MEMS Inclinometer Vibration Rectification Error Reduction
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Solution Overview
Problem
MEMS inclinometers face challenges in accurately measuring inclination due to vibration rectification errors caused by spurious vibrations, which are not effectively filtered out due to non-zero average contributions from offset variations in electrode distances, leading to measurement inaccuracies.
Innovation Solution
The design incorporates a substrate with a first mobile mass and a first sensing unit featuring elastic elements and structures that convert out-of-plane accelerations into in-plane movements, ensuring linear dependence of capacitance variations, thereby reducing vibration rectification errors by eliminating offset-induced non-linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If spurious vibrations occur during operation, then the mobile mass oscillates about the resting position, but vibration rectification error occurs due to non-linear capacitance variation
Solution Approach 1:
The patent changes the geometric parameters of the elastic structures, specifically configuring them with main axes of inertia transverse to the movement direction. This parameter change ensures that capacitance varies linearly with displacement, which eliminates vibration rectification error while maintaining robustness against vibrations.
2Adaptability or versatility
If the mobile mass is made free to rotate about a central pin to measure inclination, then inclination measurement is enabled, but vibration rectification error arises from non-linear capacitance difference
Solution Approach 1:
The patent modifies the geometric parameters of the elastic structures supporting the mobile mass. By configuring the elastic structures with specific orientations (main axes of inertia transverse to the movement direction), the patent achieves linear capacitance variation with displacement, thereby eliminating vibration rectification error while preserving inclination measurement capability.
3Measurement precision
If offset variations in electrode distances are present, then the capacitance measurement includes non-zero average contributions, but this leads to inability to filter out vibrations effectively
Solution Approach 1:
The patent changes the geometric parameters of the elastic structures to ensure that capacitance varies linearly with displacement. This parameter change eliminates offset-induced non-linearity, allowing vibration signals to have zero average contribution and can be effectively filtered out, while maintaining measurement sensitivity.
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 approach effectively reduces vibration rectification errors by ensuring linear capacitance variation with displacement, enhancing measurement accuracy and sensitivity while maintaining robustness against external stimuli.
Implementation Method 1
a plurality of elastic elements, each of which is mechanically interposed between the second mobile mass and the substrate and is compliant in a direction parallel to a first axis
Implementation Method 2
at least one first mobile electrode that is fixed with respect to the second mobile mass and configured to form a first variable capacitor with the first fixed electrode
Data Source
AI summary
A MEMS inclinometer includes a substrate, a first mobile mass and a sensing unit. The sensing unit includes a second mobile mass, a number of elastic elements, which are interposed between the second mobile mass and the substrate and are compliant in a direction parallel to a first axis, and a number of elastic structures, each of which is interposed between the first and second mobile masses and is compliant in a direction parallel to the first axis and to a second axis. The sensing unit further includes a fixed electrode that is fixed with respect to the substrate and a mobile electrode fixed with respect to the second mobile mass, which form a variable capacitor.