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1 动力与背景1.1 介绍最近，对工程师有用的著作中，行星齿轮传动就像一个简单明了的运动学解答一样给予了一个明确的分析。不幸的是没有一个出版机构愿意出版一个简单的设计与分析技术。这一技术考虑到了在普通的例子中动力在齿轮传动中表现。这论文目的是想弥补这样一个空缺，在大多数的例子中，能找到全部的速度以及周转轮系力的解决方法的技术。在这方法发展后，列线图表可被用作产生直觉设计装置，允许设计者通过视觉去分析齿轮传动的运动形式，而不许不需重复的去解方程来完成。终于,方法设计与解决装置的出现，在新的一系列双轴自行车中，把使用行星轮系的实际性当作能源单位来联结。1.2 动力2002 年研究这项上述方法。很大程度上激发了被承担由弗吉尼亚技术人的供给动力的车队。在多用车早期设计期间进入了每年ASME 竞争, 这表明，对于两名车手相对不一致输入动力最有效的办法是使用行星轮系。概念在设计之后由人力车队试图将使用一列行星齿轮象那个被显示在上图1 创造近似地会允许两个车手对脚蹬以同样速度和近似地会贡献产品力量的同样百分比的系统。行星轮系容纳在速度和功率输入上的区别由二个车手。轮系特点的本质是这份论文焦点。图1图1: 齿轮传动被使用在人供给动力的车的Team.s 设计项目中运用Willis的方法为发现齿轮传动的运动学解答, 它被发现机制被控制了。那里.代表在齿轮传动中各个元素的旋转的速度, 并且R 是齿轮传动的基本的传输比率。 执行一个静态分析, 扭矩被发现被控制那里代表转矩在各个元素在传动, 并且N 代表齿轮传动中的齿数。使用这些等式, 它变得明显, 达到力量均衡的目标以相等和相反输入速度是不可能的。 如果和被认为是相等和相反, 然后达到力量均衡, T2 和T5 必须并且是相等和对立的。 根据等式3, 这意味着R 必须是1 。 不幸地, 这采取分母等式1 到零, 可以驱动到无限。什么直觉地似乎一个简单的问题解决导致了唯一的解答空间。 以最后期限为竞争结束, 设计计划被摒弃了倾向于一种更加简单的解答。研究完成在试图设计一系列齿轮传动，成为了一个更加宽广的研究计划的基础。这个项目驱动, 而不是系列齿轮传动的设计为一个具体目的, 是创造将允许行星齿轮传动发展为任一个可能的应用的数字的一个简明的设计方法。 由处理行星在最一般的例子中, 这个项目以及允许探索HPV 队的失败的原因，设计工程师定义运动学关系在行星齿轮传动中的三个分支之间没有首先选择齿轮的一个物理安排。1.3背景 一列行星齿轮传动被定义作为任一列齿轮传动中，包含至少循轨道运行由转动关于它自转和并且关于的轴的一个齿轮, 或载体。 基本行星, 或周转圆, 齿轮传动被显示在表2, 与被简化的表示法一起被使用为这份论文剩下的人。 基本的传动包括二个齿轮, 太阳(1) 和行星(2) 齿轮, 并且第三名成员, 此后指行星载体或架(3)。图2 图2: (a) 基本的周转圆的齿轮传动和(b) 它的运动学表示法。 因为它很难直接地把转动传送到从行星齿轮, 基本的周转圆的齿轮传动有些被限制在实际应用。然而，更加有用的是，周转圆传动指简单和复杂行星齿轮传动, 那里第二个太阳齿轮被使用。 这些齿轮传动可能会在任何十二个安排被指出的图3. 是依照由L.vai 最初提出。图3图3: 简单和复杂周转圆的齿轮传动。传动在象限I 和III 被分类作为简单的周转圆传动, 因为行星齿轮是在与两个太阳齿轮啮合。那些在象限II 和IV 代表复杂齿轮传动, 那里行星齿轮部份地是在互相啮合和部份地在啮合与二个太阳齿轮。 注意那, 不管安排, 只一个行星载体也许被使用。当这个图清楚地显示周转圆的齿轮传动的十二个可能的排列, 记法使用很被难掌握。 为了援助在实际传动的形象化模拟, 图4 显示更低的布置在象限I的一级齿轮传动。图4图4: 象限I 的更低布置的周转圆的齿轮传动在表3。行星齿轮传动第一次出现在古老中国, 是大约2600BC ,。 当磁性指南针它诞生时候, 中国人面对了难题是运用它，横跨一望无际的戈壁沙漠。 克服这个困难,这机器被发展了。 这个设备使用了一列相对地复杂行星齿轮传动，附有驱动的二个轮子维护一个图在推车上面指向在同样方向, 不管道路怎样，都向前运动。这个设备的复杂似乎表明, 中国人使用有差别的驱动相当一段时间的传动的装置的诞生之前。 这时，行星齿轮传动消失从历史相当一段时间。 这更加可能归结于缺乏目标, 而不是实际原则的不用。 在装置以后, 下次出现行星传动是在什么被命名了安尼可雅机器。1901 年由海绵潜水者发现在离Antikythera 希腊海岛的沿海的附近, 它由学者辨认了作为类型计算器被使用为预言蚀和其它占星术事件。这个特殊设备建于大约82BC, 留下期间行星齿轮传动通过相对地未被注意的由人类历史大致2500 年的空白在行星齿轮的传动原理在远东拯救了欧洲的黑暗年代, 由设备的发现上见证相似与Antikythera 机器由伊朗savant 说出Al Biz4una 名字在第一个世纪广告晚期。 在巨大新生期间, 行星被获取的广泛用途在星盘和时钟里。机制的用途和发展在新生过程中一直持续到当今天。 在这点可以有趣的表明, 从2600BC行星原理成功地被使用了, 在1841机制的卫利斯的原则出版之前，任一目的都是为了创造设备的一个分析模型。1.4 文学回顾罗伯特卫利斯1857 年的出版物,即机制的原则, 广泛被看待如同第一出版物单一地致力现在叫动力学领域。 在他的工作中, 卫利斯第一次在出版文学里谈论分析塑造一周转圆的行星齿轮传动。因为这工作纯粹地在研究一关于机制的, Willis 提出唯一一种解答为旋转的速度在齿轮传动。 在研究这种解答以后, 作者让剩下的致力周转圆的齿轮传动的人去谈论机制的应用。当这次讨论很好被设想时, 它报道四种齿轮的周转传动卓而又模糊的应用, 由于工作年龄的关系。 依照早先的陈述, 这工作研究的仅仅是齿轮传动的动力学,在机制中任一次关于扭矩的讨论都没有提出。在他的博士论文关于技术大学的建筑中, 民用和运输工程学在匈牙利, 周转圆的齿轮和周转圆的变速齿轮的理论, Dr Z 。 L.vai 试图成利用所有早先书面文学关于周转齿轮传动并且他称.周转传动的变速齿轮传动, 哪些看来简单地都是些多速度传输。 在对读者解释构成一周转圆传动时L.vai第一次确切地指出, 周转圆传动有一十二种可能。他还解释到, 这十二可能清楚地被划分为有没有辅助行星或行星对。在第一版中的任一目的都是为了清楚而简捷的行星传动的所有可能的排列。在周转圆传动定义以后, L.vai 突然改变了对它的解答的关注。 在简要地谈论解答方法以后由Willis 计划, 并且通过Kutzbach的图解方法，作为它适用于没有辅助行星轮的传动。最后，他充分谈了两种不同的定义，这定义可能进行适用于Kutzbach方法有辅助行星轮的传动。再者，他没提供在这一系统中的解决扭矩的办法。麻省理工学院,机械工程Deane Lent教授在1961 年出版了他的著作 机制解析和设计。 在这著作中Lent教授再次详细提出Willis 关于找到有三个与四个齿轮传动的特别设计方法周转圆齿轮传动每一级的转动速度。当这些技术很好的被写和简单应用后, 在这一系统中还是没有关于扭结的讨论。在这出版书中包括了及比所有Willis 谈论的更相关的几种行星齿轮传动的应用。约瑟夫Shigley 和约翰Uicker 在1980 年出版了他们的动力学文本, 机器和机制的理论。 在这著作中不仅Willis.s 方法学的分析, 而且对周转圆的齿轮传动有一个更加完全的定义。他们不仅对这个定义进行了相当数量的讨论,而且他们再次生存了L.vai.的图象描述行星齿轮传动的十二可能的变异。然而，最重要地是他们在当前齿轮传动中提出了扭矩的一个解答技术。不幸地，他们不能把相近的静态力量分析作为一般事件; 他们为一个特别的安排行星轮，通过根据自由体图可提出解答。 这个方法相对地简单, 它限制设计师在早期设计过程中对一对齿轮排布。机制和机械动力学, 哈密尔顿Mabie 和查尔斯Reinholtz 的出版物,出版了大量和Shigley 和Uicker 一样的信息。 当动力学的解析和机制的静态力量是几乎相同的, Mabie 和Reinholtz 并且提出一个简要的部分来考虑在从行星轮系中的流通功率。 