Showing papers by "Rogelio Lozano published in 2012"

Quad Rotorcraft Control: Vision-Based Hovering and Navigation

Abstract: 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-rotor's and the experimental platform itself. A control strategy for the improvement of attitude stabilization in quad-rotor's 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.

Combining Stereo Vision and Inertial Navigation System for a Quad-Rotor UAV

Abstract: This paper presents the development of a quad-rotor robotic platform equipped with a visual and inertial motion estimation system. Our objective consists of developing a UAV capable of autonomously perform take-off, positioning, navigation and landing in unknown environments. In order to provide accurate estimates of the UAV position and velocity, stereo visual odometry and inertial measurements are fused using a Kalman Filter. Real-time experiments consisting on motion detection and autonomous positioning demonstrate the performance of the robotic platform.

Quad-Tilting Rotor Convertible MAV: Modeling and Real-Time Hover Flight Control

Abstract: This paper describes the modeling, control and hardware implementation of an experimental tilt-rotor aircraft. This vehicle combines the high-speed cruise capabilities of a conventional airplane with the hovering capabilities of a helicopter by tilting their four rotors. Changing between cruise and hover flight modes in mid-air is referred to transition. Dynamic model of the vehicle is derived both for vertical and horizontal flight modes using Newtonian approach. Two nonlinear control strategies are presented and evaluated at simulation level to control, the vertical and horizontal flight dynamics of the vehicle in the longitudinal plane. An experimental prototype named Quad-plane was developed to perform the vertical flight. A low-cost DSP-based Embedded Flight Control System (EFCS) was designed and built to achieve autonomous attitude-stabilized flight.

Hovering Quad-Rotor Control: A Comparison of Nonlinear Controllers using Visual Feedback

Abstract: This article presents a comparison of three control techniques: nested saturations, backstepping, and sliding modes. The control objective consists of obtaining the best control strategy to stabilize the position of a quad-rotor unmanned aerial vehicle (UAV) when using visual feedback. We propose a vision-based method to measure translational speed as well as the UAV 3D position in a local frame. The three selected controllers were implemented and tested in real-time experiments. The obtained results demonstrate the performance of such methodologies applied to the quad-rotor system.

Modeling and control of a tilt tri-rotor airplane

Abstract: A helicopter offers the capability of hover, slow forward displacement, vertical take-off and landing while a conventional airplane has the performance of fast forward movement, long reach and superior endurance. The aim of this paper is to present the modelling and control of a tilt tri-rotor UAV's configuration that combines the advantages of both rotary wing and fixed wing vehicle.

Mini Rotorcraft Flight Formation Control Using Bounded Inputs

Abstract: In this paper, the flight formation control and trajectory tracking control design of multiple mini rotorcraft systems are discussed. The dynamic model of a mini rotorcraft is presented using the Newton-Euler formalism. Our approach is based on a leader/follower structure of multiple robot systems. The centroid of the coordinated control subsystem is used for trajectory tracking purposes. A nonlinear controller based on separated saturations and a multi-agent consensus algorithm is developed. The analytic results are supported by simulation tests. Experimental results include yaw coordination and tracking only.

Real-time localization of an UAV using Kalman filter and a Wireless Sensor Network

Abstract: A real-time localization algorithm is presented in this paper. The algorithm presented here uses an Extended Kalman Filter and is based on time difference of arrivals (TDOA) measurements of radio signal. The position and velocity of an Unmanned Aerial Vehicle (UAV) are successfully estimated in closed-loop in real-time in both hover and path following flights. Relatively small position errors obtained from the experiments, proves a good performance of the proposed algorithm.

Attitude Stabilization with Real-time Experiments of a Tail-sitter Aircraft in Horizontal Flight

Abstract: This paper focusses on the attitude stabilization of a mini tail-sitter aircraft, considering aerodynamic effects. The main characteristic of this vehicle is that it operates in either the hover mode for launch and recovery, or the horizontal mode during cruise. The dynamic model is obtained using the Euler---Lagrange formulation, and aerodynamic effects are obtained by studying the propeller effects. A nonlinear saturated Proportional-Integral-Derivative (SPID) control with compensation of aerodynamic moments is proposed in order to achieve the asymptotic stabilization of the vehicle in horizontal mode. In addition, a homemade inertial measurement unit (HIMU) is built for operating the complete operational range of the vehicle (including vertical and horizontal modes). Finally, simulation results are presented for validating the control law, and practical results are obtained in real-time during the flight.

