Investigation of human subjective feelings for different surface textures of slipping objects based on the analysis of contact conditions

Humans can manipulate objects with grasp forces maintained slightly above the minimum required force to prevent slipping. When humans grasp and lift an object, they use fast acting receptors in their skin. These receptors respond to local slips that occur before the gross slip. The estimation of the coefficient of friction and the detection of the incipient slip play a key role in human grasp stability. However, it is not easy to strictly measure the coefficient of friction between the skin and the object’s surface during object manipulations because the shape and dryness of an individual’s skin vary widely. To quantitatively and continuously evaluate the slip condition during a sliding motion, we propose ‘eccentricity’ in the contact area as a measure, which is determined based on the changes in the contact area before and after the sliding motion. In this paper, we employ eccentricity-based slip condition measurement and evaluate the slip condition between a human’s skin and various surface textures. Then, we compare the results with the affective evaluation experiments to assess the subjective feeling of the surface texture and discuss the influence of the slip condition on the subjective feeling. The results reveal that the slip conditions in the contact area at the beginning and in the middle range during a sliding motion include completely different information that can be used to evaluate the subjective feeling of surface texture. This suggests that the eccentricity-based slip condition measurement is useful to evaluate a human’s subjective feeling of a product’s surface texture.