微光成型法实体模型固化过程的仿真

微光成型法在微小机械结构制造中的应用，能有效地提高设计的成功率。根据三维实体模型离散后的平面实体的特征，分别生成轮廓扫描和内部充填的行栅式扫描所需的CNC指令代码，再根据这些代码和微光成型法的基本成型原理，利用图形接口软件OpenGL和编程软件VC，实现了平面实体固化成形和立体层叠固化成型过程的仿真。从而可以检验数据处理和成型工艺参数设置的正确性，避免成型加工时可能出现的错误。该方法已在微光成型系统中得到了应用。     

微光成型法实体模型固化过程的仿真

微光成型法在微小机械结构制造中的应用,能有效地提高设计的成功率。根据三维实体模型离散后的平面实体的特征,分别生成轮廓扫描和内部充填的行栅式扫描所需的CNC指令代码,再根据这些代码和微光成型法的基本成型原理,利用图形接口软件OpenGL和编程软件VC,实现了平面实体固化成形和立体层叠固化成型过程的仿真。从而可以检验数据处理和成型工艺参数设置的正确性,避免成型加工时可能出现的错误。该方法已在微光成型系统中得到了应用。     

微光成形法平面轮廓扫描路径的生成

提出一种基于任意形状平面图形的内、外轮廓数据处理的新方法,并针对AutoCAD实体模型的等高截交面轮廓的封闭有向环及内、外环进行判别,实现了平面轮廓扫描中的方向判别和轨迹生成的自动化.     

微光成型法图形数据的提取和处理

利用对AutoCAD实体徒刑模型的等高截交处理。获取一系列截交面图形数据。再以DXF格式和LDI格式进行提取和保存,从而获得便于进一步应用的图形数据。并在此基础上进行了立体模型的再现。以验证等高截交处理的合理性和正确性。     

基于温度分区的激光沉积成形扫描路径生成方法

现有金属激光沉积成形工件是根据几何模型按照设定扫描路径层层叠加而成,不可避免造成局部热量累积,导致成形工件内部温度梯度大,产生局部应力集中,易引起工件变形开裂。对成形过程温度进行实时检测并实现动态扫描路径规划是解决工件变形开裂的根本途径。在研究不同基体温度对熔宽、熔高影响规律基础上,提出基于层面温度分区的激光沉积成形扫描路径生成方法。采用红外热像仪对沉积层面温度进行实时采集,提取不同温度分区轮廓;提出温度分区轮廓规则化方法,消除局部轮廓尖角,避免过熔覆;改进Weiler-Atherton算法,快速实现分层轮廓与温度分区轮廓的求交运算;针对不同温度分区采用适应性间距生成扫描路径,实现激光沉积成形动态扫描路径规划。试验结果表明：该扫描路径可有效提高成形工件质量。     

基于图象的刀具路径生成技术

在许多广告、艺术品、模具等雕刻零件编程中,往往是通过扫描图象来获得零件的尺寸,这就需要一种能够基于图象的刀具路长生成技术。本文主要介绍了图象的轮廓跟踪算法、轮廓点过滤拟合处理算法以及各种基于图象轮廓线二维、三维雕刻加工技术。该技术已应用于自己开发的雕刻软件中,并在自己开发的数控雕刻机上加工试验,获得了较好的样品。     

SLC文件的扫描路径生成方法

介绍了快速成形加工中常用的SLC文件的格式,分析了SLC文件的数据存储结构和特点。研究了SLC数据的读取方式,采用奇偶规则判断交点是否在轮廓区域内,区分了扫描线的虚实特性,并对轮廓垂直或重合于扫描线、极值点和凹拐点这几种特殊情况进行了讨论。最后生成了风力机叶片以及齿轮模型的扫描路径,证实了算法的有效性。     

基于图像处理和改进A*算法的激光切割路径生成方法

为了提高纸类异形吸塑包装激光切割系统的自动化程度,实现加工路径智能生成功能,提出一种将图像处理与改进的A*算法相结合的激光切割路径自动生成方法。该方法以工业摄像机采集到的底板纸排料图像为基础,通过图像处理方法获得吸塑包装底板纸的轮廓轨迹路径,对各个轮廓轨迹进行排序,并获得各个轮廓加工的起始点,最后应用改进的A*算法生成各个轮廓间的辅助连接路径,实现激光头的自动避障,最终实现全部切割路径的自动生成,既进行了切割路径优化,又实现了加工路径的智能避障。详细介绍了该方法的原理及实现步骤,并进行了实际加工验证,效果良好。     

