【中英文】機構(gòu)

1、原文mechanisma mechanism has been defined as “a combination of rigid or resistant bodies 80 formed and connected that they move upon each other with definite relative motion”mechanisms form the basic geometrical elements of many mechanical devices including automatic packaging machinery，typewriters，me

2、chanical toys，textile machinery，and othersa mechanism typically is designed to create a desired motion of a rigid body relative to a reference memberkinematic design of mechanisms is often the first step in the design of a complete machinewhen forces fire comidered, the additional problems of dynami

3、cs，baring loads，stresses，lubrication，and the like are introduced，and the larger problem becomes one of machine design the function of a mechanism is to transmit or transform motion from one rigid body to another as part of the action of a machinethere are three types of common mechanical devices tha

4、t can be used as basic elements of a mechanismgear systems gear systems，in which toothed members in contact transmit motion between rotating shaftsgears normolly are used for the transmission of motion with a constant angular velocity ratio，although noncircular gears can be used for nonuniform trans

5、mission of motioncam systems cam systems，where a uniform motion of an input member is converted into a nonuniform motion of the output memberthe output motion may be either shaft rotation，slider translation，or other follower motions created by direct contact between the input cam shape and the follo

6、werthe kinematic design of earns 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 motionplane and spatial linkages they are also useful in creating mechanical motions for a point or rig

7、id bodylinkages can be used for three basic tasks(1)rigid body guidancea rigid body guidance mechanism is used to guide a rigid body through a series of prescribed positions in space(2)path generationa path generation mechanism will guide a point on a rigid body through a series of points on a speci

8、fied path in space (3)function generationa mechanism that creates all output motion that is a specified function of the input motion mechanisms may be categorized in several different ways to emphasize their similarities and differencesone such grouping divides mechanisms into planar，spherical，and s

9、patial categoriesall three groups have many things in common；the criterion which distinguishes the groups，however，is to be found in the characteristics of the motions of the links a planar mechanism is one in which all particles describe plane curves in space and all these curves lie in parallel pla

10、nes；ie，the loci of all points are plane curves parallel to a single common planethis characteristic makes it possible to represent the locus of any chosen point of a planar mechanism in its true size and shape on a single drawing or figurethe plane four-bar linkage，the plate cam and follower，and the

11、 slider-crank mechanism are familiar examples of planar mechanismsthe vast majority of mechanisms in use today are planara spherical mechanism is one in which each link has some point which remains stationary as the linkage moves and in which the stationary points of all links lie at a common locati

12、on；ie，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 concentricthe motions of all particles call therefore be completely described by their radial projections，or ”shadows，”on the surface of a sphere

13、with properly chosen centerhookes universal joint is perhaps the most familiar example of a spherical mechanismspatial mechanisms，on the other hand，include no restrictions oil the relative motions of the particlesthe motion transformation is not necessarily coplanar，nor must it be concentrica spatia

14、l mechanism may have particles with loci of double curvatureany linkage which contains a screw pair，for example, is a spatial mechanism, since the relative motion within a screw pair is helicalthe function of mechanism is to transmit or transform motion from one rigid body to another as part of the

15、action of a machinethere are three types of common mechanical devices that can be used as basic elements of a mechanism(1)gear system，in which toothed members in contact transmit motion between rotating shafts(2)cam system，where a uniform motion of an input member is converted into a nonuniform moti

16、on of the output member(3)plane and spatial linkages are also useful in creating mechanical motions for a point or rigid body a kinematic chain is a system of linkswhich are either jointed together or are in contact with one another in a manner that permits them to move relative to one another. if o

17、ne of the links is fixed 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 unconstrained kinematic chain a mechanism or linkage is a constrained ki

18、nematic chain，and is a mechanical device that has the purpose of transferring motion andor force from a source to an outputa linkage consists of links(or bars)，generally considered rigid，which are connected byjoints，such as pin (or revolute) or prismatic joints，to form open or closed chains (or loop

19、s)such kinematic chains，with at least one link fixed，become (i) mechanisms if at least two other links remain mobility, or(ii)structures if no mobility remainsin other words，a mechanism permits relative motion between its “rigid links”; a structure does notsince linkages make simple mechanisms and c

20、an be designed to perform complex tasks，such as nonlinear motion and force transmission，they will receive much attention in mechanism study mechanisms are used in a great variety of machines and devicesthe simplest closedloop linkage is the four-bar linkage，which has three moving links (plus one fix

21、ed link) and four pin jointsthe link that is connected to the power source or prime mover and has one moving pivot and one ground pivot is called the input linkthe output link connects another moving pivot to another ground pivotthe coupler or floating link connected the two moving pivots，thereby “c

22、oupling”the input to the output link the four-bar linkage has some special configurations created by making one or more links infinite in lengththe slider-crank (or crank and slider) mechanism is a four-bar chain with a slider replacing an infinitely long output linkthe internal combustion engine is

23、 built based on this mechanismother forms of four-link mechanisms exist in which a slider is guided on a moving link rather than on a fixed linkthese are called inversions of the slidercrank，produced when another link (the crank，coupler, or slider) is fixed linkalthough the four-bar linkage and slid

24、er-crank mechanism are very useful and found in thousands of applications，we can see that these linkages have limited performance level linkages with more members are often used in more demanding circumstanceshowever it is often difficult to visualize the movement of a multiloop linkage，especially w

25、hen other components appear in the same diagramthe first step in the motion analysis of more complicated mechanisms is to sketch the equivalent kinematic or skeleton diagramthe skeleton diagram serves a purpose similar to that of the electrical schematic or circuit diagram in that it displays only t

26、he essential skeleton of the mechanism，which，however, embodies the key dimensions that affect its motionthe kinematic diagram takes one of two forms：a sketch (proportional but not exactly to scale)，and the scaled kinematic diagram (usually used to further analysis：position，displacement，velocity, acc

27、eleration，force and torque transmission，etc)for convenient reference，the links are numbered (starting with ground link as number 1)，while the joints are lettered the next step in the kinematic analysis of mechanisms is to determine the number of degree of freedom of the mechanismby degree of freedom

28、 we mean the number of independent inputs required to determine the positions of all links of the mechanism with respect to groundthere are hundreds of thousands of different linkage types that one could inventenvision a bag containing a large variety of linkage components：binary，ternary，quaternary,

29、 and so on，links；pin joints， slide joints；cams and cam followers；gears，chains，sprockets，belts，pulleys，and so on(spherical and helical joints as well as other connections that allow three-dimensional relative motion are not included，as only planar motion in parallel planes are discussed here)furtherm

30、ore，imagine the possibility of forming all sorts of linkage types by putting these components togetherare there any rules that help govern how these mechanisms are formed? actually most mechanism tasks require a single input to be transferred to a single outputtherefore，single-degree-of-freedom mech

31、anisms are the forms used most frequentlyfor example，it is easy to see intuitively that a four-bar linkage is a single-degree-or-freedom linkagethe process of drawing kinematic diagrams and determining degrees of freedom of mechanisms are the first steps in both the kinematic analysis and synthesis

32、processin kinematic analysis，a particular given mechanism is investigated based on the mechanism geometry plus possibly other known characteristicskinematic synthesis，on the other hand，is the process of designing a mechanism to accomplish a desired taskhere，both choosing the type as well as the dime

33、nsions of the new mechanism can be part of kinematic synthesisthe ability to visualize relative motionto reason why a mechanism is designed the way it is， and the ability to improve on a particular design are marks of a successful kinematicianalthough some of this ability comes in the form of innate

34、 creativitymuch of it is a learned skill that improves with practice譯文機構(gòu) 機構(gòu)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(yīng)該具有確定的相對運動?！?機構(gòu)是構(gòu)成許多機械設(shè)備的基本幾何單元，這些機械設(shè)備包括自動包裝機、打字機、機械式玩具、紡織機等等。機構(gòu)設(shè)計的目的通常是使一個剛體相對某一參考構(gòu)件產(chǎn)生所需要的相對運動。機構(gòu)的運動設(shè)計通常是設(shè)計一臺完整的機器的第一步。在考慮力的作用時，應(yīng)該考慮動力學(xué)、軸承載荷、應(yīng)力、潤滑等一系列問題。在所考慮的間題的范圍擴(kuò)大之后，機構(gòu)設(shè)計就變成了機器設(shè)計。 作

35、為機器的一個組成部分，機構(gòu)的作用是在剛體之間傳遞或轉(zhuǎn)換運動。常用的基本機構(gòu)有以下三種: 齒輪機構(gòu) 在這種機構(gòu)中，各轉(zhuǎn)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。 凸輪機構(gòu)在這種機構(gòu)中，輸入件的等速連續(xù)運動被轉(zhuǎn)換成輸出件的不等速運動。輸出的運動可以是軸的轉(zhuǎn)動、滑塊的移動、或者其他從動件的運動。這些運動都是使從動件與作為輸入件的凸輪的輪廓的直接接觸而產(chǎn)生的.凸輪的運動設(shè)計就是采用解析法或者圖解法來確定凸輪的輪廓形狀,使其能帶動從動件實現(xiàn)輸出運動是輸入運動的指定函數(shù)這一功能。平面和空間連桿機構(gòu) 這類機構(gòu)也是用來使機構(gòu)上某一點

36、或者剛體實現(xiàn)機械運動的。連桿的基本作用有三種: (1)剛體導(dǎo)向。剛體導(dǎo)向機構(gòu)用來引導(dǎo)一個剛體，使其通過空間一系列預(yù)定的位置。 (2)實現(xiàn)軌跡 實現(xiàn)軌跡機構(gòu)將引導(dǎo)剛體上的一個點，使其通過指定的空間軌跡上的一系列點。 (3)實現(xiàn)函數(shù)。這類機構(gòu)所產(chǎn)生的輸出運動是輸人運動的指定函數(shù)。 為了強調(diào)各種機構(gòu)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(jìn)行分類。一種分類方式是將機構(gòu)分為平面、球面和空間三類。這三類機構(gòu)有很多共同之處，然而，可以根據(jù)其構(gòu)件的運動特點來確定分類準(zhǔn)則。_._ 在平面機構(gòu)電所有質(zhì)點在空間所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

37、一個共同平面的平面曲線。這一特性使得平面機構(gòu)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(gòu)、平板凸輪和它的從動件、曲柄滑塊機構(gòu)是大家所熟悉的平面機構(gòu)的例子?，F(xiàn)在使用中的大多數(shù)機構(gòu)是平面機構(gòu)。在球面機構(gòu)中，當(dāng)機構(gòu)運動時，每一個構(gòu)件上都有一個點是靜止的，所有構(gòu)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都是同心的。因而，所有質(zhì)點的運動都能用它們在以適當(dāng)選取的點為中心的球面上的徑向投影來完整地進(jìn)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(gòu)的例子。從另一方面來說，在空間機械中質(zhì)點的相對運動不受約束。運動的變換既不

38、要求共面，也不要求同心?？臻g機構(gòu)上許多質(zhì)點的運動軌跡可能具有雙重曲率。例如，任何含有螺旋副的連桿機構(gòu)，由于其相對運動是螺旋線形的，因此是空間機構(gòu)。機構(gòu)是機械運動的一個部分，它的功能是把運動從一個剛體傳遞或轉(zhuǎn)換到另一個剛體。用作機構(gòu)基本零件的一般機械裝置有三種類型：(1)齒輪系統(tǒng)，在回轉(zhuǎn)軸之間通過接觸傳遞運動的齒狀零件。 (2)凸輪系統(tǒng)，把輸入零件的均勻運動轉(zhuǎn)換成輸出零件的非均勻運動的裝置。 (3)平面和空間連桿機構(gòu)，使點或剛體產(chǎn)生機械運動的實用裝置。運動鏈?zhǔn)且粋€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)生相對運動。如果鏈接中的某個連桿被固定，而其它任何一個連桿運動到新的位置將導(dǎo)致其它各個連桿也會運動到確定的預(yù)期位置，該系統(tǒng)就是一個可約束的運動鏈。否則，該系統(tǒng)是一個非約束運動鏈。機構(gòu)或連桿就是一個可約束的傳動鏈，是一個從輸入到輸出以傳遞運動和(或)力為目的的機械裝置。連桿機構(gòu)通常由被認(rèn)為是剛體的構(gòu)件或桿組成，它們之間用銷軸鉸接，例如用柱銷(圓形的)或棱柱體的銷軸鉸接，形成開式或閉式(回環(huán)式)的運動