Segmented Strain Gauge Sensor for Rocket Motor Inhibitor Shape

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Solution Overview

Problem

Conventional methods for measuring the shape and position of inhibitors in reusable solid rocket motors, such as real-time radiography, are inadequate due to slow frame rates and poor resolution, leading to undesired oscillations in the combustion chamber.

Innovation Solution

A method and system involving a sensing device with strain gauges positioned on multiple segments of the rocket motor, measuring strain on both surfaces of each segment to determine curvature and subsequently the shape and position of the inhibitor, using a Wheatstone bridge circuit to convert strain into measurable voltage signals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If real-time radiography is used to monitor inhibitor shape and position, then measurement capability is provided, but frame rate is slow and resolution is poor

Engineering Contradiction:

Improveinhibitor shape and position measurementVSAvoidframe rate

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The patent replaces the radiography-based measurement system with a strain gauge-based sensing system. Strain gauges are bonded to the inhibitor surface to directly measure strain, which is then used to calculate shape and position. This mechanical/electrical sensing approach eliminates the slow frame rate and poor resolution issues of radiography, providing real-time, high-resolution measurements.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces strain gauges as an intermediary element between the inhibitor and the measurement system. The strain gauges act as sensors that convert physical deformation of the inhibitor into electrical signals, which can be processed to determine inhibitor shape and position with high temporal and spatial resolution.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If real-time radiography is used to monitor inhibitor shape and position, then measurement capability is provided, but resolution is poor

Engineering Contradiction:

Improveframe rateVSAvoidinhibitor shape and position measurement

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If strain gauges are positioned on multiple segments to measure strain, then measurement precision is improved, but device complexity increases

Engineering Contradiction:

Improveinhibitor shape and position determinationVSAvoidsensing device structure

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent divides the sensing device into multiple segments, with each segment containing strain gauges positioned on opposite surfaces. This segmentation allows the inhibitor to be monitored at multiple locations simultaneously, improving measurement precision while keeping each individual sensor unit relatively simple.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent combines strain gauges from opposite surfaces of each segment to form a differential measurement system. By merging the signals from gauges on both surfaces, the system achieves higher measurement precision through differential strain measurement, which compensates for temperature effects and other common-mode disturbances.

Inventive Principle:

Principle #5Merging (Combining)

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 provides enhanced accuracy in determining the shape and position of inhibitors, reducing oscillations by offering real-time, high-resolution data on the strain and curvature, thereby improving the stability of the rocket motor.

Implementation Method 1

sensing a strain with each of the first sensor and the second sensor at each segment

Methodology Applied

Scientific EffectStrain measurement: Piezoresistive Effect

Implementation Method 2

using a Wheatstone bridge circuit to convert strain into measurable voltage signals

Methodology Applied

Scientific EffectWheatstone bridge: Wheatstone Bridge

Implementation Method 3

determining a curvature of each segment of the one or more segments and determining at least one of a shape and a position of the at least a portion of the object from the determined curvature of each segment

Methodology Applied

Scientific EffectCurvature determination:

Data Source

PatentUS9074864B2Device and method relating to a sensing device

Publication Date: 2015.07.07 NORTHROP GRUMMAN SYSTEMS CORP

AI summary

Methods, devices, and systems relating to a sensing device are disclosed. A device may comprise a structure including a first surface and a second, opposite surface, wherein the structure comprises one or more segments. Further, the device may include a plurality of sensors disposed on the structure, wherein each segment of the one or more segments comprises a first sensor of the plurality of sensors coupled to the first surface and an associated second sensor of the plurality of sensors coupled to the second surface. Moreover, each sensor of the plurality of sensors may be configured to measure a strain exhibited on an adjacent surface of the structure at an associated segment of the one or more segments.