Alexandra Moutinho

Hover Control of an UAV With Backstepping Design Including Input Saturations

This brief presents a backstepping-based controller with input saturations, applicable for the hover flight of an unmanned aerial vehicle (UAV). A dynamic model for a generic UAV is introduced that is valid for quasi-stationary conditions, with quaternion formulation of the kinematics equations. Based on this model, a backstepping design formulation is deduced for UAV hover control, and its global asymptotic stability is demonstrated. In order to cope with limitations due to reduced actuation, saturations are introduced in the control design, and the stability of the modified control solution is verified. Simulation results are presented for the hover stabilization of an airship UAV, which are demonstrative of the excellent performance of the proposed controller and illustrate its robustness in face of wind disturbances.

Stability and Robustness Analysis of the AURORA Airship Control System using Dynamic Inversion

This paper presents a stability and robustness analysis of a nonlinear control system for the autonomous airship of the AURORA project. A Dynamic Inversion controller is implemented with desired dynamics given by a linear optimal compensator. The stability analysis of the nonlinear system is done applying Lyapunov’s stability theory. Robustness tests are performed in order to verify the nonlinear controller performance in face of disturbances and model parameters errors. The results obtained illustrate the overall system robustness, and point at the most sensitive model parameters of the AURORA airship, for which a more careful identification/determination should be carried.

Airship Hover Stabilization Using a Backstepping Control Approach

The present paper introduces a novel approach for the airship hover stabilization problem. A synthetic modeling of the airship dynamics is introduced using a quaternion formulation of the kinematics equations. Based on this model, a backstepping design formulation is deduced for the aircraft hovering control. To deal with limitations caused by reduced actuation, saturations are introduced in the control design, and the global asymptotic stability of the system under saturation is demonstrated. The control objective is finally modified to cope with the strong lateral underactuation. Simulation results are presented for the hover stabilization of an unmanned robotic airship, with wind and turbulence conditions selected to demonstrate the behavior and robustness of the proposed solution.

Project AURORA: Infrastructure and flight control experiments for a robotic airship

Project AURORA aims at the development of unmanned robotic airships capable of autonomous flight over user-defined locations for aerial inspection and environmental monitoring missions. In this article, the authors report a successful control and navigation scheme for a robotic airship flight path following. First, the AURORA airship, software environment, onboard system, and ground station infrastructures are described. Then, two main approaches for the automatic control and navigation system of the airship are presented. The first one shows the design of dedicated controllers based on the linearized dynamics of the vehicle. Following this methodology, experimental results for the airship flight path following through a set of predefined points in latitude/longitude, along with automatic altitude control are presented. A second approach considers the design of a single global nonlinear control scheme, covering all of the aerodynamic operational range in a sole formulation. Nonlinear control solutions under investigation for the AURORA airship are briefly described, along with some preliminary simulation results.

Nonlinear Control Approaches for an Autonomous Unmanned Robotic Airship

[Abstract] This paper presents the research developments for the global nonlinear control of an autonomous airship, covering the full flight envelope from hovering to aerodynamic flight. The preliminary reports for the three nonlinear control solutions under investigation were presented, that are Dynamic Inversion, Backstepping, and the Sliding Mode Control, along with some representative simulation results. A complete airship mission, with vertical take-off, path tracking, hovering, and vertical landing was successfully simulated using the Backstepping Aproach.

Erratum on "Influence of Wind Speed on Airship Dynamics"

I N THIS Erratum the authors revise the paper “Influence of Wind Speed on Airship Dynamics” [1]. After a careful mathematical deduction, it was verified that this influence under a constant translation wind indeed does not exist, and the results presented by Thomasson [2,3] are confirmed. In other words, the airship dynamics equation is the same when expressed in terms of the inertial velocity with no wind or in terms of the relative air velocity under a constant translation wind. To confirm the results, the airship dynamics is expressed using the Lagrangian approach, instead of the originalNewtonianmethod used in Azinheira et al. [1]. In addition, the new kinematics representation with quaternions used in Azinheira et al. [4], describing the velocity changes from local to Earth frames, is used in the derivation of a compact form of the force equation. Assuming a constant translation wind, the new force equation written in terms of inertial and wind velocities is then transformed to be a function of the relative velocities. The force equation expressed in this way shows the same structure and the same terms as the one expressed with the inertial andwind velocities, confirming the invariance of the dynamics under a constant translation wind. In a last step, some terms in the kinematics force equation are discarded, as they are already accounted for in the aerodynamic forces. These terms are proportional to the squared relative velocity, and their influence is already considered through the aerodynamic coefficients measured in wind-tunnel experiments. This final step is particularly important for simulation purposes, otherwise some terms would be considered twice in the dynamicmodel. Simulation results, obtained using the AURORA simulator platform support the theoretical conclusions.

Path control of an autonomous airship using dynamic inversion

Abstract This paper introduces a new nonlinear control approach for the path tracking problem. In this methodology the control action is obtained using a dynamic inversion law. A generic formulation is presented and applied to the horizontal path tracking of the autonomous airship of the AURORA project. A standard linear LQ regulator is used in order to evaluate the performance of the dynamic inversion method, based on the results of three flight scenarios.

Preprocessing of Clinical Databases to Improve Classification Accuracy of Patient Diagnosis

Abstract In this paper, the prime importance of preprocessing in clinical databases is discussed. Specifically in intensive care units, data is often irregularly recorded, contain a large amount of missing values and sampling times are uneven. This paper proposes a systematic preprocessing procedure that can be generalized to common clinical databases. This procedure is applied to a known septic shock patient database and classification results are compared with previous studies. The goal is to estimate, as accurately as possible, the outcome (survived or deceased) of these septic shock patients. Neural modeling is used for classification. Detailed classification results are presented and show that the preprocessing is crucial to improve classifiers accuracy.

A Gain-Scheduling Approach for Airship Path-Tracking

In this chapter a gain scheduled optimal controller is designed to solve the path-tracking problem of an airship. The control law is obtained from a coupled linear model of the airship that allows to control the longitudinal and lateral motions simultaneously. Due to the importance of taking into account wind effects, which are rather important due to the airship large volume, the wind is included in the kinematics, and the dynamics is expressed as function of the air velocity. Two examples are presented with the inclusion of wind, one considering a constant wind input and the other considering in addition a 3D turbulent gust, demonstrating the effectiveness of this single controller tracking a reference path over the entire flight envelope.

The Tilt-Quadrotor: Concept, Modeling and Identification

A tilt-quadrotor is a fusion of the quad rotor and tiltrotor concepts. A tilt-quadrotor is able to move itself in all six degrees of freedom while maintaining its central core leveled, result of adding two tilting motions to two opposed rotors while the other two rotors remain fixed. Condensing the main information required to build a simulator, this paper presents the tilt-quadrotor original concept, its implementation in the ALIV3 prototype, and its modeling. The procedures and results of a thorough experimental identification of the structural, actuators and sensors parameters are also provided.