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Quad Rotorcraft Control develops original control methods for the navigation and hovering flight of an autonomous mini-quad-rotor robotic helicopter. These methods use an imaging system and a combination of inertial and altitude sensors to localize and guide the movement of the unmanned aerial vehicle relative to its immediate environment.

The history, classification and applications of UAVs are introduced, followed by a description of modelling techniques for quad-rotors and the experimental platform itself. A control strategy for the improvement of attitude stabilization in quad-rotors is then proposed and tested in real-time experiments. The strategy, based on the use low-cost components and with experimentally-established robustness, avoids drift in the UAV’s angular position by the addition of an internal control loop to each electronic speed controller ensuring that, during hovering flight, all four motors turn at almost the same speed. The quad-rotor’s Euler angles being very close to the origin, other sensors like GPS or image-sensing equipment can be incorporated to perform autonomous positioning or trajectory-tracking tasks.

Two vision-based strategies, each designed to deal with a specific kind of mission, are introduced and separately tested. The first stabilizes the quad-rotor over a landing pad on the ground; it extracts the 3-dimensional position using homography estimation and derives translational velocity by optical flow calculation. The second combines colour-extraction and line-detection algorithms to control the quad-rotor’s 3-dimensional position and achieves forward velocity regulation during a road-following task.

In order to estimate the translational-dynamical characteristics of the quad-rotor (relative position and translational velocity) as they evolve within a building or other unstructured, GPS-deprived environment, imaging, inertial and altitude sensors are combined in a state observer.

The text give the reader a current view of the problems encountered in UAV control, specifically those relating to quad-rotor flying machines and it will interest researchers and graduate students working in that field. The vision-based control strategies presented help the reader to a better understanding of how an imaging system can be used to obtain the information required for performance of the hovering and navigation tasks ubiquitous in rotored UAV operation.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction

Abstract
This chapter provides a historical introduction to the field of Unmanned Aerial Vehicles (UAVs), explaining in detail their classification and their application. The state of the art of such systems is presented, followed by the problem field that is being addressing in this work. The chapter finally presents a detailed outline of the book.
Luis Rodolfo García Carrillo, Alejandro Enrique Dzul López, Rogelio Lozano, Claude Pégard

Chapter 2. Modeling the Quad-Rotor Mini-Rotorcraft

Abstract
This chapter presents the modeling of a quad-rotor UAV. A general overview of the quad-rotor helicopter and its operation principle is given. Next, the quad-rotor modeling is addressed using two different approaches: Euler–Lagrange and Newton–Euler. How to derive Lagrange’s equations from Newton’s equations is also shown. Finally, the author presents also the Newton–Euler modeling for an “X-Flyer” quad-rotor configuration.
Luis Rodolfo García Carrillo, Alejandro Enrique Dzul López, Rogelio Lozano, Claude Pégard

Chapter 3. The Quad-Rotor Experimental Platform

Abstract
This chapter is devoted to the development of a ground station for supervising the aerial vehicle, as well as the development of three quad-rotor experimental platforms. General details concerning the most common sensing technologies available on UAVs are given, as well as the architecture of this kind of experimental platforms. The quad-rotors conceived during the research activities are described in detail. A hierarchical control strategy is introduced, which allows stabilizing the quad-rotor during autonomous flights. The performances of the vehicles are validated in real-time experiments.
Luis Rodolfo García Carrillo, Alejandro Enrique Dzul López, Rogelio Lozano, Claude Pégard

Chapter 4. Hovering Flight Improvement

Abstract
This chapter introduces an embedded control system for improving the attitude stabilization of a quad-rotor. The proposed control strategy uses low cost components and includes an extra control loop based on motor armature current feedback. The control strategy presented here is a controller that is robust with respect to external disturbances. Experimental results for indoor tests are presented to show how this additional control loop improves the performance of the quad-rotor attitude stability.
Luis Rodolfo García Carrillo, Alejandro Enrique Dzul López, Rogelio Lozano, Claude Pégard

Chapter 5. Imaging Sensors for State Estimation

Abstract
This chapter aims at the implementation of a vision system onboard the UAV, with the purpose of estimating the sates of the platform during flights. Theoretical background concerning computer vision is given in first instance. The pinhole camera model as well as the camera calibration procedure is shown. Stereo imaging, together with a method for stereo calibration and rectification are presented also. The concept of optical flow and a method for its computation are detailed. Relevant issues that must be considered when implementing an imaging system onboard a quad-rotor UAV are discussed. The development of both a monocular and a stereo imaging system are presented, as well as the software architecture conceived for estimating the data required for performing vision-based tasks.
Luis Rodolfo García Carrillo, Alejandro Enrique Dzul López, Rogelio Lozano, Claude Pégard

Chapter 6. Vision-Based Control of a Quad-Rotor UAV

Abstract
This chapter introduces two different vision-based control strategies for stabilizing a quad-rotor during flight. The first strategy is based on a homography estimation technique and an optical flow computation. Using this approach, a comparison of three control methods is addressed, with the purpose of validating the most effective approach for stabilizing the vehicle when using visual feedback. In the second strategy, the vision system is implemented for allowing altitude control, which allows stabilizing the 3-dimensional position and regulating the velocity of the vehicle using optical flow. For validating the effectiveness of the two vision-based control strategies, the tasks of autonomous hover and navigation are executed in real-time experiments.
Luis Rodolfo García Carrillo, Alejandro Enrique Dzul López, Rogelio Lozano, Claude Pégard

Chapter 7. Combining Stereo Imaging, Inertial and Altitude Sensing Systems for the Quad-Rotor

Abstract
This chapter is devoted to the design and implementation of a stereo-vision, inertial and altitude sensing system for a quad-rotor. The objective is to enable the vehicle to autonomously perform take-off, relative positioning, navigation and landing when evolving in unstructured, indoors, and GPS-denied environments. A real-time comparison study between a Luenberger observer, a Kalman filter and a complementary filter is also addressed, with the purpose of validating the most effective approach for combining the different sensing technologies.
Luis Rodolfo García Carrillo, Alejandro Enrique Dzul López, Rogelio Lozano, Claude Pégard

Chapter 8. Conclusions and Future Work

Abstract
This chapter presents final conclusions. In addition, relevant issues found during the conduction of the authors’ research are given. Finally, the chapter closes with related topics that can be addressed for improving the results presented in this book.
Luis Rodolfo García Carrillo, Alejandro Enrique Dzul López, Rogelio Lozano, Claude Pégard

Backmatter

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