当这次讨论没有直接应用这份论文, 它暗示其中使用的方法在齿轮传动中解决静态力量为一般事例。1981 年约翰Molnar 出版了他的计算图。 这著作给出了对计算图优秀介绍, 并且充分谈论他们的用途和建筑。 这著作在计算图的建筑此中被提出是有帮助的。当大多数这出版物致力于计算图的再生产，包括问题宽广的一般类别处理空气, 水, 并且相关的机械设备, 介绍为新手比足够的信息提供更多完全地了解对计算图的建筑和用途为几乎任一个问题的解答。2 CAD/CAM 2.1 CAD/CAM导论纵观工业社会的发展历史，诸多发明都被申请为专利，并且新的技术体系也逐步进化。其中比以前任何一项技术能对制造业产生更迅速、更重大影响的发明或许就是数字计算机。计算机在绘图部门正在被越来越多地应用于设计和工程零部件的详细说明中。计算机辅助设计(CAD)就是应用计算机和图形软件，在构思到文档形式的过程中来帮助或改善产品设计。计算机辅助设计通常与一个交互式计算机图形系统的应用联系在一起，称为计算机辅助设计系统。计算机辅助设计系统是进行产品和零部件的机械设计及几何建模的强有力的工具。采用CAD系统支持工程设计有以下优点：l 提高生产率l 提高设计质量l 统一设计标准l 创建制造数据库l 消除手工绘图的误差和不相容性计算机辅助制造（CAM）就是在制造计划和控制中有效地使用计算机技术。计算机辅助制造是与制造工艺联系最紧密的功能，例如工艺过程和生产规划、机械加工、进度安排、管理、质量控制和数字控制（NC）零件加工程序。计算机辅助设计和计算机辅助制造经常结合在一起构成CAD/CAM系统。这种结合在一起的系统允许在制造一种产品时，从设计阶段到计划阶段进行信息传递，不再需要手工来输入零件几何机构数据。在计算机辅助设计期间建立的数据库被储存起来，然后通过计算机复制造进行进一步的处理，转变为操作和控制生产机械、材料处理装置和进行产品质量自动检测所必需的数据和指令。2.2 CAD/CAM的基本原理CAD/CAM基本原理类似于用于在制造业中判断任何基于技术的改进原理。它产生于生产力、产品质量和竞争力不断提高的需求。还有如下一些因素促使一家公司将手工加工方式改造为应用CAD/CAM系统来进行生产：l 不断增长的生产率l 更好的产品质量l 更方便的信息交流l 在制造过程中共用数据库l 降低制造样机的费用l 加快对用户的反应2.3 CAD/CAM的硬件CAD/CAM系统的硬件部分由以下几块组成：（1）一个或多个设计工作站，（2）数字计算机，（3）绘图仪、打印机和其他输出设备，（4）储存设备。另外，CAD/CAM系统有一个通信接口允许从其他计算机系统或向其他计算机系统传递数据，因此有利于一些计算机集成。工作站是CAD系统中计算机和用户之间的接口。CAD工作站的设计和它的实用特征对用户输出的方便性、生产率和质量将产生很重要的影响。工作站必需包括一个图形显示终端和一套用户输入设备。CAD/CAM系统的应用要求有一台具有高速中央处理器（CPU）的数字计算机。它包含主存储器和逻辑/算术部分。在CAD/CAM中使用最广泛的辅助存储介质是硬盘、软盘或它们两个的结合。在CAD系统理典型的输入/输出设备如图10.2所示。输入设备一半被用来把信息从人或者储存介质传递到一台能够执行“CAD功能”的计算机中。有两种基本方法来输入已经存在的图形：在图纸上建模或把图形数字化。CAD/CAM的标准输出设备是阴极射线管显示器。有两种主要类型的阴极射线管显示器：随机扫描图形显示器和光栅扫描显示器，除阴极射线管显示器外，还有等离子平板显示器和液晶显示器。2.4 CAD/CAM的软件软件使用户从一个硬件设备进入一个强有力的设计和制造系统。根据完成的几何图形的维数，CAD/CAM软件分为两大类：二维和三维软件。在二维空间里描绘对象的CAD设计包称为二维软件。早期的系统局限于二维空间。这是一个严重的缺陷，因为用二维空间来表示三维的物体本身就容易让人混淆，而且还存在制造人员自己不能正确读懂和解释用来表示三维物体的二维图形。三维软件可使零件的三维尺寸-长、宽和高均可见。CAD/CAM的发展趋向于用三维来表示图形。这种表示法接近所描绘的物体和实际形状和外观，因此，它们更容易被读懂和理解。2.5 CAD/CAM的应用CAD/CAM的出现对整个制造业有很大的影响，它能够将产品开发标准化、降低设计强度、减少试验和样机制造工作，且能够节省相当多的成本费用并提高生产率。CAD/CAM的一些典型应用如下：l 为数控、计算机数控和工业机器人编程；l 在设计铸造的模具和模型时，可按照预编程序缩小加工余量；l 工具、固定装置和EDM（电火花机床）电极的设计；l 质量控制和检测，例如：在CAD/CAM工作站中进行坐标测量机编程；l 工艺计划与进度安排。2.6 CAD/CAM的优点使用CAD的原因有很多，最有效的动力就是竞争。为了赢得业务，公司使用CAD可以创造出更好的设计，并且在设计速度上比竞争对手更快，在成本上花费更少，。通过使用CAD,生产率得到了很大的提高，使用户能够很容易地画多边形、椭圆、多条平行线和多条平行的曲线。在绘制对称部分时、复制、旋转、镜象这些工具使用起来也是很方便的。很多飞机舱口的样式就是用CAD程序设计的。用各种不同的颜色填充空白的区域是艺术和表达的需要。CAD总是提供许多不同类型的字体。能够将不同的图形文件格式和扫描材料（照片）导入CAD也是一大优点，特别是可以对图像进行加工、润饰和加入动画效果。CAD系统另一个优点是能够储存在绘图中经常用到的实体。常用零件库可以另外购买或者由绘图员自己创建。在绘图中反复使用的一个典型的项目可以在数秒内检索并确定它的位置，也可定位在任一角度，以满足特定的要求。使用CAD的产品，可以通过插入现有的零件图到装配图中，然后按照要求把他们放在合适的位置来绘制装配图。不同零部件之间的间距能够在图中直接测量。如果需要，可以使用装配图设计出额外的零部件作为参考。CAD非常适合文件的快速归档。以前，工程师和绘图员们浪费大约30%的时间去寻找图纸和其他文档。用CAD产品可以快速而简便地编辑图样，对以前的东西进行修改，更新零件明细表。当你用纸绘图而客户希望修改图样的时候，你就得全部重画。使用CAD，你可以马上进行修改，并在几秒钟之内打印出新图，或者通过E-mail和互联网立即传送到世界各个地方。在纸上绘制复杂的几何图形时，经常要进行很多测量并且需要确定参考点。在CAD中，这是一个轻而易举的事情，修改也更容易了。许多CAD程序包含“宏”或者允许用户定制的附加程序语言。定制你的CAD系统来你的使它适合你的特定要求，并用它实现你的天才创意，从而使你的CAD系统区别于你的竞争对手。CAD能够使企业完成更出色的设计，而用手工的方式几乎是不可能，同时排除了概念设计阶段的不确定选项。91 MOTIVATION AND BACKGROUND 1.1 Introduction In the current literature available to engineers, planetary gear trains are given a clear treatment as far as a simple kinematic solution. Unfortunately, no publications to date present a simple, concise design and analysis technique that considers both the motion and forces present in a gear train in the general case. This thesis attempts to fill this void by presenting a technique for finding a total speed and force solution to an epicyclic gear train in the most general case possible. After developing this solution, nomographs will be used to create an intuitive