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【正文】 htly in design. Such machines are ideal for this purpose because they can be quickly reprogrammed to acmodate minor or even major design changes. However, as independent machines they cannot produce parts in large volumes or at high production rates. An FMS can handle higher volumes and production rates than independent CNC machines. They cannot quite match such machines for flexibility, but they e close. What is particularly significant about the middle ground capabilities of flexible manufacturing is that most manufacturing situations require medium production rates to produce medium volumes with enough flexibility to quickly reconfigure to produce another part or product. Flexible manufacturing fills this longstanding void in manufacturing. Flexible manufacturing, with its ground capabilities, offers a number of advantages for manufacturers: ? Flexibility within a family of parts ? Random feeding of parts ? Simultaneous production of different parts ? Decreased setup time and lead time ? More efficient machine usage ? Decreased direct and indirect labor costs ? Ability to handle different materials ? Ability to continue some production if one machine breaks down 三 、 Flexible Manufacturing System Components An FMS has four major ponents: ? Machine tools ? Control system ? Materials handling system ? Human operators Machine Tools A flexible manufacturing system uses the same types of machine tools as any other manufacturing system, be it automated or manually operated. These include lathes, mills, drills, saws, an so on. The type of machine tools actually included in an FMS depends on the setting in which the machine will be used. Some FMSs are designed to meet a specific, welldefined need. In these cases the machine tools included in the system will be only those necessary for the planned operations. Such a system would be known as a dedicated system. In a jobshop setting, or any other setting in which the actual application is not known ahead of time or must necessarily include a wide range of possibilities, machines capable of performing at least the standard manufacturing operations would be included. Such systems are known as general purpose systems. 2. Control System The control system for an FMS serves a number of different control functions for system: ? Storage and distribution of parts program ? Work flow control and monitoring ? Production control ? System/tool control/monitoring The control area with the puter running the FMS control system is the center from which all activities in the FMS are controlled and monitored. The FMS control software is rather plicated and sophisticated since it has to carry out many different tasks simultaneously. Despite the considerable research that has been carried out in this area, there is no general answer to designing the functions and architecture of FMS software. The scheduler function involves planning how to produce the current volume of orders in the FMS, considering the current status of machine tools, workinpocess, tooling, fixtures, and so on. the scheduling can be done automatically or can be assisted by an operator. Most FMS control systems bine automatic and manually by the operator. the dispatcher function involves carrying out the schedule and coordinating the activities on the shop floor, that is, deciding when and where to transport a pallet, when to start a process on machining center, and so on. The monitor function is concerned with monitoring work progress, machine status, alarm messages, and so on, and providing input to the scheduler and dispatcher as well as generating various production reports and alarm messages. A transport control module manages the transportation of parts and palettes within the system. Having an AGV system with multiple vehicles, the routing control logic can bee rather sophisticated and bee a critical part of the FMS control software. A load/unload module with a terminal at the loading area shows the operators which parts to introduce to the system and enables him or her to update the status of the control system when parts are ready for collection at the loading area. A storage control module keeps an account of which parts are stored in the AS/RS as well as their exact location. the tool management module keeps an account of all relevant tool data and the actual location of tools in the FMS .Tool management can be rather prehensive since the number of tools normally exceeds the number of parts in the system, and furthermore ,the module must control the preparation and flow of tools. the DNC function provides interfaces between the FMS control program and machine tools and devices on the shop floor. the DNC capabilities of the shop floor equipment are essential to a FMS。 a “ full” DNC munication protocol enabling remote control of the machines is required (see the discussion on DNC in the previous section). The fact that most vendors of machine tools have developed proprietary munication protocols is plicating the development and integration of FMSs including multivendor equipment. Furthermore, the physical integration of multivendor equipment is difficult。 for example, the differences in pallet load/unload mechanisms plicate the use of machine tools from different vendors. Therefore, the only advisable approach for implementing a FMS is to purchase a turnkey system from one of the main machine tool manufacturers. there systems are reliable and well tested and should the system not function satisfactorily a single vendor responsibility will facilitate remedy of malfunctions. 3. Materials Handing System The automated materials handing system is a fundamental ponent that helps mold a group of independent CNC machines