INERTIAL MEASUREMENT SYSTEM FOR PROJECTILES WITH CORRECTIONS OF ROLL ANGLE AND SCALE FACTOR

摘要

An inertial measurement system for a spinning projectile comprising: a first, roll gyro to be oriented substantially parallel to the spin axis of the projectile; a second gyro and a third gyro with axes arranged with respect to the roll gyro such that they define a three dimensional coordinate system; a controller, arranged to: compute a current projectile attitude from the outputs of the first, second and third gyros, the computed attitude comprising a roll angle, a pitch angle and a yaw angle; calculate a roll angle error based on the difference between the computed pitch and yaw angles and expected pitch and yaw angles; provide the roll angle error as an input to a Kalman filter that outputs a roll angle correction and a roll rate scale factor correction; and apply the calculated roll angle correction and roll rate scale factor correction to the output of the roll gyro; wherein the Kalman filter models roll angle error as a function of roll rate and one or more wind variables. The system provides improved calibration of the roll axis rate gyro scale factor, e.g. of an IMU fitted to a rolling projectile. A separate process (an Euler angle filter) is used to calculate an estimate of the roll angle error without the use of the Kalman filter and is then provided as an input to the Kalman filter which can then operate in a stable manner. The filter can be configured to estimate and correct for crosswind effects which would otherwise significantly degrade performance.