Showing papers by "Rogelio Lozano published in 2014"

Chattering-Free Sliding Mode Altitude Control for a Quad-Rotor Aircraft: Real-Time Application

Abstract: Nowadays, the chattering problem in sliding mode control is one of the most important points to consider in real-time applications. To address this problem, a real-time robust altitude control scheme is proposed for the efficient performance of a Quad-rotor aircraft system using a continuous sliding mode control. The sensing of altitude measurement sensing is performed by a pressure sensor in order to obtain a robust altitude control of the vehicle in hovering mode both indoor and outdoor. The altitude measurement has the advantage of introducing this state information directly in the closed loop control which should be very useful for achieving robust stabilization of the altitude control. Accordingly, we propose a sliding mode control strategy without chattering. The sliding mode control proposed removes the chattering phenomenon by replacing a sign function with a high-slope saturation function. The control algorithm is derived from the Lyapunov stability theorem. Moreover, we have assumed that the actuators are able to respond quickly and accurately and we have not enforced limits on the control signals for a real-time application. Finally, to verify the satisfactory performance of proposed nonlinear control law, several simulations and experimental results of the Chattering-free sliding mode control for the Quad-rotor aircraft in the presence of bounded disturbances are presented.

Dubins path generation for a fixed wing UAV

Abstract: A path generator is proposed for a fixed-wing Unmaned Aereal Vehicle (UAV). Assuming that the vehicle maintain a constant altitude, and airspeed, and that the UAV is constrained by a turning rate. The Dubins paths serve as a strategy to find the shortest path for the non-holonomic model of the UAV. Dubins paths consist of three path segments which are based on straight lines or arcs of circle of a given radius. The Dubins path generation is combined with a nonlinear Lypaunov-based path-following control. Finally we present a complete simulation environment in which the path generator and path following strategy are validated. As an example of application we propose the scenario in which a missing person is located in some known area and we use the path generator along with this path-following strategy applied to the fixed wing UAV to search and find this person.

Quad Rotorcraft Switching Control: An Application for the Task of Path Following

Abstract: This paper addresses the problem of road following using a quad rotorcraft equipped with an onboard image processing system. The main objective consists of estimating and tracking the road without a priori knowledge of the path to be tracked. Special interest is also given to the development of efficient estimation and control strategies for dealing with situations when the road is not detected in the camera image. Aiming at this goal, two operational regions are defined: one for the case when the road is detected and another for the case when it is not. A switching between the measurements of imaging and inertial sensors enables estimation of the required vehicle parameters in both operational regions. In addition, for dealing with both aforementioned cases, a switching control strategy for stabilizing the vehicle lateral position is proposed. The system stability is verified not only in the two operational regions, but also in the switching boundaries between them. The performance of the switching estimation and control strategies is tested in numerical simulations and real-time experiments, successfully validating the effectiveness of the proposed approaches.

A Vision and GPS-Based Real-Time Trajectory Planning for a MAV in Unknown and Low-Sunlight Environments

Abstract: In this paper we address the problem of real-time optimal trajectory generation of a micro Air Vehicle (MAV) in unknown and low-sunlight environments. The MAV is required to navigate from an initial and outdoor position to a final position inside of a building. In order to achieve this goal, the MAV must estimate a window of the building. For this purpose, we develop a safe path planning method using the information provided by the GPS and a consumer depth camera. With the aim of developing a safe path planning with obstacle avoidance capabilities, a model predictive control approach is developed, which uses the environment information acquired by the navigation system. The results are tested on simulations and some preliminary experimental results are given. Our system's ability to identify and estimate a window model and the relative position w.r.t. the window is demonstrated through video sequences collected from the experimental platform.

Fault Estimation for a Quad-Rotor MAV Using a Polynomial Observer

Abstract: This work addresses the problem of fault detection and diagnosis (FDD) for a quad-rotor mini air vehicle (MAV). Actuator faults are considered on this paper. The basic idea behind the proposed method is to estimate the faults signals using the extended state observers theory. To estimate the faults, a polynomial observer (Aguilar et al. 2011; Mata-Machuca et al., Commun Nonlinear Sci Numer Simul 15(12):4114---4130, 2010, BioSystems 100(1):65---69, 2010) is presented by using the available measurements and know inputs of the system. In order to investigate the diagnosability properties of the system, a differential algebra approach is proposed (Cruz-Victoria et al., J Frankl Inst 345(2):102---118, 2008; and Martinez-Guerra and Diop, IEE P-Contr Theor Ap 151(1):130---135, 2004). The effectiveness of the methodology is illustrated by means of numerical simulations.

