Station Planning of Laser Tracker Based on Combination Measurement
Xiong Tao, Li Shuanggao, Li Qi, and Zhao Ziyue
For the combination measurement system consisting of the laser tracker Leica AT901-MR, laser scanner Leica T-Scan5 (T-Scan), and industrial robot KUKA KR90R3100 extra, the rational planning of laser tracker stations to measure the frequently changing T-Scan pose is one of the key problems. To solve this problem, first, the construction of a combination measurement constraint model combining laser tracker and T-Scan measurement characteristics and proposing a station evaluation method to examine station viability is required. To improve the measurement efficiency and reduce the number of stations, the station planning method flow is designed based on the station evaluation method. Finally, implementing the station planning method based on Open CASCADE programming and designing a skin-scanning experiment for verification is required. The results show that the number of laser tracker stations planned by this method is less than that of the empirical method. Besides, the measurement of the skin under the planned station takes about 5 min, whereas, the empirical method takes about 40 min.
  • Sep. 14, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 17 1712001 (2021)
  • DOI:10.3788/LOP202158.1712001
Terahertz Nondestructive Test of Delamination Defects in Glass-Fiber-Reinforced Composite Materials
Wang Qishu, Mu Da, Zhou Tongyu, Ren Jiaojiao, Zhang Dandan, and Xin Yinjie
Finite-difference time-domain and terahertz time-domain spectroscopy are used to study the internal delamination defects in glass-fiber-reinforced composite materials. First, the optical parameters of the glass-fiber-reinforced composite material in the terahertz frequency band are obtained using transmission terahertz time-domain spectroscopy; the finite-difference time-domain method is used to simulate the defects. Second, a terahertz time-domain spectroscopy system is used to inspect the prefabricated sample. Finally, the defects are imaged and analyzed for comparison to the time-domain waveform data determined theoretically and through actual detection. It is found that both methods can detect delamination defects with a thickness of 0.3 mm at a distance of 3 and 5 mm from the upper surface of the materials. These results show that the finite-difference time-domain method can provide theoretical support for detecting defects in composite materials by using terahertz time-domain spectroscopy while reducing the dependence on standard components; the terahertz time-domain spectroscopy system can effectively detect internal defects of materials and assess their overall performance through the detection results.
  • Sep. 03, 2021
  • Acta Optica Sinica
  • Vol.41 Issue, 17 1712003 (2021)
  • DOI:10.3788/AOS202141.1712003
A New Method of Out-of-Plane Displacement Measurement for Optical Fiber Material Based on Digital Speckle Correlation Method
Zhao Ran, Hong Zhiwei, Lu Jing, Zhang Yang, Sun Yong, Huang Yonggang, and Jia Jinsheng
To monitor the micro-nano-scale deformation of optical fiber material during industrial production, this paper proposes a novel method based on the digital speckle correlation method (DSCM) to measure the out-of-plane displacement. The in-plane displacements between two consecutive images before and after material deformation are estimated by the DSCM. Then, the out-of-plane displacement field of optical fiber material under a microscope can be obtained by the wedge model. The principle of the DSCM is introduced and the measurement of out-of-plane displacement for the optical fiber material is simulated and tested based on the image spherizing algorithm. Simulation and experimental results show that the proposed method can directly extract the out-of-plane displacement from the in-plane displacement of two-dimensional images and measure the real-time deformation of optical fiber material. The experimental device used by the method is quite simple, and only an industrial camera is needed to capture two images under a microscope and thus complete the measurement. Furthermore, the out-of-plane displacement extraction process needs neither conversion of the images to the frequency domain nor phase envelope operation. The proposed method is appropriate for dynamic measurement.
  • Sep. 03, 2021
  • Acta Optica Sinica
  • Vol.41 Issue, 17 1712002 (2021)
  • DOI:10.3788/AOS202141.1712002
3D Imaging Method for Multi-View Structured Light Measurement Via Deep Learning Pose Estimation
Cui Haihua, Jiang Tao, Du Kunpeng, Guo Ronghui, and Zhao An′an
Multi-view structured light measurement is a process of utilizing structured light measurement system to achieve the complete expression of the measured object from multiple angles. Thus, the splicing of the measurement data from multiple perspectives affects the integrity of the measured object. In this paper, a new method is proposed to estimate the measurement pose using the deep learning and to directly align the multi-view data. The structure light measurement model is a four-step phase-shifting method combined with multi-frequency heterodyne method to realize the single high-precision three-dimensional reconstruction. In pose estimation, You only look once (YOLO) network is used to identify the 3D bounding box corner of the measured object, and perspective n point (PnP) algorithm is used to estimate the target pose. Since the coordinate systems of the measurement system and pose estimation are unified to the monocular camera, the data from multiple perspectives are directly spliced using the estimated pose. The feature descriptors of adjacent point clouds are established, and iterative closest point (ICP) algorithm is used to realize the high-precision stitching. The results show that the proposed measurement can effectively realize the multi-view structured light data splicing. The translation accuracy of pose estimation is better than 3 mm, the rotation accuracy is better than 1°, and the average deviation of stitching point cloud is 0.02 mm, which has a comparable accuracy level with that of using the method of the marker points. The proposed method is suitable for the multi-view structured light measurement with single pose estimation, which can improve the registration efficiency for multi-view measured data.
