1,721,105 research outputs found
Model-based diagnosis and control of unmanned aerial vehicles: application to the quadrotor system
No full textI quadrirotori sono piccoli velivoli sospinti da quattro rotori e tipicamente
progettati per essere usati come velivoli autonomi, ovvero velivoli che possono
compiere una missione senza l’aiuto diretto dell’uomo. Per poter volare autonomamente
devono fare affidamento su: sensori che forniscono l’informazione
riguardo l’ambiente circostante o gli stati interni del sistema, attuatori che
realizzano fisicamente il moto e controllore che pilota gli attuatori in base alle
misure e alla missione che deve essere portata a termine. Sia i sensori sia gli
attuatori, tuttavia, possono essere soggetti a guasti ed `e importante che il
velivolo possa essere controllato anche quando essi si verificano.
La presente tesi cerca di risolvere due problemi inerenti la capacit`a del
quadrirotore di gestire i guasti: individuazione di guasti sui sensori o sugli
attuatori e sviluppo di una legge di controllo stabilizzante che permetta al
velivolo di rimanere in volo anche in caso di perdita di un attuatore.
L’individuazione dei guasti su sensori o attuatori `e implementata mediante
lo sviluppo di un modulo diagnostico basato su un generatore di residui e un
blocco di logica decisionale. Il generatore di residui si fonda su un osservatore
non lineare (osservatore di Thau) che confronta i segnali da esso generati con
quelli provenienti dai sensori. I segnali risultanti sono valutati dalla logica
decisionale, che integra al suo interno una politica di soglie adattative. Grazie
al modo in cui `e costruito, il modulo pu`o essere applicato ad un’ampia classe
di veicoli autonomi e non solo al velivolo quadrirotore.
La legge di controllo in caso di perdita di un attuatore `e sviluppata secondo
un’architettura a doppio loop. Il controllore interno (basato su feedback
linearization) stabilizza il moto di rollio e beccheggio e regola l’altezza ad
un valore desiderato. Il controllore esterno manipola i valori desiderati degli
angoli di rollio e beccheggio per poter controllare il posizionamento lungo
il piano orizzontale. Ci`o pu`o essere fatto solo sacrificando la controllabilit`a
dell’angolo di imbardata, che non compromette la sicurezza del velivolo, ma ne
limita la capacit`a di puntare un sensore di visione nella direzione desiderata
Verification of a stress gradient theory for the fatigue life predicition of components in case of pure push-pull and pure torsion conditions
No full textA relevant number of theories has been proposed
in the last 50 years for calculation of the fatigue
limits of components containing notches or more
general geometrical discontinuities. Beyond the
most classical ones, some methods
correlate the life to the relative stress gradient, allowing to overcome the limits of the
factors Kt and Kf not definable for generally
complex shaped components. On this direction, a
recent and very promising formulation has been
proposed [11,12] to predict the local S/N curve on
the base of a Finite Elements Analysis of the
stress gradient and on an empirical formulation of
the support factor nx.Aim of the present study is to validate the present
theory in the case of shafts in pure torsion and in
push-pull, comparing the predicted values with
experimental data obtained in two different test
campaigns
Low Cycle Fatigue behaviour and anisotropy of two steels for turbogenerator coil retaining rings and rotors
No full textTurbogenerator rotors and coil retaining rings (CRR) are typically subjected to low cycle fatigue (LCF). The rotor contains uniformly spaced longitudinal slots, where copper conductors are packed: at the nominal speed of 3000 rpm a great centrifugal force acts on the copper conductors that must be restrained by CRRs, shrunk fitted onto the body over the coils. Thus, at each on-off transitory (10,000 – 15,000 in the whole machine life) both the rotor and the CRR are subjected to a cyclic load. Several contributions report the mechanical properties of the typically used steels for rotor and CRR manufacturing, but none deals with their characterization under LCF in strain controlled conditions, while investigations on the anisotropy were performed just on CRR steels in load controlled conditions. This research aims at determining the main parameters describing the LCF performance of two widely applied steels for rotors and CRRs, investigating also the anisotropy in the dynamic behaviour: for this purpose an extensive experimental campaign was carried out on specimens machined (in the tangential and radial directions) from prolongations of trial rotors and CRRs. An original approach was used for misalignment compensation, strain control and data recording, sensitivity analyses were finally performed on results
Ambient Assisted Living: Italian Forum 2019
No full textThis book documents the state of the art in the field of ambient assisted living (AAL), highlighting technologies and services which aim to improve health and quality of life, while promoting active aging. The coverage is wide ranging, with topical sections devoted to human monitoring, smart living services, biomedical and robotic solutions, including different case studies and real-world examples where assistive technologies are successfully applied. The book comprises a selection of the best, refereed papers presented at the 10th Italian Forum on Ambient Assisted Living (ForItAAL), held in Ancona, Italy, in June 2019, which represents the annual event that involves the Ambient Assisted Living Italian Association and brought together researchers, technology teams, policy makers, and stake-holders. Readers will find that the expert contributions offer clear insights into the ways in which the most recent exciting advances may be expected to assist in addressing the needs of the elderly and those with chronic conditions
