Silicon In-Plane Tuning Fork Gyroscope Mode-Matching
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Solution Overview
Problem
Conventional microgyroscopes fail to achieve inertial grade performance, specifically in terms of rate resolutions and bias stabilities, which are essential for high-precision applications such as GPS-augmented navigation, robotics, and aerospace, due to limitations in noise floor, quality factors, and mechanical sensitivity.
Innovation Solution
The implementation of a software control algorithm in conjunction with CMOS ASICs to electronically control mechanical bias voltages in MEMS in-plane tuning fork gyroscopes, allowing for mode-matching and electronic bandwidth control, thereby enhancing sensitivity and reducing bias drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional MEMS gyroscope designs are used, then device complexity and manufacturing cost are reduced, but measurement precision and bias stability deteriorate
Solution Approach 1:
The patent implements a feedback control system where the measured angular rate is fed back to the bias voltage control circuit, which automatically adjusts the mechanical bias voltage to maintain optimal frequency matching between drive and sense modes. This closed-loop feedback mechanism continuously compensates for drift and maintains high measurement precision without requiring complex manual calibration procedures
Solution Approach 2:
The patent replaces complex mechanical tuning mechanisms with electronic bias voltage control. Instead of mechanically adjusting the resonant frequencies through physical modifications, the system uses electrostatic actuation to apply precise voltage control to the proof masses, thereby electronically tuning the frequency match between modes and achieving high precision measurement
2Measurement precision
If mode-matching control is implemented, then sensitivity and measurement precision are improved, but device complexity increases
Solution Approach 1:
The patent changes the operating parameters of the gyroscope by dynamically adjusting the mechanical bias voltage to achieve frequency matching between drive and sense modes. By controlling the voltage parameter applied to the proof masses, the system optimizes the resonant frequency alignment, thereby improving rate resolution and measurement precision through parameter optimization rather than structural modification
Solution Approach 2:
The bias voltage control circuit serves multiple functions: it provides frequency tuning between modes, compensates for temperature drift, maintains quadrature nulling, and enables electronic bandwidth control. This multi-functional approach consolidates several control requirements into a single integrated circuit, improving precision without proportionally increasing overall device complexity
3Adaptability or versatility
If electronic bandwidth control is used, then adaptability to different applications is improved, but device complexity increases
Solution Approach 1:
The patent implements dynamic bandwidth control by allowing the mechanical bias voltage to be adjusted in real-time based on application requirements. The system can dynamically change the operating bandwidth by modifying the voltage applied to the proof masses, enabling the same gyroscope to adapt to different application scenarios such as navigation, stabilization, or high-rate maneuvering without requiring hardware changes
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 approach results in a low-cost microgyroscope with a bias drift of 0.2°/hr, two orders of magnitude better than commercial MEMS gyroscopes, and achieves the lowest recorded noise floor, making it suitable for high-precision applications.
Implementation Method 1
Vibratory micromachined gyroscopes rely on Coriolis-induced transfer of energy between two vibration modes to sense rotation
Implementation Method 2
Vibratory micromachined gyroscopes rely on Coriolis-induced transfer of energy between two vibration modes to sense rotation
Data Source
AI summary
Disclosed are methods and a sensor architecture that utilizes the residual quadrature error in a gyroscope to achieve and maintain perfect mode-matching, i.e., ˜0 Hz split between the drive and sense mode frequencies, and to electronically control sensor bandwidth. In a reduced-to-practice embodiment, a 6 mW, 3V CMOS ASIC and control algorithm are interfaced to a mode-matched MEMS tuning fork gyroscope to implement an angular rate sensor with bias drift as low as 0.15°/hr and angle random walk of 0.003°/√hr, which is the lowest recorded to date for a silicon MEMS gyroscope. The system bandwidth can be configured between 0.1 Hz and 1 kHz.