1,721,029 research outputs found
Modeling and attitude control of spacecraft with an unbalanced rotating device
Get PDFThis letter addresses the problem of controlling the attitude of spacecraft endowed with a rotating device, motivated by recent space applications which will make use of large rotating payloads. Due to the presence of uncertain and potentially large inertial asymmetries in the rotating device, an internal force and a torque can appear at interface between the spacecraft and the rotor, causing performance degradation and even affecting the system stability. To counteract such unbalance effects, active balancing systems, using movable masses mounted on the rotating device, are being considered in the literature. During the balancing phase, it is important for the attitude control system to maintain a stable configuration. After deriving a suitable control-oriented model of the multi-body spacecraft, we propose using a coordinate-free attitude controller that ensures safe balancing operations and desirable pointing performance
A fully consistent linearized model for vibration analysis of rotating beams in the framework of geometrically exact theory
Get PDFThe equations of motions governing the free vibrations of prismatic slender beams rotating in a plane at constant angular velocity are derived according to a geometrically exact approach. Compared to other modeling methods, additional stiffening terms induced by pre-stress are found in the dynamic equations after fully consistent linearization about the deformed equilibrium configuration. These terms include axial, bending and torsional stiffening effects which arise when second-order generalized strains are retained. It is shown that their contribution becomes relevant at moderate to high angular speeds, where high means that the equilibrium state is subject to strains close to the limit where a physically linear constitutive law still applies. In particular, the importance of the axial stiffening is specifically investigated. The natural frequencies as a function of the angular velocity and other system parameters are computed and compared with benchmark cases available in the literature. Finally, the error on the modal characteristics of the rotating beam is evaluated when the linearization is carried out about the undeformed configuration
L'ARGENIS DI JOHN BARCLAY (1582-1621) E LA SUA INFLUENZA SULROMANZO ITALIANO DEL SEICENTO
No full textIl romanzo latino Argenis di John Barclay, pubblicato a Parigi nel 1621, è stato uno dei libri più amati della sua epoca. La ragione del plauso dei lettori sarà da ricercare nella complessa macchina narrativa ideata dall'autore, unione di narrazione, storia, evocata in forma di allegoria, e magistero politico; in questo nuovo modello di scrittura è stato riconosciuto l'atto fondativo del genere cosidetto del "roman à clef" ("romanzo a chiave" in italiano). La ricerca propone un rigoroso studio dell'opera e mira alla definizione del giudizio su di essa espresso dai letterati italiani nel corso del Seicento. La tesi si sofferma in seguito sull'influenza esercitata dall'Argenis sul romanzo italiano. Attenzioni preliminari vengono così dedicate alle alterne fortune godute, nelle scritture di ambientazione fantastica, da alcune caratterizzanti scelte narrative del modello latino. Vengono quindi studiati i "romanzi a chiave" per delineare le declinazioni peculiari del genere in Italia, ponendo particolare attenzione alle forme e finalità di impiego della storia e ai nuovi indirizzi della materia politica. Gli autori di "romanzi a chiave" studiati sono: Francesco Agricoletti, Ciro Anselmi, Francesco Belli, Guidubaldo Benamati, Giovanni Francesco Biondi, Girolamo Brusoni, Niccolò Maria Corbelli, Carlo de' Dottori, Giovanni Francesco Loredano e Ferrante PallavicinoJohn Barclay's Argenis, a latin novel published in Paris in 1621, is one of the best sellers of its time. The reason for success is to be found in the complex narrative system conceived by the author, union of narration, history, recalled in the form of an allegory, and political thought; the foundative act of the so-called genre of the "roman à clef" ("novel with a key") is recognized in this new model of writing. The research aims at studying Barclay's novel and try to define its value in the opinion of the italian men of letters. The thesis focuses also on the influence of the Argenis on the seventeenth century italian novel. Preliminary attentions are dedicated to the variable success met by some characterizing narrative choices of the latin model within the fantasy setting novels. The italian "romans à clef" are examinated to determine the features of the genre in Italy, studying the forms and the finality of the use of history and the rethinkings imposed to the political argument. The authors examinated are: Francesco Agricoletti, Ciro Anselmi, Francesco Belli, Guidubaldo Benamati, Giovanni Francesco Biondi, Girolamo Brusoni, Niccolò Maria Corbelli, Carlo de' Dottori, Giovanni Francesco Loredano e Ferrante Pallavicino
Predictor-Based Adaptive Plant Augmentation Design With Application to Hierarchical Control
