Crosshead Speed Verification System Using Laser Interferometry
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Solution Overview
Problem
Existing materials testing devices face challenges in accurately verifying the speed of crosshead travel, which is crucial for reliable stress/strain analysis, as current methods lack precision and metrological traceability to international standards.
Innovation Solution
A system combining a time interval counter and a linear displacement device calibrated to the International System of Units (SI) is used to measure the crosshead travel distance over time, providing precise verification of crosshead speed in materials testing machines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional measurement methods are used for crosshead speed, then the measurement can be performed, but the accuracy and metrological traceability to international standards are insufficient
Solution Approach 1:
The patent introduces a laser interferometer as an intermediary measurement device that provides a direct, traceable connection to international length standards (SI meters). The laser interferometer acts as a mediator between the crosshead movement and the measurement system, enabling accurate speed verification through optical path length measurements that are directly traceable to NIST standards.
Solution Approach 2:
The patent replaces conventional mechanical measurement systems with an optical measurement system based on laser interferometry. This substitution eliminates mechanical errors and wear, providing non-contact measurement with direct traceability to international standards, thereby improving both measurement precision and reliability.
2Measurement precision
If a time interval counter and linear displacement device are used, then precise speed verification with metrological traceability is achieved, but the device complexity increases
Solution Approach 1:
The patent designs the measurement system to perform multiple functions: the laser interferometer simultaneously measures displacement, velocity, and acceleration; the time interval counter handles multiple timing functions; and the system can verify both crosshead speed and specimen testing parameters. This multi-functionality reduces the need for separate dedicated devices for each measurement task.
Solution Approach 2:
The system incorporates self-calibration capabilities where the laser interferometer uses its own internal reference standards to maintain accuracy. The time interval counter automatically synchronizes with the testing machine's control system, and the system performs self-verification of measurement chains, reducing the need for external calibration equipment and manual adjustment.
Data Source
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AI summary
The present disclosure relates to a system for verification of the speed of crosshead travel in a materials testing device. A linear displacement device is mounted on the crosshead of the materials testing device. The linear displacement device measures the position and displacement of the crosshead during the test. A timer interval counter measures the time of travel of the crosshead during the test. This measurements allow for accurate calculation of the average speed of the crosshead travel, based on the difference between the position values divided by the elapsed time.