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Petri Nets (petri + net)
Kinds of Petri Nets Selected AbstractsGeneralized state equation of Petri Nets with priorityINTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 11 2003Gi Bum Lee This article presents a new way of generating a generalized state equation that is useful for analyzing the token flow of the Petri Net (PN) with priority. The transition values in the firing vector as used in the conventional state equation are replaced with transition variables, which are generated by multiplying a series of firing condition functions taking the weighted inhibitor arc into account. The actual value of a transition variable is determined by taking priority and the present marking into account. The proposed state equation generalizes the conventional one by using the transition variable form and by containing the formulation of priority. Given the initial marking, the subsequent marking evolution can be determined successively from the generalized state equation as the simultaneous firings occur. A PN with deadlock is analyzed as an example to establish the validity of the generalized state equation. © 2003 Wiley Periodicals, Inc. [source] A comparative simulation study of work processes in autonomous production cellsHUMAN FACTORS AND ERGONOMICS IN MANUFACTURING & SERVICE INDUSTRIES, Issue 1 2002Christopher Schlick An approach to human-centered design and assessment of work processes in flexible manufacturing systems with the help of dynamic task networks is presented. To model and simulate the task networks, the method of timed colored Petri Nets is used. Two task networks are developed. The first task network is a model of work processes in Autonomous Production Cells (APCs). The second task network represents work processes in conventional Computer Numerically Controlled (CNC)-based manufacturing systems. The material processing technology is associated with 5-axis milling. The values of attributes of task elements were acquired empirically on a fine-grained level with reference to a sample milling order. Comparative hypotheses regarding time-on-task, supervisory control functions, levels of cognitive control, human error (HE), and labor division were then formulated. To test these hypotheses, several simulation experiments were conducted. The results from inferential statistics show that single-operator APCs have a 30% higher efficiency in relation to total time-on-task. Moreover, the level of cognitive control is significantly shifted toward rule- and knowledge-based behavior. Surprisingly, the simulation of minor HE does not demonstrate a significantly worse performance from APCs. A simulated labor division among central process planner and production operator allows an additional efficiency improvement of approximately 15%. However, the labor division has two important drawbacks: first, a sequential incompleteness of operators' task spectrum occurs; second, the operator has to cope with hierarchical task incompleteness. Finally, a sensitivity analysis was carried out to investigate the effects of varying lot sizes and number of processed orders. © 2002 John Wiley & Sons, Inc. [source] Generalized state equation of Petri Nets with priorityINTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 11 2003Gi Bum Lee This article presents a new way of generating a generalized state equation that is useful for analyzing the token flow of the Petri Net (PN) with priority. The transition values in the firing vector as used in the conventional state equation are replaced with transition variables, which are generated by multiplying a series of firing condition functions taking the weighted inhibitor arc into account. The actual value of a transition variable is determined by taking priority and the present marking into account. The proposed state equation generalizes the conventional one by using the transition variable form and by containing the formulation of priority. Given the initial marking, the subsequent marking evolution can be determined successively from the generalized state equation as the simultaneous firings occur. A PN with deadlock is analyzed as an example to establish the validity of the generalized state equation. © 2003 Wiley Periodicals, Inc. [source] Special issue on "Petri Nets for system control and automation"ASIAN JOURNAL OF CONTROL, Issue 3 2010MengChu Zhou Guest Editor No abstract is available for this article. [source] A reference model for grid architectures and its validationCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 11 2010Wil van der Aalst Abstract Computing and data-intensive applications in physics, medicine, biology, graphics, and business intelligence require large and distributed infrastructures to address the challenges of the present and the future. For example, process mining applications are faced with terrabytes of event data and computationally expensive algorithms. Computer grids are increasingly being used to deal with such challenges. However, grid computing is often approached in an ad hoc and engineering-like manner. Despite the availability of many software packages for grid applications, a good conceptual model of the grid is missing. This paper provides a formal description of the grid in terms of a colored Petri net (CPN). This CPN can be seen as a reference model for grids as it clarifies the basic concepts at the conceptual level. Moreover, the CPN allows for various