Latitude-Free Initial Alignment Under Swaying Base
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Solution Overview
Problem
Traditional strapdown attitude heading reference systems face challenges in initial alignment under a swaying base, particularly when latitude information is unknown, as they rely on external GPS and other equipment, reducing autonomy and security, and fail to align accurately due to low signal-to-noise ratio from gyroscope outputs and interference from device noise and external vibrations.
Innovation Solution
A latitude-free initial alignment method based on gradient descent optimization is developed, where the Wahba attitude determination problem is addressed by establishing an objective function using gravitational acceleration vectors, solving for inertial system conversion quaternions using gradient descent optimization, and updating attitudes solely with accelerometer and gyroscope data, thereby achieving alignment without external latitude information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If traditional initial alignment technology is used, then alignment can be performed with simple equipment, but autonomy and security are reduced due to dependence on external latitude information
Solution Approach 1:
The system performs self-alignment by extracting latitude information from its own accelerometer measurements during the alignment process. The method uses the gravitational acceleration vector components measured by the accelerometer to calculate latitude without requiring external GPS or beacon transducer equipment, making the system self-sufficient and autonomous.
2Ease of operation
If traditional analytical static base alignment method is used, then the method is simple to implement, but it cannot work under swaying base conditions due to low signal-to-noise ratio
Solution Approach 1:
The method transitions from static base alignment to dynamic alignment by accommodating swaying base conditions. It uses gradient descent optimization to dynamically adjust the alignment calculation in real-time, allowing the system to extract latitude information even when the base is swaying due to waves, thus maintaining reliability under dynamic conditions.
Solution Approach 2:
The gradient descent optimization process uses feedback from accelerometer measurements to iteratively refine the latitude estimation. The method continuously compares measured gravitational acceleration components with expected values and adjusts the alignment calculation accordingly, enabling reliable alignment under swaying conditions where traditional methods fail.
3Measurement precision
If compass alignment and Kalman filtering combined alignment method is used, then filtering accuracy is improved, but alignment cannot be achieved for arbitrarily oriented heading angles
Solution Approach 1:
The method provides a universal alignment solution that works for any heading angle orientation. By using gradient descent optimization to solve the alignment equations, the method removes the small angle constraint limitation of Kalman filtering, enabling accurate alignment regardless of the initial heading angle, thus achieving versatility across all operational scenarios.
4Reliability
If traditional swaying base alignment method using GPS and beacon transducer is used, then alignment can be accomplished, but system autonomy and security are reduced
Solution Approach 1:
The method extracts latitude information directly from accelerometer measurements during the alignment process, removing the dependency on external GPS and beacon transducer equipment. By taking out the need for external positioning systems, the method maintains alignment capability while significantly improving system autonomy and security, especially in GPS-denied environments.
Data Source
AI summary
The disclosure discloses a latitude-free initial alignment method under a swaying base based on gradient descent optimization. Firstly, swaying base latitude-free alignment is regarded as a Wahba attitude determination problem to inhibit device noise interference, and an objective function is established based on a gravitational acceleration vector under an earth system; then an exact solution of the objective function is obtained through a gradient descent optimization method, and inertial system conversion quaternion estimation is achieved under the latitude-free condition; and finally, an attitude quaternion is determined by only using information of an accelerometer and a gyroscope of a strapdown attitude heading reference system, and therefore latitude-free initial alignment under the swaying base is achieved. The disclosure can solve the problem that initial alignment cannot be accomplished with unknown latitude under the swaying base, and thus the application range of the strapdown attitude heading reference system is ensured.