Opto-Mechanical Tower Extensometer for Close-Proximity Strain Measurement
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Solution Overview
Problem
Existing extensometers face challenges with fragile materials, violent specimen failure, repetitive attachment and detachment, measurement accuracy affected by working distance, and tradeoffs between resolution, range, and speed in non-contact systems.
Innovation Solution
An opto-mechanical extensometer system with optical head assemblies positioned within the specimen test area, using small, low-resolution cameras and spot lighting, and optional alignment lasers, actively controlled to maintain proximity to the specimen, allowing for improved resolution and reduced sensitivity to environmental factors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If non-contact optical extensometers are used, then contact damage to fragile materials and violent specimen failure is avoided, but measurement accuracy is significantly affected by working distance variation and environmental factors
Solution Approach 1:
A transparent window or opening in the test apparatus serves as an intermediary that allows the optical extensometer to view the specimen from within the test chamber. This positioning minimizes working distance while maintaining non-contact measurement, thereby improving measurement accuracy without compromising the reliability benefit of avoiding contact damage.
2Length of moving object
If optical extensometers are positioned far from the specimen, then measurement range is increased, but measurement precision and resolution are reduced
Solution Approach 1:
The measurement system is segmented into multiple optical extensometers positioned at different locations. Each extensometer covers a specific segment of the specimen with high resolution, while the collective system achieves comprehensive measurement range. This allows precise local measurements without requiring any single sensor to be far from the specimen.
Solution Approach 2:
The system transitions from a single-point measurement approach to a multi-dimensional array of measurement points. By distributing multiple optical extensometers across different positions and angles, the system achieves both high resolution (through close proximity of individual sensors) and large measurement range (through collective coverage of multiple specimen regions).
3Measurement precision
If optical extensometers are positioned close to the specimen, then measurement precision is improved, but the system becomes more vulnerable to damage from specimen failure and requires more complex positioning mechanisms
Solution Approach 1:
The optical extensometer positioning system is merged with the existing test apparatus structure. Optical sensors are integrated into the grips, crossheads, or chamber walls, eliminating the need for separate positioning mechanisms. This reduces device complexity while maintaining close proximity for high-precision measurements.
Solution Approach 2:
The test apparatus components (grips, crossheads, chamber walls) are designed to serve multiple functions: their primary mechanical functions plus serving as mounting structures for optical sensors. This multi-functionality reduces the need for dedicated positioning mechanisms, simplifying the overall system while enabling close-proximity optical measurement.
4Measurement precision
If high-resolution cameras are used, then measurement precision is improved, but system cost and complexity increase
Solution Approach 1:
High-resolution cameras are positioned only at locations where maximum measurement precision is critically needed, such as at the specimen gauge section or regions of highest stress concentration. Lower-resolution sensors can be used in other areas, optimizing the balance between measurement precision and system cost.
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
Enhances measurement accuracy and speed while reducing costs, simplifying setup, and minimizing environmental interference, even with lower resolution cameras, by positioning optics close to the specimen.
Implementation Method 1
One or more optical head assemblies are positionable within the specimen test area during deformation testing of the specimen, the optical head assemblies being configured to produce images of reference patterns on the specimen throughout deformation testing
Implementation Method 2
Each optical head carries one or more camera assemblies, spot lighting, and optional alignment lasers
Data Source
AI summary
Described are opto-mechanical tower extensometers having opposing carriages whose vertical positions relative to each other are actively motor controlled so that deformation of a strain test specimen held between the grips of a mechanical testing system in a test area can be tracked and measured. Upper and lower arm assemblies are used to position optical heads within the specimen test area. Each optical head carries one or more camera assemblies, spot lighting, and optional alignment lasers. Such a system presents a compact design in which the optics can be maintained in close proximity to the test specimen throughout testing.