Inertial Sensor Spring Structure for Quadrature Noise Suppression
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Solution Overview
Problem
Existing angular velocity sensors using the deep groove etching technique often form oblique through-holes, leading to a shift in the cross-sectional shape of the vibration amplification portion, causing unnecessary vibration of the movable detection electrode in the Z-axis direction, which results in deteriorated detection characteristics due to quadrature noise.
Innovation Solution
The inertial sensor design includes a substrate with a concave portion and a lid, featuring detection springs with thin portions thinner than the detection movable bodies, which are configured to suppress quadrature vibrations by reducing the vibration component in the Z-axis direction, thereby stabilizing the attitude of the movable detection electrodes and improving detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the deep groove etching technique is used to form through-holes, then the verticality of groove side surfaces and aspect ratio are improved, but the through-holes may be formed obliquely causing the cross-sectional shape of the vibration amplification portion to shift from a rectangle
Solution Approach 1:
The patent introduces a thickness parameter control mechanism where the detection spring's thickness is varied along its length. Specifically, the thickness decreases from the base toward the free end, creating a thickness gradient. This parameter change allows the spring to compensate for the oblique through-hole formation by adjusting its structural characteristics to maintain proper vibration characteristics despite the shape deviation.
Solution Approach 2:
The patent makes the detection spring dynamic by introducing a thickness gradient that allows different portions of the spring to flex at different rates. This dynamic structure enables the spring to adapt to the oblique through-hole formation while maintaining its function of supporting the movable detection electrode and allowing controlled vibration in the X-axis direction.
2Adaptability or versatility
If the cross-sectional shape of the vibration amplification portion shifts from a rectangle, then the movable detection electrode vibrates in both Y-axis and Z-axis directions, but the detection characteristics of angular velocity are deteriorated due to quadrature noise
Solution Approach 1:
The patent applies local quality by creating a thickness gradient in the detection spring where different portions have different thicknesses. The base portion has greater thickness for structural support, while the free end has reduced thickness to minimize Z-axis vibration. This local variation in thickness allows the spring to support the movable detection electrode while suppressing quadrature vibrations in the Z-axis direction, thereby improving angular velocity detection 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
This configuration effectively suppresses quadrature noise, enhancing the detection accuracy of angular velocity by ensuring the movable detection electrodes vibrate primarily in the X-axis direction, reducing unwanted Z-axis vibrations and improving the overall detection precision.
Implementation Method 1
a first detection spring that supports the first detection movable body to be displaceable in the direction along the X-axis
Implementation Method 2
when an angular velocity around the X-axis is applied, the movable detection electrode vibrates in the Z-axis direction (this vibration mode is referred to as a 'detection vibration mode') by the Coriolis force
Implementation Method 3
an electrostatic attraction force is generated between the movable drive electrode and the fixed drive electrode to vibrate the movable detection electrode together with the movable drive electrode in the Y-axis direction
Data Source
AI summary
An inertial sensor includes a substrate, a first detection movable body and a second detection movable body which overlap the substrate in a direction along the Z-axis and are disposed side by side in a direction along the X-axis, a first detection spring that supports the first detection movable body to be displaceable in the direction along the X-axis, a second detection spring that supports the second detection movable body to be displaceable in the direction along the X-axis, a first drive portion that drives the first detection movable body with a drive component in the direction along the X-axis, a second drive portion that drives the second detection movable body with the drive component in the direction along the X-axis, and a first and second fixed detection electrodes disposed on the substrate and facing the first and second detection movable bodies. The first and second detection springs are provided with a first thin portion thinner than a thickness of the first and second detection movable bodies in the direction along the Z-axis.