Silicon micromechanical gyroscope has been paid much commercial attention and application due to its small size, low cost and medium precision, and closed-loop control is one of the important ways to improve its performance. It is well known that the silicon micromechanical gyroscope's performance with closed-loop controller can be improved significantly under the vacuum by amplifying the micro-structure's quality factor. However, the advantages of MEMS sensors such as batch quantity, low cost and small size can be weakened at the same time, and the characteristics of closed-loop control system would be changed with the vacuum variety. This paper presents a novel closed-loop silicon micromechanical gyroscope at atmosphere pressure and improves the performance. In consideration of the characteristic of ac signal feedback of resonant silicon micromechanical gyroscope's sense axis, the differences and characteristics of the closed-loop control system in the vacuum and at air pressure are described. A method of sense axis's phase adjustment and magnitude closed-loop control at atmosphere pressure is proposed in this paper, based on analysis of the phase relations of the drive and sense axes and Lyapunov control theory. Different math models of sense axis under the vacuum and the atmosphere are analysed respectively. The changed phase relation between sense axis's demodulated ac signal and drive axis's referenced resonant signal are derived, and a novel phase relation schematics of drive and sense axis's ac signal of silicon micromechanical gyroscope is provided. The sense axis's open-loop transfer function is derived through experimental results. The magnitude closed-loop design method is discussed by using Lyapunov principle while the sense axis's ac signal's phase has been adjusted. The closed-loop transfer function after intelligent control is presented, and the influence of the quadrature signal on sense axis closed-loop control is taken into account at the same time. The test results show that the gyroscope performance is improved significantly by using sense axis's closed-loop control. It is found that at the air pressure, the linearity is improved from 2% to 0.5‰, and the bias stability and the angle random walk of the silicon micromechanical gyroscope are superior to 0.01deg/sec and 0.9deg/{the square root of}(hr). By theory analysis, the bias stability of silicon micromechanical gyroscope can be improved to 0.1deg/hr in the vacuum.
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