Event-based intelligent control of saturated chemical plant using an endomorphic neural network model

An event-based control system with an endomorphic neural network model is designed and realized to control a saturated non-linear plant. The scheme employed in this system is based on an event-based control paradigm previously proposed to control monotonic plants. However, this scheme is different from the previous one in that it can be used to control plants with saturation property. This new scheme may be viewed as a combined method of a time-based diagnosis mechanism in an event-based control system and a state-based control mechanism in a neural network control system. A chemical plant having strong non-linearity and complicated dynamics is controlled using this realized event-based control system. This paper discusses the structure of an event-based controller, the neural network modelling methodology, some related problems, and the simulation results.     

基于事件的设计与控制技术及其在机器人系统中的应用

基于事件的设计与控制技术已经引起人们的广泛关注,其基本思想就是引入与系统输出相关的运动参考变量(action reference),在任意时刻使系统给定量的输入以及系统的设计都转化为这个参考变量的函数,使系统的设计部分与控制器一样成为系统的决策部件,从而使系统具备处理突发性、不确定性事件的能力,可以根据系统的实际输出来实时、自动地调整系统的输入,实现对系统的实时控制．机器人系统是一个智能控制系统．机器人间的协调协作是其智能性的主要表现．本文首先对基于事件的控制理论及其发展做了回顾,然后介绍了基于事件的控制技术在机器人队形保持、机器制造、多机器人协作等系统智能控制中的应用,实验证明该方法可以取得很好的智能控制效果,提高系统的控制性能．最后探讨了这一研究领域的发展方向．     

HIERARCHICAL SYSTEM CONCEPTS FOR SIMULATION OF HIGH AUTONOMY SYSTEMS

A high autonomy system is an intelligent system with self-determination power. Such a system must perform a variety of functions such as reasoning, planning, sensing, control, and other activities necessary to achieve predefined system objectives over an extended period of time under uncertainties in its environment. Simulation modelling can be a powerful tool for design of such complex autonomy systems. This paper describes the hierarchical, modular system concepts for simulation of high autonomy systems with an example of an intelligent control system called the AIDECS (Al-based, Distributed Environmental Control System). The paper emphasizes on development of methods, in an object-oriented manner, for isomorphic replications of complex hierarchical structures as a means of constructing hierarchical models. We show how polymorphism and inheritance in the object-oriented programming can be exploited to develop such methods in DEVS-Scheme, a realization of the DEVS formalism in a LISP-bascd, object-oriented framework.     

Self-reproducible DEVS formalism

System reproduction model to the growing system structure can be used to design modeling formalisms for variable system architectures having historical characteristics. We introduce a discrete event system specifications (DEVS)-based extended formalism that a system structure gradually grows through self-reproductions of system components. The proposed formalism is applied to atomic DEVS modeling and coupled DEVS modeling. As extended-atomic DEVS model, atomic self-reproduction (SR) DEVS modeling to a system component makes virtual-child atomic DEVS models. By SR DEVS modeling, a child coupled model can be also reproduced from a parent coupled model. When a system component model reproduces its system component, a child component model can receive its parent model characteristics including determined role or behavior, and include different structure model characteristics. A virtual-child model that has its parent characteristics can also reproduce next child model which may show similar attributes of the grand-parent model.     

Event-driven architecture for decision support in traffic management systems

Decision support systems for traffic management systems have to cope with a high volume of events continuously generated by sensors. Conventional software architectures do not explicitly target the efficient processing of continuous event streams. Recently, event-driven architectures (EDA) have been proposed as a new paradigm for event-based applications. In this paper we propose a reference architecture for event-driven traffic management systems, which enables the analysis and processing of complex event streams in real-time and is therefore well-suited for decision support in sensor-based traffic control systems. We will illustrate our approach in the domain of road traffic management. In particular, we will report on the redesign of an intelligent transportation management system (ITMS) prototype for the high-capacity road network in Bilbao, Spain.     

