A colored Pem Net model of a 'cell controller' capable of real m e control and monitoring of multiple workstations is described. The need to incorporate the ideas of both computer integrated manufacturing (CIM) and flexible manufacturing systems (FMS) is discussed and the controller is based on these concepts. The Colored Petri Net (CPN) for the cell controller is presented and described. The controller in this case controls two workstations : the Cincinnati Milacron 5VC machining center and a robotic assembly workstation using an Adept robot. An analysis of the net is performed and relevant portions are presented. A data structure for implementing this type of a CPN is given. The code for the controller is divided into application dependent and independent code. An execution algorithm is provided. The conclusions emphasize the advantages of CPNs in modelling and analysis for discrete event control of manufacturing systems.Computer integrated manufacturing (ClM) aims at improving productivity by integrating design, marketing, planning and manufacturing processes on the basis of the more recent hardware and software technologies. A simple CIM architecture, as shown in figure 1, may be viewed as a three level hierarchy: plant level, cell level and workstation level. The plant level, the topmost level, controls one or more cells, each of which in turn controls several workstations each of which are comprised of a workstation controller and several machines or devices each.Integration in c o n a~l is achieved by interconnecting the different blocks involved through an efficient information exchange mechanism.* H IFigure 1 : ducripcion of the cell level 12180-3590 &, Pi-2 : c c l l . n d~u r i o n I a y o u tRelated to CIM is the need to provide for changing market and factory conditions through flexible manufacturing systems (FMS). The degree of flexibility of a production system will not only be conditioned by the flexibility of it's elements but will depend fundamentally on the integrated control system. One of the most important goals of an FMS is to schedule resources in such a way as to meet a predefmed schedule that it receives from the manufacturing resources planner (MRP). The MRP is assumed in this work to reside at the plant level of the CIM hierarchy (see figure 1). The scheduling done by the MRP is typically at one week intervals. Therefme the MRP and the plant level scheduler have to decide on a carefully planned schedule keeping in mind the unprecedented disuptions of a factory floor. The second level in the hierarchy, the cell level, is the most interesting because it offers a wide range of problems which include scheduling (loading, routing, dispatching), monitoring, i.e., keeping track of the operations of the workstations, and reporting the cell status back to the plant. The software at this level gets complex because it has to include algorithmic aspects, real time control, database management and perhaps discrete event simulation.The workstation level has the code that directly controls the machin...
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