Self calibrating gyroscope system

• US 20100063763A1
• Filed: 09/11/2008
• Published: 03/11/2010
• Est. Priority Date: 09/11/2008
• Status: Active Grant

• Current Assignee: Northrop Grumman Guidance And Electronics Company, Inc.
• Original Assignee: Northrop Grumman Guidance And Electronics Company, Inc.
• Inventors: Rozelle, David M.
• Granted Patent: US 7,912,664 B2
• Time in Patent Office: Days
• US Class Current: 702/92
• CPC Class Codes: G01C 19/5691 of essentially three-dimensional vibrators, e.g. wine glass-type vibrators
• CPC Class Codes: G01C 21/188 for accumulated errors, e.g. by coupling inertial systems with absolute positioning systems
• CPC Class Codes: G01C 25/005 initial alignment, calibration or starting-up of inertial devices

Abstract

A self-calibrating gyroscope system provides improved estimates of, and compensation or calibration for, scale factor errors and bias errors. The gyroscope system employs a plurality of gyroscope units having sense or input axes in a mutually non-parallel arrangement. The number of gyroscope units is preferably at least one more than the number of axes for which rate estimates is required. A Mode Reversal technique is used to obtain an estimate of bias error for a selected gyroscope. A Random Closed-Loop Scale Factor technique is used to obtain an estimate of scale factor error for a selected gyroscope. Because the Mode Reversal technique temporarily disrupts operation of the affected gyroscope, each of the gyroscopes may be taken offline temporarily, in turn, for calibration, and thereafter returned to normal operation. Because at least one redundant gyroscope is provided, when a selected gyroscope is offline, rate information from the remaining operating gyroscopes can be used to derive a reference rate about the axis of the offline gyroscope.

Claims

1. A gyroscope system comprising:

a plurality of gyroscopes, each adapted to sense rate about a respective sense axis, each of said sensed rates exhibiting bias error and scale factor error;

a scale factor error estimator coupled to at least one of said gyroscopes to produce an estimate of scale factor error of such coupled ones of said gyroscopes;

a bias error estimator coupled to such coupled ones of said gyroscopes to produce an estimate of bias error of such coupled ones of said gyroscopes; and

a compensator responsive to sensed rates of such coupled ones of said gyroscopes, said bias error estimate, and said scale factor estimate to produce rate outputs for such coupled ones of said gyroscopes;

said rate outputs exhibiting reduced bias error and reduced scale factor error as compared to bias error and scale factor error of corresponding rates sensed by such coupled ones of said gyroscopes.

2. The system of claim 1 wherein said sense axes are mutually non-parallel.

3. The system of claim 1 wherein said sense axes form an octahedral tetrad.

4. The system of claim 1 wherein the arrangement of said sense axes defines a reference axis and each of said sense axes makes an angle of about 54.7 degrees with respect to said reference axis.

5. The system of claim 1 wherein said bias error estimator is a mode reversal bias estimator.

6. The system of claim 1 wherein said scale factor error estimator is a random closed-loop scale factor error estimator

7. The system of claim 1 wherein said system is further adapted to transform a selection of said rate outputs for said gyroscopes to rate outputs about a number of coordinate axes sufficient for navigation, and the number of said plurality of gyroscopes is at least one greater than said number of coordinate axes.

8. The system of claim 1 being further adapted to:

select each of said gyroscopes in turn for bias error calibration, and during said selection to;

take said selected gyroscope offline;

calibrate said selected gyroscope using said mode reversal bias error estimator; and

return said selected gyroscope online.

9. The system of claim 8 being further adapted to calculate a reference rate estimate about the sense axis of said selected gyroscope responsive to rate estimates sensed about axes of gyroscopes other than said selected gyroscope while said selected gyroscope is offline.

10. A gyroscope system comprising:

a plurality of gyroscopes;

a controller coupled to the plurality of gyroscopes;

said controller having;

a rate controller coupled to at least one of said plurality of gyroscopes, said rate controller receiving from said at least one of said plurality of gyroscopes a signal containing rate information of said gyroscope and responsive thereto producing an uncompensated gyroscope rate signal; and

a rate error compensator responsive to at least said uncompensated gyroscope rate signal for producing a compensated gyroscope rate signal.