选择性激光烧结复合扫描路径的规划与实现

激光扫描路径是选择性激光烧结系统 (SLS)的关键技术之一。针对目前常用激光扫描路径的缺陷 ,提出了基于轮廓环偏移与分区变向填充相结合的一种复合激光扫描路径规划方法。文章给出了这种激光扫描路径的轨迹生成过程、轮廓环的修整、环分组以及环偏移扫描与分区扫描之间的厚度确定方案。并对其中图形运算算法进行了优化。从模拟制造结果可以看到这种激光扫描路径规划方法能够克服其它扫描路径中的一些缺陷     

选区激光熔化快速成型矩形块扫描方式的路径生成算法

算法的核心是将待扫描区域划分为矩阵式的矩形块,块数由用户设定,相邻矩形块间扫描方向相互垂直。这种扫描方式可以改变热应力的方向,并可避免长线扫描．该算法能够有效提高轮廓形状比较简单,但截面面积较大的零件的成型质量。     

微细光成型固化工艺参数优化

为了分析紫外光对液态光敏树脂进行曝光固化成型过程中工艺参数对固化物的形状和精度的影响,根据自行研制的实验系统的大量数据,对线形固化中的主要工艺参数进行了分析和优化。结果表明,在单层液态树脂膜厚30 μm,曝光光束功率0.15 μW,扫描速度15 μm/s以及工作距650 μm时能够得到具有较高精度线宽和线高的固化直线段,利用优化的工艺参数,成功实现了三维微小实体结构的成型制造。     

Evaluation of demineralized dentin contraction by stereo measurements using environmental and conventional scanning electron microscopy

Numerous investigations of etched human dentin are performed using scanning electron microscopy (SEM). Usually specimens are fractured and cross sections of etched layers with underlying unaffected dentin are observed. Results from this study showed that the edge of the etched layer contracted and became curved after fracture of wet specimens and that tensile stresses were developed in this layer by acid etching. The degree of contraction was determined utilizing profiles of the specimen edges obtained with the help of stereo measurements. Fixation in glutaraldehyde decreased the contraction in wet specimens prepared for environmental scanning electron microscopy (ESEM). Fixation also decreased shrinkage of the demineralized layer due to gradual desiccation in the ESEM during observation. For conventional SEM, the contraction was minimized if specimens of etched and fixed dentin were fractured in the dry condition after dehydration.     

Fabrication of hierarchical micro/nanostructures via scanning probe lithography and wet chemical etching

In this study, we propose a simple and effective method for fabricating hierarchical silicon structures via the combination of scanning probe lithography (SPL) and wet chemical etching. Here, silicon oxide structures were protruded from a 100-oriented silicon surface, followed by the passivation of silicon nitride by AFM tip-induced local oxidation. Based on the two-dimensional (2D) silicon oxide patterns, three-dimensional (3D) microstructures with high aspect ratios were formed by wet etching with HF and KOH. A variety of combinations of SPL and the etching process allowed us to fabricate diverse silicon-based structures such as deep-etched microstructures and multi-terraced nanostructures.     

Algorithms and machining experiments to reduce depth errors in servo scanning 3D micro EDM

In servo-scanning 3D micro electro discharge machining (SS-3D MEDM), the depth errors of 3D micro cavities are accumulated layer by layer due to the contour scanning process with keeping discharge gap for compensating axial electrode wear in real time. In this research, the errors’ causes were analyzed, and then a layer depth constrained algorithm (LDCA) and an S-curve accelerating algorithm (SCAA) were proposed to reduce the depth errors. By LDCA, over-cutting errors can be avoided by controlling a tool-electrode feed maximum at every scanning spot. As a supplementary algorithm for LDCA, SCAA can compensate insufficient-machining errors at start and end of scanning paths. Implementation process and control strategy of the algorithms were also described. The purpose of this research is to efficiently machine complex 3D micro-cavities with high accuracies of shape and surface. By use of computer-aided manufacturing software of Pro/Engineer to plan complex 3D scanning paths, machining experiments were carried out to verify the proposed algorithms. The experimental results show: Typical 3D micro cavities <800 μm can be automatically machined, and the machining accuracies of micro surfaces and edges are obviously improved, and the depth errors can be controlled within 2 μm, and the material removal rate reaches 2.0 × 10⁴ μm³/s with tool electrode of ∅80 μm and its rotational speed of 1000 r/min. In addition, the 3D micro cavities designed on unknown edge or hollow workpieces can be successfully formed.     

