外文翻譯--機(jī)構(gòu)和機(jī)器原理【中英文文獻(xiàn)譯文】,中英文文獻(xiàn)譯文,外文,翻譯,機(jī)構(gòu),以及,機(jī)器,原理,中英文,文獻(xiàn),譯文
中文翻譯
機(jī)構(gòu)和機(jī)器原理
1.機(jī)構(gòu)介紹：
機(jī)構(gòu)的功用是作為機(jī)械作用的一個(gè)部分從一個(gè)剛體到另一個(gè)剛體傳送即傳遞運(yùn)動(dòng)。
一般能用作機(jī)構(gòu)基本零件的機(jī)械裝置有三種類(lèi)型：
1．齒輪裝置。那是在回轉(zhuǎn)軸之間進(jìn)行接觸傳動(dòng)的嚙合構(gòu)件。
2．凸輪裝置。把輸入構(gòu)件的均勻運(yùn)動(dòng)轉(zhuǎn)換成輸出構(gòu)件的非均勻運(yùn)動(dòng)的裝置。
3．平面機(jī)構(gòu)和空間機(jī)構(gòu)也是能使一個(gè)點(diǎn)或一個(gè)剛體產(chǎn)生機(jī)械運(yùn)動(dòng)的有用裝置。
運(yùn)動(dòng)鏈?zhǔn)且粋€(gè)構(gòu)件系統(tǒng)裝置即若干個(gè)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(duì)運(yùn)動(dòng)。如果構(gòu)件中的某一構(gòu)件被固定而使任何其他一個(gè)構(gòu)件運(yùn)動(dòng)到新的位置將會(huì)引起其他各個(gè)構(gòu)件也運(yùn)動(dòng)到確定的預(yù)期的位置上的話(huà)，該系統(tǒng)裝置就是一個(gè)可約束的運(yùn)動(dòng)鏈。如果構(gòu)件中的某一構(gòu)件仍保持固定而使任一運(yùn)動(dòng)到達(dá)一新的位置而不會(huì)使其他各個(gè)構(gòu)件運(yùn)動(dòng)到一個(gè)確定的預(yù)期的位置上的話(huà)，則該系統(tǒng)裝置是一個(gè)非約束運(yùn)動(dòng)鏈。
機(jī)構(gòu)或連桿構(gòu)件是一個(gè)可約束的傳動(dòng)鏈而且是一個(gè)從輸入到輸出以傳遞運(yùn)動(dòng)和（或）力為目的的機(jī)械裝置。連桿機(jī)構(gòu)是由通常被認(rèn)為是剛體構(gòu)件或桿組成的，它們是以銷(xiāo)軸鉸接的，例如用柱銷(xiāo)（圓形的）或棱柱體銷(xiāo)軸鉸接，以便成形開(kāi)式或閉式（回環(huán)式）的運(yùn)動(dòng)鏈。這樣的運(yùn)動(dòng)鏈在至少有一個(gè)構(gòu)件被固定的條件下：（1）如果至少有兩個(gè)構(gòu)件能保持運(yùn)動(dòng)，就變?yōu)闄C(jī)構(gòu)，（2）如果沒(méi)有一個(gè)構(gòu)件能夠運(yùn)動(dòng)，則就成為結(jié)構(gòu)。換句話(huà)說(shuō)，機(jī)構(gòu)是允許其“剛性構(gòu)件”之間相對(duì)運(yùn)動(dòng)，而結(jié)構(gòu)則不能。由于連桿機(jī)構(gòu)做成一簡(jiǎn)單機(jī)構(gòu)而且能設(shè)定實(shí)現(xiàn)復(fù)雜的任務(wù)，例如非線(xiàn)性運(yùn)動(dòng)和力的傳遞運(yùn)動(dòng)。它們?cè)跈C(jī)構(gòu)學(xué)研究中將受到更多的關(guān)注。