Get PDFThis letter presents a predictor-based adaptive augmentation scheme to recover the designed behavior of a baseline linear controller in presence of parametric uncertainty. Remarkably, the proposed scheme achieves the recovery of the baseline closed-loop performance without the need for explicit knowledge of the baseline controller states and structure; rather, the adaptive mechanism relies solely on the output of the baseline controller and plant states. We showcase how the proposed adaptive design seamlessly integrates into inner-outer loop control architectures, enhancing the overall performance and robustness while simultaneously reducing the control law complexity compared to available solutions
Attitude stabilization of inertial pointing spacecraft using magnetic actuators
No full textWe revisit attitude stabilization for inertial pointing spacecraft endowed with magnetic actuators. Under mild assumptions on the time-variability of the geomagnetic field, it was proven that a quaternion-based PD-like controller can guarantee global convergence to the desired attitude provided that the gains are sufficiently small, thus posing an intrinsic limiation to the achievable performance. In this paper we propose a geometric projection-based controller which guarantees almost-global stability of the desired equilibrium, thereby avoiding the so-called "unwinding phenomenon" that affects the quaternion-based controller. Furthermore, simulation examples show that the proposed design, combined with suitable state-dependent time-varying gains, provides better results than the PD-like controller both in terms of convergence rate and of stabilization error when environmental disturbances and actuators saturation are included in the model
A course on adaptive and autonomous aerospace systems
Get PDFIn this paper we present the one-semester course “Adaptive and Autonomous aerospace Systems” to be taught to master students in aerospace engineering at Politecnico di Milano starting fall 2021. The paper discusses the course motivation and objectives, how it fits within the current study program in aerospace engineering, the course syllabus and organization and the learning assessment and outcomes. While being a fundamental course in character, covering the main theoretical aspects of adaptive and autonomous control, laboratory activities will complement the students learning by showing realistic implementations of the algorithms taught in class
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
Robust Tuning of Geometric Attitude Controllers for Multirotor Unmanned Aerial Vehicles
Get PDFIn recent years there has been a significant body of literature proposing nonlinear attitude control laws for small-scale multirotor unmanned aerial vehicles (UAVs), motivated by the high maneuverability of these platforms. While tracking trajectories characterized by fast and large attitude changes makes the control problem intrinsically nonlinear, most of the works proposing nonlinear designs is concerned with establishing their stabilizing properties, often deduced by referring to simplified dynamic models, but limited attention has been devoted to performance. As a consequence, less satisfactory results than expected are typically achieved in experiments and the controller gains must be adjusted with trial-and-error procedures to obtain good performance. This paper proposes a model-based tuning method that exploits the cascade structure of the attitude dynamics and that needs only single-axis identified linear models of the angular velocity dynamics to be applied. The tuning of the controller gains is carried out on the linearized closed-loop system with structured H∞ synthesis that allows one to enforce robustness against model uncertainty in a systematic way and to achieve a desired level of performance in nominal conditions. The approach is validated by tuning the gains of a novel Proportional/Proportional Integral Derivative (P/PID)-like cascade, which has been developed in the framework of geometric control theory. A thorough analytical comparison of the proposed design with a geometric Proportional Integral (PI)-like controller borrowed from the literature is complemented with experiments conducted on a small quadrotor UAV
Trajectory tracking control of thrust-vectoring UAVs
Get PDFIn this paper a geometric approach to the trajectory tracking control of Unmanned Aerial Vehicles (UAVs) with thrust vectoring capabilities is proposed. The control problem is developed within the framework of geometric control theory, yielding a control law that is independent of any parametrization of the configuration space. The proposed design works seamlessly when the thrust vectoring capability is limited, by prioritizing position over attitude tracking. The control law guarantees almost-global asymptotic tracking of a desired full-pose (attitude and position) trajectory that is compatible with the platform underactuation according to a specific trackability condition. Finally, a numerical example is presented to test the proposed control law on a tilt-rotor quadcopter UAV. The generality of the control strategy can be exploited for a broad class of UAVs with thrust vectoring capabilities
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