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.
4.6 Feynman Hierarchical Machine Shop (1959) and Microassembly
In his famous December 1959 speech, “There’s Plenty of Room at the Bottom,” Nobel physicist Richard P. Feynman  observed that: “The principles of physics, as far as I can see, do not speak against the possibility of maneuvering things atom by atom. It is not an attempt to violate any laws; it is something, in principle, that can be done; but, in practice, it has not been done because we are too big.” Feynman then proposed the prototypical top-down strategy for building complex nanomachinery – essentially a completely teleoperated machine shop, including mills, lathes, drills, presses, cutters, and the like, plus master-slave grippers to allow the human operator to move parts and materials around the workshop.
To build a nanomachine using Feynman’s scheme [2182, 2183], the operator first directs a macroscale machine shop to fabricate an exact copy of itself, but four times smaller in size. After this work is done, and all machines are verified to be working properly (and as expected), then the reduced-scale machine shop would be used to build a copy of itself, another factor of four smaller which is a factor of 16 tinier  than the original machine shop. This process of fabricating progressively smaller machine shops proceeds until a machine shop capable of manipulations at the nanoscale is produced.* The end result is a nanomachine shop capable of reconstructing itself, or of producing any other useful nanoscale output product stream that is physically possible to manufacture, using molecular feedstock. As Feynman describes the idea, which includes massive parallelization :
“If you work through a pantograph, even today, you can get much more than a factor of four in even one step. But you can’t work directly through a pantograph which makes a smaller pantograph which then makes a smaller pantograph – because of the looseness of the holes and the irregularities of construction. The end of the pantograph wiggles with a relatively greater irregularity than the irregularity with which you move your hands. In going down this scale, I would find the end of the pantograph on the end of the pantograph on the end of the pantograph shaking so badly that it wasn’t doing anything sensible at all. At each stage, it is necessary to improve the precision of the apparatus. If, for instance, having made a small lathe with a pantograph, we find its lead screw irregular – more irregular than the large-scale one – we could lap the lead screw against breakable nuts that you can reverse in the usual way back and forth until this lead screw is, at its scale, as accurate as our original lead screws, at our scale.
“When I make my first set of slave hands at one-fourth scale, I am going to make ten sets. I make ten sets of hands, and I wire them to my original levers so they each do exactly the same thing at the same time in parallel. Now, when I am making my new devices one-quarter again as small, I let each one manufacture ten copies, so that I would have a hundred hands at the 1/16th size....If I made a billion little lathes, each 1/4000th the scale of a regular lathe, there are plenty of materials and space available because in the billion little ones there is less than two percent of the materials in one big lathe. It doesn’t cost anything for materials, you see. So I want to build a billion tiny factories, models of each other, which are manufacturing simultaneously, drilling holes, stamping parts, and so on.
“As we go down in size, there are a number of interesting problems that arise. All things do not simply scale down in proportion. There is the problem that materials stick together by the molecular (van der Waals) attractions. There will be several problems of this nature that we will have to be ready to design for....[But] if we go down far enough, all of our devices can be mass produced so that they are absolutely perfect copies of one another. We cannot build two large machines so that the dimensions are exactly the same. But if your machine is only 100 atoms high, you only have to get it correct to one-half of one percent to make sure the other machine is exactly the same size – namely, 100 atoms high!”
“Our ability to see what we are doing, and to do things on an atomic level,” Feynman concluded, “is a development which I think cannot be avoided.”
* Perhaps Feynman himself was partly inspired by the children’s book The Cat in the Hat Comes Back, published one year earlier in 1958 by Dr. Seuss , wherein a conceptually similar progressive system of manipulators is described, disguised as a young person’s primer on the alphabet. The story line: While the kids are stuck shoveling snow, the laughing Hat Cat lets himself in the house and eats a pink cake in the bathtub. He leaves behind “a big long pink cat ring,” which he then handily cleans with “MOTHER’S WHITE DRESS!” The dress then loses its pink stain to the wall, and then to “DAD’S $10 SHOES!”, the rug in the hall, and then to the bedspread, until finally the Hat Cat calls in some assistants. From inside his big hat comes Little Cat A, then progressively smaller Little Cats B, C, D, and E, each nested in the previous one’s hat, and so on down to Little Cat Z, who “is too small to see.” The Little Cats make things worse, spreading the pink stain all over the front yard snow. The mess is finally cleared by Little Cat Z who has an even smaller, mysterious “Voom” in his hat, described only as “so hard to get” but “cleans up anything.” The Hat Cat orders Cat Z to “Take the Voom off your head! Make it clean up the snow!” Acting like a janitorial utility fog (Section 3.8), spiraling clouds spin through the yard; in a whirlwind of action, all the pink is gone. Exclaims the relieved child: “Don’t ask me what Voom is. I never will know. But, boy! Let me tell you. It DOES clean up snow!” The whirling fog also leaves behind a perfectly shoveled path from the street sidewalk to the front door, sparing the kids any further work.
