XPN-FMS - A CAD TOOL FOR FMS MODELING, ANALYSIS, ANIMATION, AND SIMULATION USING PETRI NETS AND X-WINDOW

We propose a CAD tool, XPN-FMS, which is primarily based on a unique P etri net (PN) synthesis method, called the knitting technique, develop ed by the authors. Petri net theory has been applied to specification, validation, performance analysis, control code generation, and simula tion for manufacturing systems. The analysis of flexible manufacturing systems (FMSs) based on PNs suffers from the complexity problem of re achability analysis (Peterson, 1981). CAD tools are urgently needed. T here is no existing CAD tool for FMSs as comprehensive as XPN-FMS, in the sense that the latter integrates the functions of drawing, analysi s, reduction (Chao and Wang, 1992; Murata and Koh, 1980), synthesis, p roperty queries, and animation of FMS operations in one software packa ge. Using the X window graphical interface and animation, XPN-FMS make s the modeling and analysis of an FMS visualizable and easy to underst and and manipulate. It lets a user draw the factory layout of an FMS o n the screen of a monitor using the supplied tools. A corresponding PN model can also be drawn on the monitor screen. XPN-FMS can animate an d simulate the overall operating process of the FMS. It is useful for FMS specification, validation, and exploration of different design alt ernatives, status monitoring, and control. Using XPN-FMS with various inputs and comparing the resulting outputs, the user can determine how to improve efficiency, reduce cost, and pinpoint bottlenecks. For the PN models of FMSs that are decision free, we extend the theory and al gorithm of a unique matrix-based method (Chao and Wang, 1993b) to sear ch for subcritical loops (including types A and B) and to support sche duling and dealing with transition periods. XPN-FMS implements this ex tended method to find the minimum cycle time, critical loop, subcritic al loops, next critical loop, and scheduling ranges to avoid the trans ient period for static scheduling. This is implemented in XPN-FMS for the input sequence control.