MEMS Gyrocompass Heading Detection with Bias-Compensated Sense Axes
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Solution Overview
Problem
Conventional gyrocompasses are large, expensive, and unreliable, while MEMS gyroscopes face bias errors and require complex mechanisms to measure low Earth rotation rates accurately, limiting their use in precise geographical heading determination.
Innovation Solution
A MEMS gyrocompass device with multiple sense axes arranged at known offset angles uses electronic circuitry to determine heading by fitting sine or cosine functions to rotation rates, compensating for bias errors with lookup tables and temperature corrections, and incorporating GNSS and IMU for stabilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional gyrocompasses are used to achieve accurate geographical heading determination, then measurement precision is improved, but device complexity, size, and cost increase significantly
Solution Approach 1:
The patent replaces the mechanical gimballed spinning mass system of conventional gyrocompasses with electronic signal processing using MEMS gyroscopes. Multiple MEMS gyroscopes measure rotation rates along different axes, and electronic circuitry processes these signals through mathematical algorithms (fitting sine or cosine functions) to determine heading, eliminating complex mechanical components while maintaining measurement precision.
Solution Approach 2:
The patent divides the measurement function across multiple MEMS gyroscopes, each measuring rotation rates along specific axes. By segmenting the measurement task across multiple sensors with known offset angles between their sense axes, the system achieves accurate geographical heading determination through combined data processing rather than relying on a single complex mechanical gyroscope.
2Device complexity
If MEMS gyroscopes are used to reduce device size and cost, then device complexity is reduced, but bias error increases significantly
Solution Approach 1:
The patent uses multiple copies of MEMS gyroscopes arranged with their sense axes at known offset angles. By deploying multiple identical sensors rather than relying on a single sensor, the system can process the combined outputs to determine heading while compensating for individual sensor bias errors through the geometric arrangement and signal processing algorithms.
Solution Approach 2:
The patent changes the spatial arrangement parameter by positioning multiple MEMS gyroscopes with their sense axes at specific known offset angles relative to each other. This geometric parameter configuration, combined with electronic signal processing, transforms the bias error characteristic from a limiting factor into a manageable parameter that can be compensated through the mathematical relationships between the offset axes measurements.
3Measurement precision
If MEMS gyroscopes rotate slowly to average noise in carouselling method, then measurement precision improves, but productivity decreases due to very slow rotation
Solution Approach 1:
The patent employs periodic turning of the device or gyroscopes by 180 degrees (maytagging method) to cancel bias errors. This periodic action allows the system to perform calibration maneuvers at regular intervals rather than requiring continuous slow rotation, thereby maintaining measurement precision while significantly improving productivity during normal operation.
Solution Approach 2:
The patent performs bias error compensation through preliminary periodic maneuvers (180-degree turns) rather than requiring continuous slow rotation during measurement. By preparing the system through these periodic calibration actions, the device can then operate at normal speeds for heading determination, resolving the contradiction between precision and productivity.
4Device complexity
If magnetic compasses are used for heading determination, then device complexity is reduced, but measurement precision deteriorates in areas with magnetic interference
Solution Approach 1:
The patent replaces magnetic field-based measurement with mechanical rotation-based measurement using MEMS gyroscopes. This substitution eliminates dependence on the geomagnetic field, allowing accurate heading determination in environments with magnetic interference (such as areas with steel structures or electrical currents) while maintaining relatively simple device architecture through electronic processing.
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
The device provides accurate and reliable geographical heading determination with reduced size and cost, overcoming bias errors and dynamic noise, suitable for precise applications like marine navigation.
Implementation Method 1
MEMS (microelectromechanical systems) gyroscopes have historically been unable to measure the very low rotation rates of the Earth around its axis
Data Source
AI summary
A gyrocompass device is provided for determining a heading relative to a surface of a rotating planetary body. The gyrocompass device includes one or more MEMS gyroscopes that are each fixed in an orientation on a substrate that is parallel to a first plane and that each provide three or more sense axes that lie within the first plane and are each offset from one another by an offset angle. Moreover, a heading determiner receives rotation rates from the three sense axes and determines the heading of the gyrocompass device relative to the surface of the rotating planetary body by fitting a sine or cosine function to the received rotation rates from the one or more MEMS gyroscopes.