PID switching control for a highway estimation and tracking applied on a convertible mini-UAV

Abstract: This paper reports current work on development and navigation control of an experimental prototype of a new tilt-rotor convertible aircraft (Quad-plane Mini Unmanned Aerial Vehicle). The goal of the work consists of estimating and tracking a road using a vision system, without any previous knowledge of the road, as well as developing an efficient controller for treat with situations when the road is not detected by the vision sensor. For dealing with this situation, we propose a switching control strategy applied in two operational regions: road detected and no road detected. The exponential stability is proved for the subsystem formed by the lateral position taking into account the switching boundaries between the operational regions. The control law is validated in the proposed platform, showing the expected behavior during autonomous navigation.

Quad-rotor switching control: An application for the task of path following

Abstract: The problem of vision-based road following using a quad-rotor is addressed The objective consists of estimating and tracking a road without a priori knowledge of such path For this purpose, two operational regions are defined: one for the case when the road is detected, and the other one for when it is not A switching between imaging and inertial sensors measurements allows estimating the required vehicle's parameters in both regions Also, for dealing with both aforementioned cases, a switching control strategy which stabilizes the vehicle's lateral position is proposed The performance of the proposed switching methodologies is tested in real time experiments

Vision Based Tracking for a Quadrotor Using Vanishing Points

Abstract: In this paper, a vision based line tracking control strategy for mini-rotorcraft is presented. In order to estimate the 3-D position of the mini-rotorcraft over the trajectory a vanishing points technique is used. A dynamic model is derived employing the Newton---Euler approach and a nonlinear controller to stabilize, in closed-loop system, this mathematical model is proposed. To validate the theoretical results, a real-time embedded control system has been developed. The performance of the vision and control algorithms has been tested when the helicopter has tracked a line painted in a wall. The experimental results have shown the good behavior of the control laws.

Straight-line path following in windy conditions

Abstract: A straight-line following controller for a small and light airplane flying in windy conditions is proposed. In a first time, the lateral dynamics of the plane are derived and the error deviation velocity with respect to the desired trajectory is computed. A simple nonlinear control law is developed in order to impose a linear behavior for the airplane position and to track the desired trajectory. Several simulations, taking into account quasi-constant wind disturbances, are performed to analyze the performance of the closed-loop system. Improved results are obtained including the airplane orientation to counter the wind as an input for the flight planning. In order to validate the proposed control scheme an airplane has been developed based on the classic aerodynamic layout. Future work will introduce the experimental results when applying in real-time the proposed control algorithm.

Nonlinear and optimal real-time control of a rotary-wing UAV

Abstract: In this contribution nonlinear stabilizing and optimal nonlinear control strategies for a quadrotor mini helicopter are addressed. These control strategies are an alternative for the control of flying machines not much explored yet. Simulation and real-time experiences are presented in this contribution. Nonlinear stabilizing control algorithm has been successfully implemented on an autonomous aerial vehicle and demonstrates an acceptable performance.

Visual servoing applied to real-time stabilization of a multi-rotor uav

Abstract: In this paper we address the problem of stabilization and local positioning of a four-rotor rotorcraft using computer vision. Our approaches to estimate the orientation and position of the rotorcraft combine the measurements from an Inertial Measurement Unit (IMU) and a vision system composed of a single camera. In the first stage, the vision system is used to estimate the position and yaw angle of the rotorcraft, while in the second stage the vision system is used to estimate the translational velocity of the flying robot. In both cases the IMU gives the pitch and roll angles at a higher rate. The technique used to estimate the position of the rotorcraft in the first stage combines the homogeneous transformation approach for the camera calibration process with the plane-based pose method for estimating the position. In the second stage, a navigation system using the optical flow is also developed to estimate the translational velocity of the aircraft. We present real-time experiments of stabilization and location of a four-rotor rotorcraft.

A new AUV configuration with four tilting thrusters: Navigation and hover tasks

Abstract: This paper presents the study, development and implementation of an attitude controller for an AUV(Autonomous Underwater Vehicle). The goal is the hover stabilization of the prototype taking in account the dynamic modeling of translation and orientation. Missions were performed at slow speed to evaluated real time autonomous navigation. The control is based on a saturated PD control law. Results are presented from real time experiments.