离散事件系统规范DEVS研究

离散事件系统是一类常见的系统，如何对这类系统进行描述与建模是离散事件系统仿真研究的核心内容。离散事件系统规范DEVS是一种离散事件系统形式化描述方法，它具有层次化和模块化的特点，利用该方法可对复杂的离散事件系统进行建模、设计、分析和仿真。该文详细介绍了DEVS基本模型和耦合模型，给出了DEVS在耦合运算下的封闭性构造证明，并提出了一种具有嵌套层次结构的DEVS耦合模型实现算法，该算法对基于DEVS描述的离散事件系统的仿真实现具有一定参考价值。     

An event-driven high level model for the specification of laws in open multi-agent systems

The agent development paradigm poses many challenges to software engineering researchers, particularly when the systems are distributed and open. They have little or no control over the actions that agents can perform. Laws are restrictions imposed by a control mechanism to deal with uncertainty and to promote open system dependability. In this paper, we present a high level event-driven conceptual model of laws. XMLaw is an alternative approach to specifying laws in open multi-agent systems that presents high level abstractions and a flexible underlying event-based model. Thus XMLaw allows for flexible composition of the elements from its conceptual model and is flexible enough to accept new elements.     

基于网络的多机器人遥操作系统中的人机交互研究

针对基于网络的智能机器人遥操作系统中人机交互的主要难点和现有方法的不足,结合基于网络的多机器人遥操作系统的特点,应用多模式控制的方法丰富了操作者与机器人系统的交互途径,提高了操作效率。在此基础上,为解决网络时延给多机器人遥操作系统中的人机交互带来的问题,提出了一种带有时间标记的基于事件的方法,在保证系统稳定运行的同时提高系统的效率和性能。实验表明了所研究的方法的有效性和优越性。     

A review of: “FRACTALS EVERYWHERE”, by Michael Barnsley,Academic Press,San Diego,California, USA 1988

The modelling and analysis of multi-component discrete event systems is a challenging research area. Over 30 years, modelling and simulation research of discrete event system specification (DEVS) has been developed with (1) dense-time, (2) the I/O concept, and (3) hierarchical model construction. Nevertheless, DEVS model verification research began relatively recently considering the whole DEVS research history. In the meantime, over 15 years, the automata theory has been developed to cover the dense-time behaviour verification of discrete event systems. Especially, timed automata (TA) has performed the key role in the field.

This paper builds on the research results that have been achieved from both theories of DEVS and TA. Thus contributions of this paper can be seen from each side. From the viewpoint of the DEVS theory, a finite and nondeterministic DEVS has been found as a verifiable class. From the viewpoint of the TA theory, a TA which is modular and hierarchical as well as verifiable, is proposed. To show the results, this paper uses the top down manner in which a general formalism is defined first and then its sub-classes are introduced.     

The JEDI event-based infrastructure and its application to thedevelopment of the OPSS WFMS

The development of complex distributed systems demands the creation of suitable architectural styles (or paradigms) and related runtime infrastructures. An emerging style that is receiving increasing attention is based on the notion of event. In an event-based architecture, distributed software components interact by generating and consuming events. An event is the occurrence of some state change in a component of a software system, made visible to the external world. The occurrence of an event in a component is asynchronously notified to any other component that has declared some interest in it. This paradigm (usually called “publish/subscribe”, from the names of the two basic operations that regulate the communication) holds the promise of supporting a flexible and effective interaction among highly reconfigurable, distributed software components. In the past two years, we have developed an object-oriented infrastructure called JEDI (Java event-based distributed infrastructure). JEDI supports the development and operation of event-based systems and has been used to implement a significant example of distributed system, namely, the OPSS workflow management system (WFMS). The paper illustrates the main features of JEDI and how we have used them to implement OPSS. Moreover, the paper provides an initial evaluation of our experiences in using the event-based architectural style and a classification of some of the event-based infrastructures presented in the literature     