機(jī)構(gòu)被用于許多許多的機(jī)器和裝置中。最簡(jiǎn)單的封閉式的連桿機(jī)構(gòu)就是四桿機(jī)構(gòu)，四桿機(jī)構(gòu)有三個(gè)運(yùn)動(dòng)構(gòu)件（加上一個(gè)固定構(gòu)件）并且有四個(gè)銷(xiāo)軸。連接動(dòng)力源的構(gòu)件即原動(dòng)件，而具有一個(gè)移動(dòng)鉸和一個(gè)固定鉸者叫做輸入構(gòu)件。輸出構(gòu)件將一個(gè)移動(dòng)鉸和另一個(gè)固定鉸連系起來(lái)。連接構(gòu)件即浮動(dòng)構(gòu)件將兩個(gè)移動(dòng)的鉸（回轉(zhuǎn)副）連系起來(lái)，因而連接構(gòu)件就將輸入傳送到輸出。
四桿機(jī)構(gòu)若使一個(gè)或幾個(gè)構(gòu)件無(wú)限長(zhǎng)而產(chǎn)生某些特殊的構(gòu)造。曲柄滑塊（即曲柄和滑塊）機(jī)構(gòu)就是一個(gè)四桿機(jī)構(gòu)特例。其以一個(gè)滑塊替換一個(gè)無(wú)限長(zhǎng)的輸出件。內(nèi)燃機(jī)就是建立在這一機(jī)構(gòu)基礎(chǔ)上。有著另一種形式的四桿機(jī)構(gòu)，其中滑塊是在一運(yùn)動(dòng)的構(gòu)件上導(dǎo)移運(yùn)動(dòng)而不是在一固定構(gòu)件上。這些就被稱(chēng)為曲柄滑塊機(jī)構(gòu)的變換，它是其中一個(gè)構(gòu)件（曲柄、連桿或滑塊）被固定時(shí)形成的。
雖然四桿機(jī)構(gòu)和曲柄滑塊機(jī)構(gòu)是非常有用而且在成千上萬(wàn)的應(yīng)用中都可找到。但是我們還看到，這些連桿機(jī)構(gòu)其性能水平的發(fā)揮已經(jīng)受到限制。具有更多構(gòu)件的連桿機(jī)構(gòu)常常用于更多要求的情況中。然而可以設(shè)想多回環(huán)的連桿機(jī)構(gòu)的運(yùn)動(dòng)常常是更為困難的，特別是當(dāng)其他零件出現(xiàn)在同一圖中的時(shí)候，要進(jìn)行更復(fù)雜機(jī)構(gòu)的運(yùn)動(dòng)分析：第一步是繪制一等效運(yùn)動(dòng)圖即示意圖。這示意圖用于電路圖解類(lèi)似的目的，即僅僅表示機(jī)構(gòu)的主要本質(zhì)的意圖，然而它要體現(xiàn)影響其運(yùn)動(dòng)的關(guān)鍵的尺寸。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，但放大比例不精確），二是比例準(zhǔn)確的運(yùn)動(dòng)圖（通常用于進(jìn)一步分析其位置、位移、速度，加速度，力和扭矩傳遞等等）。為了便于參考，對(duì)構(gòu)件進(jìn)行順序編號(hào)，（以靜止構(gòu)件編號(hào)為1開(kāi)始編寫(xiě)），而回轉(zhuǎn)副則以字母表示。
機(jī)構(gòu)運(yùn)動(dòng)分析的第二步：畫(huà)一個(gè)圖解圖，是要確定機(jī)構(gòu)的自由度數(shù)。依據(jù)自由度，可意指需要若干個(gè)獨(dú)立輸入的運(yùn)動(dòng)的數(shù)目，以確定機(jī)構(gòu)所有的構(gòu)件相對(duì)于地面的位置。人們可以想象存在數(shù)以千計(jì)的不同類(lèi)型的連桿機(jī)構(gòu)。你可想象一個(gè)袋子包容大量的連桿機(jī)構(gòu)的組元：二桿組，三桿組，四桿組等等，以及構(gòu)件，回轉(zhuǎn)副，移動(dòng)副，凸輪隨動(dòng)件，齒輪，齒鏈，鏈輪，皮帶，皮帶輪等等。