Pub Date : 2002-10-02DOI: 10.1109/WODES.2002.1167680
E. Roszkowska
This paper presents closed AGV systems with bidirectional guide path networks, zone control for avoiding collisions, and dynamic route planning. An AGV system is represented as a colored Petri net with undirected arcs and directed tokens, which substantially reduces the number of net components and simplifies the insight into the model. We study the problem of marking liveness and associate this property with the permanent ability of the vehicles to attain any edge in the network. The requirement is a weak form of marking liveness, as it does not require that each transition be live with respect to each of its colors. For the analysis of the net dynamics, we introduce the notion of a partially directed graph, that is, a graph which can have both directed and undirected edges. The results allow us to determine uniquely the character (live or not-live) of states in the system, which can thus be applied in the design of the supervisory control for AGV systems.
{"title":"Undirected colored Petri net for modelling and supervisory control of AGV systems","authors":"E. Roszkowska","doi":"10.1109/WODES.2002.1167680","DOIUrl":"https://doi.org/10.1109/WODES.2002.1167680","url":null,"abstract":"This paper presents closed AGV systems with bidirectional guide path networks, zone control for avoiding collisions, and dynamic route planning. An AGV system is represented as a colored Petri net with undirected arcs and directed tokens, which substantially reduces the number of net components and simplifies the insight into the model. We study the problem of marking liveness and associate this property with the permanent ability of the vehicles to attain any edge in the network. The requirement is a weak form of marking liveness, as it does not require that each transition be live with respect to each of its colors. For the analysis of the net dynamics, we introduce the notion of a partially directed graph, that is, a graph which can have both directed and undirected edges. The results allow us to determine uniquely the character (live or not-live) of states in the system, which can thus be applied in the design of the supervisory control for AGV systems.","PeriodicalId":435263,"journal":{"name":"Sixth International Workshop on Discrete Event Systems, 2002. Proceedings.","volume":"54 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123323975","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-10-02DOI: 10.1109/WODES.2002.1167688
R. Luders, R. Santos-Mendes
Dioids are algebraic structures suitable to represent a timed event graph by means of a linear state-space or transfer function model, where synchronization of events can be described. This paper proposes a model reference control strategy under partial observation and control of internal system transitions, where a controller is obtained by matching the closed-loop transfer function to a given transfer function (control specification). The problem formulation is quite general, allowing to deal studied cases in the literature as particular cases and to generalize some of them.
{"title":"Generalized multivariable control of discrete event systems in dioids","authors":"R. Luders, R. Santos-Mendes","doi":"10.1109/WODES.2002.1167688","DOIUrl":"https://doi.org/10.1109/WODES.2002.1167688","url":null,"abstract":"Dioids are algebraic structures suitable to represent a timed event graph by means of a linear state-space or transfer function model, where synchronization of events can be described. This paper proposes a model reference control strategy under partial observation and control of internal system transitions, where a controller is obtained by matching the closed-loop transfer function to a given transfer function (control specification). The problem formulation is quite general, allowing to deal studied cases in the literature as particular cases and to generalize some of them.","PeriodicalId":435263,"journal":{"name":"Sixth International Workshop on Discrete Event Systems, 2002. Proceedings.","volume":"265 8","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120897874","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-10-02DOI: 10.1109/WODES.2002.1167687
Yiping Cheng, D. Zheng
The cycle time is an important performance metric associated with a min-max system. In this paper we study the cycle time of non-autonomous min-max systems. Based on the duality theorem, a general cycle time formula is derived, then we apply this formula to some special classes of min-max systems and obtain some results, which include a short proof of Olsder's theorem on the eigenvalue of separated min-max systems, a cycle time formula for min-max systems with triangular structure driven by uniform input, and a cycle time clipper for wide-sense bipartite systems.