kinds of analyses ranging from verification to performance analysis. We validate our model based on real-life experiments using a testbed grid architecture available in our group and we show how the model can be used for the estimation of throughput times for scientific workflows. Copyright © 2009 John Wiley & Sons, Ltd. [source] Two-dimensional occluded object matching using petri netsINTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 3 2002Chuan Zhou This article discusses the use of Petri nets to model the process of object matching between an image and a model under different two-dimensional geometric transformations. This transformation finds its applications in sensor-based robot control, flexible manufacturing systems, industrial inspection, and so on. Its topological structure relation, called point-line relation structure (PLRS), presents a Petri net-based description approach for object structure. It has been shown how Petri nets can be used to model the matching process, and an optimal or near optimal matching can be obtained by tracking the reachability graph of the net. The experiment result shows that objects can be successfully identified and located under two-dimensional transformation such as translations, rotations, scale changes, and distortions due to partial object occlusion. © 2002 Wiley Periodicals, Inc. [source] Performance evaluation on a double-layered satellite networkINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 6 2005Feng-Ge Wu Abstract How to evaluate the performance of satellite networks is a prerequisite to the construction of satellite networks, and is also one of challenges in the researches on satellite networks. In this paper, generalized stochastic Petri net (GSPN) models are presented to carry out the performance analysis of a double-layered satellite network. Firstly, the GSPN model of a double-layered satellite network is simplified by proper analysis. Then, two sets of experiments are conducted to analyse the performance of the satellite networks, and show that the double-layered satellite network outperforms single-layered ones on the heavy traffic load. Finally, the feasibility and effectiveness of the proposed approach is verified by simulation experiments. Copyright © 2005 John Wiley & Sons, Ltd. [source] A Petri Net Approach to Remote Diagnosis for Failures of Cardiac PacemakersQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 8 2004S. K. Yang Abstract This paper describes the application of Petri nets to remote diagnosis for failures of cardiac pacemakers. The operations, structures and basic control methods of the different types of cardiac pacemakers are first described. A combined synchronous pacemaker is modeled into a Petri net in this study. Twelve checkpoints are added into the modeled Petri net so as to construct a Petri net for failure diagnosis. A remote mode for failure diagnosis of implanted pacemakers is also designed by the Petri net approach. A low-power transmitter transmits a checking-code with 12 digits from the implanted pacemaker to the outside of the patient's body manually or automatically. By observing the markings of the checking code, the working status and the health condition of the pacemaker are clear at a glance. Applications of the Petri net method for failure diagnosis and control optimization are discussed. Copyright © 2004 John Wiley & Sons, Ltd. [source] Colored timed Petri nets for modeling and analysis of cluser tools,ASIAN JOURNAL OF CONTROL, Issue 3 2010NaiQi Wu Abstract In this paper, a colored timed resource-oriented Petri net (CTROPN) is developed to model the cluster tools in semiconductor fabrication. It is structurally simple and concise, since each module in a cluster tool corresponds to a unique place in CTROPN. It is also powerful in modeling the qualitative and temporal behavior of the cluster tools with a single-blade or dual-blade robot. The initial transient behavior, steady-state behavior and the final transient behavior can all be investigated through a single model. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] Synthesis of deadlock prevention policy using Petri nets reachability graph technique,ASIAN JOURNAL OF CONTROL, Issue 3 2010Yi-Sheng Huang Abstract This paper proposes a subclass of generalized stochastic Petri net (GSPN) model, called TS3PR, which is modified the systems of simple sequential processes with resources (S3PR) with timed information. Based on the subclass of GSPN, a new deadlock prevention policy is developed by using reachability graph technique. The foundation of the new control policy is to manipulate all the dead states of the system nets. This study is able to change dead states into vanishing ones by additional immediate transitions. A live TS3PR model can then be obtained. It is worthwhile to notice that this study is different from adding additional control place policies in previous literature. Experimental results, indicate that our new control policy is with maximally permissive markings than conventional place-control ones. As a result, we can infer that our proposed control policy seems to be used in Petri nets deadlocked systems. To our knowledge, this is the first work that employs the additional transitions to obtain the deadlock prevention policy. