Learning Pregrasp Manipulation of Objects from Ungraspable Poses

In robotic grasping, objects are often occluded in ungraspable configurations such that no feasible grasp pose can be found, e.g. large flat boxes on the table that can only be grasped once lifted. Inspired by human bimanual manipulation, e.g. one hand to lift up things and the other to grasp, we address this type of problems by introducing pregrasp manipulation – push and lift actions. We propose a model-free Deep Reinforcement Learning framework to train feedback control policies that utilize visual information and proprioceptive states of the robot to autonomously discover robust pregrasp manipulation. The robot arm learns to push the object first towards a support surface and then lift up one side of the object, creating an object-table clearance for possible grasping solutions. Furthermore, we show the robustness of the proposed learning framework in training pregrasp policies that can be directly transferred to a real robot. Lastly, we evaluate the effectiveness and generalization ability of the learned policy in real-world experiments, and demonstrate pregrasp manipulation of objects with various sizes, shapes, weights, and surface friction.