Redes de Petri híbridas adaptativas : alcanzabilidad y ausencia de bloqueos

Las redes de Petri (RdP) son un paradigma formal ampliamente aceptado para el modelado de sistemas de eventos discretos. No obstante, con poblaciones de gran tamaño, aparece el problema de la explosión de estados (crecimiento exponencial del tamaño del conjunto de estados alcanzables). Una manera de paliar este problema consiste en fluidificar el formalismo y considerar redes de Petri continuas, que permiten abordar de manera eficiente el estudio de los sistemas mediante técnicas lineales de análisis. Sin embargo, las RdP continuas no siempre preservan sus propiedades, como por ejemplo la ausencia de bloqueos. En este Trabajo se introduce, formaliza y estudia un formalismo nuevo, denominado redes de Petri híbridas adaptativas (HAPN), que combina comportamiento continuo y discreto: El comportamiento de las transiciones de la red adaptativa es variable: una transición se comporta como continua si su carga de trabajo supera un umbral establecido inicialmente, en caso contrario se comporta como discreta. Estas redes pueden aproximar mejor las redes discretas, mientras que cuando las poblaciones son elevadas el comportamiento es continuo y las técnicas lineales son aplicables, evitando el problema de la explosión de estados. De esta manera, las HAPN constituyen un marco conceptual muy general que incluye a las redes de Petri discretas,continuas e híbridas. En este trabajo, se ha definido formalmente el formalismo de redes de Petri adaptativas. A continuación, se ha caracterizado el conjunto de marcados alcanzables de las redes de Petri adaptativas, así como se compara con el de las RdP discretas. Por ultimo, se ha estudiado la propiedad de ausencia de bloqueos: se trata de determinar si la red adaptativa preserva la ausencia de bloqueos de la red discreta con misma estructura y marcado inicial

Balancing static islands in dynamically scheduled circuits using continuous petri nets

High-level synthesis (HLS) tools automatically transform a high-level program, for example in C/C++, into a low-level hardware description. A key challenge in HLS is scheduling, i.e. determining the start time of all the operations in the untimed program. A major shortcoming of existing approaches to scheduling – whether they are static (start times determined at compile-time), dynamic (start times determined at run-time), or a hybrid of both – is that the static analysis cannot efficiently explore the run-time hardware behaviours. Existing approaches either assume the timing behaviour in extreme cases, which can cause sub-optimal performance or larger area, or use simulation-based approaches, which take a long time to explore enough program traces. In this article, we propose an efficient approach using probabilistic analysis for HLS tools to efficiently explore the timing behaviour of scheduled hardware. We capture the performance of the hardware using Timed Continous Petri nets with immediate transitions, allowing us to leverage efficient Petri net analysis tools for making HLS decisions. We demonstrate the utility of our approach by using it to automatically estimate the hardware throughput for balancing the throughput for statically scheduled components (also known as static islands) computing in a dynamically scheduled circuit. Over a set of benchmarks, we show that our approach on average incurs a 2% overhead in area-delay product compared to optimal designs by exhaustive search

Manufacturing Systems Line Balancing using Max-Plus Algebra

In today\u27s dynamic environment, particularly the manufacturing sector, the necessity of being agile, and flexible is far greater than before. Decision makers should be equipped with effective tools, methods, and information to respond to the market\u27s rapid changes. Modelling a manufacturing system provides unique insight into its behavior and allows simulating all crucial elements that have a role in the system performance. Max-Plus Algebra is a mathematical tool that can model a Discrete Event Dynamic System in the form of linear equations. Whereas Max-Plus Algebra was introduced after the 1980s, the number of studies regarding this tool and its applications is fewer than regarding Petri Nets, Automata, Markov process, Discrete Even Simulation and Queuing models. Consequently, Max-Plus Algebra needs to be applied and tested in many systems in order to explore hidden aspects of its function and capabilities. To work effectively; the production/assembly line should be balanced. Line balancing is one of the manufacturing functions that tries to divide work equally across the production flow. Car Headlight Manufacturing Line as a Discrete Manufacturing System is considered which is a combination of manufacturing and assembly lines composed of different stations. Seven system scenarios were modeled and analyzed using Max-Plus to balance the car headlights production line. Key Performance Indicators (KPIs) are used to compare the various scenarios including Cycle Time, Average Deliver Rate, Total Processing Lead Time, Stations\u27 Utilization Rate, Idle Time, Efficiency, and Financial Analysis. FlexSim simulation software is used to validate the Max-Plus models results and its advantages and drawbacks compared with Max-Plus Algebra. This study is a unique application of Max-Plus Algebra in line balancing of a manufacturing system. Moreover, the problem size of the considered model is at least twice (12 stations) that of previous studies. In the matter of complexity, seven different scenarios are developed through the combination of parallel stations and buffers. Due to that the last scenario is included four parallel stations plus two buffers Based on the findings, the superiority of scenario 7 compared to other scenarios is proved due to its lowest system delivering first output time (14 seconds), best average delivery rate (24.5 seconds), shortest cycle time (736 seconds), shortest total processing lead time (11,534 seconds), least percentage of idle time (12%), lowest unit cost ($6.9), and highest efficiency (88%). However, Scenario 4 has the best utilization rate at 75%

