Multiposition Alignment for Rotational INS Based on Real-Time Estimation of Inner Lever Arms

The inner lever arm effect of the accelerometer triad, also known as the size effect, means that the sensitive centers of the three accelerometers in an inertial measurement unit (IMU) cannot be mechanically installed at one point. Without compensation, it will seriously deteriorate the accuracy of calculated velocity during rotation. For the rotational inertial navigation system (RINS), this paper analyzes the influence of the inner lever arm on the rotational alignment, and proposes a multi-position alignment method based on 2-dimensional inner lever arm online estimation. In this method, the measurement center of IMU is defined at the sensitive center of a horizontal accelerometer, so that the influential inner lever arm can be simplified to two dimensions, and a fine alignment filter is designed for on-line estimation. Simulations and experiments show that the method can effectively ensure the accuracy of multi-position alignment while reducing the state dimension and calculation amount. The repeatability of the online estimation result of the inner lever arm is better than 0.1 mm.