This paper discusses a grasp scheme for a pyramidal-like object placed on a table under the gravitational field. We assume that the contact friction is small enough to ensure that any direct grasp fails in achieving an equilibrium grasp. For an idealized 2D triangle object placed vertically on a table, we first show that a planar two-fingered hand can always achieve an equilibrium grasp under frictional contact. We also extend the basic idea to a polyhedron whose face is triangle and show two possible procedures leading to equilibrium grasps. Finally, we verify our idea experimentally for the polyhedra.

When integrating a dexterous robot hand into a hand-arm system, one has to coordinate and control the usually redundant system while taking into account the special capabilities of the subsystems "hand" and "arm". This paper presents a simple approach for hand-arm coordination in Cartesian space which subdivides the object motion into hand and arm portions using only a few easily interpretable parameters. Applying well-known stiffness control approaches for the hand and the arm respectively, the problem of controlling the subsystems appropriately (including force control) is solved. The results of experiments using a system with 15 degrees of freedom are shown and discussed.