995 resultados para Discrete events
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Traditionally, the cusp has been described in terms of a time-stationary feature of the magnetosphere which allows access of magnetosheath-like plasma to low altitudes. Statistical surveys of data from low-altitude spacecraft have shown the average characteristics and position of the cusp. Recently, however, it has been suggested that the ionospheric footprint of flux transfer events (FTEs) may be identified as variations of the “cusp” on timescales of a few minutes. In this model, the cusp can vary in form between a steady-state feature in one limit and a series of discrete ionospheric FTE signatures in the other limit. If this time-dependent cusp scenario is correct, then the signatures of the transient reconnection events must be able, on average, to reproduce the statistical cusp occurrence previously determined from the satellite observations. In this paper, we predict the precipitation signatures which are associated with transient magnetopause reconnection, following recent observations of the dependence of dayside ionospheric convection on the orientation of the IMF. We then employ a simple model of the longitudinal motion of FTE signatures to show how such events can easily reproduce the local time distribution of cusp occurrence probabilities, as observed by low-altitude satellites. This is true even in the limit where the cusp is a series of discrete events. Furthermore, we investigate the existence of double cusp patches predicted by the simple model and show how these events may be identified in the data.
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The objective of this article is to apply the Design of experiments technique along with the Discrete Events Simulation technique in an automotive process. The benefits of the design of experiments in simulation include the possibility to improve the performance in the simulation process, avoiding trial and error to seek solutions. The methodology of the conjoint use of Design of Experiments and Computer Simulation is presented to assess the effects of the variables and its interactions involved in the process. In this paper, the efficacy of the use of process mapping and design of experiments on the phases of conception and analysis are confirmed. © 2007 IEEE.
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The current solutions implanted in the majority of manufacturing systems controlled by PLCs were developed through the language of programming known as ladder. Such a language, easily learned and handled, shows to be efficient whenever the system to be implanted does not demand greater complexity of analyses. Bigger systems, presenting characteristics in which resource compartments, parallelism and synchronizing among processes are more frequent, demand the adoption of solutions differentiation. This article presents a teaching experience and practical application of Petri nets in a Mechatronics Engineering graduation course. Copyright © 2007 IFAC.
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In dealing with computer networks, these allow the flow of information through the resources of various equipment's. This work describes the implementation through the encapsulation of Protocol DNP3, usually employed in Smart Grid communication, in a simulator of discrete events. The NS-2 is a simulator in open source of network events, that facilitate the development of communication networks scenarios considering the protocols involved, in wireless or wired technologies. The objective of this work is to develop the DNP3 protocol encapsulation over a TCP/IP in the in the discrete event Simulator NS-2, allowing an analysis of behavior of a middle or large network sized in Smart Grid applications. © 2013 IEEE.
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
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Recently in most of the industrial automation process an ever increasing degree of automation has been observed. This increasing is motivated by the higher requirement of systems with great performance in terms of quality of products/services generated, productivity, efficiency and low costs in the design, realization and maintenance. This trend in the growth of complex automation systems is rapidly spreading over automated manufacturing systems (AMS), where the integration of the mechanical and electronic technology, typical of the Mechatronics, is merging with other technologies such as Informatics and the communication networks. An AMS is a very complex system that can be thought constituted by a set of flexible working stations, one or more transportation systems. To understand how this machine are important in our society let considerate that every day most of us use bottles of water or soda, buy product in box like food or cigarets and so on. Another important consideration from its complexity derive from the fact that the the consortium of machine producers has estimated around 350 types of manufacturing machine. A large number of manufacturing machine industry are presented in Italy and notably packaging machine industry,in particular a great concentration of this kind of industry is located in Bologna area; for this reason the Bologna area is called “packaging valley”. Usually, the various parts of the AMS interact among them in a concurrent and asynchronous way, and coordinate the parts of the machine to obtain a desiderated overall behaviour is an hard task. Often, this is the case in large scale systems, organized in a modular and distributed manner. Even if the success of a modern AMS from a functional and behavioural point of view is still to attribute to the design choices operated in the definition of the mechanical structure and electrical electronic architecture, the system that governs the control of the plant is becoming crucial, because of the large number of duties associated to it. Apart from the activity inherent to the automation of themachine cycles, the supervisory system is called to perform other main functions such as: emulating the behaviour of traditional mechanical members thus allowing a drastic constructive simplification of the machine and a crucial functional flexibility; dynamically adapting the control strategies according to the different productive needs and to the different operational scenarios; obtaining a high quality of the final product through the verification of the correctness of the processing; addressing