Abdelhamid Chriette

Visual servo trajectory tracking for a four rotor VTOL aerial vehicle

An image-based visual servo control design is proposed for a four rotor vertical take-off and landing (VTOL) craft, known as an X4-flyer, accomplishing a trajectory tracking task. The approach taken is an image-based visual servo design that is applicable to under-actuated dynamic systems. The work is an extension of the authors earlier work (2000) to the trajectory tracking problem. Semiglobal stability of the closed loop system is proved for bounded trajectories.

A robust guidance and control scheme of an autonomous scale helicopter in presence of wind gusts

This article deals with the problem of robust trajectory tracking for a scale model autonomous helicopter. A large class of uncertainties/disturbance is addressed, namely uncertain parameters and uniform time-varying tridimensional wind gusts occurring in the vicinity of the aircraft. Using an unknown input observer technique, it is shown that disturbances/uncertainties effects on the autonomous helicopter can be accurately reconstructed online. The analysis further extends to the design of a control law whose methodology takes the disturbance estimation procedure into account. Regarding passivity feature of the resulting model, a control law was designed using robust backstepping techniques. The approach proposed here significantly improves the performance of the control and the flight security by counteracting wind gusts in any flight phases. The framework proposed is applied to a non-linear six degree-of-freedom helicopter model. Consequently, a non-linear dynamic model of miniature helicopter is proposed, which focuses on the key effects in the dynamics of a miniature helicopter. Lyapunov stability analysis is then performed to keep the balance between robustness, short response time and large stability domain with a given security margin to guarantee obstacle avoidance during the tracking trajectory process. Simulations results are presented at the end of the article.

New predictive scheme for the control of LTI systems with input delay and unknown disturbances

A new predictive scheme is proposed for the control of Linear Time Invariant (LTI) systems with a constant and known delay in the input and unknown disturbances. It has been achieved to include disturbances effect in the prediction even though there are completely unknown. The Artstein reduction is then revisited thanks to the computation of this new prediction. An extensive comparison with the standard scheme is presented throughout the article. It is proved that the new scheme leads to feedback controllers that are able to reject perfectly constant disturbances. For time-varying ones, a better attenuation is achieved for a wide range of perturbations and for both linear and nonlinear controllers. A criterion is given to characterize this class of perturbations. Finally, some simulations illustrate the results.

Generic nonlinear model of reduced scale UAVs

This paper proposes, through a survey of models of several UAV-Structures, a generic nonlinear model for reduced scale aerial robotic vehicles (6 DOF). Dynamics of an aircraft and some VTOL UAV (quadricopter, ducted fan and classical helicopter) are illustrated. This generic model focuses only on the key physical efforts acting on the dynamics in order to be sufficiently simple to design a controller. The Small Body Forces expression which can introduce a zero dynamics is then discussed.

Continuous Differentiator Based on Adaptive Second-Order Sliding-Mode Control for a 3-DOF Helicopter

A novel control scheme for the regulation and trajectory tracking in spite of external perturbations of the three degrees of freedom (3-DOF) helicopter is presented. The scheme allows reduced control effort, vibration reduction, and accurate tracking. The proposed approach combines a continuous differentiator with an adaptive super twisting controller. The differentiator provides state estimation, whereas the adaptive super twisting algorithm is chosen such that the gains of the controller are adapted to reduce the control effort and do not require the knowledge of the bounds of the uncertainties and perturbations. Furthermore, finite time convergence of the continuous differentiator to a neighborhood of the desired trajectory, allows to design independently controller and the differentiator, satisfying the principle of separation. Finally, the proposed control scheme is validated by experimental tests under external disturbances.

Control of 3 DOF helicopter: A novel autopilot scheme based on adaptive sliding mode control

This paper presents a novel autopilot for a 3D helicopter. From desired trajectories defined by the user for elevation and travel angles, the autopilot is computing the desired trajectory of the pitch angle. Furthermore, the autopilot allows to decouple the system and to define “virtual” inputs in order to separately design controllers for each attitude angle. Travel and elevation controllers are based on adaptive version of sliding mode control: this class of controllers keeps the robustness feature of sliding mode while reducing the well-known drawback of such control approach, the chattering, thanks to the online adaptation of the controller gain. The proposed autopilot is evaluated on an experimental set-up.

A robust controller based on adaptive super-twisting algorithm for a 3DOF helicopter

This paper presents a new controller for a 3D helicopter. The main novelty of this controller is the use of adaptive super-twisting algorithm for the control of each attitude angle. This controller is a second order sliding mode controller, which is robust versus uncertainties and perturbations, ensures finite time convergence, reduces the chattering, increases the accuracy and does not require time derivative of the sliding variable. A very important point comes from its adaptive gain, which allows to design the controller with very reduced knowledge on uncertainties and perturbations. This controller is applied on the three attitude angles of a 3D helicopter, this fact being validated by simulations and experimental results.

WIND GUSTS COMPENSATION ACTING ON AN AUTONOMOUS HELICOPTER USING VARIABLE STRUCTURE DIFFERENTIATION SCHEME

Abstract This paper deals with the problem of disturbance reconstruction acting on an autonomous helicopter. The disturbance consists in wind gusts, the objective, which is original in this context, being to estimate it by using differentiation of the measurements, in order to compensate these disturbances and to improve the performances of the control. Two differentiation variable structure based strategies are used and compared in term of control performances.

Predictive scheme for observer-based control of LTI systems with unknown disturbances

In this work, it is shown that the results introduced in [1], that hold for full state measurement, can be extended to partial state measurement. In particular, it is proven that the combination of an observer with the new predictive scheme of [1] leads to a better disturbance attenuation than using the same observer with the standard predictive scheme. Finally, some simulations illustrate the results for constant and time-varying disturbances.

Nonlinear observers in vision system: Application to civil aircraft landing

In this paper, a new pose estimation solution for perspective vision system is presented and applied to a civil aircraft landing phase. Vision sensor is used to overcome the need for external technologies and runway knowledge. Two nonlinear observers are proposed for on-line estimation of the deviations of the aircraft w.r.t. the runway. These nonlinear observers are based, first, on a high-gain approach, and then on a high-order sliding-mode approach, allowing robustness and finite time convergence. The originality of the presented results consists in estimating deviations with redundant informations in order both to increase efficiency of the observer and guarantee observability. Simulation results obtained on a realistic landing scenario are presented.