Real time error determination for inertial instruments

• US 20090292497A1
• Filed: 05/20/2008
• Published: 11/26/2009
• Est. Priority Date: 05/20/2008
• Status: Active Grant

• Current Assignee: Northrop Grumman Guidance And Electronics Company, Inc.
• Original Assignee: Northrop Grumman Guidance And Electronics Company, Inc.
• Inventors: Lee, Charles A.
• Granted Patent: US 7,698,082 B2
• Time in Patent Office: Days
• US Class Current: 702/93
• CPC Class Codes: G01C 21/183 Compensation of inertial measurements, e.g. for temperature effects
• CPC Class Codes: G01C 25/005 initial alignment, calibration or starting-up of inertial devices
• CPC Class Codes: G01P 15/08 with conversion into electric or magnetic values
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

An exemplary inertial measurement apparatus has first and second inertial instruments that are oriented to have parallel sense axes and that produce respective first and second sensed output signals representative of an inertial attribute to be measured. Respective first and second scale factors are used in producing the first and second sensed output signals. Bias errors in the first and second instruments are estimated using the change in state of sign of the first and second scale factors during the first and succeeding time intervals. To facilitate measurement of bias errors in the first and second instruments, a substitute scale factor is determined to be an equivalent of the second scale factor and is based on the first scale factor and a difference between the first and second scale factors. Errors in the second scale factor are calculated based on the first scale factor and the substitute scale factor during first and succeeding time intervals where a sign of one of first and second scale factors changes from one state during the first time interval to the other state during the succeeding time intervals. First and second corrected output signals are generated based on the respective first and second sensed output signals and correction of said second scale factor error.

Claims

1. An inertial measurement apparatus comprising:

first and second inertial instruments are oriented to have parallel sense axes and produce respective first and second sensed output signals representative of an inertial attribute to be measured, the first and second inertial instruments use respective first and second scale factors which are reversible in sign in producing the first and second sensed output signals;

means for receiving said first and second output signals and for accessing the first and second scale factors;

means for determining a substitute scale factor as an equivalent of the second scale factor based on the first scale factor and a difference between the first and second scale factors;

means for calculating differences in the first and second scale factors based on the first scale factor and the substitute scale factor during first and second time intervals where a sign of one of first and second scale factors changes from one state during the first time interval to the other state during the second time interval;

means for sequencing the reversal of the signs of the first and second scale factors and for combining the corresponding outputs from the first and second gyros to measure the bias errors of the first and second gyros and the difference between the scale factors of the first and second gyros;

means for generating first and second corrected output signals based on the respective first and second sensed output signals and correction of said first and second scale factor errors.

2. The apparatus of claim 1 wherein the generating means further comprises generating first and second corrected output signals based on measurement of the first and second sensed output signals over multiple successive time intervals and arithmetically combining the sensed output signals over the multiple successive time intervals so that certain components that make up the first and second sensed output signals cancel each other.

3. The apparatus of claim 1 wherein the first and second inertial instruments also use respective first and second bias values to generate the first and second output signals, the apparatus further comprising:

said accessing means accessing the first and second bias values;

said calculating means calculating an error in the first and second bias values based on the bias values during multiple successive time intervals;

said generating means generating first and second corrected output signals based on the respective errors in the first and second bias values and correction of said first and second bias value errors.

4. The apparatus of claim 1 wherein the differences between the first and second scale factors are based on equations Eq14 and Eq15.

5. The apparatus of claim 1 further comprising means for generating a third corrected output signal representative of a value of the inertial attribute, where the third output signal is an average of the first and second corrected output signals.

9. The method of claim 1 wherein the errors in the second scale factor are based on equations Eq14 and Eq15.

10. The method of claim 1 further comprising the step of generating a third corrected output signal representative of a value of the inertial attribute, where the third output signal is an average of the first and second corrected output signals.

6. A method for correcting errors in first and second sensed output signals representative of an inertial attribute being measured, the method comprising the steps of:

said first and second sensed output signals being generated by first and second inertial instruments oriented to have parallel sense axes;

producing the first and second sensed output signals by using respective first and second scale factors;

receiving said first and second output signals and accessing the first and second scale factors;

determining a substitute scale factor as an equivalent of the second scale factor based on the first scale factor and a difference between the first and second scale factors;

calculating differences between the scale factor based on the first scale factor and the substitute scale factor during first and subsequent time intervals where a sign of one of first and second scale factors changes from one state during the first time interval to the other state during the succeeding time intervals;

generating first and second corrected output signals based on the respective first and second sensed output signals and correction of said second scale factor error.

7. The method of claim 6 further comprising the steps of generating first and second corrected output signals based on measurement of the first and second sensed output signals over multiple successive time intervals and arithmetically combining the sensed output signals over the multiple successive time intervals so that certain components that make up the first and second sensed output signals cancel each other.

8. The method of claim 6 wherein respective first and second bias values are also used to generate the first and second output signals, the method further comprising the steps of:

accessing the first and second bias values;

calculating an error in the first and second bias values based on the bias values during the first and succeeding time intervals;

generating first and second corrected output signals based on the respective errors in the first and second bias values and correction of said first and second bias value errors.