Dexterous Dynamic Optimal Grasping of a Circular Object subject to Gravity with Soft-fingertips

Usually, robotic hands are designed based on point contact model (subject to holonomic constraints) producing, essentially, low performance in virtue of it violates the physics on contact mechanics, that is, the assumption of infinitesimally small contact point model hardly applies in practice because indeed contact area occurs. Furthermore, the problem of dexterity for object manipulation necessarily requires rolling to repositioning finger contact points to exert tangent and normal contact forces, which play a fundamental role in manipulation. Thus, hemi-spherical and soft-fingertips have been proposed to facilitate rolling and contact area. In this paper, a stable grasping of a circular object is proposed through two fingers with hemi-spherical deformable fingertips. A passivity-based controller is proposed where tangential forces modulates the gravitational force while normal forces are aligned dynamically with respect to the horizontal, that corresponds to an optimal configuration. Representative simulations are presented to show the performance using two redundant fingertips.