Practical Distributed Control Synthesis

Classic distributed control problems have an interesting dichotomy: they are either trivial or undecidable. If we allow the controllers to fully synchronize, then synthesis is trivial. In this case, controllers can effectively act as a single controller with complete information, resulting in a trivial control problem. But when we eliminate communication and restrict the supervisors to locally available information, the problem becomes undecidable. In this paper we argue in favor of a middle way. Communication is, in most applications, expensive, and should hence be minimized. We therefore study a solution that tries to communicate only scarcely and, while allowing communication in order to make joint decision, favors local decisions over joint decisions that require communication.Comment: In Proceedings INFINITY 2011, arXiv:1111.267

On Fault Diagnosis of random Free-choice Petri Nets

This paper presents an on-line diagnosis algorithm for Petri nets where a priori probabilistic knowledge about the plant operation is available. We follow the method developed by Benveniste, Fabre, and Haar to assign probabilities to configurations in a net unfolding thus avoiding the need for randomizing all concurrent interleavings of transitions. We consider different settings of the diagnosis problem, including estimating the likelihood that a fault may have happened prior to the most recent observed event, the likelihood that a fault will have happened prior to the next observed event. A novel problem formulation treated in this paper considers deterministic diagnosis of faults that occurred prior to the most recent observed event, and simultaneous calculation of the likelihood that a fault will occur prior to the next observed event

Reconfigurable production control systems: beyond ADACOR

In the recent evolution of production control systems, the emergence of decentralized systems capable of dealing with the rapid changes in the production environment better than the traditional centralized architectures has been one of the most significant developments. The agent-based and holonic paradigms symbolize this approach, and ADACOR holonic control architecture is a successful example of such a system. In this paper, authors discusses the current challenges and the way to go in the direction of new, reconfigurable, evolvable and ubiquitous systems, able to respond to current production environment demands and variability

Modelado e implementación de Sistemas de Tiempo Real mediante Redes de Petri con Tiempo

The work presented in the thesis must be considered in the context of a more general project, which proposes an unified method, based on the use of the Time Petri Nets formalism (TPN), to deal with the development of Real Time Systems (RTS). This project's objective is to cover the whole development cycle of a RTS with Time Petri Nets, from the requirement specification to the testing phase, including the properties analysis an the implementation. The thesis tackles two aspects of the RTS life cycle: the modelling and the implementation, or code generation. After introducing of the RTS modelling concepts using TPN, and the analysis techniques fundamentals, the work focuses on the code generation, taking the Petri Nets implementation techniques as a base and extending them in order to make the techniques able to deal with the special temporal requirements of the RTS. The centralized technique is presented in first place. Based on the separation of the functional and control parts of the RTS, the technique proposes the use of a coordinator, which holds the control of the system execution and the supervision of the deadline meeting. This technique has several drawbacks, such as the impact in the performance of the coordinator presence. In order to cope with these evidenced drawbacks, the thesis proposes the decentralized implementation technique. Its main aim is to split the net into a set of concurrent subnets, mono-marked p-invariants, which communicate between each other through synchronous or asynchronous primitives. These subnets are called protoprocesses. After this net partition, the technique proposes the identification of a set of execution units (specific place-transition structures) that can be directly translated into Ada-95 statements. This strategy leads to the generation of the skeleton of the code that implements the control part of the RTS. As an additional result, the thesis proposes Time Petri Net based models for the real time Ada-95 statements. Finally, in cases where it is not possible to apply the decentralized techniques, the work proposes mixed implementation techniques

Coloured Petrinet for Modelling and Validation of Dynamic Transmission Range Adjustment Protocol for Ad Hoc Network

The IEEE 802.11 standard defines two operational modes for WLANs: infrastructure based and infrastructureless or ad hoc. A wireless ad hoc network comprises of nodes that communicate with each other without the help of any centralized control. Ad hoc implies that the network does not rely on a pre-existing infrastructure but rather each node participates in routing by forwarding data for other nodes. The decentralized nature improves the scalability of wireless ad hoc network as compared to wireless managed networks. Each node acts as either a host or router. A node that is within the transmission range of any other node can establish a link with the later and becomes its immediate neighbour. However, the nodes in the ad hoc networks are constrained with limited resources and computation capability. So it may not be possible for a node to serve more number of neighbours at some instant of time. This enforces a node to remain connected or disconnected with few of its existing neighbours supporting the dynamic restructuring of the network. The presence of dynamic and adaptive routing protocol enables ad hoc networks to be formed quickly. The Dynamic Transmission Range Adjustment Protocol (DTRAP) provides a mechanism for adjusting transmission range of the ad hoc nodes. They maintain a threshold number of registered neighbours based on their available resources. The node protects its neighbourhood relationship during data communication by controlling its transmission range. It registers or de-registers a communicating node as its neighbour by dynamically varying the transmission range. However a node has a maximum limit on its transmission range. If the distance between the node and its neighbour is less than the transmission range and; 1)if the number of neighbours of a node falls short of threshold value, the node dynamically increases its transmission range in steps until it is ensured of an optimal number of neighbours 2)if the number of neighbours of a node exceeds the threshold value, the node dynamically decreases its transmission range in steps until it is ensured of an optimal number of neighbours. Coloured Petri nets (CP-nets) is the modelling language tool used for systems having communication, synchronisation and resource sharing as significant aspects. It provides a framework for the design, specication, validation, and verication of systems. It describes the states in which the system may be in and the transition between these states. The CPN combines Petri nets and programming languages. Petri nets amalgamate the use of graphical notation and the semantical foundation for modelling in systems. The functional programming language standard ML provides the primitives for the definition of data types and manipulation of data values. Besides providing the strength of a graphical modelling language, CP-nets are theoretically well-founded and versatile enough to be used in practice for systems of the size and complexity of industrial projects

Petri net-based approach for web service automation resource coordination

In industrial automation, control systems and mechatronic devices are from diverse nature, supplied by different manufacturers and made of different technologies. The adoption of web services principles in an automated production system satisfies some requirements, namely the interoperability of such heterogeneous and distributed environments and the basis for flexibility and reconfigurability. Manufacturing processes require to access resources at different precedence levels and time instances, but in the other way resources may also be shared by different processes. A major challenge is then how individual services may interact, coordinating their activities. Petri nets may be used to describe complex system behaviour and therefore also applied to coordinate such systems. The paper introduces a Petri net based approach for the design, analysis and coordination of systems developed using web services to represent individual and autonomous resources. For this purpose, it is presented a Petri nets computational tool to support the design, validation and coordination of web service based automation systems.info:eu-repo/semantics/publishedVersio