  • Sep. 03, 2021
  • Acta Optica Sinica
  • Vol.41 Issue, 17 1712001 (2021)
  • DOI:10.3788/AOS202141.1712001
Measuring Method of Atmospheric Carbon Dioxide Based on Tunable Fabry-Perot Interferometer
Ji Hongcheng, Xie Pinhua, Xu Jin, Li Ang, Hu Zhaokun, Huang Yeyuan, Tian Xin, Li Xiaomei, Ren Bo, and Ren Hongmei
In order to meet the needs of accurate, fast and portable measurement of greenhouse gases such as CO2 and CH4, a multi-wavelength greenhouse gas measurement system based on tunable Fabry-Perot interferometer (FPI) sensor is introduced in this paper. Using FPI as wavelength selective element, the continuous measurement in band of 3100--4400 nm (wavenumber range is 3226--2273 cm -1) is realized through interference filter. The correlation coefficient is obtained by fitting the measured absorption spectrum with the absorption cross section of CO2, and then the gas concentration of CO2 can be calculated. To correct the non-linear absorption effect that caused by the low resolution of the instrument, the iterative algorithm is used to optimize the CO2 absorption cross section. The results show that the measurement error is reduced by 18% compared with the direct fitting calculation when concentration of CO2 is 4.08×10 -4. The interference optimization, precision, the limit of detection and other parameters of the system are verified. The experimental results show that the concentration of residual CO2 in the air chamber is less than 1×10 -6, the instrument precision is ±1.32×10 -6, and the detection limit is 1.13×10 -6 (2σ, 2 times standard deviation) when the time resolution is 10 minutes. Moreover, the system is used to carry out outdoor measurement in Hefei Science Island for one week, and the daily variation results and diurnal characteristics of concentrations of CO2 are obtained, which verified the stability and reliability of the system.
  • Sep. 03, 2021
  • Acta Optica Sinica
  • Vol.41 Issue, 18 1812004 (2021)
  • DOI:10.3788/AOS202141.1812004
Real-Time Phase Measuring Profilometry Based on Single-Shot Four-Grayscale Fringe Projection
Yang Chaozhi, and Cao Yiping
A new real-time three-dimensional (3D) measuring method is proposed based on single-shot four-grayscale fringe projection, in which different non-zero three-scale grays in the four gray levels are cyclically arranged in equal width to encode a frame of three-grayscale fringe pattern. When the three-grayscale fringe pattern is projected onto the measured object, the corresponding four-grayscale deformed pattern is captured by the imaging camera, and the fourth grayscale corresponds to the shadow area in the deformed pattern. By the image segmentation method, non-zero three-grayscale fringes in the four-grayscale deformed pattern can be extracted respectively. After binarization, three frames of binary deformed patterns with 1/3 duty cycle and relative displacement of 1/3 period can be demodulated. So three frames of sinusoidal fringes with a 2π/3 shifted phase can be extracted by the inverse Fourier transform after filtering the corresponding fundamental frequency of the three frames of binary deformed patterns, and the 3D shape of the object can be reconstructed by phase measuring profilometry (PMP). The experimental results confirm the feasibility of the proposed method. Because of the fast refreshing rate and the insensitivity to the gamma effect of the projector, the proposed method has a potential application prospect in real-time 3D measurement.
  • Sep. 03, 2021
  • Acta Optica Sinica
  • Vol.41 Issue, 18 1812003 (2021)
  • DOI:10.3788/AOS202141.1812003
Surface Defect Detection in Transparent Objects Using Polarized Transmission Structured Light
Wang Wei, Wang Jie, Huang Yiyang, Yue Huimin, and Liu Yong
Transparent objects such as glass and lenses are commonly used in optical systems, and their surface quality greatly affects the performance of the host systems. Considering polarization characteristics of light, surface defect detection method using polarized transmission structured light is proposed. The constructed transmission system generates fringe-encoded polarized structured light for projection onto the surface of the measured object. The structured light deforms after passing through the object. Then, the deformation fringes are collected, phase information is extracted, modulation is solved, and surface defect information is obtained from the measured object. Experimental results show that the proposed method can eliminate the effect of dust and improve the signal-to-noise ratio for detection. Therefore, the proposed method can be suitable for surface defect detection in transparent objects such as flat thick lenses and high-curvature optical lenses.
