Relaxed-Rigidity Constraints: In-Grasp Manipulation using Purely Kinematic Trajectory Optimization

This paper proposes a novel approach to performing in-grasp manipulation planning: the problem of moving an object with reference to the palm from an initial pose to a goal pose without breaking or making contacts. Our method to perform in-grasp manipulation uses kinematic trajectory optimization which requires no knowledge of dynamic properties of the object or the robot. We define a cost function that attempts to maintain the initial grasp points, while relaxing the constraint that the contacts between finger and object remain rigid. Hence, we name this new formulation relaxed-rigidity constraints. We implement our approach on an Allegro robot hand and perform experiments on 10 objects from the YCB dataset. However, the implementation would work for any object the robot can grasp. We perform thorough analysis and compare to alternative optimization formulations. Our method reaches the desired object pose with a median position error of 13mm across all of the 500 trials without ever dropping the object.