凸轮CAD／CAM软件的设计与开发——毕业设计中的教学与科技研发实践

通过ObjectARX技术对AutoCAD进行二次开发，实现凸轮的参数化设计，其中以圆弧代替直线逼近凸轮轮廓曲线，能自动生成相应的数控加工代码，以及实现仿真加工。     

用HOUGH变换改进的曲率法识别平面轮廓图元

针对检测精度与检测速度两大指标,提出了用HOUGH变换改进的曲率法平面轮廓图元识别方法。开发了基于邻域值的轮廓点分类算法,采用曲率阈值法筛选轮廓点、投影高度法判别图元属性及分类轮廓点,构建了基于HOUGH变换的直线图元、圆弧图元分割与融合算法。对提出的方法分别进行了特征点检测精度与检测速度对比实验和特征点检测能力测试实验。实验结果表明,提出的方法图元识别准确、检测速度快、通用性好。     

高分辨力PCB裸板图像轮廓快速圆弧探测

当前主流的在线高精度PCB裸板缺陷AOI检测系统均采用基于轮廓矢量化分析比对方法,圆弧探测是实现轮廓矢量化的关键环节。本文提出一种快速的圆弧探测方法,首先采用DP(Douglas-Peucker)算法对轮廓进行曲线抽稀处理,将轮廓分割为直线段基元并计算法向角,然后依次计算各相邻直线段基元的法向角偏差之和,并与基元中点位置值一起形成法向角变换曲线,再次采用DP算法检测变换曲线中的直线段即可完成圆弧探测。本文将圆弧探测简化为两次直线探测,算法复杂度为O(n),具有非常高的计算效率。实验结果表明,本文方法与Halcon商业软件中的圆弧检测算法相比,准确率更高且耗时更少。     

微圆弧金刚石刀具刀尖圆弧的测量及评价

为实现对微圆弧金刚石刀具刀尖圆弧的评价,提出了一种基于高分辨率扫描电镜图像的评价方法,并对刀尖圆弧轮廓提取、轮廓曲线拟合、圆弧度评价等算法进行了研究.首先,运用Canny边缘检测算子提取刀尖圆弧图像的二维轮廓数据,并用移动最小二乘法对该数据进行拟合,使所提取轮廓光滑化;接着,建立了基于最小二乘准则的刀尖圆弧评价模型,并采用二次序列规划法对模型进行求解;最后,分析了轮廓拟合误差、测量不垂直度误差对刀尖圆弧评价结果的影响,并计算了刀尖圆弧半径及圆弧度不确定度值.实验结果表明所评价微圆弧金刚石刀具的刀尖圆弧半径为30.213μm,圆弧半径不确定度为351 nm,圆弧度为0.114μm,圆弧度不确定度为24 nm.由评价结果可以看出,本文所提出的方法可以实现微圆弧金刚石刀具刀尖圆弧纳米级精度的测量及评价.     

基于分段与识别技术的平面轮廓的精确重构

解决了由直线和圆弧构成的平面轮廓精确重构问题,满足轮廓各段之间位置连续以及相切条件.在正确识别角点、切点等特征点的基础上,提出了约束最小二乘算法,可精确求解带边界约束圆弧的重构问题.将圆弧边界约束条件分为5种类型:单点约束、双点约束、单切矢约束、单点单切矢约束和双切矢约束.针对每种类型给出了具体的计算公式.详细描述了轮廓精确重构的算法流程,可实现在全局误差控制下的精确重构,最后给出了运行实例,验证了算法的有效性.     

连续运动螺纹尺寸自适应机器视觉检测

针对螺纹零件尺寸检测效率低、工作强度大、检测精度不高的问题,提出了一种连续运动螺纹尺寸自适应机器视觉的检测方法。首先设计了一套在线图像采集装置用于采集运动螺纹零件的图像;其次使用NCC(normalized cross correlation)归一化匹配算法,完成对螺纹零件的识别及追踪,在此基础上设计了自适应的ROI(region of interest)裁剪区域;然后通过Canny算法提取边缘轮廓,利用最小二乘法直线拟合技术对螺纹轮廓进行直线拟合,生成螺纹中径线,完成对螺纹中径的测量;最后在使用Harris角点检测算法提取多螺纹轮廓波峰与波谷的基础上,提出了利用螺纹中径线与各角点之间的距离来完成对角点的细化。实验表明,所提方法在螺纹尺寸检测方面具有可行性和有效性。     

基于裁剪的装配图生成方法

本文通过分析比较了己有的国内外各种装配图的生成方法，提出了一种新的装配图生成方法──裁剪装配法。这种方法将装配图信息离散为直线段、圆弧、圆三种基元，以待装配零件的轮廓所构成的环为裁剪窗口，作裁剪运算，进行消隐生成装配图。该方法能够适应复杂的、变化的装配关系，在实际运用中取得了较好的效果．     

