外文翻译--运动的综合，凸轮和齿轮

外文翻译--运动的综合，凸轮和齿轮 设计巴巴工作室www.88doc88.com 外文翻译: Kinematic Synthesis ～Cams and Gears Mechanisms form the basic geometrical elements of many mechanical devices including automatic packaging machinery, typewriters, mechanical toys, textile machinery, and others. A mechanism typically is designed to create a desired motion of a rigid body relative to a reference member. Kinematic design, or kinematic syntheses, of mechanisms often is the first step in the design of a complete machine. 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. A kinematician defined kinematics as “the study of the motion of mechanisms and methods of creating them.” The first part of this definition deals with kinematic analysis. Given a certain mechanism, the motion characteristics of its components will be determined by kinematic analysis. The statement of the tasks of analysis contains all principal dimensions of the mechanism, the interconnections of its links, and the specification of the input motion or method of actuation. The objective is to find the displacements, velocities, accelerations, shock or jerk (second acceleration) , and perhaps higher accelerations of the various members, as well as the paths described and motions performed by certain elements. In short, in kinematic analysis we determine the performance of a given mechanism. The second part of definition may be paraphrased in two ways: 1. The study of methods of creating a given motion by means of mechanisms. 2. The study of methods of creating mechanisms having a given motion. In either version, the motion is given and the mechanism is to be found. This is the essence of kinematic synthesis. Thus kinematic synthesis deals with the systematic design of mechanisms for a given performance. The area of synthesis may be grouped into two categories. 1. Type synthesis. Given the required performance, what type of mechanism will be suitable? (Gear trains? Linkages? Cam mechanisms? ) Also, how many links should the mechanism have? How many degrees of freedom are required? What configuration id desirable? And so on. Deliberations involving the number of links and degrees of freedom are often referred to as the province of a subcategory of type synthesis called number synthesis. 2. Dimensional synthesis. The second major category of kinematic synthesis is best defined by way of its objective: Dimensional synthesis seeks to determine the significant dimensions and the starting position of a mechanism of preconceived type for a specified task and prescribed performance. Significant dimensions mean link lengths or distances on binary, ternary, and so on, links, angles between axis, cam-contour dimensions and cam-follower diameters, eccentricities, gear rations, and so forth. A mechanism of preconceived type may be a slider-crank linkage, a four-bar linkage, a cam with flat follower, or a more complex linkage of a certain configuration defined topologically but not dimensionally. There 设计巴巴工作室www.88doc88.com are three customary tasks for kinematic synthesis: function generation, path generation and motion generation. In function generation mechanisms rotation or sliding motions of input and output links must be correlated. For an arbitrary function, a kinematic y,f(x) synthesis task may be to design a linkage to correlate input and output such that the input moves by, the output moves by for the range. In the y,f(x)x,x,xx0n，1 case of rotary input and output, the angles of rotation and are the linear ,, analogs of and respectively. When the input link is rotated to a value of the yx independent, the mechanism in a “black box” causes the output link to turn to the x corresponding