外文翻譯--運動的分析與綜合

1、<p><b>　　外 文 翻 譯</b></p><p>　　專 業(yè) 機械設計制造及其自動化 </p><p>　　學 生 姓 名 </p><p>　　班 級 </p><p>　　學 號

2、 </p><p>　　指 導 教 師 </p><p><b>　　運動的分析與綜合</b></p><p>　　摘　要: 最簡單最有用的機構之一是四桿機構，四桿機構具有一個自由度，相同的四桿機構，可有不同的形式，機構各構件的加速度影響慣性力，繼而影響機器零件的應力、軸承載荷、振動和噪音。運動學家把運動定義為“研究

3、機構的運動和創(chuàng)建機構的方法”，已知一個機構，其構成的運動特性將由運動學分析來確定。對于運動綜合，慣例上有三個任務：函數生成，軌跡生成和運動生成。</p><p>　　關鍵詞:機構運動特征；運動分析；運動綜合</p><p>　　最簡單最有用的機構之一是四桿機構，以下論述中的大部分內容集中在討論連桿機構上，而該程序也適用于更復雜的連桿機構。</p><p>　　我們已

4、經知道四桿機構具有一個自由度。 關于四桿機構，有沒有要知道的更多的有用內容呢？的確是有的！這些包括格拉肖夫準則，變換的概念，死點的位置（分歧點），分支機構，傳動角，和他們的運動特征，包括位置、速度和加速度。</p><p>　　四桿機構可具有一種稱作曲柄搖桿機構的形式，一種雙搖桿機構，一種雙曲柄（拉桿）機構，致力于稱作哪一種形式的機構，取決于跟機架（固定構件）相連接的兩桿的運動范圍。曲柄搖桿機構的輸入構件，曲柄可

5、旋轉360度并連續(xù)轉動，而輸出構件僅僅作搖動（即搖擺的桿件）。作為一個特例，在平行四桿機構中，輸入桿的長度等于輸出桿的長度，連接桿的長度和固定桿（機架）的長度，也是相等的。其輸入和輸出都可以作整周轉動或者轉換成稱作反平行四邊形機構的交叉機構。格拉肖夫準則（定理）表明：如果四桿機構中，任意兩桿之間能作連續(xù)相對轉動，那么，其最長桿長度與最短桿長度之和就小于或等于其余兩桿長度之和。</p><p>　　應該注意：相同的

6、四桿機構，可有不同的形式，這取決于哪一根桿被規(guī)定為機架（即作固定桿）。運動變換的過程就是固定機構傳動鏈中的不同的桿件以產生不同的機構運動過程。除了具備關于構件回轉范圍的知識之外，還要具備如何使機構在制造前就能“運轉”的良好效果，那將是很有用的。哈登伯格（Hartenberg）說到：“運轉”是一個術語，其意義是傳給輸出構件的運動的有效性。他意味著運轉平穩(wěn)，其中能在輸出構件中產生一個力或扭矩的最大分力是有效的。雖然最終的輸出力或扭矩不僅是連

7、桿幾何圖形的函數，而且一般也是動力或慣性力的結果，那常常是大到如靜態(tài)勒的幾倍。為了分析低速運轉或為了易于獲得如何能使任一機構“運轉”的指數，傳動角的概念是非常有用的。在機構運動期間，傳動角的值在改變。傳動角0度可發(fā)生在特殊位置上。在此特殊位置上輸出桿將不運動而與施加到輸入桿上的傳動角多大無關。事實上，由于運動副摩擦的影響，一般根據實際經驗，用比規(guī)定值大的傳動角去設計機構。衡量連桿機構傳遞運動能力的矩陣基礎的定義已經研究出來。一個決定性因

8、素的值（它含有對于某個給定機構圖形，位置的輸出運動變量對輸入變量的導數）是該連桿機構在具體位置中的可動性</p><p>　　如果機構具有一個自由度（例如四桿機構），則規(guī)定的一個位置參數，如輸入角，就將完全確定該機構休止的位置（忽視分支機構的可能性）。我們可研究一個關于四桿機構構件絕對價位置的分析表達式。當分析若干位置和（或）若干不同機構的時候，這將是比幾何圖形分析程序要有用的多，因為該表達式將使自動化計算易于編

