On-Line Reconfigurable Machines

run reliably for long periods of time under intense use. They have not traditionally been known for their flexibility and changeability. When something does go wrong, the entire system may need to be shut down, with every minute of down time representing lost production and possibly damaged product. Further, making changes in a factory line can require extensive redesign, retooling, and reprogramming. Recently, a trend in manufacturing technology has been toward reconfigurable manufacturing systems (Koren et al. 1999), in which factory lines are designed to support changes in their structure. Such systems, which are gradually being deployed, still need to be configured and rearranged offline, but have advantages in terms of rapid deployment of new configurations, standardization of parts, and machine design time. The next challenge in achieving true flexibility in manufacturing is to imbue factory systems with online reconfigurability, that is, the ability to swap parts out online, enable or disable capabilities in real time, and respond quickly to changes in the system or environment (including faults). In addition to the advantages conferred by offline reconfigurability, online reconfigurability would allow a manufacturing system to run more consistently and reliably, as well as allow it to be more flexible, able to change products or objectives extremely rapidly. We believe that these goals can be attained through the use of a very high level of modularity, both in hardware and software, combined with intelligent software. To test this hypothesis, Palo Alto Research Center (PARC) designed and built a prototype highly modular system in the printing domain. This “hypermodular” printer explores the extremes of modularity, reconfigurability, and parallelism in both hardware and software. The hardware prototype connects four standard Xerox marking engines (the component of a printer that does the actual printing) in parallel using a highly modular paper path. This configuration can achieve a print rate of four times that of an individual print engine. The system software stack for the prototype consists of Articles