{"title":"On the cycle time of non-autonomous min-max systems","authors":"Yiping Cheng, D. Zheng","doi":"10.1109/WODES.2002.1167687","DOIUrl":"https://doi.org/10.1109/WODES.2002.1167687","url":null,"abstract":"The cycle time is an important performance metric associated with a min-max system. In this paper we study the cycle time of non-autonomous min-max systems. Based on the duality theorem, a general cycle time formula is derived, then we apply this formula to some special classes of min-max systems and obtain some results, which include a short proof of Olsder's theorem on the eigenvalue of separated min-max systems, a cycle time formula for min-max systems with triangular structure driven by uniform input, and a cycle time clipper for wide-sense bipartite systems.","PeriodicalId":435263,"journal":{"name":"Sixth International Workshop on Discrete Event Systems, 2002. Proceedings.","volume":"29 2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120934453","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-10-02DOI: 10.1109/WODES.2002.1167696
Bruno Gaujal, E. Hyon
In this paper, we address the problem of routing a stream of customers in two parallel networks of queues in tandem with deterministic service times in order to minimize the average response time. We show that the optimal routing is a Sturmian word whose density depends on the maximum service time on each route. In order to do this, we particularly study the output process of deterministic queues when the input process is Sturmian.
{"title":"Optimal routing policies in deterministic queues in tandem","authors":"Bruno Gaujal, E. Hyon","doi":"10.1109/WODES.2002.1167696","DOIUrl":"https://doi.org/10.1109/WODES.2002.1167696","url":null,"abstract":"In this paper, we address the problem of routing a stream of customers in two parallel networks of queues in tandem with deterministic service times in order to minimize the average response time. We show that the optimal routing is a Sturmian word whose density depends on the maximum service time on each route. In order to do this, we particularly study the output process of deterministic queues when the input process is Sturmian.","PeriodicalId":435263,"journal":{"name":"Sixth International Workshop on Discrete Event Systems, 2002. Proceedings.","volume":"22 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126299458","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-10-02DOI: 10.1109/WODES.2002.1167715
J. Liu, H. Darabi
In this paper we present an algorithm to convert a controller automaton synthesized by the Ramadge-Wonham (RW) method to a ladder logic diagram. The subject of conversion from RW controller to ladder logic is not new and has already been addressed by many researchers. Our method takes a new look at this subject. We not only make sure that the same sequences of events can be generated by both the RW controller and its converted ladder logic (as done by other related literature), but we also guarantee the implementation of the converted ladder logic as a PLC program. Specifically, we use the IDEF3 standard, which views a manufacturing system as a set of activities and their required resources. We consider the resource events to define the forcing mechanisms of ladder logic, as the original RW controller cannot model these mechanisms. We also use external signals to resolve the inherent conflicts of RW controller that cannot be tolerated under a forcing controller such as ladder logic. Two examples are presented to illustrate the applicability of the proposed algorithm.
{"title":"Ladder logic implementation of Ramadge-Wonham supervisory controller","authors":"J. Liu, H. Darabi","doi":"10.1109/WODES.2002.1167715","DOIUrl":"https://doi.org/10.1109/WODES.2002.1167715","url":null,"abstract":"In this paper we present an algorithm to convert a controller automaton synthesized by the Ramadge-Wonham (RW) method to a ladder logic diagram. The subject of conversion from RW controller to ladder logic is not new and has already been addressed by many researchers. Our method takes a new look at this subject. We not only make sure that the same sequences of events can be generated by both the RW controller and its converted ladder logic (as done by other related literature), but we also guarantee the implementation of the converted ladder logic as a PLC program. Specifically, we use the IDEF3 standard, which views a manufacturing system as a set of activities and their required resources. We consider the resource events to define the forcing mechanisms of ladder logic, as the original RW controller cannot model these mechanisms. We also use external signals to resolve the inherent conflicts of RW controller that cannot be tolerated under a forcing controller such as ladder logic. Two examples are presented to illustrate the applicability of the proposed algorithm.","PeriodicalId":435263,"journal":{"name":"Sixth International Workshop on Discrete Event Systems, 2002. Proceedings.","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132118910","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-10-02DOI: 10.1109/WODES.2002.1167693
L. Aguirre-Salas, O. Begovich, A. Ramírez-Treviño
In real DES applications, the system is usually confined into a particular behavior in order to perform a specific task. In this case, the observability problem is turned into the problem of determining whether or not it is possible to recover the actual system state when the system is confined into a specific sublanguage. In this context, this paper addresses the observability problem for interpreted Petri nets (IPNs) whose behavior is confined into a cyclic sublanguage of the firing language. The concept of L-observability is introduced. A characterization of this kind of observability is derived based on the notions of L-event-detectability, and L-marking-detectability is also introduced in this paper.
