计算机辅助牙颌畸形矫治技术研究

根据牙颌模型和牙颌畸形矫正过程的特点,提出了基于牙颌数字模型和矫治器械形状与性能分步获取制造方法的计算机辅助牙颌畸形矫治技术路线和具体实施方案,选择确定了所涉及的牙颌模型数字化、复杂曲面实体数字模型操作、中间牙颌模型成形三项关键技术的具体实现方法。     

三角网格牙颌模型上的牙弓线半自动探测方法

介绍了一种在三维三角网格牙颌模型上半自动探测牙弓线的方法。首先使用三维激光测量系统对牙颌石膏模型进行测量获得数字模型;其次在网格模型上交互拾取4个参照点以确定咬合平面;接着使用顶点法矢和咬合平面作为参考,筛选出初始特征点并拟合出初始牙弓线;以初始牙弓线作为新的参考依据筛选出最终特征点,拟合最终参照点得到最终牙弓线。使用多副牙颌模型对该方法进行了测试,验证了该方法稳定、有效。     

牙颌模型的三维激光测量及模型重建

牙颌模型的数据测量是进行口腔修复CAD/CAM的基础。本文采用自制三维激光测量仪对牙颌表面数据进行三维测量,获得了单颗后磨牙缺失的牙颌模型多片三维点云数据。将各片数据在反求软件Surfacer平台上通过三点定位法进行数据拼合,准确地表示出缺失牙上下颌的咬合关系,重建牙颌的实体模型。     

逆向工程技术在古典家具保护方面的应用与研究

采用逆向工程技术对中国古典家具进行信息保存和开发,是文物保护方面的一项新课题。应用三维激光扫描技术对所需保护的古典家具文物实体进行三维数字测量或扫描,可以准确真实地获取反映物体外形的三维数字化信息;由曲面重建和实体重构,建立物体的三维CAD实体模型;生成数据文件形成数字模型库,最后对信息进行存储。采用它不但可降低文物的保护成本,使家具的三维数据信息能永久保存,还可用于复制还原,实现保护与开发并举,因而具有现实意义和实用价值。     

三维激光扫描技术在海洋领域中的应用现状与前景展望

三维激光扫描技术作为获取空间信息的一门新兴测绘技术,通过非接触式主动测量,可大面积、自动连续的采集三维数据,快速构建目标的三维可视化模型,进行空间仿真和虚拟现实,具有高精度、高速度、实时性和主动性强、全数字化以及对任何物体都能扫描的特点。在简要介绍三维激光扫描技术及其发展的基础上,阐述了其在海洋领域中的成功应用,并对其未来发展趋势进行了分析和探讨。     

三维激光扫描装备与技术在地铁测量中的应用

三维激光扫描技术通过激光测距仪对物体表面进行扫描,获取物体表面的三维坐标信息,进而生成物体表面的三维模型,然后用于工程的测量分析等各项工作。文章首先介绍了三维激光扫描技术的原理和应用优势,然后对地铁工程测量中三维激光扫描技术的具体应用进行了探讨分析,以供参考。     

三维激光扫描技术在核设施退役中的应用研究

针对目前核设施退役没有核设施三维资料的现状,提出运用三维激光扫描技术获得点云数据来进行退役核设施设备三维模型重构的的方法,介绍了三维激光扫描技术获取核设施三维模型的原理,并重点阐述了对退役核设施进行三维扫描的实施方案,给核设施的退役方法提出了一种新思路。     

基于退役电池包的逆向重构研究

以退役动力电池包壳体为研究对象，采用EinScan HX激光扫描仪获取原始点云数据、Geomagic Control软件对点云数据进行处理、Geomagic Design软件重构三维数字模型，分析和总结了逆向重构过程中的关键技术。通过Geomagic Control软件分析了重构的三维数字模型与原始点云数据的误差，确认误差在±1 mm内，满足了退役动力电池包智能拆解系统对三维数字模型的精度要求。因此，精确的逆向三维重构技术对实现机器人自动化拆解有很好的指导意义，有利于退役动力电池包智能拆解技术的发展。     

基于坐标配准的牙颌测量点云拼合技术研究

针对牙颌等待测物非接触式光学三维测量,提出了一种融入标定功能的夹具设计方法,实现了测量过程中待测物与标定靶的空间一致性;定义了单目视觉测量过程涉及到的坐标系统;提出了一种基于坐标配准的点云拼合技术,简化了点云拼合流程,实现了点云拼合理论零误差;应用张正友标定方法对摄像机进行了标定;通过实验验证,得到了具有一定精度的牙颌三维模型点云拼合数据,实现了较快的测量速度,为提高牙颌测量系统的整体精度提供了有力支撑。     

反求工程的一大利器——三维扫描仪

3D扫描仪的工作原理 三维激光扫描技术是国际上近期发展的一项高新技术.随着三维激光扫描仪在工程领域的广泛应用,这种技术已经引起了广大科研人员的关注.通过激光测距原理(包括脉冲激光和相位激光),瞬时测得空间三维坐标值的测量仪器,利用三维激光扫描技术获取的空间点云数据,可快速建立结构复杂、不规则的场景的三维可视化模型,既省时又省力,这种能力是现行的三维建模软件所不可比拟的.     

