A force control based strategy for extrinsic in-hand object manipulation through prehensile-pushing primitives

Abstract: Object manipulation is a complex task for robots. It often implies a compromise between the degrees-of-freedom of hand and its fingers have (dexterity) and its cost and complexity in terms of control. One strategy to increase the dexterity of robotic hands with low dexterity is called extrinsic manipulation and its principle is to exploit additional accelerations on the object caused by the effect of external forces. We propose a force control based method for performing extrinsic in-hand object manipulation, with force-torque feedback. For this purpose, we use a prehensile pushing action, which consists of pushing the object against an external surface, under quasistatic assumptions. By using a control strategy, we also achieve robustness to parameter uncertainty (such as friction) and perturbations, that are not completely captured by mathematical models of the system. The force control strategy is performed in two different ways: the contact force generated by the interaction between the object and the external surface is controlled using an admittance controller, while an additional control of gripping force applied by the gripper on the object is done through a PI controller. A Kalman filter is used for the estimation of the state of the object, based on force-torque measurements of a sensor at the wrist of the robot. We validate our approach by conducting experiments on a PR2 robot, available at the Robotics, Perception, and Learning lab at KTH Royal Institute of Technology.