New approach to quantifying developmental variation in the dentition using serial microtomographic imaging

Dental morphogenesis and cellular differentiation are expressed in the fully formed tooth by the topography of the dentin-enamel junction and outer enamel surface. These boundaries can be differentiated using a variety of imaging systems. In this study, we used serial microCT imaging to provide accurate 3D reconstructions of developing lower human second deciduous molars. These were used to quantify the volume of enamel and dentin of individual cusps in relation to basal crown height. As growth and differentiation proceed apically, the spatial orientation of cusp tips and their bases were used to estimate their order of initiation and coalescence. We found that the order of coalescence differed from the order of initiation. We also found that dentin cusp height and volume as well as rate and quantity of enamel apposition varied along mesio-distal and bucco-lingual axes, and were independent of order of initiation and duration of growth. These results demonstrate that the potential for variation in crown size and form is maintained throughout development. We propose that the microCT model developed in this study constitutes a new approach for the investigation of developmental variation and its contribution to phylogenetic variation expressed in crown form and size.     

直齿锥齿轮刨齿加工在线检测与机床调整

文章介绍了对齿厚、齿高、齿深等参数进行预测并在线测量,及时调整机床参数,纠正偏差,从而提高直齿锥齿轮刨齿加工精度的方法和具体步骤.     

鼓形齿联轴器成形加工的参数优化及啮合性能

本文给出了用成形法加工鼓形齿的工艺参数的优化方法，分析了用优化后的多数加出的鼓形齿联轴器的啮合性能，做了齿面接触分析，并进行了实验验证。     

基于鼓形蜗杆传动理论的内齿轮加工原理研究

针对目前内齿轮加工方法中普遍存在的精度低、效率低等不足,提出一种运用鼓形蜗杆刀具进行内齿轮连续分度的展成加工方法。以微分几何和啮合原理为基础建立鼓形蜗杆传动二次包络理论及鼓形蜗杆刀具齿面数学模型。分析内渐开包络母面重现的必然性及内齿轮加工共轭关系。研究鼓形蜗杆刀具齿面的轴向齿形特性及齿面根切规律,并给出刀具齿面根切的避免方法。应用虚拟中心距原理分析鼓形蜗杆刀具的粗加工工艺参数优化方法及其精确加工原理。该研究工作为内齿轮的高效高精加工提供了一种有效途径。     

鼓形齿联轴器在折叠机构中的应用

将鼓形齿联轴器应用于折叠运动中,得到了新型的鼓形齿联轴器折叠机构。基于Adams虚拟样机对该折叠机构开展了运动仿真及分析,得到了机构实现折叠所需要的鼓形齿联轴器的最大角位移。依据鼓形齿联轴器的最大角位移量确定了鼓形齿的修形参数。     

DESIGN OF PIC-CONTROLLED PULSED ULTRASONIC TRANSMITTER FOR MEASURING GINGIVA THICKNESS

The aim of this study is to design and implement a noninvasive ultrasonic thickness measurement device that determines the gingiva thickness, which is quite an important criterion in dentistry, by using A-mode ultrasonic method. Operating frequency of the device is selected as 8 MHz, since gingival thickness is quite slight. The measurements are performed as 192.5 μm precision by the implemented system. Surface-mounted devices integrated circuits (SMD ICs) and electronic parts are used in the implementation of the device. Thus, a small-dimension, handheld device has been design and constructed. The transmitter of the device is tested under simulated object, and encouraging results were obtained.     

一种新型电磁作动器电磁力影响参数分析

针对各参数对一种新型电磁作动器电磁力影响机理的问题,利用ANSYS软件建立了该电磁作动器的电磁力仿真计算模型,并对加工好的样机电磁力进行试验测量。结果表明,仿真计算结果能够与试验数据很好的吻合,最大相对误差仅为11.6%,从而验证了仿真模型的有效性。利用该仿真模型分析了齿高、线圈匝数、齿数、气隙、衔铁厚度和轭铁厚度等参数对电磁力的影响,揭示了其影响机理,为这种电磁作动器的进一步优化设计奠定了基础,对类似结构的电磁执行器的设计具有一定的参考价值。     

基于真实刀刃轨迹的立铣刀切削厚度模型

瞬时切削厚度是铣削加工建模研究的重要参数之一。通过分析刀刃切削轨迹,可以得到准确的瞬时切削厚度,但需要求解复杂的超越方程。通常对切削刀刃轨迹进行不同程度的简化来求解近似的瞬时切削厚度。为得到准确的瞬时切削厚度,提出一种新的切削厚度计算模型。基于立铣刀真实切削刀刃轨迹,对近似的切削厚度模型进行补偿,得到较传统计算方法更为准确的结果,计算过程也更为简单。通过切削力试验验证,该模型可以得到更好的动态切削力预测结果。     

