ITHACA, N.Y., May 11 -- Cornell University researchers announced today they have created a machine that can build copies of itself. The machine is just a proof of concept -- it performs no useful function except to self-replicate -- but the basic principle could be extended to create robots that could replicate or at least repair themselves in space or for work in hazardous environments, said Hod Lipson, Cornell assistant professor of mechanical and aerospace engineering, and computing and information science, in whose lab the robots were built and tested. Each module of the self-replicating robot is a cube, about four inches on a side, able to swivel along a diagonal. Their robots are made up of a series of modular cubes -- called "molecubes" -- each containing identical machinery and the complete computer program for replication. The cubes have electromagnets on their faces that allow them to selectively attach to and detach from one another, and a complete robot consists of several linked cubes. Each cube is divided in half on a long diagonal, which allows a robot composed of many cubes to bend, reconfigure and manipulate other cubes; for example, a tower of cubes can bend itself over at a right angle. To begin replication, the stack of cubes bends over and sets its top cube on the table. Then it bends to one side or another to pick up a new cube and deposit it on top of the first. By repeating the process, one robot made up of a stack of cubes can create another just like itself. Since one robot cannot reach across another robot of the same height, the robot being built helps to complete its own construction. The concept of self-replicating machines was introduced in the sixties by John von Neumann. However, a fully autonomous self-replicating robot has yet to be implemented. Since then, various studies of artificial self-replicating machines have followed, using models such as the cellular automata and simple mechanical units. Johns Hopkins scientists recently built a prototype that uses Lego parts assembled in a 2-D pattern by moving along tracks; the Xerox Palo Alto Research Center (PARC) in California built a robot, PolyBot, made up of a chain of simple hinge joints that could shape itself into a loop and move by rolling like a self-propelled tank tread. For more information, visit: www.mae.cornell.edu/ccsl/research/selfrep/index.htm