1,720,958 research outputs found
Fixed-Dynamics Antiwindup Design: Application to Pitch-Limited Position Control of Multirotor Unmanned Aerial Vehicles
Get PDFIn this brief, we present and validate an antiwindup (AW) control design suitable to deal with saturated discrete-time linear plants. Following the modern approach to AW design, the proposed synthesis procedure is based on the compensator paradigm in which the AW controller acts on top of a baseline one, tuned to achieve desirable performance in the unsaturated regime. After extending existing ideas for continuous-time plants to their discrete-time counterparts, the design of the AW compensator is carried out with a focus on computational efficiency and optimized performance in practical operating scenarios. The proposed approach allows one to design fixed-dynamics AW compensators for possibly open-loop unstable plants using generalized sector conditions. Then, the synthesis procedure is applied to tune a fixed-dynamics compensator having the structure of a static compensator cascaded with a unit delay to avoid algebraic loops. Finally, the benefits of such AW augmentation are assessed experimentally to counteract windup effects arising in the position control of multirotor unmanned aerial vehicles (UAVs) when pitch limitations are imposed
Experimental validation of an anti-windup design trading off position and heading direction control performance for quadrotor UAVs
Get PDFAnti-windup design for directionality compensation with application to quadrotor UAVs
Get PDFIn this letter we propose an anti-windup strategy to counteract directionality effects arising in saturated MIMO systems in which independent dynamical subsystems are coupled through a static mixing of the inputs. Since such systems are affected by undesired input cross-couplings when saturation occurs, we propose an anti-windup augmentation scheme built on top of the baseline controller and tailored to achieve satisfactory time-domain performance for reference signals of interest. Motivated by the quadrotor application, in which position control has higher priority over yaw control for safety reasons, we embed in the anti-windup synthesis procedure the possibility to prioritize the level of performance degradation during saturation for the different system outputs
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Anti-windup design for position and attitude control of quadrotor UAVs
Get PDFLAUREA MAGISTRALEIl controllo in retroazione assume un ruolo molto importante in svariate applicazioni di tipo aeronautico, automobilistico, spaziale, robotico, chimico, industriale, etc.
Il suo principale scopo consiste nel garantire adeguate prestazioni in varie condizioni operative nelle quali il sistema in studio si trova ad operare.
Purtroppo la presenza di saturazioni delle variabili di controllo comporta un peggioramento delle proprietà del sistema in anello chiuso.
Questa tesi ha lo scopo di sviluppare opportune leggi di compensazione al fine di ridurre il malfunzionamento indotto dalle saturazioni in aeromobili a pilotaggio remoto soggetti sia a limitazioni fisiche del sistema propulsivo e a vincoli di assetto.
Seguendo l'approccio di compensazione anti-windup, secondo il quale si migliora la legge di controllo esistente tramite l'aggiunta di un compensatore, è stato sviluppato un metodo di sintesi per sistemi lineari a tempo discreto basato su disuguaglianze lineari matriciali con lo scopo principale di garantire determinate prestazioni in presenza di limitazioni negli ingressi del sistema.
Il metodo di sintesi è stato poi utilizzato per modificare il controllore di un quadricottero; in particolare è stato progettato un compensatore a dinamica fissata per migliorare le risposte in anello chiuso d'assetto e posizione.
Paragonando le prestazioni ottenute con legge di controllo originale e con compensatore, le prove di volo, svolte nella Flying Arena for Rotorcraft Technologies (FlyART) del Politecnico di Milano, hanno permesso di confermare l'efficacia delle modifiche.Nowadays feedback control plays an important role in a great variety of applications such as robotics, automotive, aeronautics, space, chemical and industrial processes, etc. Its main purpose is to ensure satisfactory performance levels in the whole set of operating conditions the system is supposed to work in.
Unfortunately, when dealing with control input saturation, a worsening of the closed-loop properties is experienced. This thesis focuses on the development of appropriate control laws to reduce this saturation-induced malfunctioning for quadrotor unmanned aerial vehicles (UAVs) in presence of either saturating propellers or attitude constraints.
Following the anti-windup compensation approach, in which the compensator acts on top of a baseline controller, a linear matrix inequality (LMI) based synthesis technique for discrete-time linear systems is developed to guarantee prescribed levels of stability and performance in presence of limited control authority. This synthesis method is then used to modify well consolidated quadrotor flight control laws, by tuning fixed-dynamics anti-windup compensators to improve either position or attitude tracking performance.
The benefits of the augmentation are evaluated with flight test experiments made in the Flying Arena for Rotorcraft Technologies (FlyART) of Aerospace Systems and Control Laboratory (ASCL) of Politecnico di Milano by comparing the performance of baseline and augmented controllers in real case scenarios
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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