Optic Flow-Based Nonlinear Control and Sub-optimal Guidance for Lunar Landing

International audience— A sub-optimal guidance and nonlinear control scheme based on Optic Flow (OF) cues ensuring soft lunar land-ing using two minimalistic bio-inspired visual motion sensors is presented here. Unlike most previous approaches, which rely on state estimation techniques and multiple sensor fusion methods, the guidance and control strategy presented here is based on the sole knowledge of a minimum sensor suite (including OF sensors and an IMU). Two different tasks are addressed in this paper: the first one focuses on the computation of an optimal trajectory and the associated control sequences, and the second one focuses on the design and theoretical stability analysis of the closed loop using only OF and IMU measurements as feedback information. Simulations performed on a lunar landing scenario confirm the excellent performances and the robustness to initial uncertainties of the present guidance and control strategy

Comments on actuator fault accommodation

International audienceThe present work concerns the problem of progressive accommodation to actuator failure. An optimal nonlinear controller synthesis approach is formulated on the basis of the closed loop stability objective. The authors show the interest of the proposed method even for a local analysis when a linear approximation is used. This work focuses on a solution to ensure stability while accommodating to actuator failure. The approach is illustrated in an academic example

Attitude control of a gyroscope actuator using event-based discrete-time approach

International audienceIn this paper, a discrete state feedback Linear Quadratic Regulator (LQR) for event-triggered control is presented. To ensure zero steady state error in the case of such controllers, one normally extends the states with an integral action. Instead of using integral action, the idea is to estimate the disturbance causing the steady state error and use this to extend the states. A Lyapunov-based event triggering function is proposed. Practical results using a gyroscope actuator are presented and compared to a classical time-triggered controller. The obtained results demonstrate the simplicity and efficiency of the proposed approach

Sub-optimal Lunar Landing GNC using Non-gimbaled Bio-inspired Optic Flow Sensors

International audienceAutonomous planetary landing is a critical phase in every exploratory space mission. Autopilots have to be safe, reliable, energy-saving, and as light as possible. The 2-D Guidance Navigation and Control (GNC) strategy presented here makes use of biologically inspired landing processes. Based solely on the relative visual motion known as the Optic Flow (OF) assessed with minimalistic 6-pixel 1-D OF sensors and Inertial Measurement Unit measurements, an optimal reference trajectory in terms of the mass was defined for the approach phase. Linear and nonlinear control laws were then implemented in order to track the optimal trajectory. To deal with the demanding weight constraints, a new method of OF estimation was applied, based on a non-gimbaled OF sensor configuration and a linear least squares algorithm. The promising results obtained with Software-In-the-Loop simulations showed that the present full GNC solution combined with our OF bio-inspired sensors is compatible with soft, fuel-efficient lunar spacecraft landing and might also be used as a backup solution in case of conventional sensor failure

Local Positioning System Using Flickering Infrared LEDs

International audienceA minimalistic optical sensing device for the indoor localization is proposed to estimate the relative position between the sensor and active markers using amplitude modulated infrared light. The innovative insect-based sensor can measure azimuth and elevation angles with respect to two small and cheap active infrared light emitting diodes (LEDs) flickering at two different frequencies. In comparison to a previous lensless visual sensor that we proposed for proximal localization (less than 30 cm), we implemented: (i) a minimalistic sensor in terms of small size (10 cm 3), light weight (6 g) and low power consumption (0.4 W); (ii) an Arduino-compatible demodulator for fast analog signal processing requiring low computational resources; and (iii) an indoor positioning system for a mobile robotic application. Our results confirmed that the proposed sensor was able to estimate the position at a distance of 2 m with an accuracy as small as 2-cm at a sampling frequency of 100 Hz. Our sensor can be also suitable to be implemented in a position feedback loop for indoor robotic applications in GPS-denied environment

Insect inspired visual motion sensing and flying robots

International audienceFlying insects excellently master visual motion sensing techniques. They use dedicated motion processing circuits at a low energy and computational costs. Thanks to observations obtained on insect visual guidance, we developed visual motion sensors and bio-inspired autopilots dedicated to flying robots. Optic flow-based visuomotor control systems have been implemented on an increasingly large number of sighted autonomous robots. In this chapter, we present how we designed and constructed local motion sensors and how we implemented bio-inspired visual guidance scheme on-board several micro-aerial vehicles. An hyperacurate sensor in which retinal micro-scanning movements are performed via a small piezo-bender actuator was mounted onto a miniature aerial robot. The OSCAR II robot is able to track a moving target accurately by exploiting the microscan-ning movement imposed to its eye's retina. We also present two interdependent control schemes driving the eye in robot angular position and the robot's body angular position with respect to a visual target but without any knowledge of the robot's orientation in the global frame. This "steering-by-gazing" control strategy, which is implemented on this lightweight (100 g) miniature sighted aerial robot, demonstrates the effectiveness of this biomimetic visual/inertial heading control strategy

