingertip skin to produce corresponding action potentials and impulses signals. The signals which contain object’s physical properties are transmitted to cerebral cortex by nervous system, thus the shape and surface texture of objects are perceived. Thus the friction between the fingertip and object is an important factor to perceive objects. There exist positive connection between friction and tactile perception. However, limited quantitative parameters can be used to evaluate the perception, and they have rarely been studied scientifically. In this paper, the friction perceptions of fingertip skin rubbing against different roughness sandpapers were studied by biofeedback of frictional signals, physiological and psychological responses. An UMT-II tribometer was used to measure tribological parameters of the fingertip, and corresponding physiological response of electroencephalogram (EEG) signals were monitored by using a Physiological Monitoring and Feedback Instrument (NeXus-10) with BioTrace+software. The psychological responses were scored according to the volunteer’s perception during friction tests. The correlation models among the perception of fingertip, friction coefficient and EEG signals were established by applying regression analysis method. Results showed that the friction coefficient, amplitudes of EEG signals and psychological responses increased with the roughness of sandpapers increasing. There existed a significant correlation among the friction perception of different surface roughness, friction coefficient and amplitudes of EEG signals. By using this method, the perception of fingertip skin for different roughness surface during friction can be evaluated quantitatively. Keywords Fingertip skin ; Friction perception ; Roughness ; Ridge regression ; Quantitative evaluation prs.rt("abs_end"); 1 Introduction Tactile sense of skin is produced by contacting with the external environment, which is a response to mechanical stimulations such as contact, sliding, pressure, etc [1] . There are many mechanical stimulation receptors and sensory nerve endings embedded in human skin, which are the important tools in tactile perception. It is a complex process for human to perceive objects and friction relative motion plays an important role during this process [2] and [3] . Finger skin is the most frequent contact with the external environment, and it is also the most sensitive parts of tactile sense. When fingertips friction contact against objects, they will produce compression and tensile mechanical deformation due to friction relative motion, which can stimulate the mechanical stimulation receptors in fingertip skin to produce corresponding action potentials and impulses signals. The signals which contain object’s physical properties are transmitted to cerebral cortex by nervous system, thus the shape and surface texture of objects are perceived. Therefore, the friction between the fingertip and object is an important factor to perceive objects. There exist positive connection between friction and tactile perception. In recent years, a lot of experimental studies focused on the friction between finger and objects. For dry finger pads, the dynamic friction coefficients between the human finger and flat materials surfaces typically range from 0.2 to 1.75, measured by means of force plates or analogous measurement systems [4] , [5] , [6] , [7] , [8] , [9] and [10] . In the majority of the studies, finger friction was measured at normal forces below 5?N, covering the typical range which is used for the tactile assessment of surfaces. As we have considered, the surface properties of materials and objects are essential for the tactile properties of skin. Lisa skedung [11] inquired the feeling judgments of the participants by touching 21 different kinds of printing paper and found the surface roughness played a dominant role in tactile sense. The friction and thermal conductivity were much more important to identify the good hand feelings for printing paper. Xavier [12] examined the relationship between the tactile roughness discrimination threshold (TRDT) and the tactile spatial resolution threshold (TSRT) at the index fingertip contacting with two sets of six different sandpaper grits and found there was no significant correlation between TRDT and TRST performance. The results supported the theory that the neural mechanisms underlying the perception of tactile roughness discrimination for fine textures differ from those involved in spatial resolution acui