design aid, allowing the designer to visualize the performance of a gear train without the need to solve equations repeatedly. Finally, the solution technique and design aids presented will be used to address the practicality of using planetary gear trains as a power coupling element in a new generation of tandem bicycles.1.2 Motivation The research contained herein was motivated by a design effort undertaken by the Virginia Tech Human Powered Vehicle Team in 2002. During the early design of the multi-rider entry into the annual ASME competition, it was suggested that the most effective method for coupling the relatively inconsistent inputs of two human riders would be to use a planetary gear train. The concept behind the design attempted by the human powered vehicle team was to use a gear train like the one shown in figure 1 to create a system that would allow both riders to pedal at approximately the same speed and contribute approximately the same percentage of the output power. The planetary system accommodates differences in speed and power input by the two riders. The nature of the system behavior is the focus of this thesis. Figure 1Figure 1: Gear train to be used in the Human Powered Vehicle Teams design effort Using Williss 1 method for finding the kinematic solution of the gear train, it was found that the mechanism was governed by where the s represent rotational speeds of each element in the gear train, and R is the basic transmission ratio of the gear train. Performing a static analysis, the torques were found to be controlled by where the Ts represent torques on each element in the train, and the Ns represent number of teeth in each gear in the train. Using these equations, it became apparent that the goal of achieving power balance at equal and opposite input speeds was impossible. If 2 and 5 are assumed to be equal and opposite, then to achieve a power balance, T2 and T5 must also be equal and opposite. According to equation 3, this means R must be 1. Unfortunately, this takes the denominator of equation 1 to zero, which drives 6 to infinity. What had seemed intuitively a simple problem to solve had led to a singularity in the solution space. With deadlines for competition closing in, the design effort was abandoned in favor of a simpler solution. However, the research done in attempting to design a specific gear train became the foundation of a much broader research project. The drive of this project, rather than the design of a gear train for a specific purpose, is to create a concise design method that will allow development of planetary gear trains for any number of possible applications. By dealing with the planetary in the most general case possible, this project explores the reasons for the failure of the HPV teams design as well as allowing engineers to define the kinematic relationships between the three branches of the planetary gear train without first selecting a physical arrangement of gears.1.3 Background A planetary gear train is defined as any gear train containing at least one gear that orbits by rotating about its own axis and also about the axis of an arm, or carrier. The elementary planetary, or epicyclic, gear train is shown in figure 2, along with the simplified representation to be used for the remainder of this thesis. The elementary train consists of two gears, the sun (1) and planet (2) gears, and a third member, hereafter referred to as the planet carrier or arm (3). Figure 2: (a) The