Wyniki wyszukiwania - BazTech

1

Cannibalization policies: adoption in the maintenance of fleet systems

Diaz Ermilso, Muñoz-Añasco Mariela, Correcher-Salvador Antonio

Zeszyty Naukowe. Transport / Politechnika Śląska

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2023

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z. 121

63--75

EN

Fleet systems are considered complex due to the interaction between their units and components. Maintenance management systems face various challenges to achieve acceptable availability and reliability rates at a reasonable cost. A critical task for making maintenance decisions is understanding the system requirements to select maintenance policies appropriate for the actual and future system state. When there is a replacement shortage in a fleet system, and it is impossible to supply new spare parts quickly, cannibalization policies can mitigate this scarcity via the interchange of components. However, this procedure presents the maintenance manager with different evaluation effects, such as increased maintenance hours, decreased system reliability rate, and unavailability in some units. Finding an equilibrium between the benefits and risks has caught the attention of researchers. This work gathers diverse proposals for applying cannibalization policies and the effects that arise from using them. Models, methods, tools, and identified gaps in understanding what parameters of the components and environments of the fleet systems favor cannibalization are discussed.

2

Modelling and control of flexible manufacturing systems by means of interpreted Petri nets

Čapkovič František

Journal of Automation Mobile Robotics and Intelligent Systems

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2018

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Vol. 12, No. 4

3--10

EN

Because flexible manufacturing systems (FMS) are discrete event systems (DES), their modelling and control by means of Petri nets (PN) is widely used. While PN transitions are observable and controllable and PN places are measurable, place/transition PN (P/T PN) are suffcient for this aim. However, when some PN transitions are unobservable and/or uncontrollable and some places are non-measurable/unobservable, P/T PN are insufficient for modelling and especially for control. In such a case interpreted Petri nets (IPN) seem to be an appropriate replacement for P/T PN. In this paper a possibility of usage of IPN for FMS modelling and control is pointed out. Illustrative examples as well as the case study on a robotized assembly cell are introduced. By means of using timed PN (TPN) also the performance evaluation of the IPN model of controlled plant is accomplished whereby the simulation in Matlab.

3

Zastosowanie max-plus algebry w modelowaniu i analizie efektywności systemów produkcyjnych

Stańczyk J.

Zarządzanie Przedsiębiorstwem

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2017

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Vol. 20, nr 3

46--53

EN

In response to increased competition, manufacturing systems are becoming more complex in order to provide the flexibility and responsiveness required by the market. The increased complexity requires decision support tools that can provide insight into the effect of system changes on performance in an efficient and timely manner. This contribution discusses the usefulness of (max, +) algebra as a mathematical framework for a class of production systems. The class can be described as a dynamic and asynchronous where the state transitions are initiated by events that occur at discrete instants of time. An event corresponds to the start or the end of an activity. A common property of such examples is that the start of an activity depends on termination of several other activities. Such systems are known as discrete event systems (DES). In the paper an overview of the modeling and analysis concepts of the (max, +) algebra approach for DES is given. Also, an application examples from manufacturing systems are provided to illustrate the potential of this approach. Considered systems have been represented as (max, +) algebraic state space models. How to model different basic manufacturing systems depends on production type, like serial line, assembly line, etc. as well as impact of capacity of interoperable buffers have been presented. Based on an analytical model, effectiveness evaluation or performance indexes have been calculated for different configurations of the same production system. So, finally the best solution, for given criteria, has been obtained. All exemplary calculations have been made using the Max-Plus Algebra Toolbox for Matlab, the software package developed by author and available on his homepage.

4

Metric for calculation of system complexity based on its connections

Paiva J. R. B., Gomes V. M., Rodrigues B. A., Silva L. F. A., Aniceto B. C. M., Furriel G. P., Calixto W. P.

