基于.Net的System._ComObject类型辨析

针对在.NET平台下对COM组件进行交互编程时,遇到调用函数返回值的类型是System._ComObject而无法得到其真正类型的问题,以.NET框架与COM接口之间的通讯机制为出发点,研究和总结了System._ComObject产生的原因,最后给出了解决办法和应用实例。

Optimal deadlock avoidance Petri net supervisors for automated manufacturing systems

Deadlock avoidance problems are investigated for automated manufacturing systems with flexible routings. Based on the Petri net models of the systems, this paper proposes, for the first time, the concept of perfect maximal resourcetransition circuits and their saturated states. The concept facilitates the development of system liveness characterization and deadlock avoidance Petri net supervisors. Deadlock is characterized as some perfect maximal resource-transition circuits reaching their saturated states. For a large class of manufacturing systems, which do not contain center resources, the optimal deadlock avoidance Petri net supervisors are presented. For a general manufacturing system, a method is proposed for reducing the system Petri net model so that the reduced model does not contain center resources and, hence, has optimal deadlock avoidance Petri net supervisor. The controlled reduced Petri net model can then be used as the liveness supervisor of the system.

Modeling and Analysis of Logistics System Based on Stochastic Petri Net under Supply Chain Circumstances

In order to describe the impacts of adjustment ability of logistics system on the profit and cost of logistics system, we constructed a model of logistics system based on stochastic Petri net （ SPN）, and proposed a theorem for the adjustment ability of logistics system under supply chain circumstances on condition that the payoff of supply chain is a steadily increasing process. Then we put forward that a sequence of MGF （ moment generating function ） of out-of-goods risk process for logistics system is a martingale. The model we proposed can overcome shortcomings of the previous ones that can not describe the characteristics of the adjustment ability of logistics system. The results of simulation experiments are consistent with theoretical analysis.

Liveness Problem of Petri Nets Supervisory Control Theory for Discrete Event Systems

A quite great progress of the supervisory control theory for discrete event systems (DES)has been made in the past nearly twenty years, and now, automata, formal language and Petri nets become the main research tools. This paper focus on the Petri nets based supervisory control theory of DES. Firstly, we review the research results in this field, and claim that there generally exists a problem in Petri nets based supervisory control theory of DES, that is, the deadlock caused by the controller introduced to enforce the given specification occurs in the closed-loop systems, especially the deadlock occurs in the closed-loop system in which the original plant is live. Finally, a possible research direction is presented for the solution of this problem.

Reliability Modeling of Phased Mission System with Phase Backup by Stochastic Petri Net

This paper presents a modeling method by stochastic Petri net for reliability analysis of phased mission system( PMS) with phase backup. The model consisting of petri nets,depicts the system behaviors of unit level,system logic level and phase level. Guard functions of petri nets are used to avoid modeling complexity and make the model flexible to different reliability logical structures. It was shown that the time redundancy within phase and from phase backup for PMS can both be described by use of the proposed model.

A Method for Modeling the Virtual Instrument Automatic Test System Based on the Petri Net

Virtual instrument is playing the important role in automatic test system. This paper introduces a composition of a virtual instrument automatic test system and takes the VXIbus based a test software platform which is developed by CAT lab of the UESTC as an example. Then a method to model this system based on Petri net is proposed. Through this method, we can analyze the test task scheduling to prevent the deadlock or resources conflict. At last, this paper analyzes the feasibility of this method.

Application of the Constrained Predicated Nets and Interval Logic to Production Systems

A method to model and analyze the hybrid systems is presented. The time to be considered in the plant is taken as an explicit parameter through the constrained predicated net (CPN). The CPN's basic structure is a Petri net with predicated transition. All components of the net are expressed by annotation which is defined on rational set Q. The analysis method for the plant is interval temporal logic represented by Petri nets. This paper combines the above two methods to synthesize the hybrid system, gives a simple and clear expression of the expected action of the studied plant.