（球形運(yùn)動(dòng)副，螺旋副以及允許三維相對(duì)運(yùn)動(dòng)的其他連接尚未包括進(jìn)去，這里，僅僅討論平行平面內(nèi)的平面運(yùn)動(dòng)）。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(lèi)連桿機(jī)構(gòu)的可能性。存在如何幫助人們控制所形成這些機(jī)構(gòu)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)是使用最多的一種機(jī)構(gòu)類(lèi)型。例如，由直覺(jué)即可以看出：四桿機(jī)構(gòu)就是一個(gè)單一自由度的連桿機(jī)構(gòu)。
畫(huà)運(yùn)動(dòng)圖和確定機(jī)構(gòu)自由度的過(guò)程，就是運(yùn)動(dòng)分析和綜合過(guò)程的第一個(gè)階段。在運(yùn)動(dòng)分析中，根據(jù)機(jī)構(gòu)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(lái)研究確定具體的機(jī)構(gòu)。另一方面，運(yùn)動(dòng)綜合則是設(shè)計(jì)一個(gè)機(jī)構(gòu)以完成一個(gè)所要求的任務(wù)的過(guò)程。于此，選擇新機(jī)構(gòu)的類(lèi)型和尺寸是運(yùn)動(dòng)綜合的一個(gè)部分。設(shè)想相對(duì)運(yùn)動(dòng)的能力，能推想出之所以這樣設(shè)計(jì)一個(gè)機(jī)構(gòu)的原因和對(duì)一個(gè)具體設(shè)計(jì)進(jìn)行改進(jìn)的能力是一個(gè)成功的機(jī)構(gòu)學(xué)家的標(biāo)志。雖然這些能力來(lái)自先天的創(chuàng)造性，然而更多的是因?yàn)檎莆樟藦膶?shí)踐中提高的技術(shù)。
1.1運(yùn)動(dòng)分析：
最簡(jiǎn)單最有用的機(jī)構(gòu)之一是四桿機(jī)構(gòu)。以下論述中的大部分內(nèi)容集中討論連桿機(jī)構(gòu)上，而該程序也適用于更復(fù)雜的連桿機(jī)構(gòu)。
我們已經(jīng)知道四桿機(jī)構(gòu)具有一個(gè)自由度。關(guān)于四桿機(jī)構(gòu)，有沒(méi)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(zhǔn)則，變換的概念，死點(diǎn)的位置（分歧點(diǎn)），分支機(jī)構(gòu)，傳動(dòng)角，和他們的運(yùn)動(dòng)特征，包括位置，速度和加速度。
四桿機(jī)構(gòu)可具有一種稱(chēng)作曲柄搖桿機(jī)構(gòu)的形式，一種雙搖桿機(jī)構(gòu)，一種雙曲柄（拉桿）機(jī)構(gòu)，致于稱(chēng)作哪一種形式的機(jī)構(gòu)，取決于跟機(jī)架（固定構(gòu)件）相連接的兩桿的運(yùn)動(dòng)范圍。曲柄搖桿機(jī)構(gòu)的輸入構(gòu)件，曲柄可旋轉(zhuǎn)通過(guò)360°并連續(xù)轉(zhuǎn)動(dòng)，而輸出構(gòu)件僅僅作搖動(dòng)（即搖擺的桿件）。作為一個(gè)特例，在平行四桿機(jī)構(gòu)中，輸入桿的長(zhǎng)度等于輸出桿的長(zhǎng)度，連接桿的長(zhǎng)度和固定桿（機(jī)架）的長(zhǎng)度，也是相等的。其輸入和輸出都可以作整周轉(zhuǎn)動(dòng)或者轉(zhuǎn)換成稱(chēng)作反平行四邊形機(jī)構(gòu)的交叉結(jié)構(gòu)。格拉肖夫準(zhǔn)則（定理）表明：如果四桿機(jī)構(gòu)中，任意兩桿之間能作連續(xù)相對(duì)轉(zhuǎn)動(dòng)，那么，其最長(zhǎng)桿長(zhǎng)度與最短桿長(zhǎng)度之和就小于或等于其余兩桿長(zhǎng)度之和。
