Four-Mass MEMS Gyroscope Radial Drive for Bias Error Reduction
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Solution Overview
Problem
MEMS vibratory gyroscopes face significant non-compensatable bias errors due to mechanical coupling with the substrate, which are exacerbated by factors like hysteresis, stress relaxation, and non-repeatable thermal variations, leading to inaccuracies in rotation rate measurements.
Innovation Solution
A four-mass vibrating MEMS structure is designed with proof masses arranged symmetrically around the center, driven radially at a specific frequency, ensuring linear drive mode motion and minimizing substrate vibrations, thereby reducing bias errors through symmetrical flexures and constant gaps between comb fingers, which enhances sensitivity and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional two-mass MEMS sensors are used, then the device complexity is lower, but the measurement precision deteriorates due to substantial non-compensatable bias error
Solution Approach 1:
The sensor is divided into four separate proof masses instead of using a traditional two-mass configuration. Each proof mass is driven independently along radial lines, allowing the system to cancel out substrate coupling effects through symmetric drive patterns while maintaining relatively simple individual mass structures
Solution Approach 2:
The four proof masses are positioned asymmetrically at 90-degree intervals around the center, with each mass oriented to drive along radial lines. This asymmetric arrangement creates symmetric drive patterns that cancel substrate forces and moments, reducing bias errors while maintaining structural simplicity
2Measurement precision
If proof masses are driven along radial lines with symmetrical flexures, then the measurement precision improves by reducing substrate vibrations, but the manufacturing precision requirements increase
Solution Approach 1:
Each proof mass is equipped with dedicated drive combs and sense combs positioned at specific locations to create constant gaps during operation. The flexures are designed with specific geometric features that maintain constant spacing between opposing masses, ensuring uniform drive patterns and reducing sensitivity to fabrication variations
Solution Approach 2:
The drive frequency is selected to be different from the sense mode resonant frequency, creating a frequency separation that reduces coupling between drive and sense modes. This parameter change allows the system to operate effectively without requiring extremely tight frequency matching, relaxing manufacturing precision requirements
3Object-affected harmful factors
If four proof masses are driven at different phases, then the sensitivity to substrate vibrations is reduced, but the device complexity increases
Solution Approach 1:
The four proof masses are driven with periodic sinusoidal signals at the same drive frequency, with adjacent masses driven 180 degrees out of phase. This periodic drive pattern creates symmetric motion that cancels substrate forces and moments, reducing sensitivity to substrate vibrations while maintaining relatively simple control logic
Solution Approach 2:
Opposing proof masses are driven in opposite phases, creating counterbalancing forces that cancel out net forces and moments on the substrate. This counterweight approach eliminates the need for complex active compensation mechanisms, reducing control complexity while effectively reducing substrate vibration sensitivity
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 solution significantly reduces sensitivity to substrate vibrations, achieving high precision and accuracy in rotation rate measurements by minimizing net forces and moments on the substrate, resulting in improved fabrication yield and reduced need for closed-loop control.
Implementation Method 1
at least one substrate having one or more drive electrodes for driving the four proof masses along the radial lines at a drive frequency
Implementation Method 2
A velocity induced by driving the proof masses along the first resonant mode (drive mode) produces a Coriolis force on the second mode (sense mode) when the substrate is rotated
Implementation Method 3
MEMS vibratory sensors may consist of one or more proof masses connected to a substrate through flexible suspensions (flexures)
Data Source
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AI summary
Systems and methods for a four-mass vibrating mems structure are provided. In certain implementations, a MEMS sensor (100, 200, 300) includes four proof masses (102, 202, 302), wherein each proof mass is driven such that the proof masses oscillate along radial lines extending from the center of the MEMS sensor through the center of the respective proof mass, each proof mass comprising a plurality of drive combs (412); and a plurality of sense combs (408). In further embodiments, the MEMS sensor includes at least one substrate (504, 506) having one or more drive electrodes for driving the four proof masses along the radial lines at a drive frequency, wherein a resonant frequency of a sense mode is different from the drive frequency.