elementary epicyclic gear train and (b) its kinematical representation Since it is difficult to directly transmit motion to or from the planet gear, the elementary epicyclic gear train is somewhat limited in practical application. More useful, however, are the epicyclic trains referred to as the simple and complex planetary gear trains, where a second sun gear is used. These gear trains can be realized in any of the twelve arrangements set forth in figure 3, as originally presented by Lvai. The trains in quadrants I and III are classified as simple epicyclic trains, since the planet gears are in mesh with both sun gears. Those in quadrants II and IV represent the complex trains, where the planet gears are partially in mesh with each other and partially in mesh with the two sun gears. Notice that, regardless of arrangement, only one planet carrier may be used.Figure 3Figure 3: The simple and complex epicyclic gear trains While this figure clearly shows the twelve possible arrangements of the epicyclic gear train, the notation used is difficult to grasp. To aid in the visualization of the actual trains represented, figure 4 shows a gear train of the lower arrangement in quadrant I. Figure 4Figure 4: Epicyclic gear train of the lower arrangement of quadrant I in figure 3 The planetary gear train first appeared in ancient China, around 2600 BC, in a device referred to as the south pointing chariot. At a time when the magnetic compass was still centuries away from its birth, the Chinese faced the difficult task of navigating across the relatively featureless Gobi Desert. To surmount this difficulty, the south pointing chariot was developed. This device used a relatively complex planetary gear train attached to the two wheels of a cart to maintain a figure atop the cart pointing in the same direction, regardless of the path taken by the cart. The complexity of this device seems to indicate that the Chinese had been using differential drives for quite some time before the birth of the south pointing chariot. At this point, the planetary gear train disappears from history for quite some time. This is more likely due to a lack of writing on the subject, rather than the actual disuse of the principle. After the south pointing chariot, the next appearance of the planetary is in what has been named the Antikythera machine. Discovered by sponge divers off the coast of the Greek island ofAntikythera in 1901, it has been identified by scholars as a type of calculator used for predicting eclipses and other astrological events. This particular device has been dated back to approximately 82 BC, leaving a gap of roughly 2500 years during which the planetary gear train passed relatively unnoticed through human history 8. The principle of the planetary gear survived Europes dark ages in the Far East, evidenced by the discovery of a device similar to the Antikythera machine by an Iranian savant named Al-Bizna in the late first century AD. During the Great Renaissance, the planetary garnered wide use in astrolabes and clocks. The use and development of the mechanism continued throughout the Renaissance and on until present day. It is interesting to note at this point that, while the planetary has been successfully used since 2600 BC, it was not until the 1841 publication of Williss Principles of Mechanism 1 that any attempt was made to create an analytical model of the device.1.4 Literature Review Robert Williss 1857 publication, Principles of