This article addresses the problem of high precision attitude control for quadrotor unmanned aerial vehicle in presence of wind gust and actuator faults. We consider the effect of those factors as lumped disturbances, and in order to realize the quickly and accurately estimation of the disturbances, we propose a control strategy based on the online disturbance uncertainty estimation and attenuation method. Firstly, an enhanced extended state observer (ESO) is constructed based on the super-twisting (ST) algorithm to estimate and attenuate the impact of wind gust and actuator faults in finite time. And the convergence analysis and parameter selection rule of STESO are given following. Secondly, in order to guarantee the asymptotic convergence of desired attitude timely, a sliding mode control law is derived based on the super-twisting algorithm. And a comprehensive stability analysis for the entire system is presented based on the Lyapunov stability theory. Finally, to demonstrate the efficiency of the proposed solution, numerical simulations and real time experiments are carried out in presences of wind disturbance and actuator faults.
During the trajectory tracking process and low altitude flight of quadrotor, wind gust and ground effect will significantly affect the accuracy and stability of the controller. Therefore, it is vital for a quadrotor to have a robust controller against multiple disturbances. To mitigate this challenge, an active anti-disturbance control strategy based on generalized extended state observer is proposed in this article. Firstly, quadrotor dynamics is modeled as cascaded translational and rotational loops, and the characteristics of wind gust and ground effect are analyzed. Secondly, two generalized extended state observers are constructed for those loops respectively to estimate and attenuate the impact of wind gust and ground effect, and the position and attitude controller are designed based on backstepping method. Finally, real time experiments are carried out on hovering and circle trajectory tracking conditions. The results illustrate that the proposed controller has more advantages in high precision trajectory tracking and low altitude flight of quadrotor in existence of multiple disturbances.
During the flight of the quadrotor, the existence of a slung load will exert a swing effect on the system and the motion of which will significantly change the dynamics of the quadrotor. The external torque caused by the slung load can be considered as a kind of disturbance and it is a threat to the attitude control stability of the system. In order to solve this problem, a high precision disturbance compensation method is presented in this paper, based on the harmonic extended state observer (HESO). Firstly, a generic mathematical model for the quadrotor-slung load system is obtained via the Lagrangian mechanics, and according to the analysis of the slung load motion, we obtain the disturbance as a form of periodic equation. Secondly, based on the dynamic model of the disturbance, we propose a HESO to achieve high precision disturbance estimation and its stability is proved by Lyapunov theory. Thirdly, we designed an attitude tracking controller based on backstepping method, and discussed the stability of the entire system. Finally, numerical simulations and real time experiments are carried out to evaluate the performance of the proposed method. Our results show that the robustness of the quadrotor subject to slung load has been improved.
Human Lower-limb Exoskeleton has recently received a great deal of attention, because of providing motion similar to human walking and reducing burden on both patients and therapists. In this paper the design of the control system for HLE which is actuated by electro-hydraulic servo system is presented. To improve the flexibility of the system, a control algorithms called sliding mode variable structure control was adopted. The simulation and results show that the controller has a better dynamic performance.
Keywords-human lower-limb exoskeleton; sliding mode variable structure control; electro-hydraulic servo system.I.
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