Study on Guidance Law of UAV Net Recovery System

The design and realization of a net recovery system is introduced, which can recover UAV (unmanned aerial vehicle) reliably and safely. The mathematical model is built, and the horizontal and vertical guidance law is studied based on the aerodynamic parameters and actual flying trial data of a certain UAV. The simulation result shows that this system can realize the recovery safely, stably and accurately.

A Study on Reliability of Manufacturing System Based on Petri Net

Petri net has been used in system modeling and analyzing in many practical systems, but the system reliability has never been considered before, that is, system modeling and analysis were done based on supposing that there were no faults and no need to repair in system resources (equipment). Actually, a practical system is often at fault and needs repairs, so Petri net model does not really represent the action of the system to a certain extent. In this paper, theory of reliability is introduced to Petri net, Petri net model of repairable system is built, and the analysis method of system model is given. The importance is illustrated by imitating a product system.

Feasibility Study of Installing Rooftop PV System with Net-Metering Scheme in Iraq

Renewable energy, particularly solar energy, offers a clean and alternative energy source to meet the energy demand for sustainable development in the world. Due to its profitability and viability, PV net-metering scheme has been adopted in many countries. The feasibility of implementation PV rooftop system with net metering in residential, commercial, governmental and industrial sectors in Iraq is demonstrated in this study. A financial model has been developed to investigate the feasibility parameters NPV, IRR and annual savings of 24 kWp PV system. The results showed that increasing the capacity of the PV system in residential and commercial buildings will lead to a profitable investment return and the breakeven point that may make the PV net-metering projects feasible is very close to the tariff applied for the commercial sector (10.29 $c/kWh). In the governmental sector, the tariff needs to increase by 35.1% to reach breakeven. However, for such net-metering scheme to be attractive and feasible on a wide scale, it is crucial to back it with financial support through soft loans and grants.

Research of the Streaming Media System Architecture Based on Net-RAID

In the typical streaming media system, the streaming media server is system bottleneck with the expansion of Internet subscribers. This paper proposes an innovational high performance streaming media system architecture (HPSMS) based on the logical separation of streaming media transport protocol. The system avoids expensive store-and-forward data copies between streaming media server and storage devices, improves the system performance greatly. The system bandwidth continuously increases with the expansion of storage system capacity is the highlight. The performance of the proposed HPSMS is evaluated through a practical prototype implementation.

STOCHASTIC OBJECT-ORIENTED PETRI NETS (SOPNS) AND ITS APPLICATION IN MODELING OF MANUFACTURING SYSTEM RELIABILITY

Object-oriented Petri nets (OPNs) is extended into stochastic object-oriented Petri nets (SOPNs) by associating the OPN of an object with stochastic transitions and introducing stochastic places. The stochastic transition of the SOPNs of a production resources can be used to model its reliability, while the SOPN of a production resource can describe its performance with reliability considered. The SOPN model of a case production system is built to illustrate the relationship between the system's performances and the failures of individual production resources.

Hybrid Petri Nets for Modeling and Analysis of Microgrid Systems

Hybrid Petri nets(HPNs) are widely used to describe and analyze various industrial hybrid systems that have both discrete-event and continuous discrete-time behaviors. Recently,many researchers attempt to utilize them to characterize power and energy systems. This work proposes to adopt an HPN to model and analyze a microgrid that consists of green energy sources. A reachability graph for such a model is generated and used to analyze the system properties.

Adaptive coupled synchronization of non-autonomous systems in ring networks

The adaptive coupled synchronization method for non-autonomous systems is proposed. This method can avoid estimating the value of coupling coefficient. Under the uniform Lipschitz assumption, we derive the asymptotical synchronization for a general coupling ring network with N identical non-autonomous systems~ even when N is large enough. Strict theoretical proofs are given. Numerical simulations illustrate the effectiveness of the present method.

