Object-level Impedance Control for Dexterous In-hand Manipulation

This work presents a novel object-level control framework for the dexterous in-hand manipulation of objects with torque-controlled robotic hands. The proposed impedance-based controller realizes the compliant 6-DOF positioning of a grasped object. Enabled by the in-hand localization, the slippage of contacts is avoided by actively maintaining the desired grasp configuration. The internal forces on the object are determined by solving a quadratic optimization problem, which explicitly considers friction constraints on the contacts and allows to gradually shift the load between fingers. The proposed framework is capable of dealing with dynamic changes in the grasp configuration, which makes it applicable for the control of the object during grasp acquisition or the reconfiguration of fingers (i.e. finger gaiting). A nullspace controller avoids joint limits and singularities. Experiments with the DLR robot David demonstrate the efficiency and performance of the controller in various grasping scenarios.