1,720,959 research outputs found
Robust Time-Optimal Model Predictive Control for Rendezvous with a Moving Target
No full textThis paper presents a novel control strategy for the problem of minimum-time rendezvous with a moving target, which is relevant to several aerospace applications. The proposed approach leverages tube-based model predictive control techniques to achieve robustness against disturbances and minimize the maneuver time. By suitably adapting the terminal constraints, recursive feasibility of the optimization problem is ensured, while guaranteeing finite-time completion of the rendezvous mission. Simulation studies show that less conservative trajectories are obtained, compared to existing robust predictive control methodologies. The effectiveness of the approach is demonstrated on a simulated rendezvous maneuver with a tumbling body
Robust Output Feedback Variable-Horizon MPC With Adaptive Terminal Constraints
No full textThis letter presents a robust output feedback variable-horizon model predictive control scheme for systems in which the state is not directly available but is estimated from noisy measurements. The control scheme is designed to intercept a moving target with a known trajectory while ensuring constraint satisfaction, recursive feasibility and finite-time convergence in the presence of bounded process disturbances and measurement noise. A key novelty of the proposed approach is the online adaptation of the terminal set, which reduces conservatism and improves performance in terms of final distance to the target, compared to existing tube-based methods. The effectiveness of the proposed approach is demonstrated on a numerical example concerning an orbital rendezvous maneuver of a spacecraft with an uncontrolled rotating object
Sum-of-Norms Model Predictive Control for Spacecraft Maneuvering
No full textThis letter tackles spacecraft optimal control problems in which the cost function is defined by a sum of vector norms, in order to optimize fuel consumption while achieving sparse actuation. A model predictive control (MPC) strategy is devised for such type of problems, accounting for different spacecraft maneuvering modes. Closed-loop stability is guaranteed by a conic Lyapunov function, which is employed as a terminal cost in the formulation. A systematic method to construct such function is presented. The proposed design is compared to a standard quadratic MPC scheme on a long-range rendez-vous mission
Sum-of-Norms Periodic Model Predictive Control for Space Rendezvous
No full textModel predictive control (MPC) is receiving increasing attention in space applications, as a key technology for enhancing autonomy of the flight control system. Sum-of-norms formulations are specifically suited to this context, because they allow to optimize meaningful performance figures and to promote control sparsity. This brief presents a sum-of-norms MPC scheme for linear periodically time-varying systems. Closed-loop stability is proven by suitably defining periodic sequences of terminal weights and terminal sets. The proposed solution is applied to a rendezvous case study involving periodic dynamics due to geopotential effects and solar eclipses
Robust variable-horizon MPC with adaptive terminal constraints
Full text linkThis paper presents a novel robust variable-horizon model predictive control scheme designed to intercept a target moving along a known trajectory, in finite time. Linear discrete-time systems affected by bounded process disturbances are considered and a tube-based MPC approach is adopted. The main contribution is an adaptive mechanism for choosing the terminal constraint set sequence in the MPC optimization problem. This mechanism is designed to ensure recursive feasibility while promoting minimization of the final distance to the target. Finite-time convergence of the proposed control scheme is proven. In order to evaluate its effectiveness, the designed control law is tested through numerical simulations, including a case study involving orbital rendezvous of a satellite with a tumbling object. The results indicate a significant reduction in conservatism compared to existing state-of-the-art methods using a fixed terminal set sequence
In-Cylinder Pressure Estimation from Rotational Speed Measurements via Extended Kalman Filter
Full text linkReal-time estimation of the in-cylinder pressure of combustion engines is crucial to detect failures and improve the performance of the engine control system. A new estimation scheme is proposed based on the Extended Kalman Filter, which exploits measurements of the engine rotational speed provided by a standard phonic wheel sensor. The main novelty lies in a parameterization of the combustion pressure, which is generated by averaging experimental data collected in different operating points. The proposed approach is validated on real data from a turbocharged compression ignition engine, including both nominal and off-nominal working conditions. The experimental results show that the proposed technique accurately reconstructs the pressure profile, featuring a fit performance index exceeding 90% most of the time. Moreover, it can track changes in the engine operating conditions as well as detect the presence of cylinder-to-cylinder variations
Periodic Model Predictive Control for Tracking Halo Orbits in the Elliptic Restricted Three-Body Problem
Full text linkA periodic model predictive control (MPC) scheme is proposed for tracking halo orbits. The problem is formulated and solved in the elliptic restricted three-body problem (ER3BP) setting. The reference trajectory to be tracked is designed by using eccentricity continuation techniques. The MPC design exploits the periodicity of the tracking model and guarantees exponential stability of the linearized closed-loop system, through a suitable choice of the terminal set and weight matrices. A sum-of-norms cost function is adopted to promote fuel saving. The proposed control scheme is validated on two simulated missions in the Earth-Moon system, which, respectively, involve station keeping on a halo orbit near the L1 Lagrange point and rendezvous to a halo orbit near the L2 Lagrange point. Results illustrate the advantage of designing the reference trajectory and the periodic control directly in the ER3BP setting versus approximate solutions based on the circular restricted three-body problem (CR3BP)
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
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