Human monitoring, smart health and assisted living: techniques and technologies
No full textThis book covers the three main scientific and technological areas critical for improving people's quality of life - namely human monitoring, smart health and assisted living - from both the research and development points of view
A coordination architecture for UUV fleets
No full textThis paper presents a modular and expandable architecture, which includes diversified functions and can be applied to heterogeneous fleets of unmanned underwater vehicles (UUVs), to solve the problem of decentralized formation coordination. The architecture is modular and each module is built such that it can solve a precise task using one or more functions. Three functions among them play a key role for the whole architecture: localization, faultless formation control and fault tolerance. The localization function is performed by the use of an adaptive extended Kalman filter (A-EKF) algorithm; the fault-free formation control function is based on a nonlinear decentralized model predictive control (ND-MPC) algorithm; the fault tolerance function is based on a hierarchy graph theory. The novelty of the paper lies in the use of the above mentioned functions as the core of an architecture which is expandable, decentralized and can be applied to a wide range of vehicles
A Coordination Architecture for UUV Fleets
No full textThis paper presents a modular and expandable architecture, which includes diversified functions and can be applied to heterogeneous fleets of unmanned underwater vehicles (UUVs), to solve the problem of decentralized formation coordination. The architecture is modular and each module is built such that it can solve a precise task using one or more functions. Three functions among them play a key role for the whole architecture: localization, faultless formation control and fault tolerance. The localization function is performed by the use of an adaptive extended Kalman filter (A-EKF) algorithm; the fault-free formation control function is based on a nonlinear decentralized model predictive control (ND-MPC) algorithm; the fault tolerance function is based on a hierarchy graph theory. The novelty of the paper lies in the use of the above mentioned functions as the core of an architecture which is expandable, decentralized and can be applied to a wide range of vehicles
Effetto supporto, tensione locale e gradiente relativo di tensione nella predizione della vita a fatica
No full textObiettivo ultimo delle ricerche nelle quali si inquadra questo studio è superare, o almeno limitare, la necessità di complicate e costose prove sperimentali a favore di altri metodi predittivi della vita a fatica. Scopo specifico del presente lavoro è la valutazione di una formulazione proposta in letteratura per predire, tramite analisi agli Elementi Finiti, la vita a fatica locale, nella regione ad alto numero di cicli, di componenti con qualunque distribuzione irregolare di tensione. Concetto base di questa nuova teoria è che il fenomeno della vita a fatica sia governato dal gradiente relativo di tensione nella zona maggiormente sollecitata del componente. Le equazioni proposte dalla nuova teoria per il calcolo della pendenza delle curve S-N e del limite di fatica sono verificate tramite il confronto con dati sperimentali tratti da letteratura. Mentre la formulazione per il calcolo del limite di fatica mostra un buon accordo con i dati sperimentali (errore medio percentuale del 7%), la pendenza valutata mediante l’equazione proposta risulta sovrastimata (errore medio percentuale del 123%). Si presenta quindi una nuova formula che permette di ottenere un errore medio percentuale del 24% sulla pendenza nel confronto con i dati sperimentali
Dynamic Surface Control for Multirotor Vehicles
No full textIn this paper we present the design of Dynamic Surface Control (DSC) law for multirotor vehicles. We first propose a mathematical model which can be used for a wide class of multirotor vehicles. Then, we extend the classical DSC such that it can be applied to the proposed model for tracking pitch, roll, yaw and altitude. The DSC performances are compared with other nonlinear algorithms known in the literature, namely backstepping and sliding mode, as well as PID controller, where all the control laws were tuned via the same heuristic random search algorithm in order to ensure a fair comparison
Fault Tolerant Control of a Variable Pitch Quadrotor
No full textIn this paper, we solve the fault tolerant tracking problem for a variable pitch quadrotor. Following the Disturbance Observer Based Control design paradigm, we face the observation problem for the blade pitch, and consequently the related fault and failure diagnosis problems.The control allocation algorithm solves the optimal redistribution problem of the control effort among the propellers in case of actuation failure. The optimization problem takes into account the energy consumption, the health condition of the actuators and the presence of input constraints, such as saturation and rate of change limits. In particular, we face the specific problem of lock-in-place servo failures, which reduce the number of the control actions in the system. Indeed, together with a fault detection and isolation module, lock-in-place servo failures can be managed in the control allocation algorithm while keeping the tracking capabilities. The proposed optimal fault tolerant accommodation algorithm can be coupled with most of the nonlinear control laws commonly applied to conventional multirotor systems. Numerical simulations with noise and constraints show the capability of the scheme to handle this class of failures
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