Moiré topography using developed recording methods

Where moiré topography is used to record the shape of objects of approximately cylindrical form or that of a series of such objects, a scanning method with a slit camera can be employed. One such method takes photographs by combining conventional shadow type and projection type moiré topography with a slit camera. Laser methods of line projection combined with a scanning method developed from the projection type of moiré topography are also utilised. The main features of the latter method are that it is not affected by any diffraction effect caused by the grid and that highly accurate recording can be achieved with excellent image quality using the properties of the laser beam. Another distinct advantage is that it is capable of recording the shape of a self-luminous object without contacting by selection of laser wavelenghts and matching optical filters. The laser scanning method can therefore be considered to have considerable potential for future applications.     

Study on the position and orientation measurement method with monocular vision system

In order to estimate the position and orientation of an object with a single camera, a novel measurement method based on pinhole camera model with five reference points is presented. Taking the specially designed planar target with the monocular vision system, the projection line of the reference points is built. According to the projection model, the coordinates of the reference points in the camera coordinate system are estimated with the least-squares algorithm. Thus the position and orientation of the target are worked out. Experimental result shows that the measurement precision of angle is less than 0.2°, and that of displacement is less than 0.1 mm.     

High precision camera calibration in vision measurement

In order to ensure the measurement precision for shape recovery from a stereo vision system, a novel high precision calibration method is presented. Some standard points acquired from the object of interest are used as standard world points. There are four rotation matrices and translation matrices that need to be calibrated, the first is between the left camera and the world coordinate, the second is between the right camera and the world coordinate, the third is between the left camera and the right camera, and the last is between the right camera and the left camera. The lens distortion parameters include radial and tangential distortion. The merits of the calibration method are its high precision, easy of operation, and high reliability.     

基于交比不变性的投影仪标定

提出了一种新的投影仪标定方法以提高数字光栅投影三维测量中投影仪标定的准确性。该方法结合二次投影技术和交比不变性进行投影仪标定。采用二次投影技术解决投射图案与标定板图案互相干扰的问题;采用交比不变性以避免引入相机的标定误差。接着进行了对比实验,以验证所提方法的有效性。选取需要相机参数的传统投影仪标定方法以及根据全局单应性的投影仪标定方法作为对比方法。结果显示,本方法的反投影误差标准差分别从(0.2275,0.2264)像素和(0.1397,0.0997)像素降低到(0.0645,0.0601)像素,反投影误差的最大值分别从1.222像素和0.5617像素降低到0.2421像素。另外,该方法还可同时标定相机,从而获得整个三维测量系统的参数。本文提出的方法可以避免相机标定参数的误差传递,提高投影仪的标定精度。     

A conduction model for deep penetration laser welding based on an actual keyhole

Using a specially designed experimental setup and properly choosing the sample material and the process parameters, we obtained a clear stable keyhole with a high-speed camera. On the basis of the actual keyhole profile, a conduction model with a cylindrical surface heat source has been developed under the assumption of the keyhole per thin layer being cylindrical. The model is numerically solved by the finite-difference method, the temperature field around the keyhole and the heat flux lost on the keyhole wall can be obtained. The effects of such factors as the shape and the size of the keyhole, the welding speed on the shape of the melt pool are studied. By comparing the laser intensity absorbed on the keyhole walls with the heat flux lost there, the mechanism of energy balance on the keyhole walls was investigated.     

数码相机综合评测系统

由于光电传感器、数字图像处理、电子元器件等各领域技术的发展,数码相机的成像质量在过去的十年里有了长足的发展。加工成本的下降使光电成像系统在众多领域得到广泛使用,成像镜头和成像系统的成像性能测试和评价也受到广泛的关注。数码相机可以方便地输出计算机识别的数字图像,而数字图像可以用计算机在无人干预的条件下自动处理,这使得数码相机成像质量的客观评测成为可能。在相关标准基础上,研究了数码相机多个参数的客观评测方法与计算方法。在单个参数评测的基础上,用基于属性模型评价的方法综合多个参数,对所评测的数码相机做出一个综合的等级评价和评分。     

Application of computer vision and laser interferometer to the inspection of line scale

