MEMS Inertial Sensor Levitation Force Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
MEMS angular rate sensors experience erroneous output signals due to a levitation force caused by comb drive systems, which can be of the same order of magnitude as the actual sense signal, making it difficult to distinguish between the levitation effect and the actual sense signal, especially when geometric imperfections lead to asymmetrical out-of-plane movement.
Innovation Solution
The design incorporates a drive system with interleaved first and second drive units arranged in alternating fashion and actuated in phase opposition to compensate for the levitation force, ensuring that at least a portion of the levitation error components cancel out, thereby suppressing the erroneous output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a comb drive system is used to actuate the drive mass, then the drive mass can be oscillated at large amplitude, but a levitation force is generated in the Z-axis that causes erroneous output signals
Solution Approach 1:
The drive system is segmented into multiple comb drive units (first comb drive unit and second comb drive unit) that are independently controllable. This segmentation allows the patent to apply different drive signals to different segments, enabling the generation of opposing levitation forces that cancel each other out while maintaining large oscillation amplitude for sensing operation.
Solution Approach 2:
The patent applies the anti-weight principle by generating counteracting levitation forces through the multiple comb drive units. The first and second comb drive units produce levitation forces in opposite directions (phase opposition) that cancel each other out, effectively neutralizing the harmful levitation effect while preserving the useful large-amplitude oscillation for Coriolis force generation.
2Measurement precision
If geometric imperfections exist in the comb drive system, then asymmetrical out-of-plane movement occurs, but this makes it difficult to distinguish between levitation effect and actual sense signal
Solution Approach 1:
The system uses itself to compensate for its own defects. By employing multiple comb drive units that generate opposing levitation forces, the system self-corrects for geometric imperfections and asymmetrical movements. The interleaved arrangement and phase-opposed actuation create a self-balancing mechanism that automatically compensates for manufacturing variations without requiring external calibration or correction.
3Object-generated harmful factors
If interleaved comb drive units are used to compensate for levitation force, then the levitation error components cancel out, but the device complexity increases
Solution Approach 1:
The patent merges multiple comb drive units into a single integrated drive system that functions as one unified actuator assembly. The first and second comb drive units are interleaved and work together as a combined system, sharing common structural elements and control mechanisms. This merging approach achieves levitation cancellation while minimizing the increase in overall device complexity compared to using completely separate drive 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
This approach effectively cancels the fundamental harmonics of the levitation force, resulting in improved accuracy and reliability of the angular rate sensor output by reducing the levitation effect's impact on the sense axis.
Implementation Method 1
a drive system configured to oscillate the drive mass along the drive axis, the drive system including interleaved first and second comb drive units actuated in phase opposition
Implementation Method 2
configured to generate a sense signal in response to rotation about the sense axis due to the influence of a Coriolis acceleration component
Data Source
AI summary
An inertial sensor (110) includes a drive system (118) configured to oscillate a drive mass (114) within a plane (24) that is substantially parallel to a surface (50) of a substrate (28). The drive system (118) includes first and second drive units (120, 122) having fixed fingers (134, 136) interleaved with movable fingers (130, 132) of the drive mass (114). At least one of the drive units (120) is located on each side (126, 128) of the drive mass (114). Likewise, at least one of the drive units (122) is located on each side (126, 128) of the drive mass (114). The drive units (122) are driven in phase opposition to the drive units (120) so that a levitation force (104) generated by the drive units (122) compensates for, or at least partially suppresses, a levitation force (100) generated by the drive units (120).