Dealing with Deadlocks in Industrial Multi Agent Systems (original) (raw)
Related papers
Deadlock Control of Automated Manufacturing Systems Based on Petri Nets—A Literature Review
IEEE Transactions on Systems, Man, and Cybernetics, Part C (Applications and Reviews), 2000
Deadlocks are a rather undesirable situation in a highly automated flexible manufacturing system. Their occurrences often deteriorate the utilization of resources and may lead to catastrophic results in safety-critical systems. Graph theory, automata, and Petri nets are three important mathematical tools to handle deadlock problems in resource allocation systems. Particularly, Petri nets are considered as a popular formalism due to its inherent characteristics. They have received much attention over the past two decades to deal with deadlock problems in automated manufacturing systems, leading to a variety of deadlock control policies. This research surveys the state-of-the-art deadlock control strategies for automated manufacturing systems by reviewing the principles and techniques involved in preventing, avoiding, and detecting deadlocks. The primary focus of this research is deadlock prevention due to a large and continuing stream of efforts on it. A control strategy is evaluated in terms of computational complexity, behavioral permissiveness, and structural complexity of its liveness-enforcing or deadlock-free supervisor. This comprehensive study provides readers a conglomeration of the updated results in this area and facilitates engineers in finding a suitable approach for their industrial application cases. Future research directions are finally discussed.
Computing and Informatics, 2021
Solving the deadlocks avoidance problem in Resource Allocation Systems (RAS) in Discrete-Event Systems (DES) is a rife problem, especially in Flexible Manufacturing Systems (FMS), alias Automated Manufacturing Systems (AMS). Petri Nets (PN) are an effectual tool often used at this procedure. In principle, there are two basic approaches how to deal with deadlocks in RAS based on PN. They are listed and illustrated here. First of the approaches is realized by means of the supervisor based on P-invariants of PN, while the second one is realized by means of the supervisor based on PN siphons. While the first approach needs to know the reachability graph/tree (RG/RT) expressing the causality of the development of the PN model of RAS, in order to find (after its thorough analysis) the deadlocks, the second approach needs the thorough analysis of the PN model structure by means of finding siphons and traps. Next, both approaches will be applied on the same PN model of RAS and the effectiveness of the achievement of their results will be compared and evaluated. Several simple illustrative examples will be introduced. For the in-depth analysis of the problem of deadlock avoiding, next Part 2 of this paper is prepared, where the newest research will be introduced and illustrated on more complicated examples. If necessary (because of the limited length of particular papers), also the third part-Part 3, will be prepared.
Deadlock analysis and control based on Petri nets: A siphon approach review
Advances in Mechanical Engineering, 2017
Deadlocks should be eliminated in highly automated manufacturing systems since their occurrence implies the stoppage of the whole or partial system operation. Over the past decades, Petri nets are increasingly becoming one of the most popular and full-fledged mathematical tools to deal with deadlock problems due to their inherent characteristics. In a Petri net formalism, liveness is an important property of system safeness, which implies the absence of global and local deadlock situations in an automated manufacturing system. The liveness assessment can be performed by verifying the satisfiability of certain predicates on siphons, a well-known structural object in Petri nets. Therefore, siphons have received much attention to analyze and control systems modeled with Petri nets. Particularly, elementary siphon theory plays a key role in the development of structurally simple liveness-enforcing Petri net supervisors, leading to a variety of deadlock control approaches. This survey studies on the state-of-the-art elementary siphon theory of Petri nets including refined concepts of elementary siphons and their extended version, computation methods of siphons and elementary ones, controllability conditions, and their application to deadlock control. As a reference, this work attempts to provide a comprehensive and updated research survey on siphons, elementary siphons, and their applications to the deadlock resolution in Petri nets.
Control of Deadlocked Discrete-Event Systems Using Petri Nets
Acta Polytechnica Hungarica, 2022
In Discrete-Event Systems (DES), deadlocks frequently occur. Flexible Manufacturing Systems (FMS) have the character of DES. Namely, FMS consist of many cooperating devices (like robots, machine tools, transport belts, etc.). Frequently, deadlocks occur because of insufficient resources. Petri Nets (PN) are often used to model FMS and to synthesize control for them. To deal with deadlocks, first of all, it is necessary to find and/or avoid them. There are several principal approaches for doing this-either by computing and analyzing the PN reachability tree (RT) or by finding PN model siphons. Then, in the former concept, the supervisor is synthesized by means of P-invariants of the PN model used, while in the latter concept the supervisor, based on siphons, is synthesized. In addition to these approaches, additional techniques can sometimes, be applied-e.g. a suitable utilization of added PN transitions.
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.
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.
Deadlock control policy for a class of Petri nets without complete siphon enumeration
Siphons are special structures of a Petri net. Their number grows exponentially with the net size. Hence, the traditional siphon-based deadlock control policies have two problems, that is, generating very structurally complex supervisory controllers and requiring intractable computation efforts. This paper intends to use the newly proposed concept, elementary siphons, and a mixed integer programming (MIP) method to design structurally simple supervisory controllers and reduce the computational burden. This method is applicable to a class of Petri nets, System of Simple Sequential Processes with Resources that can well model a wide class of discrete manufacturing systems. Siphons are divided into elementary and dependent ones. The proposed policy consists of three stages: siphon control, control-induced siphon control, and the elimination of control-redundant monitors. First, a monitor (control place) is added for each elementary siphon such that it is invariant-controlled. Because of the addition of monitors to the plant model, control-induced siphons are possibly generated in the augmented net. Next, monitors are added to make control-induced siphons in the augmented net always marked sufficiently without generating new problematic siphons. A MIP technique is used to guarantee that no siphon is insufficiently marked. Finally, we systematically remove control-redundant monitors. Compared with previous work in the literature, the deadlock prevention policy developed in this paper can lead to a structurally simple liveness-enforcing Petri net supervisor with more permissive behaviour by adding only a small number of monitors and arcs. Moreover, complete siphon enumeration is avoided. A manufacturing system example is utilised to illustrate the proposed methods.
Single Controller-Based Colored Petri Nets for Deadlock Control in Automated Manufacturing Systems
Processes
Deadlock control approaches based on Petri nets are usually implemented by adding control places and related arcs to the Petri net model of a system. The main disadvantage of the existing policies is that many control places and associated arcs are added to the initially constructed Petri net model, which significantly increases the complexity of the supervisor of the Petri net model. The objective of this study is to develop a two-step robust deadlock control approach. In the first step, we use a method of deadlock prevention based on strict minimal siphons (SMSs) to create a controlled Petri net model. In the second step, all control places obtained in the first step are merged into a single control place based on the colored Petri net to mark all SMSs. Finally, we compare the proposed method with the existing methods from the literature.
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.