Stable grasping control under gravity by dual robotic fingers with soft rolling contacts

In this paper dealing with the problem of stable grasping of a rigid and rectangular object with two robotic fingers with soft tips, we consider the case of rolling fingertips under a soft contact motion model which leads to non-holonomic constraints even for the planar case while taking into consideration the gravity effect. The analytical hand-object system kinematics and dynamics are derived and a feedback controller is proposed. The controller compensates finger gravity and superimposes control signals that realize a stable grasp configuration and compensate for the object gravity forces while driving the object at the upright position. The controller is shown to achieve asymptotic convergence to the desired upright object position at a stable grasp configuration. Simulation results are presented confirming the theoretical findings.