Synthesis of supervisory controllers based on a novel representation of condition/event systems

Modeling Admissible Behavior Using Event Signals

“…C. Controllable Sequences of Steps From the structure of N and its possible steps, we can now determine the controllable sequences of steps that enable tf at p'. Before presenting the algorithm, however, we need the following assignments which we will apply to elements of N. The idea behind the following algorithm is the same used by Hanisch and Rausch in [3] to synthesize their controller function for forbidden states in a NCES. That is, we use the structure of N and systematically replace boolean expressions to obtain controllable sequences of steps that must fire to enable tf while the controller is at pz.…”

“…The composition of these sybsystems requires the description of an input/output structure, which we only illustrate here in graphical terms. This input/output structure is formally described, using matrices, in [3] and [10]. Two new arcs are defined to interconnect the modules (see figure 1 All forced transitions which are not in conflict occur at the same time instant as the event signal which forces the transition.…”

“…Here the new marking is obtained by removing a token from each input place of each firing transition, and adding a token to each output place of each firing transition. A formal description of the firing rule can be found in [3].…”

“…The main distinction in our method is the connection of the plant and specification models, which is done through the condition and event signals of Net Condition/Event Systems (NCES). Introduced by Hanisch & Rausch [3], NCES are an extension of Petri Nets that greatly facilitate modularity in their modeling framework. The scope of our work is limited to solving the problem of preventing an uncontrollable event at a specific "controller state.'…”

Modeling Techniques for Distributed Control Systems Based on the IEC 61499 Standard ɩĻ Current Approaches and Open Problems

“…In these perspectives the definition of the underlying scheduler as well as the handling of the events and concerning invocation of EC states deserves to be defined unambiguous, unfortunately this is not the case in the current standard. [19], [20] which principally used Net Condition/Event Systems (NCES) [21] and its timed extension (TNCES) for formally modeling the behavior of PLC programs. This formal approach models the basic FBs in terms of 5 different state machines which deal with the event inputs, data inputs, EC operations, ECC and output events [22].…”