Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
1999-04-22
2001-04-17
Lobo, Ian J. (Department: 3662)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
Reexamination Certificate
active
06219616
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
(Not applicable)
BACKGROUND OF THE INVENTION
This invention relates generally to strapdown inertial navigation systems and more specifically to attitude updating and coning algorithms which reduce system drift errors in the presence of coning motion.
One of the key parameters of a strapdown inertial navigation system is its response to coning motion. Substantial efforts have gone into the development of sophisticated coning algorithms which reduce system drift errors in the presence of coning motion. Present-day algorithms typically use incremental angle outputs from the gyros to form high order correction terms which reduce net coning errors (J. Mark, D. Tazartes, et. al., “Extension of Strapdown Attitude Algorithm for High-Frequency Base Motion”,
Journal of Guidance, Control, and Dynamics
, Vol. 13, No. 4, July-August 1990). These algorithms assume a flat transfer function for the processing of the incremental angle outputs and are structured to yield very high order responses.
Techniques such as gyro resolution enhancement as described in U.S. Pat. No. 5,485,273, which is hereby incorporated by reference, (also described in J. Mark & D. Tazartes, “A Resolution Enhancement Technique for Laser Gyros”,
Proceedings of Fourth St. Petersburg International Conference on Integrated Navigation Systems
, St. Petersburg, Russia, May 1997) can provide high resolution angle data. However, the gyro data processed for resolution enhancement has a “shaped” frequency response which must be accounted for in the design of coning algorithms.
While resolution enhanced data has been used for angular rate outputs, it has not been used in attitude generation although it would be very beneficial for applications requiring low noise, high resolution attitude information.
BRIEF SUMMARY OF THE INVENTION
The invention is a method and apparatus for updating the attitude of a body by utilizing a plurality of gyros to measure as a function of time the angular rate vector or the integrated angular rate vector for the body. The method comprises the steps of (1) obtaining measured values of the angular rate vector at a plurality of readout intervals, (2) obtaining a smoothed value of each of one or more smoothed representations of the angular rate vector at the end of each of a plurality of smoothing intervals, and (3) obtaining the updated attitude of the body at the end of an update interval by utilizing the attitude at the beginning of the update interval and the smoothed values of the smoothed representations of the angular rate vector obtained during the update interval. A smoothed representation is a weighted sum of the measured values obtained during a smoothing interval. The attitude is updated at the end of an update interval by applying a rotation vector to the attitude at the end of the prior update interval, the rotation vector being a weighted sum of (1) a plurality of the smoothed values and (2) the values of a plurality of cross-products of the smoothed values, the smoothed values having been obtained during the update interval.
REFERENCES:
patent: 5485273 (1996-01-01), Mark et al.
patent: 5828980 (1998-10-01), Tazartes et al.
Jiang et al., “Improved Strapdown Coning Algorithms,” IEEE Transactions on Aerospace and Electronic Suystems, vol. 28, No. 2, pp. 484-490, Apr. 1992.*
Ignagni, M. , “On the Orientation Vector Differential Equation in Strapdown Inertial Systems,” IEEE Transactions on Aerospace and Electronic Systems, vol. 30, No. 4, pp. 10761081, Oct. 1994.
Litmanovich Yury A.
Mark John G.
Tazartes Daniel A.
Litton Systems Inc.
Lobo Ian J.
Malm Robert E.
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