A laser sensor with multiple detectors for freeform surface digitization

An integrated laser scanning sensor for freeform surface digitization is presented. The sensor consists of a diode laser light source and four position-sensitive device (PSD) detectors. The stand-off distance of the sensor is 180 mm and the measurable range is 90 mm. The Lambert model is applied to calculate the displacement between the sensor and the measured point on the object surface along the optical axis, under the assumption of a diffusive surface. The inclination angle of the measured point from the vertical plane of the laser beam is calculated by mathematical inference. Those data are used in error compensation to improve system precision. The new design of multiple detectors could increase the measurable angle and could solve the dead space problem in single point laser of triangulation measurement. The computer simulation and actual measurements show that the displacement resolution reaches 50 μm, and the system performs well in regards to stability and repeatability. The sensor system could be mounted on the NC machine orX-Y platform for freeform surface digitization.     

Masked illumination scheme for a galvanometer scanning high-speed confocal fluorescence microscope

High-speed beam scanning and data acquisition in a laser scanning confocal microscope system are normally implemented with a resonant galvanometer scanner and a frame grabber. However, the nonlinear scanning speed of a resonant galvanometer can generate nonuniform photobleaching in a fluorescence sample as well as image distortion near the edges of a galvanometer scanned fluorescence image. Besides, incompatibility of signal format between a frame grabber and a point detector can lead to digitization error during data acquisition. In this article, we introduce a masked illumination scheme which can effectively decrease drawbacks in fluorescence images taken by a laser scanning confocal microscope with a resonant galvanometer and a frame grabber. We have demonstrated that the difference of photobleaching between the center and the edge of a fluorescence image can be reduced from 26 to 5% in our confocal laser scanning microscope with a square illumination mask. Another advantage of our masked illumination scheme is that the zero level or the lowest input level of an analog signal in a frame grabber can be accurately set by the dark area of a mask in our masked illumination scheme. We have experimentally demonstrated the advantages of our masked illumination method in detail.     

A laser sensor with multiple detectors for freeform surface digitization

In this paper, an integrated laser scanning sensor for freeform surface digitization is presented. The sensor consists of a diode laser light source and four position-sensitive device (PSD) detectors. The stand-off distance of the sensor is 180 mm and the measurable range is 90 mm. The Lambert model is applied to calculate the displacement between the sensor and the measured point on the object surface along the optical axis, under the assumption of a diffusive surface. The inclination angle of the measured point from the vertical plane of the laser beam is calculated by mathematical inference. Those data are used in error compensation to improve the system precision. The new design of multiple detectors could increase the measurable angle and could solve the dead-space problem in the single-point laser of triangulation measurement. The computer simulation and actual measurements show that the displacement resolution is around 50 μm, and the system performs well in terms of stability and repeatability. The sensor system could be mounted on the NC machine or on the X–Y platform for freeform surface digitization.     

Comparative analysis on measuring performances of dental intraoral and extraoral optical 3D digitization systems

Implementation of the methods of 3D digitization in dental practice is a modern and sophisticated alternative to the method of conventional impressions. Among many different methods of 3D digitization applied in dentistry, optical methods can be considered as today mostly applied, especially in the field of prosthodontics. The developments of this kind of systems have converged in two main directions – extraoral and intraoral systems. The main quality parameters for evaluating measuring performances of 3D digitization methods and systems include accuracy and precision. By introducing LED blue light in intra- and extraoral cameras, the Cerec system has significantly improved the quality of 3D digitization results. As the technical features of cameras in both types of systems are identical and the difference of the digitization methods is connected only to operating environments, the main goal of the research was to analyze whether different digitization conditions significantly influence the systems’ measuring performances. Analyzes were focused on investigating accuracy and precision of two mentioned specialized dental optical systems on the basis of CAD inspection, with special attention on evaluating statistically significant differences within the obtained results. Statistically significant difference was not found in systems’ precision, while the extra oral system was found as of significantly higher accuracy.     

