Robotic applications often involve manipulation of objects where position and orientation are not perfectly known. Pushing an object for instance by a fence, can be employed to accurately align parts, reducing uncertainty to only one degree of freedom. In this paper a pushing task involving two fingers that completely constrains an object in a plane is proposed. The stability of orientation and position of an object being pushed is discussed. The solution obtained is unique despite the fact that the distribution of forces supporting the object cannot, in general, be known. The proposed task of pushing is simple although some preliminary information about the initial position and orientation of an object is required. An approach to avoid the ambiguity in orientation, owing to the effect of friction between the object and the pusher, by introducing up and down movement of the pusher is also presented.>

A sensorless manipulation task eliminating geometrical uncertainty is proposed. It involves a two-fingered tool attached to a robot end effector. The object is assumed to be a convex polyhedron, although this assumption is later relaxed. Assuming that position and orientation are approximately known prior to operation, the initial position of the tool and the direction of movement are chosen. As the tool advances it strikes the object. If the trajectory is chosen properly, the fingers will contact the object with its corner between them. It is shown that such a configuration of contact points uniquely constrains the position of an object in all degrees of freedom.>