Realization of Static Friction Sensing Mechanism by A Use of Artificial Skin

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The objective of the study was to realize static friction sensation mechanism by developing artificial skin with mechanical structure and a sensing function equivalent to those of human skin.To begin with, structural features of a human finger were imitated: Ridges were molded on a silicone rubber surface, and the shape was formed to have a macroscopic curvature. A pair of PVDF or strain gauge film sheets confronting each other were embedded in a ridge as artificial Meissner corpuscles. Artificial skin with the above futures was used to conduct the following studies.First, the amplitude characteristic of the PVDF circuit system was examined to have a combined first-order (stress-rate) and a third-order (stress-jerk) frequency characteristics with a breakpoint in between the two. Second, the differential PVDF circuit output originating in either one kind of two film sheets generated a low frequency signal wave form pattern indicating the sign of an incipient slip, which was followed by higher frequency slip sequence signals. The results cohered with a simulation result of dynamic behavior analysis for an incipient slip using FEM.Third, it was verified that such a characteristic sequence of signals did not appear when an object rolled on the skin surface. Moreover, we demonstrated the effectiveness of the incipient slip information through grasping force control of a two-fingered hand to hold an object regardless of the weight and the surface roughness.From the above results, we conclude that incipient slip detection with a differential output from a pair of artificial Meissner corpuscles fulfils a main role of the static friction sensing mechanism.