Enhanced Digital Gradient Sensing Using Backlight Digital Speckle Target
Abstract
:1. Introduction
2. Methodology
2.1. Digital Gradient Sensing
2.2. Backlight Digital Speckle Target
- (1)
- High dynamic measurement capability. The backlight speckle target selectively shades the blue backlight through the transparent/opaque texture of digital speckle layer, and allows the light emanating from the target to be captured by the imaging system directly, which can improve the utilization of light source, shorten the exposure time, and enhance the high-speed measurement performance of the system.
- (2)
- High measurement accuracy. The measurement accuracy of DGS is associated with the speckle size, speckle distribution, and speckle contrast. The proposed backlight digital speckle target utilizes the Gaussian speckle pattern simulation algorithm to generate the digital speckle pattern whose speckle size, density, and distribution can be designed to better match the real measurement scenario (e.g., the size of the specimen and the FOV). Therefore, the measurement accuracy of DGS can be improved after employing the digital speckle target [24]. In addition, the employment of backlight illumination can enhance the speckle contrast of the acquired speckle images [25]. The optimized speckle quality and contrast promote the accuracy of DIC point-wise tracking of displacement, and therefore, improves the DGS measurement accuracy.
- (3)
- High system integration and better operation. In conventional DGS methods, the speckle target and the lighting system are two separated parts. Before the measurement, the angle of the light source needs to be cumbersomely adjusted by the operator, so as to achieve the uniform illumination of the speckle target. The proposed backlight speckle target not only combines the illumination source and the speckle target, improving the system integration, but also effectively solves the tedious light source adjustment problem.
- (4)
- Strong robustness against the ambient light variation. The backlight speckle target adopts the blue backlight source and the corresponding blue bandpass filter to realize the blue light active imaging conveniently, which is expected to suppress the light variation in the ambient environment, and improve the stability and reliability of the measurement system [23].
- (5)
- High system compatibility. Compared with the simplified r-DGS method proposed by Tippur et al. [18], the backlight speckle target solution has higher system compatibility. That is, compatible with not only the conventional r-DGS but also the conventional t-DGS and the simplified r-DGS. The high compatibility greatly promotes the proposed speckle target to improve the light source utilization and integration of all DGS systems.
3. Experiments
3.1. Validation Experiment
3.2. Stress Gradient Field Measurement Using the Enhanced t-DGS
3.3. Plane Slope Measurement Using the Enhanced r-DGS
4. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Aperture Size | Exposure Time (Conventional Method) | Exposure Time (Backlight Method) | Comparison |
---|---|---|---|
F19.2 (small) | 65,000 us | 1450 μs | 44.8 times decreased |
F9.6 (medium) | 13,500 us | 380 μs | 35.5 times decreased |
F6.4 (medium) | 8300 us | 220 μs | 37.7 times decreased |
F4.8 (large) | 5000 us | 125 μs | 40.0 times decreased |
Aperture Size | MIG (Conventional Method) | MIG (Backlight Method) | Comparison |
---|---|---|---|
F19.2 (small) | 22.50 | 32.67 | 45.2% improved |
F9.6 (medium) | 25.93 | 33.51 | 29.2% improved |
F6.4 (medium) | 24.81 | 34.43 | 38.7% improved |
F4.8 (full) | 24.34 | 35.86 | 47.3% improved |
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Fu, B.; Li, C.; Dong, B.; Ou, P. Enhanced Digital Gradient Sensing Using Backlight Digital Speckle Target. Sensors 2020, 20, 6557. https://doi.org/10.3390/s20226557
Fu B, Li C, Dong B, Ou P. Enhanced Digital Gradient Sensing Using Backlight Digital Speckle Target. Sensors. 2020; 20(22):6557. https://doi.org/10.3390/s20226557
Chicago/Turabian StyleFu, Baofei, Chenzhuo Li, Bo Dong, and Pan Ou. 2020. "Enhanced Digital Gradient Sensing Using Backlight Digital Speckle Target" Sensors 20, no. 22: 6557. https://doi.org/10.3390/s20226557
APA StyleFu, B., Li, C., Dong, B., & Ou, P. (2020). Enhanced Digital Gradient Sensing Using Backlight Digital Speckle Target. Sensors, 20(22), 6557. https://doi.org/10.3390/s20226557