Interlocking Proof Mass Tabs for MEMS Inertial Sensing
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Solution Overview
Problem
Existing MEMS inertial sensing devices face challenges in accurately limiting the motion of large proof masses under large inertial forces, as external elements like bump stops are difficult to manufacture and fragile flexures can fail when high sensitivity is required.
Innovation Solution
The integration of interlocking tabs and corresponding recesses around the periphery of the proof mass, which interact with the frame to limit motion, allowing for high sensitivity in low inertial force environments while protecting the device from high inertial forces, and are fabricated as part of the MEMS process rather than during packaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external elements like bump stops are used to limit motion of large proof mass, then motion limitation is achieved, but manufacturing difficulty increases due to difficult spacing control
Solution Approach 1:
The patent merges the motion limitation function into the proof mass structure itself by integrating interlocking tabs directly onto the proof mass. This eliminates the need for separate external bump stops and their associated spacing control issues, as the tabs are fabricated as part of the proof mass in the same MEMS process.
Solution Approach 2:
The interlocking tabs are formed during the MEMS fabrication process before final assembly, establishing precise geometric relationships between the proof mass and frame components. This preliminary formation of limiting features eliminates post-fabrication spacing adjustment requirements.
2Force
If fragile flexures are used to tether the proof mass, then restoring force is provided for small proof masses, but reliability decreases when large proof masses are employed
Solution Approach 1:
The patent segments the motion limitation function from the restoring force function. The interlocking tabs provide motion limitation without relying on fragile flexures, while the flexures can be optimized solely for providing restoring force. This segmentation allows each component to be designed for its specific function without compromise.
Solution Approach 2:
The interlocking tabs act as pre-positioned mechanical stops that prevent excessive motion before the fragile flexures can fail. By providing this protective limitation in advance, the system prevents situations where flexures would be subjected to loads beyond their承受能力.
3Measurement precision
If large proof mass is used to achieve high sensitivity, then sensitivity in low inertial force environments improves, but motion control difficulty increases under large inertial forces
Solution Approach 1:
The patent implements a dynamic motion control system where the interlocking tabs engage only when necessary (under large inertial forces) while allowing full range of motion during normal operation. This dynamic engagement maintains high sensitivity for small signals while providing protection when needed.
Data Source
AI summary
A microelectromechanical systems (MEMS) inertial sensing device having a large proof mass with interlocking tabs is disclosed. The interlocking tabs limit motion of the proof mass when subjected to large inertial forces. The interlocking tabs are formed around the periphery of the proof mass and interact with corresponding interlocking tabs formed in a frame to which the proof mass is tethered. The motion of the proof mass is limited by the interlocking tabs, which are formed during MEMS fabrication of the inertial sensing device rather than as part of the packaging process. With a large proof mass, the inertial sensing device can provide high sensitivity in low inertial force environments while the interlocking tabs protect the device when subjected to high inertial forces.