Hybrid Inertial Navigation Error Correction via Lowpass Filtered Difference

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Solution Overview

Problem

Existing navigation systems face issues with noise in pure inertial navigation and accuracy variations in hybrid navigation, leading to drift and operator fatigue when used for pointing aiming devices or aligning inertial navigation systems.

Innovation Solution

A method that performs a hybrid navigation calculation using a Kalman filter to combine inertial and non-inertial data, calculates the difference between inertial and hybrid calculations, applies lowpass filtering, and uses the filtered difference to correct the navigation calculation, ensuring stability and accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If pure inertial navigation data is used for pointing the optronic ball, then noise is reduced, but angular drift increases causing offset from target

Engineering Contradiction:

Improvenoise levelVSAvoidangular drift

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

A difference calculation unit and lowpass filter are introduced as intermediary elements between the inertial navigation data and the optronic ball control. The system calculates the difference between hybrid and inertial navigation data, filters this difference to remove high-frequency noise while preserving low-frequency drift compensation, and applies it to correct the inertial navigation data. This intermediary processing resolves the contradiction by selectively combining benefits of both navigation types.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system changes the parameter of navigation data by calculating the difference between hybrid and inertial data, then applying lowpass filtering with a specific time constant. This parameter transformation converts the raw inertial data into corrected navigation data that has both low noise and compensated drift, resolving the trade-off between measurement precision and reliability.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If hybrid navigation data is used for pointing the optronic ball, then target positioning accuracy is improved, but Kalman filter resetting causes sudden changes and visual fatigue

Engineering Contradiction:

Improvetarget positioning accuracyVSAvoidnavigation data stability

Core Design Contradiction:

Measurement precisionVSStability of the object's composition

Solution Approach 1:

The system extracts only the necessary correction component from the hybrid navigation data by calculating the difference between hybrid and inertial data. Instead of using all hybrid navigation data which contains resetting artifacts, it extracts and filters only the drift compensation component, eliminating the instability caused by Kalman filter resetting while retaining the accuracy benefits.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The system performs preliminary lowpass filtering on the navigation difference before applying it to the optronic ball control. This preliminary action removes high-frequency variations and resetting artifacts in advance, ensuring stable and smooth navigation data is provided to the control system, preventing visual fatigue while maintaining accuracy.

Inventive Principle:

Principle #10Preliminary action

3Ease of operation

If pure inertial navigation data is used for aligning navigation systems, then alignment simplicity is maintained, but drift induces oscillation at Schuler period

Engineering Contradiction:

Improvealignment simplicityVSAvoidalignment accuracy

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

A difference calculation and lowpass filtering intermediary is introduced in the alignment process between the two inertial navigation systems. Instead of directly using raw inertial data for alignment, the system calculates the navigation difference, filters it to remove Schuler oscillations, and uses this corrected difference for alignment. This maintains operational simplicity while eliminating drift-induced oscillations.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Measurement precision

If lowpass filtering with long convergence time is applied to navigation difference, then noise reduction is improved, but response speed decreases

Engineering Contradiction:

Improvenoise reductionVSAvoidresponse speed

Core Design Contradiction:

Measurement precisionVSSpeed

Solution Approach 1:

The system optimizes the lowpass filter time constant parameter to achieve the desired balance. By carefully selecting the time constant to be longer than the Kalman filter period (for noise reduction) but shorter than the Schuler period (for maintaining response speed), the system resolves the contradiction between noise reduction and response speed through parameter optimization.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS10598495B2Method for designing a navigation path and method for orienting a sighting member from said navigation path

Publication Date: 2020.03.24 SAFRAN ELECTRONICS & DEFENSE (FR)

AI summary

A method of performing a navigation calculation on the basis of a hybrid inertial navigation system on board a vehicle includes performing a hybrid first navigation calculation and an inertial second navigation calculation, calculating in real time a difference between the first navigation calculation and the second navigation calculation, and subjecting the difference to lowpass filtering having a convergence time longer than a period of the Kalman filter and shorter than the Schuler period, and using the filtered difference to correct the second navigation calculation.