機(jī)械外文翻譯---機(jī)構(gòu)介紹

1、<p>　　Introduction to mechanism</p><p>　　The function of mechanism is to transmit or transform motion from one rigid body to another as part of the action of a machine. There are three types of common

2、 mechanical devices that can be used as basic elements of a mechanism.</p><p>　　Gear system, in which toothed members in contact transmit motion between rotating shafts.</p><p>　　Cam system, whe

3、re a uniform motion of an input member is converted into a nonuniform motion of the output member.</p><p>　　Plane and spatial linkages are also useful in creating mechanical motions for a point or rigid body

4、.</p><p>　　A kinematic chain is a system of links, which are either jointed together or are in contact with one another in a manner that permits them to move relative to one another. If one of the links is f

5、ixed and the movement of any other link to a new position will cause each of the other links to move to definite predictable position, the system is a constrained kinematic chain. Otherwise, the system is an unconstraine

6、d kinematic chain.</p><p>　　A mechanism or linkage is a constrained kinematic chain, and is a mechanical divice that has the purpose of transferring motion and force from a source to an output. A linkage con

7、sists of links (or bar),generally considered rigid,which are connected by joints, such as pin (or revolute) or prismatic joints, to form open or closed chains (or loops). Such kinematic chains,with at least one link fixe

8、d, become (i) mechanisms if at least two other links remain mobility, or (ii) stuctures if no mobilit</p><p>　　Mechanisms are used in a great variety of machines and devices. The simplest closed-loop linkage

9、 is the four-bar linkage, which has three moving links (plus one fixed link) and four pin joints. The link that is connected to the power source or prime mover and has one moving pivot and one ground pivot is called the

10、input link. The output link connects another moving povit to another ground povit. The coupler or floating link connected the two moving pivots, thereby “coupling” the input to the out</p><p>　　The four-bar

11、linkage has some special configurations created by making one or more links infinite in length。The slider-crank （or crank and slider）mechanism is a four-bar chain with a slinder replacing an infinitely long output link。T

12、he internal combustion engine is built based on this mechanism。Other forms of four- bar mechanisms exist in which a slider is guided on a moving link rather than on a fixed link. These are called inversions of the slider

13、-crank，produced when another link（the crank，cou</p><p>　　Although the four-bar linkage and slider-crank mechanism are very useful and found in thousands of applications，we can see that these linkages have li

14、mited performance level。Linkages with more members are often used in more demanding circumstances。However it is often difficult to visualize the movement of a multiloop linkage，especially when other components appear in

15、the same diagram。The fist step in the motion analysis of more complicated mechanisms is to sketch the equivalent kinematic or skel</p><p>　　The next step in the kinematic analysis of mechanisms is to determi

16、ne the number of degree of freedom of the mechanism。By degree of freedom we mean the number of independent inputs required to determine the positions of all links of the mechanism with respect toground。There are hundreds

17、 of thousands of different linkage types that one could invent。Envision a bag containing a large variety of linkage components：binary，ternary，quaternary，and so on，links ；pin joints，slide joints；cams and cam follow</p&

18、gt;<p>　　The process of drawing kinematic diagrams and determining degrees of freedom of mechanisms are the first steps in both the kinematic analysis and synthesis process。In kinematic analysis，a particular given

19、 mechanism is investigated based on the mechanism geometry plus possibily other known characteristics。Kinematic synthesis，on the other hand，is the proess of designing a mechanism to accomplish a desired task。Here，both ch

20、oosing the type as well as the dimensions of the new mechanism can be part o</p><p>　　Movement analysis</p><p>　　One of the simplest and most useful mechanisms is the four-bar linkage。Most of th

21、e following description will concentrate on this linkage，but the procedures are also applicable to more complex linkages。</p><p>　　We already known that a four-bar linkage has one degree of freedom。Are there

22、 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，transmission angle and their motion feat

23、ure，including 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-link）linkage，depending on the range of

24、motion of the two links connected to the ground link。The input crank of a crank-rocher type can rotate continuously through 360，while the output link just “rocks”（or oscillates）。As a particular case，in a parallelogram li

25、nkage，where the length of the input link equals that of the output link and the lengths of the coupler and the ground link are also the </p><p>　　Notice that the same four-bar linkage can be a different type

26、，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 relative motion between links of a mechan

27、ism does not change indifferent inversions。</p><p>　　Besides having knowledge of the extent of the links，it would be useful to have a measure of how well a mechanism might“run”before actually building it。Har