基于逆向工程的零件反求设计与制造

反求设计与制造是逆向工程的重要组成部分,以PCP系列便携式光学三维扫描系统为基础,介绍逆向工程技术在零件反求设计与制造中的应用。利用三维数字化激光测量仪准确、快速地测量出工件的轮廓坐标,通过Winmoire扫描软件得到零件模型各个面的轮廓点云数据,再通过Cloudform拼接软件将各个面的轮廓点云数据合成为三维点云数据模型,最后通过Geomagic studio11建模软件进行曲面重构,并对重构的曲面进行分析和优化,最终生成STL数据,据此进行快速成形加工得到零件。     

永磁直线同步电机矢量控制系统建模与实现

针对永磁直线同步电机（PMLSM）的特点，建立PMLSM在dq两相坐标系下的数学模型。介绍了永磁直线同步电机矢量控制系统并给出了硬件和软件的设计思想。通过对控制电流以及电机位置的实验分析，验证了所研究的基于矢量控制的永磁直线同步电机矢量控制方法的有效性。     

x-y平面 3D 打印的交叉耦合矢量控制研究

目的研究3D打印机下x-y平台的双轴矢量控制精度。方法介绍永磁电机的数学模型,同时对系统的轮廓误差进行描述,对变增益交叉耦合矢量控制算法进行分析。在Matlab/Simulink软件中对两轴变增益交叉耦合矢量控制进行仿真并分析。结果变增益交叉耦合矢量控制算法能将轮廓误差控制在0.01 mm之内。结论通过变增益交叉耦合算法,提高了系统的鲁棒性,并且减小了系统的轮廓误差。     

摄像机径向畸变校正和内参估计的单图标定方法

提出了一种对摄像机的径向畸变进行校正和内参数估计的单图标定方法.拍摄一幅平面标定模板图像,提出若干条直线,拟合在单参数除法畸变模型下的圆弧参数,从而估计出径向畸变.对径向畸变进行校正后,利用标定模板点与经过校正后的图像点之间的对应关系,估计出单应性矩阵.在假定摄像机主点与畸变中心重合的条件下,线性地计算出摄像机焦距初值.以上述线性方法得到的结果为初值,进行非线性优化,最终得到准确的摄像机参数.超广角鱼眼相机和普通数码相机的实验结果表明,本文提出的算法实现简单、适用性广,结果准确,具有较强的实用性.     

Computer-aided inverse panorama on a conical projection surface

The aim of this study is to develop a practical method of direct mapping of an inverse conical panorama with computer aid. The panoramic image is a central projection onto a conical surface from the centres dispersed on a circular or straight path located outside the projection surface. The proposed method is a nonlinear projection in which the resulting image is treated as a sequence of stitched pictures of zero width taken from a moving view point. Geometric data and relations between the projected points are utilised to formulate algorithms for drawing of inverse panoramic images of straight lines, which further enables drawing of wire frame models of represented forms. Images are drawn as plots of a function in the Mathcad software. However, in order to make drawing more efficient and convenient, as well as for the practical applications of them, the algorithms can be implemented in any graphical package.     

Weak-form element differential method for solving mechanics and heat conduction problems with abruptly changed boundary conditions

Element differential method (EDM), as a newly proposed numerical method, has been applied to solve many engineering problems because it has higher computational efficiency and it is more stable than other strong-form methods. However, due to the utilization of strong-form equations for all nodes, EDM become not so accurate when solving problems with abruptly changed boundary conditions. To overcome this weakness, in this article, the weak-form formulations are introduced to replace the original formulations of element internal nodes in EDM, which produce a new strong-weak-form method, named as weak-form element differential method (WEDM). WEDM has advantages in both the computational accuracy and the numerical stability when dealing with the abruptly changed boundary conditions. Moreover, it can even achieve higher accuracy than finite element method (FEM) in some cases. In this article, the computational accuracy of EDM, FEM, and WEDM are compared and analyzed. Meanwhile, several examples are performed to verify the robustness and efficiency of the proposed WEDM.     

基于改进Hough变换的直线图形快速提取算法

为能够有效解决实时直线图形提取问题,提出了一种基于多约束Hough变换(HT)的直线提取算法.该算法首先分析了数字图像中直线边缘的三种结构特征,提出采用基元结构表示目标边缘点,并在约束条件下计算基元结构的基元倾角.在此基础上,结合传统的HT的思想对基元结构进行极角约束HT,以获得最终的直线参数.实验结果表明,对合成图像和自然图像,该算法比梯度HT的运算速度分别提高约190倍和22倍.     