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] A deadlock prevention approach for a class of timed Petri nets using elementary siphons,ASIAN JOURNAL OF CONTROL, Issue 3 2010Jinwei Guo Abstract To solve the problem of deadlock prevention for timed Petri nets, an effective deadlock prevention policy based on elementary siphons is proposed in this paper. Without enumerating reachable markings, deadlock prevention is achieved by adding monitors for elementary siphons, increasing control depth variables when necessary, and removing implicit, liveness-restricted and redundant control places. The final supervisor is live. First, a timed Petri net is stretched into a stretched Petri net (SPN). Unchanging the system performance, each transition in the SPN has a unit delay time. Then the siphon-control-based approach is applied. Monitors computed according to the marking constraints are added to the SPN model to ensure all strict minimal siphons in the net invariant-controlled. A liveness-enforcing supervisor with simple structure can be obtained by reverting the SPN into a TdPN. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] Improved controllability test for dependent siphons in S3PR based on elementary siphonsASIAN JOURNAL OF CONTROL, Issue 3 2010Daniel Y. Chao Abstract When siphons in a flexible manufacturing system (FMS) modeled by an ordinary Petri net (OPN) become unmarked, the net gets deadlocked. To prevent deadlocks, some control places and related arcs are added to strict minimal siphons (SMS) so that no siphon can be emptied. For large systems, it is infeasible to add a monitor to every SMS since the number of SMS or control elements grows exponentially with respect to the size of a Petri net. To tackle this problem, Li and Zhou propose to add control nodes and arcs for only elementary siphons. The rest of siphons, called dependent ones, may be controlled by adjusting control depth variables of elementary siphons associated with a dependent siphon after the failure of two tests. First, they test a Marking Linear Inequality (MLI); if it fails, then they perform a Linear Integer Programming (LIP) test which is an NP-hard problem. This implies that the MLI test is only sufficient, but not necessary. We propose a sufficient and necessary test for adjusting control depth variables in an S3PR to avoid the sufficient-only time-consuming linear integer programming (LIP) test (NP-complete problem) required previously for some cases. We theoretically prove the following: i) no need for LIP test for Type II siphons; and ii) Type I strongly n-dependent (n>2) siphons being always marked. As a result, the total time complexity to check controllability of all strongly dependent siphons is no longer exponential but reduced to linear if all siphons are of Type I. The total time complexity is O(|,E||,D|) (order of the product of total number of elementary siphons and total number of dependent siphons) if all siphons are of Type II. A well-known S3PR example has been illustrated to show the advantages. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] A Possibilistic Petri Net Model for Diagnosing Cracks in RC StructuresCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 6 2003Kevin F. R. Liu PPN integrates Petri nets with possibilistic reasoning and maintains the advantages of both formalisms. Two major features of PPN include the possibilistic token to carry information to describe an object and its corresponding possibility and necessity measures, and four types of possibilistic transitions,inference, duplication, aggregation, and aggregation-duplication. A reasoning algorithm, based on possibilistic Petri nets, is also developed to execute PPN. The PPN model and the reasoning algorithm are further used to diagnose possible causes of cracking in RC structures, and three basic cases are considered to demonstrate the applicability of the approach. The reliability of the results is increased by explaining the diagnostic process through the movement of tokens. Moreover, the confidence level associated with each possible cause of concrete cracking can be used to determine the relevance of the diagnosis. [source] Context-aware environments: from specification to implementationEXPERT SYSTEMS, Issue 5 2007Patrick Reignier Abstract: This paper deals with the problem of implementing a context model for a smart environment. The problem has already been addressed several times using many different data- or problem-driven methods. In order to separate the modelling phase from implementation, we first represent the context model by a network of situations. Then, different implementations can be automatically generated from this context model depending on user needs and underlying perceptual components. Two different implementations are proposed in this paper: a deterministic one based on Petri nets and a probabilistic one based on hidden Markov models. Both implementations are illustrated and applied to real-world problems. [source] Petri net model of protocol conversion for CTF service: its universal coupling criteria and property analysisINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 5 2007Xiaomin Zhu Abstract Protocol conversion is a critical issue requiring much research attention. In this paper, the protocol conversion methodology proposed originally by Green is extended with the Petri nets theory to study application layer protocol conversion among more than two interfaces. The click-to-fax (CTF) service based on the Internet intelligent network (IIN) model is taken as an example to illustrate the extended part. A two-step Petri net modelling method is