Alignment Method for an Inertial Unit
First Claim
1. An method for aligning a carrier device (P) moving in an inertial reference frame (Ri) and comprising an inertial measurement unit (IN), the inertial measurement unit comprising a plurality of inertial sensors (RV, RO) and at least one invariant Kalman filter, the method comprising repeating the following steps for estimating a state of the carrier device (P) representative of its speed and its orientation:
- a propagation step (PROP) determining an estimated current state from a preceding estimated state and measurements of the inertial sensors,a update step updating (MAJ) the estimated state by means of the information a priori on the trajectory of the carrier device (P),the method being characterized in that, to allow processing by at least one invariant Kalman filter, a simplified mode is implemented in which bias of the sensors are not estimated during propagation and updating steps, each speed occurring in the updating equations being expressed in a work reference frame (Rt) translated relative to the inertial reference frame (Ri) and whereof the origin moves along an inertial reference trajectory whereof the carrier device is deemed close.
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Abstract
The invention relates to an alignment method based on a simplified mode allowing processing using an invariant Kalman filter, in which each speed involved in the navigation equations is expressed in a work reference frame (Rt) translated with respect to an inertial reference frame (Ri) and for which the origin moves along a reference inertial trajectory, the carrier of which is assumed to be close (geographic origin for alignment with the sun at known position, GPS trajectory for alignment in-motion, etc.). This simplified mode comprises the repetition of the following steps to estimate a mobile carrier state (P): propagation (PROP) determining an estimated current state from a preceding estimated state, inertial sensor measurements and theoretical information on the carrier trajectory (P) updating (MAJ) the estimated state using theoretical information on the carrier trajectory (P). The deterministic uncertainties of the sensors (bias/drift/scale factors, etc.) are only estimated during the propagation and update steps. A perturtion step (PERT) then allows inclusion of the values ignored in the simplified mode and estimation of these values by an optimisation method.
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Citations
12 Claims
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1. An method for aligning a carrier device (P) moving in an inertial reference frame (Ri) and comprising an inertial measurement unit (IN), the inertial measurement unit comprising a plurality of inertial sensors (RV, RO) and at least one invariant Kalman filter, the method comprising repeating the following steps for estimating a state of the carrier device (P) representative of its speed and its orientation:
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a propagation step (PROP) determining an estimated current state from a preceding estimated state and measurements of the inertial sensors, a update step updating (MAJ) the estimated state by means of the information a priori on the trajectory of the carrier device (P), the method being characterized in that, to allow processing by at least one invariant Kalman filter, a simplified mode is implemented in which bias of the sensors are not estimated during propagation and updating steps, each speed occurring in the updating equations being expressed in a work reference frame (Rt) translated relative to the inertial reference frame (Ri) and whereof the origin moves along an inertial reference trajectory whereof the carrier device is deemed close. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
an embedded computer of said unit performing repetition of the following steps for estimating a state of the carrier device (P) representative of its speed and its orientation; a propagation step (PROP) determining an estimated current state from a preceding estimated state and measurements of the inertial sensors, an update step updating (MAJ) the estimated state by means of the information a priori on the trajectory of the carrier device (P), characterized in that, to allow processing by the invariant Kalman filter, the computer is configured to execute an alignment method according to one of claims 1 to 10.
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12. A computer program product, characterized in that it comprises program code instructions for execution of the steps of the method according to one of claims 1 to 10, when this program executed by a computer embedded in an inertial measurement unit can also be implemented.
Specification