A PETRI-NET APPROACH FOR MODELING CONTROLS OF A COMPUTER-INTEGRATED ASSEMBLY CELL

A computer-integrated assembly cell (CIAC) plays an important role in modern manufacturing systems. To maximize cell utilization, multiple a ssembly jobs are often scheduled concurrently without consideration fo r the complex interaction between workstations. Sharing of assembly wo rkstations among a set of concurrently flowing processes may cause dea dlocks and conflicts, which are difficult to detect during programming of the cell's controller. This paper presents an overview of the cont rol models developed for deadlock and conflict detection, and performa nce evaluation of manufacturing plans processed in a CIAC. Petri net f ormalism is used as the modelling tool for its ability to model concur rent and asynchronous activities, and for its well developed mathemati cal foundation for analysis and performance evaluation. The control mo del presented in this paper consists of modules for Petri net generati on, deadlock detection, and performance evaluation. The control model may be applied to debugging controller programs prior to beginning a p roduction run.