In the paper machine vision, laser interferometer and coordinate measuring machine (CMM) are combined to develop a vision inspection system. The measurement capability of the developed system is investigated by measuring the distances between the lines on a standard line scale. The vision camera is used to replace the probe of the CMM to take the images of the interested lines on a line scale at two different positions. Meanwhile, the displacement of the CCD camera is measured using laser interferometer. Using subpixel edge localization and outlier-excluding least-squares regression, the distance between two interested lines is computed under an image plane coordinate system. By adding the displacement of the CCD camera measured using laser interferometer, the line space can be determined. Experiments have been performed repeatedly to measure the line space on the 1.00 and 300.0 mm line scales. Results indicate that the measured data only have a little fluctuation and are close to those obtained by the NML (National Measurement Laboratory, Taiwan).     

CBERS-02B星HR相机内方位元的在轨标定方法

遥感相机内方位元素的在轨标定对遥感图像的定位和测量具有重要意义.利用线阵推扫传感器构像模型,提出了一种对CBERS-02B星HR相机内方位元素进行在轨标定的方法.该方法以内方位元素和姿态角为未知参数,建立地面控制点和相应像点的共线方程组,通过解算共线方程组获得内方位元素.实验证明,用该方法对内方位元素进行在轨标定,具有...     

Shape determination for deformed electromagnetic cavities

The measured physical parameters of a superconducting cavity differ from those of the designed ideal cavity. This is due to shape deviations caused by both loose machine tolerances during fabrication and by the tuning process for the accelerating mode. We present a shape determination algorithm to solve for the unknown deviations from the ideal cavity using experimentally measured cavity data. The objective is to match the results of the deformed cavity model to experimental data through least-squares minimization. The inversion variables are unknown shape deformation parameters that describe perturbations of the ideal cavity. The constraint is the Maxwell eigenvalue problem. We solve the nonlinear optimization problem using a line-search based reduced space Gauss–Newton method where we compute shape sensitivities with a discrete adjoint approach. We present two shape determination examples, one from synthetic and the other from experimental data. The results demonstrate that the proposed algorithm is very effective in determining the deformed cavity shape.     

Air bubbles under vertical vibrations

This paper reports on an experimental study of the splitting instability of an air bubble a few centimetres in diameter placed in a sealed cylindrical cell filled with liquid and submitted to vertical oscillations. The response of the bubble to the oscillations is observed with a high-speed video camera. It is found that the bubble dynamics is closely associated with the acceleration of the cell Γ. For small acceleration values, the bubble undergoes minor shape deformations. With increasing acceleration values, these deformations are amplified and for sufficiently large Γ the bubble becomes toroidal. The bubble may then become unstable and split into smaller parts. The onset of bubble division is studied and its dependency on physical parameters such as the fluid viscosity, the fluid surface tension and the initial size of the bubble is presented. It is found that the criterion for the bubble splitting process is associated with a threshold based on the acceleration of the oscillations. Above this threshold, the number of bubbles present in the cell is observed to grow until a final steady state is reached. Data analysis reveals that the final bubble size may be characterized in terms of Bond number.     

Polypropylene-natural fibre composites. Analysis of fibre structure modification during compounding and its influence on the final properties

The final properties of composite materials are highly dependent on the residual geometrical parameters (length, diameter, aspect ratio), orientation and distribution of the fibres in the matrix, which in turn are related to the processing conditions. This study analysed the fibre structure variation during the processing of a polypropylene matrix reinforced with cellulose flax pulp for different reinforcement concentrations. The fibre's geometrical parameters, length, diameter and aspect ratio have been measured and their statistical distributions have been assessed for each concentration. Furthermore, the effect of the microstructure variation on the final mechanical properties was analysed. In particular, changes in the interfacial area were evaluated based on the hypothesis that the fibres were cylindrical in shape and considering the average values of the diameters and the lengths calculated using a statistical distribution approach. The fibre interfacial area after the process decreases as the fibre concentration increases and this evaluation explains how the adhesion methods that are used for fibre surface modification fail because of the decrement in the modifier interfacial density. The Halpin–Tsai approach was used to model the experimental data obtained from tensile tests for different composites, so as to confirm the effect of fibre parameters, such as aspect ratio and interfacial area values, in the PP/cellulose blends final properties.     