28、tenberg mentions that“run”is a term that means effectiveness with which motion is imparted to the output link ；it implies smooth operation，in which a maximum force component is available to produce a force or torque in a

29、n output member。The resulting output force or torque is not only a function of the geometry of the linkage，it is generally the</p><p>　　If a mechanism has one degree of freedom (e.g. a four-bar linkage), the

30、n 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). We can develop an analytical expressio

31、n relating the absolute angular positions of the links of a four-bar linkage. This will be much more useful than a graphical analysis procedure when analyzing a number of positions and /or a number of differen</p>

32、<p>　　The relative velocity or velocity polygon method of performing a velocity analysis of a mechanism is one of several methods available. The pole represents all points on the mechanism having zero velocity. Lin

33、es 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 velocity polygon represents the relative ve

34、locity 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 quicker in complex linkage analysis.

35、An instantaneous center or instant center is a point at which there is no relative velocity between two links of a mechanism at that instant. In order to locate the locations of some instant centers of a given mechanism,

36、 the Kennedy’s theorem of three centers is very useful. It states that the three instantaneous centers of three bodies moving relative to one</p><p>　　The acceleration of links of a mechanism is of interest

37、because of its effect on inertia force, which in turn influences the stress in the parts of a machine, bearing loads, vibration, and noise. Since the ultimate objective is inertia-force analysis of mechanisms and machine

38、s, all acceleration components should be expressed in one and the same coordinate system : the inertia frame of reference of the fixed link of the mechanism. .</p><p>　　Notice that in general there are two c

39、omponents 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 acceleration of this body, a

40、nd is called the tangential acceleration .Its presence is due solely to the rate of change of the angular velocity. The other component, which always points toward the center of rotation of the body, is called the normal

41、 or centripetal accele</p><p><b>　　譯文：</b></p><p><b>　　機(jī)構(gòu)介紹</b></p><p>　　機(jī)構(gòu)是機(jī)械運(yùn)動(dòng)的一個(gè)部分，他的功能是把運(yùn)動(dòng)從一個(gè)剛體傳遞或轉(zhuǎn)換到另一個(gè)剛體。用作機(jī)構(gòu)基本零件的一般機(jī)械裝置有三種類(lèi)型：</p><p>　　齒輪

42、系統(tǒng)，在回轉(zhuǎn)軸之間通過(guò)接觸傳遞運(yùn)動(dòng)的齒狀零件。</p><p>　　凸輪系統(tǒng)，把輸入零件的均勻運(yùn)動(dòng)轉(zhuǎn)換成輸出零件的非今年暈運(yùn)動(dòng)的裝置。</p><p>　　平面和空間連桿機(jī)構(gòu)，使點(diǎn)或剛體產(chǎn)生機(jī)械運(yùn)動(dòng)的使用裝置。</p><p>　　運(yùn)動(dòng)鏈?zhǔn)且粋€(gè)鏈接系統(tǒng)，它們或者彼此鉸接或者互相接觸，相互間能夠產(chǎn)生相對(duì)運(yùn)動(dòng)。如果鏈接中的某個(gè)連桿被固定，而其它任何一個(gè)連桿運(yùn)動(dòng)到新的位置

43、將導(dǎo)致其它各個(gè)連桿也運(yùn)動(dòng)到確定的預(yù)期位置，該系統(tǒng)就是一個(gè)可約束的運(yùn)動(dòng)鏈。否則，該系統(tǒng)是一個(gè)非約束運(yùn)動(dòng)鏈。</p><p>　　機(jī)構(gòu)或連桿就是一個(gè)可約束的傳動(dòng)鏈，是一個(gè)從輸入到輸出以傳遞運(yùn)動(dòng)和力為目的的機(jī)械裝置。連桿機(jī)構(gòu)通常由被認(rèn)為是剛體的構(gòu)件或桿組成，它們之間用銷(xiāo)軸鉸接，例如用柱銷(xiāo)（圓形的）或棱柱體的銷(xiāo)軸鉸接，形成開(kāi)式或閉式（回環(huán)式）的運(yùn)動(dòng)鏈。如果這樣的運(yùn)動(dòng)鏈至少有一個(gè)構(gòu)件被固定并且：（i）如果至少有兩個(gè)構(gòu)件能保