value of the dependent variable. This may be regarded as a y,f(x) simple case of a mechanical analog computer. A variety of different mechanisms could be contained within the “black box”. However, the four-bar linkage is not capable of error-free generation of an arbitrary function and can match the function at only a limited number of precision points. It is widely used in industry because the four-bar linkage id simple to construct and maintain. In path generation mechanism a point on a “floating link” is to trace a path defined with respect to a fixed frame of reference. If the path points are to be correlated with either time or input-link positions, the task is called path generation with prescribed timing. An example of path generation mechanisms id a four-bar linkage designed to pitch a baseball or tennis ball. In this case the trajectory of point p would be such as to pick up a ball at a prescribed location and to deliver the ball along a prescribed path with prescribed timing for reaching a suitable throw-velocity and direction. There are many situations in the design of mechanical devises in which it is necessary either to guide a rigid body through a series of specified, finitely separated positions or to impose constraints on the velocity and/or acceleration of the moving body at a reduced number of finitely separated positions. Motion-generation or rigid-body guidance mechanism requires that an entire body be guided through a prescribed motion sequence. The body to be guided usually is a part of a floating link, of which not only is the path of a point p prescribed, but also the rotation of a line passing through the point and embedded in the body,. For instance, the line might represent a carrier link in a automatic machinery where a point located on the carrier link has a prescribed path while the carrier has a prescribed angular orientation. Prescribing the movement of the bucket for a bucket loader id another example of motion generation mechanisms, the path of tip of the bucket is critical since the tip must perform a scooping trajectory followed by a lifting and a dumping trajectory. The angular orientation of the bucket are equally important to ensure that load is dumped from the correct position. A cam is a convenient device for transforming one motion into another. This 设计巴巴工作室www.88doc88.com machine element has a curved or grooved surface which mates with a follower and imparts motion to it. The motion of the cam (usually rotation) is transformed into follower oscillation, translation, or both. Because of the various cam geometries and the large number of cam and follower combinations, the cam is an extremely versatile mechanical element. Although a cam and follower may be designed for motion, path, or function generation, the majority of applications utilize the cam and follower for function generation. The most common cam types according to cam shapes are: disk or plate translating (two-dimensional or planar), and cylindrical (three-dimensional or spatial) cams. Followers can be classified in several ways: according to follower motion, such as translation or oscillation; according to whether the translational (straight-line) follower motion is radial of offset from the center of the cam shaft; and according to the shape of the follower contact surface (e. g. , flat-face, roller, point (knife-edge), spherical, planar curved, or spatial-curved surface). In the case of a disk cam with a radial (in-line) translating roller follower the smallest circle that can be drawn tangent to the cam surface and concentric with the camshaft is the base circle. The tracer point is a point at the center of the roller center