Inductive Gyroscope Scale Factor Compensation for Magnet Aging
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Solution Overview
Problem
The performance of MEMS-based inductive gyroscopes degrades over time due to magnet aging, leading to significant scale factor errors, especially in high-accuracy systems where existing compensation methods fail to accurately account for time-dependent magnet degradation.
Innovation Solution
A feedback loop system with Automatic Gain Control (AGC) and Phase Locked Loop (PLL) adjusts the gain to maintain resonant motion, allowing for real-time compensation of scale factor changes by measuring the gain in the drive control loop and comparing it to a reference value, using a lookup table or formula to calculate and apply corrections based on magnet degradation and temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a permanent magnet is used in an inductive gyroscope to generate the magnetic field, then the gyroscope can operate effectively with inductive transducers, but the magnet deteriorates over time causing scale factor errors and performance degradation
Solution Approach 1:
The patent implements a feedback mechanism by monitoring the drive signal characteristics (amplitude, frequency, or phase) and using this information to calculate real-time scale factor corrections. The compensation unit continuously adjusts the scale factor based on the measured drive signal parameters, creating a closed-loop system that compensates for magnet aging effects without requiring external time measurement.
Solution Approach 2:
The gyroscope system performs self-diagnosis and self-compensation by using its own operational parameters (drive signal characteristics) to detect magnet degradation and automatically correct scale factor errors. The system serves itself by extracting compensation data from its normal operation without requiring separate calibration procedures or external reference measurements.
2Measurement precision
If traditional time-based compensation methods are used to account for magnet aging, then scale factor errors can be corrected, but a clock for time measurement is required which increases device complexity
Solution Approach 1:
The patent uses the drive signal characteristics as an intermediary parameter that indirectly reflects magnet aging effects. Instead of directly measuring time and applying pre-determined corrections, the system measures the drive signal amplitude, frequency, or phase which naturally changes with magnet degradation, and uses this intermediary measurement to calculate the appropriate scale factor compensation.
Solution Approach 2:
The patent replaces the mechanical/time-based compensation approach (using a clock and time-stamped calibration data) with an electrical/parameter-based approach. By substituting time measurement with drive signal parameter measurement, the system eliminates the need for a clock while achieving more accurate, real-time compensation that adapts to actual magnet conditions.
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 system effectively compensates for magnet aging throughout the gyroscope's lifetime, reducing scale factor errors by up to 1000 ppm, ensuring high accuracy and performance stability across varying conditions.
Implementation Method 1
The inductive gyroscope 1 comprises a lower pole piece 20, an upper pole piece 24 and a permanent magnet 22 sandwiched between them. The vibrating ring 10 is located between the upper pole piece 24 and the lower pole piece 20 such that it lies within the magnetic field formed between these two pieces.
Implementation Method 2
Conductive tracks are formed on the gyroscope structure (normally passing along one of the mounting legs, then forming a loop on a localised portion of the ring structure before returning along the same or a different mounting leg. An AC current is passed through these conductive tracks on the gyroscope structure which creates a corresponding alternating magnetic field. The attractive and repelling forces between this and the permanent magnetic create the oscillations within the gyroscope structure.
Implementation Method 3
When the gyroscope rotates, a Coriolis force is exerted on the vibrating mass, and this force may cause the mass to oscillate in a secondary mode of vibration, which is different to the primary mode.
Data Source
Figure 1
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AI summary
A vibrating structure gyroscope, comprising: a permanent magnet; a structure arranged in a magnetic field of the permanent magnet and arranged to vibrate under stimulation from at least one primary drive electrode; a drive system comprising: the at least one primary drive electrode arranged to induce motion in the vibrating structure, at least one primary sense electrode arranged to sense motion in the vibrating structure; and a drive control loop controlling the primary drive electrode dependent on the primary sense electrode; a compensation unit arranged to receive a signal from the drive system representative of a gain in the drive control loop and arranged to output a scale factor correction based on that signal. As the magnet degrades (e.g. naturally over time as the material ages), the magnetic field weakens. As a result, the amplitude of motion induced in the vibrating structure will reduce and the amplitude of the pick-off signal detected at the primary sense electrode will reduce. To compensate for this, the primary drive control loop will automatically increase the gain. Therefore the gain in the drive control loop can be used as a measure of magnet degradation and can be used to compensate for the change in scale factor that is caused by that magnet degradation. comparing the gain at the time of use to a reference gain value obtained at a time of calibration, the change in gain can be used to calculate a change in scale factor since calibration that is due to magnet degradation.