the operator devoted to themachine to promptly and carefully take the actions devoted to establish or restore the optimal operating conditions; managing in real time information on diagnostics, as a support of the maintenance operations of the machine. The kind of facilities that designers can directly find on themarket, in terms of software component libraries provides in fact an adequate support as regard the implementation of either top-level or bottom-level functionalities, typically pertaining to the domains of user-friendly HMIs, closed-loop regulation and motion control, fieldbus-based interconnection of remote smart devices. What is still lacking is a reference framework comprising a comprehensive set of highly reusable logic control components that, focussing on the cross-cutting functionalities characterizing the automation domain, may help the designers in the process of modelling and structuring their applications according to the specific needs. Historically, the design and verification process for complex automated industrial systems is performed in empirical way, without a clear distinction between functional and technological-implementation concepts and without a systematic method to organically deal with the complete system. Traditionally, in the field of analog and digital control design and verification through formal and simulation tools have been adopted since a long time ago, at least for multivariable and/or nonlinear controllers for complex time-driven dynamics as in the fields of vehicles, aircrafts, robots, electric drives and complex power electronics equipments. Moving to the field of logic control, typical for industrial manufacturing automation, the design and verification process is approached in a completely different way, usually very “unstructured”. No clear distinction between functions and implementations, between functional architectures and technological architectures and platforms is considered. Probably this difference is due to the different “dynamical framework”of logic control with respect to analog/digital control. As a matter of facts, in logic control discrete-events dynamics replace time-driven dynamics; hence most of the formal and mathematical tools of analog/digital control cannot be directly migrated to logic control to enlighten the distinction between functions and implementations. In addition, in the common view of application technicians, logic control design is strictly connected to the adopted implementation technology (relays in the past, software nowadays), leading again to a deep confusion among functional view and technological view. In Industrial automation software engineering, concepts as modularity, encapsulation, composability and reusability are strongly emphasized and profitably realized in the so-calledobject-oriented methodologies. Industrial automation is receiving lately this approach, as testified by some IEC standards IEC 611313, IEC 61499 which have been considered in commercial products only recently. On the other hand, in the scientific and technical literature many contributions have been already proposed to establish a suitable modelling framework for industrial automation. During last years it was possible to note a considerable growth in the exploitation of innovative concepts and technologies from ICT world in industrial automation systems. For what concerns the logic control design, Model Based Design (MBD) is being imported in industrial automation from software engineering field. Another key-point in industrial automated systems is the growth of requirements in terms of availability, reliability and safety for technological systems. In other words, the control system should not only deal with the nominal behaviour, but should also deal with other important duties, such as diagnosis and faults isolations, recovery and safety management. Indeed, together with high performance, in complex systems fault occurrences increase. This is a consequence of the fact that, as it typically occurs in reliable mechatronic systems, in complex systems such as AMS, together with reliable mechanical elements, an increasing number of electronic devices are also present, that are more vulnerable by their own nature. The diagnosis problem and the faults isolation in a generic dynamical system consists in the design of an elaboration unit that, appropriately processing the inputs and outputs of the dynamical system, is also capable of detecting incipient faults on the plant devices, reconfiguring the control system so as to guarantee satisfactory performance. The designer should be able to formally verify the product, certifying that, in its final implementation, it will perform itsrequired function guarantying the desired level of reliability and safety; the next step is that of preventing faults and eventually reconfiguring the control system so that faults are tolerated. On this topic an important improvement to formal verification of logic control, fault diagnosis and fault tolerant control results derive from Discrete Event Systems theory. The aimof this work is to define a design pattern and a control architecture to help the designer of control logic in industrial automated systems. The work starts with a brief discussion on main characteristics and description of industrial automated systems on Chapter 1. In Chapter 2 a survey on the state of the software engineering paradigm applied to industrial automation is discussed. Chapter 3 presentes a architecture for industrial automated systems based on the new concept of Generalized Actuator showing its benefits, while in Chapter 4 this architecture is refined using a novel entity, the Generalized Device in order to have a better reusability and modularity of the control logic. In Chapter 5 a new approach will be present based on Discrete Event Systems for the problemof software formal verification and an active fault tolerant control architecture using online diagnostic. Finally conclusive remarks and some ideas on new directions to explore are given. In Appendix A are briefly reported some concepts and results about Discrete Event Systems which should help the reader in understanding some crucial points in chapter 5; while in Appendix B an overview on the experimental testbed of the Laboratory of Automation of University of Bologna, is reported to validated the approach presented in chapter 3, chapter 4 and chapter 5. In Appendix C some components model used in chapter 5 for formal verification are reported.
