Joaquín Ezpeleta

A Petri net based deadlock prevention policy for flexible manufacturing systems

In this paper we illustrate a compositional method for modeling the concurrent execution of working processes in flexible manufacturing systems (FMS) through a special class of Petri nets that we call S/sup 3/PR. In essence, this class is built from state machines sharing a set of places modeling the availability of system resources. The analysis of S/sup 3/PR leads us to characterize deadlock situations in terms of a zero marking for some structural objects called siphons. In order to prevent the system from deadlocks, we propose a policy for resource allocation based on the addition of new places to the net imposing restrictions that prevent the presence of unmarked siphons (direct cause of deadlocks). Finally we present the application of this technique to a realistic FMS case. >

A Banker's solution for deadlock avoidance in FMS with flexible routing and multiresource states

Bankers-like approaches to deadlock avoidance are based on a decision procedure to grant active processes resources using information about the maximum needs of resources that a process can request in order to ensure termination. The paper presents an extension of the classical Bankers algorithm to a class of flexible manufacturing systems modeled by means of Petri nets. These systems have two interesting characteristics from the application point of view. First, flexible routing of parts is allowed, and second, a multiset of resources is allowed to be used at each processing step. The decision procedure introduced is polynomial in the Petri net model size.

A Petri Net Structure– Based Deadlock Prevention Solution for Sequential Resource Allocation Systems

A new method for the deadlock prevention problem in concurrent systems where a set of processes share a set of common resources in a conservative way is proposed. It can be applied to flexible manufacturing systems, modeled with Petri nets. In this paper, we present a set of important results related to the deadlock prevention problem in S4PR nets. First, a liveness characterization is introduced, establishing how deadlocks can be studied in terms of circular waits. Second, we show how a circular wait situation corresponds to a particular marking related to a siphon of the Petri net model. Finally, this last characterization is used to obtain an iterative method that successively forbids deadlock related states, synthesizing the control necessary to ensure a final live behavior. The method can be implemented by means of the solutions of a set of integer linear programming problems.

An Iterative Method for Deadlock Prevention in FMS

In [Tricas et al., 1999] we presented a new method for deadlock prevention in flexible manufacturing systems using Petri nets as the modelling tool. It was based on an iterative method, using the structure of the Petri net model. Here we present two things; first, we improve the algorithm which establishes the control; second, we present some experimental results which try to compare a few control methods from the perspective of their “permissivity”.

A deadlock avoidance approach for non-sequential resource allocation systems

The paper concentrates on the deadlock-avoidance problem for a class of resource allocation systems modeling manufacturing systems. In these systems, a set of production orders have to be executed in a concurrent way. To be executed, each step of each production order needs a set of reusable system resources. The competition for the use of these resources can lead to deadlock problems. Many solutions, from different perspectives, can be found in the literature for deadlock-related problems when the production orders have a sequential nature [sequential resource allocation systems (S-RAS)]. However, in the case in which the involved processes have a nonsequential nature [nonsequential resource allocation systems (NS-RAS)], the problem becomes more complex. In this paper, we propose a deadlock avoidance algorithm for this last class of systems. We also show the usefulness of the proposed solution by means of its application to a real system.

A New Technique for Finding a Generating Family of Siphons, Traps and st-Components. Application to Colored Petri Nets

In this paper we propose a new solution to the problem of finding generating families of siphons (structural dead-locks in classical terminology), traps and st-components in Petri Nets. These families are obtained as solutions of some systems of linear inequalities. Their transformation into a system of linear equations allows to interpret the technique as follows: traps (siphons, st-components) of a net N are deduced from the support of psemiflows of a transformed net NΘ(NΣ,NΣΘ).

Automatic synthesis of colored Petri nets for the control of FMS

In this paper we research a modeling methodology, applicable to a large class of flexible manufacturing systems (FMS), that takes advantage of the differentiation between the FMS layout and the set of process plans corresponding to the different types of parts to be processed, We propose a separate modeling of these two components. In a second step, both models are integrated automatically in a unique model, represented as a colored Petri net (CPN). The second aim of the paper is the application of a deadlock prevention control policy ensuring that the processing of each part can be completed.

Computing minimal siphons in Petri net models of resource allocation systems: a parallel solution

Siphons are related to the liveness properties of Petri net models. This relation is strong in the case of resource allocation systems (RASs). Siphons can be used in these systems in order to both characterize and prevent/avoid deadlock situations. However, the computation of these structural components can be very time consuming or, even, impossible. Moreover, if, in general, the complete enumeration of the set of minimal siphons must be avoided (there can exist an exponential number of such components), some deadlock prevention methods rely on its (complete or partial) computation and enumeration. The special syntactical constraints of some classes of RASs can help in developing specific algorithms to compute siphons in a more efficient way. In this work, a known method for siphon computation is adapted to get advantage of the special (syntactical) structure of a class of RASs; a parallel implementation is proposed and some experimental results are presented

Petri Nets and Manufacturing Systems: An Examples-Driven Tour

There exists ample literature on Petri nets and its potential in the modelling, analysis, synthesis and implementation of systems in the manufacturing applications domain (see for example [54, 15, 18]; besides, in [66] an important bibliography is presented). This paper provides an examples-driven perspective. Nevertheless, not only complete examples from the application domain are considered. Manufacturing systems are frequently large systems, and conceptual complexity often appears because of some particular “local” constructions.

Approaching web service coordination and composition by means of petri nets. the case of the nets-within-nets paradigm

Web service coordination and composition have become a central topic for the development of Internet-based distributed computing. A wide variety of different standards have been defined to deal with the composition of Web services (usually represented as workflows) and the execution of coordination protocols. On the other hand, some relevant research proposals have already pointed to the use of the same formalism for both aspects, being Petri nets one of the adopted formalisms. In this work we present a case study showing how the adoption of the Nets-within-Nets paradigm helps in the modelling of complex coordination protocols and workflows. We first propose a Petri net model for a Web service peer able to run any workflow and to dynamically interpret the coordination required protocols. The execution of these protocols allows the peer to integrate functionalities offered by external peers. The Linda communication model has been used to support the integration among peers.