Research On Calibration And Accuracy Evaluation Method Of The Vertical Reference Unit Based On MEMS-IMU

The Vertical Reference Unit(VRU)is an attitude reference system used to provide horizontal attitude information for the carrier.The existing VRU products mostly use Dynamically Tuned Gyro(DTG),Fiber Optic Gyro(FOG)as angular velocity measuring device.However,The VRU based on the above angular velocity measuring device has high cost,which limits its application range.MEMS Inertial Measurement Unit(MEMS-IMU)has significant cost advantages.In recent years,with the continuous improvement of the accuracy of MEMS-IMU,the VRU based on MEMS-IMU has been widely concerned.However,the disadvantages of low accuracy and large random noise of MEMS-IMU have become a key factor restricting the VRU based on MEMS-IMU to realize high-precision attitude measurement.This paper takes the VRU based on MEMS-IMU as the research object,the main research contents and innovations are as follows:1.The horizontal attitude accuracy evaluation scheme of VRU based on MEMS-IMU is studied.The horizontal attitude accuracy evaluation scheme based on three-axis angular motion simulation turntable and the horizontal attitude accuracy evaluation scheme based on Fiber Optic Gyro Inertial Navigation System are designed,which provides an overall scheme for the follow-up accuracy evaluation experiment.2.The calibration algorithm of VRU based on MEMS-IMU is studied.A systematic calibration algorithm and an accelerometer calibration algorithm based on modulus observation are proposed.By analyzing the excitation intensity of the position and rotation path to the inertial measurement unit,the position arrangement scheme of the systematic calibration algorithm and the position arrangement scheme of accelerometer calibration algorithm based on modulus observation are designed.The final experiment shows that the accelerometer component after systematic calibration,The standard deviation of gravity residual modulus is better than 0.65mg;After systematic calibration,the mean value of static output angular velocity residual modulus is reduced from 6 ° / h to 0.8 ° / h;After the accelerometer calibration algorithm based on modulus observation,the standard deviation of gravity residual modulus is better than 0.29mg。3.The systematic calibration algorithm of high-precision FOG Inertial Navigation System as the reference standard for horizontal attitude evaluation is studied.A systematic calibration algorithm based on ST-EKF and Filter Gain Constraint is proposed.Compared with the calibration accuracy of the systematic calibration algorithm based on traditional Extended Kalman Filter(EKF),the standard deviation of the gravity residual modulus is 8.39 μg decreased to 6.71 μg;Compared with the calibration accuracy of the systematic calibration algorithm without Filter Gain Constraint,the standard deviation of the gravity residual modulus in the inclined position is from 7.96 μg decreased to 6.71 μg;Compared with the calibration accuracy of systematic calibration algorithm based on accelerometer linear error model,the standard deviation of gravity residual modulus is from 24.12 μg decreased to 6.71 μg。Finally,it is verified by the pure inertial navigation experiment under the large horizontal attitude change of 4500 s.After the calibration of the new algorithm,the East and North maximum position errors of the inertial navigation system can be reduced from 192.40 m and 96.72 m to 74.64 m and 65.44 m respectively.4.The key technology of horizontal attitude accuracy evaluation experiment of VRU based on MEMS-IMU under dynamic conditions is studied.The horizontal attitude accuracy evaluation experiment based on two-axis angular motion simulation turntable is carried out.Three groups of experiments are carried out under the horizontal inclination of 2 ° / 5 ° / 10 ° and the rotating speed of 5 ° / s.The standard deviation of roll angle and pitch angle difference between VRU based on MEMS-IMU and FOG Inertial Navigation System is about 0.003 ° / 0.015 ° / 0.04 ° respectively.Under the experimental conditions of horizontal inclination of 2 ° and rotating speed of 5 ° / s,the equivalence of z-axis gyro bias estimation by filtering and z-axis gyro scale factor error estimation is verified;The horizontal attitude accuracy evaluation experiment based on three-axis angular motion simulation turntable is carried out.Under different amplitude and frequency,the standard deviation of roll angle and pitch angle difference between VRU based on MEMS-IMU and three-axis angular motion simulation turntable system is better than 0.03 °;Finally,the horizontal attitude accuracy evaluation experiment based on vehicle is given.The standard deviation of roll angle and pitch angle difference between the VRU based on MEMS-IMU and the FOG Inertial Navigation System is better than 0.03 °.