José Raul Azinheira

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.

Robotic Airships for Exploration of Planetary Bodies with an Atmosphere: Autonomy Challenges

Robotic unmanned aerial vehicles have great potential as surveying and instrument deployment platforms in the exploration of planets and moons with an atmosphere. Among the various types of planetary aerovehicles proposed, lighter-than-atmosphere (LTA) systems are of particular interest because of their extended mission duration and long traverse capabilities. In this paper, we argue that the unique characteristics of robotic airships make them ideal candidates for exploration of planetary bodies with an atmosphere. Robotic airships extend the capabilities of balloons through their flight controllability, allowing (1) precise flight path execution for surveying purposes, (2) long-range as well as close-up ground observations, (3) station-keeping for long-term monitoring of high science value sites, (4) transportation and deployment of scientific instruments and in situ laboratory facilities across vast distances, and (5) opportunistic flight path replanning in response to the detection of relevant sensor signatures. Implementation of these capabilities requires achieving a high degree of vehicle autonomy across a broad spectrum of operational scenarios. The paper outlines some of the core autonomy technologies required to implement the capabilities listed above, drawing on work and results obtained in the context of AURORA (Autonomous Unmanned Remote Monitoring Robotic Airship), a research effort that focuses on the development of the technologies required for substantially autonomous robotic airships. We discuss airship modeling and control, autonomous navigation, and sensor-based flight control. We also outline an approach to airborne perception and monitoring which includes mission-specific target acquisition, discrimination and identification, and present experimental results obtained with AURORA.

Mission path following for an autonomous unmanned airship

The development of an unmanned airship capable of autonomous flight over user-defined locations for aerial data and imagery acquisition is the objective of the AURORA project. One important mission problem is the flight path following of the vehicle through a set of pre-defined points at a given altitude and velocity. In this article, a path tracking error generation methodology is presented and two different strategies for the guidance problem, one based on a H/sub /spl infin// control technique and another based on a PI control, are proposed and compared through a simulated case study.

Visual servo control for the hovering of all outdoor robotic airship

Addresses the issue of automatic hovering of an outdoor autonomous airship using image-based visual servoing. The hovering controller is designed using a full dynamic model of the airship, in a PD error feedback scheme, taking the visual signals as output and extracted from an on-board camera. The behavior and stability of the airship motion during the task execution and subjected to the wind disturbance is studied. The approach is finally validated in simulation using an accurate airship model.

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.

Linear structures following by an airship using vanishing point and horizon line in a visual servoing scheme

In the present paper, an image-based visual servoing scheme is presented for a road following task with an autonomous airship. A new set of visual signals is introduced, namely with the vanishing point coordinates and the vanishing line parameters, which have the advantage of decoupling the rotation DOF and respecting the natural characteristics of the vehicle dynamics. An optimal control design is used for a first implementation of the approach with the simulation platform of the AURORA airship. Simulation results are presented and discussed demonstrating a fair performance even in realistic wind conditions.

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.

Image-Based Visual Servoing for Vanishing Features and Ground Lines Tracking: Application to a UAV Automatic Landing

A unified modeling framework is defined and an image-based visual servoing scheme is introduced to evaluate the feasibility of a vision-based guidance for a UAV model during survey missions and for automatic landing. Relevant image features are selected to allow for the proposed objective, namely decoupling rotation and translation in the image, and allowing to respect the natural separation between the lateral and longitudinal motions of the aircraft. The controller design is adapted to include the aircraft dynamics and the vision output in an linear optimal control approach. Simulation results are presented in order to validate the proposed solution and allow for a critical evaluation.

Optimal visual servoed guidance of outdoor autonomous robotic airships

This paper describes a visual servo control scheme for an outdoor autonomous airship in path following tasks. The visual based guidance takes full authority of the robotic airship and it is based on lines as image features, extracted from an on-board camera. An optimal controller is designed using the dynamic model of the system, which tackles the dynamics of the airship and the dynamics of the vision process. To prevent from losing image features during camera motion and to deal with noisy output measurements and modeling inaccuracies, a Kalman estimator was employed. The approach is validated through simulations using the underactuated airship of the AURORA project.