METHOD FOR INDEPENDENT ALIGNMENT OF AN INERTIAL UNIT FOR AN ONBOARD INSTRUMENT OF AN AIRCRAFT

• US 20110005298A1
• Filed: 12/02/2008
• Published: 01/13/2011
• Est. Priority Date: 12/21/2007
• Status: Active Grant

• Current Assignee: Thales SA
• Original Assignee: Thales SA
• Inventors: Chesne, Philippe, Mulhaupt, Gaël, Kerbiquet, Anne, Bresciani, Johan
• Granted Patent: US 8,607,613 B2
• Time in Patent Office: Days
• US Class Current: 73/1.78
• CPC Class Codes: G01C 25/005 initial alignment, calibration or starting-up of inertial devices

Abstract

A method for independent alignment of an inertial measurement unit for a stand-by instrument in an aircraft determining a status of the aircraft, that is to say whether or not the aircraft is in flight, and in the case where the aircraft is detected as being in flight, carrying out a flight alignment, and in the case where the aircraft is not detected as being in flight, determining a stability of the aircraft, that is to say whether the aircraft is on the ground or at sea, and in the case where the aircraft is detected as being on the ground, carrying out a ground alignment, and in the case where the aircraft is detected as being at sea, carrying out a sea alignment.

Claims

1. A method for independent alignment of an inertial measurement unit for an onboard instrument which can equip an aircraft, the method comprising the following steps:

determining a status of whether or not the aircraft is in flight, wherein in the case where the aircraft is detected as being in flight, carrying out a flight alignment, and in the case where the aircraft is not detected as being in flight;

determining a stability of the aircraft, to determine whether the aircraft is on the ground or at sea, wherein in the case where the aircraft is detected as being on the ground, carrying out a ground alignment, and in the case where the aircraft is detected as being at sea carrying out a sea alignment.

2. The method according to claim 1, wherein the inertial measurement unit comprises gyrometers and wherein the flight alignment, the ground alignment and the sea alignment comprise a step of determination of an internal drift of each gyrometer.

3. The method according to claim 1, wherein the status of the aircraft is determined at least one of by an item of information coming from landing gear of the aircraft and indicating if the wheels of the landing gear are in contact with a support and by an airspeed.

4. The method according to claim 1, wherein the stability of the aircraft is determined by at least one of an accelerometer and a gyrometer.

5. The method according to claim 1, wherein the stability of the aircraft is determined by at least one of the presence or the absence of a rotation about a yaw axis of the aircraft and a translation along the yaw axis of the aircraft, a roll axis and a pitch axis of the aircraft.

6. The method according to claim 5, wherein the presence or the absence of the at least one of the rotation and the translation is determined by a predetermined threshold.

7. The method according to claim 1, wherein the flight alignment comprises the following steps:

determining a time elapsed between a switching on of the onboard instrument and a switching off immediately preceding that switching on, wherein in the case in which that time is less than a predetermined duration, carrying out a short alignment, and in the contrary case, carrying out a long alignment.

8. The method according to claim 7, wherein the short alignment comprises a step comprising reusing the previously determined internal drifts of the inertial measurement unit.

9. The method according to claim 7, wherein the long alignment comprises a step of determination of minimal and maximal values of internal drifts of the inertial measurement unit and a step of precise determination of these internal drifts.

10. The method according to claim 9, wherein the step of precise determination of the internal drifts in the context of the long alignment does not take account of the instantaneous drifts of the inertial measurement unit not included between the minimal and maximal values of the internal drifts.

11. The method according to claim 7, wherein the ground alignment, the sea alignment and the long alignment each take place over a predetermined duration and in that the durations of the sea alignment and of the long alignment are greater than the duration of the ground alignment in order to be able to average the movements of the aircraft.

12. The method according to claim 1, wherein in the case where the aircraft is not detected as being in flight, the method furthermore comprises a step of determination of minimal and maximal values of internal drifts of the inertial measurement unit.

13. The method according to claim 12, wherein in the case where the aircraft is not detected as being in flight, the following steps are carried out successively:

simultaneously determining the minimal and maximal values of the internal drifts of the inertial measurement unit; and

determining the stability of the aircraft throughout the whole of the duration of determination of the minimal and maximal values of the internal drifts of the inertial measurement unit;

wherein in the case where the aircraft is detected as being at sea, carrying out a sea alignment, and in the contrary case, carrying out a ground alignment.

14. The method according to claim 12, wherein, in the case where the aircraft is not detected as being in flight, the following steps are carried out successively:

determining the minimal and maximal values of the internal drifts of the inertial measurement unit and

simultaneously;

carrying out a sea alignment; and

determining the stability of the aircraft throughout the whole of the duration of the ground alignment, wherein in the case where the aircraft is detected as being at sea abandoning the ground alignment, and carrying out a sea alignment.

15. The method according to claim 12, wherein, in the case where the aircraft is not detected as being in flight, the following steps are carried out successively:

determining the minimal and maximal values of the internal drifts of the inertial measurement unit; and

simultaneously;

carrying out a ground alignment;

carrying out a sea alignment; and

determining the stability of the aircraft throughout the whole of the duration of the ground alignment, wherein in the case where the aircraft is detected as being at sea abandoning the ground alignment, the sea alignment then being used, and in the contrary case, abandoning the sea alignment, the ground alignment then being used.

16. The method according to claim 1, wherein the onboard instrument is a stand-by instrument for generating and displaying speed, altitude and attitude information of the aircraft.