http://www.ifac-papersonline.net/ en Copyright 02:59 AM Saturday 18, 2013 IFAC-PapersOnline http://www.ifacpapersonline.com 02:59 AM Saturday 18, 2013 02:59 AM Saturday 18, 2013 ET webmaster@ifac-papersonline.net webmaster@ifac-papersonline.net http://www.ifac-papersonline.net/Detailed/42237.html 04:00 PM Wednesday 31, 1969 http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42238.html 04:00 PM Wednesday 31, 1969 For the formal analysis of dependability of Networked Automation Systems (NAS) it is necessary to model the whole system first. Due to the probabilistic and distributed nature of the problem, a modular automata based approach is preferable for modeling and analysis. In this paper a formal automata definition for the specific needs of modeling NAS is given including continuous density distributions. For this model a discretization procedure as well as a transformation of the resulting discrete model into the input language of the probabilistic model checking software PRISM is presented. Finally an example is given, to illustrate the approach. The results of the automata based analysis are compared to measurements. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42239.html 04:00 PM Wednesday 31, 1969 The paper presents an approximate analytical method, based on decomposition techniques, that assesses the physical performance of small flow lines with both dedicated and shared buffer. The aim of the analytical method is to capture the interdependent behaviour of the machines in the line due to the shared buffers. The method deals with discrete and deterministic processing time, limited buffer capacity, and both time to repair (TTR) and time between failure (TBF) follow a geometric distribution. The accuracy of the analytical solutions is assessed with respect to results provided by simulation. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42240.html 04:00 PM Wednesday 31, 1969 Hidden Markov Random Fields (HMRF) are widely used in solving various problems. Image segmentation is an example of such HMRF success. This paper presents a post-processing tool based on such a model and designed to increase the relevancy of a diagnosis system for rail defects detection. In this application, the hidden Markov field is not only used to define a spatial smoothness prior as it is often done in image segmentation, but it is used to learn the spatial interaction between track singular points, and so the track label patterns. For this, an approach based on a semi-parametric model is presented. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42241.html 04:00 PM Wednesday 31, 1969 Most reliability models are associated with their own parameters which are typically estimated from the history data. For the widely used distributed detection system in fault detection, the system reliability depends on the number of normally working detectors and the accuracy of its local detectors. Parameters of the reliability model of distributed detection system are subject to random variation as the detection system may be used in different purposes and environments. Hence, to evaluate the reliability accurately, it is necessary to obtain the system parameters precisely from the test data we have. In this paper, we present a Bayesian approach to estimate the unknown parameters of distributed detection system from the scarce data and quantify the uncertainty on the system reliability by measure of variance. A simulation is conducted as well to calculate the effect on the system reliability from the uncertainty of the parameters. An example is applied to illustrate the parameter estimation by Bayesian approach. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42242.html 04:00 PM Wednesday 31, 1969 Pandora is a recently proposed technique that extends classical Fault Tree Analysis to incorporate the effects of the temporal ordering of failure events. In this paper, we extend the conceptual foundation of Pandora with a new Priority-OR (POR) gate and we introduce the concept of a Temporal Truth Table as a mechanism that can be used to prove equivalence of expressions in Pandora logic. We also show how logical reduction can be performed using a set of temporal laws in the new logic and how such analysis can enrich the results of an extended FTA performed on a generic example that exhibits both PAND and POR failure characteristics. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42243.html 04:00 PM Wednesday 31, 1969 This paper presents a formal framework allowing to extend the simplification of static fault trees to fault trees built with gates PRIORITY AND. The laws which make these simplifications possible have been demonstrated thanks to a homogeneous algebraic definition of each gate studied. These definitions use a mathematical model of events able to take into account their order of appearance. The processing of an example points out the possibilities offered by this algebraic framework dedicated to non-repairable faults. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42244.html 04:00 PM Wednesday 31, 1969 In electrical power systems, the coordination of protections in time domain is important and difficult problem. The time settings of protection relays have to be adapted to the time characteristics of electrical power system plants and the delay times of the other protections. In the paper, Fault Trees with Time Dependencies (FTTDs) are used in selection of values of the delay times of primary (local) and remote backup protections. In the FTTD, events and gates are characterized by time parameters. These time parameters are derived from the time characteristics of protection devices and the inherent delay times of protection equipment. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42245.html 04:00 PM Wednesday 31, 1969 Since the ESACS and ISAAC projects, Airbus and Onera have been investigating failure propagation models and more specifically AltaRica model-based safety analysis. This paper presents results and lessons learnt from an industrial system architecture modeling experiment: rudder control system of the Airbus A340-500/600 aircraft. After introducing failure propagation model construction and analysis, the paper focuses on modeling the reconfigurations, the command/monitoring architecture and finally the latent failures. The main advantage of this approach is the improved readability of safety analysis results that facilitates a quick understanding of the system behaviour. This improves the communication between the safety and design communities. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42246.html 04:00 PM Wednesday 31, 1969 A state-based approach for detection of changes in systems modelled as Timed Event Graph and Time Stream Event Graph is presented. We assume that the net in its nominal behavior is known and transitions are partitioned as observable and unobservable transitions. Considered faults are (possibly small) variations of dynamical models by respect to this nominal behavior. Using the algebra of dioids, the approach follows the same principle as the observers used in continuous systems. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42247.html 04:00 PM Wednesday 31, 1969 This paper considers the discovery and detection of repeating patterns in event sequence data, where the event patterns may be of variable duration, may be intermingled, and may be of variable length. These properties are characteristic of many types of monitoring and diagnostic alarm sequence data, and may be used in detecting both normal and abnormal behaviours of complex dynamic systems. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42248.html 04:00 PM Wednesday 31, 1969 In this paper, a method is proposed that generically determines fault models on the basis of the fault free I/O-behavior of sensor-actuator relations. It is shown how the I/O-behavior of standard components can be represented by patterns. These patterns are extended to fault models on the basis of a set of rules. It is possible to detect and locate state faults and time faults with the extended patterns. The patterns are used as observers for the online-diagnosis of a factory automation system. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42249.html 04:00 PM Wednesday 31, 1969 This paper proposes an unconditional decentralized structure to realize the fault diagnosis of Discrete Event Systems (DES), specially manufacturing systems with discrete sensors and actuators. This structure is composed on the use of a set of local diagnosers, each one of them is responsible of a specific part of the plant. These local diagnosers are based on a modular modelling of the plant in order to reduce the state explosion. Each local diagnoser uses event-based, state based and timed models to take a decision about fault's occurrences. These models are obtained using the information provided by the plant, the controller and the actuators reactivity. All local diagnosis decisions are then merged by a Boolean operator in order to obtain one global diagnosis decision. Finally, the diagnosers are polynomial-time in the cardinality of the state space of the system. This approach is illustrated using an example of manufacturing system. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42250.html 04:00 PM Wednesday 31, 1969 This paper deals with an approach for the localization of intermittent faults in discrete events systems with partial observability. The proposed methods are based on a discrete events model representing the normal functioning of the observable behavior of the monitored system. This model based on automata formalism is built from the design data. The detection step consists of a comparison between the flow of observable events emitted by the monitored system and the flow foreseen by the model. A localization mechanism, based on diagnoser approach, points out the set of events potentially responsible for the faults. These two mechanisms are designed in order to operate on-board, in real time. An example from the automotive domain is presented. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42251.html 04:00 PM Wednesday 31, 1969 In this work, the problem of observability in switched linear systems (SLS) where the continuous part is represented by a family of linear systems (LS) and the discrete part is represented by an interpreted Petri net (IPN), is addressed. Here, the final state of the evolving linear system is mapped to the initial state of the next linear system selected during the switching using state commutation functions. These functions enlarge the class of SLS that can be analyzed. In addition, the observability characterization for SLS exhibiting the observability property is presented. Finally, an asymptotic observer design for SLS is presented. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42252.html 04:00 PM Wednesday 31, 1969 State-based fault diagnosis of discrete event systems is considered. The concept of resonating state cycles is introduced, which is used to develop a necessary and sufficient condition for diagnosability. An algorithm to test diagnosability is presented, and is shown to have polynomial complexity. Extensions of the algorithm to include a priori state estimates are discussed. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42253.html 04:00 PM Wednesday 31, 1969 The paper deals with distributed fault diagnosis of partially observed discrete event systems (DES) modelled by Interpreted Petri Nets. The diagnosability property is studied for the set of resulting sub-models of the distributed Interpreted Petri Net. An architecture for reliable distributed on-line diagnosis is presented; it includes a set of redundant diagnosers that handle the corresponding reduced sub-model and other submodels corresponding to the neighbour diagnosers. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42254.html 04:00 PM Wednesday 31, 1969 Most model-based approaches to fault diagnosis require a complete model of the system. When the model is incomplete, system outputs may be inconsistent with the model, stopping the diagnosis process. In this paper, a probabilistic approach combined with model learning is used to diagnose a system with an incomplete discrete event system model. When an inconsistency arises, probabilistic abductive inference is used to learn improved models of the system. To improve the efficiency of model learning, a tabu search scheme is developed. The improved models are combined with the system outputs for probabilistic diagnosis. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42255.html 04:00 PM Wednesday 31, 1969 In this article we propose an online fault detection and avoidance framework for distributed multi-agent systems. The main premise of our work follows the recent notions in autonomic and recovery oriented computing - not all faults can be determined and removed at the time of system design and testing. Thus some level of intelligence must be embedded into each agent's controller to ensure higher degree of system dependability. We assume that faults will eventually translate into a time-out condition in one or more agents. The proposed paradigm is illustrated for the case of unknown deadlock conditions in manufacturing applications. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42256.html 04:00 PM Wednesday 31, 1969 Operation mode handling is one of the important tasks in automation systems. Guidelines for the definition and handling of operation modes are currently provided by academicians and related organizations focusing on centralized systems. In distributed automation systems, such guidelines are seldom dealt with. Therefore, operation mode guidance compatible with the distributed application idea is proposed in this paper. Some modes such as automatic (including setup/starting-up, normal production, hold, stop, tolerance error handling and abort), semi-automatic, manual, emergency stop and idle are considered for managing the operation. The modeling using UML state machine is presented to describe the behavior of modes and their internal states. An implementation based on a task scheduling approach is presented as an example for the application of the developed strategies. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42257.html 04:00 PM Wednesday 31, 1969 This paper proposes a method for discrete controller reconfiguration of hybrid systems with uncertain linear dynamics to account for abrupt events such as the occurrence of actuator faults or changes in the product specifications. Starting from a hybrid plant model and a controller modeled as a finite state automaton, a new controller is obtained considering an updated specification or changes in the plant structure by switching among logic controllers determined offine. The automatic computation of the controllers is carried out using a controller synthesis approach, which employs the concept of model abstraction and refinement. The method is applied to a multi-tank example. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42258.html 04:00 PM Wednesday 31, 1969 This paper presents complexity metrics that can be used to compare different logic controller designs in the format of sequential function charts for the same automation task and to assess the quality characteristics of the designs like usability and maintainability. The proposed method helps to improve the quality of logic controller designs, and thereby can reduce life-cycle cost. The method is illustrated by a application example. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42259.html 04:00 PM Wednesday 31, 1969 In the context of the development of systems subjected to strong dependability and safety properties, standards such as the IEC 61508 recommend the use of formal verification tools. In this way, conceptual and practical approaches related to computer sciences and automatic control, such as model checking, theorem proving, control synthesis, have been widely explored. However, in spite of the consensus that early phases of a system definition are the most important in ensuring that the target system will satisfy the user's requirements, most of these models and tools address the design and implementation phases where the identification and formalisation of system properties remain tricky. This machinery-dedicated paper combines system specification models supported by SysML to identify the system properties and architecture with model checker. This method is based on the refinement of system global requirements and their projection on the system components to formalise local properties to be proved by the model checker. A mechanical press case study illustrates this approach. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42260.html 04:00 PM Wednesday 31, 1969 To check the quality of critical functions, recent studies have focused on the formal verification of systems properties, but such verifications are generally completed with actual testing of the system. Model-based testing approaches available may lead to combinatory explosion, which is reduced using only functional aspects. This paper describes prospects for the validation of Discrete (logical) Safety Systems to combine the advantages of test and verification. A prototype has been realized, which generates automatically test sequences, based on a minimal set of hypotheses about its structure. These hypotheses are automatically checked on the system implementation with limited formal verification techniques. The goal of the tests is to prove that a safety logic specification has been correctly implemented in a control system of a nuclear power plant. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42261.html 04:00 PM Wednesday 31, 1969 A formal development process for logic controllers using Signal Interpreted Petri Nets and FPGA technology is presented. The development process covers all steps from design to implementation and is supported by the SIPN-Editor toolbox, a graphical editor that allows design, analysis and implementation of SIPN algorithms. As a new feature to increase dependability of logic controllers the SIPN-Editor toolbox supports export to VHDL language which allows implementation of SIPN algorithms on FPGA hardware. The implementation on FPGA is not only much faster than on an ordinary PLC hardware but also more dependable in several aspects. An algorithm to calculate a guaranteed response time is also given. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif