機構設計外文翻譯

1、<p><b>　　附錄：</b></p><p><b>　　1 外文資料譯文</b></p><p><b>　　機構</b></p><p>　　機構被定義為：“是由剛體或者有承載能力的物體聯(lián)接而形成的組合體，它們在運動時彼此之間應該具有確定的相對運動?！?lt;/p><

2、;p>　　機構是構成許多機械設備的基本幾何單元，這些機械設備包括自動包裝機、打字機、機械式玩具、紡織機等等。機構設計的目的通常是使一個剛體相對某一參考構件產生所需要的相對運動。機構的運動設計通常是設計一臺完整的機器的第一步。在考慮力的作用時，應該考慮動力學、軸承載荷、應力、潤滑等一系列問題。在所考慮的問題的范圍擴大之后，機構設計就變成了機器設計。</p><p>　　作為機器的一個組成部分，機構的作用是在剛

3、體之間傳遞或轉換運動。常用的基本機構有以下三種：</p><p>　　齒輪機構 在這種機構中，各轉軸之間的運動由相互嚙合的齒輪來傳遞。齒輪通常用來傳遞角速度比為常值的運動，但是非圓齒輪可以用來傳遞角速度比為變數(shù)的運動。</p><p>　　凸輪機構 在這種機構中，輸入件的等速連續(xù)運動被轉換成輸出件的不等速運動。輸出的運動可以是軸的轉動、滑塊的移動、或者其他從動件的運動。這些運動都是使從

4、動件與作為輸入件的凸輪的輪廓的直接接觸而產生的。凸輪的運動設計就是采用解析法或者圖解法來確定凸輪的輪廓形狀，使其能夠帶動從動件實現(xiàn)輸出運動時輸入運動的指定函數(shù)這一功能。</p><p>　　平面和空間連桿機構 這類機構也是用來使機構上某一點或者剛體實現(xiàn)機械運動的。連桿的基本作用有三種：</p><p>　　(1)剛體導向。剛體導向機構用來引導一個剛體，使其通過空間一系列預定的位置。<

5、;/p><p>　　(2)導軌。實現(xiàn)導軌機構將引導剛體上的一個點，使其通過指定的空間軌跡上的一系列點。</p><p>　　(3)實現(xiàn)函數(shù)。這類機構所產生的輸出運動是輸入運動的指定函數(shù)。 </p><p>　　為了強調各種機構之間的相同之處與不同之處，可以把它們按照幾種不同的方式進行分類。一種分類方式是將機構分為平面、球面和空間三類。這三類機構有共同之處，然而，可以

6、根據其構件的運動特點來確定分類準則。</p><p>　　在平面機構中，所有質點走過的軌跡都是平面曲線，所有這些平面曲線都位于相互平行的平面上，即所有點的軌跡都是平行于一個共同平面的平面曲線。這一特點使得平面機構上任意選定的一個點都可以按其真實尺寸和形狀在一個視圖上表示出運動軌跡。平面四連桿機構、平板凸輪和它的從動件、曲柄滑塊機構是大家所熟悉的平面機構的例子?，F(xiàn)在使用中的大多數(shù)機構是平面機構。</p>

7、<p>　　在球面機構中，當機構運動時，每一個構件上都有一個點是靜止的，所有構件上的靜止點都處于同一個位置，也就是每一個構件上都有一個點是靜止的，所有構件上的靜止點都處于同一個位置，也就是每個點的軌跡都是球面曲線。所有各點運動時所在的球面是同心的。因而，所有質點的運動都能用它們在以適當選取的點為中心的球面上的徑向投影來完整地進行描述?；⒖巳f向聯(lián)軸器可能會是人們最熟悉的一個球面機構的例子。</p><p&

8、gt;　　從另一方面來說，在空間機構中質點的相對運動不受約束。運動的變換既不要求共面，也不要求同心?？臻g機構上許多質點的運動軌跡可能具有雙重曲率。</p><p>　　例如，任何含有螺旋副的連桿機構，由于其相對運動是螺旋線形的，因此是空間機構。</p><p><b>　　材料選擇</b></p><p>　　近些年來，工程材料的選擇已經顯得非

9、常重要。此外，選擇過程應該是一對材料的連續(xù)不斷的重新評價過程。新材料不斷出現(xiàn)，而一些原有的材料的可以被利用的數(shù)量可能會減少。環(huán)境污染、材料的回收利用、工人的健康及安全等方面經常會對材料選擇附加新的限制條件。為了減輕重量或者節(jié)約能源，可能會要求使用不同的材料。來自國內和國際的競爭、對產品維修保養(yǎng)方便性要求的提高和顧客的反饋等反面的壓力，都會促使人們對材料進行重新評價。由于材料選用不當造成的產品責任訴訟，已經產生了深刻的影響。此外，材料與材

10、料加工之間的相互依賴關系已經被人們認識得更清楚。新的加工方法的出現(xiàn)，通常會促使人們對被加工材料進行重新評價。因此，為了能在合理的成本和確保質量的前提下獲得滿意的結果，設計工程師和制造工程師都必須認真仔細地選擇、確定和使用材料。</p><p>　　制造任何產品的第一步工作都是設計。設計通常可以分為幾個明確的階段：（a）概念設計；（b）功能設計；（c）生產設計。在概念設計階段，設計者著重考慮產品應該具有的功能。通常

11、要設想和考慮幾個方案，然后決定著中想法是否可行；如果可行，則應該對其中一個或幾個方案作進一步的改進。在此階段，關于材料選擇唯一要考慮的問題是：是否有性能符合要求的材料可供選用；如果沒有的話，是否有較大的把握在成本和時間都允許的限度內研制出一種新材料。</p><p>　　在功能設計或工程實際階段，要做出一個切實可行的設計。在這個階段要繪制出相當完整的圖紙，選擇并確定各種零件的材料。通常要制造出樣機或者食物模型，并

12、對其進行試驗，評價產品的功能、可靠性、外觀、和維修保養(yǎng)性等。雖然這種實驗可能會表明，在產品進入到生產階段之前，應該更換某些材料，但是，絕對不能將這一點作為不認真選擇材料的借口。應該結合產品的功能，認真仔細地考慮產品的外觀、成本、可靠性。一個很有成就的公司在制造所有樣機時，所選用的材料應該和其在生產中使用的材料相同，并盡可能使用同樣的制造技術。這樣做對公司是很有好處的。功能完備的樣機如果不能根據預期的銷售量經濟地制造出來，或者是樣機與正式

13、生產的裝置在質量和可靠性方面有很大的不同，則這種樣機就沒有多大的價值。設計工程師最好能在這一階段全部完成材料分析、選擇和確定工作，而不是將其留到生產設計階段去做。因為，在生產設計階段材料的更換時由其他人進行的，這些人對產品的所有功能的了解可能不如設計工程師。</p><p>　　在生產設計階段中，與材料有關的主要問題是應該把材料完全確定下來，使它們與現(xiàn)有的設備相適應，能夠利用現(xiàn)有設備經濟地進行加工，而且材料的數(shù)量

14、能夠比較容易地保證供應。</p><p>　　在制造過程中，不可避免地會出現(xiàn)對使用材料作一些更改的情況。經驗表明，可以采用某些便宜材料作為替代品。然而，在大多數(shù)情況下，在進行生產以后改換材料要比開始生產前改換材料所花費的代價要高。在生產設計階段做好材料選擇工作，可以避免大多數(shù)的這種材料更換情況。在生產開始后出現(xiàn)了可供使用的新材料是更換材料的最常見的原因。當然，這些新材料可能降低成本、改進產品性能。但是，必須對新材

15、料進行認真評價，以確保其所有性能都被人們所了解。應當時刻牢記，新材料的性能和可靠性很少能像現(xiàn)有材料那樣為人們所了解。大部分的產品失效和產品責任事故案件是由于在選用新材料作為替代材料之前，沒有真正了解它們的長期使用性能而引起的。</p><p><b>　　1 外文資料原文</b></p><p><b>　　Mechanism</b></p

16、><p>　　A mechanism has been defined as“a combination of rigid or resistant bodies so formed and connected that they move upon each other with definite relative motion.”</p><p>　　Mechanisms form the

17、 basic geometrical element 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

18、 a rigid body relative to a reference member. Kinematic design of mechanisms is often the first step in the design of a complete machine. When force are considered, the additional problem of dynamics, bearing loads, stre

19、sses, lubrication ,and the like are intro</p><p>　　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. There are three types of c

20、ommon mechanical devices that can be used as basic elements of a mechanism.</p><p>　　Gear Systems Ger systems, in which toothed members in contact transmit motion between rotating shafts. Gear normally are u

21、sed for the transmission of motion with a constant angular velocity ratio, although noncircular gears can be used for nonuniform transmission of motion.</p><p>　　Cam Systems Cam systems, where a uniform mot

22、ion of an input member is converted into a nonuniform motion of the output member. The output motion may be either shaft rotation, slider translation, or other follow </p><p>　　motions created by direct cont

23、act between the input cam shape and the follower. 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

24、 function of the input motion.</p><p>　　Plane and Spatial Linkage they are also useful in creating mechanical motions for a point or rigid body. Linkages can be used for three basic tasks.</p><p&g

25、t;　　(1)Rigid body guidance. A rigid body guidance mechanism is used to guide a rigid body through a series of prescribed positions in space.</p><p>　　(2)Path generation. A path generation mechanism will guid

26、e a point on a rigid body through a series of points on a specified path in space.</p><p>　　(3)Function generation. A mechanism that creates an output motion that is a specified function of the input motion.

27、</p><p>　　Mechanisms may be categorized in several different ways to emphasize their similarities and differences, One such grouping divides mechanisms into planar, spherical, and spatial categories. All thr

28、ee groups have many things in common; the criterion which distinguishes the groups, however, is to be found in the characteristics of the motion of the links.</p><p>　　A planar mechanism is one in which all

29、particles describe plane curves in space and all those curves lie in parallel planes; i.e., the loci of all points re plane curves parallel to a single common plane. This characteristic makes it possible to present the l

30、ocus of any chosen point of a planar mechanism in its true size and shape on a single drawing or figure. The plane four-bar linkage, the plate cam and follower, and the slider-crank mechanism are familiar examples of pla

31、nar mechanism. The va</p><p>　　A spherical mechanism is one in which each link has some point which remains stationary as the linkage moves and in which the stationary point of all links lie at a common loca

32、tion; i.e. ,the locus of each point is a curve contained in a spherical surface ,and the spherical surfaces defined by several arbitrarily chosen points are all concentric . The motions of all particles can therefore be

33、completely described by their radial projections, or“shadows,” on the surface of a sphere with properly </p><p>　　Spatial mechanisms, on the other hand, include no restrictions on the relative motions of the

34、 particles. The motion transformation is not necessarily coplanar, nor must it be concentric. A spatial mechanism may have particles with loci of double curvature. Any linkage which contains a screw pair, for example, is

35、 a spatial mechanism, since the relative motion within a screw pair is helical.</p><p>　　Materials selection</p><p>　　During recent years the selection of engineering materials has assumed great

36、 importance. Moreover the process should be one of continual reevaluation. New materials often become available and there may be a decreasing availability of others. Concerns regarding environmental pollution, recycling

37、and worker health and safety often impose new constraints. The desire for weight reduction or energy savings may dictate the use of different materials. Pressures from domestic and foreign competition, in</p><

38、p>　　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. During the conceptual-design stage, the desi

39、gner is concerned primarily with the functions the product is so fulfill. Usually several concept are visualized and considered, and a decision is made either that the idea is not practical or that the idea is sound and

40、 one or more of the conceptual designs should be developed further.</p><p>　　At the functional- or engineering-design stage, a practical, workable design is developed. Fairly complete drawings are made, an

41、d materials are selected and specified for the various components. Often a prototype or working model is made that can be tested to permit evaluation of the product as to function, reliability, appearance, serviceabilit

42、y, and so on. Although it is expected that such testing might show that some changes may have to be made in materials before the product is advanced </p><p>　　At the production-design stage ,the primary con

43、cern 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

44、.</p><p>　　As manufacturing progresses , it is inevitable that situations will arise that may require modifications of the materials being used. Experience may reveal that substitution of cheaper materials

45、can be made .In most cases, however, changes are much more costly to make after manufacturing is in progress than before it starts. Good selection during the production-design phase will eliminate the necessity for thi

46、s type of change . The more common type of change that occurs after manufacturing st</p><p>　　Product liability actions have made it imperative that designers and companies employ the very best procedures in

47、 selecting materials. The five most common faults in material selection have been (a) failure to know and use the latest and best information available about the materials utilized; (b) failure to foresee, and take int

48、o account the reasonable uses for the product (where possible ,the designer is further advised to foresee and account for misuse of the product, as there have been ma</p><p>　　An examination of the faults a

49、bove will lead one to conclude that there is no good reason why they should exist .Consideration of them provides guidance as to how they can be eliminated. While following the very best methods in material selection ma

50、y not eliminated all product-liability claims, the use of proper procedures by designers and industries can greatly reduce their numbers.</p><p>　　From the previous discussion, it is apparent that those who