MEMS Gyroscope Shuttle Drive Phase Alternation
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Solution Overview
Problem
Micromachined gyroscopes face challenges in reducing null bias errors and increasing sensitivity, which are sensitive to manufacturing variations, temperature, and packaging issues, requiring costly calibration processes and additional structural and electronic components.
Innovation Solution
The implementation of novel shuttle drive and Coriolis sense techniques that alternate between phase and anti-phase drive signals, allowing for continuous or partial demodulation during equal times, and using phase-locked loops to maintain phase coherency, effectively canceling out dominant errors and eliminating the need for calibration in many applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional continuous drive signals are used to maintain shuttle oscillation, then the gyroscope can operate continuously, but null bias errors and sensitivity errors accumulate due to manufacturing variations and temperature effects
Solution Approach 1:
The patent applies periodic action by using alternating phase and anti-phase drive signals in periodic intervals. The shuttle is driven with a phase signal for a first given time period, then with a reversed-phase signal for a second given time period. This periodic switching allows the system to accumulate error compensation over cycles, reducing null bias and sensitivity errors while maintaining continuous operation.
Solution Approach 2:
The patent implements feedback by measuring the shuttle velocity signal and using it to generate drive signals that alternate between phase and anti-phase. The Coriolis accelerometer output is demodulated during equal times of both drive phases, and this feedback information is used to maintain phase coherency and compensate for manufacturing variations and temperature effects, thereby reducing measurement errors.
2Measurement precision
If calibration components and processes are added to reduce manufacturing variations, then measurement precision improves, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent applies self-service by enabling the gyroscope to automatically compensate for its own errors through the alternating phase drive technique. The system uses its own Coriolis accelerometer output and velocity signal to generate the alternating drive signals, eliminating the need for external calibration components or processes. The device self-corrects for manufacturing variations and temperature effects through the periodic phase reversal mechanism.
3Measurement precision
If the shuttle is driven at maximum amplitude to increase sensitivity, then measurement precision improves, but the system becomes more sensitive to manufacturing variations and temperature effects
Solution Approach 1:
The patent uses periodic action with alternating phase and anti-phase drive signals to maintain shuttle oscillation at optimal amplitude levels. By switching between phase and reversed-phase signals for equal time periods, the system maintains sufficient oscillation amplitude for high sensitivity while the periodic reversal compensates for manufacturing variations and temperature effects, preventing error accumulation that would occur with continuous maximum amplitude driving.
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
These techniques reduce sensitivity and null bias errors, eliminating the need for calibration and associated costs, while maintaining system stability and noise performance, thus enhancing the operational efficiency of MEMS gyroscopes.
Implementation Method 1
The oscillation is generated with a periodic force applied to a spring-mass-damper system at the resonant frequency. Operating at resonance allows the oscillation amplitude to be large relative to the force applied.
Implementation Method 2
When the gyroscope is rotated, Coriolis acceleration is generated on the oscillating proof mass in a direction orthogonal to both the driven oscillation and the rotation. The magnitude of Coriolis acceleration is proportional to both the velocity of the oscillating proof mass and the rotation rate.
Implementation Method 3
Each shuttle is typically driven by oppositely-acting sets of comb drives, where one set of comb drives is used to pull the shuttle in one direction and the other set of comb drives is used to pull the shuttle in the other direction.
Data Source
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AI summary
In comb drive vibratory gyroscopes, drive-induced Coriolis accelerometer offset is effectively canceled by demodulating the output during equal times of in-phase (+) and anti-phase (-) drive of the shuttle with respect to the velocity signal used for angular rate demodulation. This reduces or eliminates the corresponding thermal and die-stress effects otherwise needing calibration.