Modeling and Sliding Mode Control of a Micro Helicopter-Airplane System

Abstract: This paper presents the regulation and trajectory tracking for a Micro Coaxial Rocket Helicopter (MCR UAV), as well as the control of a mini aircraft. The former vehicle has the characteristic of performing hover and forward flight while the latter vehicle is considered as an external air transporter for the MCR UAV. For control purposes, the helicopter stabilization is based on sliding mode controllers which avoid the chattering generated during the flight and allow the MCR UAV to perform tracking of smooth trajectories, Furthermore a PD controller stabilizes the aircraft in order to execute semi-autonomous flight. A flight computer for these aerial vehicles consists of a homemade embedded system, low-cost sensors, and signal conditioning circuits, analog filters and actuator. The proposed control algorithms are implemented on the embedded system. Simulation and experimental results show the good performance of the developed system during the flight.

6-DOF hovering controller design of the Quad Tiltrotor aircraft: Simulations and experiments

Abstract: This paper presents a particular class of a convertible micro aerial vehicle (MAV) with fixed wings, the so-called Quad Tiltrotor aircraft. This aircraft is able to change its flight configuration from hover to level flight and vice versa by means of a transition maneuver. In this first part of the research, the hover dynamics of the Quad Tiltrotor is investigated. Dynamical model and nonlinear control based on Lyapunov design are studied. The presented approach focuses on the problem of finding a control law capable of stabilizing the aircraft's position. Some simulations results are given, which demonstrate the effectiveness of the controller. Further, some experimental results are presented tested on the Quad Tiltrotor experimental platform.

Human detection in uncluttered environments: From ground to UAV view

Abstract: Nowadays pedestrian detectors are fast, scale-robust and quite efficient. Embedded within a UAV such a detector would open new possibilities. In this paper the very well known HOG detector is adapted for UAV use and a new kind of training dataset is proposed in order to increase the detector's angular robustness. A more appropriate set of detection windows, together with a new detection pipeline, is proposed in order to reduce the search space and consequently reduce the computation time. Tests conducted using the improved detector show significantly better results on aerial images.

A lower limb exoskeleton with hybrid actuation

Abstract: In this paper, the lower limb exoskeleton uses a harmonic drive actuator and two pneumatic artificial muscles (PAMs). This hybrid actuation takes both advantages of harmonic drive and PAM. It provide high accuracy position control and compliant behavior. The disadvantages of each type of actuator are overcome. This exoskeleton is suitable for the strength augmentation of human lower limbs, such as the gait rehabilitation routine of hip and knee joints.

Fast and viewpoint robust human detection for SAR operations

Abstract: There are many advantages in using UAVs for search and rescue operations. However, detecting people from a UAV remains a challenge: the embedded detector has to be fast enough and viewpoint robust to detect people in a flexible manner from aerial views. In this paper we propose a processing pipeline to 1) reduce the search space using infrared images and to 2) detect people whatever the roll and pitch angles of the UAV's acquisition system. We tested our approach on a multimodal aerial view dataset and showed that it outperforms the Integral Channel Features (ICF) detector in this context. Moreover, this approach allows real-time compatible detection.

Simulation and robust trajectory-tracking for a Quadrotor UAV

Abstract: In this article, a robust control algorithm using sliding modes is proposed for the efficient regulation on the trajectory tracking tasks, in the nonlinear, multivariable, quadrotor system model, that ensures the asymptotic convergence to a desired trajectory (reference signal - r(t)) in presence of all possible uncertainties and external disturbances. A smooth piecewise continuous function trajectory is proposed where the corresponding derivatives are bounded. Furthermore, we assume that the disturbances on the vehicle are bounded and the signal r(t) are available on line. The proposed algorithm employs a sliding surface based on the errors generated from the current state of the path in order to reach the desired reference r(t). The stability analysis of the closed-loop control system is proven via the use of Lyapunov theory. Finally, a numerical simulation of tracking a smooth trajectory is performed to demonstrate the validity and effectiveness of the proposed robust algorithm in presence of disturbances onto the vehicle.

