MEMS Gyroscope Force Rebalancing via Time-Varying Voltages
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Solution Overview
Problem
Microelectromechanical (MEMS) gyroscopes face significant errors due to quadrature motion, which results in mechanical feedthrough signals that are several orders of magnitude greater than detectable Coriolis forces, affecting the accuracy of rotational motion detection.
Innovation Solution
The use of time-varying rebalancing voltages applied to torquer electrodes in MEMS inertial sensors to electrostatically null proof mass motion along the sense axis, maintaining a fixed capacitance and compensating for Coriolis and quadrature forces, thereby reducing rate bias and scale factor errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If quadrature motion is present in MEMS gyroscopes, then mechanical feedthrough signals are generated, but these signals are several orders of magnitude greater than detectable Coriolis forces, degrading measurement precision
Solution Approach 1:
The patent extracts and separately compensates for quadrature motion effects from the primary Coriolis force measurement. By detecting quadrature motion independently and applying separate compensation signals, the harmful feedthrough signals are removed while preserving the accurate detection of rotational motion.
Solution Approach 2:
The patent implements feedback control by continuously monitoring proof mass position and adjusting rebalancing voltages in real-time. The system measures quadrature motion and feeds this information back to generate compensating signals that actively cancel the harmful mechanical feedthrough effects, maintaining measurement precision.
2Productivity
If traditional capacitance sensing is used to detect proof mass displacement, then the sensor can measure rotation, but rate bias and scale factor errors increase due to quadrature forces
Solution Approach 1:
The patent introduces torquer electrodes as intermediary elements between the proof masses and the control system. These electrodes apply electrostatic rebalancing forces that mediate the compensation of quadrature-induced errors, allowing the system to maintain accurate rotational detection while eliminating bias and scale factor errors.
Solution Approach 2:
The patent changes the electrical parameters (voltages) applied to torquer electrodes dynamically based on detected proof mass position. By adjusting these voltage parameters in real-time according to the measured quadrature motion, the system compensates for errors and maintains high measurement precision across varying rotational rates.
3Speed
If proof masses oscillate in drive mode, then Coriolis forces can be sensed, but quadrature motion produces in-phase forces that contaminate the rate signal
Solution Approach 1:
The patent applies anti-weight principles by generating counteracting electrostatic forces through torquer electrodes. These counter-forces are specifically designed to balance and cancel the harmful in-phase quadrature forces produced during proof mass oscillation, allowing high-speed oscillation without signal contamination.
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 enhances the dynamic range of the sensor, improves reliability, and reduces long-term drift, allowing for more accurate detection of rotational motion across a wide range of rates.
Implementation Method 1
Time-varying rebalancing voltages applied to one or more of the torquer electrodes can be configured to electrostatically null proof mass motion along a sense axis perpendicular to the drive axis
Implementation Method 2
The displacement of sense resonant mode motion can then be determined capacitively by detecting the current induced on the proof masses due to the time-varying sense capacitance
Implementation Method 3
A motor mode of the proof masses can be driven electrostatically at its resonant frequency using a number of interdigitated comb drive fingers adapted to convert electrical energy into mechanical energy by electrostatic actuation
Implementation Method 4
When the gyroscope is rotated about its input axis perpendicular to the drive axis, the motor mode velocity of the proof masses produces a Coriolis force that drives the proof masses along a sense axis perpendicular to the drive axis and input axis
Data Source
AI summary
MEMS devices and methods employing one or more electrodes coupled to a time-varying rebalancing voltage are disclosed. A MEMS inertial sensor in accordance with an illustrative embodiment can include one or more proof masses, at least one sense electrode positioned adjacent to each proof mass, and one or more torquer electrodes. Rebalancing voltages can be applied to the torquer electrodes to electrostatically null quadrature and/or Coriolis-related proof mass motion along a sense axis of the device. The rebalancing voltages applied to each of the torquer electrodes can be adjusted using feedback from one or more force rebalancing control loops.