【The branch of scientific analysis which deals with motions time and forces is called mechanics and is made up of two parts statics and dynamics】.  对运动、时间和作用力进行科学分析的分支称为力学，它由静力学和动力学俩部分组成。【Statics deals with the analysis of Stationary ,i .e.,those in which time is not a factor,and dynamics deals with systems which change with time  静力学对静止系统进行分析，即在其中不考虑时间这个因素，动力学对随时间而变化的系统进行分析。【Forces are transmitted into machine members through mating surfaces ,e.g.,form a gear to a shaft or form one gear through meshing teeth to another gear,from a V belt to a pulley,or from a cam to a follower】.力通过接触表面传到机器中的各构件上。例如，从齿轮传到轴或者从齿轮通过与其啮合的轮齿传到另一个齿轮，从V带传到带轮，或者从凸轮传到从动件。【It is necessary to know the magnitudes of these forces for a variety of Reasons】 由于很多原因，人们必须知道这些力的大小。【The distribution of the forces at the boundaries or mating surfaces must be reasonable and their intensities must be within the working limits of the materials composing thesurfaces】这些力在边界或在接触表面的分布必须合理，它们的大小必须在构成配合表面的材料的工作极限以内。【For example if the force operating on a journal beari
ng becomes too high it will squeeze out the oil film and cause metal-to-metal contact overheating and rapid failure of the bearing】.例如，如 果作用在一个滑动轴承上的力太大，它就会将油膜挤出，造成金属与金属的直接接触，产生过热和使轴承快速失效。 【If the forces betweens gear teeth are too large the oil film may be squeezed out from between them】.如果齿轮相啮合的齿与齿之间的力过大，就会将油膜从齿间挤压出来。【This could result in flaking and spalling of the metal noise rough motion and eventual failure】这会造成金属表层的碎裂和剥落，噪音增大，运动不精确直至报废。【In the study of mechanics we are principally interested in determining the magnitude direction and location of the Forces】.在力学研究中，我们主要关心力的大小、方向和作用点。
Virtually all machines contain shafts.实际上，几乎所有的机器中都装有轴。The most common shape for shafts is circular and the cross section can be either solid or hollow.轴最常见的形状是圆形，其截面可以是实心的，也可以是空心的。Rectangular shafts are sometimes used, as in screwdriver blades, socket wrenches and control knob stems.有时也采用矩形轴，例如，螺丝刀的头、套筒扳手和控制旋转的杆。A shaft must have adequate tensional strength to transmit torque and not be overstressed.为了在传递扭矩时不发生过载，
pulleys轴应该具有适当的抗扭强度。It must also be torsion ally stiff enough so that one mounted component does not deviate excessively from its original angular position relative to a second component mounted on the same shaft.轴还应该具有足够的抗扭刚度，以确保同一个轴上的两个传动零件之间的相对转角不会过大。Generally speaking, the angle of twist should not exceed one degree in a shaft length equal to 20 diameters.一般来说，当轴的长度等于其直径的20倍时，扭转角不应该超过1度 Shafts are mounted in bearing and transmit power though such devices as gears, pulleys, cams and clutches.轴安装在轴承中，通过齿轮、皮带轮、凸轮和离合器等零件传递动力。These devices introduce forces which attempt to bend the shaft ;通过这些零件传来的力可能会使轴产生弯曲变形 hence, the shaft must be rigid enough to prevent overloading of the supporting bearing . 因此，轴应该有足够的刚度以防止支承轴承受力过大。In general, the bending deflection of a shaft should not exceed 0.5mm per meter of length between bearing supports.总而言之，在两个轴承支承之间，轴在每米长度上的弯曲变形不应该超过0.5mm
The first step in the manufacture of any product is design, which usually takes place in several distinct stages (a) conceptual (b) functional(c)production design.制造任何产品的第
一步都是设计。设计通常可以分为几个明确的阶段：a.概念设计b.概念设计c.生产设计。During the conceptual-design stage, the designer is concerned primarily with the functions the product is to fulfill.在设计概念阶段，设计者着重考虑产品应该具有的功能。Usually several concepts are visualized and considered, and a decision is made either that the idea is not practical or that the idea is sound and one or more of the conceptual designs should be developed further通常要设想和考虑几个方案，然后决定这种想法是否可行;如果可行，则应该对其中一个或几个方案作进一步的改进Here, the only concern for masteries is that materials exist that can provide the desired properties在此阶段，关于材料选择唯一要考虑的问题是：是否有性能符合要求的材料可供选用If no such materials are available, consideration is given as to whether there is a reasonable prospect that new ones could be developed within coat and time limitations如果没有的话，是否有较大的把握在成本和时间都允许的限度内研制出一种新材料
