Nullspace composition of control laws for grasping

Much of the tradition in robot grasping is rooted in geometrical, planning-based approaches in which it is assumed that object geometries are well modeled a priori. Some recent approaches have chosen instead to deal with objects of unknown geometry. These techniques treat grasping as an active sensory-driven problem. At any given time, finger contacts are incrementally displaced along the object's local surface using a single control law. In this paper, we extend this approach by allowing multiple control laws to be active simultaneously. Three control laws are combined by projecting the actions of subordinate control laws into other control law nullspaces. The resulting composite controller finds grasps that are more robust than the component primitives in isolation. Finally, we show how this approach may be used on hand/arm manipulation systems with arbitrary kinematics.