Validation of terrestrial laser scanning and photogrammetry techniques for the measurement of vertical underclearance and beam geometry in structural inspection of bridges

This research shows a novel methodology based on the application of terrestrial laser scanning and photogrammetry techniques as auxiliary metric tools for bridge inspections procedures. These methodologies are validated throughout a case study where the minimum underclearance and the overall geometry of a prestressed concrete beam are obtained. Data obtained are compared with high accurate measurements provided by a total station. Results show a good agreement for beam geometry with high statistical correlation coefficients. Minimum vertical underclearance also shows a good agreement for all the systems, which appears good enough due the metric tolerances required in these inspection works.     

Advantages of stereo imaging of metallic surfaces with low voltage backscattered electrons in a field emission scanning electron microscope

High emission current backscattered electron (HC-BSE) stereo imaging at low accelerating voltages (≤ 5 keV) using a field emission scanning electron microscope was used to display surface structure detail. Samples of titanium with high degrees of surface roughness, for potential medical implant applications, were imaged using the HC-BSE technique at two stage tilts of + 3° and − 3° out of the initial position. A digital stereo image was produced and qualitative height, depth and orientation information on the surface structures was observed. HC-BSE and secondary electron (SE) images were collected over a range of accelerating voltages. The low voltage SE and HC-BSE stereo images exhibited enhanced surface detail and contrast in comparison to high voltage (> 10 keV) BSE or SE stereo images. The low voltage HC-BSE stereo images displayed similar surface detail to the low voltage SE images, although they showed more contrast and directional sensitivity on surface structures. At or below 5 keV, only structures a very short distance into the metallic surface were observed. At higher accelerating voltages a greater appearance of depth could be seen but there was less information on the fine surface detail and its angular orientation. The combined technique of HC-BSE imaging and stereo imaging should be useful for detailed studies on material surfaces and for biological samples with greater contrast and directional sensitivity than can be obtained with current SE or BSE detection modes.     

薄片零件尺寸机器视觉检测系统中的线扫描步长自适应优化研究

借鉴自由曲面逆向工程中扫描步长自适应优化的思想,提出了基于CAD信息的线扫描步长自适应优化方法。基于曲线拟合容差开发了圆弧图元线扫描步长自适应优化算法;基于等线段长开发了直线图元线扫描步长自适应优化算法;基于图元间的拓扑结构归纳了区域线扫描步长自适应选取准则。用弹性臂薄片零件的尺寸检测实验对基于CAD信息的线扫描步长自适应优化方法的检测精度和扫描数据量进行了分析。实验结果表明,该方法能提高检测系统的检测精度,提高线扫描的扫描效率,减少扫描数据量。     

Imaging thin and thick sections of biological tissue with the secondary electron detector in a field-emission scanning electron microscope

A field-emission scanning electron microscope (FESEM) equipped with the standard secondary electron (SE) detector was used to image thin (70–90 nm) and thick (1–3 μm) sections of biological materials that were chemically fixed, dehydrated, and embedded in resin. The preparation procedures, as well as subsequent staining of the sections, were identical to those commonly used to prepare thin sections of biological material for observation with the transmission electron microscope (TEM). The results suggested that the heavy metals, namely, osmium, uranium, and lead, that were used for postfixation and staining of the tissue provided an adequate SE signal that enabled imaging of the cells and organelles present in the sections. The FESEM was also used to image sections of tissues that were selectively stained using cytochemical and immunocytochemical techniques. Furthermore, thick sections could also be imaged in the SE mode. Stereo pairs of thick sections were easily recorded and provided images that approached those normally associated with high-voltage TEM.     

Structural inspection and troubleshooting analysis of a lab-scale distillation column using gamma scanning technique in comparison with Monte Carlo simulations

In the present study, structural inspection and troubleshooting analysis of a lab-scale distillation column has been performed using gamma scanning technique and Monte Carlo simulations. MCNP4C Monte Carlo code has been used for simulations of the column and calculation of the computational density profile. The tested column is a one-pass tray type with 51 cm diameter. A Cs-137 sealed source and a 1 × 1 inch NaI (Tl) detector has been used for this gamma scanning process. According to the results, both experimental and simulation results showed the specification of trays and another section of the column accurately. Also, in addition to the flooding and damaged tray in the column, defects such as foaming with the density of 0.17 g/cm³ can be distinguished using this technique. Based on the results, using photopeak count approach the differences in the material attenuations can be better distinguished. The effectiveness of this approach in determination of malfunctions increases with the density of the material between the source and the detector. Analyzing the experimental and simulation results are indicative of the fact that the procedures and methods used in this work are quite suitable for improving the accuracy of the troubleshooting analysis based on gamma scanning technique.