and the normal to the pitch curve. The pressure angle is the angle between the direction of the path of the roller center and the normal to the pitch curve through the center of the roller and is the complement of the transmission angle. Neglecting friction, this normal is collinear with the contact force between the cam and follower. As in a linkage, the pressure angle varies during the cycle and is a measure of the ability of the cam to transfer motive effort to the follower. A large pressure angle will produce an appreciable lateral force exerted on the stem of the follower, which, in the presence of friction, would tend to bind the follower in the guide. Numerous applications in automatic machinery require intermittent motion. A typical example will call for a rise-dwell-return and perhaps another dwell period of a specified number of degrees each, together with a required follower displacement measured in centimeters or degrees. The designer’s job is to lay out the cam accordingly. The first decision to be made is to choose the cam follower type. The specified application may dictate the combination of the cam and follower. Some factors that should enter into the decision are: geometric considerations, dynamic considerations, environmental considerations and economic matters. Once a type of cam and follower pair has been selected, the follower motion must be chosen. Therefore, the velocity, acceleration, and in some cases further derivatives of the displacement of the follower are of great importance. Gears are machine elements that transmit motion by means of successively engaging teeth. Gears transmit motion from one rotating shaft to another, or to a rack that translates. Numerous applications exist in which a constant angular velocity ratio (or constant torque ratio) must be transmitted between shafts. Based on the variety of gear types available, there is no restriction that the input and the output shafts need be either in-line or parallel. Nonlinear angular velocity ratios are also available by using noncircular gears. In order to maintain a constant angular velocity, the individual tooth profile must obey the fundamental law of gearing: for a pair of gears to transmit 设计巴巴工作室www.88doc88.com a constant angular velocity ratio, the shape of their contacting profiles must be such that the common normal passes through a fixed point on the line of the centers. Any two mating tooth profiles that satisfy the fundamental law of gearing are called conjugate profiles. Although there are many tooth shapes possible in which a mating tooth could be designed to satisfy the fundamental law, only two are in general use: the cycloidal and involute profiles. The involute has important advantages: it is easy to manufacture and the center distance between a pair of involute gears can be varied without changing the velocity ratio. Thus chose tolerances between shafts are not required when utilizing the involute profile. There are several standard gear types. For applications with parallel shafts, straight spur gear, parallel helical, or herringbone gears are usually used. In the case of intersecting shafts, straight bevel of spiral bevel gears are employed. For nonintersecting and nonparallel shafts, crossed helical, worm, face, skew bevel or hypoid gears would be acceptable choices. For spur gears, the pitch circles of mating gears are tangent to each other. They roll on one another without sliding. The addendum is the height by which a tooth projects beyond the pitch circle (also the radial distance between the pitch circle and the addendum circle). The clearance is the amount by which the addendum (tooth height below the pitch circle) in a given gears exceeds the addendum of its mating gear. The tooth thickness is the distance across the tooth along the arc of the pitch circle while the tooth space is the distance between adjacent teeth along the arc of the pitch circle. The backlash is the amount by which the width of the tooth space exceeds the thickness of the engaging tooth at the pitch circle. 