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This paper describes a novel fingertip equipped with a soft elastic cover and a hard nail. The soft elastic cover of the fingertip enables changing friction coefficient at the contact with an object. It also enables detecting change of contact type with an object while manipulating it: the fingertip contact with a flat surface and with a convex sharp edge. The solid nail enables detecting a very small step of sub-millimeter on a smooth surface.
Murakami et al. (Tue,) studied this question.