Two-Mass Three-Axis Accelerometer with Differential Vibration Rejection
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Solution Overview
Problem
Existing MEMS accelerometers that measure acceleration in three orthogonal directions face challenges with single proof masses being sensitive to external vibrations and requiring significant surface area, while multi-proof mass designs are costly and inefficient.
Innovation Solution
A two-mass, three-axis accelerometer design where the proof masses rotate in opposite directions in response to accelerations in different directions, utilizing suspension and coupling structures to cancel the effect of external vibrations through differential measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a single proof mass is allowed to move in three directions, then the surface area is minimized, but the measurement becomes sensitive to vibrations which should be excluded
Solution Approach 1:
The single proof mass is divided into two separate proof masses (first proof mass and second proof mass). Each proof mass is suspended independently to allow movement in specific directions, enabling the system to maintain compact surface area while reducing vibration sensitivity through differential measurement of the two masses
Solution Approach 2:
The patent converts the harmful effect of vibrations into a beneficial differential measurement capability. By having two proof masses that can rotate in opposite directions, the system uses the vibration-induced movements of both masses to cancel out external vibration effects through differential measurement, while still accurately measuring acceleration in three orthogonal directions
2Measurement precision
If three separate proof masses are used for three measurement axes, then measurement precision is improved, but the surface area and cost increase significantly
Solution Approach 1:
The two proof masses are designed to serve multiple measurement functions simultaneously. The first proof mass measures acceleration components while the second proof mass measures other acceleration components, allowing the system to achieve three-axis measurement capability with only two masses rather than three separate dedicated masses
Solution Approach 2:
The patent merges the functions of three separate proof masses into two interconnected proof masses. The first and second proof masses are coupled through a common suspension structure that allows them to move in coordinated ways, enabling the system to measure acceleration in three orthogonal directions using fewer proof masses and thus reducing surface area
3Device complexity
If a single proof mass is used for three-axis measurement, then device complexity is reduced, but robustness against vibrations deteriorates
Solution Approach 1:
The single proof mass is segmented into two separate proof masses with independent suspensions. This segmentation allows each mass to be optimized for specific measurement directions while the combined system provides robustness against vibrations through differential measurement, achieving both reduced complexity compared to three masses and improved reliability
Solution Approach 2:
The system uses differential measurement of the two proof masses to create a feedback mechanism that cancels out vibration effects. The movements of the two masses in opposite directions provide a feedback signal that compensates for external vibrations, enhancing the robustness of the acceleration measurements without requiring complex active vibration cancellation systems
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 effectively reduces sensitivity to external vibrations and minimizes surface area requirements, achieving accurate acceleration measurements in multiple directions with improved robustness and efficiency.
Implementation Method 1
A MEMS accelerometer typically comprises a proof mass which is suspended from a fixed structure by flexible elements so that the proof mass is partly mobile. When the accelerometer undergoes acceleration, the proof mass moves in relation to the fixed structure. By measuring the resulting displacement of the proof mass, the magnitude of the acceleration can be determined.
Implementation Method 2
The first and second proof masses are suspended from a fixed structure by flexible elements which allow relative movement along the measurement axis but resists relative movement in directions which are perpendicular to the measurement axis.
Data Source
Figure 1a~1b
Figure 1c~1d
Figure 1e~1f
AI summary
An accelerometer comprising a first proof mass and a second proof mass which are coupled to each other with a coupling structure which extends from the first proof mass to the second proof mass. The coupling structure synchronizes the movement of the first and second proof masses so that the first and second proof masses may be linearly displaced from their rest position in the x-direction, rotationally displaced in opposite in-plane directions and rotationally displaced in opposite out-of-plane directions.