METHOD OF DETECTING PARASITIC MOVEMENTS WHILE ALIGNING AN INERTIAL UNIT

• US 20120185205A1
• Filed: 10/13/2010
• Published: 07/19/2012
• Est. Priority Date: 10/15/2009
• Status: Abandoned Application

• Current Assignee: Safran Electronics & Defense
• Original Assignee: Sagem Defense Securite SA (Safran SA)
• Inventors: Rosellini, Lionel, Foloppe, Yannick
• Application Number:
  US13/497,218
• Publication Number:
  US 20120185205A1
• Time in Patent Office: Days
• US Class Current: 702/141
• 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

Abstract

A method of detecting parasitic movements while aligning an inertial unit comprising a navigation unit connected to accelerometer sensors and gyros disposed in a predetermined frame of reference, the method comprising the steps of: integrating the acceleration signal in a frame of reference that is turning in accordance with the measurement of the gyros so as to obtain a raw position signal during a predetermined duration; during this predetermined duration recording the previously calculated position signals; from an error model, determining the parameters for modeling the raw position signal; calculating a residual signal between the modeling signal and the raw position signal; and identifying a parasitic movement when the residual signal overshoots a predetermined limit threshold.

Claims

1. A method of detecting parasitic movements while aligning an inertial unit that comprises a navigation unit connected to accelerometer and angle sensors placed in a predetermined frame of reference, the method comprising the steps of:

integrating the signals from the sensors, in a frame of reference that is turning in an orientation that can be detected by the accelerometer and angle sensors, in order to obtain a raw position signal during a predetermined duration;

recording the raw position signal during said predetermined duration;

determining the parameters of a theoretical signal modeling the raw position signal as a function of a predetermined error model in the absence of movement;

calculating a residual signal between the theoretical modeling signal and the raw position signal; and

identifying a parasitic movement when the residual signal overshoots a predetermined limit threshold.

2. A method according to claim 1, wherein the parameters are determined from the raw position signal by using a least squares method.

3. A method according to claim 1, wherein the determined parameters are compared with likelihood thresholds that are established as a function of the performance of the sensors.

4. A method according to claim 1, wherein the threshold is calculated to take account of a standard deviation value for the noise of the accelerometer and angle sensors.

5. A method according to claim 4, wherein the threshold is equal to a multiple of the standard deviation value, and in particular is six times the standard deviation value.

6. A method according to claim 4, wherein the threshold is constant.

7. A method according to claim 4, wherein the threshold varies as a function of time.

8. A method according to claim 1, including the step of filtering the raw position signal prior to modeling in order to eliminate therefrom components having a frequency greater than a predetermined maximum threshold.

9. A method according to claim 1, wherein identification takes account of a number of times the limit threshold is overshot by the residual signal.