Robert Valette

Petri net based modeling of hybrid systems

This paper deals with the modeling of hybrid systems by means of Petri nets. Hybrid systems are systems whose modeling requires discrete, as well as continuous variables. Time may be either continuous or discrete. Starting from a presentation of the continuous modeling and the discrete modeling, a short survey on some extensions to represent hybrid systems is given. The way continuous models are extended to consider discrete aspects and discrete models to consider continuous ones is presented and discussed.

Fuzzy Petri Nets: An Overview

Abstract This paper is a short survey about the main fuzzy Petri net models which have been recently developed. We focus on the applicability of such approaches in the field of Discrete Events Dynamic Systems. The elements that are fuzzyfied in Petri nets are also presented.

Scenario durations characterization of t-timed Petri nets using linear logic

This paper aims to handle scenario durations of t-timed Petri nets without constructing the class graph. We use a linear logic characterization of scenarios based on the equivalence between reachability in Petri nets and provability of a class of linear logic sequents. It has been shown that it was possible to characterize a scenario with concurrency induced both by the Petri net structure and by the marking. This approach, based on the rewriting of the linear logic sequent proof, is limited because some structural concurrency cannot be expressed. In this paper we develop a new approach based on a canonical proof of the sequent. It does not explicitly characterize the scenario but it delimits its duration through an algebraic symbolic expression. It allows handling non safe or cyclic Petri nets and structures which cannot be uniquely characterized by sequence and parallel operations.

Real time scheduling of Workflow Management Systems based on a p-time Petri net model with hybrid resources

Abstract The objective of this work is to propose an approach based on a p-time Petri net model with hybrid resources to solve the real time scheduling problem of Workflow Management Systems. The proposed approach uses an activity diagram to show the main activities of the system and the different routings of the Workflow Process. Based on the activity diagram, the corresponding p-time Petri net model is produced by assigning a time interval to every Workflow activity. Hybrid resource (discretexa0+xa0continuous) allocation mechanisms are modeled by an hybrid Petri net with discrete transitions in order to represent the different kinds of resources (equipment and human resources) in a more realistic way. Time constraint propagation mechanisms are presented and a token player algorithm is applied to the Petri net model in order to obtain an acceptable scenario corresponding to a specific sequence of activities which respects the time constraints. The approach is illustrated through an example of “Handle Complaint Process”.

Real time scheduling of batch systems

Abstract The approach presented in this article is based on the real time simulation of p -time Petri net for the real time scheduling of batch systems. After defining the different kinds of constraints that can exist in a linear hybrid production system, we present the conflict resolution principle used by a token player algorithm at the global coordination level.

Critical scenarios derivation methodology for mechatronic systems

Abstract This paper deals with safety in design of mechatronic systems. We propose a method based on a qualitative analysis of a Petri net model of the system. It allows deriving feared scenarios by determining the sequences of actions and state changes leading to the feared state in which the passengers safety is no longer guaranteed. The Petri net model of the system takes into account normal behaviour, failures and reconfiguration mechanisms. Our approach uses linear logic as formal framework and is based on a backward and a forward reasoning. It derives feared scenarios as causal relationships between normal states and the feared one.

Rapid and modular prototyping-based Petri nets and distributed simulation for manufacturing systems

This paper presents an approach to simulate and implement by stepwise refinement the whole manufacturing system (MS) by means of distributed simulation. This approach is based on the use of different classes of Petri nets to model different levels of a manufacturing system. Furthermore these classes may match the abstraction levels of a high-level Petri net used to model the MS. Each level can be simulated on a processor or a cluster of processors which can communicate between themselves using a network. The main contribution is to give the opportunity to combine simulation, performance evaluation and emulation. The emulation means that a part of the system can be run in real time while the other part is simulated. Moreover based on the abstraction levels of high-level Petri nets, subsystems can be integrated step-by-step from the design stage to the implementation one, allowing inter-changeability between simulated components and real-time physical systems. This approach is achieved by defining a simulation engine which involves a local simulator, an emulator and an interface to the physical process. Criteria are defined to use an emulator or a local control software for a physical process as a logical process for the conservative distributed simulation.

Modeling, Simulation and Analysis of Batch Production Systems

After a surveyof some approaches for modeling hybrid systems by means of Petrinets ( t-time Petri nets, colored Petri nets, hybridPetri nets and differential predicate transition nets), thispaper illustrates how these formal models can be used for simulationand validation. It is shown how it was possible to use aggregatedqualitative models concurrently with detailed ones.

Petri nets for the evaluation of redundant systems

Abstract This paper gives an overview of the use of Petri nets for the evaluation of redundant systems. After listing modelling criteria for this type of system, we describe the powerful characteristics of Petri nets concerning both representation and performance evaluation: descriptive ability, formal verification procedures, the ability to incorporate time and quantitative analysis. Finally, we discuss the possibilities offered by this theory, as well as certain limitations when it comes to modelling large-scale systems such as those usually encountered in industrial applications.

Landing system verification based on petri nets and a hybrid approach

One of the most important activities of control system design is its verification. Verification ensures that the controlled system will behave as expected under any circumstances it may operate. In this context, the purpose of this paper is to introduce a new method for the verification of aircraft control systems. The focus of this method is on aircraft systems that are characterized as hybrid, i.e., that merge continuous and discrete dynamics. The method proposed is divided into two main parts: the system modeling and the verification of behavioral properties. In the first part, Petri net, differential equation systems, and object oriented concepts are used concurrently in order to model complex hybrid systems. In the second part, the distributed nature of the model is explored in order to decompose a complex verification problem into series of simple local problems. Linear logic is used as a basis of a theorem-proving approach for the verification from the discrete-event point of view. The verification method has been applied to a number of case studies. Among them is the landing system of a military aircraft, which is described in this paper