Balanced MEMS Inertial Sensor With Strain-Gauge Quadrature Reduction
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Solution Overview
Problem
Existing pitch/roll microelectromechanical systems (MEMS) gyroscopes face limitations in achieving high-performance 3-axis inertial measurement units (IMUs) due to out-of-plane constraints, sensitivity issues, quadrature effects, and alignment errors, which are not adequately addressed by current piezoresistive sensing technologies.
Innovation Solution
An inertial sensor design featuring a substrate with a sense lever and multiple frames connected by elastic means, ensuring a translational motion of the sense frames with controlled tilts, enhanced coupling, and efficient quadrature compensation through balanced mechanical design and strain gauge placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If pitch/roll MEMS gyroscopes are designed with classical MEMS processes, then manufacturing is simplified, but sensitivity is reduced due to limited out-of-plane displacement and fixed gap constraints
Solution Approach 1:
The device is segmented into multiple functional layers: a substrate, a suspended structure with proof mass, and fixed electrodes. The suspended structure is further divided into drive and sense components that can move independently, allowing optimized displacement for sensitivity while maintaining standard MEMS fabrication processes for each layer.
Solution Approach 2:
The invention transitions from planar in-plane motion to out-of-plane motion by suspending the proof mass structure above the substrate. This vertical dimension enables larger displacement amplitudes for both drive and sense modes, significantly improving sensitivity while still using standard MEMS processes like sacrificial layer release.
2Measurement precision
If torsional sensing modes are used in pitch/roll gyroscopes, then sensitivity can be improved, but quadrature effects increase due to changing gap of quadrature electrodes
Solution Approach 1:
The invention uses quadrature electrodes that generate quadrature forces, but these same forces are harnessed to restore the proof mass to its neutral position after displacement. The quadrature effect is converted from a harmful artifact into a useful restoring mechanism that improves measurement accuracy.
Solution Approach 2:
The gap between quadrature electrodes is carefully controlled and maintained constant throughout the sensing range, unlike varying gap designs. This parameter control ensures that quadrature forces remain predictable and can be effectively used for restoration without introducing measurement errors.
3Adaptability or versatility
If three yaw devices are aligned to create a 3-axis MEMS IMU, then yaw measurement coverage is achieved, but device complexity and package size increase
Solution Approach 1:
The invention merges pitch/roll sensing capability into a single device by incorporating a suspended proof mass that can detect lateral accelerations. This eliminates the need for separate yaw devices, reducing the 3-axis IMU to a more compact configuration while maintaining full measurement coverage through the coupled motion detection of the suspended structure.
4Measurement precision
If the distribution of masses and anchor points is optimized for sensitivity, then measurement precision improves, but quadrature effects are enhanced
Solution Approach 1:
The proof mass distribution and anchor point locations are locally optimized: masses are concentrated at strategic positions to maximize sensitivity to lateral accelerations, while anchor points are positioned to provide symmetric support. This local optimization achieves high sensitivity without creating unbalanced quadrature forces that would degrade measurement accuracy.
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 design achieves improved sensitivity, reduced quadrature effects, and better alignment between pitch/roll and yaw devices, enabling smaller packages and meeting navigation-grade specifications for 3-axis MEMS IMUs.
Implementation Method 1
a sensing system connected to the sense lever and comprising at least one strain gauge mechanically stressed by the sense lever when said sense lever is rotating around the rotation axis
Implementation Method 2
first sense-to-drive elastic means comprising at least one first sense-to-drive spring
Implementation Method 3
an excitation device configured to force the first drive frame and the second drive frame into opposite motions going along the drive excitation direction
Data Source
Figure 1
Figure 2A
Figure 2B~2C
AI summary
The invention relates to an inertial sensor (1) comprising a substrate (2), sense frames (210, 220), drive frames (110, 120) configured to put into motion the sense frames, and a sense lever (300) pivotably mounted around a rotation axis (7). The sense frames, drive frames and sense lever are connected to each other by elastically means in such a way that when the inertial sensor is subjected to a rotational movement around the rotation axis, the first sense frame, the second sense frame and the sense lever respectively feature a first tilt θ1 a second tilt θ2 and a lever tilt θS relatively to the device plane, and both θ1/θS and θ2/θS are lower than 0.1. The inertial sensor features strain gauges that get stressed when the lever rotates due to the motion of the sense frames.