MULTIPARAMETER MEASUREMENT FOR RACEWAY GROOVE OF BEARING BASED ON 3D RECONSTRUCTION WITH DIGITAL STRUCTURED LIGHT

A fast 3D reconstruction method based on structured light to measure various parameters of the raceway groove is presented. Digital parallel grating stripes distributed with sine density are projected onto the raceway groove by a DLP projector, and distorting of stripes is happened on the raceway. Simultaneously, aided by three-step phase-shifting approach, three images covered by different stripes are obtained by a high-resolution CCD camera at the same location, thus a more accuracy local topography can be obtained. And then the bearing is rotated on a high precision computer controlled rotational stage. Three images are also obtained as the former step at next planned location triggered by the motor. After one cycle, all images information is combined through the mosaics. As a result, the 3D information of raceway groove can be gained. Not only geometric properties but also surface flaws can be extracted by software. A preliminary hardware system has been built, with which some geometric parameters have been extracted from reconstructed local topography.

Calibration for 3D Structured Light Measurement

A calibration procedure was developed for three-dimensional(3D) binocular structured light measurement systems. In virtue of a specially designed pattern, matching points in stereo images are extracted. And then sufficient 3D space points are obtained through pairs of images with the intrinsic and extrinsic parameters of each camera estimated prior and consequently some lights are calibrated by means of multi point fitting. Finally, a mathematical model is applied to interpolate and approximate all dynamic scanning lights based on geometry. The process of calibration method is successfully used in the binocular 3D measurement system based on structured lights and the 3D reconstruction results are satisfying.

Generative deep-learning-embedded asynchronous structured light for three-dimensional imaging

Three-dimensional(3D)imaging with structured light is crucial in diverse scenarios,ranging from intelligent manufacturing and medicine to entertainment.However,current structured light methods rely on projector-camera synchronization,limiting the use of affordable imaging devices and their consumer applications.In this work,we introduce an asynchronous structured light imaging approach based on generative deep neural networks to relax the synchronization constraint,accomplishing the challenges of fringe pattern aliasing,without relying on any a priori constraint of the projection system.To overcome this need,we propose a generative deep neural network with U-Net-like encoder-decoder architecture to learn the underlying fringe features directly by exploring the intrinsic prior principles in the fringe pattern aliasing.We train within an adversarial learning framework and supervise the network training via a statisticsinformed loss function.We demonstrate that by evaluating the performance on fields of intensity,phase,and 3D reconstruction.It is shown that the trained network can separate aliased fringe patterns for producing comparable results with the synchronous one:the absolute error is no greater than 8μm,and the standard deviation does not exceed 3μm.Evaluation results on multiple objects and pattern types show it could be generalized for any asynchronous structured light scene.

Nonlinear effect of the structured light profilometry in the phase-shifting method and error correction

Digital structured light （SL） profilometry is increasingly used in three-dimensional （3D） measurement technology. However, the nonlinearity of the off-the-shelf projectors and cameras seriously reduces the measurement accuracy. In this paper, first, we review the nonlinear effects of the projector-camera system in the phase-shifting structured light depth measurement method. We show that high order harmonic wave components lead to phase error in the phase-shifting method. Then a practical method based on frequency domain filtering is proposed for nonlinear error reduction. By using this method, the nonlinear calibration of the SL system is not required. Moreover, both the nonlinear effects of the projector and the camera can be effectively reduced. The simulations and experiments have verified our nonlinear correction method.

A comparison of summer precipitation structures over the South China Sea and the East China Sea based on tropical rainfall measurement mission

The three-dimensional structures of summer precipitation over the South China Sea （SCS） and the East China Sea （ECS） are investigated based on tropical rainfall measurement mission （TRMM）. The primary results are as follows. First, both the convective and stratiform precipitation rates in the SCS are much higher than those of the ECS. The contribution of the convective cloud precipitation to the surface precipitation is primarily over the SCS and the ECS with a proportion of about 70%, but the contribution of convective cloud precipitation is slightly larger in the SCS than the ECS. The contribution of stratus precipitation is slightly larger in the ECS than that in the SCS. Second, the content of cloud particles and precipitation particles in the ECS in June was greater than that in the SCS, while in July and August, the content of cloud and precipitation particles in the ECS was less than that in the SCS. Third, the latent heat profile of the ECS is quite different from that of the SCS. In June, the peak values of evaporation and condensation latent heating rates in the ECS are greater than those in the SCS. In July and August, however, the peak values of evaporation and condensation latent heating rates in the ECS are about 0.05°/h less than those in the SCS.

