Pre-Grasp Manipulation Planning to Secure Space for Power Grasping

An object can be gripped firmly through power grasping, in which the gripper fingers and palm are wrapped around the object. However, it is difficult to power-grasp an object if it is placed on a support surface and the grasping point is near the support surface. Because there is no gap between the object and the support surface, the gripper fingers and the support surface will collide when the gripper attempts to power-grasp the object. To address this, we propose a pre-grasp manipulation planning method that uses two robot arms, whereby space can be secured for power grasping by rotating the object while being supported against the support surface. The objects considered in this study are appropriately shaped for a power grasp, but power grasping cannot be performed directly because the desired power-grasping location is close to the support surface on which the object is placed. First, to power-grasp the object, candidate rotation axes on the object and in contact with the support surface are derived based on a mesh model of the object. Then, for each such axis, the object pose that allows power grasping is obtained. Finally, according to the obtained object pose, the paths for rotating and power-grasping the object are planned. We evaluate the proposed approach through simulations and experiments using two UR5e robot arms with a 2F-85 gripper.