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At the mid-latitudes of Utopia Planitia (UP), Mars, a suite of spatially-associated landforms exhibit geomorphological traits that, on Earth, would be consistent with periglacial processes and the possible freeze-thaw cycling of water. The suite comprises small-sized polygonally-patterned ground, polygon-junction and -margin pits, and scalloped, rimless depressions. Typically, the landforms incise a dark-toned terrain that is thought to be ice-rich. Here, we investigate the dark-toned terrain by using high resolution images from the HiRISE as well as near-infrared spectral-data from the OMEGA and CRISM. The terrain displays erosional characteristics consistent with a sedimentary nature and near-infrared spectra characterised by a blue slope similar to that of weathered basaltic-tephra. We also describe volcanic terrain that is dark-toned and periglacially-modified in the Kamchatka mountain-range of eastern Russia. The terrain is characterised by weathered tephra inter-bedded with snow, ice-wedge polygons and near-surface excess ice. The excess ice forms in the pore space of the tephra as the result of snow-melt infiltration and, subsequently, in-situ freezing. Based on this possible analogue, we construct a three-stage mechanism that explains the possible ice-enrichment of a broad expanse of dark-toned terrain at the mid-latitudes of UP: (1) the dark-toned terrain accumulates and forms via the regional deposition of sediments sourced from explosive volcanism; (2) the volcanic sediments are blanketed by atmospherically-precipitated (H2O) snow, ice or an admixture of the two, either concurrent with the volcanic-events or between discrete events; and, (3) under the influence of high obliquity or explosive volcanism, boundary conditions tolerant of thaw evolve and this, in turn, permits the migration, cycling and eventual formation of excess ice in the volcanic sediments. Over time, and through episodic iterations of this scenario, excess ice forms to decametres of depth. (C) 2015 Elsevier B.V. All rights reserved.
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The Ampère Seamount, 600 km west of Gibraltar, is one of nine inactive volcanoes along a bent chain, the so called Horseshoe Seamounts. All of them ascend from an abyssal plain of 4000 to 4800 m depth up to a few hundred meters below the sea surface, except two, which nearly reach the surface: the Ampère massif on the southern flank of the group and the summit of the Gorringe bank in the north. The horseshoe, serrated like a crown, opens towards Gibraltar and stands in the way of its outflow. These seamounts are part of the Azores-Gibraltar structure, which marks the boundary between two major tectonic plates: the Eurasian and the African plate. The submarine volcanism which formed the Horseshoe Seamounts belongs to the sea floor spread area of the Mid-Atlantic Ridge. The maximum activity was between 17 and 10 Million years ago and terminated thereafter. The volcanoes consist of basalts and tuffs. Most of their flanks and the abyssal plain around are covered by sediments of micro-organic origin. These sediments, in particular their partial absence on the upper flanks are a circumstantial proof and a kind of diary of the initial rise and subsequent subsidence of about 6oo m of these seamounts. The horizons of erosion where the basalt substrate is laid bare indicate the rise above sea level in the past. Since the Ampère summit is 60 m deep today, this volcano must have been an island 500 m high. The stratification of the sediments covering the surrounding abyssal plain reveals discrete events of downslope suspension flows, called turbidites, separated by tens of thousands of years and perhaps induced by changes in climate conditions. The Ampère sea mount of 4800 m height and a base diameter of 50 km exceeds the size of the Mont Blanc massif. Its southern and eastern flanks are steep with basalts cropping out, in parts with nearly vertical walls of some hundred meters. The west and north sides consist of terraces and plateaus covered with sediments at 140 m, 400 m, 2000 m, and 3500 m. The Horseshoe Seamount area is also remarkable as a kind of disturbed crossing of three major oceanic flow systems at different depths and directions with forced upwelling and partial mixing of the water masses. Most prominent is the Mediterranean Outflow Water (MOW) with its higher temperature and salinity between 900 to 1500 m depth. It enters the horseshoe unimpaired from the open eastern side but penetrates the seamount chain through its valleys on the west, thereafter diverging and crossing the entire Atlantic Ocean. Below the MOW is the North Atlantic Deep Water (NADW) between 2000 m to 3000 m depth flowing southward and finally there is the Antarctic Bottom Water (AABW) flowing northward below the two other systems.
