The drift of inertial navigation system (INS) will lead to large navigation error when a low-cost INS is used in microaerial vehicles (MAV). To overcome the above problem, an INS/optical flow/magnetometer integrated navigation scheme is proposed for GPS-denied environment in this paper. The scheme, which is based on extended Kalman filter, combines INS and optical flow information to estimate the velocity and position of MAV. The gyro, accelerator, and magnetometer information are fused together to estimate the MAV attitude when the MAV is at static state or uniformly moving state; and the gyro only is used to estimate the MAV attitude when the MAV is accelerating or decelerating. The MAV flight data is used to verify the proposed integrated navigation scheme, and the verification results show that the proposed scheme can effectively reduce the errors of navigation parameters and improve navigation precision.

Small initial frequency split is preferred to reduce the complexity of control circuits and enhance the device sensitivity for mode-matching MEMS gyroscopes. A microring gyroscope with cascaded rectangular beams as supporting springs fabricated by (100) single crystal silicon (SCS) is presented. Frequency split due to the anisotropic of Young's modulus of (100) SCS is geometrically compensated by adjusting the width of cascaded springs and adding an extra mass. The rectangular beams are designed to be wide enough to improve the immunity to fabrication imperfections, obtaining good manufacturing repeatability. The proposed method can largely attenuate the frequency difference of the gyroscope by using (100) SCS, which can reduce the processing cost and be easily integrated with CMOS circuit compared with (111) SCS. The test results show that the average initial frequency split of 15 different devices is 5.1 Hz for the ∼10,430 Hz resonant frequency. The minimum and maximum splits are 2.3 Hz (0.022%) and 7.3 Hz (0.069%), respectively, with the standard deviation of 1.3 Hz.

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