In this Master thesis a new framework for achieving fault tolerance in mechatronic systems is studied. The framework is called service-based fault tolerant control and has the advantage of being completely decentralized and modular and therefore scales very well to large system sizes. First, a method is presented for designing the signal-flow architecture of mechatronic systems of real-life size and complexity. The result is a small set of generic building blocks in the form of design patterns, a concept that has gained widespread popularity in the field of software architecture. Best practises are then established for how each of the design patterns can be extended to support fault tolerance through diagnosis and reconfiguration according to the service-based framework. These extended design patterns can be used either to aid in the construction of new and more complex mechatronic systems or as a methodology for applying service-based fault tolerant control on large existing systems. The presented methods for designing and modelling large-scale mechatronic systems have the advantages of being applicable to a large class of mechatronic systems, being easy to apply without expert knowledge, as well as having the potential for being automated in the future. Finally, a case-study demonstrates how the new methods can be used to construct a fault tolerance architecture for a real-life automotive system currently used by Scania CV AB. As a part of this study a mathematical model for the system was also constructed and implemented. The model can be used for analysis during the development phase as well as troubleshooting in a repair workshop.

ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, California / Recent emphasis has been placed on mobile robotics performing in unstructured environments. This realm of operations requires many different algorithms to interpret the various situations. This not only requires a system that is able to support, and facilitate, the fusion of the results, but it also needs to be tolerant of system errors. In modern operating systems, separate processes are able to fail without affecting other processes. Using this ability, along with fault tolerant inter-process communications, and supervisory process managers, allows the total system to continue to operate under adverse conditions. While this paper focuses primarily on the challenges faced by mobile robotics, the approach can be extended to a wide range of systems which must autonomously identify and adapt to failures/situations.

published_or_final_version / Computer Science / Master / Master of Philosophy

published_or_final_version / abstract / Computer Science / Doctoral / Doctor of Philosophy

Graduate

As human dependence on computing technology increases, so does the need for computer system dependability. This dissertation introduces Consul, a communication substrate designed to help improve system dependability by providing a platform for building fault-tolerant, distributed systems based on the replicated state machine approach. The key issues in this approach--ensuring replica consistency and reintegrating recovering replicas--are addressed in Consul by providing abstractions called fault-tolerant services. These include a broadcast service to deliver messages to a collection of processes reliably and in some consistent order, a membership service to maintain a consistent system-wide view of which processes are functioning and which have failed, and a recovery service to recover a failed process. Fault-tolerant services are implemented in Consul by a unified collection of protocols that provide support for managing communication, redundancy, failures, and recovery in a distributed system. At the heart of Consul is Psync, a protocol that provides for multicast communication based on a context graph that explicitly records the partial (or causal) order of messages. This graph also serves as the basis for novel algorithms used in the ordering, membership, and recovery protocols. The ordering protocol combines the semantics of the operations encoded in messages with the partial order provided by Psync to increase the concurrency of the application. Similarly, the membership protocol exploits the partial ordering to allow different processes to conclude that a failure has occurred at different times relative to the sequence of messages received, thereby reducing the amount of synchronization required. The recovery protocol combines checkpointing with the replay of messages stored in the context graph to recover the state of a failed process. Moreover, this collection of protocols is implemented in a highly-configurable manner, thus allowing a system builder to easily tailor an instance of Consul from this collection of building-block protocols. Consul is built in the x-Kernel and executes standalone on a collection of Sun 3 work-stations. Initial testing and performance studies have been done using two applications: a replicated directory and a distributed wordgame. These studies show that the semantic based order is more efficient than a total order in many situations, and that the overhead imposed by the checkpointing, membership, and recovery protocols is insignificant.