44、持運(yùn)動(dòng)，就變?yōu)闄C(jī)構(gòu)；（ii）如果沒(méi)有一個(gè)構(gòu)件能夠運(yùn)動(dòng)，則成為結(jié)構(gòu)。換句話說(shuō)，機(jī)構(gòu)內(nèi)部的剛性桿件之間能夠相對(duì)運(yùn)動(dòng)，而結(jié)構(gòu)則不能。由于連桿系統(tǒng)能組成簡(jiǎn)單機(jī)構(gòu)并完成復(fù)雜的任務(wù)，例如非線性運(yùn)動(dòng)的傳遞和力的傳遞，因而它們?cè)跈C(jī)構(gòu)研究中受到了更多的關(guān)注。</p><p>　　許多機(jī)器和裝置都使用機(jī)構(gòu)。最簡(jiǎn)單的閉環(huán)連接是四連桿，它具有三個(gè)動(dòng)桿（加上一個(gè)固定桿）和四個(gè)回轉(zhuǎn)副。連接動(dòng)力源或原動(dòng)件的桿叫輸入桿，有一個(gè)移動(dòng)鉸和一個(gè)固定鉸

45、。輸出桿將另一個(gè)移動(dòng)鉸和另一個(gè)固定鉸連接起來(lái)。連桿即浮動(dòng)桿將兩個(gè)移動(dòng)鉸鏈接起來(lái)，把輸入傳送到輸出桿。</p><p>　　把四連桿的一個(gè)或幾個(gè)桿無(wú)限延長(zhǎng)就會(huì)產(chǎn)生一些特殊的機(jī)構(gòu)。曲柄滑塊機(jī)構(gòu)就是一個(gè)四連桿，只不過(guò)用滑塊替換了一個(gè)無(wú)限長(zhǎng)的輸出桿。內(nèi)燃機(jī)也是類(lèi)似的一種機(jī)構(gòu)。有些其它形式的四桿機(jī)構(gòu)，其滑塊在一個(gè)動(dòng)桿上導(dǎo)移運(yùn)動(dòng)而不是在一個(gè)固定桿上。把另一個(gè)桿（曲柄，連桿或滑塊）固定，可以生成曲柄滑塊機(jī)構(gòu)的變異機(jī)構(gòu)。<

46、/p><p>　　雖然四連桿和曲柄滑塊機(jī)構(gòu)的應(yīng)用非常廣泛，但是我們可以發(fā)現(xiàn)這些連桿機(jī)構(gòu)的性能仍然有限。某些要求更高的環(huán)境使用的連桿機(jī)構(gòu)有更多的元件。然而，想象多回環(huán)的連桿機(jī)構(gòu)的運(yùn)動(dòng)常常非常困難。特別是當(dāng)其它零件出現(xiàn)在同一圖中的時(shí)候。對(duì)于比較復(fù)雜的機(jī)構(gòu)的運(yùn)動(dòng)分析，第一步是繪制等效運(yùn)動(dòng)圖或示意圖這種示意圖類(lèi)似于電路示意圖，僅僅表示出機(jī)構(gòu)的主要本質(zhì)，體現(xiàn)影響其運(yùn)動(dòng)的關(guān)鍵尺寸。運(yùn)動(dòng)圖可用兩種形式中的一種：一是草圖（按比例畫(huà)出

47、，但放大比例不精確）；二是比例運(yùn)動(dòng)圖（通常用于進(jìn)一步分析其位置.位移.速度.加速度.力.和扭矩傳遞等）。為了便于參考，用數(shù)字對(duì)構(gòu)件進(jìn)行編號(hào)（以機(jī)架為1開(kāi)始編號(hào)），而用英文字母標(biāo)注回轉(zhuǎn)副。</p><p>　　機(jī)構(gòu)運(yùn)動(dòng)分析的第二部是確定機(jī)構(gòu)的自由度數(shù)。我們所說(shuō)的自由度，指的是使機(jī)構(gòu)所有構(gòu)件相對(duì)于機(jī)架具有確定位置所需要的獨(dú)立輸入的數(shù)目。人們可以發(fā)明有數(shù)以千計(jì)的不同類(lèi)型的連桿機(jī)構(gòu)。就像一個(gè)裝有各種各樣連桿的袋子，里面有

48、：二桿組.三桿組.四桿組以及連桿.回轉(zhuǎn)副.滑動(dòng)副.凸輪隨動(dòng)件.齒輪.鏈條.鏈輪.皮帶.皮帶輪等。（球形運(yùn)動(dòng)副 .螺旋副.以及允許三維相對(duì)運(yùn)動(dòng)的其它連接尚未包括進(jìn)去，因?yàn)檫@里僅僅討論的是平行平面內(nèi)的平面運(yùn)動(dòng)。）你還可以設(shè)想這些元件在一起形成各種類(lèi)型連桿機(jī)構(gòu)的可能性。存在幫助人們形成這些的規(guī)律嗎？實(shí)際上，大多數(shù)機(jī)構(gòu)的任務(wù)是要求一個(gè)單一的輸入被傳遞到一個(gè)單一的輸出。因此單一自由度的機(jī)構(gòu)是使用最多的機(jī)構(gòu)類(lèi)型。例如，由直覺(jué)很容易可以看出四連桿就是