proposed, which is easier compared to constructing the overall model directly in just one step. Universal coupling criteria of Petri net model of protocol conversion (PNPC) are abstracted. The PNPC of CTF service is analysed using analytical techniques of Petri nets, which are proved to be effective in finding and eliminating potential bugs. The necessity of the concept of service layer is also emphasized. Copyright © 2006 John Wiley & Sons, Ltd. [source] Two-dimensional occluded object matching using petri netsINTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 3 2002Chuan Zhou This article discusses the use of Petri nets to model the process of object matching between an image and a model under different two-dimensional geometric transformations. This transformation finds its applications in sensor-based robot control, flexible manufacturing systems, industrial inspection, and so on. Its topological structure relation, called point-line relation structure (PLRS), presents a Petri net-based description approach for object structure. It has been shown how Petri nets can be used to model the matching process, and an optimal or near optimal matching can be obtained by tracking the reachability graph of the net. The experiment result shows that objects can be successfully identified and located under two-dimensional transformation such as translations, rotations, scale changes, and distortions due to partial object occlusion. © 2002 Wiley Periodicals, Inc. [source] A Petri Net Approach to Remote Diagnosis for Failures of Cardiac PacemakersQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 8 2004S. K. Yang Abstract This paper describes the application of Petri nets to remote diagnosis for failures of cardiac pacemakers. The operations, structures and basic control methods of the different types of cardiac pacemakers are first described. A combined synchronous pacemaker is modeled into a Petri net in this study. Twelve checkpoints are added into the modeled Petri net so as to construct a Petri net for failure diagnosis. A remote mode for failure diagnosis of implanted pacemakers is also designed by the Petri net approach. A low-power transmitter transmits a checking-code with 12 digits from the implanted pacemaker to the outside of the patient's body manually or automatically. By observing the markings of the checking code, the working status and the health condition of the pacemaker are clear at a glance. Applications of the Petri net method for failure diagnosis and control optimization are discussed. Copyright © 2004 John Wiley & Sons, Ltd. [source] Fault tolerant control design via hybrid petri nets,ASIAN JOURNAL OF CONTROL, Issue 5 2010Hao Yang Abstract This paper proposes a novel fault tolerant control (FTC) scheme for hybrid systems modeled by hybrid Petri nets (HPNs). The HPNs model consists of discrete and continuous PNs. The faults are represented by unobservable discrete transitions or the normal observable discrete transitions with abnormal firing time in discrete PNs. First, an observer-based fault diagnosis method is proposed to estimate the marking in discrete places with unknown initial marking and diagnose the faulty behavior simultaneously. Then, an adaptive fault tolerant controller is designed to maintain the general mutual exclusion constraints (GMEC) of discrete PNs, and a scheme that adjusts firing speeds of continuous transitions is provided to maintain the optimality of continuous PNs. Finally, an example of an intelligent transportation system consisting of automated vehicles on a bridge is included to demonstrate the effectiveness of our developed techniques. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] Design of liveness-enforcing supervisors via transforming plant petri net models of FMS,ASIAN JOURNAL OF CONTROL, Issue 3 2010Chun-Fu Zhong Abstract This paper focuses on the deadlock prevention problems in a class of Petri nets, systems of simple sequential process with resources, S3PR for short. By structure analysis, we propose an approach that can transform a plant net model into a weighted S3PR (WS3PR) that is behaviorally equivalent to the plant model. The WS3PR is made to be live by properly reconfiguring its weight distribution such that its all strict minimal siphons are self-max'-controlled. The resulting WS3PR can serve as a liveness-enforcing Petri net supervisor for the plant model after removing some idle and operation places. A live controlled system can be accordingly obtained by synchronizing a plant model and the places whose weights are regulated. This research shows that a small number of monitors is obtained, leading to more permissive behavior of the controlled system. Examples are used to demonstrate the proposed concepts and methods. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] Colored timed Petri nets for modeling and analysis of cluser tools,ASIAN JOURNAL OF CONTROL, Issue 3 2010NaiQi Wu Abstract In this paper, a colored timed resource-oriented Petri net (CTROPN) is developed to model the cluster tools in semiconductor fabrication. It is structurally simple and concise, since each module in a cluster tool corresponds to a unique place in CTROPN. It is also powerful in modeling the qualitative and temporal behavior of the cluster tools with a single-blade or dual-blade robot. The initial transient behavior, steady-state behavior and the final transient behavior can all be investigated through a single model. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] Process vs resource-oriented Petri net modeling of automated manufacturing systems,ASIAN JOURNAL OF CONTROL, Issue 3 2010NaiQi Wu Abstract 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 [source] A petri nets-based process planning system for wastewater treatment,ASIAN JOURNAL OF CONTROL, Issue 3 2010Albert W. L. Yao Abstract It is always challenging to simulate, debug or diagnose automated systems. The aim of this paper is to present the development of a convenient tool for reengineering the control system in a complicated industrial wastewater treatment plant. In this project, a PC-based Human-Machine Interface (HMI) in conjunction with Petri nets (PN) theory is adopted to develop and simulate the operational process for wastewater treatment. The resultant tool offers many advantages to the reality of the automated control world. It not only reduces the process reengineering time and the cost of error recovery, but also builds a panel of human interface for the process. The discrete event control sequence of wastewater treatment can be easily modeled and evaluated before its build-up. Furthermore, this PN-based system can be used as an online diagnostic tool when the wastewater treatment process is malfunctioning. That is, the presented PN tool provides an adequate means for offline process development, simulation, performance evaluation, and quick online process diagnosis. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] Petri nets based FPGA controller of PDP sustainer with half-voltage energy recovery circuit,ASIAN JOURNAL OF CONTROL, Issue 3 2010Jian-Long Kuo Abstract This paper proposes a FPGA controller design of a driver circuit based Petri nets for the Plasma Display Panel (PDP). In such a driver circuit, complicated control logic is required in the PDP sustainer circuit to implement the sustaining voltage waveform. The control logic has the zero-switching behaviour for the driver circuit to provide better efficiency for the driving circuit. Conventionally, the VHDL programmer does not have a systematic way to program the control logic. Time delay problem of logic components in logic controller may occur under high frequency operation. With the help of the proposed Petri nets approach, the VHDL programming for the PDP driver circuit can be easier in a systematic way. Also, this paper illustrates three types of sustainers with Petri nets based FPGA controller. The basic full-bridge and full-voltage sustainers are used to compare the performance with the proposed half-voltage sustainer. Details of the circuit operation are described. From the experimental results, the performance such as efficiency, luminance, and gamma curve are assessed to show the effectiveness of the proposed half-voltage sustainer. It is believed that the proposed Petri nets based control circuit is very powerful for the practical application of the PDP sustainer circuit. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] Constructing an abstract model for ladder diagram diagnosis using Petri nets,ASIAN JOURNAL OF CONTROL, Issue 3 2010Jui-I Tsai Abstract This paper proposes a method for constructing an abstract model for analyzing and diagnosing electrical circuit ladder diagrams (LDs) using Petri nets, and also supporting network-based monitoring and supervision. This approach converts normal open (NO) and normal close (NC) contacts in the LD into Petri net transitions, and converts devices (e.g. relay coils) in the LD into Petri net places. This study introduces the concepts of composite transitions, composite places, and relevant state to reduce complexity and increase readability of Petri nets for constructing abstract models. The current study constructing diagnosis of fault modeling, introduces simple matrix manipulation and the difference output vector (DOV) to determine the faulty area for diagnosis in the ladder diagram. An LD controller example demonstrates the usable approach. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] Non-blocking decentralized control of discrete event systems based on Petri nets,ASIAN JOURNAL OF CONTROL, Issue 3 2010Feihua Lu Abstract The non-blocking property of discrete event systems can formulate many practical and important properties of manufacturing systems, such as deadlock freeness, liveness and reversibility. But it is difficult to guarantee non-blocking control. This paper presents a hybrid approach to decentralized control of discrete event systems. More generalized constraints are considered in this approach, which gives a graphical way of designing coordinators to keep the non-blocking property of the closed-loop system with decentralized supervisors. This approach also guarantees that the closed-loop system is maximally permissive. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] A deadlock prevention approach for a class of timed Petri nets using elementary siphons,ASIAN JOURNAL OF CONTROL, Issue 3 2010Jinwei Guo Abstract To solve the problem of deadlock prevention for timed Petri nets, an effective deadlock prevention policy based on elementary siphons is proposed in this paper. Without enumerating reachable markings, deadlock prevention is achieved by adding monitors for elementary siphons, increasing control depth variables when necessary, and removing implicit, liveness-restricted and redundant control places. The final supervisor is live. First, a timed Petri net is stretched into a stretched Petri net (SPN). Unchanging the system performance, each transition in the SPN has a unit delay time. Then the siphon-control-based approach is applied. Monitors computed according to the marking constraints are added to the SPN model to ensure all strict minimal siphons in the net invariant-controlled. A liveness-enforcing supervisor with simple structure can be obtained by reverting the SPN into a TdPN. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] An optimal maintenance policy based on generalized stochastic Petri nets and periodic inspectionASIAN JOURNAL OF CONTROL, Issue 3 2010Ching-Kao Chang Abstract Periodic maintenance of equipment is essential for its optimum performance, thereby enabling production efficiency. In the past, studies on preventive maintenance of automated manufacturing systems (AMS) determined the optimal preventive maintenance policy under different performance indexes. Generally, most hypotheses indicate that equipment reliability can be restored to 1.0 through preventive and corrective maintenance. However, in practical application, the implementation of preventive maintenance results in partial deterioration of equipment; moreover, the reliability of equipment cannot be restored to as-good-as-new. In addition, the greater the complexity of connections of the equipment, the greater is the difficulty in determining the timing for preventive maintenance. On account of these characteristics, generalized stochastic Petri nets (GSPN) are well-suited for the implementation of preventive maintenance. Therefore, this paper applies GSPN for deciding the optimal maintenance policy and constructing models for different levels of maintenance and renewal for an AMS with a serial-parallel layout. As a result of the application of GSPN, the following optimal maintenance policy for an AMS was obtained in this study: Preventive maintenance conducted at intervals of every 240 hours will reduce cost by 46% as opposed to the practice of replacing defective parts when necessary. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] Two-dimensional occluded object matching using petri netsINTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 3 2002Chuan Zhou This article discusses the use of Petri nets to model the process of object matching between an image and a model under different two-dimensional geometric transformations. This transformation finds its applications in sensor-based robot control, flexible manufacturing systems, industrial inspection, and so on. Its topological structure relation, called point-line relation structure (PLRS), presents a Petri net-based description approach for object structure. It has been shown how Petri nets can be used to model the matching process, and an optimal or near optimal matching can be obtained by tracking the reachability graph of the net. The experiment result shows that objects can be successfully identified and located under two-dimensional transformation such as translations, rotations, scale changes, and distortions due to partial object occlusion. © 2002 Wiley Periodicals, Inc. [source] Fault tolerant control design via hybrid petri nets,ASIAN JOURNAL OF CONTROL, Issue 5 2010Hao Yang Abstract This paper proposes a novel fault tolerant control (FTC) scheme for hybrid systems modeled by hybrid Petri nets (HPNs). The HPNs model consists of discrete and continuous PNs. The faults are represented by unobservable discrete transitions or the normal observable discrete transitions with abnormal firing time in discrete PNs. First, an observer-based fault diagnosis method is proposed to estimate the marking in discrete places with unknown initial marking and diagnose the faulty behavior simultaneously. Then, an adaptive fault tolerant controller is designed to maintain the general mutual exclusion constraints (GMEC) of discrete PNs, and a scheme that adjusts firing speeds of continuous transitions is provided to maintain the optimality of continuous PNs. Finally, an example of an intelligent transportation system consisting of automated vehicles on a bridge is included to demonstrate the effectiveness of our developed techniques. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] A petri nets-based process planning system for wastewater treatment,ASIAN JOURNAL OF CONTROL, Issue 3 2010Albert W. L. Yao Abstract It is always challenging to simulate, debug or diagnose automated systems. The aim of this paper is to present the development of a convenient tool for reengineering the control system in a complicated industrial wastewater treatment plant. In this project, a PC-based Human-Machine Interface (HMI) in conjunction with Petri nets (PN) theory is adopted to develop and simulate the operational process for wastewater treatment. The resultant tool offers many advantages to the reality of the automated control world. It not only reduces the process reengineering time and the cost of error recovery, but also builds a panel of human interface for the process. The discrete event control sequence of wastewater treatment can be easily modeled and evaluated before its build-up. Furthermore, this PN-based system can be used as an online diagnostic tool when the wastewater treatment process is malfunctioning. That is, the presented PN tool provides an adequate means for offline process development, simulation, performance evaluation, and quick online process diagnosis. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] | |||||||||||||