Dual-Mass Gyroscope Linkage for Common Mode Rejection
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Solution Overview
Problem
Existing in-plane angular velocity sensors with two oscillating proof masses struggle to achieve accurate common mode rejection due to variations in actuator effectiveness and mass velocities, leading to reduced performance and increased sensitivity to linear acceleration.
Innovation Solution
Mechanically constraining the two masses to move in opposite directions through a linkage system, with a center plate and edge plates connected to a base via torsional hinges, ensuring equal and opposite velocities, and using bulk MEMS technology for larger proof masses and increased travel distance, while integrating sense and drive electronics for reduced cost and improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two proof masses are driven into oscillation to sense angular velocity, then measurement capability is improved, but common mode interference rejection deteriorates due to variations in actuator effectiveness and mass velocities
Solution Approach 1:
The patent inverts the traditional approach by mechanically constraining the masses to move in opposite directions through a linkage system, rather than relying on actuators to produce equal and opposite velocities. This mechanical constraint ensures that the masses always move in opposite directions regardless of actuator variations, thereby improving common mode rejection while maintaining angular velocity measurement capability
Solution Approach 2:
The linkage system acts as an intermediary between the actuators and the proof masses. Instead of actuators directly controlling mass velocities, the linkage mediates the motion, ensuring that masses move in opposite directions with equal velocities. This intermediary mechanism decouples the actuator performance from the mass motion symmetry, resolving the common mode rejection issue
2Shape
If standard MEMS technology is used for in-plane angular velocity sensing, then device planarity is maintained, but performance deteriorates due to limitations in mass size and travel distance
Solution Approach 1:
The patent transitions from purely in-plane MEMS technology to a three-dimensional bulk MEMS structure. By allowing masses to move in the out-of-plane direction (Z-axis) while maintaining a planar device footprint, the invention achieves larger mass sizes and increased travel distances, thereby improving sensing performance without sacrificing device planarity when viewed from above
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 solution enhances measurement accuracy, reduces cost, and improves performance by effectively rejecting common mode interference and increasing mass travel distance, resulting in a more reliable and cost-effective in-plane angular velocity sensor.
Implementation Method 1
The two masses are linked together by a linkage such that they move in opposite directions along Z (i.e., when one mass moves in the +Z direction, the other mass moves in the -Z direction, and vice versa)
Implementation Method 2
an actuator for driving the linkage into oscillation
Implementation Method 3
Rotation of the sensor imparts a Coriolis force to the oscillating mass that is proportional to the angular velocity (or rotation rate)
Implementation Method 4
a center plate and edge plates connected to a base via torsional hinges
Data Source
Figure 1
Figure 1A
Figure 1B
AI summary
An angular velocity sensor has two masses which are laterally disposed in an X-Y plane and indirectly connected to a frame. The two masses are linked together by a linkage such that they necessarily move in opposite directions along Z. Angular velocity of the sensor about the Y axis can be sensed by driving the two masses into Z-directed antiphase oscillation and measuring the angular oscillation amplitude thereby imparted to the frame. In a preferred embodiment, the angular velocity sensor is fabricated from a bulk MEMS gyroscope wafer, a cap wafer and a reference wafer. In a further preferred embodiment, this assembly of wafers provides a hermetic barrier between the masses and an ambient environment.