Recent advances in petri nets and concurrency

CEUR Workshop Proceeding

An agile and adaptive holonic architecture for manufacturing control

In the last decades significant changes in the manufacturing environment have been noticed: moving from a local economy towards a global economy, with markets asking for products with high quality at lower costs, highly customised and with short life cycle. In this environment, the manufacturing enterprises, to avoid the risk to lose competitiveness, search to answer more closely to the customer demands, by improving their flexibility and agility, while maintaining their productivity and quality. Actually, the dynamic response to emergence is becoming a key issue, due to the weak response of the traditional manufacturing control systems to unexpected disturbances, mainly because of the rigidity of their control architectures. In these circumstances, the challenge is to develop manufacturing control systems with autonomy and intelligence capabilities, fast adaptation to the environment changes, more robustness against the occurrence of disturbances, and easier integration of manufacturing resources and legacy systems. Several architectures using emergent concepts and technologies have been proposed, in particular those based in the holonic manufacturing paradigm. Holonic manufacturing is a paradigm based in the ideas of the philosopher Arthur Koestler, who proposed the word holon to describe a basic unit of organisation in biological and social systems. A holon, as Koestler devised the term, is an identifiable part of a (manufacturing) system that has a unique identity, yet is made up of sub-ordinate parts and in turn is part of a larger whole. The introduction of the holonic manufacturing paradigm allows a new approach to the manufacturing problem, bringing the advantages of modularity, decentralisation, autonomy, scalability, and re-use of software components. This dissertation intends to develop an agile and adaptive manufacturing control architecture to face the current requirements imposed to the manufacturing enterprises. The architecture proposed in this dissertation addresses the need for the fast reaction to disturbances at the shop floor level, increasing the agility and flexibility of the enterprise, when it works in volatile environments, characterised by the frequent occurrence of unexpected disturbances. The proposed architecture, designated by ADACOR (ADAptive holonic COntrol aRchitecture for distributed manufacturing systems), is based in the holonic manufacturing paradigm, build upon autonomous and cooperative holons, allowing the development of manufacturing control applications that present all the features of decentralised and holonic systems. ADACOR holonic architecture introduces an adaptive control that balances dynamically between a more centralised structure and a more decentralised one, allowing to combine the global production optimisation with agile reaction to unexpected disturbances. Nas últimas décadas têm-se assistido a mudanças significativas no ambiente de fabrico: evoluindo de uma economia local para um economia global, com os mercados a procurar produtos com elevada qualidade a baixos preços, altamente customizados e com um ciclo de vida curto. Neste ambiente, as empresas de manufactura, para evitar o risco de perda de competitividade, procuram responder às solicitações dos clientes, melhorando a sua flexibilidade e agilidade, mantendo os mesmos índices de produtividade e qualidade. Na verdade, a resposta dinâmica à emergência está a tornar-se num assunto chave, devido `a fraca resposta a perturbações que os sistemas de controlo de fabrico tradicionais apresentam, principalmente devido à rigidez das suas arquitecturas de controlo. Nestas circunstâncias, é fundamental o desenvolvimento de sistemas de controlo de fabrico com capacidades de autonomia e inteligência, rápida adaptação às mudanças, maior robustez à ocorrência de perturbações e fácil integração de recursos físicos e sistemas legados. Diversas arquitecturas usando conceitos e tecnologias emergentes têm sido propostas, em particular algumas baseadas no paradigma da produção holónica. O paradigma da produção holónica é inspirado nas ideias de Arthur Koestler, que propôs a palavra holon para descrever uma unidade básica de organização de sistemas biológicos e sociais. Um holon, de acordo com a definição de Koestler, é uma parte identificável do sistema com identidade única, composta por sub-partes e fazendo simultaneamente parte do todo. A introdução do paradigma da produção holónica permite uma nova abordagem aos sistemas de controlo de fabrico, trazendo vantagens de modularidade, descentralização, autonomia, escalabilidade e reutilização de componentes. Esta dissertação pretende desenvolver uma arquitectura de controlo ágil e adaptativa que suporte os requisitos actuais impostos `as empresas de manufactura. A arquitectura proposta visa a necessidade de uma reacção rápida a perturbações, ao nível da planta fabril, melhorando a flexibilidade e agilidade da empresa quando esta opera em ambientes voláteis, caracterizados pela ocorrência frequente de perturbações inesperadas. A arquitectura proposta, designada por ADACOR (ADAptive holonic COntrol aRchitecture for distributed manufacturing systems), é baseada no paradigma da produção holónica e construída sobre holons autónomos e cooperativos, permitindo o desenvolvimento de aplicações de controlo de fabrico que apresentem todas as características dos sistemas descentralizados e holónicos. A arquitectura holónica ADACOR introduz um controlo adaptativo que balança dinamicamente entre uma estrutura de controlo mais centralizada e uma mais descentralizada, permitindo combinar a optimização da produção com a ágil reacção a perturbações