改正镜作为LAMOST真空相机封窗的可行性研究

为提高真空相机光学性能,对现有改正镜作为真空相机封窗进行了可行性研究。通过现有改正镜几何模型,将力学场映射到有限元模型中,计算改正镜在受大气压强差状态下的变形。利用最小二乘法求解Zernike多项式前6项系数和拟合求解改正镜面形方程,分析变形后的改正镜对真空相机像质影响。研究结果表明:相对于原有像质的弥散半径,变形后的改正镜使得真空相机点阵图的弥散半径增大且最大增大41.9%,通过调节CCD焦距从249.554 mm变为249.574 mm,使得CCD点阵图弥散半径相对于原来增大0.301%~1.09%,保持了LAMOST低分辨率光谱仪相机原有的像质要求,说明现有改正镜可直接用于真空相机设计方案。     

Size and shape effects on the orientation of solutes in nematic liquid crystals

A new model is introduced to describe the ordering of solute molecules in nematic liquid crystals where the average electric field gradient experienced by the solute is zero. For such cases the average orientation of the solute correlates with its size and shape. We assume a mean-field potential that depends on the length of the projection of the solute onto the axis parallel to the director and the circumference of the projection onto the plane perpendicular to the director. The model is used to fit the experimental values of the order parameters of a variety of rigid molecules having different symmetries. Very good fits for the order parameters of 1CB and the quadrupolar coupling of 5CB were obtained using the same set of parameters used to fit the rigid solutes. This shows that the contribution to orientational order from size and shape effects can be calculated from a potential with solute-independent parameters.     

Focusing properties of concentric piecewise cylindrical vector beam

The focusing properties of a concentric piecewise cylindrical vector beam is investigated theoretically in this paper. The beam consists of three portions with different and changeable phase retardation and polarization. Numerical simulations show that the evolution of the focal shape is very considerable by changing the radius and polarization rotation angle of each portion of the vector beam. And some interesting focal spots may occur, such as two- or three-peak focus, dark hollow focus, ring focus, and two-ring-peak focus. Corresponding gradient force patterns are also computed, and novel trap patterns, including cup shell shape trap with one trap at its each side along axis, rectangle shell shape trap with one trap at its each side, dumbbell optical trap, spherical shell optical trap, may occur, which shows that the concentric piecewise cylindrical vector beam can be used to construct controllable optical tweezers.     

C型臂造影系统成像模型和运动模型标定方法研究

C型臂数字造影系统成像原理与相机成像原理类似,但自身机械结构导致其内参随方位改变而变化.提出了一种利用系统提供的方位参数直接计算成像系统内参和外参的新方法,该方法建立在造影系统成像特点和C型臂运动规律的基础上,并利用计算机视觉中的相关理论进行了描述.根据对精度、复杂度和灵活性的不同要求,提出了三种不同层次的模型,模型1用于计算一组特定方位下的系统内参和外参,模型2用于计算发射源到像增强器的距离固定时系统的内外参数,模型3用于计算仟意方位下的系统内外参数.实验结果表明模型1的精度达到亚像素级,可以应用于对精度要求较高的场合;模型2和模型3的精度稍低,但具有较好的灵活性.     

A rigorous evaluation of spin-Hamiltonian parameters and linewidth from a polycrystalline EPR spectrum.

Details are given of a procedure to evaluate the spin-Hamiltonian (SH) parameters and the linewidth from a polycrystalline EPR spectrum by using a least-squares fitting (LSF) technique in conjunction with numerical diagonalization of the SH matrix. The required resonance line positions are computed rather quickly using a homotopy technique, in which the position at an external magnetic field (B) orientation (theta, phi) is used as the initial value in a LSF procedure to estimate the position at an infinitesimally close B-orientation, (theta + deltatheta, phi + deltaphi). The resonance line positions are calculated successively in this procedure for all orientations of B over a grid of (theta, phi) values for the unit sphere. The eigenvectors of the SH matrix are used to calculate the intensities of the EPR lines exactly for each orientation of B. Details are given of how to compute rigorously the first and second derivatives of the chi(2)-function with respect to the SH parameters and the linewidth using the eigenvalues and eigenvectors of the spin-Hamiltonian matrix for a polycrystalline spectrum required in the LSF procedure. It is explained how this technique is generalized to include two or more magnetically inequivalent paramagnetic species, as well as how it is used for the simulation of other EPR-related spectra. The procedure is illustrated by evaluation of the Mn(2+) SH parameters and Lorentzian linewidth from the 249.9-GHz EPR spectrum of Mn(gamma-picoline)(4)I(2).     

