1,721,009 research outputs found
Monitoraggio e controllo di sistemi distribuiti in condizioni operative incerte
No full textProtocollo 2004099019_006
Area 09 - Ingegneria industriale e dell'informazione
Durata 24 mesi
L’obiettivo della ricerca è stato lo studio di architetture per la diagnostica e riconfigurazione di sistemi complessi modellati mediante sistemi ad eventi discreti
Diagnosticare un guasto in un sistema ad eventi discreti significa rilevare l’occorrenza di un evento non osservabile (il guasto) mediante le osservazioni sul sistema. La metodologia di diagnostica studiata è la cosiddetta metodologia a diagnoser che prevede la costruzione, partendo da una modellistica mediante Automi, di un osservatore strutturato che fornisca la stima dello stato del sistema arricchita con informazioni sulle condizioni del sistema. Tale automa può essere usato sia per testare se il sistema è diagnosticabile, sia ”on the fly” per rilevare guasti e forzare le riconfigurazioni
Il problema principale di tale approccio è che la complessità della procedura di costruzione del diagnoser è esponenziale nella cardinalità dello spazio degli stati dell’automa di partenza. Inoltre questi è costruito partendo dalla composizione parallela dei modelli dei sottosistemi fisici di interesse, quindi da un lato si ha un’esplosione della dimensione dell’insieme degli stati del diagnoser, dall’altro non si sfrutta l’architettura tipicamente distribuita del sistema.
L’idea è stata quella di esplorare nuove tipologie di modelli ad eventi discreti ed applicare a questi una versione modificata della metodologia. In questa direzione sono stati studiati i cosiddetti modelli a state-charts, ovvero automi con gerarchia verticale. In questo senso si cerca di sfruttare solo le informazioni (osservazioni) di più alto livello sul sistema (procedura di lifting) usando le informazioni di più basso livello solo quando servono (procedura di zoom).
Il passo successivo è stato quello di studiare le condizioni di riconfigurazione del sistema dopo un guasto. Supervisionare un sistema ad eventi discreti significa limitarne l’evoluzione naturale in modo da soddisfare certe specifiche sul comportamento. Normalmente il supervisore viene costruito sulla base del modello nominale del sistema e delle specifiche (descritte anche esse in termini di evoluzione ad eventi discreti). Quando accade un può accadere che eventi solitamente proibiti vengano eseguiti. Il problema è quello di rilevare l’occorrenza del guasto prima che uno di questi eventi occorra e, in seguito, cambiare la strategia di supervisione in modo da evitarne l’occorrenza.
Si è quindi introdotta una nuova definizione di diagnosticabilità considerando anche vincoli di safety (safe-diagnosability) rispetto a tali eventi proibiti. Se il sistema è safe diagnosable assicuriamo che tra l’evento guasto e un eventuale evento illegale esista almeno un evento osservabile che permetta la rilevazione del malfunzionamento (sintomo).
Per la relazione finale, contenente risultati, partecipanti, consuntivo finanziario, consultare:
http://prin.cineca.it/php4/relazione/2004/home_page.ph
Discrete Variable Structure Integral Controllers
No full textThe subject of this paper is the analysis and the design of a class of robust discrete-time Variable-Structure controllers of integral type. We refer to the Discontinuous Integral Control (DIC) technique, already developed by the authors for the time-continuous case, where a nonlinear integral action is used for estimating the external disturbance and keeping small the discontinuous term in the control law and the subsequent chattering effect. A discretised version of the DIC algorithm, which is properly modified in order to take into account the time-derivative information on the controlled variable, is introduced and discussed. The so-obtained discrete-time controller shows to be very effective in reducing the chattering when the system parameters are known. Moreover, to cope with a specific case of unknown parameters, a new adaptive control structure is proposed and analysed. The local asymptotic stability of the resulting closed-loop system is proved in the case of constant external disturbances. Finally, simulation results on the velocity control of a DC motor end the paper
Output regulation of nonlinear systems by sliding mode
No full textThis paper focuses on the design of an output feedback sliding mode regulator able to achieve the asymptotic tracking of a reference trajectory for nonlinear systems. It is assumed that the reference trajectory is generated by means of a neutrally stable unforced system (exosystem) whose state is known. The design methodology is based on the center manifold theory and on the equivalent control concept and can be applied to both minimum and nonminimum-phase systems
A Cascade Structure For Robust Control Design
No full textIn the context of robust control theory and applications, the well-known Variable Structure approach and the so-called Binary Control approach, offer both interesting properties and disadvantages. In this note, the idea of combining the two techniques in order to define a cascade structure exploiting the desirable features of both approaches is discussed, and its natural applicability to the control of a nonlinear electrical actuator is shown by a simulation case
Automatic tuning of myoelectric prostheses
No full textIn this paper a software package that uses a Fuzzy Logic Expert System (FLES) to compute myoelectric prosthesis control parameter values is presented and the experimental results from its preliminary practical application are discussed. The prosthesis system is the INAIL artificial arm powered by an electrical motor controlled by a microprocessor using myoelectric signals acquired from skin-surface electrodes placed on the patient muscle stump. The software package here presented, named MCA (Microprocessor Controlled Arm) Auto Tuning, is a software tool for a step-by-step controller parameters tuning procedure, useful for expert operators as well as unskilled amputee patients. The control parameters set-up and subsequent recurrent adjustment are necessary for the prosthesis correct working. These tasks are usually performed by skilled operator together with the patient in the prosthesis-maker laboratory, however this is quite unpractical and involves technicians' waste of time and patients' uneasiness. The MCA Auto Tuning package embodies technician expertize in control parameters set-up in a FLES module. The unskilled patient interacts with the graphical interface of the software, and is guided by the programme to tune the controller parameters in a step-by-step procedure that emulates the traditional expert-aided tuning procedure. The adoption of this program on a large scale may yield considerable economic benefits and improve the service quality supplied to the prosthesis users. In fact the time required to set the prosthesis parameters is remarkably reduced and, consequently, working time of technicians is reduced too, decreasing costs of prostheses makers and providers. Moreover, by using MCA Auto Tuning package the present troubles and outlays for the patient can be dramatically lowered since any artificial arm resetting requires only a few easy adjustment staying at hom
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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