外啮合珩齿的间齿啮合过程分析

为了研究间齿珩齿加工方法中的空间间齿啮合过程,将该过程分为标准渐开螺旋面啮合过程和顶刃啮合过程。基于空间几何学和啮合原理,本文分别建立两个啮合过程的三维模型,得到各过程的接触点,以及两个齿面上接触点的对应关系。根据跳牙蜗杆与齿轮的几何关系,提出了确定各个过程分界点的方法。以具体参数的跳牙蜗杆与齿轮为例,对齿面上各个过程的接触点迹线进行三维仿真,并绘制接触点迹线上不同位置的相对速度曲线图,针对相对速度的大小和方向进行了分析,为间齿珩齿加工机理的研究奠定基础。绘制了整体误差单元曲线,与实体求交法对比,完全吻合,验证了该模型的正确性。

基于平衡剃齿的剃齿刀间齿刃磨技术

剃齿是齿轮精加工的高效传统工艺,广泛应用于汽车、拖拉机和机床制造行业,但标准剃齿刀在剃齿时会产生齿形中凹,从而影响了齿轮齿形的加工精度和齿轮的传动质量(高噪声、低寿命).通过分析剃齿的加工过程,推导出了平衡剃齿的条件,即:剃齿过程中,剃齿齿面两侧在啮合线上同时接触点的数目相等;提出了间齿刃磨剃齿刀在剃齿加工过程中可以满足剃齿区域间的平衡条件,能较好地解决齿形中凹问题,弥补剃齿加工的工艺缺陷.该技术通过合理选择间齿的削薄方式及削薄量,就可实现平衡剃齿无法达到的齿形加工精度.经大量的生产实践应用验证:剃齿刀间齿刃磨技术是一种简便、可行、高效的工艺技术.

间齿外啮合珩齿运动模型

为了解决外啮合珩齿中出现的中凹齿形现象,将间齿啮合原理应用在齿轮珩磨加工技术中,提出了间齿珩齿加工方法,这种方法采用了特殊的跳牙蜗杆珩磨轮.以齿轮齿条为例,利用运动学原理,建立了间齿珩齿全过程运动模型,这为间齿珩齿加工方法奠定了理论基础.该模型综合考虑了齿条顶刃啮合过程、齿轮顶刃啮合过程和渐开线啮合过程,分析了被加工齿轮与齿条的运动关系,并推导了各段过程的分界点.以具体齿轮为例,绘制了间齿珩齿过程中被加工齿轮的速度曲线.结果表明:将间齿啮合原理应用于珩齿加工过程,对提高珩齿效率,改善齿轮质量有重要意义.

保留痔间齿线区组织的环状混合痔切除术

痔是一种常见病，多发病。如何防止手术后遗症．特别是肛门狭窄，是肛肠学科亟待解决的问题，为此我们根据痔的解剖结构，设计了保留痔间齿线医组织治疗环状混合痔，疗效满意，特报告如下。

黄土高原及周边地区间齿螺（Metodontia）种类的数量分布及其温度和降水量最适范围的定量估算

间齿螺（Metodontia）是我国现生陆生蜗牛的常见属，也是黄土地层中常见的蜗牛化石，汉山间齿螺（Metodontiahuaiensis）和烟台间齿螺（Metodontiayantaiensis）是该属的两个常见种。我国现生间齿螺的地理分布调查取得了丰硕的成果，为间齿螺化石作为夏季风气候变化的代用指标提供了依据，但对现生间齿螺的数量分布和生态因子最适区域，还缺少系统的研究，限制了对间齿螺古生态古气候意义的深入理解。通过对黄土高原及周边地区356个表土蜗牛组合的研究，揭示了间齿螺及其优势种的数量分布与气候参数的关系，以及与经纬度和海拔高度的关系，并利用加权平均方法定量估算了汉山间齿螺和烟台间齿螺的温度和降水量最适范围。结果表明，在我们的研究区域内，含量大于20％的间齿螺，主要分布在年均温大于11℃、年降水量550～850mm的地区，36°N以南、110°E以东的地区，海拔在750m以下的地区；含量低于10％的间齿螺，在年均温5～15℃、年降水量380～700mm的地点都有分布，主要分布在33°～40．5°N、103．7°～117．5°E范围内，海拔在2000m以下的地区；年均温低于5℃、年降水量低于380mm的地区，海拔2000m以上的地区，基本上没有间齿螺生长；汉山间齿螺和烟台间齿螺年均温度最适范围分别为10．2～14．1cC左右和8．9～14．O℃左右（实测值与推导值R2=0．70，推导误差RMSEP=1．99），年降水量最适范围分别为530～800mm左右和470～750mm左右（R=0．81，RMSEP=90．87）。上述结果为间齿螺的古生态古气候研究和物种多样性保护提供了基础生态数据。

“王”字齿中间小齿的加工方案

"王"字齿广泛应用于如车床变速箱中,结构要求紧凑的场合,而"王"字齿中间小齿的加工一直困扰着不少工程师。本文,笔者通过实例介绍了如何利用普通插齿机解决这一问题的方案。

