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In this paper, the modeling and design for frictional loads applied by robotic fingertips through a soft contact interface are investigated. The dependence of the sustainable friction forces and moments due to the normal force applied on the contact area is studied. A model that considers the dependence of both the contact area and the coefficient of friction on the application of normal force is proposed. Specimens of simplified fingertips, made with different materials and shaped with different thickness of the covering soft layer, were tested in order to validate the proposed model via designed experiments. The results obtained have very important relevance to the design of robotic hands and fingers equipped with soft pads or skins, and can help in the choice of suitable features for the different layers of contact pads or skins.

The paper describes an experimental activity concerning the mechanical characterization of soft fingertips for robotic hands, focusing on the effects of the presence of an inner rigid core, as in robotic fingers with an endo-skeletal articulated frame covered by an external layer of soft material. By means of a purposely-designed test equipment, fingertips with differently sized cores have been tested, showing the influence of the thickness of the compliant layer on the resultant fingertip stiffness with respect to different materials and loading conditions (pure normal load, normal and tangential load, normal load and torque)