Modelling and PLC-based Implementation of Modular Supervisory Control
Paper i proceeding, 2002
Implementation of supervisory control in Programmable Logic Controllers (PLCs) typically requires that the underlying discrete event models of plant, specification as well as the supervisor itself fulfil a number of properties. These properties are discussed and methods for solving related problems are given. In particular, determinism and synchronisation issues are investigated.
In a manufacturing system, for instance, there are typically a set of processes using a set of shared resources. Uncareful modelling may cause the system model to become nondeterministic. This can be circumvented by relabelling the relevant models. For industrial-sized models, though, this must be done automatically, something that we achieve by parameterising the models.
Given a deterministic model, consisting of several interacting entities, we discuss its PLC-based implementation. In addition to the synchronisation of plant and supervisor, a modular supervisor must be internally synchronised. However, synchronisation of the submodules is not well defined in the PLC-world. This may be achieved by using event monitors and an immediate transit/immediate action execution model.