Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
1999-06-18
2001-03-27
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C701S200000, C244S171000
Reexamination Certificate
active
06208936
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to the field of navigation systems, and particularly to navigation systems for projectiles.
BACKGROUND OF THE INVENTION
The recent emergence of micro-electro-mechanical systems (MEMS) inertial sensors has made it possible to integrate a MEMS inertial measurement unit (IMU) and a global positioning system (GPS) receiver on board small missiles, rockets or the like type of projectiles or vehicles to perform strapdown navigation. Some types of missiles are imparted with a roll about a longitudinal axis in order to provide stability during flight. However, as the vehicles spins, a rapidly growing roll attitude error accumulates due to the scale factor error of the MEMS roll gyro, and the accumulated roll error eventually causes the navigation solution to become unstable. Thus, there lies a need for a method and apparatus that compensates for the accumulated roll attitude error in rolling vehicles.
Furthermore, strapdown navigation equations are linearized by small angle approximations. Therefore, the angular change in body attitude must not exceed a small amount between computation intervals, otherwise the equations become invalid. For rolling missiles, the roll angle continuously changes at a very high rate that imposes an extremely high computational rate requirement on the navigation processor. Thus, there also lies a need for a navigation system and method that allows for a reasonable computational rate requirement on the navigation processor of a rolling missile.
SUMMARY OF THE INVENTION
The invention utilizes measurements from a magnetoresistance ratio (MR) sensor to compensate the navigation solution of a MEMS-IMU/GPS navigation system to effectively keep the roll attitude error in check whereby a stable navigation solution is maintained. The MR sensor measures the angle of the sensor's sensitive axis relative to a local magnetic field (i.e. the earth's natural magnetic field). The MR sensor is mounted on a body axis of the vehicle perpendicular the spin axis of the vehicle. As the vehicle spins, the MR sensor provides an analog output voltage that varies sinusoidally with vehicle roll with the zero crossings occurring when the sensor's sensitive axis is perpendicular to the local magnetic field. The MR sensor measurements combined with a priori knowledge of the local magnetic field relative to the local level reference is used to correct the navigation solution's roll error.
The present invention further utilizes computational de-spin in the navigation solution by taking advantage of the fact that, even though a missile may have a high roll rate, the accelerations and pitch and yaw rates are not excessively high by conventional navigation processing standards. Following high rate sampling of accelerometers and gyros, a de-spin algorithm is implemented whereby processing may be implemented with a non-rolled vehicle body frame algorithm.
In one embodiment, the present invention is directed to a method for compensating the roll attitude error in the navigation solution for a rolling vehicle wherein the method includes steps for sampling navigation data for a rolling vehicle, generating an inertial attitude error estimate from the sampled navigation data, monitoring an output of a magnetic field sensor, the magnetic field sensor having a sensitive axis being disposed perpendicular to an axis of rotation of the rolling vehicle, the output of the magnetic field sensor being generated as the rolling vehicle passes through a local magnetic field, detecting a zero crossing point in the output of the magnetic field sensor, calculating a measurement residual based on the navigation data at a time corresponding to the zero crossing point, and updating the inertial attitude error estimate with the calculated measurement residual whereby the navigation solution remains stable.
In another embodiment, the present invention is directed to a method for computationally de-spinning strapdown inertial sensor measurements for navigation on a rolling vehicle. The method includes steps for sampling navigation data of a rolling vehicle wherein the sampled data includes accelerometer data, roll data, pitch data and yaw data for the rolling vehicle, integrating roll data of the sampled data over a predetermined interval, computing a roll angle change transform, updating the roll angle change transform with incremental roll change data, transforming and integrating accelerometer data with the roll angle change transform whereby the accelerometer data is de-spun, transforming and integrating pitch and yaw data with the roll angle change transform whereby the pitch and yaw data are de- spun, and computing a navigation solution strapdown at a predetermined navigation processing rate.
In a further embodiment, the invention is directed to a method for computing a navigation solution in a rolling vehicle. The method includes steps for sampling navigation data of a rolling vehicle wherein the sampled data includes accelerometer data, roll data, pitch data and yaw data for the rolling vehicle, calculating a measurement residual based upon the output of a magnetic sensor that detects the orientation of the rolling vehicle with respect to a local magnetic field, updating an inertial attitude error estimate with the calculated measurement residual whereby the navigation solution remains stable, computationally de-spinning accelerometer and pitch and yaw data, and computing a navigation solution strapdown at a predetermined navigation processing rate with the de-spun accelerometer, pitch and yaw data.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and together with the general description, serve to explain the principles of the invention.
REFERENCES:
patent: 4254465 (1981-03-01), Land
patent: 4460964 (1984-07-01), Skutecki et al.
patent: 5455591 (1995-10-01), Hui
Minor Roy R.
Rowe David W.
Arthur Gertrude
Cuchlinski Jr. William A.
Eppele Kyle
Jensen Nathan O.
O'Shaughnessy J. P.
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