基于数学模型的视觉测量系统图像畸变校正方法

视觉测量系统图像中存在的各种非线性畸变对测量精度产生影响,必须进行校正。生产过程中的干扰使畸变随机变化,因此采用不变参数的图像畸变校正模型难以实现工件尺寸的精确测量。提出一种新的畸变校正方法,采用自回归时间序列模型的一般表达式建立被测工件直线边缘的数学模型,并采用最小二乘方法以及综合考虑计算量的损失函数最小准则实现模型的参数估计和定阶。根据模型的输出滤除被测工件直线边缘的趋势成分,获得被测工件的真实边界位置。通过计算两边界之间的垂直距离达到测量工件尺寸的目的。试验证明,该算法简单可行,可用于加工过程的在线检测。     

Assessment and correction of geometric distortions in low-magnification scanning electron microscopy images

A method is introduced to assess and correct the geometric distortions which frequently occur in low-magnification scanning electron microscopy (SEM) images. Such images typically exhibit a complex pattern of varying deviations from orthogonality which cannot be adequately corrected by simple geometric transformations such as shifting, scaling, rotation, or shearing. A suitable approach to rectify low-magnification SEM images is polynomial warping, a correction procedure which also accomplishes rubber sheet transformation. To demonstrate the approach, a reference grid for low magnifications has been scanned at 40- and 55-fold magnifications by means of a microanalyzer. Calculated geometric distortions range from 1.5 to 3.5% of the image dimensions; applying polynomial warping, distortions could be reduced to approximately 0.1% of the image dimensions. Because of its easy application and the widespread availability in image processing packages, polynomial warping can be recommended as a routine procedure for rectifying low-magnification SEM images.     

一种面向球姿态检测的图像透视畸变校正方法

针对球姿态视觉检测中图像的“近大远小”透视畸变问题,提出了一种面向球姿态检测的图像透视畸变校正方法。基于相机成像模型分析了透视畸变的特点及产生原因,根据已知的球体特征模型、相机标定技术和逆透视变换原理构建了图像透视畸变校正模型,进而实现球体任意姿态图像的透视畸变校正。实验结果表明,利用该方法测量直径60 mm以内的球体姿态时平均绝对误差低于0.6°,且该方法适用于工业生产中球体的其他视觉测量。     

基于计算几何的曲面造型方法研究

以Pro/Engineer和UGNX为代表的计算机辅助设计和辅助制造软件,在制造行业已经成为产品设计和产品制造工程师的重要工具。这些CAD/CAM软件都必须能够胜任曲面造型的功能,它是产品三维设计的必然前提,因此曲面造型成为计算机辅助几何设计和计算机图形学的一项研究重要内容,而计算几何正是对曲面造型进行研究的数学方法。通过对曲面造型和计算几何的相关概念的介绍,详细阐述了基于计算几何方法建立曲面参数曲线的各种数学建模过程。这些数学建模方法能为各种CAD/CAM系统实现曲面功能提供理论指导。     

A genuine face milling cutter geometric model for spiral bevel and hypoid gears

Accurate tooth surface and good surface quality are critical to achieve the low-noise bevel gear drives. Face milling, traditionally works as tooth roughing process, can now possibly be used for finishing process because its high speed can produce good tooth surface quality. But with the previous simplified cutter geometric model in tooth modeling, the high accurate tooth surface cannot be obtained. In this paper, a genuine face milling cutter geometric model for spiral bevel and hypoid gears is proposed. This model exactly matches with the cutter geometry in the industrial application when not considering the fabrication tolerances and tool wear . In the modeling, the blades of the genuine cutter are parameterized with blade angle, rake angles, and relief angles. The side and circular cutting edges of blades are represented on the blade rake plane, rather than the normal plane as the simplified cutter geometry. The mathematic model of the genuine tool profiles on the normal plane is derived. It can be conveniently used by the existing tooth modeling program and easily customized by specifying the geometric parameters. In comparison with the genuine tool profile with the simplified tool profile, the big geometric errors of the simplified blade profile are founded, which proves that the genuine cutter geometric model is correct and essential.     