Research on Visual Detection Algorithm for Groove Feature Sizes by Means of Structured Light Projection

The visual inspection is an economical and effective method for welding. For measuring the feature sizes of grooves,a method based on line structured light is presented. Firstly,an adaptive algorithm to extract the subpixel centerline of structured light stripes is introduced to deal with the uneven width and grayscale distributions of laser stripes,which is based on the quadratic weighted grayscale centroid. By means of region-of-interest(ROI)division and image difference,an image preprocessing algorithm is developed for filtering noise and improving image quality. Furthermore,to acquire geometrical dimensions of various grooves and groove types precisely,the subpixel feature point extraction algorithm of grooves is designed. Finally, experimental results of feature size measuring show that the absolute error of measurement is 0.031—0.176 mm,and the relative error of measurement is 0.2%—3.6%.

Three-Dimensional Thermo-Elastic-Plastic Finite Element Method Modeling for Predicting Weld-Induced Residual Stresses and Distortions in Steel Stiffened-Plate Structures

The objective of the present paper is to develop nonlinear finite element method models for predicting the weld-induced initial deflection and residual stress of plating in steel stiffened-plate structures. For this purpose, three-dimensional thermo-elastic-plastic finite element method computations are performed with varying plate thickness and weld bead length (leg length) in welded plate panels, the latter being associated with weld heat input. The finite element models are verified by a comparison with experimental database which was obtained by the authors in separate studies with full scale measurements. It is concluded that the nonlinear finite element method models developed in the present paper are very accurate in terms of predicting the weld-induced initial imperfections of steel stiffened plate structures. Details of the numerical computations together with test database are documented.

High-accuracy 3-D deformation measurement method with an improved structured-light principle

In this paper,a high-accuracy 3-D deformation measurement(HADM)method with structured light is proposed and applied to wing deformation measurement in wind tunnel experiments.The present method employs an arbitrarily arranged fringe projector and a perpendicularly placed camera.The exact phase-height mapping using the phase differences of the projected sinusoidal fringe patterns,as well as the spatial distribution of the fringe,is accurately derived.It not only presents high feasibility but also reduces systemic uncertainties arising from deviations between the ideal model and the real-world conditions.Meanwhile,a dynamic boundary process algorithm is proposed to reduce the measurement uncertainty caused by fringe fracture near the object boundary.It is calibrated that a high accuracy with the average measurement uncertainty of 0.0237 mm is achieved,which is less than 0.01%of the side length of 25 cm of the field of view.In the wind tunnel experiments,the 3-D deformations of the elastic wing,particularly the key geometric parameters such as wing tip position,angle of attack,and dihedral angle,are well reconstructed to provide an in-depth explanation for the aerodynamic characteristics.

Development of an In-Situ Laser Machining System Using a Three-Dimensional Galvanometer Scanner

In this study, a three-dimensional (3D) in-situ laser machining system integrating laser measurement and machining was built using a 3D galvanometer scanner equipped with a side-axis industrial camera. A line structured light measurement model based on a galvanometer scanner was proposed to obtain the 3D information of the workpiece. A height calibration method was proposed to further ensure measurement accuracy, so as to achieve accurate laser focusing. In-situ machining software was developed to realize time-saving and labor-saving 3D laser processing. The feasibility and practicability of this in-situ laser machining system were verified using specific cases. In comparison with the conventional line structured light measurement method, the proposed methods do not require light plane calibration, and do not need additional motion axes for 3D reconstruction;thus they provide technical and cost advantages. The insitu laser machining system realizes a simple operation process by integrating measurement and machining,which greatly reduces labor and time costs.

Dynamically measuring the holo-information of light fields in three-dimensional space using a periodic polarization-structured light

Spatially structured light field has attracted great attention due to its novel properties and application potential in numerous fields.Among them,the most striking one is the polarization-structured light,known as the vector beam.Here,using a periodic polarization-structured light,we propose a method to dynamically measure the holo-information of light fields,including the amplitude,phase,and polarization distributions,in three-dimensional(3D)space.The measurement system is composed of a Mach-Zender interferometer involving a liquid crystal polarized grating in the reference arm,which is simple,stable,and easy to operate.Featuring the single-shot measurement,this method supports observing the dynamic variation of object light fields.The accuracy,3D polarimetry,and dynamic observation of this method are validated by measuring a calibrated quarter-wave plate,a vector vortex beam,a Poincarébeam,and a stressed polymethyl methacrylate sample.

Studies of surface plasmon resonance sensor using bi-beam differential measurement approach

In this paper, a low-cost measurement approach with bi-beam was presented, which can be used for real-time detection and online analysis of solution refractive index, based on systematical analysis and experiments of conventional detection methods on surface plasmon resonance sensor. This novel method was analyzed theoretically and based on it a sensor system set was established. The factors that affect the sensor's sensitivity and working range were discussed. The angular adjustment setup was simplified, errors produced by movable components were avoided and the maneuverability was enhanced with this new method. The noiseproof feature and stability of the sensor system were greatly improved as well.

