1,721,389 research outputs found
Residuals-based fault diagnosis of industrial automation systems using timed and untimed Interpreted Petri nets
No full textThe problem of detecting and isolating a fault using a discrete event model has received a lot of attention over the last two decades. Indeed, industrial automated systems can be usually modelled by a discrete event system. The problem is particularly significant if a fault-free model is used. Recently, residuals, well-known in continuous time systems context, have been proposed to obtain set of candidate faults from real time observations for discrete event system also. They have been obtained using finite state automata. In this paper, inspired by these works, residuals are formulated using Petri net models, both timed and un-timed ones. The computation of residuals for net models requires some efforts to update and predict the state, especially in timed models, but it returns to be highly efficient and scalable thanks to the local state representation and intrinsic distributed nature of the these models. A practical example, consisting of a plant simulated by using a 3D environment interfaced to a Programmable Logic Controller to simulate/emulate the closed-loop behaviour, is used to illustrate the results of the paper
Validation of Industrial Automation Systems Using a Timed Model of System Requirements
No full textValidation of industrial automation systems is the process of checking that commissioner requirements are successfully implemented. Formal approaches are needed when the considered system is critical. The method presented in this article relies on a model-based approach that exploits the compactness and graphical representation of time-interpreted Petri nets, which adds input-output interpretation to transitions/places and embeds time information. These nets are here used with multiple-server semantic to allow effective modeling of typical automation system requirements. The key idea of the system validation approach is to compare the observed behavior of the automation system with the expected behavior, as generated by updating online the model of system requirements using a state estimation algorithm. Also, an off-line procedure is provided to evaluate the evolutions admitted by the model but not observed. Both procedures yield useful data to the validation engineer, allowing to speed up the validation process. Technological issues due to the synchronous nature of controllers and the implications of their programming are considered
An approach based on timed Petri nets and tree encoding to implement search algorithms for a class of scheduling problems
No full textScheduling problems have been approached several times by Petri nets. Indeed, the usage of a Petri net model guarantees the feasibility of the candidate solutions, but it does not provide an accurate evaluation of the time required to complete the considered workshop. For this purpose, a class of timed Petri nets, namely structured nets, is defined and the encoding of the structure and time information of such nets as a tree is presented. This encoding, in combination with the resolution of some linear matrix inequalities, is used to estimate the residual time required to complete each job of the considered workshop. The main advantage of this computation is to provide an estimation of the residual time as an interval that includes necessarily the exact residual duration. Consequently, the lower bound of the interval never overestimates the exact duration and can be used as a part of the cost function involved in many exploration algorithms as the A* or the Beam Search algorithms. In this paper, the proposed estimation function is used with the Hybrid Filtered Beam Search algorithm and performances are discussed for several examples of workshops. The paper also illustrates that the approach can be combined with supervisory control to accelerate the convergence of the exploration since deadlocked solutions can be eliminated directly in the model
A Matlab toolbox implementing MSCG computation
No full textModified State Class Graph collects in a compact form the main information on all the possible evolutions of a given labeled TPN system initialized at a given marking. Recently, it has been used to solve different problems, in particular supervisor control synthesis, state estimation and system validation. It employs a symbolic characterization of the firing time intervals of the enabled transitions. This paper presents a set of MATLAB functions implementing the computation of MSCG in different ways, useful for applications
From supervisory control to PLC code: A way to speed-up Constructive/Virtual Commissioning of Manufacturing Systems
No full textThis paper demonstrates that it is nowadays possible to successfully adopt a virtual/constructive approach in the contest of automated manufacturing systems. The design and the implementation of the control software is usually not considered a crucial step in the development cycle of these systems but it plays a key role to reduce time and costs of the real commissioning. In this paper, recent computer technology progress, some results from discrete event systems research and a proposed software are exploited to show that a virtual/constructive approach can effectively speed-up the design and the implementation of the control software
Assessment of Bisimulation Non-Interference in Discrete Event Systems Modelled with Bounded Petri Nets
No full textNon-interference in discrete event systems deals with the possibility by an intruder to infer the occurrences of private and non observable events, the so called high-level ones, by interacting with the system at a user level, i.e., by observing the occurrence of the so called low-level ones. When bisimulation non-interference is considered, the security objective is not only to avoid the detection of high-level event occurrences, but also to avoid the detection of their non occurrences; i.e., the secret includes also the non occurrences of some events. This letter deals with such a more restrictive security property in the framework of discrete event systems modelled as Petri nets. A necessary and sufficient condition is given to assess bisimulation non-interference in bounded Petri nets. Such a condition requires the solution of integer linear programming optimization problems, whose solution can be used also to statically enforce bisimulation non-interference when this condition is not satisfied by the original system
Assessment of multilevel intransitive non-interference for Discrete Event Systems
No full textPrivacy of distributed cyber-physical systems can be compromised by the presence of information leaks which permit to external intruders to infer the state of the system itself. These systems are built using several off-the-shelf components with communication capabilities that provide a significant level of control, and lower operational costs in comparison to the traditional vendor-specific proprietary and closed-source systems. However, these components expose the control systems to more vulnerabilities and threats. This work focuses on the multi-level intransitive non-interference, a property particularly suitable to tackle privacy problems of control systems under attack. The property is characterized and verified using Petri net models and mathematical programming
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