11. The system of claim 10 wherein each of said gyroscopes have a sense axis and said sense axes are arranged to form an octahedral tetrad.

12. The system of claim 10 wherein said system is used for vehicle navigation requiring rate information in a number of dimensions;

and said plurality of gyroscopes numbers at least one more than said number of dimensions.

13. The system of claim 10 wherein said system is used for vehicle navigation requiring rate information about a number of axes;

and said plurality of gyroscopes numbers at least one more than said number of axes.

14. The system of claim 10 wherein said rate error compensator is further responsive to a signal representing scale factor error of said gyroscope.

15. The system of claim 14 wherein said gyroscope has a resonator exhibiting a pattern of standing waves having an orientation, and further comprising:

a scale factor error determinator having a signal generator adapted to produce signals instructing said gyroscope to displace said pattern of standing waves to positions corresponding to values of said signals;

an integrator adapted to integrate said instructing signals and responsively produce signals describing an expected position of said pattern;

and a scale factor estimator responsive to said signals describing an expected position of said pattern and a measured position of said pattern to determine a scale factor error of said gyroscope.

16. The system of claim 10 wherein said rate error compensator is further responsive to a signal representing bias error of said gyroscope.

17. The system of claim 16 wherein said gyroscope has a resonator exhibiting a pattern of standing waves, and further comprising a bias error determinator having:

a bias error extractor; and

mode sequencing logic adapted to produce signals to alternately in time represent a first mode and a second mode, such that when in said first mode, said signals instruct said gyroscope to align said pattern of standing waves along a first axis of said resonator, and when in said second mode, said signals instruct said gyroscope to align said pattern of standing waves along a second axis of said gyroscope different from said first axis;

said bias error extractor responsive to a comparison of rate estimate signals from said gyroscope when in said first mode and said second mode to produce said signal representing bias error of said gyroscope.

18. A method of operating a gyroscope system having a plurality of gyroscopes, comprising:

operating the gyroscope system with a number of gyroscopes at least one greater than the number of rate estimate axes required for navigation of a vehicle;

selecting one gyroscope for calibration;

taking the selected gyroscope offline;

determining an estimate of bias error of said selected gyroscope;

updating a bias error compensation parameter used in compensating a rate estimate of said selected gyroscope with said bias error estimate;

and returning said selected gyroscope online.

19. The method of claim 18 wherein said selecting step further comprises selecting in turn for calibration each of said plurality of gyroscopes.

20. The method of claim 18 further comprising:

operating said selected gyroscope in a first mode where maximum vibration amplitude of a resonator of the gyroscope is aligned along a first axis thereof;

recording a first-mode rate estimate from said selected gyroscope;

operating the selected gyroscope in a second mode where maximum vibration amplitude of the resonator of the gyroscope is aligned along a second axis thereof different from said first axis;

recording a second-mode rate estimate from said selected gyroscope; and

and comparing said first-mode rate estimate with said second-mode rate estimate to determine an estimate of bias error affecting said selected gyroscope.

21. The method of claim 18 further comprising determining an estimate of scale factor error of said selected gyroscope.

22. The method of claim 20 further comprising:

operating said gyroscope such that maximum vibration amplitude of a resonator of the gyroscope is driven to alignment with a control axis having a position responsive to an instruction signal;

producing instruction signals from time to time so as to change the position of said control axis;

comparing an instructed position of said control axis as defined by said instructions signals with information from said gyroscope of the actual position of maximum vibration amplitude of the resonator to produce said estimate of scale factor error of said gyroscope.

23. The method of claim 22 wherein said instruction signals command movement of the position of maximum vibration amplitude of the resonator in a substantially random manner.

24. The method of claim 22 wherein said instruction signals command movement of the position of maximum vibration amplitude of the resonator according to a pseudo random sequence.