Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
1999-06-09
2001-01-16
Issing, Gregory C. (Department: 3662)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
Reexamination Certificate
active
06175807
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
(Not applicable)
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 continuous temperature compensation methods.
In previous generations of inertial navigation systems, gimbaled platforms were used to spatially stabilize the accelerometers and thereby provide a coordinate system in which velocity and position could be propagated. The advantage of the gimbaled systems was the isolation of the instruments from large angular motions, the cancellation of errors in many scenarios, and the ability to re-calibrate the instruments by using simple gimbal rotations. The advent of strapdown instruments such as laser gyroscopes and high-speed computers has rendered the platform systems obsolete. Strapdown systems offer a high degree of ruggedness, unsurpassed reliability, wide-bandwidth capabilities, and multi-function capabilities. A typical strapdown ZLG system has an MTBF an order of magnitude higher than a platform system of old while providing equal or better performance and enhanced capabilities. Unfortunately, the strapdown systems are at a disadvantage from the point of view of continuous calibration. While gimbaled systems could self-calibrate with commanded gimbal rotations, such possibilities were non-existent in the strapdown, gimbal-free systems. Furthermore, while platform systems were generally temperature controlled, modem strapdown systems operate at the ambient temperature and employ thermal models to compensate for instrument temperature sensitivity. For systems with extremely long field longevity such as the ZLG-based units, a continuous calibration method is highly desirable in order to track any potential aging effects and to guarantee superior navigation accuracy over the life of the unit.
BRIEF SUMMARY OF THE INVENTION
The invention is a method for continuously compensating for the output error in each of one or more navigation instruments in a system comprising a plurality of navigation instruments after the system is introduced into its operating environment. The method is predicated on the system operating for a plurality of time periods and occasionally being subjected to specified types of motion and occasionally being supplied with data by other navigation data sources. The method is a way of compensating during a time period for the output error in each of the one or more navigation instruments as a function of temperature based on measurements obtained in one or more prior time periods.
The practice of the method begins with determining the values of one or more of a set of coordinates that specify the position, velocity, and orientation of the system in space together with the error in a compensated output for each of the one or more navigation instruments. The method continues with determining a compensation model for each of the one or more navigation instruments. A compensation model specifies for a current time period an adjustment in amplitude of the output of a navigation instrument as a function of time and temperature. A compensation model is expressed as the sum of a first compensation model and a present second compensation model where the present second compensation model is a future second compensation model determined during the prior time period. The final steps of the method consist of measuring the time and the temperature of the navigation instruments and then obtaining a compensated output for each of the one or more navigation instruments by adjusting the output of a navigation instrument in accordance with its compensation model.
REFERENCES:
patent: 4303978 (1981-12-01), Shaw et al.
patent: 4675820 (1987-06-01), Smith et al.
patent: 5527003 (1996-06-01), Diesel et al.
patent: 5570304 (1996-10-01), Mark et al.
Neil Dahlen et al, “Tightly-Coupled IFOG-Based GGP Implementation and Field Test Results”, IEEE, Apr. 1996, pp. 213-221.
Buchler Robert J.
Fann Shaw-Wen
Mark John G.
Moeller Larry R.
Tazartes Daniel A.
Issing Gregory C.
Litton Systems Inc.
Malm Robert E.
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