Vision-based autonomous hovering for a miniature quad-rotor

Abstract: In this paper, a vision-based scheme for the autonomous hovering of a miniature quad-rotor is developed. Cameras are used to estimate the position and the translational velocity of the vehicle. The dynamic model of the miniature quad-rotor is developed using the Newton-Euler approach. A nonlinear controller based on a separated saturation control strategy for a miniature quad-rotor is presented. To validate the theoretical results, an embedded control system for the miniature quad-rotor has been developed. Thus, the analytic results are supported by experimental tests. Experimental results have validated the proposed control strategy.

Modelado y Control de un Exoesqueleto para la Rehabilitación de Extremidad Inferior con dos grados de libertad

Abstract: Los exoesqueletos mecanicos son robots acoplados a las extremidades del cuerpo humano enfocados en el incremento de su fuerza, velocidad y rendimiento principalmente. Las principales aplicaciones son en la milicia, en la industria y en la medicina. El exoesqueleto se puede utilizar para la rehabilitacion de las extremidades cuando por causas de algun accidente o enfermedad se tiene una actividad muscular reducida o nula. En este articulo se presenta un exoesqueleto de dos grados de libertad para realizar ejercicios de rehabilitacion para tobillo y rodilla. El diseno y fabricacion del exoesqueleto esta basado en la instrumentacion de una ortesis del miembro inferior derecho. El Exoesqueleto utiliza sensores que estiman la fuerza producida por el humano y se encuentran incorporados en los actuadores de tipo SEA (Series Elastic Actuator) que se utilizan para amplificar la fuerza humana. Ademas mediante sensores se estima la posicion y velocidad angular de las articulaciones, que se utilizan para controlar el movimiento de la pierna. En el articulo se presentan: un estudio del modelo dinamico del exoesqueleto y de los actuadores acoplados por medio del metodo de perturbaciones singulares, el diseno de un control basado en la suma de fuerzas generadas por el humano y el exoesqueleto, el diseno y fabricacion del prototipo experimental y sus actuadores. Se realizaron simulaciones que muestran el buen desempeno del controlador propuesto. Los resultados experimentales muestran que existe una amplificacion de la fuerza generada por el portador y amplificada por la mecanica del exoesqueleto, ofreciendo una disminucion en el esfuerzo del usuario para mantenerse de pie y realizar ejercicios de flexion y extension de las articulaciones. De manera que la amplificacion de la fuerza puede aumentarse o disminuirse segun se necesite, permitiendo al usuario una mejora evolutiva hasta llegar a la rehabilitacion completa.

Task-based control of a multirotor miniature aerial vehicle having an onboard manipulator

Abstract: The paper presents the modeling and control of a class of multirotor miniature aerial vehicle (MAV) having an onboard robotic manipulator. These kind of configuration represents the logical evolution in the MAV development race. The main goal is to outstrip the current operational profile, specially in the civilian field, by endowing classical MAV config- urations with novel capabilities to interact with the surrounding environment. The equations that describes the dynamic model of this class of aerial robot, for translation and rotational motion, are obtained through the Euler-Lagrange formalism. This energy-based modeling approach allows to obtain the mechanical couplings between both aerial and manipulation systems, the aerial and manipulation. In terms of control, our main goal is to provide a simple-to-implement controller to perform aerial manipulation tasks using multirotor MAVs. A task-based control strategy is then proposed to cancel the couplings in the overall dynamic model (model simplification). The control law for the aerial system relies on a classical two- level scheme to fullfil tracking problem. On the other hand, the motion problem of the manipulation system is addressed via a switching-based controller. The controller corresponding stability proofs are presented and the performance of the control strategy is evaluated at simulation level. I. INTRODUCTION The pace of development of Unmanned Aerial Vehicles (UAVs) has increased over the last few years, due to the wide range of military or civilian applications were they could potentially be deployed. In the military field, applications such as delivering survival-kits to the troops, mobile commu- nication link with a ground station for information exchange, risk evaluation of hostile area, are just a few examples of drone-based applications. It is well know that growth rate of MAVs civilian application is not as high as that of its military counterpart. However, the operational profile offered by interactive MAVs unveils interesting novel applications, for instance, recovering mineral samplings in volcanic study, air- quality cartography/monitoring, placing/recovering sensors in constrained strategic areas, recovering potential explosive packages in sensitive facilities. The interactive MAV configu- ration represent a unique profile endowing manipulator robot with the 3D mobility of aerial vehicles. The latter allows to perform teleoperated/autonomous interactivity within hostile environments. Whereas this concept is very promising, it also comes with significant robotic and automation challenges. Foremost amongst these is the modeling the compound mechanical system and designing controllers that will work, in theory and practice, over partial or complete operational scope of the flying robot and an appropriate and optimized mechanical design to meet the desired flight performance requirements. Recent research activities related to interactive flying rotorcrafts can be found in the literature: (2)where the authors have presented the planar model and attitude control analysis of helicopter equipped with a gripper that is capable of grasping and transporting loads of different geometries and sizes. GRASP Research team uses different cooperative quadrotors fleet configurations to transport corresponding load geometries by means of gripper and cables (3). An alternative UAV configuration featuring a hook aiming at vision-based delivering and retrieving of cargo, is presented in (4). In (5) and (6), the problem of load transportation using autonomous small size helicopters is addressed. Likewise, the modeling and control of a variable number of helicopters transporting a load is presented. Indeed, the proposed con- troller prevent and compensate load oscillations during flight, which is demonstrated by real flight load transportation by three helicopters. The paper presents the study of a class of a multirotor MAV evolving in the longitudinal plane and capable of interacting with the surrounding environment by means of