Phase Error Compensation of Three-Dimensional Reconstruction Combined with Hilbert Transform

Nonlinear response is an important factor affecting the accuracy of three-dimensional image measurement based on the fringe structured light method.A phase compensation algorithm combined with a Hilbert transform is proposed to reduce the phase error caused by the nonlinear response of a digital projector in the three-dimensional measurement system of fringe structured light.According to the analysis of the influence of Gamma distortion on the phase calculation,the algorithm establishes the relationship model between phase error and harmonic coefficient,introduces phase shift to the signal,and keeps the signal amplitude constant while filtering out the DC component.The phase error is converted to the transform domain,and compared with the numeric value in the space domain.The algorithm is combined with a spiral phase function to optimize the Hilbert transform,so as to eliminate external noise,enhance the image quality,and get an accurate phase value.Experimental results show that the proposed method can effectively improve the accuracy and speed of phase measurement.By performing phase error compensation for free-form surface objects,the phase error is reduced by about 26%,and about 27%of the image reconstruction time is saved,which further demonstrates the feasibility and effectiveness of the method.

High Curvature Stripe Profile Extraction Algorithm of Line Structured Light Measuring System

In the line structured light measuring system, the accuracy of the process of laser stripe directly affects the measurement results. Therefore, the extraction algorithm for the laser stripe, especially the surface with high reflection and high curvature, is very important. The imaging principle of line structured light, the light intensity distribution law of laser stripe and the extraction algorithm have been studied, and a stripe profile extraction method based on real light intensity distribution has been proposed. In this algorithm, fast region of interest extraction, stripe width estimation, and adaptive filtering on the striped image are performed. Then the energy center of the stripe at the sub-pixel level is extracted. Finally, the low-quality center points are eliminated, and the context information is used to recover the missing central points. Simulated images generated based on the imaging principle of line structured light and real experimental images were used to evaluate the accuracy and repeatability of the proposed method. The results show that the method behaves excellently at the edges of high-curvature stripes;the maximum error is only 1.6 pixels, which is 1/10 of the classic Steger algorithm;the experiment repeatability is only 8.8 μm, which is 2.7 times that of the Steger method. Therefore, the proposed method improves the accuracy of object contour extraction, and it is especially suitable for contour detection of objects with high curvature.

Quantum Inverse Measurement Theory Contributing to the Birth of Interpretation System of Quantum Mechanics of Local-Realism and Determinism

The existing interpretation of quantum mechanics is contrary to common sense. The existing quantum mechanical interpretation schemes are puzzling. The confusing theory is unconvincing, and needs to be amended and completed. The successful interpretation program of quantum mechanics of local-realism and determinism is undoubtedly the most attractive. Preparing the interpretation program deserves to be chosen as a research goal. It is a very good premise to believe that an object particle consists of light-knot of monochromatic waves. According to this premise, the erroneous recognition about “superposition principle, wave-particle duality and uncertainty principle” can be corrected. Under this premise, above research goal is achieved by establishing, applying quantum mechanics inverse measurement theory, adhering to the principle that there must be a complete empirical chain in the derivation process of experimental conclusion, and using the side effect caused by accompanying-light to explain the diffraction experiment of object particles. Electron secondarily diffraction and other experiments directly prove that there is the measurement (observation) which may not destroy quantum coherence. The diffraction experiments of all kinds of particles show that the Keeping and playing of the coherence of moving particles in the vacuum have nothing to do with their previous experience. These are the existing experiments, to be found, that support the theory of quantum inverse measurements. The verification experiment of quantum inverse measurement is designed. The absolute superiorities of quantum inverse measurement and the new view of measurement of quantum mechanics are listed. These superiorities are that: it has the characteristics of local-realism and determinism;it is not contrary to common sense and there is no confusing place;it can predict several phenomena that cannot be predicted by other theories. A solid theoretical foundation has been laid for “correctly understanding the microscopic world” and establishment of local realism quantum mechanics.

