A comparative study between centralization and decentralization of diagnostic reasoning in EPS

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa de Lisboa para obtenção do grau de mestre em Engenharia Electrotécnica e de ComputadoresThis thesis addresses the problem of performing diagnosis in recent production paradigms that appear in response to the requirements imposed by the evolution of society. These systems are composed by intelligent modules, which interact and coordinate with each other in a distributed fashion to perform a particular task. These modules follow the concept of "Plug and Play", which means they must be able to organize themselves, without any kind of reprogramming, so that they can meet the production requirements. These new distributed production systems increase flexibility and agility on the production line, thus providing the necessary support for custom production. The diagnostic systems are in the context of these new paradigms, seen as essential not only to monitor and diagnose faults, but also as an effective means of prevention and maintenance in the short and long term. However, due to the complexity and dynamics at interactions level between modules, it becomes particularly difficult to implement effective procedures for diagnosis,to identify and understand the faults between modules. The nature of the interactions between modules goes beyond the logic control, making the traditional diagnostic systems, usually focusing on equipment rather than the relationships between them, not the suitable solutions to these new paradigms. This thesis provides a comparison study of two diagnostic systems that follow different approaches (one centralized and other distributed). To implement and validate this comparison, is defined and used a metric that relates the performance of diagnostic systems with the complexity of the interactions network formed by several modules