To help motivate progress in top-down mechanical engineering, in his 1959 lecture  Feynman also issued two seemingly “impossible” challenges: (1) to build a working electric motor no larger than a 1/64th-inch cube, and (2) to write a page of a book on an area 1/25,000 times smaller in linear scale “in such manner that it can be read by an electron microscope,” each challenge backed by a $1000 prize. Just 11 months later, engineer William McLellan had constructed a 250-microgram 2000-rpm motor out of 13 separate parts that would fit inside a 0.4-mm cube, and collected his reward against the first challenge . (The second prize was won in 1985 by Tom Newman, who used e-beam lithography (Section 4.7) to meet the second challenge by writing the first page of Dickens’ A Tale of Two Cities legibly in a 6.25-micron square, taking about 60 seconds .)*
* Regis  reports that a publisher of Buddhist texts subsequently contacted Newman to ask if he had any interest in creating a line of microscopic prayer books. Explained the publisher: “Miniature texts have potential ritual uses that are very intriguing. One requirement would be that the texts be in Tibetan script, rather than the standard Roman alphabet, but we already have or could modify a bit map of the Tibetan alphabet.”
The field of micromechanical engineering gathered momentum after lithographically-produced silicon-chip-based working micromotors were fabricated in the late 1980’s by groups at Berkeley and MIT. By 1990, tiny electrostatic motors with 100-micron rotors boasted operating speeds of ~250 Hz  and operating lifetimes of ~106 revolutions . Wobble micromotors such as those fabricated in silicon by the University of Utah’s micromachine lab demonstrated very little friction or abrasion, with measured operating lifetimes in excess of 300 million revolutions . Microelectromechanical or “MEMS” research has since produced multi-micron-scale accelerometers [2189-2191], diverse microsensors (e.g., blood pressure microsensors attached to cardiac catheters), microscale cantilevers and jointed crank mechanisms , 5-micron barbs , flow microvalves and pressure microtransducers [2194, 2195], micropistons and micropumps , microgear trains , microactuators , piezo-driven micromotors , micromirrors and microshutters [2199-2201], Fresnel lens microarrays , microgyroscopes , a 2-mm long combustion chamber suitable for turbine use [2204, 2205], and multidevice microsystems  that were available customized or off-the-shelf in mass quantities by the late 1990s. MEMS had also produced microgrippers that could manipulate individual 2.7-micron polystyrene spheres, dried red blood cells of similar size, and various protozoa .