Wind Estimation for Accurate Airplane Path Following Applications

Abstract: This paper explores the flight of small fixed-wing Unmanned Aerial Vehicle (UAV) in a non-steady environment. The vulnerability of light airplanes to wind is analyzed and the effect of such perturbations on airplane performance is incorporated in the equations of motion. A straightforward wind computation approach, which relies on the difference between the predicted motion of the aircraft and the real motion measured by sensors, is presented in order to be used for a path following application. The analysis takes into account the effect of the noise in sensors measurements and in estimates of orientation and airspeed components. One approach to reducing noise in wind estimates is proposed based on on-line adaptation techniques. Parameter estimation with minimum-order design is obtained using tuning functions. Simulations are carried out representing real flight scenarios in which the wind field is not constant and the sensor measurements are imperfect.

Discrete optimal control for a quadrotor UAV: Experimental approach

Abstract: In this paper we propose a discrete time optimal control law to stabilize the four-rotor rotorcraft in attitude and position. The main objective of this kind of control law is to save energy and therefore increase the effective time in takeoff and hover flight phases for this robotic platforms. The optimal control law is synthesized considering a infinite horizon combined with an exact linearization by applying a nonlinear control law over nonlinear equations describing the robot dynamic model. The control law obtained is simple, easy and better adapted to be programmed in a micro-controller. Both simulation and experimental test and results show a satisfactory UAV behavior.

Stability Analysis of a Vision-Based UAV Controller

Abstract: The stability analysis of a vision-based control strategy for a quad rotorcraft UAV is addressed. In the present application, the imaging sensing system provides the required states for performing autonomous navigation missions, however, it introduces latencies and time-delays from the time of capture to the time when measurements are available. To overcome this issue, a hierarchical controller is designed considering a time-scale separation between fast and slow dynamics. The dynamics of the fast-time system are stabilized using classical proportional derivative controllers. Additionally, delay frequency and time domain techniques are explored to design a controller for the slow-time system. Simulations and experimental results consisting on a vision-based road following task are presented.

Linear controllers implementation for a fixed-wing MAV

Abstract: This paper deals with the experimental validation of linear controllers for a fixed-wing Miniature Air Vehicle (MAV). We are interested to realize a comparative analysis of two linear controllers, Proportional Integral Derivative (PID) and Proportional Derivative (PD), in order to know what controller has a better performance when they are used on an autonomous flight (altitude, yaw and roll). Experimental results are obtained in order to analyze the controllers and validate the performance of the fixed-wing MAV in presence of perturbations like wind gusts.