Image distortion correction for micromanipulation system based on SLM microscopic vision

Stereo light microscope (SLM) simulates stereo imaging principle of human eyes. Microscopic vision system based on SLM has become an important visual tool for micro measurement, micromanipulation, and microinjection. We develop a micromanipulation system based on SLM and present an image distortion correction method. We mainly correct two kinds of image distortions: lateral and vertical distortion. Distortion correction consists of two steps. First, a linear fitting algorithm for each row or column of target points is developed, and the fitting errors are calculated. If the fitting errors are smaller than a given threshold, the linear fitting results are kept and used. Otherwise polynomial fitting procedure will be used. Second, the parallelism of straight lines is corrected. The results show that a line in world coordinate frame (WCF) is not necessarily a straight line in image coordinate frame (ICF), or two parallel lines in WCF may be not parallel in ICF. Distortion correction can restore the parallel and linear relationship. For distorted left and right images, the magnitude of distortion exceeds 6 pixels and 4 pixels in the horizontal direction, and 1.2 pixels and 1.7 pixels in the vertical direction, respectively. After corrected, for left and right image, distortion can be reduced to 0.8 pixels and 0.7 pixels in the horizontal direction, and 0.96 pixels and 1.3 pixels in the vertical direction, respectively. The results show that distortion parameters obtained from the proposed method can effectively correct distorted images. Microsc. Res. Tech. 79:162–177, 2016. © 2016 Wiley Periodicals, Inc.     

压印对正系统中标记图像几何畸变的校正

在综合分析了多种线性及非线性畸变后,建立了三次多项式图像系统畸变模型。采用基于控制点偏差目标函数最小优化法进行畸变模型的求解,并通过计算自标定偏差均方差与互标定偏差均方差对标定结果进行了评定。结果表明,模型求解误差为0.22 μm,通过校正标记图像几何畸变引入的定位误差由2.5 μm降低到0.25 μm,可实现压印对正系统中标记图像几何畸变的校正,实现精确定位。     

GREEN MACHINING ORIENTED TO DIMINISH DENSITY GRADIENT FOR MINIMIZATION OF DISTORTION IN ADVANCED CERAMICS

After sintering advanced ceramics, there are invariably distortions, caused in large part by the heterogeneous distribution of density gradients along the compacted piece. To correct distortions, machining is generally used to manufacture pieces within dimensional and geometric tolerances. Hence, narrow material removal limit conditions are applied, which minimize the generation of damage. Another alternative is machining the compacted piece before sintering, called the green ceramic stage, which allows machining without damage to mechanical strength. Since the greatest concentration of density gradients is located in the outer-most layers of the compacted piece, this study investigated the removal of different allowance values by means of green machining. The output variables are distortion after sintering, tool wear, cutting force, and the surface roughness of the green ceramics and the sintered ones. The following results have been noted: less distortion is verified in the sintered piece after 1 mm allowance removal; and the higher the tool wear the worse the surface roughness of both green and sintered pieces.     

A concurrent manufacturing strategy for One-of-a-Kind Products with complicated sculptured surfaces

In this paper, we propose a computer-aided system for concurrently designing and manufacturing a customised or One-of-Kind Production (OKP) mould or die which has complicated sculptured surfaces. Considering the OKP production characteristics of high customisation and concurrent product development and production, we believe that the concurrent consideration of both the design and the manufacturability of a mould or a die would be necessary. This concurrence can be realised by providing timely manufacturability information feedback after a design is completed or a feature is modified or added in the design. The other problem is that the sculptured surface geometry model of a mould or a die does not contain any machining information. Hence we developed an intermediate data model for capturing manufacturing features when we are modelling the geometric form of a mould or a die. The system is based on CADDS5 which is a commercial CAD/CAM system. Two modules for data extraction, coverting and modelling as well as for manufacturability analysis have been developed and added to CADDS5. Using this computer-aided system; a designer can interrogate geometry and machining constraint information through a user friendly interface to avoid defects and inefficiency resulting from an earlier design, and can finalise the design by making quick incremental adjustments. The system has been implemented in a mould and die manufacturing company in China. This implementation leads to less rework and shorter lead time.     

Grain mapping to freeform surface for machining using parameter-based incremental tracking method

This paper presents a novel method for mapping a texture for machining onto a freeform surface. When a grain texture designed on a 2D plane is projected onto a freeform surface simply, the texture is distorted along the curvature of the surface in the projection direction. Therefore, a method is required to suppress this distortion. The algorithm proposed in this paper rapidly generates a point cloud that represents a texture with less distortion on a simply connected parametric surface. Specifically, four equations that express local geometry constraints instead of conventional parameterization methods are presented to reduce the distortion between adjacent points on the point cloud. Solving these equations can generate grain textures on freeform surfaces. This paper examines two grain images mapped to two freeform surfaces that were prepared as case studies to demonstrate the effectiveness of the proposed method.     

