A Petri net based deadlock prevention policy for flexible manufacturing systems (original) (raw)
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IEEE Transactions on Systems, Man, and Cybernetics - Part A: Systems and Humans, 2004
A variety of important Petri net-based methods to prevent deadlocks arising in flexible manufacturing systems (FMS) are to add some control places and related arcs to strict minimal siphons (SMS) such that no siphon can be emptied. Since the number of minimal siphons grows in general exponentially with respect to a Petri net size, their disadvantages lie in that they often add too many additional places to the net, thereby making the resulting net model much more complex than the original one. This paper explores ways to minimize the new additions of places while achieving the same control purpose. It proposes for the first time the concept of elementary siphons that are a special class of siphons. The set of elementary siphons in a Petri net is generally a proper subset of the set of all SMS. Its smaller cardinality becomes evident in large Petri net models. This paper proves that by adding a control place for each elementary siphon to make sure that it is marked, deadlock can be successfully prevented. Compared with the existing methods, the new method requires a much smaller number of control places and, therefore, is suitable for large-scale Petri nets. An FMS example is used to illustrate the proposed concepts and policy, and show the significant advantage over the previous methods.
Smart deadlock prevention policy for flexible manufacturing systems using Petri nets
IET Control Theory & Applications, 2009
Deadlocks are a highly undesired situation in automated production systems including flexible manufacturing systems. Based on a Petri net formalism, a novel deadlock prevention policy is proposed for a class of Petri nets, S 3 PR, by using an MIP-based deadlock detection method and elementary siphons of Petri nets. Deadlock prevention is achieved by synthesising a set of monitors that are added to the plant net model. The concept of dominated transitions is proposed, to which the output arcs of the monitors are led. The monitors are computed according to a set of elementary siphons in a plant net model, which is found by using an established algorithm in the literature. When compared with the existing policies, the proposed method leads to a liveness-enforcing Petri net supervisor with a small number of monitors but more permissive behaviour. Examples are used to demonstrate the proposed method.
Deadlock Prevention for Flexible Manufacturing Systems via Controllable Siphon Basis of Petri Nets
IEEE Transactions on Systems, Man, and Cybernetics: Systems, 2015
Siphons are a kind of special structural objects in a Petri net, and plays a key role in synthesizing a live Petri net controller for flexible manufacturing systems. In order to obtain a small size Petri net controller, this paper introduces the concept of a controllable siphon basis. It then proves that a live Petri net controller can be established by adding a control place and related arcs to each strict minimal siphon (SMS) in a controllable siphon basis. The initial markings of control places are determined by an integer linear program. The number of control places in the obtained controllers is the same as the number of SMSs in the controllable siphon basis, while the latter is no more than that of the activity places in a Petri net model. An algorithm for constructing a controllable siphon basis is proposed, and a new deadlock prevention policy based on it is established. A few examples are provided to demonstrate the proposed concepts and policy and used to compare them with the state-of-the-art methods. Index Terms-Discrete event systems, flexible manufacturing systems, integer linear program (ILP), Petri nets. I. INTRODUCTION A FLEXIBLE manufacturing system (FMS) handles multiple concurrent flows of job processes that can make different products at the same time, and often exploits shared
Deadlock prevention and deadlock avoidance in flexible manufacturing systems using Petri net models
IEEE Transactions on Robotics and Automation, 1990
Deadlocks constitute an important issue to he addressed in the design and operation of flexible manufacturing systems (FMS's). In this paper, we show that prevention and avoidance of FMS deadlocks can he implemented using Petri net models. For deadlock prevention, we use the reachability graph of a Petri net model of the given FMS, whereas for deadlock avoidance, we propose a Petri net-based on-line controller. We discuss the modeling of the General Electric FMS at Erie, PA. For such real-world systems, deadlock prevention using the reachability graph is not feasible. We develop a generic, Petri net-based on-line controller for implementing deadlock avoidance in such real-world FMS's.