應(yīng)該注意：相同的四桿機(jī)構(gòu)，可有不同的形式，這取決于哪一根桿被規(guī)定作為機(jī)架（即作固定桿）。運(yùn)動(dòng)變換的過(guò)程就是固定機(jī)構(gòu)傳動(dòng)鏈中的不同的桿件以產(chǎn)生不同的機(jī)構(gòu)運(yùn)動(dòng)過(guò)程。除了具備關(guān)于構(gòu)件回轉(zhuǎn)范圍的知識(shí)之外，還要具備如何使機(jī)構(gòu)在制造之前就能“運(yùn)轉(zhuǎn)”的良好措施，那將是很有用的。哈登伯格（Hartenberg）說(shuō)到：“運(yùn)轉(zhuǎn)”是一個(gè)術(shù)語(yǔ)，其意義是傳給輸出構(gòu)件的運(yùn)動(dòng)的有效性。它意味著運(yùn)轉(zhuǎn)平穩(wěn)，其中能在輸出構(gòu)件中產(chǎn)生一個(gè)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(dòng)力或慣性力的結(jié)果，那常常是大到如靜態(tài)力的幾倍。為了分析低速運(yùn)轉(zhuǎn)或?yàn)榱艘子讷@得如何能使任一機(jī)構(gòu)“運(yùn)轉(zhuǎn)”的指數(shù)，傳動(dòng)角的概念是非常有用的。在機(jī)構(gòu)運(yùn)動(dòng)期間，傳動(dòng)角的值在改變。傳動(dòng)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(yùn)動(dòng)而與施加到輸入桿上的力多大無(wú)關(guān)。事實(shí)上，由于運(yùn)動(dòng)副摩擦的影響，一般根據(jù)實(shí)際經(jīng)驗(yàn)，用比規(guī)定值大的傳動(dòng)角去設(shè)計(jì)機(jī)構(gòu)。衡量連桿機(jī)構(gòu)傳遞運(yùn)動(dòng)能力的矩陣基礎(chǔ)的定義已經(jīng)研究出來(lái)。一個(gè)決定性因素的值（它含有對(duì)于某個(gè)給定機(jī)構(gòu)圖形，位置的輸出運(yùn)動(dòng)變量對(duì)輸入變量的導(dǎo)數(shù)）是該連桿機(jī)構(gòu)在具體位置中的可動(dòng)性的一個(gè)尺度。
如果機(jī)構(gòu)具有一個(gè)自由度（例如四桿機(jī)構(gòu)），則規(guī)定的一個(gè)位置參數(shù)，如輸入角，就將完全確定該機(jī)構(gòu)休止的位置（忽視分支機(jī)構(gòu)的可能性）。我們可研究一個(gè)關(guān)于四桿機(jī)構(gòu)構(gòu)件絕對(duì)角位置的分析表達(dá)式。當(dāng)分析若干位置和（或）若干不同機(jī)構(gòu)時(shí)候，這將是比幾何圖形分析程序要有用得多，因?yàn)樵摫磉_(dá)式將使自動(dòng)化計(jì)算易于編程。實(shí)現(xiàn)機(jī)構(gòu)速度分析的相對(duì)速度法即速度多邊形是幾種有效的方法之一。這端（頂）點(diǎn)代表著機(jī)構(gòu)上所有的點(diǎn)，具有零速度。從該點(diǎn)到速度多邊形上的各點(diǎn)畫(huà)的線(xiàn)代表著該機(jī)構(gòu)上相應(yīng)各點(diǎn)的絕對(duì)速度。一根線(xiàn)連接速度多邊形上的任意兩點(diǎn)就代表著作為該機(jī)構(gòu)上兩個(gè)對(duì)應(yīng)的點(diǎn)的相對(duì)速度。