9、程。實現機構速度分析的相對速度法即速度多邊形是幾種有效的方法之一。這端（頂）點代表著機構上所有的點，具有零速度。從該點到速度多邊形上的各點劃的線代表著該機構上相應各點的絕對速度。一根線連接速度多邊形上的任意兩點就代表著作為該機構上的兩個對應點的相對速度。</p><p>　　另外的方法就是瞬時中心發(fā)，即瞬心發(fā)，該方法是非常有用的而且常常是在復雜連桿機構分析時較快的方法。瞬心是一個點，該點在那一瞬間，機構上的兩個構

10、件之間不存在相對運動。為了找出已知機構某些瞬心的位置，肯尼迪（Kennedy）三中心理論就非常有用。它是說：彼此相對運動的三個物體的三個瞬心必定是在一直線上。</p><p>　　機構各構件的加速度是令人感興趣的，因為它影響慣性力，繼而影響機器零件的應力、軸承載荷、振動和噪音。由于最終的目的是機器和機構慣性力的分析，所有加速度的各分量都應一次性地畫在同一坐標系中——機構的固定構件的慣性坐標系中表示出來。</

11、p><p>　　應注意的是，相對于固定回轉副的回轉剛體上的一點加速度分量通常有兩個。一個分力方向切于該點的軌跡，其指向與該物體的角加速度方向相同，并被稱為切向加速度。它的存在完全是由于角加速度的變化率引起的。另一個分量，總指向物體的回轉中心，被稱為標準的向心加速度，這個分量有于速度矢量的方向發(fā)生改變而存在。</p><p>　　機構是形成許多機械裝置的基本幾何結構單元，這些機械裝置包括自動包裝

12、機、打印機、機械玩具、紡織機械和其他機械等。典型的機構要設計成使剛性構件相對基準構件產生所希望的運動。機構的運動設計即運動的綜合，第一步常常是先設計整部機器。當考慮受力時，要提出動力學方面的問題，軸承的載荷、應力、潤滑等類似的問題，而較大的問題是機器結構問題。</p><p>　　運動學家把運動定義為“研究機構的運動和創(chuàng)建機構的方法”。這個定義的第一部分就涉及運動學分析。已知一個機構，其構成的運動特性將由運動學分

13、析來確定。敘述運動分析的任務包含機構的主要尺寸、構件間的相互連接和輸入運動的技術特性或驅動方法。目的是要找出位移、速度、加速度、沖擊或跳動（二階加速度），和可能發(fā)生的各構件的高階加速度以及所描述軌跡和由某些構件來實現的運動。定義的第二部分可用以下兩方面來解釋：</p><p>　　1. 研究借助機構來產生給定運動的方法。</p><p>　　2. 研究建造能產生給定運動機構的方法，在兩個方

14、案中，運動是給定的而機構是創(chuàng)建的。這就是運動綜合的本質。這樣運動綜合涉及到為給定性能的機構的系統設計。運動綜合方面又可歸結為以下兩類：</p><p>　　1. 類型綜合。規(guī)定所要求的性能，怎樣一種類型的機構才是合適的？（齒輪系，連桿機構？還是凸輪機構？）而機構應有多少構件？需要多少自由度？怎樣的輪廓結構才是所希望的？等等。關于連桿數目和自由度的考慮通常被認為是類型中被稱為數量綜合的一個分支領域。</p&g

15、t;<p>　　2. 尺寸綜合。運動綜合的第二個主要類型是通過目標法來確定的最佳方法。尺寸綜合試圖確定機構的重要尺寸和啟動位置，該機構是為著實現規(guī)定的任務和預期的性能而事先設置的。</p><p>　　所謂重要的尺寸意思是指關于兩桿、三桿等的長度或桿間距離，構件數和軸間的角度，凸輪的輪廓尺寸，凸輪隨動件的直徑，偏心距，齒輪配額等等。預想機構類型可能是曲柄滑塊機構、四桿機構，帶盤型從動件凸輪機構，或者

16、是以拓撲學方法而非因次分析法所確定的具有某種結構形狀更為復雜的連桿機構。對于運動綜合，慣例上有三個任務：函數生成，軌跡生成和運動生成。</p><p>　　在函數生成機構中輸入和輸出構件的轉動或移動必須是相互關聯的。對于一個任意函數y=f(x)，一個運動綜合的任務可能是設計一個連桿機構使輸入和輸出建立起關系以便使得在x0<x<xn+1的范圍內輸入按x運動，而輸出按y=f(x)運動。在輸入和輸出件回轉運

