Accelerometer Bias Error Reduction via Opposite Polarity Proofmasses
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Solution Overview
Problem
Accelerometer bias uncertainty, arising from transient behavior, non-modelability, and temperature-related instability, leads to errors in inertial measurement and navigation systems, as existing technologies fail to achieve linear relation between feedback force and sensed input effectively.
Innovation Solution
An accelerometer system employing two matched proofmasses that accelerate in opposite directions, with a force rebalance controller generating control signals to rebalance the proofmasses and calculate external acceleration by subtracting the magnitudes of output signals from opposite polarity displacements, thereby mitigating bias errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electrostatic forcing is used to position the proofmass in a closed loop system, then the output signal can be obtained, but the relation between feedback force and sensed input becomes non-linear
Solution Approach 1:
The patent inverts the conventional approach by using two proofmasses that accelerate in opposite directions. Instead of trying to linearize the non-linear electrostatic forcing relationship, the system exploits the symmetry of opposite-direction acceleration to cancel out the non-linearities and bias errors through differential measurement.
Solution Approach 2:
The patent changes the operational parameters by applying charge pulses with opposite polarities to two proofmasses. By varying the polarity and timing of charge application, the system achieves linearized output while maintaining the benefits of electrostatic forcing.
2Device complexity
If a single proofmass is used with electrostatic forcing, then the device structure is simpler, but bias uncertainty increases due to transient behavior and temperature instability
Solution Approach 1:
The patent uses a second proofmass as a counterweight to the first proofmass. Both proofmasses are subjected to opposite polarity charge pulses, creating symmetric responses that cancel out bias errors, transient behavior effects, and temperature-related instabilities when measured differentially.
Solution Approach 2:
The patent creates a copy of the proofmass system with the second proofmass that mirrors the first. By fabricating matched proofmasses and applying opposite polarity charges, the system generates correlated signals that can be differentially processed to eliminate common-mode bias errors.
3Measurement precision
If opposite polarity charge pulses are applied to two proofmasses, then bias error is reduced, but the control system complexity increases
Solution Approach 1:
The patent employs periodic charge pulse application to the two proofmasses in opposite polarities. By using periodic excitation with controlled duty cycles and timing, the system achieves bias error reduction while maintaining manageable control complexity through rhythmic, predictable operation.
Solution Approach 2:
The patent implements feedback control by monitoring the positions of both proofmasses and adjusting the charge pulse timing and duration accordingly. The feedback mechanism ensures that the opposite polarity charging achieves the desired bias cancellation while maintaining system stability.
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 system achieves accurate calculation of external acceleration that is substantially free from bias error, improving the performance of inertial measurement and navigation systems by canceling out bias uncertainty and reducing noise through the use of matched proofmasses and a self-calibrating mechanism.
Implementation Method 1
A force rebalance controller applies control signals to at least one control element to provide a first force to accelerate the first proofmass toward a first null position
Data Source
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AI summary
An accelerometer system can include a sensor element comprising first and second proofmasses, the first proofmass accelerating in a first direction and the second proofmass accelerating in a second direction opposite the first direction in response to an external acceleration. A force rebalance controller applies control signals to at least one control element to provide a first force to accelerate the first proofmass toward a first null position and to at least one control element to provide a second force to accelerate the second proofmass toward a second null position. The force rebalance controller can also generate opposite polarity first and second output signals associated with respective displacements of the first and second proofmasses relative to the respective first and second null positions. An acceleration component calculates the external acceleration based on the first and second output signals.