Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
2001-09-28
2003-09-16
Cuchlinski, Jr., William A (Department: 3661)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C701S220000
Reexamination Certificate
active
06622091
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to navigation systems, and more particularly, to methods of improving the performance of navigational systems by utilizing one or more external sources of information, for example a global positioning (GP) system (also referred to herein as GPS).
Typical prior art inertial guidance (IG) systems can calculate position with a high degree of accuracy. To attain such accuracy, these IG systems require precise gyroscopes that are extremely costly, but are characterized by a low measurement error, typically on the order of 100 degrees per hour. By contrast, many commercial applications use a lower grade of gyroscope, typically a micro-machine gyroscope, which is relatively inexpensive. These micro-machine gyroscopes include a relatively large measurement error, typically ranging from approximately one degree to ten degrees per second. Such low-grade gyroscopes are most suitable for gross movement detection (e.g., detection of automobile roll-over, and air bag deployment systems) rather than fine movement detection required by an IG system.
Gyroscope measurement error can generally be divided into the categories of bias error and scaling error. All gyroscopes have a certain degree of measurement error that is present upon initialization, referred to as bias error. The instrument using the gyroscope can apply some measure of compensation for this error, but the effectiveness of such compensation is limited because the actual degree of initialization error may be different for each individual gyroscope. In addition, each time an individual gyroscope is turned on, the amount of bias error may be different. For instance, one initialization might result in an error of one degree per second and the next initialization might result in an error of two degrees per second.
The second category of error, referred to herein as scaling error, that accumulates over the angle through which a gyroscope is being rotated. Scale factor error is essentially an “input to output” error, i.e., the difference between the actual angle of rotation the gyroscope experiences and the angle of rotation indicated at the gyroscope output. A gyroscope indicating that it had turned ninety degrees when it had, in fact, turned ninety-two degrees, is an example of scaling error. The amount of scaling error may be affected by various environmental factors, so that a fixed compensation value will not be sufficient to produce completely accurate data.
GPS navigation systems are widely used and are rapidly being incorporated into many newly manufactured commercial vehicles. Such vehicles often operate in city environments, however, resulting in substantial blackout periods while in so-called “urban icanyons,” i.e., while between tall buildings that obscure the line-of-sight to the GPS satellites. A collocated IG system can provide continuous navigational information during these blackout periods, but the high cost of the precise gyroscopes required by typical prior art IG systems virtually precludes their use in a commercial vehicle. Hence, a general need exists for a method of improving the accuracy of low grade gyroscopes. It is an object of the present invention to substantially overcome the above-identified disadvantages and drawbacks of the prior art.
U.S. Pat. No. 4,590,569, entitled “Navigation System Including An Integrated Electronic Chart Display”, assigned to Navigation Sciences Inc. (Bethesda, Md.), describes a navigation system particularly adapted for ships making a passing within a harbor or the like. The system utilizes signal inputs from on-board vessel position determining equipment such as Loran or Decca apparatus and an on-board object detecting equipment such as a radar or sonar apparatus. The system further includes an on-board vessel position computer which operates in a differential Loran mode in response to observed Loran time differences, stored data from an initial calibration, and Loran grid offset data from an on-shore monitor system to compute a highly accurate current or present position fix in longitude and latitude whereupon the computer causes a predetermined electronic chart to be displayed in color on the screen of a cathode ray tube, being generated from a plurality of electronic charts stored in the form of digital files in memory. The selected chart, together with the present position of the ship, is displayed along with preselected alpha-numeric indicia of data relating to bearings, way points, ranges, “time to go”, etc., also generated in accordance with the computed vessel position. Radar target returns of the local land mass and other stationary moving targets are additionally received by the ship's radar. The radar image of the target echoes is next referenced to and superimposed on the electronic chart generated; however, the radar's land mass echoes are suppressed in favor of the electronic chart land mass while displaying all other targets.
U.S. Pat. No. 5,194,872, entitled “Inertial Navigation System With Automatic Redundancy And Dynamic Compensation Of Gyroscope Drift Error,” assigned to Charles Stark Draper Laboratory, Inc. (Cambridge, Mass.), describes an inertial navigation system with automatic redundancy and dynamically calculated gyroscopic drift compensation. The system utilizes three, two-degree of freedom gyroscopes arranged whereby any two of the gyroscopes form an orthogonal triad of measurement sensitive axes. The input axes of the three gyroscopes form three pairs of parallel input axes, each pair of parallel input axes corresponding to one axis of the orthogonal triad of axes. The three gyroscopes are operated in a plurality of pre-selected combinations of both clockwise and counter clockwise directions, thus changing the direction of the angular momentum vector by 180.degree. Parity equations are formed from each pair of gyroscope outputs whose measurement sensitive axes are parallel. The parity equations include combinations of gyroscope pairs that have been operated in both the clockwise and counterclockwise directions. Gyroscope drift estimates are then computed using the parity equations to provide individual gyroscope lumped drift corrections (self-calibration) to the inertial guidance and navigation system.
U.S. Pat. No. 5,527,003, entitled “Method For In-Field Updating Of The Gyro Thermal Calibration Of An Inertial Navigation System”, assigned to Litton Systems, Inc. (Woodland Hills, Calif.), describes an in-field method for correcting the thermal bias error calibration of the gyros of a strapdown inertial navigation system. The method is begun after initial alignment while the aircraft remains parked with the inertial navigation system switched to navigation mode. Measurements are made of navigation system outputs and of gyro temperatures during this data collection period. A Kalman filter processes the navigation system outputs during this time to generate estimates of gyro bias error that are associated with the corresponding gyro temperature measurements. Heading error correcting is performed after the extended alignment data collection period as the aircraft taxis prior to takeoff. The gyro bias error-versus-temperature data acquired, along with the heading error corrections, are employed to recalibrate the existing thermal model of gyro bias error by means of an interpolation process that employs variance estimates as weighting factors.
U.S. Pat. No. 5,786,790, entitled “On-The-Fly Accuracy Enhancement For Civil GPS Receivers,” assigned to Northrop Grumman Corporation (Los Angeles, Calif.), describes a method and means for enhancing the position accuracy of a civil or degraded accuracy GPS receiver by compensating for errors in its position solution with data derived from a military, or precise accuracy, GPS receiver. The civil GPS receiver may be disposed in a mobile expendable vehicle and the military receiver in a mobile launch vehicle. The compensating data is obtained by a comparison of the pseudorange measurements of the military GPS set and another civil GPS set disposed wit
Humphrey Ian
Perlmutter Michael S.
Cuchlinski, Jr. William A
Fibersense Technology Corporation
McDermott, WIll & Emery
Pipala Edward
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