Motion Compensation for Shearography Using Adjustable Fold Mirrors
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Solution Overview
Problem
Performing motion-based shearography from a moving platform or moving target surface is challenging due to the need for precise alignment and comparable conditions for specklegrams, which is compromised by relative motion, leading to unreliable data comparisons.
Innovation Solution
A motion compensation system using adjustable and stationary fold mirrors to compensate for motion by adjusting the angles of reflection, making the laser radiation appear as if the shearography apparatus is stationary with respect to the target surface, allowing for comparable specklegrams to be obtained even during platform or target surface movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If shearography is performed from a moving platform or with a moving target surface, then the inspection coverage and application range are improved, but the measurement precision and reliability deteriorate due to motion-induced misalignment of specklegrams
Solution Approach 1:
The system performs preliminary motion compensation by calculating the expected platform motion between pulse periods and pre-adjusting the angles of the fold mirrors accordingly. This preliminary action ensures that the laser radiation paths are corrected before the actual measurement occurs, maintaining specklegram alignment precision despite platform movement.
Solution Approach 2:
The fold mirrors serve as intermediary elements that mediate between the moving platform and the stationary target surface. By adjusting the mirror angles, the system creates a virtual stationary reference frame, allowing specklegrams to be captured as if the platform were stationary, thus preserving measurement precision while enabling motion-based operation.
2Productivity
If the platform speed is increased to improve inspection efficiency, then the productivity is improved, but the reliability of shearography measurements deteriorates due to greater motion effects
Solution Approach 1:
The system calculates and compensates for platform motion in advance, before the laser pulses are emitted. This preliminary compensation allows the system to maintain measurement reliability even at higher platform speeds, as the motion effects are corrected before they can degrade the quality of the specklegrams.
Solution Approach 2:
The fold mirrors are made dynamically adjustable, allowing their angles to change in real-time according to the platform's motion. This dynamic adaptation enables the system to maintain reliable measurements across a range of platform speeds, transforming a static alignment system into a dynamic one that can track and compensate for motion.
3Measurement precision
If multiple pulse periods are used to capture specklegrams for motion compensation, then the measurement precision is improved, but the loss of time increases due to additional pulse periods required
Solution Approach 1:
The system uses periodic laser pulses at optimized intervals, capturing specklegrams at specific time points that maximize motion compensation effectiveness. By using periodic action with carefully chosen pulse periods, the system achieves high measurement precision while minimizing the total time required, as the periodic sampling captures the essential motion information efficiently.
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 system enables effective motion compensation, allowing for higher platform speeds and wider range of motion-based shearography applications, reducing the sensitivity to motion and enabling faster inspection of large areas, even in handheld devices.
Implementation Method 1
an adjustable first fold mirror to reflect laser radiation to a receiving aperture of the shearography apparatus during separate pulse periods at corresponding angles of reflection; and corresponding second fold mirrors to reflect the laser radiation from a target surface to the first fold mirror during the respective pulse periods
Data Source
AI summary
A motion compensation system for a shearography apparatus includes: an adjustable first fold mirror to reflect laser radiation to a receiving aperture of the shearography apparatus during separate pulse periods at corresponding angles of reflection; and corresponding second fold mirrors to reflect the laser radiation from a target surface to the first fold mirror during the respective pulse periods. The shearography apparatus moves with respect to the target surface between the separate pulse periods. The angles of reflection make the laser radiation reflected from the target surface via the respective second fold mirrors appear to the receiving aperture as if the shearography apparatus is stationary with respect to the target surface. In another system, the second fold mirrors are replaced by an adjustable second fold mirror to reflect the laser radiation from the target surface to the first fold mirror during the pulse periods at corresponding second angles of reflection.