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譯文題目： Mechanisms And Machine Theory
機構和機器原理
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Mechanisms And Machine Theory
Introduction to Mechanism：
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 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 motion 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 links, that is, rigid bodies , 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 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. If one of the links is held fixed and the movement of any other link to a new position will not cause each of the other links to move to a definite predictable position then the system is an unconstrained kinematic chain,
A mechanism or linkage is a constrained kinematic chain, and is a mechanical device that has the purpose of transferring motion and/or force from a source to an output. A linkage consists of links (or bars), generally considered rigid, which are connected by joints, such as pin Cor revolute) or prismatic joints, to form open or closed chains (or loops). Such kinematic chains, with at least one link fixed, become mechanisms if at least two other links remain mobility, or structures if no mobility remains. In other words, a mechanism permits relative motion between its "rigid links"; a structure does not. Since linkages make simple mechanisms and can 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 devices. The simplest closed-loop linkage 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 input link. The output link connects another moving pivot to another ground pivot. The coupler or floating link connected the two moving pivots, thereby "coupling" the input to the output link.
The four-bar 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 slider replacing an infinitely long output link. The internal combustion engine is built based on this mechanism. Other forms of four-link 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-crank, produced when another link (the crank, coupler, or slider) is fixed link.
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 limited 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 the same diagram. The first step in the motion analyses of more complicated mechanisms is to sketch the equivalent kinematic or skeleton diagram. The skeleton diagram serves a purpose similar to that of the electrical schematic or circuit diagram .
Organization movement analysis second step: Draws a graphic chart, is must determine the organization the number of degrees of freedom. Based on degree of freedom, but Italy refers needs certain independent inputs the movement number, by determined organization all components are opposite in the ground position. The people have thousands of different types conceivably the link motion gear. You may imagine a bag containing massive link motion gear the component: Two pole groups, three pole groups, four pole groups and so on, as well as components, rotation, motion, cam follower, gear, tooth chain, chain wheel, leather belt, belt pulley and so on. (Sphere movement, screw vice-as well as the permission three dimensional relative motion other connections not yet includes, here, discusses in parallel planes merely plane motion). Moreover you conceivable put these components various types link motion gear possibility which forms in the same place. How exists helps the people to control forms these organizations the rule? In fact, the majority organization duty is requests a sole input to transmit to a sole output. Therefore the single degree of freedom organization uses most one kind of organization type. For example, namely may see by the intuition: Four pole organizations are a single degree of freedom link motion gear.
The picture motion diagram and the determination organization degree of freedom process, is the movement analysis and the synthesis process first stage. In the movement analysis, adds on its characteristic according to the organization geometry shape which possibly knew (for example input angle, speed, angle acceleration and so on) studies the determination concrete organization. On the other hand, the movement synthesis is designs an organization to complete the duty process which an institute requests. In this, chooses the new organization the type and the size is a movement synthesis part. Conceives the relative motion ability, can guess the reason that designs an organization the reason and makes the improvement to a concrete design ability is like this a successful organization scientist's symbol. Although these abilities come from the congenital creativity, however more is because has grasped the technology which enhances from the practice.
The movement analysis：
simple one of most useful organizations is four pole organizations. In on following elaboration majority of content centralism discussion link motion gear, but this procedure is also suitable for the more complex link motion gear.
We already knew four pole organizations have a degree of freedom. About four pole organizations, has the useful more contents which must know? Indeed is some! These pull the Xiao husband criterion including the standard, the transformation concept, the blind spot position (divergence point), branch office, transmission angle, with theirs movement characteristic, including position, speed and acceleration.
Four pole organizations may have one kind of being called as crank rocker organization form, one kind of double rocking lever organization, one kind of double crank (tension bar) does the organization, which one form send in is called as the organization, is decided in two pole movement scopes which (fixed component) connects with the rack. The crank rocker organization input component, the crank may revolve through 360° and the continuous rotation, but outputs the component to make the undulation merely (i.e. swing member). As an exceptional case, in the parallel four pole organization, inputs the pole the length to be equal to outputs the pole the length, the go-between length and the fixed link (rack) length, also is equal. Its input and the output all may make the complete alternation rotation or transform the being called as antiparallel quadrangle organization the overlapping structure. The standard pulls the Xiao husband criterion (theorem) to indicate that,If in four pole organizations, between two poles can do willfully relatively rotates continuously, that, its longest pole length is smaller than sum of with the shortest pole length or is equal to sum of the other two pole length.
