多孔陶瓷锥束CT重建质量优化

利用锥束CT检测系统对多孔陶瓷试样进行扫查与重建,讨论滤波板位置、透照管电压、旋转轴倾斜校正和投影张数等工艺参数对CT重建图像质量的影响。结果表明:在探测器侧进行滤波可以减少试样的散射,提高图像的信噪比和对比度;与85、140 kV透照管电压下的图像相比,透照管电压为130 kV时CT重建的图像噪声低、对比度和清晰度高;对旋转轴进行?1.06°校正可以减少CT重建图像的伪影和几何畸变;CT重建投影数量增加,重建图像的信噪比、对比度和清晰度等随之提高。调整工艺参数可以改善CT重建图像质量,保证多孔陶瓷缺陷检测和微观形貌分析的准确性,拓展CT技术在陶瓷材料检测领域的应用。     

基于多元统计的线阵CT图像环形伪影去除方法

针对线阵工业CT重建图像中环形伪影干扰问题,设计一种基于多元统计的新型校正方法。首先采用灰度直方图统计结合最大类间方差法对CT图像中不同材料密度进行分类,根据材料密度分布对原始CT图像进行材料去除,然后进行极坐标系转换,对转换后的极坐标图像进行横坐标像素值统计,提取不同半径r下伪影灰度幅值统计值,最后采用原始CT图像消减伪影统计值的方式进行伪影校正。采用6 MeV线阵探测器高能工业CT系统,对含有环形伪影的不同结构CT图像进行校正试验。试验结果表明:该方法在有效去除CT图像环形伪影的同时,还能较好地保持图像细节和分辨率,显著提高了处理速度。     

等角扇形束投影的CT重建算法研究

通过线阵探测器CT系统CD-300BX获得C/C复合材料多个角度下的扇形束CT扫描投影数据,设计并实现了滤波反投影算法。讨论了常用滤波函数和内插方式对CT重建质量的影响,采用峰值信噪比和平均梯度对CT图像重建质量进行客观评价,并与CT系统算法重建结果进行对比。研究结果表明:选用R-L滤波和紧邻内插时CT图像重建质量最好,本文开发的滤波反投影算法重建质量达到了CT系统的重建质量,可满足扇形束投影的CT重建需求。     

锥束工业CT射束硬化校正方法

锥束X射线CT系统中,X射线束具有宽能谱的特性,会导致X射线硬化效应的产生,从而使得重建图像中出现杯状和条状伪影等,故有必要研究硬化校正方法以减少硬化效应带来的影响。提出了基于试验能谱和蒙特卡罗模拟的多项式拟合硬化校正方法,基于试验测量X射线初始能谱,利用蒙特卡罗模拟得到透射厚度与多能投影的关系,再利用多项式拟合得到多能投影与等效单能投影的转换关系,从而实现硬化校正。分别采用该方法和传统的滤波片法对一铝制标准件进行射束硬化校正试验。结果表明,所提出的方法比滤波片法能更好地消除锥束CT的硬化伪影。     

锥束CT工艺参数对成像质量的影响

影响锥束CT成像质量的工艺参数较多，通过研究关键工艺参数对CT图像质量的影响规律，可获得更好的锥束CT成像效果。基于德国卡尔蔡司公司的METROMTOM 1500型微焦点锥束CT系统，研究了管电压、管电流、焦点尺寸、试样的几何位置、投影数量、积分时间、Binning模式等关键工艺参数对CT图像质量的影响。结果表明，在管电压足够的情况下调整管电压和管电流，将焦点尺寸和体素尺寸控制在接近时获得的图像清晰度最好；减小被测物体与射线源的距离，能够明显提高图像清晰度；增加投影数量可以明显减少干扰噪声；高Binning模式能够提高图像的细节分辨率；积分时间对图像的质量影响不明显。     

EM算法在X射线CT重建中的应用研究

计算机断层成像（CT）广泛地应用于医疗诊断和工业无损检测等领域。具有无损、无接触、高分辨率等优点。X射线CT是目前最为常用的计算机断层成像技术。在X射线CT成像系统中，重建算法是其核心部分。本文将最大似然估计理论推广到X射线CT，基于投影数据统计模型，实现了期望最大化（EM）算法在X射线CT中的应用。并进行了实际X射线扫描数据的实验，结果表明该算法有效可行，重建图像清晰准确。     

