Inertial navigation system
AssigneeAtlantic Inertial Systems Limited
InventorsJohn Keith Sheard, Nicholas Mark Faulkner
Life of this patent
Estimating the term…
Abstract
An inertial measurement system for a spinning projectile includes: 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; 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; 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.
Claims14
An inertial measurement system for a spinning projectile comprising:
- a first gyro to be oriented substantially parallel to a spin axis of the projectile;
- a second gyro and a third gyro with axes arranged with respect to the first gyro such that they define a three dimensional coordinate system;
- the first gyro, the second gyro and the third gyro each being arranged to produce an output;
- a Kalman filter;
- and
- 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 a difference between the computed pitch and yaw angles and expected pitch and yaw angles;
- provide the roll angle error as an input to the Kalman filter that outputs a roll angle correction and a roll rate scale factor correction;
- and
- apply the calculated roll angle correction and the roll rate scale factor correction to the output of the first gyro;
- wherein the Kalman filter models roll angle error as a function of roll rate having a component correlated with roll rate and a separate component correlated with crosswind effects;
- and
- wherein using observations made over time, the Kalman filter isolates the component correlated with roll rate and the component correlated with crosswind effects, thereby maintaining an estimate of the prevailing crosswind and using the remaining component correlated with roll rate to calculate the roll rate scale factor correction.
A method of correcting roll angle in an inertial measurement system for a spinning projectile, comprising carrying out the following steps on a controller:
- computing a current projectile attitude comprising a roll angle, a pitch angle and a yaw angle;
- calculating a roll angle error based on the difference between the computed pitch and yaw angles and expected pitch and yaw angles;
- providing 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
- applying the calculated roll angle correction and roll rate scale factor correction to the output of a roll gyro;
- wherein the Kalman filter models roll angle error as a function of roll rate having a component correlated with roll rate and a separate component correlated with crosswind effects;
- and
- wherein using observations made over time, the Kalman filter isolates the component correlated with roll rate and the component correlated with crosswind effects, thereby maintaining an estimate of the prevailing crosswind and using the remaining component correlated with roll rate to calculate the roll rate scale factor correction.
A method of correcting roll angle in an inertial navigation system for a longitudinal projectile, comprising carrying out the following steps on a controller:
- computing a current projectile attitude comprising a roll angle, a pitch angle and a yaw angle;
- calculating the rates of change of the pitch angle and yaw angle, using these rates to calculate a roll angle error and providing this as an input to a Kalman filter that outputs a roll angle correction and a roll rate scale factor correction;
- and
- applying the calculated roll angle correction to the computed attitude and the roll rate scale factor correction to the roll gyro output;
- wherein the Kalman filter models roll angle error as a function of roll rate having a component correlated with roll rate and a separate component correlated with crosswind effects;
- and
- wherein using observations made over time, the Kalman filter isolates the component correlated with roll rate and the component correlated with crosswind effects, thereby maintaining an estimate of the prevailing crosswind and using the remaining component correlated with roll rate to calculate the roll rate scale factor correction.
Dependencies are inferred from the claim text.