  • Sep. 03, 2021
  • Acta Optica Sinica
  • Vol.41 Issue, 18 1812002 (2021)
  • DOI:10.3788/AOS202141.1812002
High-Precision Angular Displacement Measurement Based on Rotating Optical Field
Fu Min, Chen Fan, Zhu Ge, Shi Hailin, Wei Xiaobo, Qiao Junhong, and Leng Congyang
To tackle the problems in traditional high-precision angular displacement measurement, such as complicated manufacturing process, complex multi-probe structure and difficult installation, this paper proposes a new relevant full-circle method based on the construction of a rotating optical field, inspired by the generation principle of a rotating magnetic field. A sinusoidal uniform grating surface on the full circle is divided by an equal interval into four groups of 0°, 90°, 180°, and 270°. Alternating light intensity signals are provided for the full-circle grating surface by a one-way alternating optical field, which are transformed into electric traveling wave signals via photoelectric conversion and micro-controlled phase shift. The angular displacement measurement is realized by the interpolation of the phase difference between reference signals and electric traveling wave signals with a high-frequency clock pulse. An experimental platform is established for the comparative experiment on different principle prototypes. The influence of manufacturing precision and number of pole pairs on the measurement error is verified by experiments. The measurement error can reach ±5.0″ when the grating surface with a central angle of 2° is used in the full-circle measurement range. Since the measurement error is mainly composed of periodic error components, the measurement precision will be greatly improved after the correction of harmonic error and the quality improvement of optical field distribution. This paper verifies the suppressing effect of the proposed method on manufacturing and installation errors and provides an effective solution to the high-precision measurement for low-precision manufacturing processes.
  • Sep. 03, 2021
  • Acta Optica Sinica
  • Vol.41 Issue, 18 1812001 (2021)
  • DOI:10.3788/AOS202141.1812001
Online Phase Measurement Profilometry Based on Super-resolution Image Reconstruction
GAO Jie, CAO Yiping, and CHEN Jin
Due to the fast-moving measured online object,the captured deformed fringe patterns with motion blur may lose the phase information. Therefore, by adjusting the CCD image acquisition mode ,the CCD acquisition frame rate can be increased to adapt to the online measurement of fast moving objects. In order to obtain high-resolution deformed fringe patterns, this paper adopts a super resolution reconstruction method based on the maximum a posteriori, using Gauss and markov-gibbs random field models to construct posteriori probability of the high-resolution deformed fringe pattern, the optimal estimation of high-resolution deformed fringe patterns is obtained as the result of minimizing the objective function. In this way the deformed fringe patterns can be purified. Finally all the purified equivalent phase-shift deformed fringe patterns are used for online 3D reconstruction. The experimental results prove the effectiveness of this method. The proposed method has good application prospects in high-precision and fast online 3D measurement.
  • Sep. 01, 2021
  • Acta Photonica Sinica
  • Vol.50 Issue, 7 152 (2021)
  • DOI:10.3788/gzxb20215007.0712003
Micro-angle Measurement Method and Its Accuracy Evaluation Based on Fabry-Perot Etalon
LIU Yuan, SHEN Xiaoyan, ZHOU Shinan, GUO Xubo, YU Jing, LI Dongsheng, and LAN Xuhui
A micro-angle measurement method based on Fabry-Perot etalon is proposed. Particularly, by calculating the displacement of center of the imaging concentric rings and the focal length of the imaging objective lens, the micro angle of the deflected mirror is obtained. The evaluation model of the micro angle uncertainty, based on the uncertainty components of the center displacement and the focal length of the imaging objective lens, is constructed. The Fabry-Perot etalon with an interval of 2 mm is selected to carry out the experimental research on the measurement of micro angles, and the data is processed. The experimental results indicate that the maximum measurement uncertainty is 0.132" and 0.045" in the range of 600" and 40", respectively. The proposed method can provide a reference for the realization of the self-calibrated, higher-accuracy micro-angle measurement.
  • Sep. 01, 2021
  • Acta Photonica Sinica
  • Vol.50 Issue, 7 161 (2021)
  • DOI:10.3788/gzxb20215007.0712004