Passive Transverse Extensometer with Optical Encoder
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Solution Overview
Problem
Current transverse extensometers face challenges in achieving stringent accuracy and minimizing external loads on test specimens due to limited measurement ranges and resolution, often requiring complex and heavy driven systems, which can interfere with specimen testing and produce erroneous data.
Innovation Solution
A transverse strain extensometer with a passive vertical system utilizing a linear optical encoder, where sensor arms on carriages traverse on linear tracks with a low-friction design and encoder read-heads for precise positioning, allowing for accurate measurement of specimen width and minimizing external loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a driven system with sophisticated mechanisms and sensors is used to ensure accurate vertical positioning, then measurement precision is improved, but device complexity and weight increase
Solution Approach 1:
The patent replaces the driven mechanical positioning system with a passive mechanical tracking system. The extensometer uses a low-friction mechanical design that allows the specimen motion to automatically move the extensometer vertically, eliminating the need for motors, actuators, and complex control mechanisms while maintaining measurement accuracy through the encoder system.
Solution Approach 2:
The patent employs a counterbalanced design where the extensometer is weighted to offset its own weight and the weight of the sensor arms. This counterbalancing creates a neutral equilibrium that minimizes friction in the vertical tracks, allowing the extensometer to follow specimen motion passively without requiring active positioning mechanisms.
2Weight of moving object
If a lightweight manual clip-on extensometer is used, then device weight is reduced, but external loads on the specimen increase
Solution Approach 1:
The extensometer uses a counterbalanced mechanism where springs or weights compensate for the weight of the sensor arms and measurement unit. This counterbalancing reduces the net external load on the specimen to near-zero, allowing accurate measurement of small forces while maintaining a relatively lightweight design.
Solution Approach 2:
The patent uses an optical encoder system that creates a optical copy or representation of the position information. The encoder scale and read-head system allows the measurement of position without direct mechanical coupling that would transmit external loads to the specimen.
3Measurement precision
If the measurement unit is located close to the specimen, then measurement precision is improved, but the risk of interference with loading and removal increases
Solution Approach 1:
The extensometer is designed with dynamic capabilities including automatic vertical motion along the tracks and retractable sensor arms. The measurement unit can dynamically adjust its position and configuration to maintain optimal measurement accuracy while clearing the test area when not in use, preventing interference with specimen loading and removal.
Solution Approach 2:
The extensometer is divided into separate functional modules: a fixed housing mounted on the testing machine, movable sensor arms on vertical tracks, and a measurement unit with encoder system. This segmentation allows the measurement components to be positioned close to the specimen during testing while the housing and other components remain clear of the test area.
4Measurement precision
If inductive sensors, strain gauges, or magnetic scales are used, then measurement precision is improved, but measurement range is limited
Solution Approach 1:
The patent replaces limited-range inductive sensors and magnetic scales with a mechanical encoder system based on optical principles. The encoder scale can be made arbitrarily long along the vertical tracks, providing a large measurement range while maintaining high precision through the optical reading mechanism.
Solution Approach 2:
The patent transitions from using field-based sensors (inductive, magnetic) that have inherent range limitations to a mechanical-optical encoder system where the measurement range is determined by the physical length of the encoder scale, which can be extended along the vertical dimension of the tracks.
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 configuration provides high accuracy and robustness, reduces the need for expensive measurement systems, and allows for precise tracking of specimen strain without slipping, enabling the use on delicate specimens while maintaining compact and cost-effective packaging.
Implementation Method 1
a passive vertical system making use of a linear optical encoder
Data Source
AI summary
The disclosed embodiment is an extensometer to measure transverse strain with a passive vertical system making use of a linear optical encoder. The sensor arms are mounted on respective carriages which traverse on respective linear tracks. The carriages are spring-loaded so as to bias the sensor arms toward a closing direction. In order to separate the sensor arms and act against the force of the springs, the carriages are responsive to or pushed by upper and lower drive brackets which are affixed to respective upper and lower portions of a looped timing belt. The extensometer makes use of a low-friction design to minimize rolling friction in the movement of the two sensor arms. One carriage includes an encoder read-head which directly faces an encoder scale on the other carriage. In this configuration, the exact relative position of the two carriages, and hence the two sensor arms, can be read.