Asymmetric MEMS Accelerometer Proof Mass Shock Distribution
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Solution Overview
Problem
MEMS accelerometers are prone to damage and measurement errors due to undesired external forces, such as shocks, which can cause proof masses to contact fixed surfaces, leading to wear and accuracy issues, and vibration rectification errors that are difficult to compensate for during operation.
Innovation Solution
A micromechanical MEMS accelerometer design featuring symmetric and asymmetric proof mass portions that rotate collectively about a rotational axis, coupled by springs to anchors, with bump stops to prevent over-travel and distribute shock forces, reducing the likelihood of damage and measurement errors by rotating proof masses to distribute force and reduce stiction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If proof masses are located in close proximity to fixed surfaces for compact design, then device size is reduced, but proof masses are more susceptible to contact with fixed surfaces causing wear or damage from undesired external forces
Solution Approach 1:
The proof mass is designed with asymmetric geometry featuring a first portion and a second portion of different sizes. The smaller first portion is positioned closer to fixed surfaces while the larger second portion extends away from them. This asymmetric configuration allows the proof mass to rotate about a rotational axis during shock events, causing the smaller portion to contact fixed surfaces first and distribute impact forces, thereby protecting the larger portion and maintaining reliability while maintaining compact device volume.
2Volume of moving object
If proof masses are positioned close to fixed surfaces for compact design, then device volume is reduced, but measurement precision deteriorates due to vibration rectification errors that are difficult to compensate for during operation
Solution Approach 1:
The asymmetric proof mass configuration with distinct first and second portions creates a rotational mechanism that mitigates vibration rectification errors. During operation, the asymmetric geometry causes the proof mass to rotate in response to undesired vibrations, distributing the vibrational energy and preventing the accumulation of measurement errors that would occur with symmetric designs, thereby maintaining measurement precision in a compact device volume.
Solution Approach 2:
The proof mass is designed to be rotatable about a rotational axis, transforming the proof mass from a static element to a dynamic one. This rotational degree of freedom allows the proof mass to adapt to undesired vibrations and shocks by rotating to distribute forces, thereby reducing vibration rectification errors and improving measurement precision while maintaining compact dimensions.
3Ease of manufacture
If symmetric proof mass design is used, then manufacturing is simplified, but shock forces are not effectively distributed causing increased risk of damage from undesired external forces
Solution Approach 1:
The proof mass employs asymmetric design with a larger second portion and smaller first portion positioned at different distances from fixed surfaces. This asymmetric configuration creates an effective shock distribution mechanism where, during impact events, the smaller portion contacts fixed surfaces first and rotates the proof mass to distribute shock forces across multiple contact points and the larger portion, thereby enhancing structural strength while remaining manufacturable using standard semiconductor fabrication processes.
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
The design enhances the durability and accuracy of MEMS accelerometers by distributing shock forces and reducing stiction, thereby minimizing damage from undesired forces and vibration rectification errors, while maintaining measurement precision.
Implementation Method 1
One or more springs within the MEMS device layer couple the proof mass to the one or more anchors, wherein the one or more springs couple the proof mass to the one or more anchors such that the proof mass rotates about the rotational axis in response to the linear acceleration along the sense axis
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
A microelectromechanical (MEMS) accelerometer senses linear acceleration perpendicular to a MEMS device plane of the MEMS accelerometer based on a rotation of a proof mass out-of-plane about a rotational axis. A symmetry axis is perpendicular to the rotational axis. The proof mass includes a symmetric portion that is symmetric about the symmetry axis and that is contiguous with an asymmetric portion that is asymmetric about the symmetry axis.