MEMS Accelerometer Calibration via Static Phase Offset Subtraction
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Solution Overview
Problem
Existing acceleration measurement systems for missiles and other critical devices face high initial measurement errors due to offset voltage in accelerometers, which are costly and time-consuming to calibrate, and often require software corrections, compromising security and robustness.
Innovation Solution
An acceleration measurement system utilizing two MEMS accelerometers, one for a wide range and another for a narrow range, determines the system's state to calibrate measurements by storing reference values during static phases and subtracting them from operational phase measurements, reducing errors and eliminating the need for expensive calibration facilities and software corrections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional calibration procedures using calibration benches are used, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The system performs self-calibration using its own accelerometers. The first accelerometer (wide range) and second accelerometer (narrow range) work together to automatically determine calibration parameters without external calibration equipment. The microprocessor analyzes data from both accelerometers to compute offset voltage and sensitivity corrections, enabling the system to calibrate itself
Solution Approach 2:
The calibration function is divided into distinct operational phases: static phase detection, calibration data collection, and calibration parameter computation. The system segments the calibration process into discrete steps that can be executed autonomously by the microprocessor based on acceleration threshold comparisons
2Measurement precision
If software-based calibration correction is implemented, then measurement precision is improved, but reliability decreases
Solution Approach 1:
The patent replaces software-based calibration correction with a hardware-based solution. Calibration parameters (offset voltage and sensitivity values) are stored in non-volatile memory and applied through hardware correction circuits. The determination of static vs. operational phases and the application of calibration corrections are performed through hardware logic and dedicated circuits rather than software execution, eliminating security vulnerabilities associated with software
3Manufacturing precision
If calibration is performed using dedicated calibration benches, then manufacturing precision is improved, but loss of time increases
Solution Approach 1:
The system performs calibration actions preliminarily by continuously monitoring acceleration data and automatically detecting when calibration should occur. The microprocessor analyzes acceleration patterns to determine when the system is in a static phase, pre-calculating calibration parameters before operational phases begin, rather than requiring separate calibration sessions
Solution Approach 2:
The calibration process is integrated into continuous operation. The system continuously collects acceleration data from both accelerometers, continuously monitors for static phase conditions, and continuously updates calibration parameters without interrupting normal system operation. This eliminates the need for separate calibration sessions and maintains continuous useful action
Data Source
Figure 1~2
AI summary
The system has a determination unit determining that the system is in a static phase if an acceleration value delivered by a reference accelerometer (beta) is lower than absolute value at threshold value and the system is in operational phase if the value is not less than the absolute value. A differential amplifier (14) determines an acceleration value in the operational phase by a difference between the acceleration measured by a main accelerometer (alpha) and a measurement of reference acceleration of the system in the static phase stored in a memory (10). : The main and reference accelerometers are microelectromechanical system (MEMS) accelerometers. An independent claim is also included for a method for measuring acceleration. USE : Acceleration measuring system for use in a safety and arming device (claimed) of a missile or rocket to determine attitude or speed of the missile or rocket. Can also be used in firing devices used by fuse of bombs, cannon and artillery. ADVANTAGE : The system utilizes hardware devices so as to provide high reliability, robustness and maximum safety to the system. The system possesses a calibration function so as to avoid expensive calibration installations or procedures during manufacturing of the system. DESCRIPTION OF DRAWINGS : The drawing shows a perspective view of an acceleration measurement system with calibration function. alpha : Main accelerometer beta : Reference accelerometer 10 : Memory 12 : Calculating unit 14 : Differential amplifier.