Armand Toguyeni

A Switched System Approach to Exponential Stabilization Through Communication Network

This paper considers a networked control loop, where the plant is a “slave” part, and the remote controller and observer constitute the “master”. Since the performance of networked control systems (NCS) depends on the quality of service (QoS) available from the network, it is worth to design a controller that takes into account qualitative information on the QoS in realtime. The goal of the design is to provide a controller that guarantees the following two things: 1) high performances (here expressed by exponential decay rates) when the QoS remains globally the same and 2) global stability when the QoS changes. In order to guarantee the global stability, the controller will switch by respecting a dwell time constraint. The dwell time parameters are obtained by using the switched system theories and the obtained conditions are linear matrix inequalities. An experiment illustrates how the controller can be implemented for a control over Internet application (remote control of a small robot).

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.

A framework to design a distributed diagnosis in FMS

When a failure occurs in a flexible manufacturing system (FMS), it is crucial to react quickly in order to maintain the productivity of the system. This requirement leads us to introduce the concept of on-line monitoring. The basic idea is the automation of the procedures of detection, diagnosis and error recovery. In this paper, reasoning mechanisms are proposed for the implementation of an on-line diagnostic system. These mechanisms are based on a distributed processing of symptoms that enables the problem of real-time constraint to be solved. They implement two kinds of reasoning: temporal and an hypothetical.

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.

Comparison of multipath algorithms for load balancing in a MPLS network

Traffic Engineering aims to optimize the operational performance of a network. This paper focuses on multipath routing for traffic engineering that routes the demand on multiple paths simultaneously for balancing the load in the network. According to the schematic approach of multipath routing that we propose in this paper, a multipath routing algorithm selects candidate paths using multicriteria simultaneously and then distributes the traffic demand among selected paths. Among multipath routing algorithms, we select four algorithms which fit our expectations in terms of architecture: WDP, MATE, multipath-AIMD and LDM. We focused exclusively on technologies designed for MPLS networks. Each algorithm is compared with respect to complexity and stability of two stages: the computation of multiple paths and the traffic splitting among multiple paths.

Indirect predictive monitoring in flexible manufacturing systems

Abstract In this paper, a new method of monitoring of failures in flexible manufacturing systems (FMS) is developed. The main objective is to manage progressive failures in order to avoid breakdown state for FMS. To achieve these requirements an indirect predictive monitoring approach is proposed. The main ideas of this approach are first to follow the state evolution of the resources indirectly by the perturbations on the manufactured products. The parameter used is the production flow for which a drift rate indicator is defined for each of the family. Detection and diagnostic methods based on the on-line exploitation of the drift rates are presented in this paper. Another idea developed is the necessity to integrate different approaches of monitoring to obtain a global management of failures. For this purpose a functional framework of integrated monitoring in the control command of an FMS is proposed.

Toward an Implementation of Recovery Procedures for FMS Supervision

Abstract This paper first specifies Recovery and gives some trends about Recovery strategies. Then, it focuses on Reconfiguration. Several reactivity levels are defined according to the failure impact, flexibilities reserved during the exploitation phase, and flexibilities corresponding to the whole potentialities of the architecture. These enable to know if the FMS can react with its current configuration, or if its configuration has to be changed to go on with the production, or if the production has to be changed to maintain FMS availability. The Recovery procedures are implemented through a model named Operational Accessibility Graph, that has been emphasized by the definition of new attributes and methods. Some algorithms, based on the graph theory, are presented.

Performance Analysis of IEEE 802.11b Wireless Networks with Object Oriented Petri Nets

Communication protocols are often investigated using simulation. This paper presents a performance study of the distributed coordination function of 802.11 networks. Firstly, our study illustrates the different classes of Petri Nets used for modeling network protocols and their robustness in modeling based on formal methods. Next we propose a detailed 802.11b model based on Object-oriented Petri Nets that precises backoff procedure and time synchronization. Then, performance analyses are evaluated by simulation for a dense wireless network and compared with other measurements approaches. Our main goal is to propose a modular model that will enable to evaluate the impact of network performances on the performances of distributed discrete event systems.

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 functional graph approach for alarm filtering and fault recovery for automated production systems

Alarm processing is one of the functions of the monitoring and the supervision of automated productions systems. However, these systems become more and more complex. Actually, this induces that standard alarm processors do not manage efficiently all the alarms that occur. This paper deals with intelligent alarm processing system (IAPS). The goal of this type of system is to reduce the number of alarms that are presented to the operators and to assist them to select corrective actions in case of fault occurrence. In this paper, we propose a prototype developed under PROLOG. Different concepts such as validation, causal inhibition or synthesis alarms characterize this prototype features. The filtering process is independent of the nature of the process (continuous or discrete) and of the way the raw alarms are produced.