一种数码相机几何畸变的检测方法

针对数码相机普遍存在的几何畸变现象,提出了一种基于数字图像处理的畸变检测方法.在阐述数码相机畸变产生原因和检测原理的基础上,将待测数码相机拍摄目标靶板后的图片输入计算机,利用MatLab工具对图片进行数字图像处理,由像素间距获取实际像大小,由几何光学演算获得理想像大小,从而计算出相对畸变量.实验表明,该方法过程简单,易...     

FEM-based progressive drawing process design

Progressive drawing die is the most formidable and thus among the most difficult of all progressive dies. A FEM-based progressive drawing die analysis and design method is proposed in this study and demonstrated on forming an automotive lighting component bulb shield. FEM simulation prediction not only matches well on both thinning and strain, but also helps to remove surface distortion. Compared to traditional experience-based design, the FEM-based development method allows an engineer to identify potential forming defects before the tooling is manufactured and thus shortening the tooling development time.     

Module-based method for design and analysis of reconfigurable parallel robots

This paper presents a method for the design and analysis of reconfigurable parallel robots. The inherent modularity in a parallel robot lends itself as a natural candidate for reconfiguration. By taking the branches as building blocks, many modular parallel robots can be constructed, from which a reconfigurable parallel robot can be realized. Among three types of reconfigurations, namely, geometry morphing, topology morphing, and group morphing, the method presented here is for the last two reconfigurations, thereby advancing the current research that is mainly limited to geometry morphing. It is shown that the module-based method not only provides a systematic way of designing a reconfigurable parallel robot, but also offers a unified modeling for robot analysis. Two examples are provided, one showing the topology morphing and the other showing the group morphing.     

点云数据的二次曲面几何测量方法

基于点云的几何测量方法是非接触式测量的重要方法。针对点云数据,提出了一种基于待定系数的二次曲面的几何测量方法,建立了求解不同二次曲面（球面、柱面和圆锥面）的统一框架。根据二次曲面方程与不同类型二次曲面几何量的关系,给出了球面、柱面和圆锥面的具体几何参数的求解方法。实验证明,该方法能在短时间内精确地测量所需的几何值,方法切实可行。     

小视场图像系统的非线性畸变校正方法的研究

分析了小视场图像系统的成像特性,针对其非线性畸变提出了基于平行光栅技术的数字图像校正方法,应用图像系统的一阶综合径向畸变数学模型,求解畸变参数和校正参数并对图像进行校正。理论分析和试验表明,本方法简单有效,校正后的畸变影响降低到0.25个像素。并对图像的畸变中心和纵横比例因子对校正的影响做了探讨。     

基于包络理论新构形插齿刀凸曲前刀面数学建模

提出一种以异形凸曲前刀面代替传统锥面前刀面的硬质合金插齿刀新构形方法。运用微分几何包络理论建立了新构形插齿刀凸曲前刀面、侧刃空间曲线数学模型,对插齿刀齿形误差、侧刃前角分布进行分析,并提出新构形插齿刀齿形角修正方法。根据新构形理论设计、制造出具有高齿形精度、抗崩刃的新构形硬质合金插齿刀。     

计及设备因素的成形制件精度驱动的模具结构分析

依据某厂万吨液压机尺寸,应用有限元软件建立了液压机的分析模型。在液压机系统中提出并定义了耦合刚度的概念。应用实验数据得到了锻件平面度误差与垫板、滑块高度变化关系规律,即:模具高度越大,锻件精度越高;垫板越高,同样也是精度越大,但是精度变化的范围越来越小;并建立了垫板高度和模具高度的2阶响应面数学模型并对其验证。运用这些规律和数学模型,可以更好地以产品的精度作为驱动性能,控制模具、垫板尺寸,进一步提高液压机装备的耦合刚度。     

Image distortions in SEM and their influences on EBSD measurements

The high sample tilt angle commonly necessary for an orientation determination by EBSD (electron back-scatter diffraction) is responsible for some simple geometrically caused, but nevertheless essential, image distortions. First of all, the influence of the tilt correction and also the trapezium distortion which appears at low magnifications will be discussed. In the second part, an additional rhomboidal distortion will be introduced which is independent of the magnification used. This distortion appears if the scanned sample surface is out of plane to the tilted stage. Even a small deviation from the parallelity produces an approximately three times bigger error of the Euler angle phi(1) when the sample alignment is based on the image captured from the highly tilted sample. This effect especially concerns small samples (e.g. FIB-lamellae) since they cannot be exactly aligned, but the measurements of bigger samples can also be influenced. As an example a correction procedure is described in detail, based on a repetition of the measurement after a 180 degrees sample rotation.