Physical Quantity Sensor Gravity Center Alignment
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Solution Overview
Problem
Existing physical quantity sensors, such as those disclosed in JP-A-2021-032819, face issues with increased sensitivity in directions other than the intended detection axis, leading to inaccurate detection of physical quantities due to the thickness differences in movable electrodes and support beams, which results in detection of unnecessary accelerations and reduced accuracy.
Innovation Solution
The physical quantity sensor design includes a movable body with a support beam acting as a torsion spring, where the thicknesses of the first and second movable electrode groups are equal to the support beam's thickness, ensuring the gravity center positions of the movable body and support beam are aligned, reducing sensitivity in other axial directions and maintaining the signal-to-noise ratio by equalizing the heights of the rotation axis and gravity center positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the thickness of movable electrodes is made different from the support beam thickness, then the manufacturing process is simplified, but the sensitivity in other axial directions increases and detection accuracy deteriorates
Solution Approach 1:
The patent changes the thickness parameter of movable electrodes to be equal to the support beam thickness. This parameter modification ensures that the gravity center of the movable body aligns with the rotation axis, thereby eliminating unnecessary sensitivity in other axial directions while maintaining manufacturing feasibility through standard fabrication processes.
2Device complexity
If the gravity center of the movable body is misaligned with the rotation axis, then the structure becomes simpler, but sensitivity in other axial directions increases causing inaccurate detection
Solution Approach 1:
The patent introduces asymmetric mass distribution by adding a mass portion to the movable body. This asymmetric structure is specifically designed to balance the gravity center with the rotation axis, thereby eliminating parasitic sensitivity in directions other than the intended detection axis while maintaining overall structural simplicity.
3Device complexity
If the movable body structure is simplified without mass portion, then the device complexity is reduced, but the signal-to-noise ratio deteriorates due to increased sensitivity in other directions
Solution Approach 1:
The patent introduces a mass portion as a counterweight element in the movable body. This mass portion serves as a gravitational counterbalance that aligns the gravity center with the rotation axis, thereby suppressing unwanted sensitivity in other axial directions and improving the signal-to-noise ratio for the intended detection direction.
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 enhances the accuracy of physical quantity detection by minimizing sensitivity in other axial directions and maintaining the signal-to-noise ratio, allowing for precise detection of accelerations in the intended direction while preventing unnecessary axis detection.
Implementation Method 1
a support beam having one end coupled to the fixed portion and provided along the second direction; a movable body coupled to the other end of the support beam
Implementation Method 2
a first fixed electrode group provided at the substrate and disposed in the first direction of the support beam; and a second fixed electrode group provided at the substrate and disposed in a fourth direction opposite to the first direction of the support beam
Data Source
AI summary
A physical quantity sensor includes a fixed portion, a support beam, a movable body, a first fixed electrode group, and a second fixed electrode group. The support beam has one end coupled to the fixed portion and is provided along a second direction. The movable body is coupled to the other end of the support beam. The first fixed electrode group and the second fixed electrode group are provided at a substrate. The movable body includes a first coupling portion, a first base portion, a first movable electrode group, a second coupling portion, a second base portion, a second movable electrode group, and a mass portion. The first coupling portion is coupled to the other end of the support beam, and the first base portion is coupled to the first coupling portion. The second coupling portion is coupled to the other end of the support beam, and the second base portion is coupled to the second coupling portion.