动态图像的拼接与运动目标检测方法的研究

动态图像运动目标检测是图像处理中的热点,但动态图像的识别范围却成了目标检测的限制,针对此问题,本文提出了一种利用图像拼接技术扩展图像识别范围、并在此基础上完成运动目标检测的方法。在图像拼接中采用了SURF图像匹配算法,运动目标识别利用背景差分法,实验中使用的是开源的Linux操作系统、以及为图像处理提供了大量算法和函数的Open CV软件开发库。针对不同分辨率、不同角度采集的图像进行了实验研究,结果表明,可以在较好满足图像识别范围的同时,明确地检测出运动目标的相关信息。同时,本文提出一种通过图像拼接实现扩展运动目标检测的方法,满足了实时性要求,达到了增加图像清晰度的目的,但是,在摄像设备与场景之间的相对运动方面还存在着有待解决的问题,这将成为今后研究的重点方向。     

In-vivo synthetic aperture flow imaging in medical ultrasound

A new method for acquiring flow images using synthetic aperture techniques in medical ultrasound is presented. The new approach makes it possible to have a continuous acquisition of flow data throughout the whole image simultaneously, and this can significantly improve blood velocity estimation. Any type of filter can be used for discrimination between tissue and blood flow without initialization, and the number of lines used for velocity estimation is limited only by the nonstationarity of the flow. The new approach is investigated through both simulations and measurements. A flow rig is used for generating a parabolic laminar flow, and a research scanner is used for acquiring RF data from individual transducer elements. A reference profile is calculated from a mass flow meter. The parabolic velocity profile is estimated using the new approach with a relative standard deviation of 2.2% and a mean relative bias of 3.4% using 24 pulse emissions at a flow angle of 45 degrees. The 24 emissions can be used for making a full-color flow map image. An in-vivo image of flow in the carotid artery for a 29-year-old male also is presented. The full image is acquired using 24 emissions.     

Numerical study on effect of external magnetic field, current profile, arc current and arc column radius on helical instabilities of arcs

This model differs from previous works in that the electrical conductivity (and the current profile) is approximated in a more realistic way (parabolic instead of flat profile). The magnetohydrodynamic equations in an electrostatic approximation serve as the starting point of the theory. The effects of the external axial magnetic field, current profile, arc current and arc column radius on the helical instabilities of arcs were numerically studied. Numerical results show that the short wavelength perturbation can be stabilized by positive direction magnetic field, whereas the long wavelength perturbation can be stabilized by reverse magnetic field when the current profile is the uniform distribution. In the short wavelength perturbation case, the effect of positive direction magnetic field on the arc stability is very small when the current profile has a parabolic distribution. However, its stabilizing effect is enhanced for the long wavelength perturbation. The intermediate and long wavelength perturbation can also be stabilized by reverse magnetic field. The low current is beneficial for stabilizing arcs.     

Machining damage of monocrystalline silicon by specific crystallographic plane cutting of wire electrical discharge machining

The machining damage on the certain crystal face of single crystal silicon, the manufacture of which are under diverse parameters of wire electrical discharge machining (WEDM), is tested by means of the micro-observation and X-ray diffraction rocking curve method. In the process of monocrystalline silicon machined by WEDM, when the pulse width is small, the basic methods of material removal are melting and gasification, which are also called normal removal methods. When the pulse width increases to a certain degree beyond the normal removal, thermal spalling removal also occurs, which is considered a compound removal method. The depth of machining damage is difficult to control. The structure of machining damage under two conditions is divided into normal removal and compound removal in this study. To make the depth of machining damage easy to control, compound removal should be avoided when processing the single crystal silicon by certain crystal face cutting of WEDM. Such an approach can provide the premise and guarantee for the subsequent processing of single crystal silicon with certain crystal face in the future.     

An X-ray beam position monitor based on the photoluminescence of helium gas

A new method for white beam position monitoring for both bend magnet and wiggler synchrotron X-ray radiation has been developed. This method utilizes visible light luminescence generated as a result of ionization by the intense X-ray flux. In video beam position monitors (VBPMs), the luminescence of helium gas at atmospheric pressure is observed through a view port using a CCD camera next to the beam line. The beam position, profile, integrated intensity and FWHM are calculated from the distribution of luminescence intensity in each captured image by custom software. Misalignment of upstream apertures changes the image profile making VBPMs helpful for initial alignment of upstream beam line components. VBPMs can thus provide more information about the X-ray beam than most beam position monitors (BPMs). A beam position calibration procedure, employing a tilted plane-parallel glass plate placed in front of the camera lens, has also been developed. The accuracy of the VBPM system was measured during a bench-top experiment to be better than 1 μm. The He-luminescence-based VBPM system has been operative on three CHESS beam lines (F hard-bend and wiggler, A-line wiggler and G-line wiggler) for about a year. The beam positions are converted to analog voltages and used as feedback signals for beam stabilization. In our paper we discuss details of VBPM construction and describe further results of its performance.     

A proposed circle/circular arc detection method using the modified randomized hough transform

Abstract

The randomized Hough transform (RHT) is a useful tool to locate patterns in an image. In this study, we propose a modified RHT to detect circles/circular arcs efficiently. First, we segment an image into sub‐images based on edge information, then we use the proposed circular arc analysis and density check rule to modify RHT for circle/circular arc detection. In the experiments, real images are used to show the capability of the proposed method.