Deadlock control methods in automated manufacturing systems

Since the 1980s, Petri nets (PN) have been widely used to model automated manufacturing systems (AMS) for analysis, performance evaluation, simulation, and control. They are mostly based on process‐oriented modeling methods and thus termed as process‐oriented PN (POPN) in this paper. The recent study of deadlock avoidance problems in AMS led to another type of PN called resource‐oriented PN (ROPN). This paper, for the first time, compares these two modeling methods and resultant models in terms of modeling power, model complexity for analysis and control, and some critical properties. POPN models the part production processes straightforwardly, while ROPN is more compact and effective for deadlock resolution. The relations between these two models are investigated. Several examples are used to illustrate them. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society

The paper is a partial synthesis of the work that a team within the Faculty of Managerial and Technological Engineering has in the field of modeling and simulation of systems with Petri nets. The paper deals with three issues. The first part is Modeling and simulation of manufacturing systems with timed Petri nets. The first part presents the way in which the performances of some manufacturing systems are evaluated using timed Petri nets. The first example is a manufacturing system specific to the textile industry. The system has three production lines. In this case, the modeling with timed Petri nets allows the analysis of the operation of the flow lines and highlights the bottleneck. Another modeled manufacturing system is specific to a series production, more precisely it refers to the manufacture of gas cookers within a company from Oradea. The model with Petri nets also describes the supply sequences of the stocks of parts and subassemblies. The next modeled system is an automated manufacturing system for the packaging of detergents. The complexity of the Detergent Packing System and the high level of automation, require the use of efficient modeling and simulation methods to verify the validity of the solutions adopted. In this chapter is present the model of a robotic welding cell. The second part of the paper, the transition from timed Petri nets to hierarchical colored Petri nets, shows how Petri nets were developed for a robotic cell for metallographic analysis. The third part is dedicated to modeling with colored Petri nets timed with complex colors of the flexible manufacturing cell A007 within the Department of Industrial Engineering.

For automated manufacturing systems (AMSs), deadlock resolution in terms of Petri nets remains an attractive topic to which many approaches are dedicated. However, few of them can quantitatively optimize certain indices during their supervisor synthesis process. This causes unnecessary control limitations and often leads to high implementation cost. In the framework of Petri nets, this paper proposes a method to synthesize a cost-effective supervisor with the aid of a set of mathematical programming formulations. Along the same vein, we also show some results by investigating timed Petri nets, which can be utilized to make a good tradeoff between implementation cost and system cycle time. Examples are used to validate the effectiveness of our result.

On the basis of the assumption that no resource failure occurs, a variety of deadlock control policies have been developed for automated manufacturing systems (AMSs). However, in practical manufacturing systems, the occurrence of resource failures is always inescapable. In case, if resources fail to work, the existing deadlock control strategies can no longer be applied to the changed system; therefore, redesigning a new strategy is necessary. Because of their powerful modeling capabilities, Petri nets are used to model the considered AMSs allowing multi-type and multi-quantity resource acquisition. This paper focuses on extending a deadlock prevention method to be applied to AMSs with unreliable resources. Strict minimal siphons are controlled by added control places (monitors) to ensure the system’s liveness. To prevent blocking issues caused by resource failures, we develop a set of shared resource constraints represented by a set of inequalities based on the minimal resource requirements of processes and the capacity of shared resources. Robust monitors are designed for them to limit the distribution of tokens in unreliable neighborhood places. Our objective is to control resource allocation such that those parts not necessarily requiring any failed resource can continue progressing smoothly even if some unreliable resources break down. Examples are given to elucidate our proposed method clearly.