另外的方法就是瞬時(shí)中心法，即瞬心法，該方法是非常有用的而且常常是在復(fù)雜連桿機(jī)構(gòu)分析時(shí)較快的方法。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）三中心理論就非常有用。它是說(shuō)：彼此相對(duì)運(yùn)動(dòng)的三個(gè)物體的三個(gè)瞬心必定是在一直線(xiàn)上。
機(jī)構(gòu)各構(gòu)件的加速度是令人感興趣的，因?yàn)樗绊憫T性力，繼而影響機(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，所有加速度的各分量都應(yīng)一次性地畫(huà)在同一坐標(biāo)系中——機(jī)構(gòu)的固定構(gòu)件的慣性坐標(biāo)系中表示出來(lái)。
應(yīng)注意的是：相對(duì)于固定回轉(zhuǎn)副的回轉(zhuǎn)剛體上的一點(diǎn)加速度分量通常有兩個(gè)。一個(gè)分力方向切于該點(diǎn)的軌跡，其指向與該物體的角加速度方向相同，并被稱(chēng)為切向加速度。它的存在完全是由于角速度的變化率引起的。
另一個(gè)分量，總是指向物體的回轉(zhuǎn)中心，被稱(chēng)為標(biāo)準(zhǔn)的向心加速度，這個(gè)分量由于速度矢量的方向發(fā)生改變而存在。
運(yùn)動(dòng)的綜合：
機(jī)構(gòu)是形成許多機(jī)械裝置的基本幾何結(jié)構(gòu)單元，這些機(jī)械裝置包括自動(dòng)包裝機(jī)、打印機(jī)、機(jī)械玩具、紡織機(jī)械和其他機(jī)械等。典型的機(jī)構(gòu)要設(shè)計(jì)成使剛性構(gòu)件相對(duì)基準(zhǔn)構(gòu)件產(chǎn)生所希望的運(yùn)動(dòng)。機(jī)構(gòu)的運(yùn)動(dòng)設(shè)計(jì)即運(yùn)動(dòng)的綜合，第一步常常是先設(shè)計(jì)整部機(jī)器。當(dāng)考慮受力時(shí)，要提出動(dòng)力學(xué)方面的問(wèn)題，軸承的荷載、應(yīng)力、潤(rùn)滑等類(lèi)似的問(wèn)題，而較大的問(wèn)題是機(jī)器結(jié)構(gòu)問(wèn)題。
運(yùn)動(dòng)學(xué)家把運(yùn)動(dòng)學(xué)定義為“研究機(jī)構(gòu)的運(yùn)動(dòng)和創(chuàng)建機(jī)構(gòu)的方法”。這個(gè)定義的第一部分就涉及運(yùn)動(dòng)學(xué)分析。已知一個(gè)機(jī)構(gòu)，其構(gòu)成的運(yùn)動(dòng)特性將由運(yùn)動(dòng)學(xué)分析來(lái)確定。敘述運(yùn)動(dòng)分析的任務(wù)包含機(jī)構(gòu)的主要尺寸、構(gòu)件間的相互連結(jié)和輸入運(yùn)動(dòng)的技術(shù)特性或驅(qū)動(dòng)方法。目的是要找出位移、速度、加速度、沖擊或跳動(dòng)（二階加速度），和可能發(fā)生的各構(gòu)件的高階加速度以及所描述徑跡和由某些構(gòu)件來(lái)實(shí)現(xiàn)的運(yùn)動(dòng)。定義的第二部分可用以下兩方面來(lái)解釋?zhuān)?