A modular timed graph transformation language for simulation-based design

We introduce the MoTif (Modular Timed graph transformation) language, which allows one to elegantly model complex control structures for programmed graph transformation. These include modular construction, parallel composition, and a temporal dimension in addition to the usual transformation control structures. The first part of this contribution formally introduces MoTif and its semantics is based on the Discrete EVent system Specification (DEVS) formalism which allows for highly modular, hierarchical modelling of timed, reactive systems. In MoTif, graphs are embedded in events and individual transformation rules are embedded in atomic DEVS models. A side effect of the use of DEVS is the introduction of an explicit notion of time. This allows one to model a time-advance for every rule as well as to interrupt (pre-empt) rule execution. In the second part, we design a case study to show how the explicit notion of time allows for the simulation-based design of reactive systems such as modern computer games. We use the well-known game of PacMan as an example and model its dynamics in MoTif. This also allows the modelling of player behaviour, incorporating data about human players’ behaviour, and reaction times. Thus, a model of both player and game is obtained which can be used to evaluate, through simulation, the playability of a game design. We propose a playability performance measure and change the value of some parameters of the PacMan game. For each variant of the game thus obtained, simulation yields a value for the quality of the game. This allows us to choose an “optimal” (from a playability point of view) game configuration. The user model is subsequently replaced by a visual interface to a real player, and the game model is executed using a real-time DEVS simulator.     

REALIZATION THEORY OF DISCRETE-EVENT SYSTEMS AND ITS APPLICATION TO THE UNIQUENESS AND UNIVERSALITY OF DEVS FORMALISM

Many man-made systems have discrete event nature. Many modeling formalisms for discrete-event mechanisms have invented and been used for many problems. Among those models, the DEVS formalism is to provide natural and universal models in some sense.

This paper first provides a realization theory of general discrete-event systems. That is, a behavioral definition of discrete-event system is defined, and then a state transition function of the system is constructed. Based on the realization, the uniqueness problem of representations for discrete-event systems is positively solved. Furthermore, as an application of that solution, this paper shows both the fact that a legitimate DEVS with surjective internal transition function is unique up to isomorphism in the class of state representations of the state system defined from the DEVS, and the fact that any discrete-event system has a DEVS realization. In this sense the DEVS modeling facility has the uniqueness and universality in modeling discrete event mechanisms.     

DEVS methodology for evaluating time-constrained message routing policies

Due to its ability to support temporal issues of systems, discrete event simulation is widely applicable to real-time system design. This paper presents a methodology for the modeling and simulation of time-constrained message routing policies for hypercube interconnected real-time systems. The methodology is based on a framework called the DEVS (discrete event systems specification) formalism which supports modular and hierarchical specification of discrete event models. Within the methodology, we first develop DEVS specification for models for hypercube computers and experimental frames to measure the performance of alternative message routing policies. We then implement such specification in DEVSIM++, a C++-based modeling/simulation environment that implements the DEVS formalism. Simulations of various message routing policies are performed, and the performances of such policies are compared.     

A new cell space DEVS specification: Reviewing the parallel DEVS formalism seeking fast cell space simulations

This paper introduces a new specification for cellular DEVS models that assures high performance. It starts with the parallel DEVS specification and derives a high performance cellular DEVS layer using the property of closure under coupling. This is done through converting the parallel DEVS into its equivalent non-modular form which involves computational and communication overhead tradeoffs. The new specification layer, in contrast to multi-component DEVS, is identical to the modular parallel DEVS in the sense of state trajectories which are updated according to the modular message passing methodology. The equivalency of the two forms is verified using simulation methods. Once the equivalency has been ensured, analysis of the models becomes a decisive factor in employing modularity in cellular DEVS models. Non-modular models guarantee the efficiency of the models in contrast to the current cellular DEVS implementation approaches. This was achieved by converting the cell space partially or fully into atomic model in order to eliminate inter-cell messages. However, the new specification needs an automated way to implement and verify models since they might become complicated ones.     

