Cross-Hatch Vibratory Gyroscope Resonator Design
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Solution Overview
Problem
Micromachined gyroscopes are sensitive to manufacturing variations, packaging errors, linear acceleration, and temperature, which affect their performance and accuracy in measuring angular rates.
Innovation Solution
A gyroscope design featuring a resonator with four beams in a cross-hatch configuration, driven into specific flexural modes to sense rotations, with compensation signals from variable-overlap trim electrodes to mitigate modal coupling and improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional MEMS gyroscope uses discrete masses and spring-mass-damper systems, then the basic angular rate sensing function is achieved, but the device becomes sensitive to manufacturing variations, packaging errors, and environmental factors
Solution Approach 1:
The resonator is divided into multiple beams (first set and second set) arranged in a cross-hatch configuration, with each beam contributing to the overall sensing function. This segmentation allows for distributed sensing that reduces sensitivity to local manufacturing variations and packaging errors affecting any single beam.
Solution Approach 2:
The patent combines drive and sense functions into a single integrated resonator structure. The same cross-hatch resonator performs both driving (through flexural modes of the first set of beams) and sensing (through deflections of the beams), eliminating the need for separate proof mass and accelerometer components, thereby reducing sensitivity to packaging errors and improving reliability.
2Device complexity
If the gyroscope uses a simple resonator structure, then the device complexity is reduced, but the accuracy and robustness against manufacturing errors and environmental factors deteriorates
Solution Approach 1:
The cross-hatch resonator employs asymmetric beam arrangements with specific nodal point configurations. The beams are coupled at nodal points that are remote from the ends, creating specific mode shapes that enhance measurement accuracy while maintaining a relatively simple monolithic structure that is robust to manufacturing variations.
Solution Approach 2:
The patent utilizes specific flexural mode shapes (drive mode and sense mode) of the beams, characterized by particular nodal point locations and vibration patterns. By operating at these specific modal parameters, the device achieves high measurement accuracy while the overall structural parameters remain simple and manufacturable.
3Ease of operation
If the gyroscope operates in a single mode, then the operation is simpler, but the adaptability to different conditions and environmental factors is reduced
Solution Approach 1:
The cross-hatch resonator is designed to support multiple vibrational modes (different flexural modes of the beams) that can be used for both driving and sensing. This multi-functionality allows the same structure to operate effectively under different conditions and provides adaptability to various operational requirements while maintaining a single integrated device.
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
Enhances the accuracy and robustness of angular rate measurements by reducing the impact of manufacturing errors and environmental factors, while maintaining efficient operation across different modes.
Implementation Method 1
driving the resonator into a drive mode that includes a fundamental or higher order flexural mode of the first set of beams
Implementation Method 2
The oscillation is generated with a periodic force applied to a spring-mass-damper system at the resonant frequency. Operating at resonance allows the oscillation amplitude to be large relative to the force applied.
Implementation Method 3
When the gyroscope is rotated, Coriolis acceleration is generated on the oscillating proof mass in a direction orthogonal to both the driven oscillation and the rotation. The magnitude of Coriolis acceleration is proportional to both the velocity of the oscillating proof mass and the rotation rate.
Implementation Method 4
The electrical and mechanical structures used to sense such deflections of the proof mass are referred to generally as the accelerometer.
Data Source
AI summary
One-axis and two-axis vibratory gyroscopes include a unitary resonator structure conceptually having four beams interconnected in a cross-hatch configuration. While each beam can be considered a unitary piece of material, each beam's attachment to two cross beams conceptually divides the resonant beam into a central section between the attachment points and two tail sections aft of the attachment points. The attachment points are preferably nodal points of the beam with respect to both a drive mode shape and a sense mode shape of the beam for the resonant mode in which the resonator is configured to operate. Thus, the location where two beams intersect is preferably a nodal point for both beams. The tail sections of each beam allow the resonant mode of the resonator to be carefully configured.