MEMS Accelerometer Side Arm Spring Structure for Vibration Isolation
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Solution Overview
Problem
MEMS acceleration sensors face challenges in distinguishing desired signals from error signals due to unwanted vibrations and parasitic resonance modes, which can cause instability and multi-modality, especially when seismic masses vibrate in unintended directions.
Innovation Solution
The introduction of a side arm and shoulder means structure that increases the distance between the seismic mass and the axis of rotation, effectively stiffening the spring structure to isolate unwanted vibrations and enhance the separation of parasitic resonance modes from the signal-generating modes, thereby improving signal clarity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the seismic mass is connected to the anchor by springs in a conventional configuration, then the structure is simple and easy to manufacture, but the seismic mass vibrates in multiple directions causing unwanted parasitic resonance modes and multi-modality
Solution Approach 1:
The patent introduces side arms that extend the spring structure perpendicular to the primary oscillation plane, adding a dimensional element that increases the moment of inertia about axes perpendicular to the oscillation plane. This dimensional extension suppresses unwanted vibrations in Y and Z directions while maintaining simple manufacturing processes.
2Reliability
If the distance between the seismic mass and the axis of rotation is increased, then the moment of inertia increases and parasitic resonance modes are suppressed, but the spring structure becomes more complex
Solution Approach 1:
The spring structure is segmented into multiple components: the original spring, side arms extending from the spring ends, and shoulder means connecting the side arms to the seismic mass. This segmentation allows the distance between the seismic mass and rotation axis to be increased through geometric arrangement rather than simply extending a single spring, thereby reducing parasitic resonance while managing structural complexity.
3Volume of moving object
If conventional spring mounting is used, then the device is compact, but the seismic mass surrounds the anchor causing unwanted vibrations in unintended directions
Solution Approach 1:
The side arms and shoulder means act as intermediary elements between the spring and the seismic mass. These intermediaries increase the distance between the spring anchor point and the seismic mass center, thereby increasing the moment of inertia and suppressing parasitic resonance modes, while still maintaining a relatively compact overall device volume.
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 reduces unwanted vibrations and enhances the clarity of the desired signal by increasing the moment of inertia and resonance frequency, leading to more stable and accurate measurements.
Implementation Method 1
springs (101, 102) that support the seismic mass to an anchor (103)
Implementation Method 2
output signals are generated from the changing capacitances between the moving electrodes and the static electrodes
Data Source
Figure 1~2
Figure 3A~4
Figure 5
AI summary
A MEMS structure comprises an anchor (1), a spring (2), and a seismic mass (3) that is suspended to the anchor (1) via the spring to pivot around an axis of rotation. Errors from unwanted vibration modes are reduced by including in the MEMS structure a spring structure (2,4,6) that extends from the seismic mass (3) to the anchor(1). Said spring structure (2,4,6) comprises a side arm (4) that is connected to the seismic mass (3) or the anchor (1). At least part of the spring structure (2,4,6) is formed by a side arm (4) that extends in the spring structure in a direction parallel to the axis of rotation of the seismic mass; and is attached to one end of the spring (2).