17、動的情況下，轉角φ和ψ分別是x和y的先行模擬。當輸入件回轉到一個獨立x值時，在一個“黑箱”的機構中，使輸出構件轉到相對應的由函數y=f(x)決定的數值上。這可被認為機械模擬計算機的最簡單的情形。各種不同的機構都可以包含在這個“黑箱”中，然而對于任意函數的無誤差生成，四桿機構是無能為力的，僅僅可能在有限精度內與之相匹配。它廣泛用于工業(yè)上，因為四桿機構在構件和維修都是簡單的。</p><p>　　在軌跡生成機構中，在

18、“浮動桿”上一個點要描畫一條相對于一個固定坐標系確定的軌跡。如果該軌跡點既要與時間相關又要與位置相關，該任務被稱之為預定周期的軌跡生成。軌跡生成機構的一個例子就是設計來投擲棒球或網球的四桿機構。在這種情況下，點P的軌跡將是這樣：在預定的位置撿起一個球，并在預定的時間周期內沿著預定的徑跡把球傳出去，能達到合適的速度和方向。</p><p>　　機械裝置設計中有著許多情形，在這些情形中既要導引剛體通過一系列規(guī)定的、受

19、限制的獨立位置，又要在減少受限制而且獨立的位置的數目時，對運動體的速度和（或）加速度加以約束，那是必要的。運動生成或減少剛體導引機構要求：一個完整的物體要被導引通過一預定的運動序列。作為被導引的物體通常是“浮動構件”的一部分，那不僅是預定點P的軌跡，也是通過該點并嵌入該物體內的線的轉動。例如，該線可能代表自動化機械中的一個載體，那是在載體件上的一個點具有一個預定的軌跡而該載體件又具有一個預定的角度防衛(wèi)。預定方式裝料機的吊斗的運動是運動生

20、成機構的另一個例子。吊斗端的軌跡是有極限的。因為其端口必須實現挖掘的運動軌跡，緊跟著要實現提升和傾瀉的軌跡。吊斗的角度方位對保證斗中物料從正確的位置傾瀉（倒）同樣是重要的。</p><p>　　Movement Analysis and Synthesis</p><p>　　LI can,HUANG Yun-yao</p><p>　　Abstract: One

21、of the simplest and most useful mechanisms is the four-bar linkage. A four-bar linkage has one degree of freedom. The same four-bar linkage can be a different type. The acceleration of links of a mechanism is of interest

22、 because of its effort on inertia force, which in turn influence the stress in the parts of a machine, bearing loads, vibration, and noise. A kinematician defined kinematics as “the study of the motion of mechanisms and

23、methods of creating them.” Given a certain mec</p><p>　　Key words: Linkage motion feature; Movement Analysis; Dimensional synthesis</p><p>　　One of the simplest and most useful mechanisms is the

24、 four-bar linkage. Most of the following description will concentrate on this linking, but the procedures are also applicable to more complex linking.</p><p>　　We already know that a four-bar linkage has one

25、 degree of freedom. Are there any more that are useful to know about four-bar linkage? Indeed there are! These include the Grashof criteria, the concept of inversion, dead-center position (branch points), branching, tran

26、smission angle and their motion feature, include positions, velocities and accelerations.</p><p>　　The four-bar linkage may take form of a so-called crank-rocker or a double-rocker or a double-crank (drag-li

27、nk) linkage, depending on the range of motion of the two links connected to the ground link. The input crank of a crank-rocker type can rotate continuously through 360,while the output link just “rocks” (or oscillates).

28、As a particular case , ina parallelogram linkage, where the length of the input link equals that of the output link and the lengths of the coupler and the ground link are a</p><p>　　Notice that the same four

29、-bar linkage can be a different type, depending on which link is specified as the frame (or ground). Kinematic inversion is the process of fixing different links of a chain to create different mechanisms. Note that the r

30、elative motion between links of a mechanism does not change in different inversion.</p><p>　　Besides having knowledge of the extent of the rotations of the links, it would be to have a measure of how well a

31、mechanism might “run” before actually building it. Hartenberg mentions that “run” is a term effectiveness with which motion is imparted to the output link; it implies smooth operation, in which a maximum force component

32、is available to produce a force or torque in an output member. Although the resulting output force or torque is not only a function of the geometry of the linkage, bu</p><p>　　If a mechanism has one degree o

33、f freedom(e.g. a four-bar linkage), then prescribing one position parameter, such as the angle of the input link, will completely specify the position of the rest of the mechanism (discounting the branching possibility).