基于极间虚齿的表贴式永磁电机六倍频振动噪声的削弱

采用极间虚齿结构对表贴式永磁电机的六倍频振动噪声进行削弱,与传统的优化方法相比,该方法结构简单,且基本不影响基波磁场和平均转矩。首先,基于麦克斯韦张量法,推导了考虑力波分量相角的六倍频电磁力谐波表达式,分析了六倍频电磁力的产生机理,并以一台8极48槽表贴式永磁电机为例,采用有限元法进行验证;接着,引入凸极磁导函数,基于磁场调制原理,分析了虚齿对磁通密度时间谐波的调制作用及对六倍频电磁力的削弱机理;然后,建立多物理场有限元模型,对比了优化前后电机的关键电磁性能以及振动和噪声频谱,结果表明,极间虚齿可有效削弱电机的六倍频电磁力和振动噪声;最后对优化后的样机进行噪声实验,与仿真结果对比,验证了理论和有限元模型的正确性。

辊式磨粉机辊间长齿齿轮传动的优化设计

提出了一种用于辊式磨粉机辊间传动的非标准、长齿渐开线齿轮参数的优化设计数学模型,并对辊径250毫米辊式磨粉机的辊间齿轮传动进行了优化计算。结果表明,采用本文论述的方法所设计的齿轮,与进口辊式磨粉机所采用的辊间长齿齿轮传动的实测结果基本一致。

齿轮滚刀双参数造形法

1 双参数中间齿形设计法以m6、前角为7°齿轮滚刀为例按双参数中间设计法设计齿形,新刀造形误差左侧为—2.4μm占AA级滚刀制造公差的40％,占A级公差的24％;右侧为2.5μm,占AA级公差42％,占A级公差25％,在齿长二分之一截面左侧造形误差为—4.5μm占A级公差45％;右侧为3.9μm占A级公差39％,而现有但单参数造形法滚刀新刀造形误差两侧均为—5.8μm占AA级公差的97％占A级公差的58％,是双参数中间设计法的2.4倍多,在齿长二分之一截面两侧均为—9.5μm占A级公差的95％,是双参数中间设计法的2.1倍。从上述实例计算结果来看采用双参数中间设计法对于部分规格齿轮滚刀可以使齿形精度有一定提高。

特种复合材料在离心式制冷压缩机级间密封上的应用

分析离心式制冷压缩机级间梳齿密封的设计原理和对材质的性能要求,介绍CH-2特种复合材料的性能特点及其在多级离心式风机级间密封和多级离心泵级间轴承上的应用情况和使用效果,探讨特种复合材料在离心式制冷压缩机级间密封上的应用可能性,最后提出2个应用方向:1采用特种复合材料替代铝合金制造梳齿密封环;2采用特种复合材料制造可磨式接触密封。

四川鳞跳属Tomocerus记述(弹尾目、长角跳科、鳞跳亚科)

鳞跳属 Toocerus,是1841年由 H·Nicolet 所建立的,该属的系统分类尚未统一。Gisin 将该属直接归为长角跳科 Entomobryidae 下的一个属;Christiansen 及 Bellinger则将该属归于长角跳科下鳞跳亚科 Tomocerinae 的一个属;而 Pilissa 及 Yossi 等将鳞跳亚科提升为与长角跳科并列的一个独立的科。该属属以下的分类亦无定论。Gisin 及Pillssa 将该属分为三个亚属,即(Pogonognathellus)亚属、(Tritomurus)亚属、

The Tip Leakage Flow Structure of an Axial Fan with Tip Clearance

Experiment and numerical simulation technique are used to investigate the tip leakage flow in an axial fan with tip clearance at the design condition. The flow field in the tip region of fan is measured using a PDA (Particle Dynamics Analysis) system. The flow is surveyed across the whole passage at fifteen axial locations (from the 100% axial chord in front of the leading edge to the 100% axial chord behind the trailing edge), mainly focusing on the outer 90% blade span. Both experiment measurement and numerical simulation indicates the leakage flow originated from the tip clearance along the chord rolls up into three dimensional spiral structure to form leakage flow vortex. The interaction of leakage flow and main flow will produce the low velocity zone, and block the flow. The leakage flow almost occupies the most part of flow passage behind the trailing edge.

Effect of nonlinear impact damping with non-integer compliance exponent on gear dynamic characteristics

A nonlinear impact damping model of single-degree-of-freedom spur cylindrical gear with backlash and time-varying stiffness was established. Systematic analyses of the dynamic responses were performed. First, the nonlinear damping coefficient was considered as a constant parameter with two types of compliance exponent, meanwhile, dynamic factors were adopted to depict the dynamic characteristics. Second, the bifurcation graphs were plotted, where the damping coefficient was obtained along with the impact velocity and coefficient of restitution. The results show that light and heavy load conditions have an effect on the responses when the compliance exponent is integer. On the contrary, when the compliance exponent is non-integer, the dynamic responses are slightly affected, namely the system is more stable than the former situation.