{"title":"Observability with respect to a language in discrete event systems modeled by IPN","authors":"L. Aguirre-Salas, O. Begovich, A. Ramírez-Treviño","doi":"10.1109/WODES.2002.1167693","DOIUrl":"https://doi.org/10.1109/WODES.2002.1167693","url":null,"abstract":"In real DES applications, the system is usually confined into a particular behavior in order to perform a specific task. In this case, the observability problem is turned into the problem of determining whether or not it is possible to recover the actual system state when the system is confined into a specific sublanguage. In this context, this paper addresses the observability problem for interpreted Petri nets (IPNs) whose behavior is confined into a cyclic sublanguage of the firing language. The concept of L-observability is introduced. A characterization of this kind of observability is derived based on the notions of L-event-detectability, and L-marking-detectability is also introduced in this paper.","PeriodicalId":435263,"journal":{"name":"Sixth International Workshop on Discrete Event Systems, 2002. Proceedings.","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133688440","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-10-02DOI: 10.1109/WODES.2002.1167714
M. H. D. Queiroz
Supervisory control theory is applied to a manufacturing cell commanded by a programmable logic controller (PLC). By means of a local modular approach -a methodology that exploits modularity of the plant and of the behavioral specifications models - optimal supervisors are obtained without state-space explosion. For the purpose of simplifying the ladder diagram implementation in the PLC, reduced supervisors are implemented in a three level structure that executes modular supervisor concurrent action and interfaces the theoretical model with the real system. The flexible and productive manufacturing cell behavior, after practical implementation of the control system, and the final PLC code readability and flexibility are positive quality indicators to the applied methodology.
{"title":"Synthesis and implementation of local modular supervisory control for a manufacturing cell","authors":"M. H. D. Queiroz","doi":"10.1109/WODES.2002.1167714","DOIUrl":"https://doi.org/10.1109/WODES.2002.1167714","url":null,"abstract":"Supervisory control theory is applied to a manufacturing cell commanded by a programmable logic controller (PLC). By means of a local modular approach -a methodology that exploits modularity of the plant and of the behavioral specifications models - optimal supervisors are obtained without state-space explosion. For the purpose of simplifying the ladder diagram implementation in the PLC, reduced supervisors are implemented in a three level structure that executes modular supervisor concurrent action and interfaces the theoretical model with the real system. The flexible and productive manufacturing cell behavior, after practical implementation of the control system, and the final PLC code readability and flexibility are positive quality indicators to the applied methodology.","PeriodicalId":435263,"journal":{"name":"Sixth International Workshop on Discrete Event Systems, 2002. Proceedings.","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115199985","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-10-02DOI: 10.1109/WODES.2002.1167716
Y. Wardi, G. Riley
This paper considers congestion-related performance metrics in tandem networks of Stochastic Fluid Models (SFMs), and derives their IPA gradient estimators with respect to buffer sizes. Specifically, the performance metrics in question are the total loss volume and the cumulative buffer workload (buffer contents), and the control parameter consists of buffer limits at both the node where the performance is measured and at an upstream node. The IPA estimators are unbiased and nonparametric, and hence can be computed on-line from field measurements as well as off-line from simulation experiments. The IPA derivatives are applied to packet-based networks, where simulation results support the theoretical developments. Possible applications to congestion management in telecommunications networks are discussed.