Virtualization is often used as a tool for resource consolidation in the server market. Virtualization is also used to simplify management tasks and provide high availability. However, the ultimate high availability feature, fault-tolerance, has been limited to special and costly hardware and software. This thesis will give an overview of how one can use virtualization tech- nologies to build a fault tolerant system, and show what would be the cost, in the sense of performance degradation when compared to a non-fault-tolerant system. 1

Les convertisseurs statique à structure tension sont des éléments essentiels de nombreux systèmes d'électronique de puissance tels que les variateurs de vitesse des machines alternatives, les alimentations sans interruption et les filtres actifs. Les défaillances d’un convertisseur, qu’elles proviennent d’un des composants de puissance commandables ou d’un des capteurs mis en œuvre, conduisent à la perte du contrôle des courants de phase. Ces défaillances peuvent provoquer de graves dysfonctionnements du système, voire conduire à sa mise hors tension. Par conséquent, afin d'empêcher la propagation de défauts aux autres composants et assurer la continuité de service en présence de défaut, des méthodes efficaces et rapides de détection et de compensation de défauts doivent être mises en œuvre. Dans ces travaux de thèse nous avons étudié un convertisseur triphasé à structure tension "fault tolerant". Ce convertisseur assure la continuité de service, en mode normal, en présence de défauts éventuels d’un semi-conducteur ou d’un capteur de courant. Dans ces travaux, nous avons choisi comme cas d’application le filtre actif parallèle (FAP) triphasé afin de valider la continuité de service du convertisseur "fault tolerant" lors de défauts. Les résultats expérimentaux montrent les performances et l’efficacité du convertisseur "fault tolerant" proposé. Pour réduire autant que possible le temps de détection du défaut, nous avons ciblé un composant numérique de type FPGA (Field Programmable Gate Array). Nous avons également proposé dans ce mémoire un nouveau flot de conception et de prototypage dit "FPGA in the loop" qui permet de réduire le temps de développement. / Voltage source converters (VSC) are essential components of many power electronics systems such as variable speed AC machines, uninterrupted power supplies and active power filters. A sudden failure in one of the used power switches or the current sensors decreases system performances and leads to disconnect the system. Moreover, if the fault is not quickly detected and compensated, it can lead to hard failure. Hence, to reduce the failure rate and to prevent unscheduled shutdown, effective and fast fault detection and compensation schemes must be implemented. In this thesis work we have studied a fault tolerant VSC. This converter provides the continuity of service in the presence of a semiconductor or a current sensor fault. In this work, we have chosen the shunt active power filter application to validate the studied fault tolerant VSC performances. The experimental results confirms the satisfactory performances and efficiency of the proposed fault tolerant VSC. To minimize the fault detection time, we targeted a FPGA (Field Programmable Gate Array) component. We also proposed in this thesis a new methodology to design and prototype so-called “FPGA in the Loop” that will reduce development time of the digital controllers.

The need to achieve dependability in critical infrastructures has become indispensable for government and commercial enterprises. This need has become more necessary with the proliferation of malicious attacks on critical systems, such as healthcare, aerospace and airline applications. Additionally, due to the widespread use of web services in critical systems, the need to ensure their reliability is paramount. We believe that patterns can be used to achieve dependability. We conducted a survey of fault tolerance, reliability and web service products and patterns to better understand them. One objective of our survey is to evaluate the state of these patterns, and to investigate which standards are being used in products and their tool support. Our survey found that these patterns are insufficient, and many web services products do not use them. In light of this, we wrote some fault tolerance and web services reliability patterns and present an analysis of them. / by Ingrid A. Buckley. / Thesis (M.S.C.S.)--Florida Atlantic University, 2008. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2008. Mode of access: World Wide Web.

Reliability is a key system characteristic that is an increasing concern for current systems. Greater reliability is necessary due to the new ways in which services are delivered to the public. Services are used by many industries, including health care, government, telecommunications, tools, and products. We have defined an approach to incorporate reliability along the stages of system development. We first did a survey of existing dependability patterns to evaluate their possible use in this methodology. We have defined a systematic methodology that helps the designer apply reliability in all steps of the development life cycle in the form of patterns. A systematic failure enumeration process to define corresponding countermeasures was proposed as a guideline to define where reliability is needed. We introduced the idea of failure patterns which show how failures manifest and propagate in a system. We also looked at how to combine reliability and security. Finally, we defined an approach to certify the level of reliability of an implemented web service. All these steps lead towards a complete methodology. / by Ingrid A. Buckley. / Thesis (Ph.D.)--Florida Atlantic University, 2012. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2012. Mode of access: World Wide Web.