Abstract

Consider the task of grasping the handle of a door, and then pushing it until the door opens. These two fundamental robotics problems (selecting secure grasps of a hand on an object, e.g. the door handle, and planning collision-free trajectories of a robot arm that will move that object along a desired path) have predominantly been studied separately from one another. Thus, much of the grasping literature overlooks the fundamental purpose of grasping objects, which is typically to make them move in desirable ways. Given a desired post-grasp trajectory of the object, different choices of grasp will often determine whether or not collision-free post-grasp motions of the arm can be found, which will deliver that trajectory. We address this problem by examining a number of possible stable grasping configurations on an object. For each stable grasp, we explore the motion space of the manipulator which would be needed for post-grasp motions, to deliver the object along the desired trajectory. A criterion, based on potential fields in the post-grasp motion space, is used to assign a collision-cost to each grasp. A grasping configuration is then selected which enables the desired post-grasp object motion while minimising the proximity of all robot parts to obstacles during motion. We demonstrate our method with peg-in-hole and pick-and-place experiments in cluttered scenes, using a Franka Panda robot. Our approach is effective in selecting appropriate grasps, which enable both stable grasp and also desired post-grasp movements without collisions. We also show that, when grasps are selected based on grasp stability alone, without consideration for desired post-grasp manipulations, the corresponding post-grasp movements of the manipulator may result in collisions.