{"title":"IPA for loss volume and buffer workload in tandem SFM networks","authors":"Y. Wardi, G. Riley","doi":"10.1109/WODES.2002.1167716","DOIUrl":"https://doi.org/10.1109/WODES.2002.1167716","url":null,"abstract":"This paper considers congestion-related performance metrics in tandem networks of Stochastic Fluid Models (SFMs), and derives their IPA gradient estimators with respect to buffer sizes. Specifically, the performance metrics in question are the total loss volume and the cumulative buffer workload (buffer contents), and the control parameter consists of buffer limits at both the node where the performance is measured and at an upstream node. The IPA estimators are unbiased and nonparametric, and hence can be computed on-line from field measurements as well as off-line from simulation experiments. The IPA derivatives are applied to packet-based networks, where simulation results support the theoretical developments. Possible applications to congestion management in telecommunications networks are discussed.","PeriodicalId":435263,"journal":{"name":"Sixth International Workshop on Discrete Event Systems, 2002. Proceedings.","volume":"321 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123167016","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-10-02DOI: 10.1109/WODES.2002.1167713
A. Hellgren, B. Lennartson, Martin Fabian
Implementation of supervisory control in Programmable Logic Controllers (PLCs) typically requires that the underlying discrete event models of plant, specification and the supervisor itself fulfil a number of properties. These properties are discussed and methods for solving related problems are given. In particular, determinism and synchronisation issues are investigated. In a manufacturing system, for instance, there is typically a set of processes using a set of shared resources. Poor modelling may cause the system model to become nondeterministic. This can be circumvented by relabelling the relevant models. For industrial-sized models, though, this must be done automatically, something that we achieve by parameterising the models. Given a deterministic model, consisting of several interacting entities, we discuss its PLC-based implementation. In addition to the synchronisation of plant and supervisor, a modular supervisor must be internally synchronised. However, synchronisation of the submodules is not well defined in the PLC-world. This may be achieved by using event monitors and an immediate transit/immediate action execution model.
{"title":"Modelling and PLC-based implementation of modular supervisory control","authors":"A. Hellgren, B. Lennartson, Martin Fabian","doi":"10.1109/WODES.2002.1167713","DOIUrl":"https://doi.org/10.1109/WODES.2002.1167713","url":null,"abstract":"Implementation of supervisory control in Programmable Logic Controllers (PLCs) typically requires that the underlying discrete event models of plant, specification and the supervisor itself fulfil a number of properties. These properties are discussed and methods for solving related problems are given. In particular, determinism and synchronisation issues are investigated. In a manufacturing system, for instance, there is typically a set of processes using a set of shared resources. Poor modelling may cause the system model to become nondeterministic. This can be circumvented by relabelling the relevant models. For industrial-sized models, though, this must be done automatically, something that we achieve by parameterising the models. Given a deterministic model, consisting of several interacting entities, we discuss its PLC-based implementation. In addition to the synchronisation of plant and supervisor, a modular supervisor must be internally synchronised. However, synchronisation of the submodules is not well defined in the PLC-world. This may be achieved by using event monitors and an immediate transit/immediate action execution model.","PeriodicalId":435263,"journal":{"name":"Sixth International Workshop on Discrete Event Systems, 2002. Proceedings.","volume":"86 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124800185","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-10-02DOI: 10.1109/WODES.2002.1167704
B. Krogh
A standard approach to the formal analysis of hybrid systems (that is, systems with both continuous and discrete state variables) is to first construct purely discrete-state models, usually by building transition systems based on finite partitions of the continuous state space. Analysis and synthesis techniques for discrete-state systems are then applied to the discrete model to verify properties of the hybrid system and to synthesize supervisory controllers. This brief paper reviews the theory for discrete analysis of hybrid systems.
{"title":"Recent advances in discrete analysis and control of hybrid systems","authors":"B. Krogh","doi":"10.1109/WODES.2002.1167704","DOIUrl":"https://doi.org/10.1109/WODES.2002.1167704","url":null,"abstract":"A standard approach to the formal analysis of hybrid systems (that is, systems with both continuous and discrete state variables) is to first construct purely discrete-state models, usually by building transition systems based on finite partitions of the continuous state space. Analysis and synthesis techniques for discrete-state systems are then applied to the discrete model to verify properties of the hybrid system and to synthesize supervisory controllers. This brief paper reviews the theory for discrete analysis of hybrid systems.","PeriodicalId":435263,"journal":{"name":"Sixth International Workshop on Discrete Event Systems, 2002. Proceedings.","volume":"169 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114372684","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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