41 research outputs found

    Experimental Study on Real-Time Wireless Networks for Motion Control of Manipulator and Mobile Platform in Industrial Robotics

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    The integration of ICT with manufacturing technologies is a key step towards intelligent manufacturing. The goal is to investigate some industrial application scenarios and evaluate the performance of selected wireless technologies. A recently standardized industrial wireless technology, WIA-FA, has shown good performance in practical deployments. Two experimental applications are considered: path planning testing with different wireless technologies and CANbus bridging with WIA-FA.openEmbargo temporaneo per motivi di segretezza e/o di proprietà dei risultati e informazioni di enti esterni o aziende private che hanno partecipato alla realizzazione del lavoro di ricerca relativo alla tes

    Using phase space attractors to evaluate system safety constraint enforcement : case study in space shuttle mission control procedure rework

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    Thesis (Ph. D.)--Massachusetts Institute of Technology, Engineering Systems Division, 2009.Vita. Cataloged from PDF version of thesis.Includes bibliographical references (p. 390-409).As the complexity and influence of engineering systems in modern society increases, so too does their potential to create counterintuitive and catastrophic accidents. Increasingly, the accidents encountered in these systems are defying the linearized notions of accident causality that-though developed for the simpler engineered systems of the past-are prevalently used for accident prevention today. In this dissertation, an alternative approach to accident prevention based on systems theory-the Systems-Theoretic Accident Model and Processes (STAMP) and STAMP-based hazard analysis (STPA)-is augmented with the notion of using phase space attractors to evaluate how well STAMP safety control structures enforce system safety constraints. Phase space attractors are mathematical results that emerge from the behavior of systems with dynamic structures that draw or constrain these systems to specific regions of their phase space in spite of a range of conditions. Accordingly, the goal in using this notion for the evaluation of safety constraint enforcement is to identify and analyze the attractors produced by a safety control structure to determine if it will adequately "attract" the system to safe states in spite of a range of unforeseeable conditions. Support for this approach to evaluating STAMP safety control structures is provided through the study of a safety control structure in an existing complex, socio-technical system. This case study is focused on a safety control process-referred to as Procedure Rework-used in Space Shuttle Mission Control to update procedures during in-flight operations as they are invalidated by changes in the state of the Space Shuttle and its environment.(cont.) Simulation models of procedure rework are developed through physical and human factors principles and calibrated with data from five Space Shuttle missions; producing simulation results with deviations from the historical data that are-as characterized by Theil Inequality Statistics-small and primarily due to cycles and noise that are not relevant to the models' purpose. The models are used to analyze the attractor produced by the Procedure Rework Process across varied conditions, including a notional crewed spacecraft mission to a distant celestial body. A detrimental effect in the process is identified-and shown to be potentially far more severe than light delay on a mission to a distant celestial body-and approaches to mitigating the effect are explored. Finally, the analysis conducted is described as a generalizeable process for using phase space attractors to evaluate system safety constraint enforcement in engineering systems.by Brandon D. Owens.Ph.D

    Spectrum Sharing Methods in Coexisting Wireless Networks

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    Radio spectrum, the fundamental basis for wireless communication, is a finite resource. The development of the expanding range of radio based devices and services in recent years makes the spectrum scarce and hence more costly under the paradigm of extensive regulation for licensing. However, with mature technologies and with their continuous improvements it becomes apparent that tight licensing might no longer be required for all wireless services. This is from where the concept of utilizing the unlicensed bands for wireless communication originates. As a promising step to reduce the substantial cost for radio spectrum, different wireless technology based networks are being deployed to operate in the same spectrum bands, particularly in the unlicensed bands, resulting in coexistence. However, uncoordinated coexistence often leads to cases where collocated wireless systems experience heavy mutual interference. Hence, the development of spectrum sharing rules to mitigate the interference among wireless systems is a significant challenge considering the uncoordinated, heterogeneous systems. The requirement of spectrum sharing rules is tremendously increasing on the one hand to fulfill the current and future demand for wireless communication by the users, and on the other hand, to utilize the spectrum efficiently. In this thesis, contributions are provided towards dynamic and cognitive spectrum sharing with focus on the medium access control (MAC) layer, for uncoordinated scenarios of homogeneous and heterogeneous wireless networks, in a micro scale level, highlighting the QoS support for the applications. This thesis proposes a generic and novel spectrum sharing method based on a hypothesis: The regular channel occupation by one system can support other systems to predict the spectrum opportunities reliably. These opportunities then can be utilized efficiently, resulting in a fair spectrum sharing as well as an improving aggregated performance compared to the case without having special treatment. The developed method, denoted as Regular Channel Access (RCA), is modeled for systems specified by the wireless local resp. metropolitan area network standards IEEE 802.11 resp. 802.16. In the modeling, both systems are explored according to their respective centrally controlled channel access mechanisms and the adapted models are evaluated through simulation and results analysis. The conceptual model of spectrum sharing based on the distributed channel access mechanism of the IEEE 802.11 system is provided as well. To make the RCA method adaptive, the following enabling techniques are developed and integrated in the design: a RSS-based (Received Signal Strength based) detection method for measuring the channel occupation, a pattern recognition based algorithm for system identification, statistical knowledge based estimation for traffic demand estimation and an inference engine for reconfiguration of resource allocation as a response to traffic dynamics. The advantage of the RCA method is demonstrated, in which each competing collocated system is configured to have a resource allocation based on the estimated traffic demand of the systems. The simulation and the analysis of the results show a significant improvement in aggregated throughput, mean delay and packet loss ratio, compared to the case where legacy wireless systems coexists. The results from adaptive RCA show its resilience characteristics in case of dynamic traffic. The maximum achievable throughput between collocated IEEE 802.11 systems applying RCA is provided by means of mathematical calculation. The results of this thesis provide the basis for the development of resource allocation methods for future wireless networks particularly emphasized to operate in current unlicensed bands and in future models of the Open Spectrum Alliance

