We report for the first time an implementable method to identify and suppress the driving force misalignment angle for a MEMS gyroscope working either in AM or LFM mode using parametric excitation. By introducing driving force misalignment angle into gyroscope dynamic equations, we illustrate that gyroscope angular rate output is affected by driving force misalignment angle and cross-axis damping jointly. We propose parametric excitation as a way to both identify and calculate the driving force misalignment angle. The identification results for a gyroscope working in both AM and LFM mode are similar, which indicates the effectiveness of the proposed identification method. Instead of using traditional amplitude control loop by adjusting the driving force, we do the automatic gain control by adjusting the parametric pump voltage so that a fixed drive voltage can be used, which also indicates fixed force coupling. Experimental results show that after suppression, the bias instability (BI) of AM mode is improved from 4.7 deg/h to 2.3 deg/h and the BI of LFM mode is improved from 1.4 deg/h to 0.9 deg/h which is the lowest result reported for LFM gyroscope.
In this paper, an improved area-varying tuning electrode with better immunility to fringe capactor is proposed, analyzed and tested, which is mainly used for frequency tuning of micromechanical gyroscopes. Based on the existing area-varying tuning electrode[23], this paper firstly analyzes the capacitance of the tuning electrode, and obtains the relationship between the capacitance and the displacement using both the analytic formula and finite element analysis, verifying that the fringe capacitance in area-varying tuning electrode decreases the tuning ability of both up-tuning electrode and down-tuning electrode. Then, parametric scanning method is used to optimize the geometry parameter of the tuning electrode, which reduces the influence of fringe capacitance and increases the tuning ability of the tuning electrode. Contrast experiments and tests are carried with gyroscope samples with tuning electrodes before and after optimizing. The tested mean value of tuning ability of the improved tuning electrode is improved by 95.7% after opimization.
We report a digital control architecture which demodulates both amplitude modulated (AM) and frequency modulated (FM) rate information simultaneously from gyroscope working in Lissajous frequency modulated (LFM) mode. The angular rate information is derived from both quadrature (X and Y) resonance modes of the gyroscope simultaneously. Noise model for the AM signal processing channel of the LFM gyroscope is built, analyzed and compared with that of conventional AM gyroscope, which shows that methods to improve performance of conventional AM gyroscope also applies to the AM signal processing channel of LFM gyroscope. The angular rate output obtained from the AM information of LFM gyroscope has better noise characteristics which therefore supplements the low precision inadequacy of the FM signal channel of LFM mode. Test results for the same gyroscope working in different control architectures are conducted. The ARW and BI of the AM channel of the proposed architecture is 0.51 deg/√h and 1.8 deg/h respectively, which is better than the results obtained from the FM channel in the same architecture with value of 0.99 deg/√h and 4.3 deg/h respectively. Also the AM output of the proposed architecture is better than the result of 0.50 deg/√h and 5.2 deg/h respectively using the same gyroscope working in conventional AM mode.
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