49、一個(gè)單一自由度的連桿機(jī)構(gòu)。</p><p>　　畫(huà)運(yùn)動(dòng)圖和確定機(jī)構(gòu)自由度的過(guò)程，是機(jī)構(gòu)運(yùn)動(dòng)分析和綜合過(guò)程的第一個(gè)階段。具體機(jī)構(gòu)的運(yùn)動(dòng)可以根據(jù)機(jī)構(gòu)的幾何形狀和可能知道的其它特性來(lái)分析。另一方面，運(yùn)動(dòng)綜合是設(shè)計(jì)一個(gè)機(jī)構(gòu)以完成所要求的任務(wù)的過(guò)程。因此，選擇新機(jī)構(gòu)的類(lèi)型和尺寸是運(yùn)動(dòng)綜合的一部分。想象相對(duì)運(yùn)動(dòng)的能力，推想出一個(gè)機(jī)構(gòu)按現(xiàn)在那樣的方式設(shè)計(jì)的原因并對(duì)一個(gè)具體設(shè)計(jì)進(jìn)行改進(jìn)的能力是一個(gè)成功的運(yùn)動(dòng)學(xué)家的標(biāo)志。雖然這些能

50、力有些來(lái)自先天的創(chuàng)造性，然而更多的是因?yàn)樵趯?shí)踐中提高了技術(shù)水平。</p><p><b>　　運(yùn)動(dòng)分析</b></p><p>　　最簡(jiǎn)單、最有用的機(jī)構(gòu)之一是四連桿。以下論述中的大部分內(nèi)容集中討論這種連桿機(jī)構(gòu)，其分析步驟也適用于更復(fù)雜的連桿機(jī)構(gòu)。</p><p>　　我們已經(jīng)知道四連桿具有一個(gè)自由度。關(guān)于四連桿，還有其它更有用的內(nèi)容需要了解嗎？

51、確實(shí)有！它們包括格拉肖夫準(zhǔn)則、變異的概念、死點(diǎn)的位置(分歧點(diǎn))、分支機(jī)構(gòu)、傳動(dòng)角以及它們的運(yùn)動(dòng)特征，包括位置、速度和加速度。</p><p>　　四連桿的形式可能有所謂的曲柄搖桿、雙搖桿或者雙曲柄（拉桿）機(jī)構(gòu)，這主要取決于與固定桿相連接的兩根桿的運(yùn)動(dòng)范圍、曲柄搖桿機(jī)構(gòu)的輸入構(gòu)件曲柄可以持續(xù)旋轉(zhuǎn)360，而輸出構(gòu)件僅僅搖動(dòng)或擺動(dòng)。作為一個(gè)特例，某些平行四連桿的長(zhǎng)度等于輸出 桿的長(zhǎng)度，連桿的長(zhǎng)度和固定桿的長(zhǎng)度也相等，輸

52、入桿和輸出 桿都可以作整周轉(zhuǎn)動(dòng)或者轉(zhuǎn)換成稱(chēng)為反平行四邊形機(jī)構(gòu)的交叉結(jié)構(gòu)。格拉肖夫準(zhǔn)則表明：如果任意兩桿之間能作連續(xù)的相對(duì)轉(zhuǎn)動(dòng)，那么平面連桿中最長(zhǎng)桿與最短桿的長(zhǎng)度之和。</p><p>　　應(yīng)該注意：相同的四連桿可能 類(lèi)型并不相同，這取決于哪一根桿被規(guī)定為機(jī)架（固定桿）。運(yùn)動(dòng)變異就是固定傳動(dòng)鏈中不同的桿件產(chǎn)生不同機(jī)構(gòu)的過(guò)程。值得注意的是，不同變異機(jī)構(gòu) 連桿間的相對(duì)運(yùn)動(dòng)并沒(méi)有改變。</p><p&