Should pay attention: The same four pole organization, may have the different form, which pole is this decided in was stipulated (i.e. makes fixed link) as the rack. The movement transformation process is in the fixed organization transmission chain different member has the different organization rate process. Besides has about the component rotation scope knowledge, but also must have how causes the organization before the manufacture on energy “the revolution” the good measure, that will be very useful. Hardenbergh (Hartenberg) speaks of: “The revolution” is terminology, its significance passes to outputs the component the movement validity. It meant the revolution is steady, in which can in output in the component to have a strength or the torque biggest force component is effective. Not only although the final output strength or the torque are the connecting rod geometric figure functions, moreover also is generally the power or the force of inertia result, that is frequently big to like static strength several times. In order to analyze the idling or in order to easy to obtain how can cause any organization “the revolution” the index, the transmission angle concept is extremely useful. In organization movement period, the transmission angle value is changing. The transmission angle 0° may occur in the special position. Will output the pole but in this special position the movement with not to exert inputs on the pole the strength many to have nothing to do with greatly. In fact, as a result of the movement vice-friction influence, the general basis practical experience, with the transmission angle planning board which is bigger than the rating. The weight link motion gear transmission movement ability matrix foundation definition already studied. A determining factor value (it includes regarding some assigns organization graph, position output movement variable to input variable derivative) is a this link motion gear in concrete position mobility criterion.
If the organization has a degree of freedom (e.g. four pole organizations), then stipulated a location parameter, if the input angle, completely determined this organization stops position (neglect branch office's possibility). We may study one about four pole organization component absolute angular position analysis expression. When analyzes certain positions and (or) certain different organization time, this will be must be much more useful than the geometric figure analysis program, because this expression will cause the automated computation easy to program. The realization organization speed analysis relative velocity law is the speed polygon is one of several effective methods. This end (goes against) the spot to represent on the organization all spots, has the zero speed. From this the line which stipples respectively to the speed polygon in is representing the absolute speed which this organization photograph well should select respectively. In a line connection speed polygon random two points represents is taking on this organization two corresponding spot relative velocity.
機構和機器原理
機構介紹：
一個機構的功能是傳送或從一個剛體變換運動到另一個機器的動作的一部分。有三種類型的普通的機械裝置的，可以用來作為一種機構的基本元素。
1．齒輪裝置。那是在回轉軸之間進行接觸傳動的嚙合構件。
2．凸輪裝置。把輸入構件的均勻運動轉換成輸出構件的非均勻運動的裝置。
