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

Abstract

Slip, especially incipient slip, is a complicated process for soft fingertips; and detection of this slip is important for stable manipulations by both human and robotic fingertips. Experimental research has attempted to explain this phenomenon, but dynamic changes during this process could not be fully delineated. We propose here a dynamic model to investigate the sliding motion of soft fingertips on a plane with friction. The fingertip is 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 a finite element method based on the coordinates of the contact points. By introducing Coulomb's law and contact compliance into each contact point, we were able to assess the frictional characteristics of the sliding motions of the fingertips. We also could successfully describe the dynamically localized displacements on the contact surface during stick-slip transition, displacements that represent the sliding motion of a soft fingertip. This model can be applied to different shapes of robotic fingertip, including the cylindrical and hemispherical models tested here. We also performed experiments to validate the proposed simulation, including force/moment and vision setups.