34、 We can develop an analytical expression relating the absolute angular positions of a four-bar linkage. This will be much useful than a graphical analysis procedure when analyzing a number of position and/or a number of

35、different mechanisms, because</p><p>　　The relative velocity or velocity polygon method of performing a velocity analysis of a mechanism is one of several method available. The pole represents all points on

36、the mechanism having zero velocity. Lines drawn from the pole to points on the velocity polygon represent the absolute velocities of the corresponding points on the mechanism. A line connecting any two points on the velo

37、city polygon represents the relative velocity for the two corresponding points on the mechanism.</p><p>　　Another method is the instantaneous center or instant center method, which is a very useful and often

38、 quicker in complex linkage analysis. An instantaneous center or instant center is a points at which is no relative velocity between two links of a mechanism at the instant. In order to locate the locations of some insta

39、nt centers of a given mechanism, the Kennedy’s theorem of three centers is very useful. It states that the three instantaneous center of three bodies moving relative to one anothe</p><p>　　The acceleration o

40、f links of a mechanism is of interest because of its effort on inertia force, which in turn influence the stress in the parts of a machine, bearing loads, vibration, and noise. Since the ultimate objective is inertia-for

41、ce analysis of mechanisms and machines, all acceleration components should be expressed in one and the same coordinate system: the inertia frame of reference of the fixed of the mechanism.</p><p>　　Notice th

42、at in general there are two components of acceleration of a point on a rigid body rotating about a ground pivot. One component has the direction tangent to the path of this point, pointed in the same sense of the angular

43、 acceleration of the body, and is called the tangential acceleration. Its presence is due solely to the angular velocity. The other component, which always points toward the center of rotation of the body, is called the

44、normal or centripetal acceleration. This component </p><p>　　Mechanisms form the basic geometrical elements of many mechanical device including automatic packing machinery, typewriters, mechanical toys, and

45、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 mechanism often is the first step in the design of a compl

46、ete machine. When force are considered, the additional problem of dynamics, bearing loads, stresses, lubrication, and the like are int</p><p>　　A kinematician defined kinematics as “the study of the motion o

47、f 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 analysi

48、s. The statement of the tasks of analysis contains all principal dimensions of mechanism, the interconnections of its links, and the specifications, of the input motion or method of actuation. The objective is to find<

49、;/p><p>　　1. The study of methods of creating a given motion by means of mechanisms.</p><p>　　2. The study of methods of creating mechanisms have a given motion.</p><p>　　In either ver

50、sion, the motion is given and the mechanism is to be found. This is the essence of kinematic analysis. Thus kinematic synthesis deals with the systematic design of mechanisms for a given performance. The area of synthesi

51、s may be grouped into two categories.</p><p>　　1. Type synthesis. Given the required performance, what type of mechanism will be suitable? (Gear trains? Linkages? Cam mechanism?)Also, how many links should t

52、he mechanism have? How many degrees of freedom are required? What configuration is desirable? And so on. Deliberations involving the number of links and degrees of freedom are often referred to as province of a subcatego

53、ry of type synthesis called number synthesis.</p><p>　　2. Dimensional synthesis. The second major category of kinematic analysis is best defined by way of its objective: Dimensional synthesis seeks to determ

54、ine the significant dimensions and the starting position of a mechanism of preconceived type for a specified task and prescribed performance.</p><p>　　Significant dimensions mean link lengths or distance on

55、binary, ternary, and so on, links, angles between axis, cam-contour dimensions and cam-follower diameters, eccentricities, gear rations, and so on. A mechanism of preconceived type may be a slider-crank linkage, a four-b

56、ar linkage, a cam with flat follower, or a more complex linkage of a certain configuration defined topologically but not dimensionally. There are three customary tasks for kinematic synthesis: function generation, path g

57、ener</p><p>　　In function generation mechanisms rotation or sliding motions of input and output links must be correlated. For an arbitrary rotation y=f(x), a kinematic synthesis task may be to design a linka

58、ge to correlate input and output such that the input moves by x, the output moves by y=f(x) for the range x0<x<xn+1. In the case of rotary input and output, the angles of rotation φ and ψ are the linear analogs of

59、x and y respectively. When the input link is rotated to a value of the independent x, the mec</p><p>　　In path generation mechanism a point on a “floating link” is to trace a path defined with respect to a f

60、ixed frame of reference. If the path points are to be corrected with either time or input-link positions, the task is called path generation with prescribed timing. An example of path generation mechanism is a four-bar l

61、inkage 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 a</p><p>　　There are many situat

62、ions is 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 constrains on the velocity and/or acceleration of th

63、e moving body at a reduced number 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 fl