Modular logic controllers for machining systems: Formal representation andperformance analysis using Petri nets

The machining systems considered in this paper are high volume transfer lin es which are widely used in automotive manufacturing. In these machining sy stems, several machines linked together provide complete processing of a pa rt. A logic controller is a discrete event supervisory system which control s parallel and synchronized sequences of elementary operations of each mach ine to achieve the goal of the machining system, Normal operation is govern ed by the auto-cycle function of a logic controller. A modular logic contro ller is introduced and formalized for high volume transfer lines. Its event -based functional properties are verified and its reconfigurability is cons idered. A live and safe marked graph can be directly transformed into Seque ntial Function Chart (which is one of the IEC 1131-3 languages) and, using this SFC representation, a modular logic controller can be implemented. The performance analysis of the modular logic controller is also introduced, T he cycle time during normal operation is used as the performance metric of a transfer line. By adding time specifications to the model, a tinted modul ar logic controller is generated. The time-based cyclic behavior of high vo lume transfer lines is thus characterized using timed Petri nets. Two effic ient algorithms to compute the cycle time and critical operations are devel oped.