MEMS Gyroscope Real-Time Scale Factor Calibration
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Solution Overview
Problem
MEMS gyroscopes face challenges in maintaining stable scale factor over time due to external disturbances such as temperature variations, stress, and material aging, leading to unreliable angular velocity detection and requiring disruptive calibration methods that do not interrupt operation.
Innovation Solution
A MEMS gyroscope with an in-run measurement circuit that applies a quadrature stress perpendicular to the driving stress and measures capacitive variations to track scale factor drift, allowing for continuous calibration and correction without interrupting operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional calibration methods are used to correct scale factor drift, then measurement precision is improved, but operation is interrupted and productivity is reduced
Solution Approach 1:
The patent applies preliminary action by continuously measuring the scale factor using a reference angular velocity during normal operation, so that calibration data is prepared in advance and correction can be applied without interrupting the gyroscope's primary function. The reference angular velocity measurement serves as a preliminary calibration step that occurs concurrently with normal operation.
Solution Approach 2:
The patent implements continuity of useful action by maintaining the gyroscope's angular velocity measurement function uninterrupted while simultaneously performing scale factor calibration. The dual-mode operation allows the device to continue its primary measurement function while periodically updating calibration parameters, ensuring both productivity and measurement precision are maintained.
2Reliability
If real-time calibration is implemented to maintain scale factor stability, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent applies universality by designing the measurement circuit to perform multiple functions: it measures both the reference angular velocity for calibration purposes and the actual angular velocity for operational use. This multi-functionality reduces the need for separate dedicated calibration hardware, thereby limiting the increase in device complexity while achieving real-time calibration.
Solution Approach 2:
The gyroscope performs self-calibration by using its own measurement capabilities to detect scale factor drift. The device generates and processes its own calibration data through the reference angular velocity measurement, eliminating the need for external calibration equipment or complex external control systems, thus improving reliability without proportionally increasing complexity.
3Measurement precision
If quadrature stress measurement is added to track scale factor drift, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent merges the quadrature stress measurement function with the existing angular velocity measurement circuit. By combining these measurement capabilities into a unified circuit architecture, the patent achieves improved scale factor drift detection without the complexity increase that would result from completely separate measurement systems. The merged circuit efficiently handles both measurement tasks using shared hardware resources.
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
Enables real-time regulation of the scale factor, improving detection reliability by monitoring and correcting variations in the scale factor without requiring external disturbance measurement or knowledge of the disturbance source, thus maintaining operational continuity.
Implementation Method 1
The mobile mass is coupled to the supporting body generally capacitively and forms therewith capacitors with variable capacitance. In particular, the movement of the mobile mass with respect to the fixed electrodes on the supporting body, due to the action of forces acting thereon, modifies the capacitance of the capacitors.
Implementation Method 2
A second mobile mass is driven through the first mobile mass and, in case of rotation of the gyroscope about an axis thereof perpendicular to the first direction and at an angular velocity, is subject to a Coriolis force proportional to the angular velocity and perpendicular to the driving direction and to the rotation axis.
Implementation Method 3
respective damping elements 4.2 and 5.2 (having respective elastic constants rx and ry)
Data Source
AI summary
The MEMS gyroscope has a mobile mass carried by a supporting structure to move in a driving direction and in a first sensing direction, perpendicular to each other. A driving structure governs movement of the mobile mass in the driving direction at a driving frequency. A movement sensing structure is coupled to the mobile mass and detects the movement of the mobile mass in the sensing direction. A quadrature-injection structure is coupled to the mobile mass and causes a first and a second movement of the mobile mass in the sensing direction in a first calibration half-period and, respectively, a second calibration half-period. The movement-sensing structure supplies a sensing signal having an amplitude switching between a first and a second value that depend upon the movement of the mobile mass as a result of an external angular velocity and of the first and second quadrature movements. The first and second values of the sensing signal are subtracted from each other and compared with a stored difference value to supply information of variation of the scale factor.