An Exploration of Nonprehensile Two-Palm Manipulation

This paper describes our current research into nonprehensile palm manipulation. The term “palm” refers to the use of the entire device surface during ma- nipulation, as opposed to use of the fingertips alone. The term “nonprehensile” means that the palms hold the object without wrapping themselves around it, as distinguished from a force/form closure grasp often employed by a fingered hand. Indeed, nonprehensile operations such as purposeful sliding and constrained dropping constitute important palm primitives. We have implemented a system for orienting parts using two palms. The system consists of a planner and an executive. As input, the system expects a geometric description of a part, its center of mass, the coefficients of friction between the part and each of the palms, and a start and goal configuration of the part in stable contact with one of the palms. As output, the system computes and executes a sequence of palm motions designed to reorient the part from the specified start to the specified goal configuration.