Transactions on Environment and Electrical Engineering

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2017

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Vol. 2, No. 1

67--73

EN

This paper proposes a methodology based on system connections to calculate its complexity. Two study cases are proposed: the dining Chinese philosophers’ problem and the distribution center. Both studies are modeled using the theory of Discrete Event Systems and simulations in different contexts were performed in order to measure their complexities. The obtained results present i) the static complexity as a limiting factor for the dynamic complexity, ii) the lowest cost in terms of complexity for each unit of measure of the system performance and iii) the output sensitivity to the input parameters. The associated complexity and performance measures aggregate knowledge about the system.

5

Control design for untimed Petri nets using Markov Decision Processes

Daoui C., Lefebvre D.

Operations Research and Decisions

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2017

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Vol. 27, No. 4

27--43

EN

Design of control sequences for discrete event systems (DESs) has been presented modelled by untimed Petri nets (PNs). PNs are well-known mathematical and graphical models that are widely used to describe distributed DESs, including choices, synchronizations and parallelisms. The domains of application include, but are not restricted to, manufacturing systems, computer science and transportation networks. We are motivated by the observation that such systems need to plan their production or services. The paper is more particularly concerned with control issues in uncertain environments when unexpected events occur or when control errors disturb the behaviour of the system. To deal with such uncertainties, a new approach based on discrete time Markov decision processes (MDPs) has been proposed that associates the modelling power of PNs with the planning power of MDPs. Finally, the simulation results illustrate the benefit of our method from the computational point of view.

6

Algebraic approach for model decomposition: Application to fault detection and isolation in discrete-event systems

Berdjag D., Cocquempot V., Christophe C., Shumsky A., Zhirabok A.

International Journal of Applied Mathematics and Computer Science

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2011

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Vol. 21, no 1

109-125

EN

This paper presents a constrained decomposition methodology with output injection to obtain decoupled partial models. Measured process outputs and decoupled partial model outputs are used to generate structured residuals for Fault Detection and Isolation (FDI). An algebraic framework is chosen to describe the decomposition method. The constraints of the decomposition ensure that the resulting partial model is decoupled from a given subset of inputs. Set theoretical notions are used to describe the decomposition methodology in the general case. The methodology is then detailed for discrete-event model decomposition using pair algebra concepts, and an extension of the output injection technique is used to relax the conservatism of the decomposition.

7

Application of agent cooperation by means of DES supervision to manufacturing system

Čapkovič F.

Archives of Control Sciences

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2011

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Vol. 21, no. 4

395-417

EN

The supervision of complex manufacturing systems is handled in this paper. Production lines of manufacturing systems are understood here to be hybrid agents. Such an agent expresses continuous material flow together with a set of imperative discrete operations. In other words, the hybrid agent makes a cooperation of continuous and discrete event devices possible. The results are applied to complex continuous manufacturing system. First Order Hybrid Petri Nets (FOHPN) are utilized in order to model the elementary autonomous hybrid agents. The cooperation of hybrid agents is based on the DES (discrete-event systems) control theory. It is realized by means of DES supervision methods and the agent negotiation is based on place/transition Petri nets (P/T PN). The proposed approach is illustrated in details on the cooperation of hybrid production lines in the real complex manufacturing systems recycling waste plastics into plastic bags. The usefulness and applicability of the approach consists especially in the fact that the procedures in analytical terms can be employed. In such a way the approach turns lucid also in complicated cases.

8

Decentralized structural control approach for Petri nets

Aybar A.

Control and Cybernetics

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2007

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Vol. 36, no 1

143-159

EN

The structural controller, described by adding the control places to the Petri nets, is introduced in this work to lead the Petri net to the desired marking vectors. An algorithm (Algorithm I) is developed to determine the control places for the given Petri net. The connections and the initial marking of each control place are determined in this algorithm. Moreover, a decentralized structural control approach, based on overlapping decompositions, is introduced in this work. In this decentralized approach, all disjoint Petri subnets, which are obtained by using overlapping decompositions, are determined. The control places for each Petri subnet are determined by using the given algorithm. Then, the control places for the orginal Petri net are obtained by the control places of each PSN by another algorithm (Algorithm II) and these places are added to the orginal Petri net. Therefore, a decentralized structural controller which guarantees to lead the Petri net to the desired marking vectors is obtained.

