Research On Rotational Modulation North Seeking Orientation Based On Three-axis MEMS-IMU

Since ancient times,the north seeking technology has been continuously improved.From the original compass to the current north finder,people have invested a lot of human and material resources in the field of north seeking navigation.With the great development of micro electro mechanical system(MEMS)technology,MEMS inertial devices not only inherit the advantages of small size,but also have the advantages of low price,low quality and mass production.This makes MEMS gyroscope can replace fiber-optic gyroscope and other high-precision gyroscopes for north seeking.In this paper,the rotation modulation north seeking orientation based on MEMS-IMU(Micro Electro Mechanical System Inertial Measurement Unit)is studied.Through the error analysis and output filtering noise reduction of MEMS gyroscope,considering the possible inclination of the north seeker base in practical engineering applications,the static north seeking compensation algorithm with inclination error is designed.Combined with the dynamic north seeking method with better north seeking effect in the horizontal plane,the fusion north seeking scheme is designed,Finally,even if the base is inclined,the north finding accuracy can reach within 1°.To sum up,the main research contents of this paper are as follows:1.This paper expounds the research background and significance of north seeking based on MEMS-IMU,and introduces the development and research status of north seeking technology at home and abroad.Then,according to the basic knowledge of north seeking,several common north seeking schemes(including static north seeking and rotating dynamic north seeking)are introduced,the four position north seeking method in the static north seeking scheme is improved,the advantages and disadvantages of each north seeking scheme are compared,and the feasibility of using MEMS gyroscope for north seeking is analyzed.2.The principles of MEMS gyroscope and Allan variance are introduced.The noise of MEMS gyroscope is analyzed.The gyro data obtained are processed by Kalman filter.Finally,the quantization noise of three axes is reduced by 0.2401 °/h,0.1122 °/h and0.1471 °/h respectively,and the other four kinds of noise are also reduced by 1 ～ 2 orders of magnitude.A calibration scheme is proposed to solve the installation error in MEMS-IMU,which reduces the output angle error of MEMS Gyro three axes by two orders of magnitude.3.A rotation modulation north seeking scheme based on MEMS-IMU is designed.When IMU tilts,an error compensation model based on static north seeking method is proposed.Then,the principle of dynamic north seeking is explained in detail,and the specific implementation scheme of dynamic north seeking is designed.The rotation speed and sampling frequency are determined according to the fast Fourier change method,and then the Butterworth filter is designed to filter the output data of MEMS Gyro when it rotates at a uniform speed,The north seeking accuracy of dynamic north seeking is calculated by the phase difference method.The north seeking results obtained from the Y-axis and Z-axis of the horizontal plane at this time are obtained by the weighted average fusion algorithm to obtain the dynamic north seeking value with higher accuracy.Finally,the final north seeking value is obtained after weighted average with the static north seeking value obtained by tilt error compensation.Through the analysis of experimental results,the maximum root mean square error is 0.920°,and the north seeking accuracy error is no more than 1°.Through the north seeking scheme designed in this paper,it is verified that even in the case of inclination error in IMU,it still has the advantages of high north seeking accuracy and good repeatability.