Automated manufacturing systems (AMSs) are developing rapidly with increasingly sophisticated operations and complex topologies. In this paper, we propose a new kind of AMS structure, namely, AESMs, with processes expressed by flexible routes and embedded by marked graph blocks. Flexible routes and assembly operations are combined organically in this model, making it structurally complex and applicably adaptable. Deadlock resolution in AMSs is a fundamental and prerequisite issue. Conventional approach is based on monolithic methodologies by means of siphons, i.e., a special structural object closely related to deadlocks. Analysis shows that siphon-based mechanism is of limited applicability to control AESMs. On the contrary, we utilize a distributed approach in accordance with the philosophy of model predictive control techniques, which can create a trajectory dynamically leading the entire system to its desired destination. In our strategy, whether or not concerned tokens can reach critical places or critical place unities determines the feasibility of each step's execution. Control strategy is applied to processes locally such that they can concurrently proceed at the same pace. Global goals become attainable through the local observation, control, and execution upon local processes without knowing external and extra information.

Modelling automated manufacturing systems using a modification of coloured petri nets

For automated manufacturing systems (AMSs), deadlock-free operation is an important control objective, encouraging many researchers to focus their efforts on obtaining a computationally tractable and efficient control policy for the sake of deadlock resolution. However, much of the work existing in the literature obtains such control policies, by restricting the research model to some structurally simple ones, implying that extending these currently existing results to more complex models is usually nontrivial. In this work, we develop an on-line distributed control method for deadlock problem arising in the Petri nets where subnets are forward-conflict free nets. Without knowing the external and extra information, deadlocks can be avoided in real-time through local observation, control, and execution upon processes, thus greatly reducing computational complexity and time. Moreover, the results concluded by our control method can be easily extended to more structurally complex AMSs.

This paper presents a liveness analysis method for sequential automated manufacturing systems (AMSs), which can be modeled by a class of Petri nets named systems of sequential systems with shared resources (S4PR). We show that deadlocks in S4PR can be characterized by the saturation of its structural object named a perfect activity circuit (PA-circuits). Thus, S4PR is live if and only if no PA-circuits in it is saturated at all reachable states. A PA-circuits of an S4PR may not be saturated at any state; hence, we propose an integer linear program (ILP) to determine whether a PA-circuits can be saturated or not. Then an algorithm is proposed to compute the set of PA-circuits that may be saturated. This presented method nontrivially generalizes deadlock characterization and liveness condition of ordinary Petri nets to a broader class of nonordinary ones. Note to Practitioners —In the context of AMS, liveness is the most important property since it implies that there is no partial deadlock during the system evolution, and hence, all part types can be produced smoothly. We study the problem of liveness for AMS with the most general resource allocation and flexible routing, which can be modeled by S4PRs or disjunctive/conjunctive (D/C) resource allocation systems (RASs). Given such a complex AMS, based on its Petri net model, this paper presents a sufficient and necessary liveness condition by utilizing the structural properties, and develops an algorithm to identify all the structural objects that may lead the systems to deadlocks. This paper is significant in liveness-enforcing supervisor design for S4PR.

Modern complex systems require intensive application of complicated supervisors. Structural simplification techniques are one of the fundamental researches in the context of automated manufacturing systems (AMSs). They can reduce implementation cost, mitigate fabrication complexity, and improve reliability. Several typical methods are developed along this direction. In order to thoroughly explore their effectiveness and performance, we make a comparison and contrast investigation among them. Several analytical results and performance measures are proposed for their qualitative and quantitative comparison. Our approach can assist researchers and practitioners better comprehend the inherit mechanisms and relative merits of these simplification methodologies and their applicability in AMSs. This research is motivated by AMSs' control; however, they are also applicable to other systems with discrete event controllers.

Reconfigurable systems have received much attention from academia and industry because they are efficient, agile, and reasonably priced, and they are the trend of all future systems. The chapter focuses on dynamic automatic reconfigurations of Control Systems to be classically modeled by Petri nets. Several modeling and verification methods for such systems are shown and compared before the introduction of the research work on feasible dynamic reconfigurations and the implementation of manufacturing systems based on Petri nets. Three different reconfiguration scenarios can be applied at run-time to such systems: Addition/Removal of places, Addition/Removal/Update of transitions, or finally, the simple modification of the initial marking. Three formal modules are defined accordingly, which allow the reconfigurations of the system’s Petri nets model: the first module to dynamically change places of the model, the second to dynamically reconfigure transitions within a given subset of places, and the third to modify the initial markings of places. To check the correct behavior of this architecture according to user requirements, the model checker SESA is applied for the verification of CTL-based properties of the proposed modules and also of the system. The contribution is applied to a real-world Benchmark Production System.

