Capacitive Strain Sensor for Aircraft Landing Gear

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Solution Overview

Problem

Aircraft landing gear strains are difficult to accurately assess due to subjective inspection criteria and limitations in existing strain gauges, which can lead to unnecessary inspections or missed opportunities, and current strain gauges have limited sensing range and are affected by temperature and material properties.

Innovation Solution

A capacitance-based strain sensor system for aircraft landing gear that includes upper and lower end caps with metalized capacitor plates and a metal bellows, allowing for precise measurement of strain through changes in capacitance, with adjustable attachment mechanisms and microadjustment devices for fine calibration.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If traditional metal foil strain gauges are used, then the gauge factor is limited, but the sensing range is also limited by maximum stress allowed (3,000 micro-strain)

Engineering Contradiction:

Improvegauge factorVSAvoidsensing range

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent replaces the traditional metal foil mechanical strain gauge with a capacitive sensing system. The capacitive sensor uses electrical field interactions rather than mechanical deformation of a foil element, allowing it to measure strains beyond the 3,000 micro-strain limit of traditional gauges while providing higher gauge factor through capacitance changes.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The invention changes the measurement parameter from resistance change (in traditional gauges) to capacitance change. This parameter change enables the sensor to operate at higher strain levels without the mechanical failure limitations of foil gauges, extending the sensing range while maintaining high sensitivity through the capacitive effect.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If piezoresistive strain gauges are used to improve gauge factor by 100x, then measurement precision improves, but temperature and material properties affect the detected resistance

Engineering Contradiction:

Improvegauge factorVSAvoidtemperature interference

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent substitutes the piezoresistive effect with a capacitive sensing mechanism. By measuring capacitance changes rather than resistance changes, the system eliminates the temperature-dependent resistance variations that plague piezoresistive gauges, while maintaining high gauge factor through the capacitive measurement principle.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Productivity

If subjective determination of landing gear inspection is used, then inspection frequency can be reduced, but it leads to over-or under-reporting of strain conditions

Engineering Contradiction:

Improveinspection efficiencyVSAvoidstrain assessment accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent implements continuous strain monitoring with capacitive sensors that provide objective feedback on the actual strain conditions of landing gear. This real-time data feedback replaces subjective inspection decisions, enabling optimized inspection schedules based on actual measured strain levels rather than subjective assessment, thus improving both inspection efficiency and accuracy.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The invention replaces subjective human assessment with automated capacitive sensing and measurement systems. The objective electrical measurements of strain replace the subjective visual or tactile inspection methods, providing quantifiable data that eliminates over- or under-reporting while improving inspection productivity through automated monitoring.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 capacitance-based strain sensor system provides accurate and reliable strain measurement beyond the limitations of traditional gauges, enabling more precise assessment of landing gear health and extending the sensing range while minimizing interference from temperature and material properties.

Implementation Method 1

A capacitance-based strain sensor system for aircraft landing gear that includes upper and lower end caps with metalized capacitor plates

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

For a polysilicon piezoresistive type of element, the resistance is changed with load applied

Methodology Applied

Scientific EffectPiezoresistive effect: Piezoresistive Effect

Data Source

PatentEP2410307B1Sensor for measuring large mechanical strains with fine adjustment device

Publication Date: 2019.12.11 GOODRICH CORP

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AI summary

A capacitive strain sensor for sensing strain of a structure. The sensor includes a first section attached to the structure at a first location and a second section attached to the structure at a second location. The first section includes a capacitor plate electrically isolated from the structure and the second section includes two electrically isolated capacitive plates, both of the plates being electrically isolated from the structure. A flexible connector connects the first section to the second section. The capacitor plate of the first section is separated from the two capacitive plates of the second section by at least one capacitive gap. When strain is experienced by the structure, a change occurs in the capacitive gap due to relative motion between the first and second sections.