Casing an assembler

摘要

Assemblers have been proposed as general purposemanufacturing devices, able to build a wide range of usefulproducts as well as copies of themselves. Most proposals forassemblers involve an inside and an outside, separated by abarrier or casing. The outside is a relatively uncontrolledenvironment (a liquid solvent with dissolved feedstock moleculesand impurities) while the inside environment is both bettercontrolled (on impurities or undesired contaminants) andunreactive (a vacuum, or a moble gas such as neon).A graphite casing would be strong, flexible, relativelyunreactive, and largely impenetrable. The use of a graphite casingraises a number of desing issues: how to manufacture the newcasing within the confines of the old casing, what shape thecasing should have and what maintains that shape, the conditionsunder which the casing might fail, how to eject the new casinginto the outside solvent, etc.We also discuss an improved method of using acousticsignals to power and control the assembler. In particular, the(possibly bulky) pressure-actuated pistons that were locatedinternally to the casing in previous proposals are moved outsidethe casing. This lets us use pressurized neon, internally, tomaintain the shape of the casing, much as the shape of an inflatedballoon is maintained by internal air pressure. It also makes iteasier to use larger pistons which can be driven by smaller pressure changes.