53、gt;　　除了要具備構(gòu)件回轉(zhuǎn)范圍的知識(shí)，制造這前先建立一個(gè)檢驗(yàn)機(jī)構(gòu)“運(yùn)轉(zhuǎn)”效果的度量方法也是很有用的。哈登伯格（Hartenberg）說(shuō)到：“運(yùn)轉(zhuǎn)”這個(gè)術(shù)語(yǔ)是指運(yùn)動(dòng)傳給輸出構(gòu)件的有效性，這意味著運(yùn)轉(zhuǎn)平穩(wěn)，用最大的分力產(chǎn)生驅(qū)動(dòng)輸出構(gòu)件的力或扭矩。最終輸出的力或扭矩不僅與連桿的幾何形狀有關(guān)，通常還與動(dòng)力或慣性力有關(guān)，并且常常是靜態(tài)力的幾倍。為了分析低速運(yùn)動(dòng)或者為了更方便地掌握任一機(jī)構(gòu) 如何運(yùn)動(dòng)的方法，傳動(dòng)角的概念是非常有用的。在機(jī)構(gòu)運(yùn)動(dòng)期間

54、，傳動(dòng)角在改變。零度傳動(dòng)角可能發(fā)生在某些特殊位置上。這時(shí)無(wú)論 施加到輸入桿上的力有多大，輸出桿都無(wú)法運(yùn)動(dòng)。實(shí)際上，由于回轉(zhuǎn)副中存在摩擦，根據(jù)經(jīng)驗(yàn)，實(shí)際設(shè)計(jì)的機(jī)構(gòu)的傳動(dòng)角一般比給定值要大?，F(xiàn)在已經(jīng)研究出用矩陣來(lái)衡量連桿機(jī)構(gòu)運(yùn)動(dòng)傳遞的效果的定義。矩陣中行列式的值（它含有給定幾何形狀的連桿的輸出運(yùn)動(dòng)變量相對(duì)輸入變量的導(dǎo)數(shù)）是該連桿機(jī)構(gòu)在具體位置上可去性的一個(gè)尺度。</p><p>　　如果機(jī)構(gòu)具有一個(gè)自由度（例如四連桿

55、），則確定一個(gè)位置參數(shù)，如輸入桿的角度，就完全確定了該機(jī)構(gòu)其余桿件的位置（忽視分支機(jī)構(gòu)的可能性）。我們可以研究出一個(gè)關(guān)于四連桿各桿件絕對(duì)角位置的分析表達(dá)式。當(dāng)分析各種位置或各種不同機(jī)構(gòu)的時(shí)候，這個(gè)分析表達(dá)式比幾何圖形分析程序要有用得多，因?yàn)檫@種表達(dá)式更易于編程進(jìn)行自動(dòng)化計(jì)算。</p><p>　　在機(jī)構(gòu)速度分析中相對(duì)速度 法或速度多邊形法是幾個(gè)經(jīng)常采用的方法之一。原點(diǎn)代表機(jī)構(gòu)上所有速度為零點(diǎn)。從原點(diǎn)到速度多邊形上

56、的各點(diǎn)所畫(huà)的線代表機(jī)構(gòu)上相應(yīng)各點(diǎn)的絕對(duì)速度。速度多邊形上的任意兩點(diǎn)間的連線代表了該機(jī)構(gòu) 對(duì)應(yīng)兩點(diǎn)的相對(duì)速度。</p><p>　　另一種方法是瞬時(shí)中心法或瞬心法，這是一種非常有用的、快速對(duì)復(fù)雜連桿機(jī)構(gòu)進(jìn)行分析的方法。瞬心是一個(gè)點(diǎn)，該點(diǎn)在那一瞬間，機(jī)構(gòu)上的兩構(gòu)件之間不存在相對(duì)運(yùn)動(dòng)。為了找出已知機(jī)構(gòu)某些瞬心的位置，肯尼迪（Kennedy）的三心理論是非常有用的。該理論認(rèn)為：彼此相對(duì)運(yùn)動(dòng)的三個(gè)瞬心必定在一條直線上。&l

57、t;/p><p>　　機(jī)構(gòu)各構(gòu)件的加速度也令人關(guān)注，因?yàn)閷?shí)驗(yàn)室影響慣性力，繼面影響機(jī)器零件的應(yīng)力、軸承載荷、振動(dòng)和噪音。由于最終的目的是機(jī)器和機(jī)構(gòu)慣性力的分析，因而所有加速度的各分量都應(yīng)該同時(shí)畫(huà)在同一坐標(biāo)系中，即畫(huà)在機(jī)構(gòu)的固定構(gòu)件的慣性坐標(biāo)系中。</p><p>　　應(yīng)該注意的是：繞固定鉸旋轉(zhuǎn)的剛體上的點(diǎn)的加速度分量通常有兩個(gè)。一個(gè)分量方向與該點(diǎn)的軌跡相切，指向與該物體的角加速度的方向相同，叫