It occurs frequently in robotic applications that a robot manipulates a workpiece which is free to slide on a work surface. Because the pressure distribution supporting the workpiece on the work surface cannot in general be known, the motion of the workpiece cannot be calculated uniquely. Yet despite this indeterminacy, several researchers have shown that sliding motions can be employed to accurately align workpieces without visual or other feedback. Here we find the locus of centers of rotation of a workpiece for all possible pressure distributions. The results allow a quantitative understanding of open-loop robot motions which guarantee the alignment of a workpiece. Several sample problems are solved using the results, including the distance that a flat "fence" or robot finger must push a polygonal workpiece to assure that a facet of the workpiece comes into alignment with the fence.

No abstract

In automated packing or assembly it is often necessary to bring randomly oriented parts into uniform alignment. Mechanical methods such as vibratory bowl feeders are often used for this purpose, although there is no theory for the systematic design of such feeders. A slanted "fence" attached to the stationary sides of a conveyor belt is also capable of orienting a stream of parts and a sequence of such fences has been shown [14] to function as a systematically designable linear parts feeder.A limitation of fence alignment is that once a part has left contact with a fence, its final orientation is confined to a narrow range of angles but is not unique. Here we consider the design of an individual fence, consisting of a straight slanted section followed by an optimal curved tail. The straight section selectively aligns certain edges of the part, while the curved tail preserves this alignment precisely as the part leaves contact with the fence. We have found the shortest tail which guarantees alignment.

In automated packing or assembly it is often necessary to bring randomly oriented parts into uniform alignment. Mechanical methods such as vibratory bowl feeders are often used for this purpose, although there is no theory for the systematic design of such feeders. A slanted “fence” attached to the stationary sides of a conveyor belt is also capable of orienting a stream of parts and a sequence of such fences has been shown [17] to function as a systematically designable linear parts feeder. A limitation of fence alignment is that once a part has left contact with a fence, its final orientation is confined to a narrow range of angles but is not unique. Here we consider the design of a single fence, consisting of a straight slanted section followed by an optimal curved tail. The straight section selectivity aligns certain edges of the part, while the curved tail preserves this alignment precisely as the part leaves contact with the fence. We have found the shortest tail which guarantees alignment. Optimal curved fences may be used individually for alignment of parts on a conveyor belt. They also lend themselves to systematic design of multi-fence linear parts feeders [8], [17].