Abstract
The divide and conquer strategy in this paper is used to investigate the deadlock prevention of the AMS modeled by Resource-oriented Petri net when multitype resources are introduced. Based ...on the production process circuits, the plant ROPN model is divided into an idle subnet, an autonomous subnet, and some independent topologies. By adding liveness enforcing controllers to each topology, deadlock-free AMS can be achieved. It is shown that if the ROPN satisfies the separation condition, the computational effort of the controller will be greatly reduced. The proposed method is illustrated with the large AMS example.
In this paper, we consider the on-line estimation of current subsequences for Partially Observable P-time Petri Nets and their starting markings on a sliding horizon composed of steps defined by two ...successive occurrences of observable transition firings. We propose a general strategy composed of two phases: Phase 1 exploits a simplification of the P-time Petri net under the form of a Timed Petri net; considering a candidate count vector and the relevant starting marking proposed at Phase 1, Phase 2 makes a schedulability analysis by building a system of relations which can be represented by an acyclic conflict-free computation graph. The complete approach avoids the generation of sets which is generally time and space consuming, and provides an optimal solution for each subproblem by using efficient standard tools.
A discrete event system is said to be critically observable if the observer can always determine whether the current state necessarily belongs to a set of critical states. This paper focuses on two ...issues related to the safety and security of discrete event systems, namely critical observability verification and enforcement of labeled Petri nets. First, given a bounded net, we verify its critical observability by using basis markings and solving some integer linear programming problems, thus avoiding the enumeration of the full state space of a net system. Moreover, for a non-critically observable net system, we obtain a feasible stop-free event set from a twin basis reachability graph such that a valid control policy can be always found, if the feasible stop-free event set is non-empty. Finally, according to the feasible stop-free event set, a set of disabled edges is generated, and an online control policy is developed based on the supervisory control theory, which guarantees that the closed-loop system is critically observable and deadlock-free.
This article investigates the enforcement of generalized mutual exclusion constraints (GMECs) and deadlock-freeness on a time Petri net (TPN) system with uncontrollable transitions, motivated by the ...fact that the existing methods enforcing GMECs may degrade the performance of a closed-loop system and lead to deadlock states. A supervisor enforcing a set of GMECs and deadlock-freeness on an underlying untimed Petri net system is assumed to be available. By exploiting timing information and mathematical programming, a control function is designed to restrict the firing intervals of transitions such that a TPN system can avoid entering forbidden states. The key idea behind the proposed approach is the online computation of a graph, called reduced modified state class graph (RMSCG), that is an extension of the partial modified state class graph recently introduced by the authors. Based on the RMSCG, an online control synthesis procedure is developed, which can enforce the originally given GMECs and deadlock-freeness in a maximally permissive way.
Proportions of web users are becoming more and more. To secure their information they create their own login identification and password. Secret word confirmation is a cycle that includes a client ...contributing an ID and key that is then checked against certifications. They are probably been approached to make or potentially enter a secret key to access an individual record, regardless of whether that is a web-based portal or applications. In general the password will be in the form of string with the characters. Securing the information has become a challenging factor for web users. When the user creates a highly secured password it takes time for the hackers to crack it with the help of available tools. Cracking the password has created a serious challenge to the users to provide a highly secured password. Many authentication methods have been proposed to secure their data. Password authentication using Petri nets, Colored Petri nets have been used to create a secured login password. In this paper, we proposed and developed the application of Interval Timed colored Petri nets to generate password which will be more secured. This research work provides a new platform for the web users to create a matrix type password in a secured way. This helps them to secure their information more than ever before. To create this matrix type password, applications of Interval Timed colored Petri nets are used.
•To secure their information they create their own login identification and password.•To improve the information and web security.•To create matrix type of password using Interval Timed Colored Petri nets.