Mechanism, is widely regarded as the first publication dedicated solely to the field now called kinematics. In his work, Willis discusses for the first time in published literature the analytical modeling of an epicyclic gear train. As this work is a study purely in mechanism, Willis presents only a solution for the rotational speeds in the gear train. After developing this solution, the author spends the remainder of the work dedicated to epicyclic gear trains in discussing applications of the mechanism. While this discussion is well conceived, it covers four remarkably obscure applications of the epicyclic gear train, owing to the age of the work. As stated previously, this work studied only the pure kinematics of the gear train, without any discussion of the torques present in the mechanism.In his doctoral dissertation for The Technical University of Building, Civil and Transport Engineering in Hungary, Theory of Epicyclic Gears and Epicyclic Change-Speed Gears, Dr Z. Lvai attempts to unify all of the previously written literature on epicyclic trains and what he calls “epicyclic change speed gears”, which appear to simply be multiple speed transmissions. In explaining to the reader exactly what constitutes an epicyclic train Lvai identifies, for the first time, the twelve possible variations on the epicyclic train. It is also stated that these twelve variations can be neatly divided into those with and without auxiliary planets or planet pairs. This is the first publication where any attempt was made to clearly and concisely define all possible arrangements of the planetary train.After defining the epicyclic train, Lvai turns his attention to its solution. After briefly discussing the solution method laid out by Willis, and the graphical method of Kutzbach 5 as it applies to trains without auxiliary planets, he discusses at length two different modifications that can be performed to apply the Kutzbach method to a train with auxiliary planets. Again, he offers no treatment of the torques present in the system.Deane Lent, professor of Mechanical Engineering at Massachusetts Institute of Technology, published his work, Analysis and Design of Mechanisms, in 1961. In this work Lent again presents in detail the methodology of Willis for finding the rotational speeds of each branch of the epicyclic gear train, along with specific methods for the design of three and four gear trains. While these techniques are well written and simple to follow, there is again no discussion of torques present in the system. Also included in this publication are several applications of the planetary gear train, all significantly more relevant than those discussed by Willis.Joseph Shigley and John Uicker published their kinematics text, Theory of Machines and Mechanisms, in 1980. Within this work are not only a treatment of Williss methodology, but also a more complete definition of the epicyclic gear train. Not only do they dedicate a significant amount of discussion to this definition, but they also reproduce Lvais figure demonstrating the twelve possible variations of the planetary gear train. Most importantly, however, they present a solution technique for the torques present in the gear train. Unfortunately they do not approach the static force analysis for the general case; rather they present the solution in terms of free body diagrams for a specific arrangement of the planetary. While this method is relatively simple, it limits the designer