MEMS Out-of-Plane Motion Detection Using Segmented Rotating Masses
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Solution Overview
Problem
Current microelectromechanical devices designed for out-of-plane acceleration detection face challenges in distinguishing between out-of-plane and in-plane linear accelerations, leading to parasitic resonances that affect sensitivity and robustness, especially in vibration-rich environments.
Innovation Solution
The device structure incorporates a linear mass and two rotating masses, each elastically coupled to the support through axial springs, allowing for both rotary and linear modes of motion, which enhances sensitivity to out-of-plane accelerations while minimizing sensitivity to in-plane accelerations by balancing the center of mass and using a linear mass structure for capacitive detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single rotating mass structure is used for out-of-plane acceleration detection, then the device can detect out-of-plane accelerations, but it becomes sensitive to parasitic in-plane accelerations causing false signals
Solution Approach 1:
The device divides the rotating mass structure into two separate rotating mass parts (first and second rotating mass parts) that rotate in opposite directions. Each rotating mass part is coupled to the support through its own axial spring structure. This segmentation allows the system to detect out-of-plane accelerations while the opposing rotation directions cancel out parasitic signals from in-plane accelerations.
Solution Approach 2:
The two rotating mass parts function as counterweights to each other, with their centers of mass positioned to balance the overall center of mass of the device structure. When in-plane accelerations occur, the opposing rotational responses of the two mass parts cancel each other out, eliminating parasitic signals while maintaining sensitivity to out-of-plane accelerations.
2Reliability
If the center of mass is positioned to eliminate parasitic resonances, then robustness against in-plane accelerations improves, but detection signal level decreases
Solution Approach 1:
The patent introduces a linear mass structure that moves in the out-of-plane direction, adding a linear motion dimension to the traditional rotational motion. The linear mass is coupled to both rotating mass parts through axial spring structures, creating a coupled rotational-linear motion system. This dimensional addition increases the detection signal level while the balanced center of mass position maintains robustness against parasitic accelerations.
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 significantly increases the detection signal level and robustness against parasitic in-plane accelerations, providing improved accuracy and resistance to vibrations, making it suitable for demanding applications like automotive sensors.
Implementation Method 1
two rotating mass parts, each elastically coupled to the support through an axial spring structure
Implementation Method 2
displacements of these masses relative to fixed electrodes
Data Source
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AI summary
The disclosure relates to a microelectromechanical device where the device structure (102) includes a rotating mass structure (206) and a linear mass structure (208). The rotating mass structure (206) is formed of two rotating mass parts elastically coupled to the support (100) through one or more springs (214, 216) that enable rotary motion of each of the rotating mass parts (210, 212) about respective rotary axes (218, 220) that extend parallel to each other along a first in-plane direction (IP1). The linear mass structure (208) includes at least one elongate rigid body (230) that extends in a second in-plane direction (IP2). Each end of the linear mass structure (208) is coupled to the first and second rotating mass parts (210, 212), respectively, such that rotary motions of the first and second masses (210, 212) result into linear motion of the linear mass structure (208) in the out-of-plane direction (OP).