Aide à la prise de décision en temps réel dans un contexte de production adaptative

La dynamique des marchés a évolué et les entreprises manufacturières ont dû s’adapter pour rester compétitives. Une usine se définissait historiquement par les biens qu’elle produisait. La valeur de ces biens était évaluée avant tout par leurs composants. Mais sous la pression du marché et de son dynamisme accru, les usines souhaitant rester compétitives deviennent de plus en plus des centres de service. Cela provoque des changements et des problèmes de gestion pour lesquels elles n’étaient pas préparées. L’efficacité économique de la création de valeur n’est plus aujourd’hui la seule propriété des produits, mais se déplace vers les processus. Cela signifie que les potentiels qui seront décisifs ne sont pas à chercher dans les capacités des produits, mais dans les capacités des processus. En effet, la mondialisation accroit l’anonymat des produits tout au long de chaînes d’approvisionnement plus longues et plus complexes. Toute entreprise souhaitant se démarquer de la compétition doit proposer à ses clients de la valeur ajoutée additionnelle tels qu’une flexibilité accrue, des délais de livraison plus courts, un meilleur respect des délais, un plus grand choix d’options. Ces propriétés sont le fruit des processus. Leur valeur ajoutée se transfère à leur résultat et donc au client. Une des conditions nécessaires à la transparence des processus est leur capacité à coller en temps réel au flux de valeur de l’entreprise. Les processus doivent être en mesure de s’adapter aux conditions changeantes de l’environnement, de réagir à des événements imprévus et de résoudre ces difficultés en collaborant. C’est à ces conditions qu’ils pourront devenir des processus adaptatifs. Cette thèse s’intéresse aux processus de réordonnancement en milieu industriel. Elle vise l’implantation de composantes d’aide à la prise de décision en temps réel ainsi que des mécanismes de boucle rétroactive intégrant l’optimisation et les techniques de simulation au sein d’applications ERP et MES permettant ainsi de connecter l’atelier de production au reste de l’entreprise. La plateforme qui a été mise en place permet de répondre en temps réel aux divers aléas survenant dans l’atelier et peut être étendue au-delà de la problématique de l’ordonnancement.----------ABSTRACT The market dynamics have evolved and manufacturing facilities have followed this trend to stay competitive. The classic factory has been defined by its manufactured goods. The value of these goods has been measured primarily by their material components. But under the market pressure and its increasing dynamism, factories wishing to stay competitive are becoming modern service centers. It has resulted in management problems for which many companies are not yet prepared. Today, the economic efficiency of value creation is not a property of the products but rather of the process. It means the decisive potentials of companies are to be found not so much in their production capability but in their process capability. Indeed, increasing globalization is necessarily leading towards more anonymous products out of long supply chains. Any enterprise wishing to stand out from the competition in the future needs a strategy which offers the customer an additional added value, such as, for example, high flexibility, short delivery times, high delivery reliability, and wide range of variants. These properties are created by the processes. The requirement for process capability gives rise in turn to the requirement that all value-adding processes be geared to the process result and thus to the customer. A necessary condition of process transparency is the ability to map the company's value stream in real time. Processes must be able to adapt to environmental changing conditions, react to unforeseen events and to solve these difficulties by collaborating. Under these conditions they can be called adaptive processes. This thesis focuses on scheduling process in manufacturing environments. The main objective is to implement real time decision-making support components as well as feedback loop mechanisms integrating optimization and simulation techniques in ERP and MES applications allowing connecting the shop floor to the rest of the enterprise. The proposed platform responds in real time to various events occurring on the shop floor and may be extended beyond the scheduling issue. The works developed during this thesis are based on four published, accepted or submitted papers to specialized papers

DETERMINATION OF END-TO-END DELAYS OF SWITCHED ETHERNET LOCAL AREA NETWORKS

The design of switched local area networks in practice has largely been based on heuristics and experience; in fact, in many situations, no network design is carried out, but only network installation (network cabling and nodes/equipment placements). This has resulted in local area networks that are sluggish, and that fail to satisfy the users that are connected to such networks in terms of speed of uploading and downloading of information, when, a user’s computer is in a communication session with other computers or host machines that are attached to the local area network or with switching devices that connect the local area network to wide area networks. Therefore, the need to provide deterministic guarantees on the delays of packets’ flows when designing switched local area networks has led to the need for analytic and formal basis for designing such networks. This is because, if the maximum packet delay between any two nodes of a network is not known, it is impossible to provide a deterministic guarantee of worst case response time of packets’ flows. This is the problem that this research work set out to solve. A model of a packet switch was developed, with which the maximum delay for a packet to cross any N-ports packet switch can be calculated. The maximum packet delay value provided by this model was compared from the point of view of practical reality to values that were obtained from literature, and was found to be by far a more realistic value. An algorithm with which network design engineers can generate optimum network designs in terms of installed network switches and attached number of hosts while respecting specified maximum end-to-end delay constraints was developed. This work revealed that the widely held notion in the literature as regards origin-destination pairs of hosts enumeration for end-to-end delay computation appears to be wrong in the context of switched local area networks. We have for the first time shown how this enumeration should be done. It has also been empirically shown in this work that the number of hosts that can be attached to any switched local area network is actually bounded by the number of ports in the switches of which the network is composed. Computed numerical values of maximum end-to-end delays using the developed model and algorithm further revealed that the predominant cause of delay (sluggishness) in switched local area networks is the queuing delay, and not the number of users (hosts) that are connected to the networks. The fact that a switched local area network becomes slow as more users are logged on to it is as a result of the flow of bursty traffic (uploading and downloading of high-bit rates and bandwidth consuming applications). We have also implemented this work’s model and algorithms in a developed C programming language-based inter-active switched local area networks’ design application program. Further studies were recommended on the need to develop method(s) for determining the maximum amount of traffic that can arrive to a switch in a burst, on the need for the introduction of weighting function(s) in the end-to-end delay computation models; and on the need to introduce cost variables in determining the optimal Internet access device input and output rates specifications