9

A Novel Continuous Model to Approximate Time Petri Nets: Modelling and Analysis

Gu T., Dong R.

International Journal of Applied Mathematics and Computer Science

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2005

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Vol. 15, no 1

141-150

EN

In order to approximate discrete-event systems in which there exist considerable states and events, David and Alla define a continuous Petri net (CPN). So far, CPNs have been a useful tool not only for approximating discrete-event systems but also for modelling continuous processes. Due to different ways of calculating instantaneous firing speeds of transitions, various continuous Petri net models, such as the CCPN (constant speed CPN), VCPN (variable speed CPN) and the ACPN (asymptotic CPN), have been proposed, where the continuous flow is specified uniquely by maximal firing speeds. However, in applications such as chemical processes there exist situations where the continuous flow must be above some minimal speed or in the range of minimal and maximal speeds. In this paper, from the point of view of approximating a time Petri net, the CPN is augmented with maximal and minimal firing speeds, and a novel continuous model, i.e., the Interval speed CPN (ICPN) is defined. The enabling and firing semantics of transitions of the ICPN are discussed, and the facilitating of continuous transitions is classified into three levels: 0-level, 1-level and 2-level. Some policies to resolve the conflicts and algorithms to undertake the behavioural analysis for the ICPN are developed. In addition, a chemical process example is presented.

10

Hybrid modelling and performance evaluation of switched discrete-event systems

Wang L.

Control and Cybernetics

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2004

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Vol. 33, no 2

311-321

EN

Motivated by the integrated complexity of real-time intelligent control and optimization of industrial/manufacturing processes, this paper discusses hybrid modelling and asymptotic periodic behavior of a class of switched discrete event systems, and shows how to evaluate the asymptotic performance/efficiency of such systems. We prove that, under some mild conditions, the switched discrete event system will achieve asymptotic periodic dynamics, and its performance/efficiency can be evaluated by calculating the eigenvalue of certain matrix in max-plus algebra. Illustrative examples are provided.

11

Analyzing and reducing simultaneous firing in signal-event nets

Roch S.

Fundamenta Informaticae

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2000

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Vol. 43, Nr 1-4

321-330

EN

Signal-event nets provide a modular modeling technique based on Petri nets. Actions of a module can be activated or can be prevented by another module through condition arcs. One-sided synchronization of modules is done by signal-events, which cause the execution of actions in steps. But due to condition arcs and signal-events simultaneous firing of steps may lead to markings, which are not reachable by conventional sequential interleaving. We give a criterion, in which situations simultaneous firing of steps can be safely omitted, without missing reachable markings.

12

An application of rough set methods in control design

Peters J.F., Skowron A., Suraj Z.

Fundamenta Informaticae

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2000

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Vol. 43, Nr 1-4

269-290

EN

The paper deals with an automatic concurrent control design method derived from the specification of a discrete event control system represented in the form of a decision table. The main stages of our approach are: the control specification by decision tables, generation of rules from the specification of the system behavior, and converting rules set into a concurrent program represented in the form of a Petri net. Our approach is based on rough set theory.

13

A signal extension for Petri nets and its use in controller design

Hanisch H.-M., Lüder A.

Fundamenta Informaticae

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2000

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Vol. 41, Nr 4

415-431

EN

Petri nets have a longstanding history in controller design and implementation, and it is often told that they have the dominating position in this field due to the close relationship between Petri nets and Graphcet or other sequential function diagrams. We want to show that there are some severe problems when Petri nets are used to describe both: the controller and the plant under control. The nature of these problems is the lack of a concept of input and output signals and, moreover, the lack of a formal concept to interconnect systems modeled by Petri nets via signals. Although this is often neglected, it turns out to be a key issue if a model of the closed-loop behavior must be established as a precondition for formal controller verification. We present a signal extension for Petri nets and means for interconnecting an arbitrary number of those extended Petri nets. We come up with the conclusion that the resulting models are suited for controller verification. Although the graphical appearance shows similarities to Petri nets, the resulting models are no longer Petri nets.