On-line self-calibration for inertial platform system with a single totally free axis

An on-line self-calibration method for estimating the error coefficients of an inertial platform system is proposed to avoid the troublesome process of dismounting the system from the carriers, such as vessels and missiles. This method belongs to the type of continuous self-calibration method according to which we implement the calibration scheme by making the platform revolve through a specified rotation trajectory at a given angular rate. Our method distinguishes from the existed continuous self-calibration methods in three aspects. First, the gyros applied in this paper are assumed to be dynamically tuned gyros which have two sensitive axes rather than a single one. Second, the process of revolving is realized by assigning instructional angular speed to the gyros not revolved by rotating the gimbals directly, which implies that the platform system operates under an autonomous navigation state throughout the calibration process, relaxing the requirement of switching the operating mode of the system. Third, the gyros are assumed to have a rotational limit of ±60° on outer gimbal and inner gimbal axes. A modified dynamic model is established to adapt to the changes mentioned previously. The observation model is based on the output model of accelerometers. Then the EKF is applied to estimate the coefficients since the model is nonlinear. The simulation results substantiate the effectiveness of the method.