Influence of tooth modifications on tooth contact in face-hobbed spiral bevel gears

In this study the influence of tooth modifications induced by machine tool setting and head-cutter profile variations on tooth contact characteristics in face-hobbed spiral bevel gears is investigated. The concept of face-hobbed spiral bevel gear generation by an imaginary generating crown gear is applied. The modifications of tooth surfaces are introduced into the teeth of both members. The lengthwise crowning of teeth is achieved by applying a slightly bigger radius of lengthwise tooth flank curvature of the crown gear generating the concave side of pinion/gear tooth-surfaces, and by the variation of machine tool settings in the generation of pinion/gear teeth. The ease-off in the tooth height direction of meshing tooth surfaces is achieved by applying a head-cutter whose profile consists of two circular arcs, instead of a straight-line. The method of tooth contact analysis applied determines the path of contact, the potential contact lines, the separations along these lines, and the transmission errors. A computer program implements the method. By using this program the influence of the variation of machine tool settings and of head-cutter geometry on tooth contact is investigated and discussed.     

调控齿轮啮合侧隙的齿厚控制参数精度设计与应用

为了满足齿轮副正常的安装与啮合,需通过对齿厚控制参数及其精度进行设计以保证最小侧隙。在设定最小侧隙的情况下,推导了法向齿厚、法向弦齿厚、公法线长度和跨棒尺寸等齿厚控制参数及其精度设计公式,借助通用CAD系统进行实例应用分析,解决了生产实际中齿厚控制参数计算繁琐、复杂和工作量大等问题。     

Confocal laser scanning microscopy for the study of the morphological changes of the postextraction sites

A better understanding of the remodeling process of postextraction sockets is essential in dental treatment planning. The aim of this study was to evaluate whether confocal laser scanning microscopy (CLSM) can be applied to imaging contour changes of postextraction sites, as well as to its quantification with image analysis of obtained three‐dimensional images. This work describes a new application of the CLSM technique. The system used was the OLS3100‐USS, LEXT model (Olympus®). CLSM was used for the surface analysis of the extraction site. The measurements taken with CLSM were: (1) mesio‐distal distance, (2) alveolar ridge thickness, and (3) vestibular and lingual alveolar ridge height. Results of study cast scanning at baseline, 1 and 3 months after tooth extraction, with CLSM are well‐detailed images of postextraction areas. The CLSM technique used in study casts is a valid method to measure the dimensional changes that happen in the edentulous area after tooth extraction. This technique allows the evaluation of changes in mesio‐distal distance, thickness of the alveolar ridge and alveolar ridge height based on the measurements on the alveolar contours. Microsc. Res. Tech., 2011. © 2011 Wiley‐Liss, Inc.     

A numerical analysis of drop impact on liquid film by using a level set method

Splashing and spreading of a liquid by drop impact on liquid film depends on the impact velocity, drop size, drop properties and liquid film thickness. These parameters can be summarized by three main dimensionless parameters: Weber number, Ohnesorge number and non-dimensional film thickness. Upon impact of a drop on liquid film, these parameters influence the shape of the splash and the formation and propagation of the crown. In the present study, the splashing and spreading resulting from drop impact on liquid film has been numerically investigated by using a Level Set method for the interface tracking of the two-phase flow simulation. For various dimensionless parameters, characteristics of the crown formation and spreading were predicted, and the results were found to show good agreement with available experimental data in the earlier stage of crown formation and show some discrepancies in the later stage of crown spreading due to the present 2D axi-symmetric computation, which cannot predict the secondary drops.     

平面包络凸环面蜗杆齿形研究

针对一种新型平面包络凸环面蜗杆,应用啮合原理建立了齿面数学模型,对其进行齿形分析,研究母平面倾角等参数对齿面根切及中齿变尖的影响规律。提出了一种均化磨削余量的粗加工方法,运用虚拟中心距原理试制出平面包络凸环面蜗杆样件。基于蜗杆齿面离散点坐标值对平面包络凸环面蜗杆进行了齿形加工精度检测。结果表明:齿面磨削余量优化方法正确、可行、有效,样件齿形达8级加工精度,解决了平面包络凸环面蜗杆在设计、制造及检测中的关键问题。     

错齿BTA深孔钻削切屑变形断裂影响因素研究

利用错齿BTA深孔钻削切屑弯曲变形规律,对导致错齿BTA内排屑深孔钻切屑断裂的影响因素进行了分析,通过试验研究了错齿BTA深孔钻削切屑的变形断裂随刀齿钻削半径、钻削工艺参数、断屑台尺寸的变化规律。研究结果表明,刀齿钻削半径对切屑厚度影响很大,随钻削半径的增大,各刀齿切屑厚度增大,切屑厚度最大值点均位于刀齿切屑大径边缘且中心齿、中间齿、外齿的切屑厚度最大值依次减小;与转速相比,进给量对切屑厚度和切屑应变增量的影响更大,随进给量增大,切屑厚度增大,切屑应变增量增大;随断屑台宽度减小、高度增大,切屑应变增量增大,断屑条件改善。     