A tiny lensless position sensing device for the tracking of active markers

International audienceActive markers tracking is performed using an innovative insect-based visual sensor. Without any optics and a field-of-view of about 60°, our novel miniature visual sensor is able to locate flickering markers (LEDs) with accuracy much greater than the one dictated by the pixel pitch. With a size of only 1cm3 and a mass of only 0.33g, the lensless sensor, called HyperCube, is dedicated to 3D motion tracking and fits perfectly with the drastic constraints imposed by micro-aerial vehicles. This small cubic position sensing device is composed of only three photosensors placed on each side of the cube, making this sensor very cheap and light. HyperCube provides the azimuth and elevation of infrared LEDs flickering at high frequency (>1kHz) with a precision of only few degrees. The simplicity, small size, low mass, and low power consumption of this optical sensor make it suitable for many applications in the field of cooperative flight of unmanned aerial vehicles, swarm robotics and more generally robotic applications requiring active beacons. Experimental results show that HyperCube provides useful angular measurements that can be used to estimate the relative position between the sensor and the infrared markers

Commande robuste pour l'assistance au contrôle latéral d'un véhicule routier

Le contrôle latéral trouve de nombreuses applications dans le domaine de l'assistance à la conduite. Un grand nombre d'accidents de la route sont provoqués par des mouvements de roulis et de lacet excessifs engendrant des sorties de route. De plus, ce type d'accidents se produisent généralement sur les routes nationales et départementales, et environ 30 % des incidents impliquent des véhicules seuls.L'objectif de cette thèse est de mettre en œuvre un correcteur qui soit en mesure d'assister le conducteur dans les situations de suivi de voies et de rejeter diverses perturbations auxquelles est soumis le véhicule telles que des vents latéraux ou un dévers de la route, tout en respectant les contraintes de confort, d'agrément de conduite et les limitations pratiques de l'actionneur de direction. La stratégie d'assistance retenue consiste à ajouter un couple à celui délivré par le conducteur grâce à l'intégration d'un moteur à courant continu sur la colonne de direction. Elle tient compte des trois composantes que sont le véhicule, la colonne de direction et le conducteur.Les travaux se sont donc focalisés sur les techniques de commande robuste qui utilisent les synthèses Hinfini et Hinfini-LPV complétées des méthodes de réduction de modèles.D'abord dans le cadre d'une synthèse de correcteur Hinfini à vitesse fixe, les spécifications sont respectées. Le dispositif d'assistance active confère au système en boucle fermée de bonnes propriétés de robustesse comme l'a montré la mu-analyse.Ensuite pour améliorer le domaine de stabilité du système commandé, un correcteur séquencé par la vitesse longitudinale est synthétisé. Il est plus performant.Lateral control finds many applications in the field of driving assistance. A large number of vehicle accidents results from unexpected excessive yaw motion such as spin-out and lane departure. In addition, such type of accidents generally occurs on rural road, and about 30 % of fatalities in France are due to accidents with vehicle alone.The thesis aims at synthesizing a controller which assists the driver in the situations of lane keeping and disturbance rejections. The vehicle is subject to lateral wind and road banking and the control strategy must ensure driving comfort criteria and must respect the physical limitations of the actuator.The assistance strategy adopted consists in adding a supplementary torque using a motorized direction system to that of the driver. It takes into account three components which are the vehicle, the steering column and the driver.The developments focus on the Hinfinity and Hinfinity-LPV robust control theory completed with the model reduction methods.First, in the context of an Hinfinity synthesis at fixed longitudinal velocity, the specifications are satisfied. The active assistance system ensures good closed loop robustness properties as shown by the mu-analysis.Secondly, in order to increase the stability of the controlled system, a controller scheduled by the longitudinal velocity is synthesized. The performances are better.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Low-speed optic-flow sensor onboard an unmanned helicopter flying outside over fields

International audienceThe 6-pixel low-speed Visual Motion Sensor (VMS) inspired by insects' visual systems presented here performs local 1-D angular speed measurements ranging from 1.5 °/s to 25 °/s and weighs only 2.8g. The entire optic flow processing system, including the spatial and temporal filtering stages, has been updated with respect to the original design. This new lightweight sensor was tested under free-flying outdoor conditions over various fields onboard a 80kg unmanned helicopter called ReSSAC. The visual disturbances encountered included helicopter vibrations, uncontrolled illuminance, trees, roads, and houses. The optic flow measurements obtained were finely analyzed online and also offline, using the sensors of various kinds mounted onboard ReSSAC. The results show that the optic flow measured despite the complex disturbances encountered closely matched the approximate ground-truth optic flow