Grasping Curved Objects through Rolling

Grasping a curved object free in the plane may be done through rolling a pair of fingers on the object’s boundary. Each finger is equipped with a tactile sensor able to record any instantaneous point contact with the object. Contact kinematics reveal a relationship between the amount of finger rotations and the total curvatures of the boundary segments of the fingers and the object respectively traversed by the two contact points during the same period of rolling. Such relationship makes it possible to localize both fingers relative to the object from a few pairs of simultaneously taken finger contacts at different time instants. A least squares formulation of this localization problem can then be solved by the Levenberg-Marquardt algorithm. Simulation results are presented. After localization, a simple open loop strategy is used to control the continual rolling of the fingers until they simultaneously reach two locations on the object’s boundary where a grasp is finally performed.