设计巴巴工作室www.88doc88.com 中文: 运动的综合～凸轮和齿轮 机构是形成许多机械装置的基本几何结构单元～这些机械装置包括自动包装机、打印机、机械玩具、纺织机械和其他机械等。典型的机构要设计成使刚性构件相对基准构件产生所希望的运动。机构的运动设计或者运动学综合～第一步常常是先设计整部机器。当考虑受力时～要提出动力学方面的问题～轴承的何载、应力、润滑等类似的问题～而较大的问题是机器结构问题。 运动学家把运动学定义为“研究机构的运动和创建机构的方法”。这个定义的第一部分就涉及运动学分析。已知一个机构～其构成的运动特性将由运动学分析来确定。叙述运动分析的任务包含机构的主要尺寸、构件间的相互连结和输入运动的技术特性或驱动方法。目的是要找出位移、速度、加速度、冲击或跳动,二阶加速度,～和可能发生的各勾结的高阶加速度以及所描述径迹和由某些构件来实现的运动。定义的第二部分可用以下两方面来解释: 1. 研究借助机构来产生给定运动的方法 2. 研究建造能产生给定运动机构的方法～在两个方案中～运动是给定的而 机构是创建 的。这就是运动综合的本质。这样运动综合涉及到为给定性能的机构的系统设计。运动综合方面又可以归结为以下两类: 1. 类型综合。规定所要求的性能～怎样一种类型的机构才是合适的,,齿轮 系～连杆 机构,还是凸轮机构,,而机构应具有多少构件,需要多少个自由度,怎样的轮廓结构才是所希望的,等等。关于杆件数目和自由度的考虑通常被认为是类型综合中被称作为数量综合的一个分支领域。 2. 尺寸综合。运动综合的第二个主要类型是通过目标法来确定的最佳方法。 尺寸综合 试图确定机构的重要尺寸和起动位置～该机构是为着实现规定的任务和预期的性能而事先设想的。 所谓重要的尺寸意思是指关于两杆、三杆等的长度或杆间距离～构件数和轴线间的角度～凸轮轮廓尺寸～凸轮随动件的直径～偏心距～齿轮配额等等。预想机构类型可能是曲柄滑块机构、四杆机构～带盘型从动件的凸轮机构～或者是以拓扑学方法而非因次分析法所确定的具有某种结构形状更为复杂的连杆机构。对于运动综合～惯例上有三个任务:函数生成～轨迹生成和运动生成。 在函数生成机构中输入和输出构件的转动和移动必须是相互关联的。对于一个任意函数～一个运动综合的任务可能是设计一个连杆机构使输入和输y,f(x) 出建立起关系以便使得在的范围内输入按运动～而输出按x,x,xy,f(x)x0n,1 运动。在输入和输出件回转运动情况下～转角和分别是和的线性模拟。,,xy当输入件回转到一个独立值时～在一个“黑箱”的机构中～使输出构件转到相对x 应的由函数决定的数值上。这可被认为是机械模拟计算机的最简单的情y,f(x) 形。各种不同的机构都可以包含在这个“黑箱”内～然而对于任意函数的无误差生成～四杆机构是无能为力的～仅仅可能在有限精确度内与之相匹配。它广泛用于设计巴巴工作室www.88doc88.com 工业上～因为四杆机构在构建和维修上都是简单的。 在轨迹生成机构中～在“浮动杆”上一个点要描画一条相对于一个固定坐标系确定的轨迹。如果该轨迹点是既要与时间相关又要与位置相关～该任务被称之为预定周期的轨迹生成。轨迹生成机构的一个例子就是设计来投掷棒球或网球的四杆机构。在这种情况下～点P的轨迹将是这样:在预定的位置捡起一个球～并在预定的时间周期内沿着预定的径迹把球传送出去～能达到合适的速度和方向。 机械装置设计中有着许多情形～在这些情形中既要导引刚体通过一系列规定的、受限制的独立位置～又要在减少受限制而且独立的位置的数目时～对运动体的速度和,或,加速度加以约束～那是必要的。运动生成或刚体导引机构要求:一个完整的物体要被导引通过一预定的运动序列。作为被导引的物体通常是“浮动件”的一部分～那不仅是预定点P的轨迹～也是通过该点并嵌入该物体内的线的转动。例如～该线可能代表自动化机械中一个载体件～那是在载体件上的一个点具有一个预定的轨迹的而该载体件又具有一个预定的角度方位。预定方式装料机的吊斗的运动是运动生成机构的另一个例子。吊斗端的轨迹是有极限的。因为其端口必须实现挖掘的运动轨迹～紧跟着要实现提升和倾泻的轨迹。吊斗的角度方位对保证斗中物料从正确的位置倾泻,倒,同样是重要的。 凸轮装置是把一种运动改变成另一种运动的方便装置。这种机器零件具有曲面或槽面～该曲面或槽面与从动件相配合并将运动传给从动件。凸轮的运动,通常是转动,被传递给从动件作摇动或移动～或两者均有。由于各种各样的几何体和大量的凸轮与从动件相结合～因此凸轮是一种极多功能的万用的机械零件。虽然凸轮和从动件可以为运动、轨迹和功能生成而设计～但其主要是利用凸轮和从动件作为功能生成构件。 根据凸轮形状～最普遍的凸轮种类是:盘形传动凸轮,两维的～即平面的,和圆柱形凸轮,三维的～即空间的,机构。从动件可以用几个方法分类:根据从动件的运动～例如移动或摇动来分类～根据平移式,直线,从动件运动是沿径向的还是从凸轮轴中心偏心的和根据从动件接触面的形状,比如平面、辊子、点——刀尖式～球面～平面曲线或空间曲面,。 对于一个对心直动滚子从动件盘形凸轮～可画出的与凸轮表面相切且与轮轴同心的最小圆是基圆。随动件的点就是产生节线的辊子中心的点。压力角就是辊中心轨迹方向线和通过辊子中心的节线的法线之间的尖角而且是传动角的余角。忽略摩擦形象～在法线方向跟凸轮与从动件之间接触力方向是重合一致的。像在一连杆机构中～压力角在循环运转过程中变化且是凸轮把运动作用力传递到从动件去的一种量度。大压力角将产生施加到从动件杆上的侧向力～因摩擦力存在～那将势必把从动件限制在导槽中。在自动化机械中的许动应用需要间歇运动。一个典型的例子将要求一个含有上升—停歇—返回和可能另一个停歇的周期～每阶段经过一个指定的角度～伴随着一个所要求的从动件的位移～这个位移以厘米或度来度量。设计者的工作就是相应地设计出该凸轮。首先要做的决策就是要选择凸轮从动件的类型。规定的应用可能要求凸轮和从动件相结合。转化为决策的某些因素有:几何形状条件～动力条件～环境条件和经济因素。一旦凸轮与从动件运动副类型被选定～则从动件运动就必定选定。因此～速度、加速度和在某些情况下～从动件位移的进一步的方案实属极端重要。 齿轮是借助于轮齿成功啮合来传递运动的机器零件。齿轮从一根回转轴到另一回转轴传递运动或传递运动到一传动齿条。多数应用中都以恒定角速比,或常定扭矩比,而存在。恒定角速比应用中必定是轴向传动。在各种各样有用的齿轮设计巴巴工作室www.88doc88.com 类型基础上～输入轴和输出轴需要在一直线上或需要互相平行都不受什么限制。由于使用非圆齿轮～非线性角速比也是很有用的。为了保持恒定的角速度～各个齿轮齿廓的必须服从齿轮啮合的基本规律:为了一对齿能传递恒定角速比～他们接触齿廓的形状必须是这样:公法线通过两齿轮中心连线上的固定点。 满足啮合基本规律的两啮合齿廓被称为共轭齿廓。尽管有着许多满足相啮合齿的可能齿行能被设计出来～以满足基本啮合规律～但一般仅有两种在使用:摆线齿廓和渐开线齿廓。渐开线具有若干重要的优点:它易于加工制造和一对渐开线齿轮之间的中心距可以变化而不改变速比～当使用渐开线齿廓时～可不要求精密的轴间公差。 有几种标准齿轮可供选用。为了在平行轴条件下应用～通常使用直齿圆柱齿轮～平行轴斜齿轮或人字齿齿轮。在相交轴的情况下使用直齿锥齿轮或螺旋齿轮。对于非相交轴和非平行轴齿轮传动～交错轴螺旋齿轮～蜗杆蜗轮～端面齿轮、斜齿圆锥齿轮或准双曲面齿轮将被选用。对于直齿圆柱齿轮～相啮合齿轮的节圆是彼此相切的。他们互相滚动而无滑动。齿顶高是轮齿伸出超过节圆的高度,也是节圆和齿顶圆之间在径向的距离,。顶隙是一个给定齿的齿根高,在节圆以下的齿高,大于与它相啮合的齿轮的齿顶高的量,差值,。齿厚是沿着节圆圆弧上跨齿的距离～而齿间距,齿槽S,是沿着节圆圆弧是相邻两齿间的空间距离。而齿侧间隙是在节圆上的齿槽宽度大于其相啮合齿轮在节圆上的齿厚的差值。 设计巴巴工作室www.88doc88.com