Low-Pass Filter Heave Measurement Eliminates Phase Delay
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Solution Overview
Problem
Traditional high-pass digital filters used in heave measurement technologies introduce phase delays and amplitude attenuation, leading to errors in measuring the vertical motion of ships, which are critical for maritime operations like aircraft take-off and landing and oil drilling platform operations.
Innovation Solution
A strapdown inertial navigation heave measurement method employing multiple low-pass filter units, specifically a double-filter unit and a triple-filter unit with defined transfer functions, to accurately measure heave velocity and displacement without introducing significant phase errors, thereby eliminating the need for additional filters to compensate for phase delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a high-pass filter is added to filter out low-frequency Schuler period term in heave acceleration, then low-frequency harmful components are eliminated, but phase delay and amplitude attenuation occur introducing new errors
Solution Approach 1:
Instead of using a high-pass filter to remove low-frequency components, the patent inverts the approach by using a low-pass filter to remove high-frequency noise. The low-pass filter transfers heave acceleration to heave velocity and displacement through integration, naturally attenuating high-frequency components while preserving low-frequency useful signals, thus avoiding the phase delay and amplitude attenuation problems of high-pass filters
Solution Approach 2:
The patent changes the filter type parameter from high-pass to low-pass, and adjusts the cutoff frequency parameter to achieve the desired filtering effect. By selecting appropriate cutoff frequency for the low-pass filter, the system effectively removes high-frequency noise while maintaining measurement accuracy for heave motion
2Measurement precision
If an all-pass filter is added to compensate for phase, then phase error is corrected, but additional filters introduce new error amounts and increase system complexity
Solution Approach 1:
The patent extracts and eliminates the need for phase compensation filters by fundamentally changing the filtering approach. Instead of adding corrective filters, the solution uses a single low-pass filter combined with integration, which naturally provides both filtering and phase preservation without requiring additional phase compensation components
Solution Approach 2:
The low-pass filter in the patent serves multiple functions simultaneously: it filters out high-frequency noise, preserves low-frequency useful signals, and maintains phase accuracy through its inherent characteristics combined with integration. This multi-functional approach replaces the need for separate filtering and phase compensation stages
3Measurement precision
If multiple filters are added to improve measurement accuracy, then measurement precision improves, but device complexity and cost increase
Solution Approach 1:
The patent merges the filtering function and integration function into a unified low-pass filter system. By combining these functions, the system achieves high measurement accuracy for heave velocity and displacement without requiring separate filter stages, thereby reducing device complexity and cost while maintaining precision
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method provides high-accuracy heave velocity and displacement measurements with minimal phase error, reducing costs and complexity, and achieving an error within 3 cm, meeting the 5 cm index requirement, thus enhancing navigation accuracy and operational safety.
Implementation Method 1
The disclosure includes a strapdown inertial navigation heave measurement method using multiple low-pass filter units
Data Source
AI summary
A strapdown inertial navigation heave measurement method using multiple low-pass filter units includes: firstly, collecting data of a gyroscope and an accelerometer by a system, obtaining attitude information of a carrier by using initial alignment, and then, obtaining a relationship matrix between a body coordinate system and a geographic coordinate system by using the attitude information; obtaining a relationship matrix between the geographic coordinate system and a reference coordinate system according to a geographic position, and obtaining a rough vertical acceleration by using a direction cosine matrix, output information of the accelerometer and gravity information; then, filtering out low-frequency signals by using a first filter unit and integration to obtain a relatively accurate velocity signal; and furthermore, enabling the vertical acceleration to be subjected to a second filter unit and integration to obtain an accurate heave displacement.