Effective capture of non-graspable objects for space robots using geometric cage pairs

Capture and removal of space debris is challenging in robotic on-orbit servicing (OOS) activities. A large portion of space debris does not possess any graspable features, which makes conventional grippers inapplicable. To handle such non-graspable objects, a space robotic capture system is presented. A dual-arm space robot simulator that has the advantages of miniaturization and scalability is designed for ground tests. Inspired by robotic caging, we propose a novel capture method that uses a series of hollow-shaped end-effector pairs to cage the antipodal pairs of non-graspable objects. To apply the caging-pair method steadily, space robots need exerting a squeezing action on objects, which can be characterized by the motion and force manipulation of two robotic arms in the assigned directions. Based on the velocity and force manipulability transmission ratios, a caging compatibility index is proposed to describe the capturing ability in this manner. Via the optimization of the desired caging compatibility index, an effective algorithm is proposed to plan near-optimal joint configurations for pre-grasping cages. Finally, both simulation studies and experimental tests are conducted to evaluate the performance of the proposed capture method.