Chunhua He

Virtual Rate-Table Method for Characterization of Microgyroscopes

In this paper, we demonstrate a testing method for characterization of microgyroscopes using a virtual rate-table, which uses a series of voltage signals to emulate the Coriolis force induced by the angular rate inputs to obtain the frequency response of the gyroscope. The proposed approach holds the following advantages: 1) it provides a convenient and efficient way to evaluate the scale factor and bandwidth of the gyroscope operating in either open-loop mode or closed-loop mode, the laborious debugging by frequently utilizing the real rate-table can be avoided; 2) it can easily identify the dynamic response to external angular rate, which is the control plant during the rebalance control design for the sense mode in a large frequency range, avoiding the performance limit of the ordinary rate-table; and 3) it can be used in a self-test for the microgyroscope system for the error calibration and malfunction checking. The method was applied to a decoupled z -axis gyroscope. The test results show that the measured scale factor and bandwidth are 30.2 mV/(deg/s) and 8.0 Hz by the virtual rate-table method, which are in close agreement with the conventional rate-table method, i.e., 31.0 mV/(deg/s) and 7.4 Hz. The static calibration with the virtual rate-table was also evaluated. The scale factors measured with the conventional rate-table method and the virtual rate-table method are 31.0 mV/(deg/s) and 30.1 mV/(deg/s) with R2 nonlinearity of 0.03% and 0.02%, respectively.

A MEMS Vibratory Gyroscope With Real-Time Mode-Matching and Robust Control for the Sense Mode

This paper presents a method to accomplish automatic and real-time mode-matching control for a microelectromechanical systems vibratory gyroscope based on improved fuzzy algorithm and neural network algorithm. Meanwhile, robust control for the sense mode is applied to enhance the reliability of the closed-loop system. Experimental results demonstrate that it only needs ~8 s to achieve mode-matching intelligently in the improved fuzzy control system. In addition, a mismatching error <;0.32 Hz is achieved over the temperature range from -40 °C to 80 °C in the neural network real-time control system, which is improved by more than one order of magnitude compared with that of once-time control system. In addition, the temperature coefficient of the zero bias is also improved to be 0.5°/h/°C in the real-time mode-matching control system. Experimental results of phase margin, gain margin, and sensitivity margin indicate that the closed-loop system is stable and robust enough over the full temperature range. Moreover, the bandwidth and bias instability of the mode-matching gyroscope with closed-loop controlled sense mode are >85 Hz and <;5°/h, respectively.

A research of the bandwidth of a mode-matching MEMS vibratory gyroscope

A novel electrostatic force feedback approach is presented for extending the bandwidth of a mode-matching vibratory microgyroscope. A 0.02 Hz mode-mismatch gyroscope is achieved by applying a DC voltage of 26 V to the squeeze-film combs to adjust the stiffness of the sense mode. Sweep-frequency tests demonstrate that the open loop frequency response is close to a one-order system with a bandwidth of 7.9 Hz, which agrees well with the theoretical simulation. Moreover, both experiment and simulation results show that the bandwidth can be extended to about 94Hz from 7.9Hz after adopting an electrostatic force feedback control.

Design of a digital closed control loop for the sense mode of a mode-matching MEMS vibratory gyroscope

This paper presents a digital closed loop control method for the sense mode of a mode-matching MEMS vibratory gyroscope. The sense closed loop system reported in our previous work is relatively complex and unreliable due to the existence of notch filter. In this work, a more simple and robust control system is realized with the help of mode-matching control. With a tuning voltage automatically applied on the tuning combs of the gyroscope, a frequency split of less than 0.3 Hz is achieved. Experimental results show that the mode-matched gyroscope achieves a scale factor of 18.5mV/deg/s with a nonlinearity of 0.088% and a bias instability of 2.7deg/h.

A novel scale factor calibration method for a MEMS gyroscope based on virtual coriolis force

This paper presents a novel scale factor calibration method for a MEMS vibratory gyroscope based on virtual Coriolis force. Frequency and amplitude programmable voltage signals generated by the system can be used to emulate the Coriolis force induced by external angular rate signals. The system contributes to the development procedure of control system for gyroscope and provides a scale factor calibration method for the digital control system of a gyroscope. The experiment results show the digital system can acquire the frequency response of gyroscope and detect the frequency response of reference virtual rate signal effectively.

Investigation of reliability of MEMS gyroscopes under different shock conditions

In this work, the shock survivability of MEMS gyroscopes under different shock conditions are investigated. Both shock experiments and numerical simulations are carried out to study the influences of the shock load level, duration and damping conditions. The simulation results are consistent with the experimental results. The results indicate that the selections of natural frequencies and air-damping conditions are all critical to reach a desired shock resistances of the gyroscopes.

Research on the resonant frequency of MEMS gyroscopes under varying tuning voltage

In this paper, the influence of MEMS gyroscopes tuning voltage on its resonant frequency is investigated analytically and experimentally. The theoretical deduction shows that, with the increase of the tuning voltage, the frequency of drive mode is constant due to area-changing electrostatic driving scheme, while the square of the frequency of the sense mode is linearly dependent on the square of the tuning voltage due to the gap-changing electrostatic sensing scheme. Experimental results demonstrate good agreement with the theoretical analysis. Furthermore, the frequency of sense mode is affected by the structure and fabrication process of MEMS gyroscopes.

Digital closed-loop driver design of micromechanical gyroscopes based on coordinated rotation digital computer algorithm

A novel digital closed-loop driver is presented for a micromechanical vibratory gyroscope in this paper. Coordinated rotation digital computer algorithm is applied to generate the sine and cosine signals for driving and demodulation processing. Meanwhile, automatic gain control and phase-locked loop are adopted to maintain a constant velocity of the drive mode and guarantee the gyroscope working in the resonant mode. All the control methods are implemented in FPGA device. Experimental results demonstrate that the stability of the amplitude of the drive velocity is about 18ppm, which verifies the effectiveness and accuracy of the digital closed loop for the drive mode. The scale factor, nonlinearity and bias instability of the gyroscope with closed loop controlled sense mode are measured to be 18.5mV/deg/s, 0.088% and 19.4deg/h, respectively.

Research on the ring-diode based readout circuit for MEMS vibratory gyroscopes

This work presents the analysis with experimental verification of ring-diode based readout circuit for MEMS vibratory gyroscopes. Detailed deductions on the C-V conversion and signal demodulation process were given with performance prediction using MATLAB simulation. Experimental verification of the analysis results was also carried out using a MEMS vibratory gyroscope. This work provided theoretical insights on the ring-diode based readout scheme, which could benefit further optimization of the readout circuits. Experiment results shows that the output of the optimized readout circuits (9.0V) is 15 times as much as what we used before optimization (0.6V).

Research on the Zero-Rate Output compensation for MEMS vibratory gyroscopes

This paper presents the analysis of the source of Zero-Rate Out(ZRO) of MEMS vibratory gyroscopes. The temperature effects on the performance of MEMS gyroscopes is studied. Related experiments demonstrate that ZRO of MEMS vibratory changes significantly with temperature. On the basis of the ZRO analysis, a novel temperature compensation method is proposed, in which a compensation model is established by polynomial fitting using data of the drive signal output(DSO) and the ZRO. Experimental results show that the compensation method is effective and technically feasible for application.