Kinematic Self-Replicating Machines
© 2004 Robert A. Freitas Jr. and Ralph C. Merkle. All Rights Reserved.
Robert A. Freitas Jr., Ralph C. Merkle, Kinematic Self-Replicating Machines, Landes Bioscience, Georgetown, TX, 2004.
3.12 Bradley Self-Replicating Teleoperated Machine Shop (1980)
William E. Bradley studied concepts for building in space in the 1960s when he was associated with the Institute of Defense Analysis, during which time he coined the word telefactor (a slaved machine operated by remote control; or, more commonly today, teleoperation or telepresence). He later became an emeritus member of the board of directors of Telefactor, a company formed in 1972. In 1980, while consulting at NASA Headquarters, Bradley became interested in von Neumann’s assertion  that “it is in principle possible to set up a machine shop which can make a copy of any machine, given enough time and raw materials.” Bradley decided to personally investigate the question of whether a machine shop (Figure 3.34), if properly utilized by knowledgeable human operators and supplied with adequate raw materials, could completely replicate itself.* Bradley concluded that the answer was yes (indeed, building a number of “homebrew” shop machines such as an entire lathe [1023-1025], drill press  and milling machine  from simpler tools has been demonstrated**). The following material is largely excerpted from Bradley’s report .
* Von Neumann also observed  that a machine tool that just stamps out parts is an example of a fabricator that is more complex than that which it fabricates. Such a machine tool is “an organization which synthesizes something ... necessarily more complicated…than the organization it synthesizes,” so that “complication, or [re]productive potentiality in an organization, is degenerative.” In 1970, Nemes  discussed artificial self-replicating machines and described how to construct “an automatic lathe able to reproduce itself,” a simple concept said to have been developed even before von Neumann’s work on machine replication. Custom machined parts can now be ordered online .
** Evidently Doug Goncz  “constructed a self-reproducing machine tool and sold it for $300 in 1997. The machine incorporated its own reproduction template, a drill jig made from 3/8 cold rolled steel.” An image of this device was still available online in 2003 .
The town of Muncy is located in a somewhat remote part of central Pennsylvania. It is remarkable because of a nearly self-sufficient machine manufacturing capability in the Sprout-Waldron Company (now a division of another corporation, and therefore subject to change without notice). This company has manufactured agricultural and food-processing equipment as well as heavy machinery for the paper industry, especially pulp grinders. I became acquainted with them while searching for machines able to produce dense pellets for use as solid fuel from agricultural cellulosic wastes. In the course of my visit, I was shown an excellent machine shop, a foundry, a woodworking shop, and a factory assembly space in which their machines were put together, painted and tested. They also had complete drafting and design engineering facilities. Of special interest was their toolmaking and repair shop, with which all of the milling machines, lathes, jig borers, punch presses, and so forth were kept in fine working order.
This complex, with the possible exception of the foundry, seemed to be a system which, with human assistance, could duplicate itself. In retrospect, it seems worthwhile to explore the possibility that the human operators might be replaced by general purpose automata, manufactured almost completely by the complex itself. The result would then be a major component of a self-replicating system. To complete the system would require manufacture of a prime power source which could be expanded as the complex grows, manufacture of a shelter system (sheds with roofs, walls, windows, and doors) similarly expandable, and possibly a casting and/or forging subsystem, and electronic and computer components of the automata. The foundry with its requirement for refractory furnace linings and high temperatures is a special problem and in some versions of the system may be bypassed.
Present-day machine shops. Each machine in a machine shop has a functional domain or “scope,” assuming unlimited operator attention and guidance. Thus, a lathe (with no attachments) is able to produce objects with cylindrical symmetry having axial length and maximum diameter determined by the “bed length” and the “swing” of the machine. It can also make threads (helical structures), and, to a limited extent, can also make straight-line cuts or grooves which are more properly the work of a milling machine. Lathes [1023-1025] can drill holes most readily on the axis of a workpiece of cylindrical symmetry and can achieve a high degree of accuracy of concentricity for this one type of drilling. Most drilling, however, is best accomplished on a jig borer.
The second major machine type in a shop is some form of drill press, or, better, a jig borer. The workpiece is held firmly in an accurately translatable and rotatable fixture, remaining stationary while holes are drilled by a drill or boring tool held in a chuck rotating about the principal axis of the machine. Such a device can produce clusters of accurately located holes with parallel axes.
The third important shop component is the milling machine. The workpiece is clamped firmly to an accurately controlled table. The workpiece moves continuously, slowly, during operations while the rotating milling cutter shaves or saws the surface being worked. The milling machine is usually used to make rectilinear cuts to form accurately related plane surfaces or grooves.
Finally, a well-equipped machine shop usually also includes a power hacksaw, a powerful press with forming dies for forming sheet metal and for punching holes with “punch and die” sets, a bending brake, tool grinders, and possibly a surface grinder to be used like a milling machine to produce flat surfaces.
Self-replicating shop and general purpose machines. Each machine or subsystem of such a shop can be separated into parts from which it can be reassembled. Each machine therefore has a “parts list,” and each part either can or cannot be fabricated by the set of machines and subsystems comprising the shop. The criterion for replication thus may be stated as follows:
If all parts of all machines and subsystems [including all necessary “scaffold” devices] can be fabricated within the shop, then if properly operated the entire shop can be replicated.