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Until a few years ago, most of the network communications were based in the wire as the physical media, but due to the advances and the maturity of the wireless communications, this is changing. Nowadays wireless communications offers fast, secure, efficient and reliable connections. Mobile communications are in expansion, clearly driven by the use of smart phones and other mobile devices, the use of laptops, etc… Besides that point, the inversion in the installation and maintenance of the physical medium is much lower than in wired communications, not only because the air has no cost, but because the installation and maintenance of the wire require a high economic cost. Besides the economic cost we find that wire is a more vulnerable medium to external threats such as noise, sabotages, etc… There are two different types of wireless networks: those which the structure is part of the network itself and those which have a lack of structure or any centralization, in a way that the devices that form part of the network can connect themselves in a dynamic and random way, handling also the routing of every control and information messages, this kind of networks is known as Ad-hoc. In the present work we will proceed to study one of the multiple wireless protocols that allows mobile communications, it is Optimized Link State Routing, from now on, OLSR, it is an pro-active routing, standard mechanism that works in a distributed in order to stablish the connections among the different nodes that belong to a wireless network. Thanks to this protocol it is possible to get all the routing tables in all the devices correctly updated every moment through the periodical transmission of control messages and on this way allow a complete connectivity among the devices that are part of the network and also, allow access to other external networks such as virtual private networks o Internet. This protocol could be perfectly used in environments such as airports, malls, etc… The update of the routing tables in all the devices is got thanks to the periodical transmission of control messages and finally it will offer connectivity among all the devices and the corresponding external networks. For the study of OLSR protocol we will have the help of the network simulator “Network Simulator 2”, a freeware network simulator programmed in C++ based in discrete events. This simulator is used mainly in educational and research environments and allows a very extensive range of protocols, both, wired networks protocols and wireless network protocols, what is going to be really useful to proceed to the simulation of different configurations of networks and protocols. In the present work we will also study different simulations with Network Simulator 2, in different scenarios with different configurations, wired networks, and Ad-hoc networks, where we will study OLSR Protocol. RESUMEN. Hasta hace pocos años, la mayoría de las comunicaciones de red estaban basadas en el cable como medio físico pero debido al avance y madurez alcanzados en el campo de las comunicaciones inalámbricas esto está cambiando. Hoy día las comunicaciones inalámbricas nos ofrecen conexiones veloces, seguras, eficientes y fiables. Las comunicaciones móviles se encuentran en su momento de máxima expansión, claramente impulsadas por el uso de teléfonos y demás dispositivos móviles, el uso de portátiles, etc… Además la inversión a realizar en la instalación y el mantenimiento del medio físico en las comunicaciones móviles es muchísimo menor que en comunicaciones por cable, ya no sólo porque el aire no tenga coste alguno, sino porque la instalación y mantenimiento del cable precisan de un elevado coste económico por norma. Además del coste económico nos encontramos con que es un medio más vulnerable a amenazas externas tales como el ruido, escuchas no autorizadas, sabotajes, etc… Existen dos tipos de redes inalámbricas: las constituidas por una infraestructura que forma parte más o menos de la misma y las que carecen de estructura o centralización alguna, de modo que los dispositivos que forman parte de ella pueden conectarse de manera dinámica y arbitraria entre ellos, encargándose además del encaminamiento de todos los mensajes de control e información, a este tipo de redes se las conoce como redes Ad-hoc. En el presente Proyecto de Fin de Carrera se procederá al estudio de uno de los múltiples protocolos inalámbricos que permiten comunicaciones móviles, se trata del protocolo inalámbrico Optimized Link State