Deadlock prevention and avoidance in FMS: A Petri net based approach

Petri nets are a popular mathematical tool to investigate the deadlock problems in resource allocation systems. As an important problem solution paradigm in computer science, the divide-and-conquer strategy is used in this paper to investigate the deadlock prevention for flexible manufacturing systems (FMSs) that are modeled with Petri nets. Based on the concept of resource circuits, a plant net model is divided into an idle subnet, an autonomous subnet, and a number of small but independent subnets, called toparchies, from the viewpoint of deadlock control. A liveness-enforcing supervisor, called toparch, is designed for each toparchy. If a particular separation condition holds in a plant net model, the computational complexity of toparches is significantly reduced. This research shows that the resultant net, called monarch, by composing the toparches derived for the toparchies can serve as a liveness-enforcing Petri net supervisor for the whole plant model. FMS examples are given to illustrate the proposed method.

In this paper we present a Petri-net-based approach to consider fault tolerance aspects in a modified control track vehicle system. The proposed approach is based on fuzzy time G-nets which is the integration of two Petri nets extensions: fuzzy time Petri net (timing Petri net extension) and G-nets (Petri net extended with object-oriented concepts). We also show how to model such system by means of fuzzy time G-nets.

This paper details our experience integrating a transaction manager component called Pern with Process Weaver Process Weaver s Petri net based approach is ex cellent for explicitly modeling concurrent activities of cooperating agents but there is no underlying mechanism for treating con icting actions of concurrent independent agents In addition there is a need for advanced transaction support if we are to extend petri nets to use object management systems to store and access data This paper shows several experiments we performed and our resulting implementation

Automated manufacturing systems, including flexible manufacturing systems (FMSs), belong to the class of discrete event dynamic systems. In such a system, potentially conflicting events may occur due to concurrency. The problem of collision and deadlock avoidance can be investigated using Petri nets which are powerful techniques suitable for modeling concurrent processes. A Petri net based approach is employed in this paper to model, detect and avoid collisions and deadlocks in FMSs. Unlike the existing Petri net based techniques, the proposed approach uses the concept of critical states to avoid the system from entering a state leading toward a deadlock state. A multirobot assembly example is used to illustrate the proposed scheme.

Combined Petri net modelling and AI based heuristic hybrid search for flexible manufacturing systems—part 1. Petri net modelling and heuristic search

To solve the problem of deadlock prevention for flexible manufacturing systems (FMS), an effective approach based on the State Class Graph (SCG) is proposed in a framework of time Petri nets (TPN). The first step determines the SCG of TPN. In the second step, since the SCG and discrete state graph (DSG) of a TPN have the same markings and obey the same linear temporal logic (LTL) properties, deadlock-freedom can be obtained by performing the required marking/transition separations. The theory of regions is used to design control places added to the original TPN model to realize the desired behavior. A parameterized example is used to show the performance of the proposed approach.

Deadlocks are of paramount importance in resource allocation systems, which are usually treated from the perspective of discrete event systems. This paper develops a deadlock prevention strategy for a system modeled with Petri nets, by endowing appropriate time constraints with certain transitions to schedule the firing priority of enabled transitions in a Petri net such that transition sequences leading to deadlocks are prohibited, i.e., expanding an untimed Petri net model into a time Petri net to prevent deadlocks. To increase the system permissiveness of a time Petri net with time constraints endowed, a control place is designed, which does not expand the reachable space of the original Petri net. The predominant role of the control place is to convert continuously enabled transitions at certain markings into newly enabled transitions, which can prolong the firing time of transitions. Furthermore, we propose a method that merely enumerates deadlock prevention condition inequalities to derive a series of time constraints by probing the connection between deadlock prevention conditions and transitions. The developed method only needs to designate time constraints for partial transitions. Examples are provided to demonstrate the effectiveness of the presented methodology.

Deadlock/livelock problems can cause catastrophic results in flexible manufacturing systems (FMS) by forcing them to stop production processes at an unpredictable stage of production. Therefore, they must be handled properly in order to obtain flawless production in FMS. Petri net (PN) based deadlock/livelock studies for FMS have been widely carried out to obtain live PN models. When a PN model is live, this ensures that the modelled FMS is deadlock-free. Firstly, an uncontrolled (plant) PN model is constructed for the FMS suffering from deadlocks/livelocks. Then reachability graph (RG) analysis of this PN model is carried out to provide all possible reachable states of the modelled system. An RG of a PN model of an FMS suffering from deadlock/livelock problems can be split into the live zone (LZ) and the deadlock zone (DZ). The former is the set of system states considered to be legal (good), while the latter is the set of system states regarded to be illegal (bad). The LZ represents the optimal (maximally permissive) system behavior that must be provided by an optimal control policy. Generally, in PN based liveness studies, a liveness enforcing supervisor (LES) consisting of a set of control places (CP) is computed. Then the controlled (closed-loop) PN model is obtained by merging the plant PN model and the LES. If the number of reachable live states of the controlled PN model is the same as the ones that exist in the LZ, then the controlled model is optimal. Otherwise, it is suboptimal. The greater the number of live reachable states of the RG, the more products to be produced within the FMS. Therefore, the number of reachable live states of the controlled PN model is considered as a quality measure. It defines the behavioral permissiveness of the controlled model. In the literature, to verify the behavioral permissiveness of the PN models, the PN tool called INA (Integrated Net Analyzer) has been widely used. Recently, by means of INA, a method was proposed to compute the number of states within the LZ and the DZ of a given PN model suffering from deadlocks/livelocks. Unfortunately, INA cannot compute RGs of large PNs having a few millions of states. Therefore, in this paper by means of TINA (TIme petri Net Analyzer), an alternative faster and much more efficient method is proposed for the computation of the number of states within the LZ and the DZ for PN models with large RGs. In addition, in order to enable the development of new PN based deadlock prevention methods, further computations are also proposed. These include the computation of the set of states in the DZ, LZ and first met bad markings (FBMs) for a given PN model suffering from deadlocks/livelocks. The applicability and the effectiveness of the proposed methods are demonstrated by considering several well-known examples of FMS from the relevant literature.INDEX TERMS Flexible manufacturing systems (FMS), deadlock, deadlock prevention, Petri Nets (PN), liveness enforcing supervisor (LES), PN computation tools.