曲面零件带槛拉深的力学分析

给出了曲面零件带槛拉深时的阻力计算方法，并以此为基础，推导了槛的成形力、最小压边力公式。为了保证压槛时不起外皱并使毛坯完全包槛，初始毛坯的几何参数还应满足一定的限制条件。     

CT图像重建中基于指数形式的滤波函数优化

计算机断层成像(CT)技术广泛应用于工业、医疗、国防、航空航天等领域。随着科学技术的不断发展,对使用CT来获得更加精确的材料内部结构信息提出了更高的要求,希望能在重建图像中更加完整地表达组织结构信息。为了获取更好的图像质量,提出一种基于指数形式的滤波函数(EBFF),在MATLAB平台下采用EBFF对图像进行重建,并通过相似系数、归一化平均值以及归一化均方根距离等评价手段与几种传统的滤波函数重建图像结果进行对比,同时在锥束CT实验平台下采用EBFF进行图像重建。模拟与试验均表明EBFF对重建图像质量有一定改善,其较传统滤波函数能给出更好的重建结果,有助于图像重建结果的优化。     

联轴器几何参数对其性能影响的有限元分析

建立了联轴器性能指标的评价模型,给出了衡量联轴器传递转角性能的指标——传递误差度,根据联轴器的实际工程模型建立了有限元模型,计算分析了联轴器在不同几何参数下的轴向传递误差度和径向传递误差度,得到了联轴器的几何参数对传递误差度的影响规律:当联轴器几何参数不变时,联轴器的传递误差度也不变,可以作为衡量联轴器转角误差的指标;当联轴器几何参数不变时,联轴器的径向传递误差度是轴向传递误差度的5~14倍,所以径向传递误差度是衡量联轴器转角误差的重要指标;适当减小联轴器悬臂的宽度,增大联轴器悬臂厚度,可有效减小联轴器的传递误差度;改变悬臂长不能有效减小联轴器的传递误差度。     

基于线阵列探测器的多角度平行投影数据及其图像重建算法

针对工业断层CT进行三维结构成像的应用需求,提出了由多角度的平行投影数据重建三维CT图像的TV-ART迭代算法的新实现方法,其中将Chambolle方法推广至三维情形并用于求解CT图像全变差(TV)最小。使用该方法进行TV求解的重建图像的质量优于基于最速下降法或共轭梯度法的TV-ART迭代算法。此外,该方法具有高度并行性,适合在GPU,FPGA等高速并行计算硬件上实现,从而可以大幅提高图像重建速度。在扫描时间相同的情况下,该方法重建的三维CT图像质量优于已有方法,特别是显著提高了CT图像的轴向分辨率。     

A calibration method for misaligned scanner geometry in cone-beam computed tomography

Computed tomography (CT) images often suffer from artifacts caused by misaligned scanner geometry of CT system. Calibration and correction must be done before image reconstruction. A method for calibration of misaligned scanner geometry in cone-beam CT with single-circle orbit is proposed. In this method, a four-point phantom is used to estimate a set of parameters that describe the geometry of a cone-beam CT system. It requires only one projection of the phantom, instead of several projections at multi-angles. An analytical formula is derived, which avoids falling into local minimum. In addition, there is no restriction on any one of the geometric parameters. The simulated results are illustrated. It is proved that this method is applicable and efficient for misaligned scanner.     

Integrated Inspection and Machining for Maximum Conformance to Design Tolerances

Designers' intent for the form, fit and function of products is expressed by design tolerances the conformance to which is the main objective of manufacturing processes. A methodology for maximizing the adherence to the specified tolerances using an integrated machining and inspection system is presented. Considering the desired tolerance envelope of the part, an error decomposition technique is developed to model machining errors caused by the systematic and non-systematic errors in the machine tool. The model is used to adaptively plan the final machining cuts, based on inspection feedback, to enhance the geometric accuracy of the final product and is illustrated by an example. This approach reduces scrap and rework and their associated costs.     

