Computing all form-closure grasps of a rectilinear polyhedron with seven frictionless point fingers

Object immobilization is important to robot hand grasping and to many manufacturing processes. A huge number of existing papers considered issues such as the analysis of grasps, the existence of immobilizing grasps for various classes of objects, and the synthesis of immobilizing grasps for two- and three-dimensional objects. However, no algorithm has been proposed to efficiently enumerate all form-closure grasps for any class of three-dimensional objects. As an initial step towards a general solution to this complex problem, we propose the first efficient algorithm for computing all form-closure grasps of a rectilinear polyhedron. Our approach is based on a decomposition of the original problem in the abstract six- dimensional wrench space into closely related subproblems in three-dimensional subspaces, and a subsequent transformation of these subproblems into two-color intersection problems on planar screens in these spaces. We then use techniques from computational geometry to efficiently solve the planar intersection problems. The resulting algorithm reports all K sets of six to seven faces of a rectilinear polyhedron that yield at least one form-closure grasp in O(n²K´ log⁴ n + K) time, where n is the number of the faces, and K´ is the size of an intermediate output. We show that K = Omega(n²K´) in the worst case.