A computer-aided simulation tool based on Petri nets for the design and analysis of FMSs

Discrete-event simulation has been recognized as an invaluable tool in analyzing and designing FMSs. In this dissertation, a computer-aided simulation tool based on Petri nets is presented to facilitate simulation projects in the manufacturing area. For modeling and simulation of FMSs, Conserved nets which are a subclass of Petri nets are proposed and implemented. The structural characteristics and liveness conditions of Conserved nets are investigated. While hardware components are modeled by hierarchically-classified Petri net objects, high-level, real-time control systems in FMSs are separately modeled and integrated with a Petri net model to resolve conflicts occurring in Petri net execution. The structure of the Petri net-based simulation tool is presented. Also, the use of the simulation tool is illustrated with several case studies including performance comparison of push- and pull-based AGV dispatching rules in an FMS. Finally, strengths and weaknesses of the developed simulation tool are discussed including areas for future study

Integrating behavioural design into the virtual environment development process

A number of specifications formalisms have been developed (or applied) to support the abstract design of the behavioural component of the virtual environment interface. These formalisms subscribe to the philosophy that virtual environments should be viewed as hybrid systems which combine discrete and continuous behaviour. A significant deficiency in designing behaviour in this way is that the designs cannot be directly executed and explored in the same manner as an implementation. This limitation makes it di#cult for a designer to evaluate the suitability of designs. The thesis presents the Marigold toolset which supports two approaches to evaluating behaviour described using the Flownet hybrid formalism

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