FOG Calibration Circuit Mitigating Bias Error
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Solution Overview
Problem
Fiber-optic gyroscope (FOG) systems face bias errors due to environmental and process variations affecting the optical path, which degrade the accuracy and bandwidth of rotation measurements.
Innovation Solution
A calibration circuit that periodically alternates the direction of optical beams through the FOG coil, allowing for the estimation and subtraction of bias errors by reversing the scale factor in each switching state, using a rapid optical switch, such as a solid-state switch, to ensure continuous operation without data loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the FOG coil length is increased to improve measurement precision, then the bias error increases due to environmental and process variations affecting the optical path
Solution Approach 1:
The patent applies inversion by periodically reversing the direction of light propagation through the FOG coil. By switching between clockwise and counter-clockwise propagation directions, the system creates two measurements with opposite scale factors. This allows the bias error to be isolated and subtracted, effectively eliminating its impact on measurement accuracy while maintaining the benefits of a longer FOG coil.
2Device complexity
If a multi-period delay is used to process gyroscope output and compute feedback step size, then manufacturing complexity increases, but bandwidth is reduced
Solution Approach 1:
The patent implements preliminary action by pre-computing the bias error compensation value during the integration period before the feedback step is applied. The calibration circuit continuously estimates the bias error and prepares compensation values in advance, so that when the feedback step needs to be applied, the compensation is already ready. This eliminates the need for complex multi-period delay processing while maintaining system stability and improving bandwidth.
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 effectively mitigates bias errors by comparing measurements in alternating states, enhancing the accuracy and stability of rotation rate calculations in FOG systems, particularly in applications requiring precise navigation.
Implementation Method 1
A fiber-optic gyroscope (FOG) can measure angular rotation using light transmitted through a fiber optic coil of the FOG and use the Sagnac effect to sense the angular rotation
Implementation Method 2
The optical beam controller includes an optical switch configured to periodically alternate between a first switching state and a second switching state. In the first switching state, a first optical beam of the pair of optical beams is provided to a first input of the FOG and a second optical beam of the pair of optical beams is provided to a second input of the FOG
Data Source
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AI summary
One example includes a fiber-optic gyroscope (FOG) system that includes a fiber coil. The coil includes an optical fiber wound around a spool of a FOG. The optical fiber includes a first input and a second input. The system also includes an optical beam controller comprising an optical switch that provides a first optical beam to the first input and a second optical beam to the second input during a first switching state, and provides the first optical beam to the second input and the second optical beam to the first input during a second switching state. The system further includes a controller that mitigates bias error in determining rotation of the FOG based on comparing the first and second optical beams output from the FOG during the first and second switching states.