| As an emerging angular velocity sensor,MEMS gyroscopes which are benefited microelectronics and micromachining have found applications in various field in modern society.However,parameter variations caused by fabrication imperfections and external environmental disturbances result that the precision of most MEMS gyro is in middle and low level.In order to restrain the effect of parameter variations and external disturbances and improve the detect precision of MEMS gyro,the mode motion tracking technique of MEMS gyro via sliding mode control is studied in this paper.Firstly,the basic theory of MEMS gyro is introduced in this paper,including the theoretical derivation of Coriolis acceleration,the conventional operation mode and the so-called Park S operation mode,and two common nondimensional mathematical models : the vector form and the statespace form.Besides,the basic principles of adaptive control and sliding mode control are introduced,as well as their advantages.The two key problems in sliding mode control are indicated: the high-frequency chattering in control signal and the sensitivity to unmatched disturbance.Secondly,regarding the chattering and the unmatched disturbance,the detailed analysis and proof are presented in this paper.In chattering reduction,some common chattering reduction methods are discussed,especially the dynamic sliding mode,approaching law method,slowly time-varying disturbance observer,gain adaptation and so on.It also indicates that combining different methods for application is necessary.A reasonable chattering reduction scheme is proposed: the exponential approaching law is selected to depict the approaching motion and lower the velocity when system state reaches the sliding mode surface,the slowly time-varying disturbance observer is utilized to estimate the disturbance in real-time,then the switching gain can be set as a smaller value so that the chattering on the sliding mode surface can be reduced greatly.On this basis,for overcoming the asymptotical convergence of conventional sliding mode surface,a nonsingular terminal sliding mode controller combining slowly time-varying disturbance observer is designed to realize the finite-time tracking of MEMS gyro mode motion.The simulation results are performed to verify the effectiveness of the proposed scheme.In dealing with the unmatched disturbance,several classical strategies are analysed,and it should be pointed out that the unmatched disturbance attenuation ability of these classical strategies is achieved at the price of sacrificing its nominal control performance,like the overshoot and long settling time.So a novel improvement scheme is proposed.It contains: design a novel sliding mode surface to describe the desired sliding mode motion;use a nonlinear disturbance observer based on auxiliary variables to estimate the unmatched disturbance;finally there needs an extra velocity compensation.The improvement scheme can not only attenuate unmatched disturbance but also actualize chattering reduction.In simulation,one compares the proposed scheme with the common H?-based integral sliding mode control,indicating the superiority of disturbance observer in attenuating the nmatched disturbance.Finally,the nonlinear input effect of MEMS gyro is investigated.Taking the sector-bounded input nonlinearity for example,two adaptive controllers are designed for zero adjustment of a Z-axis MEMS gyro and mode motion tracking of a MEMS triaxial gyroscope according to Popov's Hyperstability theory and Lyapunov's direct method respectively.Simulation results show that the proposed adaptive control strategies has better attenuation ability to the sector-bounded input nonlinearity. |
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