Computer Aided Verification

This open access two-volume set LNCS 10980 and 10981 constitutes the refereed proceedings of the 30th International Conference on Computer Aided Verification, CAV 2018, held in Oxford, UK, in July 2018. The 52 full and 13 tool papers presented together with 3 invited papers and 2 tutorials were carefully reviewed and selected from 215 submissions. The papers cover a wide range of topics and techniques, from algorithmic and logical foundations of verification to practical applications in distributed, networked, cyber-physical, and autonomous systems. They are organized in topical sections on model checking, program analysis using polyhedra, synthesis, learning, runtime verification, hybrid and timed systems, tools, probabilistic systems, static analysis, theory and security, SAT, SMT and decisions procedures, concurrency, and CPS, hardware, industrial applications

Simulation product fidelity: a qualitative & quantitative system engineering approach

La modélisation informatique et la simulation sont des activités de plus en plus répandues lors de la conception de systèmes complexes et critiques tels que ceux embarqués dans les avions. Une proposition pour la conception et réalisation d'abstractions compatibles avec les objectifs de simulation est présentée basés sur la théorie de l'informatique, le contrôle et le système des concepts d'ingénierie. Il adresse deux problèmes fondamentaux de fidélité dans la simulation, c'est-à-dire, pour une spécification du système et quelques propriétés d'intérêt, comment extraire des abstractions pour définir une architecture de produit de simulation et jusqu'où quel point le comportement du modèle de simulation représente la spécification du système. Une notion générale de cette fidélité de la simulation, tant architecturale et comportementale, est expliquée dans les notions du cadre expérimental et discuté dans le contexte des abstractions de modélisation et des relations d'inclusion. Une approche semi-formelle basée sur l'ontologie pour construire et définir l'architecture de produit de simulation est proposée et démontrée sur une étude d'échelle industrielle. Une approche formelle basée sur le jeu théorique et méthode formelle est proposée pour différentes classes de modèles des systèmes et des simulations avec un développement d'outils de prototype et cas des études. Les problèmes dans la recherche et implémentation de ce cadre de fidélité sont discutées particulièrement dans un contexte industriel.In using Modeling and Simulation for the system Verification & Validation activities, often the difficulty is finding and implementing consistent abstractions to model the system being simulated with respect to the simulation requirements. A proposition for the unified design and implementation of modeling abstractions consistent with the simulation objectives based on the computer science, control and system engineering concepts is presented. It addresses two fundamental problems of fidelity in simulation, namely, for a given system specification and some properties of interest, how to extract modeling abstractions to define a simulation product architecture and how far does the behaviour of the simulation model represents the system specification. A general notion of this simulation fidelity, both architectural and behavioural, in system verification and validation is explained in the established notions of the experimental frame and discussed in the context of modeling abstractions and inclusion relations. A semi-formal ontology based domain model approach to build and define the simulation product architecture is proposed with a real industrial scale study. A formal approach based on game theoretic quantitative system refinement notions is proposed for different class of system and simulation models with a prototype tool development and case studies. Challenges in research and implementation of this formal and semi-formal fidelity framework especially in an industrial context are discussed