Building meaningful timed models of closed-loop DES for verification purposes

Abstract

Formal verification methods require that a model of the system to analyze, in the form of a network of automata for instance, be built previously. Every evolution of this formal model must represent a real evolution of the modeled system; if the model contains indeed spurious evolutions, meaningless states, which do not correspond to physically possible states, can be reached and the verification results are surely not trustworthy. This paper focuses on construction of the formal model of a closed-loop system which can be represented as a Discrete Event System (DES) and where all evolutions and states are meaningful wrt to the real system behavior. A closed-loop system is composed of a physical system to control, named plant, and a controller. A modular approach to build the plant model is presented in the first part of the paper; to prevent from meaningless evolutions and states in this model, a solution based on the concept of urgent edges is proposed and exemplified. Then, construction of the formal model of the closed-loop system is addressed; it is shown that restriction of the evolutions of this model to the only meaningful ones can be easily achieved by introducing variables that represent the modification of the inputs of the logic controller and the stability condition of the control specification.

Coupling timed plant and controller models with urgent transitions without introducing deadlocks

“…As the TADD formalism is not tool-supported, the models presented in this paper have been translated into the formalism of the UPPAAL suite, according to the translation rules presented in [14]. Formal verification of these models by the model-checker of this suite has per- …”

Comparing detailed and abstract timed models of automated discrete manufacturing systems

“…The structure of this network is depicted at Figure 9 and examples of actuator model and sensors model are given on Figure 10. As the aim of this paper is not to discuss the construction of these models, no further explanation will be given on this topic; the interested reader is referred to [5] for an accurate presentation.…”

“…This formalism is an extension of the timed automata formalism presented in [7] and is particularly suitable to model urgency and discrete variables evolutions in time. As detailed in [4] and [5] indeed, building meaningful timed models of plants or closed-loop systems requires to select a formalism that is able to model urgency.…”

“…Several works have addressed previously the construction of detailed models of the controller ( [1], [2]), plant elements ( [3], [4]) or the complete closed-loop ( [5]) with different classes of DES -Discrete Event Systems-formalisms. However, few results on the comparison of detailed and abstract models have been published, to the best of our knowledge.…”

Modelling and Formal Verification of Timing Aspects in Large PLC Programs

“…Indeed, Mader and Wupper (1999) or Perin and Faure (2013) proposes an approach for modelling PLC timers using timed automaton models, but does not present verification results. As time is considered as a linear and monotonic function, the generated models would have a huge state space, making verification impossible if this approach would be applied to large systems, as the systems developed at CERN.…”