Discrete Event Net Based Modeling and Control System Design for Real-Time Concurrent Control of Multiple Robot Systems

This paper deals with control system design and implementation problems encountered in multiple robot systems. The methodology developed is depicted by a set of coordination mechanisms using hierarchical net structures and their accompanying rules. With the net models, the hierarchical and distributed control system is designed for an assembly task. Synchronization commands allow coordination of the movements of the robots. The net models make concurrency of the movements of the robots transparent to users. The net based machine controller executes robot motion control through the communication with the external robot controller using the command/response concept. Sensory signals indicating the change of state of robots are used to trigger or initiate tasks. Simultaneous movement of the robots is obtained by creating different background threads running in parallel under Windows OS. The multilevel hierarchical control system can be consistently constructed using net models.

Petri net model for diagnosis of permanent faults of a hydraulic system

Petri net model is applied to diagnose the permanent fault of hydraulic system within the framework of interpreted Petri net. The permanent fault is described as redundant structure of the model. A definition and a theorem are proposed to determine the diagnosability of the hydraulic system. The relations bwtween the diagnosability and other structure properties are also discussed. An example of actual hydraulic system is presented and its permanent fault can be diagnosed by the proposed method efficiently.

Reconfiguration Cost Analysis Based on PetriNet for Manufacturing System

Nowadays, manufacturers are faced with severe challenges to response rapidly to changing demands and meet various customers’ needs with respect to production volume and product profile. Reconfigurable manufacturing paradigm was proposed as an advanced manufacturing philosophy to enhance the adaptability and flexibility of manufacturing sys-tems. By physical and logical reconfiguration, Reconfigurable Manufacturing System (RMS) is able to fulfil customers’ needs in a cost-effective way by making full use of the resources currently available. This paper focuses on studying of reconfiguration cost of such systems. In this paper, DEDS modelling method Petri Net is used to construct the model for reconfiguration process of RMS which includes physical reconfiguration cost factors and conjunction matrix is used to describe the production processes. By highlighting the differences in the process set before and after reconfiguration, the reconfiguration principles have been proposed to describe and guide the process of the manufacturing system re-configuration. The simulation example is given to prove the validation of the proposed model.

Deadlock-free dynamic resource assignment in multi-robot systems with multiple missions:application in wireless sensor networks

In unstructured environments, dynamic resource assignment is required for effective cooperation of robot teams. In some scenarios, robots are in charge of executing multiple missions simultaneously. This creates risks of deadlock due to the presence of shared resources among various missions. The main contribution of this paper is the development of a novel approach that combines the one-step look-ahead deadlock avoidance policy with dynamic resource assignment. The dynamicresource assignment is achieved using greedy resource assignment for multi-mission robot teams in the framework of a matrix-based discrete event controller. Simulation results are presented in MATLAB to discuss in detail the proposed control strategy. The paper also discusses the toolkit developed in LabVIEW which is used to implement this control framework using a suitable example.

A New Formalism for Modeling a Multi Agent Systems: Agent Petri Nets

In this paper, we present a new formalism for Modeling Multi Agent Systems (MAS). Our model based a PN is able to describe not only not the internal state of each agent modeled but also its behavior. Owing to these features, one can model naturally the dynamic behavior of complex systems and the communication between these entities. For this, we propose mathematical definitions attached to firing transitions. To validate our contribution, we will deal with real examples.

The Relation between the Stabilization Problem for Discrete Event Systems Modeled with Timed Petri Nets via Lyapunov Methods and Max-Plus Algebra

A discrete event system is a dynamical system whose state evolves in time by the occurrence of events at possibly irregular time intervals. Timed Petri nets are a graphical and mathematical modeling tool applicable to discrete event systems in order to represent its states evolution where the timing at which the state changes is taken into consideration. One of the most important performance issues to be considered in a discrete event system is its stability. Lyapunov theory provides the required tools needed to aboard the stability and stabilization problems for discrete event systems modeled with timed Petri nets whose mathematical model is given in terms of difference equations. By proving stability one guarantees a bound on the discrete event systems state dynamics. When the system is unstable, a sufficient condition to stabilize the system is given. It is shown that it is possible to restrict the discrete event systems state space in such a way that boundedness is achieved. However, the restriction is not numerically precisely known. This inconvenience is overcome by considering a specific recurrence equation, in the max-plus algebra, which is assigned to the timed Petri net graphical model.