to a single arrangement early in the design process.Mechanisms and the Dynamics of Machinery, the publication of Hamilton Mabie and Charles Reinholtz, presents largely the same information as Shigley and Uicker. While the treatment of the kinematics and static forces of the mechanism are nearly identical, Mabie and Reinholtz also present a brief section considering circulating power flow in controlled planetary gear systems. While this discussion has no direct application to this thesis, it does hint at the methods used herein to solve for the static forces in the gear train for the general case.John Molnar published his Nomographs in 1981. This work presents an excellent introduction to nomographs, as well as discussing at length their use and construction. This work was instrumental in the construction of the nomographs presented herein. While the bulk of this publication is dedicated to the reproduction of nomographs covering the broad general category of problems dealing with air, water, and related mechanical devices, the introduction provides more than enough information for a novice to completely understand the construction and use of nomographs for the solution of nearly any problem.2 CAD/CAM2.1 Introduction to CAD/CAMThoughout the history of our industrial society,many inventions have been patented and whole new technologies have evolved.Perhaps the single development that has impacted manufacturing more quickly and significantly than any previous technology is the digital computer.Computer are being used increasingly for both design and detailing of engineering components in the drawing office.Computer-aided design (CAD) is defined as the application of computers and graphics software to aid or enhance the product design from conceptualization to documentation.CAD is most commonly associated with the use of an interactive computer graphics system,referred to as a CAD system.Computer-aided design systems are powerful tools and are used in the mechanical design and geometric modeling of products and components.There are several good reasons for using a CAD system to support the engineering design function:l To increase the productivity l To improve the quality of the design l To uniform design standards l To eliminate inaccuracies caused by hand-copying of drawings and inconsistency between drawings Computer-aided manufacturing (CAM) is defined as the effective use of computer technology in manufacturing planning and control.CAM is most closely associated with functions in manufacturing engineering,such as process and production planning, machining, scheduling, management, quality control, and numerical control (NC) part programming, Computer-aided design and computer-aided manufacturing are often combined into CAD/CAM systems.This combination allows the transfer of information from the design stage into the stage of planning for the manufacturing of a product,without the need reenter the data on part geometry manually.The database developed during CAD is stored; then it is processed further,by CAM,into the necessary data and instructions for operating and controlling production machinery,material-handling equipment,and automated testing and inspection for product quality.2.2 Rationale for CAD/CAMThe rationale for CAD/CAM is similar to that used to justify any technology-based omprovement in manufacturing.It grows out of a need to continually improve productivity,quality and competitiveness.There are also other reasons