Routing, de ahora en adelante OLSR, un mecanismo estándar de enrutamiento pro-activo, que trabaja de manera distribuida para establecer las conexiones entre los nodos que formen parte de las redes inalámbricas Ad-hoc, las cuales carecen de un nodo central y de una infraestructura pre-existente. Gracias a este protocolo es posible conseguir que todos los equipos mantengan en todo momento las tablas de ruta actualizadas correctamente mediante la transmisión periódica de mensajes de control y así permitir una completa conectividad entre todos los equipos que formen parte de la red y, a su vez, también permitir el acceso a otras redes externas tales como redes privadas virtuales o Internet. Este protocolo sería usado en entornos tales como aeropuertos La actualización de las tablas de enrutamiento de todos los equipos se conseguirá mediante la transmisión periódica de mensajes de control y así finalmente se podrá permitir conectividad entre todos los equipos y con las correspondientes redes externas. Para el estudio del protocolo OLSR contaremos con el simulador de redes Network Simulator 2, un simulador de redes freeware programado en C++ basado en eventos discretos. Este simulador es usado principalmente en ambientes educativos y de investigación y permite la simulación tanto de protocolos unicast como multicast. El campo donde más se utiliza es precisamente en el de la investigación de redes móviles Ad-hoc. El simulador Network Simulator 2 no sólo implementa el protocolo OLSR, sino que éste implementa una amplia gama de protocolos, tanto de redes cableadas como de redes inalámbricas, lo cual va a sernos de gran utilidad para proceder a la simulación de distintas configuraciones de redes y protocolos. En el presente Proyecto de Fin de Carrera se estudiarán también diversas simulaciones con el simulador NS2 en diferentes escenarios con diversas configuraciones; redes cableadas, redes inalámbricas Ad-hoc, donde se estudiará el protocolo antes mencionado: OLSR. Este Proyecto de Fin de Carrera consta de cuatro apartados distintos: Primeramente se realizará el estudio completo del protocolo OLSR, se verán los beneficios y contrapartidas que ofrece este protocolo inalámbrico. También se verán los distintos tipos de mensajes existentes en este protocolo y unos pequeños ejemplos del funcionamiento del protocolo OLSR. Seguidamente se hará una pequeña introducción al simulador de redes Network Simulator 2, veremos la historia de este simulador, y también se hará referencia a la herramienta extra NAM, la cual nos permitirá visualizar el intercambio de paquetes que se produce entre los diferentes dispositivos de nuestras simulaciones de forma intuitiva y amigable. Se hará mención a la plataforma MASIMUM, encargada de facilitar en un entorno académico software y documentación a sus alumnos con el fin de facilitarles la investigación y la simulación de redes y sensores Ad-hoc. Finalmente se verán dos ejemplos, uno en el que se realizará una simulación entre dos PCs en un entorno Ethernet y otro ejemplo en el que se realizará una simulación inalámbrica entre cinco dispositivos móviles mediante el protocolo a estudiar, OLSR.
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Proper management of supply chains is fundamental in the overall system performance of forestbased activities. Usually, efficient management techniques rely on a decision support software, which needs to be able to generate fast and effective outputs from the set of possibilities. In order to do this, it is necessary to provide accurate models representative of the dynamic interactions of systems. Due to forest-based supply chains’ nature, event-based models are more suited to describe their behaviours. This work proposes the modelling and simulation of a forestbased supply chain, in particular the biomass supply chain, through the SimPy framework. This Python based tool allows the modelling of discrete-event systems using operations such as events, processes and resources. The developed model was used to access the impact of changes in the daily working plan in three situations. First, as a control case, the deterministic behaviour was simulated. As a second approach, a machine delay was introduced and its implications in the plan accomplishment were analysed. Finally, to better address real operating conditions, stochastic behaviours of processing and driving times were simulated. The obtained results validate the SimPy simulation environment as a framework for modelling supply chains in general and for the biomass problem in particular.
