Control of robotic object pivoting based on tactile sensing

Robotic manipulation of objects using the sole tactile feedback is a challenge. If the contact between the robot end effector and the manipulated object is distributed, the robot can exchange both friction forces and torques with it. The friction highly influences the motion of the object. By controlling the friction it is possible to perform complex manipulation tasks, such as moving the object with respect to the end effector by executing a controlled sliding motion. If the motion is a rotation with respect to the end effector, the corresponding maneuver is called pivoting. Control of the pivoting motion is considerably difficult, especially without any visual feedback. This paper proposes a novel method to regulate the object angular position, by means of a pivoting maneuver, through a parallel gripper endowed with force/tactile sensors. The strategy is based on a novel nonlinear observer that estimates the sliding velocity from force/torque measurements and a model of the sliding dynamics. We exploit the Limit Surface concept and the LuGre friction model to build a dynamic model of a planar slider. We show, through experimental results, that simple parallel grippers are able to execute such maneuvers that correspond to adding a virtual joint between the fingers, thus enlarging the robot workspace.