why a company might make a conversion from manual processes to CAD/CAM:l Increased productivityl Better quality l Better communication l Common database with manufacturing l Reduced prototype construction costsl Faster response to customers 2.3 CAD/CAM HardwareThe hardware part of a CAD/CAM system consists of the following components:(1)oneor more design workstaions,(2)digital computer,(3)plotters,printers and other output devices,and (4)storage devices. The relationship among the components is illustrated in Fig.10.1.In addition,the CAD/CAM system would have a communication interface to permit transmission of data to and from other computer systems,thus enabling some of the benefits of computer integration.The workstation is the interface between computer and user in the CAD system.The design of the CAD workstation and its available features have an important influence on the convenience,productivity,and quality of the users output.The workstation must include a graphics display terminal and a set of user input devices.CAD/CAM applications require a digital computer with a high-speed control processing unit(CPU).It contains the main memory and logic/arithmetic section for the system.The most widely used secondary storage medium in CAD/CAM is the hard disk,floppy diskette,or a combination of both.The typical I/O devices used in a CAD system are shown in Fig.10.2. Input devices are generally used to transfer information from a human or storage medium to a computer where “CAD functions”are carried out.There are two basic approaches to input an existing drawing:model the object on a drawing or drawing or digitize the drawing.The standard output device for CAD/CAM is a CRT display.There are two major types of CRT displays:random-scan-line-drawing displays and aster-scan displays.In addition to CRT,there are also plasma panel displays and liquid-crystal displays.2.4 CAD/CAM SoftwareSoftware allows the human user to turn a hardware configuration into a powerful design and manufacturing system.CAD/CAM software falls into two broad categories,2-D and 3-D, based on the number of dimensions visible in the finished geometry.CAD packages that represent objects in two dimensions visible in the finished geometrey.CAD packages that represent objects in two dimensions are called 2-D software.Early systems were limited to 2-D.This was a serious shortcoming because 2-D representations of 3-D objects is inherently confusing.Equally problem has been the inability of manufacturing personnel to properly read and interpret complicated 2-D representations of objects.3-D software permits the parts to be viewed with the three-dimensional planes-height,width,and depth-visible.The trend in CAD/CAM is toward 3-D representation of graphic images.Such representations approximate the actual shape and appearance of the object to be produced;therefore,they are easier to read and understand.2.5 Applications of CAD/CAMThe emergence of CAD/CAM has had a major impact on manufacturing,by standardizing product development and by reducing design effort,tryout,and prototype work;it has made possible significantly reduced costs and improved productivity.Some typical applications of CAD/CAM are as follows:l Programming for NC,CNC,and industrial robots;l Design of dies and molds for casting,in which,for example,shrinkage allowances are preprogrammed;l Design of tools and fixtures and EDM(electrical-discharge machining)electrodes;l Quality control and inspection-for