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Wu D.,Tianjin University | Wu D.,Key Laboratory of Opto Electronics Information Technology of Ministry of Education | Lu Q.,Tianjin University | Lu Q.,Key Laboratory of Opto Electronics Information Technology of Ministry of Education | And 2 more authors.
Zhongguo Jiguang/Chinese Journal of Lasers | Year: 2014

According to the measurement of oil film thickness on the sea, an oil film thickness sensor based on buoy is developed using vertical incidence differential laser trigonometry. The composition and principle of sensor is introduced and the process of the system integration and debugging is presented. Ceramic grade 0 gauge block is measured as a standard thickness and high order curve is fitted based on least square method for the calibration of the sensor. 1.4~9.4 mm gauge blocks are measured to verify the precision. The results show that the measurement relative error is less than 1%.


Geng Y.,Tianjin University | Geng Y.,Key Laboratory of Opto Electronics Information Technology of Ministry of Education | Chen X.,Tianjin University | Jin W.,Tianjin University | And 4 more authors.
Zhongguo Jiguang/Chinese Journal of Lasers | Year: 2015

The analysis on the seawater refractive index which increases the error of oil film thickness measured by differential laser triangulation are taken to discover the relationship between the change of refractive index and error. Accordingly a method based on two-dimensional curved surface fitting is proposed to compensate the error. The data of thickness are measured in the water of different refractive indexes and the quadratic polynomial curved surface fitting is adopted to formulate the error, thickness and refractive index. Then the measurement of thickness is compensated by using the above the formula and the refractive index. The experiments taken on different refractive indexes show the thickness measurement compensated is closer to the true value and the error is minimized. ©, 2015, Science Press. All right reserved.


Qingguo T.,Tianjin University | Qingguo T.,Key Laboratory of Opto Electronics Information Technology of Ministry of Education | Xiangyu Z.,Tianjin University | Xiangyu Z.,Key Laboratory of Opto Electronics Information Technology of Ministry of Education | And 4 more authors.
Pattern Recognition | Year: 2016

Light stripe centerline extraction is the basic and key procedure in line-structured laser three-dimensional (3D) scanner. Based on the fact that light stripe's contour is approximately parallel to its centerline, a novel contour polygon segmentation method is proposed for extracting and optimizing centerline. Different light stripe segments are identified in images by contour tracking, and then each of them is segmented into several parts using contour polygonization. Interior angle is defined to trim open light stripe polygon and contour to make sure that centerlines extracted from open light stripes do not include superfluous points. Taking advantage of polygon segmentation, piecewise polynomial fitting method and self-adaptive interpolating strategy are adopted to acquire smoother and evenly spaced centerline points. Simulated experiments show that the proposed method can calculate centerlines from images robustly with a 0.309 pixel average accuracy. Point clouds and surface models of different objects acquired by a line-structured laser scanner demonstrate that the proposed method can produce more complete and smoother 3D models compared to other classical methods. Processing time for the proposed method is approximately positive proportional to the number of pixels in image. Quantitative analysis of time used for each sub-procedure puts forward an improvement direction for the proposed method. © 2016 Elsevier Ltd.


Pan L.,Tianjin University | Pan L.,Key Laboratory of Opto Electronics Information Technology of Ministry of Education | Zhang F.,Tianjin University | Zhang F.,Key Laboratory of Opto Electronics Information Technology of Ministry of Education | And 8 more authors.
Journal of Quantitative Spectroscopy and Radiative Transfer | Year: 2016

Use of laser diffraction is considered as a method of reliable principle and mature technique in measurements of particle size distributions. It is generally accepted that for a certain relative refractive index, the size of the scattering pattern (also called Airy disk) of spherical particles monotonically decreases with increasing particle size. This fine structure forms the foundation of the laser diffraction method. Here we show that the Airy disk size of non-absorbing spherical particles becomes larger with increasing particle size in certain size ranges. To learn more about this anomalous change of Airy disk (ACAD), we present images of Airy disk and curves of Airy disk size versus particle size for spherical particles of different relative refractive indices by using Mie theory. These figures reveal that ACAD occurs periodically for non-absorbing particles and will disappear when the absorbing efficiency is higher than certain value. Then by using geometrical optics (GO) approximation, we derive the analytical formulae for the bounds of the size ranges where ACAD occurs. From the formulae, we obtain laws of ACAD as follows: (1) for non-absorbing particles, ACAD occurs periodically, and when the particle size tends to infinity, the period tends to a certain value. As the relative refractive index increases, (2) the particle size ranges where ACAD occurs shift to smaller values, (3) the period of ACAD becomes smaller, and (4) the width of the size ranges where ACAD occurs becomes narrower. In addition, we can predict from the formulae that ACAD also exists for particles whose relative refractive index is smaller than 1. © 2015 Elsevier Ltd.


Ge B.,Tianjin University | Ge B.,Key Laboratory of Opto Electronics Information Technology of Ministry of Education | Pan L.,Tianjin University | Pan L.,Key Laboratory of Opto Electronics Information Technology of Ministry of Education | And 3 more authors.
Guangxue Xuebao/Acta Optica Sinica | Year: 2013

Laser particle sizer which based on Mie scattering theory is one of the most widely used instruments in particle size measurement. Generally the smaller the particles are, the bigger the scattering angle is. The main peak position of Mie scattered energy distribution received by the detector array moves outward. However, for some particles of relative index of refraction in certain size ranges, the main peak position of scattered energy distribution moves toward the inside of the detector array as the particle size decreases, which can be called the abnormal moving of scattered energy distribution. Based on Mie scattering theory, the patterns of such abnormal moving and abnormal particle size interval of different relative indexes of refraction are obtained, the effect on particle size analysis is analysed, a method to reduce the effect is proposed. An actual sample is measured and compared. The results show that this method can reduce the effect of abnormal moving on particle size analysis.

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