Force Balance Accelerometer CTE Matching
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Solution Overview
Problem
Accelerometers face accuracy limitations due to thermal expansion-induced errors caused by coefficient of thermal expansion (CTE) mismatches between components, leading to hysteresis and false acceleration readings.
Innovation Solution
Matching the CTE of the proof mass assembly with the excitation rings in accelerometers, using materials like Zerodur K20 for the proof mass and Invar for the excitation rings, and adjusting the outer support structure's CTE to maintain axial compression preload forces, thereby reducing thermal expansion-induced errors and hysteresis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If different materials are used for the proof mass assembly and excitation rings, then ease of manufacture is improved, but measurement precision deteriorates due to CTE mismatch and thermal expansion errors
Solution Approach 1:
The patent applies parameter changes by carefully selecting materials with specific CTE values that match between the proof mass assembly and excitation rings. This involves changing the material parameters (CTE values) to be substantially equal, thereby eliminating thermal expansion mismatches while maintaining manufacturability through standard materials like Invar and Zerodur.
2Measurement precision
If the CTE of the proof mass assembly is matched with the excitation rings, then measurement precision is improved, but device complexity increases due to material selection constraints
Solution Approach 1:
The patent applies homogeneity by ensuring that the CTE values of different components (proof mass assembly and excitation rings) are substantially matched. This creates a homogeneous thermal expansion behavior across the accelerometer assembly, simplifying the thermal management considerations while improving measurement accuracy.
3Reliability
If the outer support structure uses a material with different CTE, then reliability is improved by maintaining axial compression preload force, but manufacturing precision becomes more difficult due to CTE mismatch management
Solution Approach 1:
The patent applies local quality by using a different CTE material for the outer support structure (bellyband) compared to the internal components. This localized material differentiation allows the support structure to maintain axial compression preload force and accommodate thermal expansion differently, ensuring reliable operation while managing manufacturing precision through targeted material selection.
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 reduces thermal expansion-induced errors and improves the accuracy and reliability of acceleration measurements by minimizing strain and hysteresis effects across varying temperatures.
Implementation Method 1
Matching the CTE of the proof mass assembly with the excitation rings in accelerometers... reducing thermal expansion induced errors... CTEs of the proof mass assembly and the excitation rings matching to within 0.5 parts per million per degree Celsius (ppm/° C.)
Data Source
AI summary
An example accelerometer includes a first excitation ring comprising a first material having a first coefficient of thermal expansion (CTE), a second excitation ring comprising the first material having the first CTE; and a proof mass assembly disposed between and in contact with the first excitation ring and the second excitation ring. The proof mass assembly comprises a second material having a second CTE, wherein a difference between the first CTE and the second CTE is equal to or less than 0.5 parts per million per degree Celsius (ppm/° C.).