Investigation On Friction Perception Of Fingertip Skin

There are many mechanical stimulation receptors and sensory nerve endings in human skin which are important tools in tactile perception. It is a complex process for human to perceive objects and friction motion plays an important role during this process. The fingertips will produce compression, tensile mechanical deformation when they are in contact with the surfaces of objects, which can activate the mechanical stimulation receptors in fingertip skin to produce corresponding action potentials. Then the impulses which contain objects’physical properties are transmitted to cerebral cortex by nervous system, in this way, the shape and surface texture of objects are perceived. Thus, sliding friction of fingertips has an important significance on human perception of external environment. In this paper, taking human’s fingertips which are the most sensitive parts for perception as the research object and using the UMT-II multi-specimen tribometer, two groups of experiments are conducted to study the tactile perception of fingertip skin, which include touching sticks with regular texture spacing and four types of sand paper with different roughness. Combining subjective feelings of the human body with friction signals and EEG signals, some basic mechanisms and rules of human tactile perception are revealed, the main conclusions as follows:1. The touch force, texture spacing, contact medium and sticks’diameter will have effects on the judging results. The accuracy of judgment improves and perception ability enhances with normal force and sample spacing increasing. The friction between fingertip and samples decreases as a result of the liquid detergent which plays as lubrication medium, thereby the accuracy of perception reduces. The sample of bigger diameter causes the larger fingertip deformation and volunteers’tactile perception are more sensitive.2. The sand paper with different roughness has different effect on the wave of electroencephalogram and subjective judgment of roughness. The friction force and friction coefficient increase with the roughness increasing. Besides, the amplitude and high-value wave crest number of electroencephalogram also increase observably. The research indicates that roughness perception has much consistency with friction coefficient and physiological response of EEG, and the frictiona coefficient and electroencephalogram can be used as indexes to characterize the roughness perception during friction process of fingertip skin.3. Two kinds of mathematical models:ridge regression and partial least-square regression are established by using MATLAB and SIMCA-P respectively to describe the relationship among roughness perception, friction coefficient and electroencephalogram. Both of the fitting effect is pretty satisfied. By using these model equations, the roughness perception of fingertip skin could be evaluated quantitatively.