Calibration of the Inertial Measurement Unit in Critical Conditions

Abstract

Calibration of the inertial measuring unit (IMU) is an independent task and is the most important stage in preparing for operation both platform and strapdown inertial navigation systems (INS). The traditional calibration of IMU, containing at least three gyroscopes and three accelerometers, carried out in specialized testing laboratories, has been studied in sufficient detail. However, the widespread use of IMUs using MEMS sensors with characteristic instability of parameters leads to the need for additional calibration of IMUs IMUediately before INS operation in critical or field conditions. Under such conditions, firstly, there is no testing equipment necessary for the full implementation of traditional calibration, and secondly, the recalibration process itself is limited in time.In the article, studies were carried out on the possibility of using the method of successive rotations for the recalibration of IMU in the field. With this approach, in contrast to the test rotation method, there is no need to rotate the IMU by 180 degrees, but it is enough to rotate the IMU by small angles. Calculation ratios are obtained for determining the scale factors and zero signals of the accelerometer unit for two positions of the IMU. The experiment carried out confirmed the validity of the calculated ratios obtained. In addition, a recalibration method is described, which makes it possible to estimate, in addition to scale factors and zero signals of the accelerometer unit, also the tilt angles of the base on which the IMU is installed. To do this, you must have at least five different IMU positions.In addition, the calibration of the gyroscope unit when tactical and navigational accuracy class gyroscopes are used is considered. For gyroscopes of the tactical accuracy class and which are manufactured using MEMS technology, biases are determined in the critical conditions, which are not stable from start to start. Algorithms for determining biases and scale factors were obtained for the calibration of the gyroscope unit of the navigation accuracy class, for which the same two positions in which the accelerometer unit was calibrated were used. That is, during the calibration of the IMU in critical conditions, it is possible to simultaneously calibrate the gyroscope unit and the accelerometer unit, which saves the overall calibration time.