Long Exposure Short Pulse Synchronous Phase Lock Method for Capturing High Dynamic Surface Shape
<p>(<b>a</b>) Signal flow. The red line represents optical paths, and the black line represents electronic paths. (<b>b</b>) Synchronization relationship.</p> "> Figure 2
<p>(<b>a</b>) Vibrating mirror (VM) diagram. (<b>b</b>) Coordinate system.</p> "> Figure 3
<p>(<b>a</b>) Relationship between dwell time (<span class="html-italic">dt</span>) and blur angle (<math display="inline"><semantics> <mrow> <mi>d</mi> <mi>θ</mi> </mrow> </semantics></math>). (<b>b</b>) The synchronization relationship.</p> "> Figure 4
<p>Experimental setup. (<b>a</b>) Experiment setup using long exposure short pulse synchronous phase lock (LSPL). (<b>b</b>) Interference optical path (IOP) setup in the laboratory. (<b>c</b>) Computer and controller. (<b>d</b>) The experiment setup using a traditional interferometer.</p> "> Figure 5
<p>Experimental results using the traditional interferometer approach. (<b>a</b>) Interference pattern on a static VM. (<b>b</b>) No interference pattern on a vibrating VM.</p> "> Figure 6
<p>Experimental results using the LSPL approach at <span class="html-italic">SL</span>(0). (<b>a</b>) Interference pattern with a static VM. S1, S2, and S3 are the interference patterns on a single image. (<b>b</b>) Interference pattern with a vibrating VM at position synchronization signal (PSS) = 10 Hz. (<b>c</b>) Interference pattern at PSS = 20 Hz. (<b>d</b>) Interference pattern at PSS = 30 Hz. (<b>e</b>) Interference pattern at PSS = 50 Hz. (<b>f</b>) Interference pattern at PSS = 100 Hz.</p> "> Figure 7
<p>Experimental results using the LSPL approach. (<b>a</b>) Interference pattern with the VM in a vibrating state when PSS = 10 Hz, <span class="html-italic">SL</span>(−110). (<b>b</b>) Interference pattern when PSS = 10 Hz, <span class="html-italic">SL</span>(110).</p> ">
Abstract
:1. Introduction
- LSPL: Long Exposure Short Pulse Synchronous Phase Lock
- VM: vibrating mirror
- LPW: laser pulse width
- : sampling location
- IOP: Interference optical path
2. Approach Overview
- The laser pulse must arrive at the VM just at the moment that the VM is reaching the .
- The interference pattern must be generated at the blur angle () within the dwell time ().
- The laser pulse controlled by the PSS must be strictly aligned with the SL, so the accuracy of the PSS must meet the condition that the synchronization accuracy is .
- Only one laser pulse is generated within the period of the camera’s exposure time to produce one interference pattern, otherwise the interference fringe captured by the camera will be blurred.
3. Experimental Setup
4. Results
4.1. Experimental Results with the Traditional Interferometer
4.2. Experimental Results Using LSPL
5. Discussion and Conclusions
- Unlike high-speed projection-imaging technology that uses expensive high-frequency cameras to capture dynamic images, our proposed method uses inexpensive commercial cameras to acquire the surface interference pattern vibrating at 3033 Hz using a frame rate as low as 10 fps.
- Acquiring the interference pattern at the sample location SL(i) has two meanings: (1) the one-dimensional turntable rotates at the corresponding angle according to the sampling location (SL) of the VM to be measured; and (2) the phase shifter moves a phase offset corresponding to SL(i) and a PSS is generated. The PSS synchronizes the laser pulse and the camera for the generation and acquisition of the interference fringe of the VM at SL(i). Since the frame frequency of the camera is 10 Hz, each image frame captured by the camera is separated by 303.3 VM vibration cycles, but they are all interference patterns captured at a fixed position SL(i) of each vibration cycle. When the turntable rotates from SL(−110) to SL(110) (a total of 221 SLs), all positions within a single vibration cycle of the VM are measured.
- Compared to the traditional interference methods, the proposed approach can realize dynamic surface shape measurement while the VM is vibrating, while the traditional interference method failed.
- In addition, the difference between our proposed approach and the traditional interference method is that the laser we used is a pulsed laser that can capture the dynamic surface shape on a single frame image using a single pulse.
- The proposed approach adopts the method of LSPL, where a PSS forms a nanosecond-precision phase-lock relationship between the VM’s phase and the laser pulse and camera acquisition.
- The constraint conditions for capturing the dynamic surface shape must be satisfied, such as “the laser pulse controlled by the PSS must be strictly aligned with the SL”.
- The experiment shows that the VM’s dynamic surface shape can be captured using only a single pulse within the period of the camera’s exposure time. If more than one pulse is emitted within the period of the camera’s exposure time, the interference patterns will be blurred.
- The experimental results verify the correctness of the LSPL approach.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Parameter | Value | Unit |
---|---|---|
VM Frequency | 3033 | Hz |
VM Amplitude | rad | |
MAV | 48.8 | |
MAA | ||
exposure time | 100 | ms |
Camera Frame Rate | 10 | fps |
LPW | 129 | ns |
Laser wavelength λ | 532 | nm |
rad | ||
476 | ns | |
Location interval | 1494 | ns |
2 | m | |
90 (<495.5) | ns | |
221 |
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Han, W.; Gao, X.; Fan, Z.; Bai, L.; Liu, B. Long Exposure Short Pulse Synchronous Phase Lock Method for Capturing High Dynamic Surface Shape. Sensors 2020, 20, 2550. https://doi.org/10.3390/s20092550
Han W, Gao X, Fan Z, Bai L, Liu B. Long Exposure Short Pulse Synchronous Phase Lock Method for Capturing High Dynamic Surface Shape. Sensors. 2020; 20(9):2550. https://doi.org/10.3390/s20092550
Chicago/Turabian StyleHan, Weiqiang, Xiaodong Gao, Zhenjie Fan, Le Bai, and Bo Liu. 2020. "Long Exposure Short Pulse Synchronous Phase Lock Method for Capturing High Dynamic Surface Shape" Sensors 20, no. 9: 2550. https://doi.org/10.3390/s20092550
APA StyleHan, W., Gao, X., Fan, Z., Bai, L., & Liu, B. (2020). Long Exposure Short Pulse Synchronous Phase Lock Method for Capturing High Dynamic Surface Shape. Sensors, 20(9), 2550. https://doi.org/10.3390/s20092550