Improvement of image characteristics in high-voltage computed tomography (CT) by applying a compressed-sensing (CS)-based image deblurring scheme

We have established a high-voltage computed tomography (CT) system with a 1–3 MV LINAC x-ray generator for industrial nondestructive testing. However, reconstructed CT images are typically blurred, limiting its image performance, mainly due to the finite focal spot size of the x-ray source, aspects inherent to detector such as the detector pixel size and the detector resolution, and the reconstruction procedure as well. Thus the recovery of the reconstructed CT images from their degraded version is essential for improving the image characteristics. In this work, we investigated the compressed-sensing (CS)-based deconvolution scheme for more accurate image deblurring in CT. We implemented the proposed image deblurring algorithm for CT and performed a systematic simulation and experiment to demonstrate its viability. Our results indicate that the proposed deblurring scheme appears to be effective for the blurring problems in CT and is applicable to improve its present image characteristics.     

Measurement of spindle thermal errors in machine tool using hemispherical ball bar test

The assurance of top-quality products in machining processes requires improved machine tool accuracy. Among the various errors related to machine tools, thermal errors of a spindle have a significant effect on machining accuracy and directly influence both the surface finish and the geometric shape of the finished workpiece. Accordingly, the current paper proposes a new measurement method for spindle thermal errors in a machine tool based on the use of a ball bar system instead of the conventional capacitance sensor system. The novel measurement method is more efficient and easier to use compared to conventional measurement systems. Furthermore, a single ball bar system is sufficient for the simultaneous measurement of both geometric and thermal errors.     

A new geometric error modeling approach for multi-axis system based on stream of variation theory

This paper introduces a new geometric error modeling approach for multi axes system (MAS) based on stream of variation (SOV) theory, especially for multi-axis precision stage. SOV is used for measuring product quality for some complicated multi operations system, which is widely used in error propagation in engineering field. This paper introduces SOV concept into geometric error modeling for MAS. Instead of different process in manufacture, the new error modeling approach regards each axis as a station in MAS, and calculates the deviations after each station which is considered as upstream factor to next station. It is clear to observe how geometric errors give influence and how deviations accumulate. Different with conventional methods which are only used for error compensation in machine tools, the new error model is beneficial for sensitive error control and optimal configuration selection in design part. In addition, the new error modeling has some merits such as debugging easily due to observe the deviations after every station. A case study of new error modeling procedure for six-axis stage (SAS) in optoelectronic packaging system (OPS) is developed, and applications related to error reduction order and optimal configuration selection are processed based on the new error model.     

基于SVMD和自适应MOMEDA的齿轮箱故障诊断

受背景噪声和传输路径的影响，故障信号往往被淹没，故障特征难以提取。基于此，提出一种连续变分模态分解(SVMD)和自适应MOMEDA相结合的故障诊断方法，通过SVMD前处理得到重构信号，然后以平均谱负熵为适应函数，通过人工鱼群优化算法自适应选择MOMEDA的最优参数。利用所得参数对重构信号进行MOMEDA滤波，最后进行包络谱分析，做出故障类型诊断。将所提方法应用于齿轮箱主动轮断齿故障的仿真信号和实验信号中，在包络频谱中可以清楚地分辨出小齿轮转频及其倍频， 同时所提方法相对其他方法具有更好的表现效果。     

四轴联动加工中心几何误差软件补偿技术研究

以多体系统理论为基础,通过分析位移变换矩阵和位置变换矩阵,建立了四轴联动加工中心的几何误差模型.基于Windows平台开发了误差补偿软件,可以对测量数据进行机床几何误差的软件补偿,有效地提高了在线检测精度.软件系统在MAKINO立式加工中心上进行了实验验证,补偿效果明显.     

液压挖掘机反铲工作机构运动分析与包络线的研究

对液压挖掘机反铲工作机构运动分析和包络线进行研究。推导工作机构运动学分析公式,详细叙述了反铲工作机构包络线11种不同的圆弧曲线,对于具体的反铲工作机构,包络线最多只有10段圆弧曲线,最少是6段圆弧曲线。选择step函数作为3个液压缸的驱动函数,编写了能产生3个液压缸的驱动step函数的C++程序。用改变机构尺寸参数的方法,找到了包络线由6～10段圆弧曲线组成反铲工作机构的6个数例,并绘制了6个数例工作机构的包络线。