Characteristics of a Drainage Channel with Staggered Indented Sills for Controlling Debris Flows

The characteristics of a new type of drainage channel with staggered indented sills for controlling debris flows were studied. The intermediate fluid in the non-viscous debris flow exhibited a helical movement, whereas the fluid near the sidewall had a stop-start movement pattern; the viscous debris flow exhibited a stable structure between the indented sills. The experimental results indicate that the mean velocity of the debris flow increased with increasing channel gradients, and the debris flow velocity was slightly affected by the angle of the sills. The average velocity of the non-viscous debris flow increased in the range of(0.5–1.5) interval between the indented sills, whereas the average velocity of the viscous debris flow increased initially and then decreased in the range of(0.75–1.25) interval between the indented sills. The depth of the non-viscous debris flow tended to gradually increase as the channel gradients increased, whereas the depth of the viscous debris flow gradually decreased as the channel gradients increased. When the discharge of the debris flow was constant, the angle and the interval between the indented sills had a slight effect on the depth of the viscous debris flow, whereas the depth of the non-viscous debris flow exhibited a different trend, as the sill angles and intervals were varied.

Meshing Theoretical Study and Simulation on Cylindrical Tri-sine Oscillating Tooth Gear Drive

The structure of cylindrical tri-sine oscillating tooth gear drive is presented. Based on the space meshing theory, equations of meshing and tooth profile are established and its meshing theory is studied. Using Pro/E, this system is modeled and simulated,which is compared with the above-established equations.

Caffeine Intake during Pregnancy： What Are the Real Evidences？

Caffeine is a substance presented in foods such as coffee, tea, soft drinks, chocolates and medicines and is commonly consumed by pregnant women. Due to its ability to cross the placental membrane and accumulate in the fetus body, caffeine and its metabolites have been contraindicated or recommended in small doses during pregnancy. Studies in rodents relate caffeine intake to lower rates of fertilization, embryonic implantation, changes in placental structure, increased occurrence of low fetal and placental weights, abortion and stillbirth. However, in humans, studies involving caffeine consumption are inconclusive. Methodological complexity, difficulty for measuring caffeine intake and ethical reasons are limiting factors for a more accurate conclusion. So far, caffeine recommendation ranges from 100 to 300 mg/day. Even though researches have recommended low caffeine consumption by pregnant women in order to avoid deleterious consequences during gestation, a safe dose has not been established until now. The aim of the present review is to describe the main findings on the effects of caffeine consumption during pregnancy in both human and rodent experimental models.

Timing Belts Dynamics Model Approach

Design of composites and usage of new polymer materials allows for improvement of constructional properties of belts. Different applications： transmission, conveying or controlling have different meshing in gear. The work presents meshing model between timing belt and pulley and constructional features of transmission timing belts depending on materials used for their production. While designing timing belt, much attention should be paid to selection of materials, which has significant influence on mechanical properties of belts. This paper attempts to identify the model material and the nature of cooperation of timing belt-pulley; this is basic knowledge for the development of timing belt gear.

Dynamic load sharing behavior of transverse-torsional coupled planetary gear train with multiple clearances

A new nonlinear transverse-torsional coupled model with backlash and bearing clearance was proposed for planetary gear set. Meanwhile, sun gear and planet's eccentricity errors, static transmission error, and time-varying meshing stiffness were taken into consideration. The differential governing equations of motion were solved by employing variable step-size Rung-Kutta numerical integration method. The behavior of dynamic load sharing characteristics affected by the system parameters including input rate, sun gear's supporting stiffness and eccentricity error, planet's eccentricity error, sun gear's bearing clearance, backlashes of sun-planet and planet-ring meshes were investigated qualitatively and systematically. Some theoretical results are summarized at last which extend the current understanding of the dynamic load sharing behavior of planet gear train, enrich the related literature and provide references for the design of planetary gear train.

Bifurcation and chaos study on transverse-torsional coupled 2K-H planetary gear train with multiple clearances

A new non-linear transverse-torsional coupled model was proposed for 2K-H planetary gear train, and gear's geometric eccentricity error, comprehensive transmission error, time-varying meshing stiffness, sun-planet and planet-ring gear pair's backlashes and sun gear's bearing clearance were taken into consideration. The solution of differential governing equation of motion was solved by applying variable step-size Runge-Kutta numerical integration method. The system motion state was investigated systematically and qualitatively, and exhibited diverse characteristics of bifurcation and chaos as well as non-linear behavior under different bifurcation parameters including meshing frequency, sun-planet backlash, planet-ring backlash and sun gear's bearing clearance. Analysis results show that the increasing damping could suppress the region of chaotic motion and improve the system's stability significantly. The route of crisis to chaotic motion was observed under the bifurcation parameter of meshing frequency. However, the routes of period doubling and crisis to chaos were identified under the bifurcation parameter of sun-planet backlash; besides, several different types of routes to chaos were observed and coexisted under the bifurcation parameter of planet-ring backlash including period doubling, Hopf bifurcation, 3T-periodic channel and crisis. Additionally, planet-ring backlash generated a strong coupling effect to system's non-linear behavior while the sun gear's bearing clearance produced weak coupling effect. Finally, quasi-periodic motion could be found under all above–mentioned bifurcation parameters and closely associated with the 3T-periodic motion.