TDI imaging and scanning moiré for online defect detection

This paper explains the application of scanning moiré in association with TDI (Time Delay and Integration) imaging for complete peripheral inspection of cylindrical objects. Based on the structured light technique, a grating pattern modulated by deformations, such as dents on the surface of a rotating cylindrical object, is recorded using a TDI camera. The illumination system consists of an intensity modulated, line generating laser diode aligned at an angle to the camera axis. By using the TDI option for recording every nth line, an online scanning moiré pattern is generated. After providing a simple explanation of the scanning moiré, the effects of object rotation speed and TDI scan speed on the fringe pattern are discussed and demonstrated. The techniques presented here offer low cost solutions to industrial machine vision tasks related to peripheral imaging and inspection of cylindrical objects.     

A unified approach for least-squares surface fitting

This paper presents a novel approach for least-squares fitting of complex surface to measured 3D coordinate points by adjusting its location and/or shape. For a point expressed in the machine reference frame and a deformable smooth surface represented in its own model frame, a signed point-to-surface distance function is defined,and its increment with respect to the differential motion and differential deformation of the surface is derived. On this basis, localization, surface reconstruction and geometric variation characterization are formulated as a unified nonlinear least-squares problem defined on the product space SE(3)×m. By using Levenberg-Marquardt method, a sequential approximation surface fitting algorithm is developed. It has the advantages of implementational simplicity, computational efficiency and robustness. Applications confirm the validity of the proposed approach.     

The shape gradient of the least-squares objective functional in optimal shape design problems of radiative heat transfer

Optimal shape design problems of steady-state radiative heat transfer are considered. The optimal shape design problem (in the three-dimensional space) is formulated as an inverse one, i.e., in the form of an operator equation of the first kind with respect to a surface to be optimized. The operator equation is reduced to a minimization problem via a least-squares objective functional. The minimization problem has to be solved numerically. Gradient minimization methods need the gradient of a functional to be minimized. In this paper the shape gradient of the least-squares objective functional is derived with the help of the shape sensitivity analysis and adjoint problem method. In practice a surface to be optimized may be (or, most likely, is to be) given in a parametric form by a finite number of parameters. In this case the objective functional is, in fact, a function in a finite-dimensional space and the shape gradient becomes an ordinary gradient. The gradient of the objective functional, in the case that the surface to be optimized is given in a finite-parametric form, is derived from the shape gradient. A particular case, that a surface to be optimized is a “two-dimensional” polyhedral one, is considered. The technique, developed in the paper, is applied to a synthetic problem of designing a “two-dimensional” radiant enclosure.     

Online self-camera orientation based on laser metrology and computer algorithms

An online self-camera orientation for mobile vision is presented. In this technique, the camera orientation is determined during the vision task. This procedure is carried out by Bezier networks of a laser line. Here, the camera orientation is calibrated when the camera is turned during the vision task. Also, the networks perform the three-dimensional vision. The network structure is built based on the behavior of the line shifting, which is provided by the surface depth. From this structure, the initial calibration and the online self-camera orientation are deduced. The proposed technique avoids calibrated references and physical measurements, which are used in the traditional calibration of camera orientation. Thus, calibration limitations caused by camera orientation modifications are overcome to perform the three-dimensional vision. Therefore, the proposed self-camera orientation improves the accuracy and performance of the mobile vision. It is because online data of calibrated references are not passed to the vision system. This procedure represents a contribution in the field of the calibration of camera orientation. To elucidate this contribution, an evaluation is performed based on the reported methods of self-calibration of camera orientation. Also, the time processing is described.