Method and apparatus for improving performance of an inertial navigation system having global positioning system corrections

• US 20020026283A1
• Filed: 05/23/2001
• Published: 02/28/2002
• Est. Priority Date: 05/30/2000
• Status: Active Grant

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Litton Marine Systems Inc.
• Inventors: Tucker, Terry A., Coleman, Albert L.
• Granted Patent: US 6,631,323 B2
• Time in Patent Office: Days
• US Class Current: 701/221
• CPC Class Codes: G01C 21/165 combined with non-inertial navigation instruments

Abstract

Performance of an inertial navigation system (INS) corrected with GPS position data is enhanced with the addition of a filter that smooths the GPS-INS position difference data and couples the smoothed data to the INS position data. Difference data provided to the filter is edited to eliminate GPS-INS position data that excceeds a predetermined level. Performance is further improved by applying position resets from the INS Kalman filter in a ramp like manner.

Claims

1. In an inertial navigation system (INS),at an INS location, of the type having inertial sensors coupled to a navigator, the navigator having an output coupled to provide position data and to a differencing element to which a global positioning system (GPS) receiver, at a GPS location, is also coupled to provide GPS-INS position difference data that is coupled to a Kalman filter, the Kalman filter having an output from which correction position data is provided to the navigator, the improvement comprising:

a filter coupled to receive said position difference data and provide filtered position difference data; and

means for adding said filtered position difference data to said navigator position data, to provide navigator corrected position data.

2. The inertial navigation system of claim 1 further including an editor coupled between said differencing element and said filter for eliminating position difference data exceeding a predetermined value.

3. The inertial navigation system of claim 2 further including:

a reset smoothing coupled to said Kalman filter output for providing correction data from said Kalman filter output in incremental steps; and

means coupled between said navigator and said adding means and to receive said incremental steps for applying each incremental step to said navigator position data until said correction data is completed.

4. The inertial navigation system of claim 3 further including a lever arm corrector coupled between said GPS receiver and said INS to correct GPS position data to said INS location.

5. The inertial navigation system of claim 4 further including another lever arm corrector coupled between said INS and an other INS, at an other location, for correcting said INS position data to said other INS location.

6. The inertial navigation system of claim 4 wherein said filter processes said GPS-INS position difference data in accordance with

(Δ

F)_n−

(Δ

F)<sub>n−

1</sub>+K[(Δ

I)_n(Δ

F)<sub>n−

1</sub>]

where (Δ

F)_n is an output of said filter after an n^th iteration, (Δ

F)<sub>n−

1</sub> is an output of said low pass filter at an n−

1 iteration, (Δ

I)_n is an input to said low pass filter for said nth iteration, and K is a constant that is a ratio of an iteration period to said low pass filter time constant.

7. The inertial navigation system of claim 4 wherein said filter comprises:

a subtraction element coupled to receive said GPS-INS position difference data at a nth predetermined time interval and said filtered position difference data at a (n−

1) predetermined time interval to provide difference data;

a multiplier coupled to receive said difference data to provide multiplied difference data;

a summing element coupled to receive said multiplied difference data and said filtered position difference data at said (n−

1) predetermined time interval to provide a sum of said multiplied difference data and said filtered position difference data, said sum being said filtered difference position data for said nth predetermined time interval.

8. The inertial navigation system of claim 1 wherein said filter processes said GPS-INS position difference data in accordance with

(Δ

F)_n=(Δ

F)<sub>n−

1</sub>+K[(Δ

I)_n−

(Δ

F)<sub>n−

1</sub>]

where (Δ

F)_n is an output of said filter after an nth iteration, (Δ

F)<sub>n−

1</sub> is an output of said low pass filter after an n−

1 iteration, (Δ

I)_n is an input to said low pass filter for said nth iteration, and K is a constant that is a ratio of an iteration period to said low pass filter time constant.

9. The inertial navigation system of claim 1 wherein said filter comprises:

a subtraction element coupled to receive said GPS-INS position difference data at a nth predetermined time interval and said filtered position difference data at a (n−

1) predetermined time interval to provide difference data;

a multiplier coupled to receive said difference data to provide multiplied difference data;

a summing element coupled to receive said multiplied difference data and said filtered position difference data at said (n−

1) predetermined time interval to provide a sum of said multiplied difference data and said filtered position difference data at said (n−

1) predetermined time interval, said sum being said filtered difference position data at said n^th predetermined time interval.

10. The inertial navigation system of claim 1 further including a lever arm corrector coupled between said GPS receiver and said INS to correct GPS position data to said INS location.

11. A method for correcting position data of an inertial navigation system (INS),at an INS location, of the type having inertial sensors coupled to a navigator, the navigator having an output coupled to provide position data and to a differencing element to which a global positioning system (GPS), at a GPS location, is also coupled to provide GPS-INS position difference data that is coupled to a Kalman filter, the Kalman filter having an output from which corrected position data is provided to the navigator comprising the steps of:

filtering said position difference data to provide filtered position difference data; and

adding said filtered position difference data to said navigator position data.

12. The method of claim 11 further including the step of eliminating position difference data that exceed a predetermined level.

13. The method of claim 12 further including the steps of:

receiving correction data from said Kalman filter;

dividing said correction data into incremental steps; and

applying each incremental step to said navigation position data until said correction data is completed.

14. The method of claim 13 further including the step of correcting GPS position data to said INS location.

15. The method of claim 14 further including the step of correcting INS position data to an other INS at an other location.

16. The method of claim 13 wherein said filtering is in accordance with

(Δ

F)_n−

(Δ

F)<sub>n−

1</sub>+K[(Δ

I)_n−

(Δ

F)<sub>n−

1</sub>]

where (Δ

F)_n is an output of said filter after an nth iteration, (Δ

F)<sub>n−

1</sub> is an output of said low pass filter at an n−

1 iteration, (Δ

I)_n is an input to said low pass filter for said n^th iteration, and K is a constant that is a ratio of an iteration period to said low pass filter time constant.

17. The method of claim 13 wherein said filtering step includes the steps of:

subtracting said filtered position difference data at a (n−

1) predetermined time interval from said GPS-INS difference data at said nth predetermined time interval to provide difference data;

multipling said difference data by a predetermined constant;

adding said difference data to said filtered position difference data at said (n−

1) predetermined time interval to obtain filtered position difference data at said nth predetermined time interval.

18. The method of claim 11 wherein said filtering is in accordance with

(Δ

F)_n=(Δ

F)<sub>n−

1</sub>+K[(Δ

I)_n−

(Δ

F)<sub>n−

1</sub>]

where (Δ

F)_n is an output of said filter after an nth iteration, (Δ

F)<sub>n−

1</sub> is an output of said low pass filter at an n−

1 iteration, (Δ

I)_n is an input to said low pass filter for said n^th iteration, and K is a constant that is a ratio of an iteration period to a time constant of said low pass filter.

19. The method of claim 11 wherein said filtering step includes the steps of:

subtracting said filtered position difference data at a (n−

1) predetermined time interval from said GPS-INS difference data at a nth predetermined time interval to provide difference data;

multiplying said filter difference data by a predetermined constant to obtain multiplied difference data;

adding said multiplied difference data to said filtered position difference data at said (n−

1) predetermined time interval to obtain filtered position difference data at said nth predetermined time interval.

20. The method of claim 11 further including the step of correcting GPS position data to said INS location.