Dual Mass Inertial Sensor with Integrated Damping
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Solution Overview
Problem
MEMS accelerometers face challenges in reducing the size of sense masses while maintaining sensitivity and reliability, especially in multi-axis sensing applications, where traditional designs struggle to balance sensitivity and damping ratios effectively.
Innovation Solution
The implementation of a dual proof mass configuration with asymmetric mass distribution and integrated damping structures allows for large deformation under in-plane torsion motion, enhancing sensitivity and damping ratios without compromising device sensitivity, facilitating efficient in-plane torsion motion in three-axis accelerometers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the size of sense masses is reduced to shrink device size, then device compactness is improved, but sensitivity deteriorates
Solution Approach 1:
The patent divides a single sense mass into multiple discrete sense masses (first sense mass and second sense mass) that are distributed around the Z-axis. This segmentation allows the device to maintain compact dimensions while the collective arrangement of multiple masses provides sufficient sensitivity for acceleration sensing along X and Y axes.
Solution Approach 2:
The patent transitions from traditional single-axis or planar mass arrangements to a three-dimensional configuration where sense masses are positioned at different radial distances from the Z-axis. This dimensional arrangement enables the device to achieve both compactness and enhanced sensitivity by utilizing spatial distribution rather than simply increasing mass size.
2Volume of moving object
If the size of sense masses is reduced, then device compactness is improved, but reliability deteriorates
Solution Approach 1:
By segmenting the sensing function across multiple sense masses rather than relying on a single large mass, the patent improves reliability. The distributed configuration ensures that if one sense mass is affected by manufacturing variations or damage, the other masses continue to contribute to the sensing function, maintaining overall device reliability in a compact form factor.
Solution Approach 2:
The patent assigns different radial positions to different sense masses, creating local quality variations in the mass distribution. This allows each sense mass to be optimized for its specific position and function, improving overall system reliability while maintaining compact dimensions.
3Ease of manufacture
If traditional accelerometer configurations are used, then manufacturing simplicity is maintained, but sensitivity and damping ratio balance deteriorates
Solution Approach 1:
The patent creates a multi-functional structure where the same sense mass configuration serves multiple purposes: sensing acceleration along both X and Y axes, providing appropriate damping ratios, and maintaining compact form factor. The distributed sense masses function simultaneously for multiple sensing objectives without requiring separate structures, achieving sensitivity-damping balance while remaining manufacturable.
Solution Approach 2:
By arranging sense masses in a three-dimensional configuration around the Z-axis at different radial distances, the patent achieves superior sensitivity and damping characteristics without complicating the manufacturing process. This spatial arrangement allows a single manufacturing process to create a structure that naturally provides both sensitivity and damping functions.
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 achieves improved sensitivity and reliability in small form factors by enabling large deformation and increased damping ratios, effectively addressing the limitations of traditional MEMS accelerometers in multi-axis sensing.
Implementation Method 1
a first spring system couples the first movable element to the substrate and a second spring system couples the second movable element to the substrate. The first and second spring systems enable the first and second movable elements to move together in response to force imposed upon the first and second movable elements
Implementation Method 2
The second damping structure is operatively coupled with the first damping structure to dampen an oscillatory response of the first and second movable masses resulting from the in-plane torsion motion
Implementation Method 3
Each of the first and second movable elements has a mass that is asymmetric relative to a rotational axis... This configuration achieves improved sensitivity and reliability in small form factors by enabling large deformation and increased damping ratios
Data Source
Figure 1~2
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AI summary
An inertial sensor includes first and second movable elements suspended from a substrate and interconnected by a beam. The second movable element is positioned laterally adjacent to the first movable element, and each of the movable elements has a mass that is asymmetric relative to a rotational axis. A first spring system couples the first movable element to the substrate and a second spring system couples the second movable element to the substrate. The spring systems and the beam enable the movable elements to move together in response to force imposed upon the movable elements. In particular, the first and second movable elements can undergo in-plane torsion motion in response to force, such as acceleration, imposed in a sense direction. Additionally, damping structures may be integrated into the first and second movable elements to effectively increase a damping ratio of the device resulting from the in-plane torsion motion.