This paper is concerned with large-angle attitude tracking control for quadrotors in the presence of time-varying inertia and external disturbances using a switched linear parameter-varying (LPV) system method. The attitude system of the quadrotor is divided into two parts, that is, the outer attitude-angle loop and inner angular-velocity loop. A feedback linearization controller is designed in the outer loop to generate the desired angular velocities. In the inner loop, the nonlinear quadrotor dynamics with time-varying inertia is approximated by a switched LPV system that consists of a series of LPV models. The persistent dwell time (PDT) switching logic is adopted to describe the fast and slow switches coexist among these LPV models. Then, both the continuous-time state-feedback and dynamic output-feedback controllers are designed, which ensure the globally uniformly asymptotically stability and 2 − ∞ external disturbance attenuation performance of the attitude tracking error system. Finally, the effectiveness of the proposed tracking control method of quadrotors is validated with an example.
K E Y W O R D S 2 − ∞ performance, persistent dwell time, quadrotor, switched linear parameter-varying systems
INTRODUCTIONIn recent years, the quadrotors have been broadly applied in surveillance, facilities inspection, and rescue missions because of their maneuverability and maintainability. [1][2][3] As the core part of the flight control system in quadrotors, the attitude controller determines the overall performance of quadrotors in various missions. 4 However, the attitude control system of quadrotors is characterized by nonlinearity and strong coupling, which is sensitive to external disturbances and model uncertainties. 5,6 Therefore, it is a challenge to design a satisfactory attitude tracking controller with fast response and high precision.
We present a technique to reconstruct the environment for telerobotic welding. The welding environment consists of typical textureless object, which causes problem in stereo matching of traditional spacial stereo. Under the novel framework of spacetime stereo, we add artificial texture onto the surface of objects by projecting a multi-level dual monotonously changLQJ "saw-tooth" stripe gray light patterns. The SSD of different image pairs are normalized before added together to find the best matched pixels of the two image sequence. Subpixel disparity is obtained by interpolation and the unreliable regions are removed by intensity tracking and left-right consistent check.
The experimental results show the validity of the presented techniqueIndex Terms -spacetime stereo, 3D reconstruction, telerobotic welding, subpixel disparity.
With the localizing character of wavelet transform, acoustic signal from water surface using laser light can be decomposed into the detail part of every scale by multi-resolution analysis. The results of experiment show that wavelet analysis has the great ability of noise rejection and is fit for weak signal detection and feature extraction.
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