Understanding Slip Perception of Soft Fingertips by Modeling and Simulating Stick-Slip Phenomenon

Slip, especially incipient slip, is a complicated process for soft fingertips; and detection of this slip is of important factor assuring the stable manipulation for both human and robotic fingertips. By experimental tools, previous research attempted to perceive this phenomenon, but none of them could explain fully dynamic change during this process. In this paper, we propose a dynamic model to investigate the sliding motion of soft fingertips on a plane with friction. The fingertip is virtually comprised of a finite number of elastic compressible and bendable cantilevers whose free ends act as infinitesimal contact points. The contact surface is afterward meshed using finite element method based on coordinates of contact points. By introducing Coulomb's law and contact compliance into each contact point, we are able to assess the frictional characteristic during sliding motions of the fingertip. We also successfully described dynamically localized displacements on the contact surface during stick-slip transition, which are typical of the sliding motion of a soft fingertip. This model can be applied to different typical shapes of robotic fingertip. In this paper, we use two models of fingertips: cylindrical, and hemispherical ones. In addition, we conducted experiments to valid proposed simulation, including force/moment and vision setups.