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, according to Hod Lipson, Cornell assistant professor of mechanical and aerospace engineering, and computing and information science, in whose lab the robots were built and tested.
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 cubes linked together. Each cube is divided in half along 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 assists in completing its own construction.
Although these experimental robots work only in the limited laboratory environment, Lipson suggests that the idea of making self-replicating robots out of self-contained modules could be used to build working robots that could self-repair by replacing defective modules. For example, robots sent to explore Mars could carry a supply of spare modules to use for repairing or rebuilding as needed, allowing for more flexible, versatile and robust missions. Self-replication and repair also could be crucial for robots working in environments where a human could not survive.
Self-replicating machines have been the subject of theoretical discussion since the early days of computing and robotics, but only two physical devices that can replicate have been reported. One uses Lego parts assembled in a two-dimensional pattern by moving along tracks; another uses an arrangement of wooden tiles that tumble into a new arrangement when given a shove.
Inside of cube half that contains the motor and gear and electromagnet
Exactly what qualifies as "self-replication" is open to discussion, Lipson points out. "It is not just a binary property -- of whether something self-replicates or not, but rather a continuum," he explains. The various possibilities are discussed in "A Universal Framework for Analysis of Self-Replication Phenomena," a paper by Lipson and Bryant Adams, a Cornell graduate student in mathematics, published in Proceedings of the European Conference on Artificial Life, ECAL '03, September 2003, Dortmund, Germany.
The new robots in Lipson's lab are also very dependent on their environment. They draw power through contacts on the surface of the table and cannot replicate unless the experimenters "feed" them by supplying additional modules.
"Although the machines we have created are still simple compared with biological self-reproduction, they demonstrate that mechanical self-reproduction is possible and not unique to biology," the researchers say.
A video of the robots in action can be seen here.