    Engineering Self-Adaptive Collective Processes for Cyber-Physical Ecosystems

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    The pervasiveness of computing and networking is creating significant opportunities for building valuable socio-technical systems. However, the scale, density, heterogeneity, interdependence, and QoS constraints of many target systems pose severe operational and engineering challenges. Beyond individual smart devices, cyber-physical collectives can provide services or solve complex problems by leveraging a “system effect” while coordinating and adapting to context or environment change. Understanding and building systems exhibiting collective intelligence and autonomic capabilities represent a prominent research goal, partly covered, e.g., by the field of collective adaptive systems. Therefore, drawing inspiration from and building on the long-time research activity on coordination, multi-agent systems, autonomic/self-* systems, spatial computing, and especially on the recent aggregate computing paradigm, this thesis investigates concepts, methods, and tools for the engineering of possibly large-scale, heterogeneous ensembles of situated components that should be able to operate, adapt and self-organise in a decentralised fashion. The primary contribution of this thesis consists of four main parts. First, we define and implement an aggregate programming language (ScaFi), internal to the mainstream Scala programming language, for describing collective adaptive behaviour, based on field calculi. Second, we conceive of a “dynamic collective computation” abstraction, also called aggregate process, formalised by an extension to the field calculus, and implemented in ScaFi. Third, we characterise and provide a proof-of-concept implementation of a middleware for aggregate computing that enables the development of aggregate systems according to multiple architectural styles. Fourth, we apply and evaluate aggregate computing techniques to edge computing scenarios, and characterise a design pattern, called Self-organising Coordination Regions (SCR), that supports adjustable, decentralised decision-making and activity in dynamic environments.Con lo sviluppo di informatica e intelligenza artificiale, la diffusione pervasiva di device computazionali e la crescente interconnessione tra elementi fisici e digitali, emergono innumerevoli opportunità per la costruzione di sistemi socio-tecnici di nuova generazione. Tuttavia, l'ingegneria di tali sistemi presenta notevoli sfide, data la loro complessità—si pensi ai livelli, scale, eterogeneità, e interdipendenze coinvolti. Oltre a dispositivi smart individuali, collettivi cyber-fisici possono fornire servizi o risolvere problemi complessi con un “effetto sistema” che emerge dalla coordinazione e l'adattamento di componenti fra loro, l'ambiente e il contesto. Comprendere e costruire sistemi in grado di esibire intelligenza collettiva e capacità autonomiche è un importante problema di ricerca studiato, ad esempio, nel campo dei sistemi collettivi adattativi. Perciò, traendo ispirazione e partendo dall'attività di ricerca su coordinazione, sistemi multiagente e self-*, modelli di computazione spazio-temporali e, specialmente, sul recente paradigma di programmazione aggregata, questa tesi tratta concetti, metodi, e strumenti per l'ingegneria di ensemble di elementi situati eterogenei che devono essere in grado di lavorare, adattarsi, e auto-organizzarsi in modo decentralizzato. Il contributo di questa tesi consiste in quattro parti principali. In primo luogo, viene definito e implementato un linguaggio di programmazione aggregata (ScaFi), interno al linguaggio Scala, per descrivere comportamenti collettivi e adattativi secondo l'approccio dei campi computazionali. In secondo luogo, si propone e caratterizza l'astrazione di processo aggregato per rappresentare computazioni collettive dinamiche concorrenti, formalizzata come estensione al field calculus e implementata in ScaFi. Inoltre, si analizza e implementa un prototipo di middleware per sistemi aggregati, in grado di supportare più stili architetturali. Infine, si applicano e valutano tecniche di programmazione aggregata in scenari di edge computing, e si propone un pattern, Self-Organising Coordination Regions, per supportare, in modo decentralizzato, attività decisionali e di regolazione in ambienti dinamici

    Abstracts of manuscripts submitted in 1993 for publication

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    This volume contains the abstracts of manuscripts submitted for publication during calendar year 1993 by the staff and students of the Woods Hole Oceanographic Institution. We identify the journal of those manuscripts which are in press or have been published. The volume is intended to be informative, but not a bibliography. The abstracts are listed by title in the Table of Contents and ar grouped into one of our five departents, Marine Policy Center, Coastal Research Center, or the student category. An author index is presented in the back to facilitate locating specific papers
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