Petri nets are used to design deadlock control strategies for flexible manufacturing systems (FMS), which typically involve the addition of monitors and the associated arcs to the FMS. The addition of several monitors and associated arcs to first constructed Petri net model significantly complicates the Petri net controller. This paper develops a two-step method for preventing deadlocks based on a colored Petri net and a structurally minimal approach that significantly reduces the number of monitors. In the first step, a vector covering technique is applied to generate a minimal covered sets of first-met bad markings (FBMs) and legal markings that are respectively smaller than the sets of FBMs and legal markings. At one iteration, place invariants (PIs) corresponding to monitors are constructed by solving an integer linear programming problem (ILPP) to prohibit the maximum number of FBMs, while allowing all legal markings in the minimal covering set. The purpose of the ILPP is to maximize the number of FBMs forbidden by the PIs. Then, based on a colored Petri net, all generated monitors are combined into a global control place. Therefore, a supervisor with minimal structural complexity can be constructed. The obtained net model is controlled after the addition of the designed supervisor. Two instances from the literature are considered to illustrate the proposed approach.

Anemia of chronic disorders is a very important phenomenon and iron is a crucial factor of this complex process. To better understand this process and its influence on some other factors we have built a mathematical model of the human body iron homeostasis, which possibly most exactly would reflect the metabolism of iron in the case of anemia and inflammation. The model has been formulated in the language of Petri net theory, which allows for its simulation and precise analysis. The obtained results of the analysis of the model’s behavior, concerning the influence of anemia and inflammation on the transferrin receptors, and hepcidin concentration changes are the valuable complements to the knowledge following from clinical research. This analysis is one of the first attempts to investigate properties and behavior of a not fully understood biological system on a basis of its Petri net based model.

Public bicycle sharing systems control and performance evaluation: A Petri net-based approach

To solve the problem of deadlock prevention for timed Petri nets, an effective deadlock prevention policy based on elementary siphons is proposed in this paper. Without enumerating reachable markings, deadlock prevention is achieved by adding monitors for elementary siphons, increasing control depth variables when necessary, and removing implicit, liveness‐restricted and redundant control places. The final supervisor is live. First, a timed Petri net is stretched into a stretched Petri net (SPN). Unchanging the system performance, each transition in the SPN has a unit delay time. Then the siphon‐control‐based approach is applied. Monitors computed according to the marking constraints are added to the SPN model to ensure all strict minimal siphons in the net invariant‐controlled. A liveness‐enforcing supervisor with simple structure can be obtained by reverting the SPN into a TdPN. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society

We describe a case study of the design and verification of a parallel and pipe-lined image processing unit based on an extended Petri net, which is called a Logical Colored Petri net (LCPN). This is suitable for Flexible-Manufacturing System (FMS) modeling and discussion of structural properties. LCPN is another family of colored p/t-net(CPN) with the addition of the following features: integer value assignment of marks, representation of firing conditions as marks' value based formulae, and coupling of output procedures with transition firing. Therefore, to study the behavior of a system modeled with this net, we provide a means of searching the reachability tree for markings.

Driven by fierce global competition, reducing costs while improving customer services by effective supply chain logistics management has become one main concern of most companies. This has created needs for modelling, performance analysis and optimisation tools that can help these companies to improve their logistics networks and operations. In this paper, the advantages of Petri nets as modelling and analysis tools for logistics systems are demonstrated, the recent developments of using Petri net based approaches for modelling, performance analysis, and optimisation of supply chains are reviewed, and future research directions for this important area are explored.

Formalization of process behavior is a key issue for semantic Web services. However, this bears the disadvantage of clumsy specifications. In this paper we introduce a Petri net based approach to capture the semantics of Web services. It offers a visual modeling technique and means of refinement and composition. The model is very formal allowing for a clear specification of the semantics a process has. We combine ideas from the Petri net community with ideas from the description logic area focusing on ontologies