“Proper operation” in this context includes supplying raw materials, energy, and manipulatory instructions or actions necessary to carry out the large number of machine operations, parts storage, and parts assembly required. Human labor is now used for these functions, or to marshal the necessary raw materials and energy.
It is not necessary that the shop be able to produce anything except a replica of itself which is in turn capable of producing another. Therefore, some simplifications appear possible, such as standardization and limitation of scope where feasible. For example, a general purpose machine can be imagined with a wider cross feed table than a conventional lathe and with a standardized vise and tool holder so that it can be used for milling. All three dimensions of translation and one axis of rotation could be provided on the table. The head stock could be arranged to hold workpieces, milling cutters or drills. Hardened tools for the necessary cutting operations could be fabricated by the machine from carbon steel in the annealed condition, then tempered, drawn, and sharpened by a separate simpler machine including a small furnace and a tool grinding wheel equipped with tool-holder and feeds. By careful standardization of parts, tools, and fixtures, it is conceivable that such a “one-machine shop” could succeed in reproducing itself.
Factons. After a shop had been tested with human operators and proven capable of self-replication, it would be possible to explore the replacement of the human operators by mobile computer-controlled manipulators, or “factons.” Hopefully, all of the “numerical control” features could be contained in these general-purpose programmable devices which could handle the machines like a human operator. The factons would transfer work from operation to operation, adjust the machine, perform each operation, then transfer the work to a parts storage array. Finally, the parts would be assembled by the factons and the entire shop set up in a selected location and floor plan. The facton itself has a parts list, most designed to be manufacturable by the shop. Here it is practically inevitable that computer chips plus enormous memories will be needed which would fall outside the scope of the shop thus far envisioned. In other words most, but not all, of facton components could be fabricated by factons in the shop. Still, given these extra components provided as feedstock from outside, the factons could probably fully assemble themselves. The shop itself would require some exogenous elements, as noted above: prime power, shaft power transmission such as belting or electric motors, abrasives, furnace heating arrangements for tool heat treatment, and raw material such as basic feedstock including steel rods, strips, and plates are among the most obvious.
Using the same facton design, it should be possible to implement extensions of the shop, including an optical shop, a pneumatic and/or hydraulic equipment manufacturing shop, and ultimately even an integrated circuit shop. Note, however, that only the original shop with its factons and their programs would have to possess the capability for self-replication. Computer components, probably provided from outside the system, might be furnished in an unprogrammed condition. Thus, factons would program the tapes, discs, or read-only memories by replication (and verification) of their existing programs.
Program extension beyond self-replication. The “scope” of a self-replicating shop is much larger than is required for self-replication. Apparently the ability to replicate utilizes only a vanishingly small fraction of total capabilities (to produce various sizes and shapes of parts and to assemble them into machines and structures). The essential characteristic for self-replication is that the scope must be adequate to produce every part of every machine in the shop by means of a feasible program. This “closure condition” (Section 5.6) can be satisfied using only a small part of the shop’s full capabilities.
A generic self-replicating machine shop can therefore, by means of a simple addition to its program, manufacture other machines and structures and, by means of them, interact with its environment. For example, it can construct and operate foraging systems to procure fuel or materials, waste disposal systems, or transporters to carry replica shops to other locations. Obviously, self-replication of such an extended system requires replication of the program-memory. This memory can be partitioned into two parts: (1) the self-replication process memory, and (2) the external process (manufacturing) memory. The distinction between these two memories is that the first is required to reproduce the basic unit (shop machines plus factons) while the second memory contains the program to produce process equipment not essential to the self-replicating nucleus.
At this point it is clear that the effect of a self-replicating system on its environment may take many forms dependent on the external process program. Using such a program, the scope of the system can be extended by construction of machines and structures capable of producing complex subsystems including mineral processing plants, solar energy power supplies, etc. All of these extended self-replicating systems would embody the same basic nucleus of machines, factons and self-replication programming. They would differ only by addition of the external process program segment peculiar to each type.
Reliability and redundancy. Reliability is a primary concern, especially in the case of self-replicating processes. Two ideas are most important here.
First, the self-replicating program accuracy can be verified by comparison with other replicas of the same program. If a discrepancy is found between two self-replicating programs, a third or fourth replica can be consulted and the error pinpointed and corrected. The test of correctness is the ability to self-replicate.
Second, machines tend to wear, and ultimately to fail, from normal use. On the other hand, if the system can replicate itself it can make spare parts and install them itself. [Authors’ note: this is not a logical necessity, since the shop can in theory produce multiple copies before any part needs to be replaced, and then simply shut down] A special program segment, the “maintenance program,” should be devised to check machine wear and perform repairs as needed. This segment would be part of the self-replication program, although another somewhat similar maintenance program should probably be used to care for machines and structures of the external process. This external maintenance program would be specialized for each extended system and is properly part of the second memory. [Authors’ note: high fecundity can to some degree compensate for a lack of reliability.]
Last updated on 1 August 2005