【正文】 state. The visitstate, Sv, indicates an interaction between two machines and hence requires coordination among them. The symbol of this state has the pattern RM for the robot, as an example, the state RvMnm. The small letter v represents the visitstate of the robot associated with location, Mn represents a machine served by the robot, and m represents the index of one of the visit locations. During the pletion of the task, the busy states are employed, and indicate 6 transitional states between operations or two executions without interaction. They can be recognized from the robot state symbol, Rtn. The small letter t indicates the state of the robot associated with transition. These states are useful in avoiding collisions with obstacles. The condition operator C, defines the set of state and guiding conditions necessary for each operation OPi . C(Opi). The output operator O, defines the set of states resulting from each operation OPi, ., O(OPi). 4. Control architecture for VFMC Cell operation involves tasks to be performed on single machines independent of others, and tasks that to require the cooperation of two or more machines. In cases where a task calls for the coordination of two or more machines, the cell controller has to be involved to ensure proper execution of that task. For tasks involving a single machine, the primary function of a controller is to schedule the start of the task, and waits for its pletion to mand the nest task. In order to acplish these functions, the cell controller is designed as a hybrid structure of both hierarchical controller and decentralized controllers as shown in Fig. 3. The controller consists of three different layers. The Scheduler, the Decentralized Control layer, and the Virtual Device layer. In the figure, the passing of information and message are indicated by arrows. The Scheduler is a core ponent that receives the states of all the machines in the VFMC from the Decentralized Control layer, and decides the appropriate next task. It then dispatches the next task to be executed to the Decentralized Control layer. It uses the process knowledge bases that contain the routine cell task rules that are generated from the TID. The Decentralized Control layer consists of virtual drivers for the virtual machine that mimic to physical machines. Their main role is to perform the harmonization and the cooperation between the cell ponents in order to carry out the task called for by the Scheduler layer. They provide a device independent interface to the actual cell ponents by translating the generic mands and error messages of the corresponding machine. The virtual driver in the layer municator and pass messages with each other. A virtual driver send mands to the corresponding physical machine, and receives the state of that machine, through that Virtual Device in the Virtual Device layer. The lowermost layer of the controller consists of the Virtual Devices which monitor and continuously mirror, in real time, the state of the physical machine they represent. Each machine state is analyzed by its Virtual Device and reported to the corresponding Virtual holons as required. The Virtual Devices also serve as conduits for mands from the Virtual holons to the physical machines. 7 5. Conclusion In this study, the concept of virtual manufacturing is investigated, and three models, such as the product, the facility, and the process model, are developed for virtual flexible manufacturing cells. A product model is a generic model used for representing all types of parts, which appear in the process of manufacturing. A facility model contains information about machines consisted of a virtual flexible manufacturing cell. A process model is used for representing all the physical processes that are required for representing product behavior and manufacturing processes. The methodology behind developing VFMC is an objectoriented paradigm that provides a powerful representation and classification tools. For the implementation IGRIP/QUEST is used to model all 3D virtual machines involved models, and to simulate the whole factories where manufacturing events are concerned. The concrete behaviors of simulation are described by the taskoriented description (TID). Also the result of simulation is demonstrated to prove the applicability of the virtual manufacturing paradigm. The potential of virtual manufacturing is to support manufacturability assessments and provide accurate cost, leadtime, and quality estimate is a major motivation for further research and development in this area. References 1. Iwata, Kazuaki Virtual Manufacturing System as Advanced Information Infrastructure for Integrating Manufacturing Resources and Activities, Annals of CIRP, Vol. 46, No. 1, pp. 399, 1997. 2. Kimura Fumihito Product and Process Modeling as a Kernel for Virtual Manufacturing Environment, Annals of CIRP, Vol. 42, No. 1, pp. 147151, 1993. 3. Bodner, D., Park, J., Reveliotis, A., and McGinnis, F., Integration of structural and perfromanceoriented control in flexible automated manufacturing , Proceedings of 1999 IEEE/ASME International Conference on Advanced Intelligent Mechatronics, USA, , 1999. 4. Onosato, M., and Iwata, K., Development of a Virtual manufacturing System by Integrating Product Models and Factory Models, Annals of the CIRP, Vol. 42, , pp. 475478, 1993. 8 9 摘要 虛擬 制造系統(tǒng)的重要性是在新的制造業(yè)發(fā)展過程中逐漸凸顯出來