遗传算法在高齿准双曲面齿轮设计中的应用

遗传算法是一种模拟生命进化机制的搜索优化方法,具有通用性好的特点,本文提出一种基于遗传算法的高齿准双曲面齿轮的优化设计方法。通过增加工作齿高,可达到增大重合度的目的,并保证所设计的准双曲面齿轮不根切、齿顶不变尖,可在现有机床上用标准系列刀具加工。     

连续波状粗糙度对直齿轮热弹流润滑的影响

工程实践中没有理想光滑的表面,在齿轮弹流润滑中,油膜的厚度通常与某些切削工艺形成的金属表面粗糙度处于同一数量级,所以表面粗糙度对齿轮弹流润滑的影响是不应该忽略的。在考虑不同啮合点处的曲率半径、卷吸速度、轮齿载荷随时间变化的基础上,考虑轮齿表面连续波状粗糙度对弹流润滑的影响,利用多重网格技术求得齿轮瞬态微观热弹流润滑的完全数值解。结果表明,连续波状粗糙度会造成齿轮瞬态弹流润滑的油膜压力和温升产生振荡,并使最小膜厚变薄,最高压力变大,最大温升增大。轮齿间振荡的高压和高温会造成齿轮振动疲劳破坏,所以连续的波状粗糙度对齿轮的润滑是不利的。     

Modelling, Implementation, and Manufacturing of Spiral Bevel Gears with Crown

The operational performance of gears in terms of smoothness, quietness, wear and life span is largely affected by how gear and pinion teeth make contact. To enhance the operational performance, a crown is often applied to a standard (nominal) gear tooth surface. Regardless of the presence of a crown, all the gears are machined by special types of machine tools, such as gear hobbers and shapers. This paper develops a tooth surface for a spiral bevel gear with a crown so that it can be machined by numerically controlled machine tools. Specifically, we derived: 1. A bi-parametric tooth surface model for a standard spiral bevel gear. 2. A crown model along the spiral curve direction. 3. A crown model along the involute curve direction. The developed algorithm was tested and implemented in a prototype software system called GearCAM. With the GearCAM system, a set of spiral bevel gear and pinion was machined using a 4-axis CNC milling machine to check the validity and effectiveness of the crowning method. Through various verifications, it is shown that the models developed for the standard and crown gears can be used as a means for design and verification of spiral bevel gears.     

基于条件生成对抗网络的缺失牙体功能性咬合面形态设计方法

针对牙齿修复体设计中未考虑牙齿磨耗形态分布以及标准牙难以表达天然牙形态多样性的问题,提出基于颌位空间约束以及牙齿磨耗面引导的缺失牙体功能性咬合面形态设计方法.利用启发式搜索算法半自动提取牙齿磨耗面,并采用自适应视距的正交投影法计算出牙冠及其磨耗面在正视方向上的深度图像.通过对缺失牙齿功能性咬合面特征分级表达,采用基于颌...     

混合式步进电动机结构参数智能协同优化

为了探究混合式步进电动机关键结构参数对其静态转矩的影响规律,找寻最优设计方案,提出一种基于正交试验、反向传播(Back Propagation,BP)神经网络和遗传算法的智能协同优化方法。通过对电机的磁路分析与ANSYS Maxwell-3D有限元仿真,讨论了电机结构和运行参数对输出转矩的影响,并据此对电机的气隙g、齿宽比b_t/t、齿高h_t和转子壁厚h_r进行协同优化,采用电机的最大静转矩T_m作为优化目标,运用智能协同优化方法得到最优解,并对优化结果进行有限元验证。结果表明:优化结果与仿真结果相近,最大静态转矩相对误差为4.8%,最优结构参数为:g=0.1 mm,b_t/t=0.37,h_t=0.84 mm,h_r=2.5 mm。     

小模数齿轮极坐标快速测量技术研究

为了解决小模数齿轮齿距、齿厚、齿轮偏心等参数的测量,利用非接触式距离传感器及直驱旋转平台构建了一个极坐标式测量系统。通过旋转平台的光栅信号控制距离传感器的触发,实现了被测小模数齿轮横截面数据的等角度采样。开发软件对获取到的数据进行处理,获得了齿距、齿厚、齿轮偏心等误差。试验表明,该系统可实现小模数齿轮上述参数的快速测量。