激光选区熔化单道扫描与搭接数值模拟及试验

激光选区熔化(Selective laser melting, SLM)单道扫描的数值模拟,在数值建模时多采用规则实体模拟铺设的粉末层,通过等效定义材料热物理属性模拟铺设粉末层中粉末与气体共存的情况,难以模拟粉末颗粒的随机性而带来的扫描结果的随机性,且难以分析熔池形貌、内部缺陷的微观衍变过程。针对SLM成形过程中激光功率和单道搭接率对扫描单道和单道搭接质量的影响,以316L不锈钢材料为例,建立SLM首层单道扫描与单道搭接数值模拟模型。SLM的铺粉过程在基于离散单元法的EDEM中建立,并得到数值化的粉床几何模型。SLM的单道扫描与搭接的模拟基于有限体积法,在FLUENT中实现,采用两相流模型与熔化/凝固模型捕捉熔池形貌变化过程,得到不同激光功率和扫描搭接率下成形单道与单道搭接的数值模型。最后结合试验表明了在100～300 W激光功率下成形单道表面形貌与缺陷的形成,当激光功率为100～150 W时,单道形貌不规则,且容易形成局部缺陷;在200～300W功率下,激光功率越大,保证搭接质量的最低搭接率越小,当激光功率为250 W时,应保证单道填充间距不大于0.1 mm。研究成果对SLM工艺参数...     

基于UG逆向工程对涡轮的计算机辅助设计

在三坐标测量机的基础上给出了一种数字化测量曲面轮廓的方法,通过测球半径的补偿、坐标系的建立、最佳测量路径的规划以及混合编程扫描,提高了测量精度及扫描测量的效率,采集到的数据可以反映曲面的几何特征,并结合UG/CAD/CAM软件创建涡轮数字化的几何模型。     

An integrated reverse engineering approach to reconstructing free-form surfaces

An integrated reverse engineering approach to generating free-form surfaces has been developed to create CAD-compatible free-form surface models with a coordinate measurement machine and a touch trigger probe. The approach integrates data digitization and surface modelling to obtain an efficient and accurate digitization process with a collisionfree exploration path, and to reconstruct least-squares bi-cubic B-spline surface models for rapid product prototyping. The whole approach is divided into two stages: the planning of boundary digitization; and the adaptive model-based digitizing process (AMDP). The planning of boundary digitization defines the exploration surface region. The AMDP then automatically explores the whole measured surface region with a collision-free exploration path, continuing until a satisfactory surface model corresponding to the user's specified digitizing accuracy is obtained. This approach significantly reduces the product development lead time and obtains a surface model with controlled digitizing accuracy. The validity and applicability of this approach are demonstrated by three practical industrial examples.     

在机测量激光测头位姿的线性标定

针对在机激光扫描测量中激光测头安装位置和姿态引起的测量误差,提出了一种适用于在机激光测量的测头标定方法。构造了在机激光扫描测量原型系统,建立了激光测头随机床运动的测量模型;通过多角度扫描标准球球面拟合球心,给出了一种线性求解测头安装位姿参数的算法,避免了非线性优化求解中的大量计算和不稳定问题。分析了测量过程中机床各个轴的运动误差对测量结果的影响,建立了误差模型,并给出补偿机床系统误差的方法。实验显示,对直径已知的标准球进行测量时,测头在不同摆角测得的标准球直径误差小于0.05 mm,误差补偿后球心位置误差减小了83%。实验结果验证了该标定方法的可行性,以及机床误差对测量精度影响的模型及补偿方法的正确性。     

Imaging of endodontic biofilms by combined microscopy (FISH/cLSM – SEM)

Scanning electron microscopy is a useful imaging approach for the visualization of bacterial biofilms in their natural environments including their medical and dental habitats, because it allows for the exploration of large surfaces with excellent resolution of topographic features. Most biofilms in nature, however, are embedded in a thick layer of extracellular matrix that prevents a clear identification of individual bacteria by scanning electron microscopy. The use of confocal laser scanning microscopy on the other hand in combination with fluorescence in situ hybridization enables the visualization of matrix embedded bacteria in multi-layered biofilms. In our study, fluorescence in situ hybridization/confocal laser scanning microscopy and scanning electron microscopy were applied to visualize bacterial biofilm in endodontic root canals. The resulting fluorescence in situ hybridization /confocal laser scanning microscopy and scanning electron microscopy and pictures were subsequently combined into one single image to provide high-resolution information on the location of hidden bacteria. The combined use of scanning electron microscopy and fluorescence in situ hybridization / confocal laser scanning microscopy has the potential to overcome the limits of each single technique.