Micromachined Inertial Sensor Offset Detection and Compensation
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Solution Overview
Problem
Micromachined inertial sensors, such as gyroscopes, face challenges in reducing offset errors due to manufacturing variations, temperature changes, and other environmental factors, which affect their accuracy and reliability.
Innovation Solution
The method involves modulating the drive signal using techniques like amplitude modulation, frequency modulation, or spread spectrum modulation to detect and cancel in-phase and quadrature errors, and using compensating electrodes to mitigate errors caused by drive imperfections and aerodynamic effects, without disturbing the Coriolis acceleration signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If resonant amplification is increased to magnify Coriolis signals, then signal size increases and electronics requirements are eased, but accelerometer phase shift becomes more sensitive to frequency perturbations
Solution Approach 1:
The patent implements a feedback mechanism where the accelerometer frequency is tightly servoed to the shuttle frequency. The system continuously monitors the phase relationship between the accelerometer and shuttle, and adjusts the accelerometer frequency to maintain optimal alignment, thereby compensating for frequency perturbations and reducing phase shift sensitivity
Solution Approach 2:
The patent utilizes the mechanism for controlling the frequency of a differential capacitance accelerometer by changing the applied common mode voltage. This allows dynamic adjustment of the accelerometer frequency to match the shuttle frequency, optimizing the resonant amplification while maintaining phase stability
2Measurement precision
If offset error reduction techniques are implemented, then gyroscope accuracy improves, but device complexity increases due to additional sensing and control mechanisms
Solution Approach 1:
The patent employs a single accelerometer structure that serves multiple functions: it senses Coriolis acceleration for rotation rate measurement and simultaneously detects offset errors through modulation techniques. The same sensor element is used for both primary measurement and error detection, reducing the need for additional dedicated error sensing components
Solution Approach 2:
The patent uses periodic modulation of the drive signal at a specific frequency to induce and detect offset errors. By modulating the drive signal and analyzing the accelerometer response at the modulation frequency, the system can distinguish offset errors from Coriolis signals, enabling error reduction without requiring separate continuous error sensing mechanisms
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 effectively reduces offset errors, improving the accuracy and reliability of micromachined inertial sensors by measuring and canceling error sources in real-time, thereby enhancing their performance and stability across varying conditions.
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.
Implementation Method 3
The resulting Coriolis acceleration can be measured by sensing the deflections of the proof mass. The electrical and mechanical structures used to sense such deflections of the proof mass are referred to generally as the accelerometer.
Data Source
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AI summary
Error sources relating to the drive signal applied to the resonator of an inertial sensor, such as in-phase offset errors relating to the drive signal and/or electronic pass-through of the drive signal to accelerometer sense electronics, are detected by modulating the drive signal and sensing accelerometer signals that are induced by the modulated drive signal. Error sources related to aerodynamics of an inertial sensor resonator are detected by modulating the distance between the resonator and the underlying substrate and sensing accelerometer signals that are induced by such modulation. Compensating signals may be provided to substantially cancel errors caused by such error sources.