Accelerometer Stress Reduction via Compliant Mounting Flexures
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Temperature extremes and mismatched coefficients of thermal expansion between sensor components cause stress, deformation, and errors in accelerometers, particularly in downhole environments where materials with non-ideal thermal expansion properties are used.
Innovation Solution
Incorporating flexures in the mounting points between the sense element and the return path of a quartz flexure accelerometer, which reduces stress and maintains co-axiality by using compliant out-of-plane flexures and strategically designed mounting devices with pad and neck areas, and spiral or zig-zag attachment features to isolate stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the excitation ring is made stronger and mounted to the reed by compression, then the mounting is more secure, but thermal expansion mismatch causes radial pulling on mounting points leading to stress and sensor error
Solution Approach 1:
The mounting structure is segmented into distinct components: the excitation ring, mounting points, and reed are separated by compliance features. The mounting points are not rigidly fixed but allow controlled movement through the compliance features, dividing the rigid structure into manageable segments that can accommodate thermal expansion independently.
Solution Approach 2:
The patent changes the mechanical parameters of the mounting system by introducing compliance features that alter the stiffness characteristics. The mounting points are designed with specific geometric features (such as rounded corners, reduced thickness, or integrated flexures) that change the local compliance to allow thermal expansion while maintaining secure mounting.
2Ease of manufacture
If compression mounting is used to attach the reed to the magnetic circuit, then assembly is simplified, but slip occurs at high temperature due to decreased clamping force and increased shear stress
Solution Approach 1:
The mounting system transitions from a static rigid connection to a dynamic compliant connection. The compliance features allow the mounting points to move and adjust their position in response to thermal expansion, maintaining contact and preventing slip while accommodating the changing dimensions of the reed and excitation ring.
Solution Approach 2:
The compliance features act as intermediary elements between the excitation ring and the reed. These features (such as flexible mounting pads, rounded corners, or integrated flexures) mediate the interaction between the two components, allowing relative movement and stress redistribution without requiring complex assembly procedures.
3Strength
If the reed is made from fused silica to maintain elasticity, then the material can accommodate stress, but the CTE mismatch with metal excitation ring causes deformation and mounting point stress
Solution Approach 1:
The patent applies different local qualities to different parts of the mounting system. The reed maintains its fused silica material properties for elasticity, while the mounting points and excitation ring incorporate compliance features with specific geometric characteristics. This local differentiation allows the reed to maintain its elastic properties while the mounting structure accommodates thermal expansion independently.
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 solution effectively reduces stress and maintains accuracy over temperature variations, enhancing the reliability and precision of the accelerometer by mitigating deformation and slip issues.
Implementation Method 1
Because the fused silica (commonly referred to as quartz) of the reed 16 is a highly elastic material, the reed 16 does not plastically deform to accommodate the metal of the excitation ring 13
Implementation Method 2
The coefficient of thermal expansion (CTE) (α) of the excitation ring 13 is higher than a of the attached reed 16
Implementation Method 3
Some other mechanism of stress accommodation occurs: a) slip of the mounting points 18; b) local yielding of metal part; and c) the rim of the reed 16 becomes an oval shape
Data Source
AI summary
An accelerometer device for reducing stress on the sensor resulting from temperature extremes and multiple coefficients of thermal expansion. An exemplary accelerometer device includes upper and lower stators and a reed. The reed includes a support ring and a paddle that is flexibly connected to the support ring. The support ring includes a ring section and at least two mounting devices. The mounting devices are at least partially mechanically isolated from the ring section. The ring section flexibly receives the paddle. The mounting devices include a pad area and a neck area that connect the pad area to the ring section. The neck area includes a width dimension that is narrower than a diameter dimension of the pad area.