基于线结构光扫描的工件高精度三维测量方法

为了提高工业中对复杂轮廓工件的测量精度和效率,设计了一套高精度非接触三维测量系统,并提出了一种基于线结构光扫描的工件轮廓三维测量方法。首先,利用高精度相机和三轴移动平台采集线结构光图像。然后,通过基于差分区间的灰度质心算法,精确而高效地提取出线结构光中心线,并生成原始点云模型。接着,对采集到的点云数据进行必要的点云滤波和精简预处理。最后,将预处理后的点云数据与CAD模型精确配准,进行工件表面轮廓的测量与误差评定。实验结果表明:测量工件轮廓高度的绝对误差小于0.07 mm,相对误差小于0.5%。所提出的三维测量系统及方法测量误差较低,能够实现工件的高精度三维测量,具有一定的工业应用价值。

圆结构光系统深孔圆度测量方法研究

圆结构光系统测量深孔(通孔)圆度时存在激光器、相机和深孔难以保持平行或同轴的问题,导致无法测量准确的圆截面,从而产生系统误差。搭建了基于圆结构光的测量系统,分析了系统误差的产生机理并提出了一种基于圆结构光系统测量圆度的方法,可对系统误差进行一定补偿:首先,获取待测深孔的内表面高分辨率三维点云,拟合点云轴线,通过刚体变换将三维点云变换到深孔轴线与相机光轴平行的位置;然后,选定一个测量截面,搜索该截面上的点和与该截面范围较近的点作为圆度评定点;最后,采用网格搜索算法完成圆度评定。测量实验的结果表明,该方法对于圆度误差的补偿效果良好,其中测量不确定度为4.78μm。

基于结构光的铆钉凹凸量双目视觉检测方法

为了弥补飞机铆钉凹凸量的传统检测方式在精度、效率及稳定性方面的不足,提出了一种基于结构光的铆钉凹凸量双目视觉检测方法。首先通过工业投影仪将结构光投射到铆接表面,由双目相机采集投影图像。然后根据铆钉边缘特征提取出铆接区域,并采用改进的格雷码解相位方法计算铆接区域表面的相位信息。根据相位信息匹配特征点,利用视差原理计算出点云。最后通过点云数据处理,计算出铆钉的凹凸量。制作标准件并完成了凹凸量测量试验,测量误差在±20μm以内,重复测量标准差小于3μm,单个铆钉测量用时约2.2 s,能够满足现场测量精度和效率要求。

基于线结构光的零件三维尺寸测量系统

针对原有接触式三维测量技术测量时间长、效率低、对零件有损伤等问题,提出一种基于线结构光的零件三维尺寸测量系统。建立光平面数学模型,采用基于平面靶标的自由移动标定法标定光平面,利用基于Hessian矩阵的Steger方法对线结构光中心提取,通过坐标变换得到零件的三维尺寸。在Visual Studio软件中的Winform窗体应用设计三维测量系统的软件交互界面,搭建实验测量平台进行多个零件的测量实验。实验结果表明,对不同零件三维尺寸测量相误差均小于4%,提出的测量系统及方法具有较高的精度和稳定性,能够满足工程应用。

单目结构光在异形工件三维重构及测量中的应用

针对工业生产中异形工件尺寸在线测量的难题,将单目相机与线激光相结合,以突破传统测量技术在复杂几何形状、成本、避免表面损伤和测量精度方面的局限性。针对线结构光条纹中心提取的挑战,对传统的Steger算法改进提出双重调节优化算法,优化Steger算法中的二值化阈值参数和光条宽度参数,以提高算法在检测条纹中心时的准确性和鲁棒性。实验结果表明:采用基于线结构光和单目相机的测量方法以及改进的结构光条纹中心提取技术,对异形工件进行了三维重构,测量误差在0.10 mm以内,处于可接受的范围。相较于传统方法,基于线结构光和单目相机的新测量方法提取的条纹中心位置更准确,能实现对异形工件的高精度测量。

基于服装个性化智能定制的三维人体测量系统物-像结构算法的研究

目前,我国基于服装个性化智能量身定制的理念日趋完善。但是,在消费者目标尺寸自动获取方面仍然缺乏实用的设备和技术,成为了大多数企业个性化智能定制发展的一个瓶颈,其根本原因是缺少实用性强的个性化智能定制系统。人体动态测量与其他工业产品精密测量相比具有自身独有的特殊性和困难。在探讨了现有的光学类基于个性化智能定制系统的现状的前提下,针对目前存在的激光三维人体扫描测量系统普遍存在硬件设备庞大、结构复杂的问题,对文中提出的基于个性化智能定制系统进行了原理设计,建立了系统的物-像结构算法的数学模型。该算法采用了扫描单元旋转的测量方式,使系统能够在垂直方向上获得较大的测量范围,目的是使系统采用较小的硬件获取满意的三维人体空间坐标,有利于节省竖直空间、减小体积。该算法已成功应用于基于服装个性化智能定制系统。为了验证本算法的精度,设计了与法国力克系统的三维人台对比扫描实验,实验数据验证了本系统结构算法的精度、工程实用性和可靠性。