The paper considers the methods of modeling and control of discrete event robotic manufacturing systems using Petri nets and proposes a methodology of decomposition and coordination for hierarchical and distributed control. First, a task specification is defined as a Petri net model at the conceptual level, and then transformed to the detailed Petri net representation of the subtasks. Finally, the overall Petri net is decomposed and the constituent subnets are assigned to local Petri net based controllers. The coordinator is introduced to coordinate the distributed controllers so that the behavior of the distributed system is the same as that of the original Petri net. A coordination algorithm by two control levels is developed for defining robot and machine activation conditions. Based on the proposed method, a distributed control system has been implemented for a robotic manufacturing cell.

The automation of manufacturing systems is one of the most important aspects that need to be taken care of during a design process. The Product Lifecycle Management (PLM) tools allow for the designing of automated systems even before acquiring all the hardware and/or software. This paper shows the use of this PLM kind of tools for mixing virtual and real components on an automated manufacturing system through the implementation of four different case scenarios: using the real process/real controller to the virtual process/virtual controller, real process/real controller to real process/virtual controller and finally, virtual process/real controller to virtual process/virtual controller. These scenarios will be described along with their purposes and the tools used to achieve them. Dassault Systemes DELMIA Automation is used as a PLM tool and is combined with the hardware and software required to achieve each case scenario. The case study used is the Flexible Manufacturing System in the Mechatronics laboratory at the Tecnologico de Monterrey; it’s also presented an implementation of these scenarios in a Manufacturing Systems Automation laboratory class. This study examines students’ use of technology for learning compared to more traditional learning methods. Results suggest that there is more than one good way to learn.

Automated manufacturing systems, which is characterized by dynamics, concurrence and synchronization, is a Hybrid dynamic system involving discrete and continuous behaviors. The static attribute and the dynamic actions of automated manufacturing system can be modeled through hybrid Petri net. This paper describes a hybrid Petri modeling for automated manufacturing systems, based hybrid Pertri nets, and capable of fault detection. A successful example of automatic manufacturing system is presented and analysis of the model is given using VisObjNet in this paper.

A flexible manufacturing system (FMS) due to its ability of being flexible in nature is concerned with automatic production of different parts in medium range. In short, it can be regarded as an automated manufacturing system. In this paper, an insight on previous work in the area of FMS modelling has been provided with an overview of research and development for better understanding of FMS. It serves as a medium for investigation of work that are accomplished by using different modelling techniques in FMS like mathematical, artificial intelligence, hierarchical, multi criteria decision-making method, Petri Nets and simulation. This paper will help researchers who are keen to do research in the area of FMS modelling, by highlighting contribution of available techniques in the field of FMS. It will also help them in deciding which modelling techniques can be used for a given problem. At last, comparison of different parameters considered in the recent papers of modelling FMS has been provided in the form of Table, along with a clear vision related to those works that still need to be investigated.

This paper studies the robust deadlock control issues in automated manufacturing systems (AMSs) with unreliable resources. The purpose of this paper is to synthesize a robust prevention supervisor to guarantee that the controlled system can operate smoothly when unreliable resources work well, and to ensure that parts that do not require any failed resources in their remaining routes can continue to be processed even if unreliable resources malfunction. In this paper, Petri nets (PNs) are employed to model the considered AMSs, which allow multi-quantity and multi-type of resource acquisitions. First, to avoid the resource’s underflow, a set of resource constraints denoted as a set of inequalities are developed based on the nominal capacity of shared resources and the minimal resource requirements of processes. Control places (monitors) are derived along with their control variables so as to resolve the blocking states caused by resource failures. Second, to guarantee the system’s liveness, a monitor is designed for each considered siphon in the different subnets derived from a system net. As a result, a robust prevention supervisor is synthesized for AMSs with unreliable resources. The effectiveness and superiority of our method are elucidated by some analyses and discussions.