Mohamed Ghazel

State Observer for DES Under Partial Observation with Time Petri Nets

This paper deals with a state observation approach for Discrete Event Systems with a known behavior. The system behavior is modeled using a Time Petri Net model. The proposed approach exploits temporal constraints to assess the system state and therefore detect and determine faults given partial observability of events. The goal here is to track the system state and to identify the event scenarios which occur on the system. Our approach uses the class graph of the Time Petri Net which models the complete system behavior to develop a state observer which is a base to perform online fault detection and diagnosing.

Validation of a New Functional Design of Automatic Protection Systems at Level Crossings with Model-Checking Techniques

Level crossings (LCs) are considered to be a safety black spot for railway transportation since LC accidents/incidents dominate the railway accident landscape in Europe, thus considerably damaging the reputation of railway transportation. LC accidents cause more than 300 fatalities every year throughout Europe, which represents up to 50% of all deaths for railways. That is why LC safety is a major concern for railway stakeholders in particular and transportation authorities in general. LCs with an important traffic moment1 are generally equipped with automatic protection systems (APSs). Here, we focus on two main risky situations, which have caused several accidents at LCs. The first is the short opening duration between successive closure cycles relative to trains passing in opposite directions. The second is the long LC closure duration relative to slow trains. In this paper, we suggest a new APS architecture that prevents these kinds of scenarios and therefore increases the global safety of LCs. To validate the new architecture, a method based on well-formalized means has been developed, allowing us to obtain sound and trustworthy results. Our method uses a formal notation, i.e., timed automata (TA), for the specification phase and the model-checking formal technique for the verification process. All the steps are progressively discussed and illustrated.

A MONITORING APPROACH FOR DISCRETE EVENT SYSTEMS BASED ON A TIME PETRI NET MODEL

Abstract We develop in this paper a monitoring approach for Discrete Event Systems (DES) starting from a time Petri net model representing the a priori known behavior of such a system. The originality of our approach lies in the combination made of the concept of event observability with the exploitation of the temporal constraints on these events in order to refine the result of the monitoring process.

A semi-formal approach to build the functional graph of an automated production system for supervision purposes

Abstract This paper presents a functional analysis approach, called an analytical approach, used to model automated production systems (APSs). In addition, Unified Modelling Language models taking into account the various business concepts (i.e. the concepts used in our interest field) involved in this approach are proposed. The final goal of this study is the automation of an analytical approach to enable an expert to obtain the functional graph of an existing APS. This graph has proved useful in developing fault detection and isolation, and fault-tolerant control techniques for flexible manufacturing systems (FMSs) and complex plants such as nuclear power plants or chemical plants. However, industrial applications have revealed difficulties in manually constructing functional graphs for complex systems, thus justifying automation for this modelling process. The originality of our approach lies in the fact that it is generic, i.e. it is not specific to a particular set of APSs. This property results both from the use of generic concepts such as the notion of function that is independent of the application context and from the adoption of an object-oriented approach for our analysis process. This study allows us to develop an efficient software tool. It also allows enrichment of an existing reference frame which regroups different models of an FMS from various points of view.

Monitoring of Temporal Requirements with Stocharts Observation Patterns, Application to a Level Crossing Control System

Works in the field of verification systems have shown the critical importance of time. The non-satisfaction of time may have important consequences for both security and performance points of view. For automated systems with level of security, the verification of time requirements is an essential part of the process validation system. In this paper, we are laying the foundations for a new and systematic approach for the verification of discrete event systems with time constraints. The contribution of this approach is threefold: first, unlike existing approaches, it allows for the verification of several requirements at once. Therefore, the approach is generic because we focus on developing mechanisms that take into account different types of requirements rather than the system to be verified. Finally, the implementation of the approach is almost as systematic because the verification tools we are developing are based on the instantiation of patterns. These patterns are designed on the basis of a classification of temporal requirements that we have established. The concepts of parallelism and hierarchy which characterize the Stocharts formalism compared to other state-transitions models help us build the foundations of our approach. An example of application to the control-command in the railway field is presented to illustrate the key concepts of our approach and its implementation.