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A method for phase reconstruction in optical three-dimensional shape measurement
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作者 乔闹生 贺志 《Chinese Physics B》 SCIE EI CAS CSCD 2012年第9期267-270,共4页
In optical three-dimensional shape measurement, a method of improving the measurement precision for phase reconstruction without phase unwrapping is analyzed in detail. Intensities of any five consecutive pixels that ... In optical three-dimensional shape measurement, a method of improving the measurement precision for phase reconstruction without phase unwrapping is analyzed in detail. Intensities of any five consecutive pixels that lie in the x-axis direction of the phase domain are given. Partial derivatives of the phase function in the x- and y-axis directions are obtained with a phase-shifting mechanism, the origin of which is analysed. Furthermore, to avoid phase unwrapping in the phase reconstruction, we derive the gradient of the phase function and perform a two-dimensional integral along the x- and y-axis directions. The reconstructed phase can be obtained directly by performing numerical integration, and thus it is of great convenience for phase reconstruction. Finally, the results of numerical simulations and practical experiments verify the correctness of the proposed method. 展开更多
关键词 phase reconstruction optical three-dimensional shape measurement measurement pre-cision
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Multi-Schlieren CT Measurements of Supersonic Microjets from Circular and Square Micro Nozzles 被引量:1
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作者 Ahmad Zaid Nazari Yojiro Ishino +6 位作者 Yuta Ishiko Fumiya Ito Harumi Kondo Ryoya Yamada Takanori Motohiro Yoshiaki Miyazato Shinichiro Nakao 《Journal of Flow Control, Measurement & Visualization》 2020年第3期77-101,共25页
Instantaneous three-dimensional (3D) density distributions of a shock-cell structure of perfectly and imperfectly expanded supersonic microjets escaping into an ambient space are measured. For the 3D observation of su... Instantaneous three-dimensional (3D) density distributions of a shock-cell structure of perfectly and imperfectly expanded supersonic microjets escaping into an ambient space are measured. For the 3D observation of supersonic microjets, non-scanning 3D computerized tomography (CT) technique using a 20-directional quantitative schlieren optical system with flashlight source is employed for simultaneous schlieren photography. The 3D density distributions data of the microjets are obtained by 3D-CT reconstruction of the projection’s images using maximum likelihood-expectation maximization. Axisymmetric convergent-divergent (Laval) circular and square micro nozzles with operating nozzle pressure ratio 5.0, 4.5, 4.0, 3.67, and 3.5 have been studied. This study examines perfectly expanded, overexpanded, and underexpanded supersonic microjets issued from micro nozzles with fully expanded jet Mach numbers <em>M</em><em><sub>j</sub></em> ranging from 1.47 - 1.71, where the design Mach number is <em>M<sub>d</sub></em> = 1.5. A complex phenomenon for free square microjets called axis switching is clearly observed with two types “upright” and “diagonal” of “cross-shaped”. The initial axis-switching is 45<span style="white-space:nowrap;">°</span> within the first shock-cell range. In addition, from the symmetry and diagonal views of square microjets for the first shock-cells, two different patterns of shock waves are viewed. The shock-cell spacing and supersonic core length for all nozzle pressure ratios are investigated and reported. 展开更多
关键词 Supersonic Microjet Multi-Directional Quantitative Schlieren optical System three-dimensional (3D) measurement Computerized Tomography (CT) Circular and Square Micro Laval Nozzles
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凹透镜的焦距测量误差与光心指示偏差间关系 被引量:5
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作者 王云创 邢娟 李向民 《实验室研究与探索》 CAS 北大核心 2012年第1期15-17,28,共4页
透镜加工很难避免光心不出现偏离,同时在测量透镜的焦距过程中需要将透镜利用支架置于光具座上,这些因素必然导致光心的实际位置与轨道刻度尺上的指示位置出现偏差(简称光心指示偏差),最终必然给焦距测量带来误差。实际测量过程中经常发... 透镜加工很难避免光心不出现偏离,同时在测量透镜的焦距过程中需要将透镜利用支架置于光具座上,这些因素必然导致光心的实际位置与轨道刻度尺上的指示位置出现偏差(简称光心指示偏差),最终必然给焦距测量带来误差。实际测量过程中经常发现,即便是同一套光学仪器,多次测量结果间时常出现很大的偏差。通过分析研究,对辅助法测量凹透镜焦距系统建立了数学模型,推导出透镜的焦距与物距、光心指示偏差之间的函数关系式,总结了光心指示偏差对焦距测量误差的影响规律,即物距越大焦距测量误差越小,并且光心指示偏差左偏情形导致焦距测量值大于标称值;反之,小于标称值。实验验证显示,依据该规律可显著提高焦距的测量精度。 展开更多
关键词 凹透镜 光心指示偏差 焦距测量误差 理论分析
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Performance Analysis and Evaluation of Geometric Parameters in Stereo Deflectometry 被引量:3
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作者 Yongjia Xu Feng Gao Xiangqian Jiang 《Engineering》 SCIE EI 2018年第6期806-815,共10页
This paper presents a novel geometric parameters analysis to improve the measurement accuracy of stereo deflectometry.Stereo deflectometry can be used to obtain form information for freeform specular surfaces.A measur... This paper presents a novel geometric parameters analysis to improve the measurement accuracy of stereo deflectometry.Stereo deflectometry can be used to obtain form information for freeform specular surfaces.A measurement system based on stereo deflectometry typically consists of a fringe-displaying screen,a main camera,and a reference camera.The arrangement of the components of a stereo deflectometry system is important for achieving high-accuracy measurements.In this paper,four geometric parameters of a stereo deflectometry system are analyzed and evaluated:the distance between the main camera and the measured object surface,the angle between the main camera ray and the surface normal,the distance between the fringe-displaying screen and the object,and the angle between the main camera and the reference camera.The influence of the geometric parameters on the measurement accuracy is evaluated.Experiments are performed using simulated and experimental data.The experimental results confirm the impact of these parameters on the measurement accuracy.A measurement system based on the proposed analysis has been set up to measure a stock concave mirror.Through a comparison of the given surface parameters of the concave mirror,a global measurement accuracy of 154.2 nm was achieved. 展开更多
关键词 optical METROLOGY ERROR analysis STEREO DEFLECTOMETRY three-dimensional SHAPE measurement Performance evaluation Simulation
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三维光学测量仪在小孔直径测量中的应用 被引量:2
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作者 金文胜 张俊 顾春梅 《哈尔滨轴承》 2009年第4期36-37,共2页
简述了利用三维光学测量仪测量定点高度的小孔(10mm以下)内径尺寸的方法,解决了用塞规测量小孔内径传统方法无法测量定点高度内径尺寸的生产难题。
关键词 三维光学测量仪 小孔内径 测量方法
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