The International Journal of Advanced Manufacturing Technology, 2004
In a flexible manufacturing system (FMS) with multiple products, deadlocks can arise due to limited shared resources, such as machines, robots, buffers, fixtures etc. The development of efficient deadlock prevention policies, which can optimise the use of system resources, while preventing deadlocks from occurring, has long been an important issue to be addressed. In [1], an optimal deadlock prevention policy was proposed, based on the use of reachability graph (RG) analysis of the Petri net model (PNM) of a given FMS and the synthesis of a set of new net elements, namely places with initial marking and related arcs, to be added to the PNM, using the theory of regions. The policy proposed in [1] is optimal in the sense that it allows the maximal use of resources in the system according to the production requirements. For very big PNMs, the reachability graph of the PNMs becomes very large and the necessary computations to obtain an optimal deadlock prevention policy become more difficult. In this paper, we propose the use of the Petri net reduction approach to simplify very big PNMs so as to make necessary calculations easily in order to obtain an optimal deadlock prevention policy for FMSs. An example is provided for illustration.
2012
Deadlocks are an undesirable situation in automated flexible manufacturing systems. Their occurrences often deteriorate the utilization of resources and may lead to catastrophic results. The solution of a maximally permissive, i.e., optimal, supervisor in general belongs to the class of NP-hard problems. A computationally efficient policy, however, often implies a behaviorally restricted supervisor. This paper develops a deadlock prevention policy that establishes a trade-off between the behavioral permissiveness and computational tractability for a class of Petri nets, which can model many flexible manufacturing systems. The theory of regions guides our efforts towards the development of near-optimal solutions for deadlock prevention. Given a plant net structure, a minimal initial marking is first decided by structural analysis, and an optimal live controlled system is computed. Then, a set of inequality constraints is derived with respect to the markings of monitors and the places in the plant model such that no siphon can be insufficiently marked. A method is proposed to identify the redundancy condition for a constraint. For a new initial marking of the plant net structure, a deadlock prevention controlled system can be obtained by regulating the markings of the monitors such that the inequality constraints are satisfied, without changing the structure of the controlled system obtained previously. The behavioral performance of a controlled net system via the proposed method is shown to be nearly optimal by experimental studies.
Analysis of Flexible Manufacturing System using Petri Nets to design a Deadlock Prevention Policy
International Journal of Engineering Research and, 2016
This paper illustrates the Petri net modeling of a conceptual model of flexible manufacturing system (FMS) and addresses the problem of deadlock by establishing deadlock prevention policy. The first part introduces the problem of deadlock in FMS, deadlock handling strategies and basic concepts of petri net modeling. Literature review is presented in the second part and third part shows an illustration of Petri net modeling of a conceptual model of FMS processing two part types, consisting of three machines, a load/unload station and single robots. It is assumed that each of the part has three machining operations to be performed. Reachability graph is then generated for this model and is used to detect the possible deadlock states. Finally deadlock prevention policy is established for this conceptual FMS model based on reachability graph analysis. I.
A live subclass of petri nets and their application in modeling flexible manufacturing systems
The International Journal of Advanced Manufacturing Technology, 2009
In this paper a novel policy is proposed to solve the deadlock problem in a class of flexible manufacturing systems based on the notion that each shared buffer is partitioned into parts to store different types of products, respectively. A subclass of Petri nets called resource-shared net with buffers (RSNB) is defined. An RSNB is constructed by synthesizing some marked graphs, and each marked graph can model the process of manufacturing one type of product. RSNB cannot only model the concurrent execution of manufacturing processes, but also ensure that the modeled system is live. The process of constructing RSNB is described in detail, and a minimal siphon based necessary and sufficient condition is provided to characterize the liveness of RSNB.
A Petri Net Structure–Based Deadlock Prevention Solution for Sequential Resource Allocation Systems
… and Automation, 2005 …, 2005
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 Ë È Ê 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.