Eichstätt, Germany
We present a modular formalism and methodology for modelling and control of discrete event systems, such as flexible manufacturing systems. The formalism is based on Petri net modules which communicates via signals. Two kinds of signals are employed, namely active signals, which force occurrence of (enabled) events (typically switches), and passive signals which enable/prohibit occurring of events (typically sensors). We motivate both kinds of signals, illustrate their using on several examples and discuss their relationships. Modelling with such modules appears to be very natural from engineering perspective, enables hierarchical structuring, and support locality principle. We discuss concepts of equivalence between modules, which support interchanging of modules with the same signal environment (same functionality). Further, we discuss the role of both kinds of signals in control tasks and we focus on the control aspects in general.