Guillaume Ducard

Efficient Nonlinear Actuator Fault Detection and Isolation System for Unmanned Aerial Vehicles

In this paper, three main limitations of the classical implementation of the multiple-model adaptive-estimation method to isolate faults based on predefined fault hypotheses are highlighted. The first concerns the number of filters that must be designed to span the range of possible fault scenarios, which must be limited due to computational load. The second limitation appears when an actuator is locked at an arbitrary nonzero position that biases the residuals of the Kalman filters, leading to inaccurate fault detection and state estimation. Third, most of the implementations of a multiple-model adaptive-estimation method only work efficiently around predefined operating conditions. This paper presents a nonlinear actuator-fault detection and isolation system, which properly works over the entire operating envelope of an aircraft. Locked-in-place and floating actuator faults can be handled. The robustness of the fault detection and isolation system is enhanced by the usage of auxiliary excitation signals. The fault detection and isolation system is also capable of handling two simultaneous actuator failures with no increase of the computational load. The complete system was demonstrated in simulation with a nonlinear model of a model aircraft in moderate to severe wind conditions.

Implementation of a Nonlinear Attitude Estimator for Aerial Robotic Vehicles

Attitude estimation is a key component of the avionics suite of any aerial robotic vehicle. This paper details theoretical and practical solutions in order to obtain a robust nonlinear attitude estimator for flying vehicles equipped with low-cost sensors. The attitude estimator is based on a nonlinear explicit complementary filter that has been significantly enhanced with an effective gyro-bias compensation via the design of an anti-windup nonlinear integrator. A measurement decoupling strategy is proposed in order to make roll and pitch estimation robust to magnetic disturbances that are known to cause errors in yaw estimation. In addition, this paper discusses the fixed-point numerical implementation of the algorithm. Finally, simulation and experimental results confirm the performance of the proposed method.

Extended Multiple Model Adaptive Estimation for the Detection of Sensor and Actuator Faults

A combination of the multiple model adaptive estimation method (MMAE) with an extended Kalman filter (EKF) is considered. The ability of the MMAE method to detect faults based on a predefined hypothesis and the parameter-estimating ability of an EKF results in a very efficient fault detection approach. This so-called extended multiple model adaptive estimation method (EMMAE) has been investigated on a nonlinear model of an aircraft. The results show that it is a very capable method to detect faults of various types.

A reconfigurable flight control system based on the EMMAE method

The ability of the multiple model adaptive estimation method (MMAE) to detect faults based on a predefined hypothesis and the parameter-estimating ability of an extended Kalman filter (EKF) results in an efficient fault detection approach. This extended multiple model adaptive estimation method (EMMAE) has been investigated on a nonlinear model of an aircraft to estimate on-line the state vector of the system and the control surface deflection in case of failed actuators. A supervision module has been designed to enhance the performance of the EMMAE method and to appropriately change settings in a control allocation module. The results show that this reconfigurable flight control system is capable of detecting, isolating, and compensating for actuator faults of various types, without any need to add additional sensors to measure control-surface deflections or to change the flight controller

Hardware and Software Architecture for Nonlinear Control of Multirotor Helicopters

This paper presents the design and implementation of a nonlinear control scheme for multirotor helicopters that takes first-order drag effects into account explicitly. A dynamic model including the blade flapping and induced drag forces is provided and a hierarchical nonlinear controller is presented. This controller is designed for both high-precision flights as well as robustness against model uncertainties and external disturbances. This is achieved by using saturated integrators with fast desaturation properties. The implementation of the controller on the flybox hexacopter platform is described. The hardware and software architecture of this UAV is discussed, and useful hints and insights gained during its design process are presented. Finally, experimental results and videos are reported to demonstrate the successful implementation and the performance of the overall system.

Nonlinear control of VTOL UAVs incorporating flapping dynamics

This paper presents the design and evaluation of a nonlinear control scheme for multirotor helicopters that takes first-order drag effects into account explicitly. A dynamic model including the blade flapping and induced drag forces is presented. Based on this model, a hierarchical nonlinear controller is designed to actively compensates for the nonlinear effects these drag forces. Reported simulation and experimental results indicate the significant performance improvement of the proposed drag-augmented control scheme with respect to a conventional nonlinear controller. For completeness, an offline procedure allowing for efficiently identifying the drag parameters is proposed.

A Robust Attitude Controller and its Application to Quadrotor Helicopters

Abstract In this paper, a novel nonlinear hierarchical controller for attitude control is proposed. This controller is obtained using Lyapunov methodology. Model uncertainties in the system are estimated on-line based on a time-delay control approach. The robustness of the flight controller is enhanced using an anti-windup integrator technique and semi-global asymptotical stability is proven. The control law obtained is simple enough for an implementation on a small microcontroller. Simulation results for a model of a quadrotor helicopter illustrate the performance of the proposed control algorithm.

Bilateral haptic teleoperation of VTOL UAVs

This paper presents an intuitive teleoperation scheme to safely operate a wide range of VTOL UAVs by an untrained user in a cluttered environment. This scheme includes a novel force-feedback algorithm that enables the user to feel the texture of the environment. In addition, a novel mapping function is introduced to teleoperate the UAV in an unlimited workspace in position control mode with a joystick which has a limited workspace. An obstacle avoidance strategy is designed to autonomously modify the position set point of the UAV independently of the pilots commands. The stability analysis of the whole teleoperation loop is provided. Experiments demonstrate the successful teleoperation of a UAV using an haptic joystick and a hexacopter UAV equipped with a 2D laser-range scanner.

Airspeed control for unmanned aerial vehicles: a nonlinear dynamic inversion approach

This paper presents a nonlinear airspeed controller for an unmanned aerial vehicle (UAV). It is designed using the technique of nonlinear dynamic inversion. The thrust force of the UAV is generated by a propeller. The nonlinear dynamics of the airspeed are appropriately expressed as a function of the thrust force, which is a nonlinear function of the engine speed. The latter variable is the only physical control input of the system. The airspeed control system is constituted of a linear controller responsible for the generation of the desired airspeed dynamics, which are successively converted into a desired thrust command and an engine speed command through two consecutive nonlinear transformations. The proposed architecture is modular, easy to implement, and computationally efficient. Nonlinear simulation results demonstrate the effectiveness of the method.

Nonlinear attitude estimation with measurement decoupling and anti-windup gyro-bias compensation

Abstract Any low-cost IMU is subject to biased measurement in its gyroscopes. This paper presents a nonlinear attitude observer which incorporates anti-windup gyro-bias compensation. It also provides an extension of the decoupling strategy of IMU measurement recently proposed in the literature by providing almost global stability proof along with a comprehensive study of the decoupling strategy. Simulation and experimental results are given to illustrate the concept.