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Two sediment cores retrieved from the continental slope in the Benguela Upwelling System, GeoB 1706 (19°33.7'S 11°10.5'E) and GeoB 1711 (23°18.9'S, 12°22.6'E), reveal striking variations in planktonic foraminiferal abundances during the last 160,000 years. These fluctuations are investigated to assess changes in the intensity and position of the upwelling centres off Namibia. Four species make up over 95% of the variation within the core, and enable the record to be divided into episodes characterized by particular planktonic foraminiferal assemblages. The fossil assemblages have meaningful ecological significance when compared to those of the modern day and the relationship to their environment. The cold-water planktonic foraminifer, Neogloboquadrina pachyderma sinistral [N. pachyderma (s)], dominates the modern-day, coastal upwelling centres, and Neogloboquadrina pachyderma dextral and Globigerina bulloides characterize the fringes of the upwelling cells. Globorotalia inflata is representative of the offshore boundary between newly upwelled waters and the transitional, reduced nutrient levels of the subtropical waters. In the fossil record, episodes of high N. pachyderma (s) abundances are interpreted as evidence of increased upwelling intensity, and the associated increase in nutrients. The N. pachyderma (s) record suggests temporal shifts in the intensity of upwelling, and corresponding trophic domains, that do not follow the typical glacial-interglacial pattern. Periods of high N. pachyderma (s) abundance describe rapid, discrete events dominating isotope stages 3 and 2. The timing of these events correlates to the temporal shifts of the Angola-Benguela Front (Jansen et al., 1997) situated to the north of the Walvis Ridge. Absence of high abundances of N. pachyderma (s) from the continental slope of the southern Cape Basin indicates that Southern Ocean surface water advection has not exerted a major influence on the Benguela Current System. The coincidence of increased upwelling intensity with the movement of the Angola-Benguela Front can be interpreted mainly by changes in strength and zonality of the trade wind system.
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En el mundo de la simulación existen varios tipos de sistemas reales, entre los que se encuentran los sistemas de eventos discretos. Para poder simular estos sistemas se pueden utilizar, entre otras, herramientas basadas en el formalismo DEVS (Discrete EVents system Specification), como la utilizada en este proyecto: xDEVS. La simulación posee una importancia muy elevada en campos como la educación y la ciencia, y en ocasiones es necesario incluir datos del medio físico o sacar información al exterior del simulador. Por ello es necesario contar con herramientas que puedan realizar simulaciones utilizando sensores, actuadores, circuitos externos, etc., o lo que es lo mismo, que puedan realizar co-simulaciones entre software y hardware. De esta forma se puede facilitar el desarrollo de sistemas por medio de modelado y simulación, pudiendo extraer el hardware gradualmente y analizar los resultados en cada etapa. Este proyecto es de carácter incremental, y trata de extender la funcionalidad de la plataforma xDEVS para poder realizar co-simulaciones entre hardware y software sobre una Raspberry Pi. Para ello se van a utilizar circuitos lógicos como hardware externo y se enlazarán al simulador a través de ficheros de dispositivo, gestionados por módulos del kernel de Linux. Como caso de estudio se desarrolla la co-simulación entre hardware y software completa de un ascensor de siete plantas para mostrar el uso y funcionamiento en xDEVS, extrayendo los circuitos integrados de uno en uno.
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[EN]In this paper, a basic conceptual architecture aimed at the design of Computer Vision System is qualitatively described. The proposed architecture addresses the design of vision systems in a modular fashion using modules with three distinct units or components: a processing network or diagnostics unit, a control unit and a communications unit. The control of the system at the modules level is designed based on a Discrete Events Model. This basic methodology has been used to design a realtime active vision system for detection, tracking and recognition of people. It is made up of three functional modules aimed at the detection, tracking, recognition of moving individuals plus a supervision module.