基于DEVS的交叉路口建模与仿真

考虑有信号控制的交叉路口内车辆之间、车辆与行人之间的冲突，在离散事件仿真规范（DEVS）框架下构建了交叉路口微观交通仿真模型.以某市典型交叉路口观察数据标定仿真参数，将仿真结果与按《城市道路设计规范》计算得到的通行能力进行比较，验证了模型.在此基础上，首先，仿真分析了不同左转比例对交叉路口通行能力的影响；然后，基于各方向等待通过交叉路口的车辆数目设计了智能绿信比控制策略.仿真试验表明：通行能力随着左转车比例的增加先上升后下降；智能绿信比控制能显著提升交叉路口通行能力，明显降低平均引道延误时间.由此证明仿真模型能真实地模拟交叉路口各因素间的相互作用，且易于扩充，通用性强，能够用于其它智能交通问题的研究.     

A Real-Time Discrete Event System Specification Formalism for Seamless Real-Time Software Development

We present a time domain extension of the hierarchical and modular discrete event specification (DEVS) formalism. This extension is important for establishing a seamless real-time software development framework. Formalisms help describe a system unambiguously. If formal models are implemented without any consistent frameworks, however, it is hard to guarantee that there is no semantic gap between models and codes. Real-Time DEVS, named RTDEVS, is an extension of DEVS that can be characterized in three perspectives: the real time execution of models, the addition of time interval functions, and the activity specification for each state. After analyzing a system, the framework based on RTDEVS helps to expand each model of the system for executing in a real-time environment. In order to support the RTDEVS formalism, we propose abstract executive concepts based on the abstract simulator concepts of the DEVS formalism. Also, we implement an RTDEVS execution engine, named DEVS Executive, which runs on real-time Mach.     

On time-triggered and event-based control of integrator systems over a shared communication system

When analyzing networked control systems, where the control loop is closed over a communication system, it is crucial to take the communication system into account. Hence, time-triggered and event-based control of an integrator system with noise over a shared communication system is analyzed. Thereby, analytical models of different communication systems are used and the analysis is focused on the effect of the communication system on the performance, as well as the interaction between control and communication. For time-triggered control, where the event times are known in advance, a deterministic communication protocol can be used. Hence, time-triggered control with the two most well-known deterministic communication protocols, time division multiple access (TDMA) and frequency division multiple access (FDMA), is analyzed. For event-based control, where the events appear at random times, a contention-based communication protocol should be used. Hence, event-based control is analyzed with different contention-based communication protocols: pure ALOHA, slotted ALOHA, a queueing system, and Erlang’s loss model. It turns out that time-triggered control with either TDMA or FDMA outperforms event-based control with pure or slotted ALOHA. However, event-based control with a properly designed queueing system gives an even better performance. Thus, we conclude that it is crucial to take the details of the communication system into account.     

State-based versus event-based specifications for information systems: a comparison of B and eb 3

This paper compares two formal methods, B and eb³, for specifying information systems. These two methods are chosen as examples of the state-based paradigm and the event-based paradigm, respectively. The paper considers four viewpoints: functional behavior expression, validation, verification, and evolution. Issues in expressing event ordering constraints, data integrity constraints, and modularity are thereby considered. A simple case study is used to illustrate the comparison, namely, a library management system. Two equivalent specifications are presented using each method. The paper concludes that B and eb³ are complementary. The former is better at expressing complex ordering and static data integrity constraints, whereas the latter provides a simpler, modular, explicit representation of dynamic constraints that are closer to the user’s point of view, while providing loosely coupled definitions of data attributes. The generality of these results from the state-based paradigm and the event-based paradigm perspective are discussed.     

Reachability Graph of Finite and Deterministic DEVS Networks

This paper shows how to generate a finite-vertex graph, called a reachability graph for discrete-event system specification (DEVS) network. The reachability graph is isomorphic to a given original DEVS network in terms of behavior but the number of vertices as well as the number of edges of the reachability graph are finite.