Thermally Insensitive Accelerometer with Radial Flexure Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing open-loop hung mass accelerometers require tight thermal control to achieve desired bias stability and scale factor error performance, as axial or transverse temperature gradients can produce false accelerations.
Innovation Solution
A thermally insensitive open-loop hung mass accelerometer design is implemented with a radial symmetry and low CTE materials, featuring a stepped internal cavity and multiple flexures to minimize thermal expansion effects, and photolithographically defined thin Eddy current sensor heads to reduce thermal sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If tight thermal control is implemented to achieve desired bias stability and scale factor error performance, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent converts the harmful effect of thermal expansion into a beneficial self-compensating mechanism by designing the accelerometer body with specific radial symmetry and material selection (low CTE materials) such that thermal expansion in one direction is compensated by contraction in another direction, naturally canceling out thermal effects on measurement accuracy without requiring external thermal control systems
Solution Approach 2:
The patent changes the physical parameters of the accelerometer structure, specifically using low coefficient of thermal expansion (CTE) materials and designing radial symmetry with specific geometric parameters, to inherently resist thermal expansion effects and achieve thermal insensitivity without active thermal control
2Ease of operation
If axial or transverse temperature gradients are allowed, then ease of operation is improved, but false accelerations are generated reducing measurement precision
Solution Approach 1:
The patent strategically uses asymmetry in the attachment geometry of flexures to compensate for thermal expansion. By positioning flexure attachments at specific asymmetric locations on the proof mass, the design creates thermal compensation where expansion in certain directions is offset by the geometric arrangement, allowing the system to tolerate temperature gradients without generating false acceleration signals
Solution Approach 2:
The patent segments the accelerometer into functionally independent components (body, proof mass, flexures, sensor heads) with optimized material properties and geometric relationships. This segmentation allows each component to be designed for specific thermal characteristics, with the overall assembly achieving thermal insensitivity through the coordinated behavior of segmented parts
3Ease of manufacture
If traditional sensor heads are used, then manufacturing is simpler, but sensitivity to temperature gradients increases
Solution Approach 1:
The patent replaces traditional mechanical sensor heads with Eddy current sensor heads that use electromagnetic fields instead of direct mechanical contact. This substitution eliminates the mechanical thermal expansion paths between the sensor head and proof mass, dramatically reducing sensitivity to temperature gradients while maintaining manufacturing feasibility through electromagnetic sensing principles
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 design achieves a 3x reduction in sensitivity to axial temperature gradients and a 10x reduction in sensitivity to transverse temperature gradients, providing bias stability and scale factor error performance without stringent thermal control, with a proof mass bias less than 10 micro-g's and scale factor error less than 10 ppm.
Implementation Method 1
differential Eddy current sensing to provide improved sensitivity
Implementation Method 2
Eddy current sensor heads extend through holes in the body and through the flexures along axis 110
Data Source
Figure 1
Figure 2A~2B
Figure 2C
AI summary
A thermally insensitive open-loop hung mass accelerometer utilizes a transverse geometry to attach the body/flexures/proof mass so that thermal expansion effects due to thermal gradients across the accelerometer or bulk temperatures changes of one flexure relative to the other cause minimal or no axial displacement of the proof mass. In this geometry, multiple flexures may be stacked to achieve the required stiffness, thus reducing manufacturing costs and any tolerancing issues, without affecting thermal sensitivity. The accelerometer is suitably designed to exhibit a radial symmetry. The accelerometer is suitably designed to use low CTE materials for at least the proof mass and body and a low thermal expansion differential Eddy current sensor head.