Yifan Hou, Zhenzhong Jia, Matthew T. Mason
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A shared grasp is a grasp formed by contacts between the manipulated object and both the robot hand and the environment. By trading off hand contacts for environmental contacts, a shared grasp requires fewer contacts with the hand, and enables manipulation even when a full grasp is not possible. Previous research has used shared grasps for non-prehensile manipulation such as pivoting and tumbling. This paper treats the problem more generally, with methods to select the best shared grasp and robot actions for a desired object motion. The central issue is to evaluate the feasible contact modes: for each contact, whether that contact will remain active, and whether slip will occur. Robustness is important. When a contact mode fails, e.g., when a contact is lost, or when unintentional slip occurs, the operation will fail, and in some cases damage may occur. In this work, we enumerate all feasible contact modes, calculate corresponding controls, and select the most robust candidate. We can also optimize the contact geometry for robustness. This paper employs quasi-static analysis of planar rigid bodies with Coulomb friction to derive the algorithms and controls. Finally, we demonstrate the robustness of shared grasping and the use of our methods in representative experiments and examples.
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| 07/16 15:00 UTC | 07/16 17:00 UTC |
Automatic generation of hybrid force-position control commands for object manipulation is exciting. This paper makes important contributions to this line of work, particularly analyzing the conditions for the stability/feasibility of contact modes and also proposing a way to quantify the stability of a contact mode. My suggestions for improving the paper are: * While the demonstrated manipulation experiments are impressive, the paper can provide a deeper connection to the algorithms. For example in Section VII-B, it is said that object/hand velocity is input, but it would be good to be clear what these velocities are and whether they leave any freedom in terms of which mode to choose. A presentation of the different stability margin values for these different modes that could have been chosen by the algorithm, and even experiments with different contact modes, would have connected the experiments better to the paper's main body. * While the experiments in VII-D show that checking whether the stability margin is positive or not can be used to analyze the feasibility with respect to different geometries, it does not really say anything about whether a positive stability margin that is larger than another positive stability margin, makes the former contact mode more stable than the latter. * Some symbols used in the algorithms are not defined: G, bG, C_{AF}. * Equation 23 should use \Delta(Fj,Ei), not D(Fj,Ei).
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