Calibrating Vibratory Gyroscope Scale Factor Errors
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Solution Overview
Problem
High-precision strapdown inertial navigation systems require accurate gyroscopic measurements, but conventional laser gyroscopes are expensive, and HRG-type vibratory gyroscopes in whole angle mode suffer from bias errors and angular noise, while operating in rate mode degrades measurement quality.
Innovation Solution
A calibration method for HRG-type vibratory gyroscopes in rate mode using a system of at least four gyroscopes, where a first measurement is corrected using a second measurement to isolate the angular displacement caused by the precession command, allowing for the determination of a calibrated scale factor value that minimizes bias and noise, and potentially averaging multiple calibration steps to refine the scale factor value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser gyroscopes are used to achieve high measurement precision in strapdown inertial navigation systems, then measurement precision is improved, but device cost increases significantly
Solution Approach 1:
The patent replaces expensive laser gyroscopes with cheaper HRG-type vibratory gyroscopes. Although HRGs have inherent errors (bias errors and scale factor errors), these can be corrected through calibration methods described in the patent, enabling cost-effective high-precision navigation systems.
2Measurement precision
If HRG-type vibratory gyroscopes are used in whole angle mode to reduce scale factor errors, then measurement precision is improved, but angular noise increases
Solution Approach 1:
The patent changes the operating parameter from whole angle mode to rate mode for HRG gyroscopes. In rate mode, the vibration position is fixed and maintained by an electrical command, which eliminates angular noise. The patent then provides calibration methods to correct the bias errors and scale factor errors that arise in rate mode, thus achieving both low noise and high accuracy.
3Stability of the object's composition
If HRG-type vibratory gyroscopes are used in rate mode to eliminate bias errors and angular noise, then measurement stability is improved, but scale factor errors increase
Solution Approach 1:
The patent employs calibration methods that use feedback from multiple measurements to determine and correct scale factor errors. By applying calibration commands and measuring the resulting vibration position changes, the system can calculate correction factors that compensate for scale factor errors, thereby maintaining both stability and accuracy.
Solution Approach 2:
The patent introduces calibration procedures as an intermediary process between the gyroscope and the navigation system. These calibration procedures use auxiliary measurements and calculations to determine correction factors, which then serve as mediators to eliminate scale factor errors from the navigation calculations.
4Measurement precision
If calibration procedures are applied to correct scale factor errors in rate mode operation, then measurement precision is improved, but system complexity increases
Solution Approach 1:
The patent performs calibration procedures in advance during system initialization or maintenance periods. By determining scale factor correction factors beforehand, the actual navigation operation can proceed with simple application of these pre-calculated corrections, rather than requiring complex real-time calibration calculations.
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 enables high-quality, precise measurements in rate mode by correcting scale factor errors and reducing angular noise, thereby meeting the precision requirements of strapdown inertial navigation systems while using less expensive vibratory gyroscopes.
Implementation Method 1
The level of precision required for the measurements provided by the gyroscopes used in these inertial units depends on the type of inertial unit considered
Implementation Method 2
in a rate mode in which its vibration position is fixed and maintained by application of an electrical command
Data Source
Figure 1~3
AI summary
In a gyroscopic system comprising at least four vibratory gyroscopes, a first measurement is provided by said vibratory gyroscope to be calibrated, and a second measurement is provided by a combination of the measurements from the other vibratory gyroscopes of the system. At the level of the vibratory gyroscope to be calibrated, an initial command is applied in order to command a change in position from a first vibration position to a second vibration position. A calibrated scale factor value of the vibratory gyroscope to be calibrated is then determined to the basis of a calculated value in relation to the change in position, based on the period of time during which the initial command is applied, the initial command, an angular difference between the first and second vibration position measured according to the first measurement and an angular difference measured according to the second measurement.