Could these microscale components be assembled into complex machines? Very simple mobile robots of ~1 cm3 volume were commonplace in the 1990s [2208-2211], so for a more challenging demonstration of MEMS’ ability to manufacture complete working microrobots, in 1994 Japanese researchers at Nippondenso Co. Ltd. fabricated a 1/1000th-scale working electric car [2212, 2213]. As small as a grain of rice, the micro-car was a 1/1000-scale replica of the Toyota Motor Corp’s first automobile, the 1936 Model AA sedan. The tiny vehicle incorporated 24 assembled parts, including tires, wheels, axles, headlights and taillights, bumpers, a spare tire, and hubcaps carrying the company name inscribed in microscopic letters, all manually assembled using a mechanical micromanipulator of the type generally used for cell handling in biological research. In part because of this handcrafting, each microcar cost more to build than a full-size modern luxury automobile. The Nippondenso microcar was 4.8 mm long, 1.8 mm wide, and 1.8 mm high, consisting of a chassis, a shell body, and a 5-part electromagnetic step motor measuring 0.7 mm in diameter with a ~0.07-tesla magnet penetrated by an axle 0.15 mm thick and 1.9 mm long. Power was supplied through thin (18 micron) copper wires, carrying 20 mA at 3 volts. The motor developed a mean torque of 7 x 10-7 N-m (peak 13 x 10-7 N-m) at a mean frequency of ~100 Hz (peak ~700 Hz), propelling the car forward across a level surface at a top speed of 10 cm/sec. Some internal wear of the rotating parts was visible after ~2000 sec of continuous operation; the addition of ~0.1 microgram of lubricant to the wheel microbearings caused the mechanism to seize due to lubricant viscosity. The microcar body was a 30-micron thick 20-milligram shell, fabricated with features as small as ~2 microns using modeling and casting, N/C machine cutting, mold etching, submicron diamond-powder polishing, and nickel and gold plating processes. Measured average roughness of machined and final polished surfaces was 130 nm and 26 nm, respectively. The shell captured all features as small as 2 mm on the original full-size automobile body. Each tire was 0.69 mm in diameter and 0.17 mm wide. The license plate was 10 microns thick, 0.38 mm wide and 0.19 mm high.
Nippondenso subsequently used similar manufacturing techniques to build a prototype of a capsule intended to crawl through tiny pipes in a power plant or a chemical plant like an inchworm , hunting for cracks [2215, 2216], and other miniature mobile robots have been announced [2217, 2218]. In 1999, three Japanese electronics companies revealed the creation of a 0.42-gram, 5-mm long “ant-size” robot  reportedly able to lift 0.8-gm loads and move at ~2 mm/sec, as part of the government’s ongoing Micro Machine Project . In early 2003, James Ellenbogen announced  that researchers at MITRE Corp. were constructing a motorized silicon chip with 6 legs as a prototype millimeter-size robot or “millibot”, to demonstrate control engineering with coordinated walking and obstacle avoidance by 2004. Kristofer Pister’s group at UC Berkeley is working on millimeter-scale “smart dust with legs” and a micro rocket project, the details of which are not publicly available . In late 2003, Ebefors  had the closest to a working walking microrobot.
What about Feynman’s vision of a progressively miniaturized factory? Fearing et al [1582, 2224] at UC Berkeley “plan to build a self-contained desktop rapid prototyping system” combining folding, bonding, and microassembling operations on 100-micron-scale parts to make a fully-automatic, desktop assembly process for millirobots, as part of their laboratory’s NSF-supported Desktop Rapid Prototyping Millirobots project  and their interest in automated microassembly  – though oriented to “minimal bootstrapping for millirobot desktop factories, rather than self-replicating” . The Agile Assembly project at Carnegie Mellon University [2228, 2229] is developing an “agile assembly architecture” applied specifically to tabletop-sized factories or “minifactories” for microassembly including modular elements such as high-precision platens, bridges for mounting modular robotic elements, precision 2-DOF manipulators, 2-DOF couriers, and parts feeders, with the assembly of high-density mechatronic equipment as the prototypical application. (See also Section 3.20.)
Ongoing research efforts in precision or automated microassembly, desktop manufacturing [2230, 2231], microfactories [2232, 2233] and parallel micromanufacturing are currently in progress at the Agency of Industrial Science and Technology, AIST (Mechanical Engineering Laboratory) , Carnegie Mellon University (Microdynamic Systems Laboratory  and Robotics Institute ), European IST Program (MiCRoN Project) , Innovation On Demand, Inc. [2236, 2237], Institute for Machine Tools and Industrial Management (Munich Microassembly Research) , Lawrence Livermore National Laboratory (Micro Assembly Automation Laboratory) , Nagoya University (Department of Micro System Engineering) , Nelson’s group [2241, 2242], Rensselaer Polytechnic Institute (Center for Automation Technologies) , Sandia National Laboratories (Precision Micro Assembly Laboratory) , University of California at Berkeley (Robotics and Intelligent Machines Laboratory) , University of Minnesota (Advanced Microsystems Laboratory) , USATU (Center of High Technologies in Manufacturing Systems) , Zyvex Corp. (Assembly of Microsystems) [2247, 2248], and elsewhere [2249-2252].
Last updated on 1 August 2005