1．研究借助機(jī)構(gòu)來(lái)產(chǎn)生給定運(yùn)動(dòng)的方法
2．研究建造能產(chǎn)生給定運(yùn)動(dòng)機(jī)構(gòu)的方法，在兩個(gè)方案中，運(yùn)動(dòng)是給定的而機(jī)構(gòu)是創(chuàng)建的。這就是運(yùn)動(dòng)綜合的本質(zhì)。這樣運(yùn)動(dòng)綜合涉及到為給定性能的機(jī)構(gòu)的系統(tǒng)設(shè)計(jì)。運(yùn)動(dòng)綜合方面又可歸結(jié)為以下兩類(lèi)：
1．類(lèi)型綜合。規(guī)定所要求的性能，怎樣一種類(lèi)型的機(jī)構(gòu)才是合適的？（齒輪系，連桿機(jī)構(gòu)？還是凸輪機(jī)構(gòu)？）而機(jī)構(gòu)應(yīng)具有多少構(gòu)件？需要多少個(gè)自由度？怎樣的輪廓結(jié)構(gòu)才是所希望的？等等。關(guān)于桿件數(shù)目和自由度的考慮通常被認(rèn)為是類(lèi)型綜合中被稱(chēng)作為數(shù)量綜合的一個(gè)分支領(lǐng)域。
2．尺寸綜合。運(yùn)動(dòng)綜合的第二個(gè)主要類(lèi)型是通過(guò)目標(biāo)法來(lái)確定的最佳方法。尺寸綜合試圖確定機(jī)構(gòu)的重要尺寸和起動(dòng)位置，該機(jī)構(gòu)是為著實(shí)現(xiàn)規(guī)定的任務(wù)和預(yù)期的性能而事先設(shè)想的。
所謂重要的尺寸意思是指關(guān)于兩桿、三桿等的長(zhǎng)度或桿間距離，構(gòu)件數(shù)和軸線(xiàn)間的角度，凸輪輪廓尺寸，凸輪隨動(dòng)件的直徑，偏心距，齒輪配額等等。預(yù)想機(jī)構(gòu)類(lèi)型可能是曲柄滑塊機(jī)構(gòu)、四桿機(jī)構(gòu)，帶盤(pán)型從動(dòng)件的凸輪機(jī)構(gòu)，或者是以拓?fù)鋵W(xué)方法而非因次分析法所確定的具有某種結(jié)構(gòu)形狀更為復(fù)雜的連桿機(jī)構(gòu)。對(duì)于運(yùn)動(dòng)綜合，慣例上有三個(gè)任務(wù)：函數(shù)生成，軌跡生成和運(yùn)動(dòng)生成。
在函數(shù)生成機(jī)構(gòu)中輸入和輸出構(gòu)件的轉(zhuǎn)動(dòng)或移動(dòng)必須是相互關(guān)聯(lián)的。對(duì)于一個(gè)任意函數(shù)y＝f（x），一個(gè)運(yùn)動(dòng)綜合的任務(wù)可能是設(shè)計(jì)一個(gè)連桿機(jī)構(gòu)使輸入和輸出建立起關(guān)系以便使得在xo＜x＜xn-1的范圍內(nèi)輸入按x運(yùn)動(dòng)，而輸出按y＝f（x）運(yùn)動(dòng)。在輸入和輸出件回轉(zhuǎn)運(yùn)動(dòng)情況下，轉(zhuǎn)角φ和φ分別是x和y的線(xiàn)性模擬。當(dāng)輸入件回轉(zhuǎn)到一個(gè)獨(dú)立x值時(shí)，在一個(gè)“黑箱”的機(jī)構(gòu)中，使輸出構(gòu)件轉(zhuǎn)到相對(duì)應(yīng)的由函數(shù)y＝f（x）決定的數(shù)值上。這可被認(rèn)為是機(jī)械模擬計(jì)算機(jī)的最簡(jiǎn)單的情形。各種不同的機(jī)構(gòu)都可以包含在這個(gè)“黑箱”內(nèi)，然而對(duì)于任意函數(shù)的無(wú)誤差生成，四桿機(jī)構(gòu)是無(wú)能為力的，僅僅可能在有限精確度內(nèi)與之相匹配。它廣泛用于工業(yè)上，因?yàn)樗臈U機(jī)構(gòu)在構(gòu)建和維修上都是簡(jiǎn)單的。
