# US 10,502,573 B2 · Heading inconsistency mitigation for inertial navigation using low-performance inertial measurement units with relative aiding

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- Number: US 10,502,573 B2
- Document ID: US10502573B2
- Status: Granted
- Kind: B2
- Application number: 15/866,125
- Filed: 2018-01-09
- Published: 2018-05-10
- Granted: 2019-12-10
- Earliest claimed: 2016-06-06
- Assignees: Honeywell International Inc.
- Applicants: Honeywell International Inc.
- Inventors: Ryan Ingvalson; Michael Ray Elgersma; Vibhor L Bageshwar
- Web page: https://patentgrep.com/patent/US10502573B2

## CPC

- G01C 21/188: {for accumulated errors, e.g. by coupling inertial systems with absolute positioning systems}
- G01C 25/005: {initial alignment, calibration or starting-up of inertial devices}
- G01C 21/206: {specially adapted for indoor navigation}
- G01C: MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY (measuring liquid level G01F; radio navigation, determining distance or velocity by use of propagation effects, e.g. Doppler effects, propagation time, of radio waves, analogous arrangements using other waves G01S)

## Abstract

A method of mitigating filter inconsistency of a heading estimate in an inertial navigation system is provided. The method includes inputting inertial measurements from at least one low-performance inertial measurement unit (IMU) in the inertial navigation system; inputting an initial-heading from at least one heading-information source; inputting an initial-heading uncertainty level associated with an error in the inputted initial-heading; initializing an initial-heading estimate with the inputted initial-heading; initializing an initial-heading uncertainty estimate with the inputted initial-heading uncertainty level; initializing an accumulated heading-change estimate to zero at a startup of the at least one low-performance IMU; and initializing an accumulated heading-change uncertainty estimate with an initial accumulated heading-change uncertainty level that is a value less than the inputted initial-heading uncertainty level; and periodically updating the accumulated heading-change estimate with the inertial measurements input from the at least one low-performance IMU.

## Claims

### Claim 1

A method of mitigating filter inconsistency in a heading estimate from a navigation filter designed to estimate a joint probability density function (PDF) of a position, a velocity, an attitude, and a heading of a strapdown inertial navigation system that uses at least one inertial measurement unit (IMU), the method comprising:
estimating an initial-heading error using a first filter error state; and
estimating an accumulated heading-change error using a second filter error state;
wherein the first error state is an independent and distinct error state from the second filter error state.

### Claim 2 (depends on 1)

The method of claim 1, wherein selecting an error-state vector with components for estimating the error in the initial-heading and the error in the accumulated heading-change since the startup comprises:
defining the first filter error state and the second filter error state to directly correspond to navigation quantities explicitly computed in the inertial navigation system.

### Claim 3 (depends on 1)

The method of claim 1, further comprising:
initializing filter uncertainties by:
assigning an initial-heading uncertainty level to a third component of an ϵ-vector; and
assigning a value that is less than the initial-heading uncertainty level to a third component of a γ-vector.

### Claim 4 (depends on 3)

The method of claim 3, further comprising:
initializing a heading component of an uncertainty estimate in an Earth-to-Local-Vertical transformation with an initial-heading uncertainty level; and
initializing a heading component of an uncertainty estimate in a Body-to-Local-Vertical transformation with the initial accumulated heading-change uncertainty level, which is a value less than the initial-heading uncertainty level.

### Claim 5 (depends on 4)

The method of claim 4, further comprising:
initializing a Local-Vertical frame so a wander angle is equal to the initial-heading angle; and
initializing a heading component of the Body-to-Local-Vertical transformation with a value of zero.