Nonprehensile Two Palm Manipulation with Non-Equilibrium Transitions between Stable States

Manipulation without prehension is a natural way of handling objects for both humans and machines. Nonprehensile operations are appropriate when complete constraint over the object to be manipulated is either undesirable or impractical, but some control over the object is desired over its entire trajectory, in order to bring the object reliably to a desired final state. Research to date has explored only a small portion of this class. We are interested in controlling the shape of the constraint surfaces so that constraint and external forces naturally attract the system to the desired state, even if the object momentarily loses stability during the motion. We present a preliminary analysis of the nonprehensile orientation of planar objects by two low friction palms joined at a central hinge. These palms support an object in a gravitational field, without grasping or gripping. We determine connected regions of stable states of the object, and give a method of planning part orientation based on a graph search over these regions, allowing non-equilibrium transitions between them. We conclude with the the results of simulations and tests of an example plan.