This work studies the scheduling problem of a single-arm multicluster tool with a linear topology and process-bound bottleneck individual tool. The objective is to find a one-wafer cyclic schedule ...such that the lower bound of cycle time is reached by optimally configuring spaces in buffering modules that link individual cluster tools. A Petri net (PN) model is developed to describe the dynamic behavior of the system by extending resource-oriented PNs such that a schedule can be parameterized by robots' waiting time. Based on this model, conditions are presented under which a one-wafer cyclic schedule with the lower bound of cycle time can be found. With the derived conditions, an algorithm is developed to find such a schedule and optimally configure buffer spaces. The algorithm requires only simple calculation to set the robots' waiting time and buffer size. Illustrative examples are presented to demonstrate the proposed method.
We address a robotic flow shop scheduling problem where two part types are processed on each given set of dedicated machines. A single robot moving on a fixed rail transports one part at a time, and ...the processing times of the parts vary on the machines within a given time interval. We use a reinforcement learning (RL) approach to obtain efficient robot task sequences to minimise makespan. We model the problem with a Petri net used for a RLenvironment and develop a lower bound for the makespan. We then define states, actions, and rewards based on the Petri net model; further, we show that the RL approach works better than the first-in-first-out (FIFO) rule and the reverse sequence (RS), which is extensively used for cyclic scheduling of a robotic flow shop; moreover, the gap between the makespan from the proposed algorithm and a lower bound is not large; finally, the makespan from the RL method is compared to an optimal solution in a relaxed problem. This research shows the applicability of RL for the scheduling of robotic flow shops and its efficiency by comparing it to FIFO, RS and a lower bound. This work can be easily extended to several other variants of robotic flow shop scheduling problems.
Time-triggered (TT) network provides a low-cost service to meet the strong demand of modern industry networks for real-time communication. Both simulation and reachability analysis provide effective ...research methods for TT networks. This article presents a verification framework for the TT network based on timed colored Petri nets (TCPNs). We propose an automatic formal modeling method for the behavior of message transmissions in the TT network. We harness timed multisets of TCPN to model and analyze TT message transmission latencies. For a holistic system evaluation, we characterize the critical system properties, such as boundedness and liveness. We substantiate the properties by the reachability analysis. We demonstrate the effectiveness through a case study by simulating the message transmission and reachability analysis in the state space. Finally, we analyze the influencing factors of the state space in the automotive scenario. The proposed automatic modeling method can effectively reduce the state space scale.
This paper deals with the enforcement of generalized mutual exclusion constraints (GMECs) on time Petri nets (TPNs) with uncontrollable transitions by restricting the firing intervals of controllable ...transitions. Existing approaches do not exploit the timing information and consequently the system permissiveness is limited. The key idea behind the proposed approach is the online computation of a graph representing a reduced portion of the state space of a TPN system, and precisely the states that can be reached from the current one by firing only uncontrollable transitions. Such a graph is called partial modified state class graph (PMSCG) and is derived from another graph recently presented in the literature. Based on the PMSCG, a procedure to compute a supervisory control law enforcing a GMEC on a TPN system in a maximally permissive way is presented.
This article proposes a risk assessment method based on interval intuitionistic integrated cloud Petri net (IIICPN). The cloud model is widely used in data mining and knowledge discovery, especially ...in risk assessment problems with linguistic variables. However, the cloud models proposed in the literature do not express interval-valued intuitionistic linguistic satisfactorily, and the reasoning methods based on the cloud models cannot perform risk assessment well. The work in this article includes the definition of IIIC and IIICPN, the method of converting the interval-valued intuitionistic uncertain linguistic numbers into IIIC, and the reasoning method of IIICPN. As proofs, a subway fire accident model is adopted to confirm the feasibility of the proposed method, and comparison experiments between the IIICPN with general fuzzy Petri net and the trapezium cloud model are conducted to verify the superiority of the proposed model. Note to Practitioners -This work deals with the subway fire risk assessment problem. It proposes a cloud model based on interval-valued intuitionistic uncertain linguistic and builds a cloud-based Petri net model. The methods of fire risk assessment use the existing fault trees or aggregation operators to combine all the factors into consideration, but they do not take the interaction of factors. The goal of this work is to assess the risk of subway fire accident of subway, using fuzzy linguistic decision variables. The simulation results indicate that the proposed method is highly effective. The obtained results can help assessors better determine which factors may cause the disaster.