3．平面機構和空間機構也是能使一個點或一個剛體產(chǎn)生機械運動的有用裝置。
運動鏈是一個構件系統(tǒng)裝置即若干個剛體，它們或者彼此鉸接或者互相接觸，方式上是允許它們彼此間產(chǎn)生相對運動。如果構件中的某一構件被固定而使任何其他一個構件運動到新的位置將會引起其他各個構件也運動到確定的預期的位置上的話，該系統(tǒng)裝置就是一個可約束的運動鏈。如果構件中的某一構件仍保持固定而使任一運動到達一新的位置而不會使其他各個構件運動到一個確定的預期的位置上的話，則該系統(tǒng)裝置是一個非約束運動鏈。
機構或連桿構件是一個可約束的傳動鏈而且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。連桿機構是由通常被認為是剛體構件或桿組成的，它們是以銷軸鉸接的，例如用柱銷（圓形的）或棱柱體銷軸鉸接，以便成形開式或閉式（回環(huán)式）的運動鏈。這樣的運動鏈在至少有一個構件被固定的條件下：如果至少有兩個構件能保持運動，就變?yōu)闄C構，如果沒有一個構件能夠運動，則就成為結構。換句話說，機構是允許其“剛性構件”之間相對運動，而結構則不能。由于連桿機構做成一簡單機構而且能設定實現(xiàn)復雜的任務，例如非線性運動和力的傳遞運動。它們在機構學研究中將受到更多的關注。
機構被用于許多許多的機器和裝置中。最簡單的封閉式的連桿機構就是四桿機構，四桿機構有三個運動構件（加上一個固定構件）并且有四個銷軸。連接動力源的構件即原動件，而具有一個移動鉸和一個固定鉸者叫做輸入構件。輸出構件將一個移動鉸和另一個固定鉸連系起來。連接構件即浮動構件將兩個移動的鉸（回轉副）連系起來，因而連接構件就將輸入傳送到輸出。
四桿機構若使一個或幾個構件無限長而產(chǎn)生某些特殊的構造。曲柄滑塊（即曲柄和滑塊）機構就是一個四桿機構特例。其以一個滑塊替換一個無限長的輸出件。內(nèi)燃機就是建立在這一機構基礎上。有著另一種形式的四桿機構，其中滑塊是在一運動的構件上導移運動而不是在一固定構件上。這些就被稱為曲柄滑塊機構的變換，它是其中一個構件（曲柄、連桿或滑塊）被固定時形成的。
雖然四桿機構和曲柄滑塊機構是非常有用而且在成千上萬的應用中都可找到。但是我們還看到，這些連桿機構其性能水平的發(fā)揮已經(jīng)受到限制。具有更多構件的連桿機構常常用于更多要求的情況中。然而可以設想多回環(huán)的連桿機構的運動常常是更為困難的，特別是當其他零件出現(xiàn)在同一圖中的時候，要進行更復雜機構的運動分析：第一步是繪制一等效運動圖即示意圖。這示意圖用于電路圖解類似的目的，即僅僅表示機構的主要本質(zhì)的意圖，然而它要體現(xiàn)影響其運動的關鍵的尺寸。運動圖可用兩種形式中的一種：一是草圖，二是比例準確的運動圖。
機構運動分析的第二步：畫一個圖解圖，是要確定機構的自由度數(shù)。依據(jù)自由度，可意指需要若干個獨立輸入的運動的數(shù)目，以確定機構所有的構件相對于地面的位置。人們可以想象存在數(shù)以千計的不同類型的連桿機構。你可想象一個袋子包容大量的連桿機構的組元：二桿組，三桿組，四桿組等等，以及構件，回轉副，移動副，凸輪隨動件，齒輪，齒鏈，鏈輪，皮帶，皮帶輪等等。（球形運動副，螺旋副以及允許三維相對運動的其他連接尚未包括進去，這里，僅僅討論平行平面內(nèi)的平面運動）。而且你可以想象一下把這些組元放在一起而形成的各種類連桿機構的可能性。存在如何幫助人們控制所形成這些機構的規(guī)律嗎？實際上，大多數(shù)機構的任務是要求一個單一的輸入被傳遞到一個單一的輸出。因此單一自由度的機構是使用最多的一種機構類型。例如，由直觀可以看出：四桿機構就是一個單一自由度的連桿機構。
畫運動圖和確定機構自由度的過程，就是運動分析和綜合過程的第一個階段。在運動分析中，根據(jù)機構的幾何形狀加上可能知道的其特性（如輸入角、速度，角加速度等）來研究確定具體的機構。另一方面，運動綜合則是設計一個機構以完成一個所要求的任務的過程。于此，選擇新機構的類型和尺寸是運動綜合的一個部分。設想相對運動的能力，能推想出之所以這樣設計一個機構的原因和對一個具體設計進行改進的能力是一個成功的機構學家的標志。雖然這些能力來自先天的創(chuàng)造性，然而更多的是因為掌握了從實踐中提高技術。
運動分析：
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(nèi)容集中討論連桿機構上，而該程序也適用于更復雜的連桿機構。
我們已經(jīng)知道四桿機構具有一個自由度。關于四桿機構，有沒有要知道的有用的更多內(nèi)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。
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，曲柄可旋轉通過360°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結構。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。
應該注意：相同的四桿機構，可有不同的形式，這取決于哪一根桿被規(guī)定作為機架（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(chǎn)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之前就能“運轉”的良好措施，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。它意味著運轉平穩(wěn)，其中能在輸出構件中產(chǎn)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桿幾何圖形的函數(shù)，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)力的幾倍。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(shù)，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°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力多大無關。事實上，由于運動副摩擦的影響，一般根據(jù)實際經(jīng)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(jīng)研究出來。一個決定性因素的值（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(shù)）是該連桿機構在具體位置中的可動性的一個尺度。
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(shù)，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角位置的分析表達式。當分析若干位置和（或）若干不同機構時候，這將是比幾何圖形分析程序要有用得多，因為該表達式將使自動化計算易于編程。實現(xiàn)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畫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兩個對應的點的相對速度。