1,721,048 research outputs found
Passivity-based Control for Hybrid Systems with Applications to Mechanical Systems Exhibiting Impacts
Full text linkMotivated by applications of systems interacting with their environments, we study the design of passivity-based controllers for a class of hybrid systems in which the energy dissipation may only happen along either the continuous or the discrete dynamics. A general definition of passivity, encompassing the said special cases, is introduced and, along with detectability and solution conditions, linked to stability and asymptotic stability of compact sets. The proposed results allow us to take advantage of the passivity property of the system at flows or at jumps and are employed to design passivity-based controllers for the class of hybrid systems of interest. Two applications, one pertaining to a point mass physically interacting with a wall and another about controlling a ball bouncing on an actuated surface, illustrate the definitions and results throughout the paper
Robust trajectory tracking for underactuated VTOL aerial vehicles: Extended for adaptive disturbance compensation
No full textThis work proposes a feedback control strategy to let the dynamics of an under-actuated Vertical Take-Off and Landing (VTOL) aerial vehicle to track a desired trajectory thanks to an adaptive robust compensation of the aerodynamic disturbances. The novelty of the proposed approach consists in employing an aerodynamic disturbance observer derived using the NonLinear Geometric Approach and Radial Basis Functions (RBF). The obtained estimation is directly employed by a nonlinear robust feedback law which relies on a cascade control paradigm in which the attitude dynamics and the position dynamics of the vehicle play the role of the inner and of the outer loop, respectively. The robustness of the proposed approach is also demonstrated by means of simulation results in which the aerodynamic model of a multi-propeller aircraft is considered
Modeling and Control of a Class of Modular Aerial Robots Combining Under Actuated and Fully Actuated Behaviour
No full textThe design, modeling, and control of a new class of modular aerial robots, obtained by rigidly interconnecting a number of ducted-fan aircraft, are presented in this paper. A remarkable feature of the proposed class of vehicles is the fact that different dynamical behaviors, ranging from underactuated to fully actuated, can be obtained by adopting a suitable interconnection topology. To exploit this variety of actuation scenarios, a combination of control allocation and feedback control algorithms is proposed. The control allocation module exploits actuator redundancy by identifying the directions in the input space that affect the vehicle dynamics, whereas the feedback controller provides stabilization of the actuated degrees of freedom over desired attitude and position trajectories. A physical prototype, realized by interconnecting two ducted-fan vehicles, is employed to experimentally demonstrate the effectiveness of the proposed methodology
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
Robust Global Trajectory Tracking for Underactuated VTOL Aerial Vehicles Using Inner-Outer Loop Control Paradigms
Full text linkThis paper proposes a feedback control strategy to let the dynamics of a class of under-Actuated vertical take-off and landing (VTOL) aerial vehicle tracking a desired position and attitude trajectory globally with respect to the initial conditions. The proposed feedback controller is derived following an inner-outer loop control paradigm, namely by considering the attitude, which is governed by means of a hybrid controller so as to overcome the well-known topological constraints, serving as a virtual input to stabilize the aircraft position. Two different approaches, the first one obtained by assuming perfect knowledge of the vehicle dynamics and the second one obtained by considering uncertainties and exogenous disturbances, are proposed and compared by analyzing the interconnection between the hybrid attitude and the continuous-Time position closed-loop subsystems. The effectiveness of the obtained results is demonstrated by means of simulations and experiments using a miniature quadrotor prototype
A combined GP-State space method for efficient crowd mapping
Full text linkCrowd sensing is an effective zero-cost method to map physical spatial fields by exploiting sensors already embedded in smartphones. The potentially huge amount of generated data and random measurement positions represent serious challenges to be addressed. In this paper we propose a combined Gaussian process (GP)-State space method for crowd mapping whose complexity and memory requirements for field representation do not depend on the number of data measured. The method is validated through an experimental campaign involving a high accuracy positioning system and a magnetic mobile sensor as data collector
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
- …
