Capacitive Strain Sensor for Aircraft Landing Gear
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Solution Overview
Problem
Aircraft landing gear struts experience deformation due to strain, leading to potential catastrophic failure, and existing strain gauges have limitations in sensing range and accuracy, particularly beyond 3,000 microstrain, causing subjective determination of inspection needs and potential missed opportunities.
Innovation Solution
A capacitive strain sensor device comprising two independently mounted rings with capacitive plates and serpentine flexures, securely anchored to the strut piston, allowing for accurate measurement of strains up to 10,000 microstrain with minimal crosstalk and resistance to thermal and radial deformations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional strain gauges are used, then the device complexity is low, but the measurement precision is limited beyond 3,000 microstrain
Solution Approach 1:
The sensor is divided into multiple independent capacitive plates (first capacitive plate, second capacitive plate, third capacitive plate, fourth capacitive plate) arranged in a bridge configuration. Each plate independently measures strain in different directions, and their combined output provides comprehensive strain measurement with enhanced precision beyond conventional single-element gauges.
Solution Approach 2:
The patent replaces conventional resistive strain gauge elements with a capacitive sensing system. Instead of measuring resistance changes in metal foil or polysilicon elements, the system uses capacitive plates that measure strain through changes in capacitance, enabling accurate measurement up to 10,000 microstrain while eliminating the fatigue limitations of traditional gauges.
2Measurement precision
If the sensing range is extended beyond 3,000 microstrain, then the measurement precision improves, but the reliability of conventional gauges deteriorates due to fatigue
Solution Approach 1:
The patent replaces fatigue-prone metal foil and polysilicon resistive elements with capacitive plates that have no moving parts or material fatigue issues. The capacitive sensing mechanism measures strain through electrical field changes rather than material deformation, eliminating the 3,000 microstrain fatigue limit while maintaining measurement precision.
Solution Approach 2:
The sensor employs a composite structure combining conductive capacitive plates with flexible support elements and adhesive layers. This composite design allows the sensing system to accommodate large strains up to 10,000 microstrain while maintaining structural integrity and measurement accuracy, overcoming the limitations of single-material conventional gauges.
3Measurement precision
If multiple strain gauges are added to improve measurement accuracy, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The patent merges multiple capacitive sensing elements into a single integrated sensor assembly mounted on one strut piston. The four capacitive plates are arranged in a compact bridge configuration, combining the functionality of multiple independent strain measurements into one unified device that provides comprehensive strain data without requiring multiple separate gauge installations.
Solution Approach 2:
The capacitive bridge sensor performs multiple functions simultaneously: it measures axial strain, radial strain, and shear strain through its four capacitive plates. This multi-functional capability replaces what would traditionally require multiple separate strain gauge installations, reducing overall device complexity while enhancing measurement precision across multiple strain components.
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
The device provides accurate and reliable strain measurements beyond conventional limits, enabling precise detection of strains in aircraft landing gear, ensuring timely inspection and maintenance, and accommodating high-G loads and shock conditions.
Implementation Method 1
a plurality of capacitive plates integral with the first and second rings respectively, the capacitive plates being mounted to a surface that is approximately perpendicular to the first and second inner walls
Implementation Method 2
the first ring is configured to mount to the strut piston by fastening the first and second half together thereby placing the first ring in radial compression over the strut piston
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A device configured to mount to a structure, the device comprising: a first ring comprising two portions with inner wall; a second ring comprising two portions with inner wall; a plurality of capacitive plates integral with the first and second rings, the capacitive plates being mounted to a surface that is approximately perpendicular to the inner walls, wherein the capacitive plates are electrically isolated from their respective rings.