Variable Time Constant Filter for Gyroscope Control Loops
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Solution Overview
Problem
High performance Coriolis gyroscope sensors with vibrating structures, such as MEMS, face challenges due to variable Q-factors and temperature variations, leading to inconsistent frequency responses, particularly at low frequencies, which are problematic for high performance and dynamic systems.
Innovation Solution
A method using an electronic control system with a filter having a variable time constant, which adapts to the estimated characteristics of the vibrating structure, such as frequency, Q-factor, or temperature, to optimize the time constant and enhance the measurement of rotation rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed time constant filter is used in the control loop, then the device complexity is reduced, but the measurement precision deteriorates due to low frequency gain variations
Solution Approach 1:
The patent applies the dynamics principle by making the filter time constant variable rather than fixed. The time constant is dynamically adjusted based on the measured Q-factor of the vibrating structure, allowing the filter to adapt to changing system characteristics and maintain consistent low frequency gain response across different operating conditions.
Solution Approach 2:
The patent implements feedback by continuously measuring the Q-factor of the vibrating structure and using this information to adjust the filter time constant. This closed-loop approach ensures that the filter remains optimized for the current system state, preventing low frequency gain variations while maintaining measurement precision.
2Adaptability or versatility
If the Q-factor of the vibrating structure varies due to manufacturing tolerances and temperature, then the adaptability of the system to different conditions is improved, but the frequency response consistency deteriorates
Solution Approach 1:
The system uses feedback by measuring the actual Q-factor and using this information to adjust the filter time constant, thereby maintaining consistent frequency response despite Q-factor variations from manufacturing tolerances or temperature changes.
Solution Approach 2:
The patent applies parameter changes by adjusting the filter time constant based on the measured Q-factor. This dynamic parameter adjustment compensates for Q-factor variations and maintains consistent frequency response characteristics across different operating conditions.
3Adaptability or versatility
If pole-zero cancellation is used to shape the frequency response, then the frequency response shaping capability is improved, but the measurement precision at low frequencies deteriorates due to inconsistent responses
Solution Approach 1:
The patent replaces the mechanical pole-zero cancellation approach with an electronic filtering solution. By using a filter with a time constant adjusted based on the measured Q-factor, the system achieves frequency response shaping without the low frequency inconsistencies associated with pole-zero cancellation.
Data Source
AI summary
There is provided a method of sensing a rotation rate using a vibrating structure gyroscope, said gyroscope comprising an electronic control system comprising one or more control loops, wherein at least one of said control loops comprises a filter having a variable time constant, said method comprising the steps of: determining or estimating a characteristic of the vibrating structure of said gyroscope; and adapting or varying said time constant of said filter with the determined or estimated characteristic of said vibrating structure.