Fast and viewpoint robust human detection in uncluttered environments

Abstract: Human detection is a very popular field of computer vision. Few works propose a solution for detecting people whatever the camera's viewpoint such as for UAV applications. In this context even state-of-the-art detectors can fail to detect people. We found that the Integral Channel Features detector (ICF) is inoperant in such a context. In this paper, we propose an approach to still benefit from the assets of the ICF while considerably extending the angular robustness during the detection. The main contributions of this work are: 1) a new framework based on the Cluster Boosting Tree and the ICF detector for viewpoint robust human detection, 2) a new training dataset for taking into account the human shape modifications occuring when the pitch angle of the camera changes. We showed that our detector (the PRD) is superior to the ICF for detecting people from complex viewpoints in uncluttered environments and that the computation time of the detector is real-time compatible.

Real-time parameters identification for a quad-rotor mini-aircraft using adaptive control

Abstract: In this article an adaptive controller is developed in order to estimate the inertia tensor, the mass and the wind parameters (considering wind as a parameter in the input) for the underactuated quad-rotor mini-aircraft. Experimental tests are performed in an educational platform. The proposed control scheme uses the parameter estimation issued from gradient type algorithm. Finally simulations and experimental results are included to illustrate the performance of the parameters identification for the quad-rotor helicopter.

Design and modelling of a backbone pneumatic exoskeleton

Abstract: In this paper, preliminary studies are presented to model and design a device that will be part of an exoskeleton actuated by Pneumatic Artificial Muscles (PAM's). The aim of the device is to assist the user in lifting weights, avoiding backbone lesions. The device increases the strength of the operator. It uses sensors to detect the force to be applied and to detect the position of the user's trunk. The complete dynamical model of the system consists of the model of a planar robot with 3 rotation joints and the PAM's model, that is taken from some references. At this stage only the mechanical part of the prototype is adjustable.

Fault Estimation and Control for a Quad-Rotor MAV Using a Polynomial Observer. Part I: Fault Detection

Abstract: This work addresses the problem of fault detection and diagnosis (FDD) for a quad-rotor mini aerial vehicle (MAV). Actuator faults are considered on this paper. The basic idea behind the proposed method is to estimate the faults signals using the extended state observers theory. To estimate the faults, a polynomial observer is presented by using the available measurements and know inputs of the system. In order to investigate the observability and diagnosability properties of the system, a differential algebra approach is proposed. Furthermore, an evaluation function depending on the system states is developed, in order to be used in a controller, which will compensate the failures. The effectiveness of the methodology is illustrated by means of numerical simulations and some experimental tests.

Trajectory tracking for inertial systems using a right inverse approach

Abstract: A new hybrid control scheme for inertial systems is proposed. The horizontal displacement controller is such that, the system moves from one hovering position to another one by following a desired continuous trajectory. The closed-loop behaves as a discrete first order system. The control scheme is illustrated in a numerical simulation of a PVTOL (Planar Vertical Take-Off and Landing).

Quadrotors data fusion using a particle filter

Abstract: This paper presents a data fusion algorithm by means of a particle filter (PF) for estimate the position of a quadrotor equipped with multiple sensors. A global positioning system (GPS) is considered for position measurement in a loosely coupled scheme, velocity can be obtained from an optic flow sensor, whilst an inertial measurement unit (IMU) can provide orientation and angular rate measurements. Simulations were carried out, where real noise from a not expensive GPS is added to the simulated position to test the proposed algorithm.

Study of the interaction between a one degree of freedom force augmenting device and a human operator

Abstract: In this paper a one degree of freedom (DOF) force augmenting device (FAD) is presented. A laboratory set-up has been built and some tests of the interaction between the FAD and a user were performed. The stability of the closed loop system is essential for the performance of the FAD. The FAD by itself is a stable device, but what is important is to assure the stability of the interaction between the FAD and a human being. To deal with this matter, two situations were analyzed. The case of no delays in the model is first considered. This situation might appear unrealistic, for this reason, a second analysis is performed considering a human model with delays. In order to deal with delays a Rekasius substitution is used. To perform the stability analysis, it is sufficient to apply the Routh-Hurtwitz criteria. Attempts with other techniques have given more conservative stability results. The stability has been proven for delays smaller than upper-bounds which have been computed. None of these upper-bounds are reached by any healthy human being. Therefore, we can assure that the whole system is stable for most of the practical situations. This proves the robustness of the closed loop system with respect to delays. In real time experiments, measurement from the sensors are normally noisy. In order to reduce the effect of the noise, a low pass filter was included. The introduction of this filter alters the order of the system, changing the stability conditions of the whole set up. So the stability analysis is performed again with the inclusion of the filter.