Study on the method of compensation for the heading effect of the rate offset frequency laser inertial measurement unit

For the rate offset frequency laser inertial measurement unit (IMU), the errors of its three attitude angles, laser gyroscope, and accelerometer are coupled, which will affect the initial alignment result of the IMU and will make the measurement results of the IMU at different positions and angles deviate from the truth value. Meanwhile, with the increase of tilt angle, the heading effect becomes more obvious, and the error value is distributed positively cosine with the heading angle. In order to ensure the adaptability of the IMU to various operating conditions, it is necessary to compensate for the heading effect. The contribution of each error source of IMU to the heading effect is theoretically studied in this paper. We present a new method for compensating for the heading effect of the rate offset frequency laser IMU, in which the normal drift error of the vertical direction laser gyroscope and the zero bias error of the accelerometer under the turntable coordinate system are compensated. Based on the above method, simulation analysis and test verification are carried out. The experimental results show that the compensation method has a remarkable effect. In the case of two horizontal attitude angles tilted 0.0873 rad and 5 min initial alignment, the error of the rate offset frequency laser IMU reduced from 5.02E-04 rad $({3}\sigma)$(3σ) to 1.45E-04 rad $({3}\sigma)$(3σ), and the accuracy increased by 71%. High-precision initial alignment is achieved, which can meet the requirements of high-precision engineering applications.