Stereo vision for the stabilization of a quadrotor

Abstract: Stereo vision is a broad field that is part of computer vision. Autonomous mobile robots make use of stereo vision to detect obstacles and measure their relative distance to them for path planning. Technically, it consists of the processing of two images simultaneously adquired by two cameras, from a given scene. Stereo vision is a field with multiple applications and many resources had been invested for research in this subject. In this paper, we present a stereo vision based controller design and its implementation on a mini helicopter with 4 rotors known as quadrotor. The dynamic model is obtained using the well known Euler-Lagrange approach. Experiment results show good performance of the proposed controller using "real-time" optical flow and image processing from two cameras.

Modeling and control of a lower limb exoskeleton with two degrees of freedom

Abstract: The exoskeletons are bio-mechanisms used for amplification of strength, load heavy objects, increase speed and human resistance. for this reason the exoskeletons have many medical and military applications. The present paper concerns about construction and control of exoskeleton assisted by SEA (Series Elastic Actuators) having two degrees of freedom (knee and ankle). This exoskeleton offers a reduction in effort required by the user to reach and keep the stand up position as well as to performs some exercises like flexing the leg, etc.

Depth control using artifitial vision with time-delay of an AUV

Abstract: The purpose of this paper is to present the analysis of the dynamics immersion of an Autonomous Underwater Vehicle considering the time-delay produced by implementing artificial vision algorithm. The parameter tuning of the PD controller is based on the analysis of the stability region taking into account the vision delay. The PD controller goal is to keep the vehicle in a region close to the landmark, and the performance is shown in simulation and real-time experimental results.

Stability analysis and experiments for a force augmenting device

Abstract: We present preliminary results of a one degree of freedom (DOF) linear moving force augmenting device (FAD) with a force sensor for enhancing the lifting capabilities of a human user. We perform a stability test of the feedback loop formed by the device and a model of the human operator. It is shown that the operator lifts a small fraction of the total weight of the load. The proposed control scheme is illustrated using numerical simulations and an experiment.

Modeling and control of a vertical take-off airplane

Abstract: This paper presents the mathematical model of a fixed wing UAV (Unmanned Aerial Vehicle). The UAV is not a tail-sitter configuration and takes-off with the fuselage at the horizontal position. An experimental prototype driven by four brushless motors has been built including the onboard avionics. The applied control law is based on separated saturation functions. Numerical simulations have shown the satisfactory performance of the proposed control law. The prototype has also been tested experimentally in hover only and the control strategy has achieved that orientation angles have been regulated close to the origin.

The Transition Phase of a Gun-Launched Micro Air Vehicle

Abstract: The present paper addresses the transition stage of a Gun-Launched Micro Air Vehicle (GLMAV) whose main goal is to rapidly position a rotorcraft MAV over a high-risk scene (Prison riots, blind zones: e.g. over-the-hill, etc.). The development of this robotic platform is part of an overall ongoing project (GLMAV) headed by the St. Louis French- German Research Institute (ISL). The vehicle is launched at a distance of 500 m and a height of 100 m, where the GLMAV will collect and transmit visual information from the scene. Issues raising from the use of the gun-based launching technique are discussed in detail. A control strategy is proposed to overcome such problems and to stabilize the GLMAV. High- fidelity simulations, covering ballistic and transition phases, validate the control policy adopted to face the MAV gun- launching problem.

Attitude control improvement of a small Quad-rotor aircraft platform based on singular perturbations approach: Real-Time application

Abstract: In this article, an attitude control in real-time is proposed using a inner loop control in each BrushLess DC (BLDC) motor to improve performance of a small Quad-rotor aircraft platform. The inner loop control is implemented by motor speed sensing feedback through reflex sensors in order to obtain a robust stabilization of the vehicle in hovering mode for indoor and outdoor applications. In addition, a control law based on Lyapunov Control Function (LCF) is proposed and extended to the singular perturbations problem for the corresponding stability analysis of the inner loop control that manages the angular velocity of the BLDC motors. Finally, experimental results show that the proposed real-time controller-based motor speed sensing feedback produces better control performance, particularly in handling external disturbances.

Modeling and control of a convertible airplane

Abstract: This paper presents the mathematical model of a fixed wing mini-UAV (Unmanned Aerial Vehicle). The mini-UAV is not a tail-sitter configuration and takes-off with the fuselage at the horizontal position. An experimental prototype driven by four brushless motors has been built including the onboard avionics. The applied control law is based on separated saturation functions algorithm. Numerical simulations have shown the satisfactory performance of the proposed control law in vertical take-off and hover. The prototype has also been tested experimentally in hover only and the control strategy has achieved that orientation angles have been regulated close to the origin.