Modelling automated manufacturing systems using a modification of coloured petri nets

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.

Reliability modeling and deadlock control have become important issues in automated manufacturing systems (AMSs) with reliable and unreliable resources. Therefore, this paper develops a reliability modelling approach and deadlock control based on colored resource-oriented timed Petri net (CROTPN) and neural networks to find crucial reliability measures in AMSs. In the first step, a CROTPN with considering resource failures is developed to obtain "sufficient and necessary conditions" for the CROTPN liveness. In the second step, a fault diagnosis and treatment approach is proposed that integrates the obtained unreliable net with neural networks to ensure that the system is reliable. Furthermore, a neural unreliable CROTPN is used to analyze the system reliability. A simulation is carried out to illustrate the approach and compare the results to those found in the literature. The developed approach has been proved to be simpler in structure and can solve the deadlock problem and model AMS reliability.

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

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.

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.

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.

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.

The context of our work is the complex systems simulation. Complex systems modelling and simulation require to take into account the interactions between the different components. For instance, an airport ground traffic simulation requires to model the planes with the pilots, the control tower, the

With the aim of solving the problems of the Petri nets to the place/transition nets automatic conversion and realization of Petri nets parallel control and running, the algorithm is proposed to transform Color Petri net systems transform into P/T nets. The algebraic model of colored Petri nets and P/T nets, and its intrinsic mechanism is analyzed, the process and theory verification of the colored Petri nets into P/T nets are given. The colored Petri nets into P/T network algorithm is proposed, through the network model of formal, colored Petri nets correlation matrix pretreatment. Experimental results show that it is an effective method to solve Color Petri Net systems transform into P/T nets, lay the foundation for various senior Petri nets system transformation into P/T nets and achieve the parallelism and simulation of running.

We propose rewriting logic as a unifying framework for a wide range of nets models. We treat in detail place/transition nets and important extensions of the basic model by individual tokens, test arcs, and time. Based on the idea that Petri nets are monoids suggested by Meseguer and Montanari we define a rewriting semantics that maps place/transition nets into rewriting logic specifications. We furthermore generalize this result to a general form of algebraic net specifications subsuming also colored nets as a special case. The soundness and completeness results we state relate the commutative process semantics of nets proposed by Best and Devillers to the model-theoretic semantics of rewriting logic in the sense of natural isomorphisms between suitable functors. In addition we show how place/transition nets with test arcs and timed nets can be equipped with a rewriting semantics and discuss how other extensions can be treated along similar lines. Beyond the conceptual unification of quite different kinds of nets within a single framework, the rewriting semantics can provide a guide for future extensions of nets and help to cope with the growing diversity of models in this field. On the practical side, a major application of the rewriting semantics is its use as a logical and operational representation of net models for formal verification and for the efficient execution and analysis using a rewriting engine such as Maude, which also allows us to specify different execution and analysis strategies in the same rewriting logic language by means of reflection.

In Hu (Transactions of the Institute of Measurement and Control 33:59–76, 2011), Petri nets are utilized to describe, analyse and control automated manufacturing systems (AMS). In order to suppress deadlock occurrences in AMS, a method to derive the bad markings iteratively using a mixed integer programming-based algorithm is proposed. To validate the effectiveness and efficiency of the proposed approach, two examples were demonstrated in Hu (Transactions of the Institute of Measurement and Control 33:59–76, 2011). This paper shows that the uncontrolled Petri net model in one of the examples is incorrect. It is also shown that the structural complexity of the computed monitors for both examples can be reduced with the same or more permissive system behaviours.

Specification and properties of a cache coherence protocol model.- GAMERU: A language for the analysis and design of human communication pragmatics within organizational systems.- Recent results on the complexity of problems related to Petri nets.- Algebraic structure of flows of a regular coloured net.- On equivalent execution semantics of concurrent systems.- Mathematical methods for calculating invariants in Petri nets.- On Petri nets with deterministic and exponentially distributed firing times.- An accurate performance model of CSMA/CD bus LAN.- Petri net models for the ?-calculus.- Fair processes.- Operational Petri net semantics for CCSP.- Infinitary languages of Petri nets and logical sentences.- A strong part of concurrency.- Concurrency and continuity.- Parallel systems specifications with coloured Petri nets and algebraic specifications.- Bibliography of Petri nets.

As automated manufacturing systems become more complex, the need for an effective design tool to produce both high-level discrete event control systems (DECS) and low-level implementations becomes more important. Petri nets represent the most effective method for both the design and implementation of DECSs. In this paper, automation Petri nets (APN) are introduced to provide a new method for the design and implementation of DECSs. The APN is particularly well suited to multiproduct systems and provides a more effective solution than Grafcet in this context. Since ordinary Petri nets do not deal with sensors and actuators of DECSs, the Petri net concepts are extended, by including actions and sensor readings as formal structures within the APN. Moreover, enabling and inhibitor arcs, which can enable or disable transitions through the use of leading-edge, falling-edge and level of markings, are also introduced. In this paper, the methodology is explained by considering a fundamental APN structure. The conversion of APNs into the IEC1131-3 ladder diagrams (LD) for implementation on a PLC is also explained by using the token passing logic (TPL) concept. Finally, an illustrative example of how APNs can be applied to a discrete manufacturing problem is described in detail.

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.

As more and more producers move to use flexible and agile manufacturing as a way to keep them with a competitive edge, the investigations on deadlock resolution in automated manufacturing have received significant attention for a decade. Deadlock and related blocking phenomena often lead to catastrophic results in automated manufacturing systems. Their efficient handling becomes a necessary condition for a system to gain high productivity. This paper intends to present a tutorial survey of state-of-the art modeling and deadlock control methods for discrete manufacturing systems. It presents the updated results in the areas of deadlock prevention, detection and recovery, and avoidance. It focuses on three modeling methods: digraphs, automata, and Petri nets. Moreover, for each approach, the main and relevant contributions are selected enlightening pros and cons. The paper concludes with the future research needs in this important area in order to bridge the gap between the academic research and industrial needs.