At the production-design stage, the primary concern relative to materials should be that they are specified fully, that they are compatible with, and can be processed economically by, existing equipment, and that they are readily available in the needed quantities 在生产
设计阶段中，与材料有关的问题是应该把材料完全确定下来，使它们与现有的设备相适应，能够利用现有设备经济的进行加工，而且材料的数量能够比较容易的保证供应。  【 A mechanism has been defined as "a combination of rigid or resistent bodies so formed and connected that they move upon each other with definite relative motion.】
机构被定义为:"是由刚体或者有承载力的物体连接而形成的组合体，它们在运动时彼此之间应该具有确定的相对运动。
【Mechanisms form the basic geometrical elements of many mechanical devices including automatic packaging machinery,fixtures,mechanical toys,textile machinery,and others.】机构是构成许多机械设备的基本几何单元，这些机械设备包括自动包装机、夹具、机械式玩具、纺织机等等。【A mechanism typically is designed to create a desired motion of a rigid body relative to a reference Member】机械设计的目的通常是使一个刚体相对某一参考构件产生所需要的相对运动。【Kinematic design of mechanisms is often step in the design of a complete machine.】 机构的运动设计通常是设计一台完整的机器的第一步。【When forces are considered the additional problems of dynamics bearing loads,stresses,lubrication,and
the like are introduced ,and the larger problem becomes one of machine design.】在考虑力的作用时，应该考虑力学、轴承载荷、应力、润滑等一系列问题。在所考虑的问题的范围扩大之后，机构设计就变成了机器设计。【The function of a mechanism is to transmit or transform motion from one rigid body to another as part of the action of a machine】  作为机器的一个组成部分，机构的作用是在刚体之间传递或转换运动。【There are three types of common mechanical devices that can be used as basic elements of a mechanism.】常用的基本机构有以下三种:
【Gear systems,in which toothed members in contact transmit motion between rotating Shafts】 齿轮机构，在这种机构中，各转轴之间的运动由相互啮合的齿轮来传递。
【Gears normally are used for the transmit motion with a constant angular velocity ratio,although noncircular gears can be used for nonuniform transmission of motion.】
齿轮通常用来传递角速度比为常值的运动，但是非圆齿轮可以用来传递角速度比为变数的运动。【Cam systems,where a uniform motion of an input member is converted into a nonuniform motion of the output member】凸轮机构，在这种机构中，输入件的等速连续运
动被转换成输出件的不等速运动。【The output motion may be either shaft rotation,slider translation,or other follower motions created by direct contact between the input cam shape and the follower】输出的运动可以是轴的转动、滑块的移动、或者其它从动件的运动。  这些运动都是使从动件与作为输入件的凸轮的轮廓的直接接触而产生的。  【The kinematic design of cams involves the analytical or graphical specification of the cam surface shape required to drive the follower with a motion that is a prescribed function of the input motion.】凸轮的运动设计就是采用解析法或者图解法来确定凸轮的轮廓形状，使其能够带动从动件实现输出运动运动是输入运动的指定函数这一功能。Automatic Tracer Lathes 自动仿形车床  Since surface roughness depends greatly upon material turned, tooling, and feeds and speeds employed, minimum tolerances that can be held on automatic tracer lathes are not necessarily the most economical tolerances.  因为零件的表面粗糙度在很大程度上取决于工件材料、刀具、进给量和切削速度，采用自动仿形车床加工所得到的最小公差不一定是最经济的公差。In some cases, tolerances of ±0.05mm are held in continuous production using but one cut.  在某些情况下，在连续生产过程中，只进行一次切削加工时的公差可以达到±0.05mm。Groove width cam be held to ±0.125mm on some parts. 对于某些零件，槽
宽的公差可以达到±0.125mm。On high-production runs where maximum output is desirable, a minimum tolerances of ±0.125mm is economical on both diameter  and length of turn. 在希望获得最大产量的大批量生产中，进行直径和长度的车削时的最小公差值为±0.125mm是经济的。

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