在軌跡生成機(jī)構(gòu)中，在“浮動(dòng)桿”上一個(gè)點(diǎn)要描畫(huà)一條相對(duì)于一個(gè)固定坐標(biāo)系確定的軌跡。如果該軌跡點(diǎn)是既要與時(shí)間相關(guān)又要與位置相關(guān)，該任務(wù)被稱(chēng)之為預(yù)定周期的軌跡生成。軌跡生成機(jī)構(gòu)的一個(gè)例子就是設(shè)計(jì)來(lái)投擲棒球或網(wǎng)球的四桿機(jī)構(gòu)。在這種情況下，點(diǎn)P的軌跡將是這樣：在預(yù)定的位置撿起一個(gè)球，并在預(yù)定的時(shí)間周期內(nèi)沿著預(yù)定的徑跡把球傳送出去，能達(dá)到合適的速度和方向。
機(jī)械裝置設(shè)計(jì)中有著許多情形，在這些情形中既要導(dǎo)引剛體通過(guò)一系列規(guī)定的、受限制的獨(dú)立位置，又要在減少受限制而且獨(dú)立的位置的數(shù)目時(shí)，對(duì)運(yùn)動(dòng)體的速度和（或）加速度加以約束，那是必要的。運(yùn)動(dòng)生成或剛體導(dǎo)引機(jī)構(gòu)要求：一個(gè)完整的物體要被導(dǎo)引通過(guò)一預(yù)定的運(yùn)動(dòng)序列。作為被導(dǎo)引的物體通常是“浮動(dòng)構(gòu)件”的一部分，那不僅是預(yù)定點(diǎn)P的軌跡，也是通過(guò)該點(diǎn)并嵌入該物體內(nèi)的線(xiàn)的轉(zhuǎn)動(dòng)。例如，該線(xiàn)可能代表自動(dòng)化機(jī)械中的一個(gè)載體件，那是在載體件上的一個(gè)點(diǎn)具有一個(gè)預(yù)定的軌跡而該載體件又具有一個(gè)預(yù)定的角度方位。預(yù)定方式裝料機(jī)的吊斗的運(yùn)動(dòng)是運(yùn)動(dòng)生成機(jī)構(gòu)的另一個(gè)例子。吊斗端的軌跡是有極限的。因?yàn)槠涠丝诒仨殞?shí)現(xiàn)挖掘的運(yùn)動(dòng)軌跡，緊跟著要實(shí)現(xiàn)提升和傾瀉的軌跡。吊斗的角度方位對(duì)保證斗中物料從正確的位置傾瀉（倒）同樣是重要的。
凸輪和齒輪：
凸輪裝置是把一種運(yùn)動(dòng)改變成另一種運(yùn)動(dòng)的方便裝置。這種機(jī)器零件具有曲面或槽面，該曲面或槽面與從動(dòng)件相配合并將運(yùn)動(dòng)傳給從動(dòng)件。凸輪的運(yùn)動(dòng)（通常是轉(zhuǎn)動(dòng)）被傳遞給從動(dòng)件作搖動(dòng)或移動(dòng)，或兩者均有。由于各種各樣的幾何體和大量的凸輪與從動(dòng)件相結(jié)合，因此凸輪是一種極多功能的萬(wàn)用的機(jī)械零件。雖然凸輪和從動(dòng)件可以為運(yùn)動(dòng)、軌跡和功能生成而設(shè)計(jì)，但其主要是用于利用凸輪和從動(dòng)件作為功能生成構(gòu)件。
根據(jù)凸輪形狀，最普遍的凸輪種類(lèi)是：盤(pán)形傳動(dòng)凸輪（兩維的，即平面的）和圓柱形凸輪（三維的，即空間的）機(jī)構(gòu)。從動(dòng)件可以用幾個(gè)方法分類(lèi)：根據(jù)從動(dòng)件的運(yùn)動(dòng)，例如移動(dòng)或搖動(dòng)來(lái)分類(lèi)，根據(jù)平移式（直線(xiàn)）從動(dòng)件運(yùn)動(dòng)是沿徑向的還是從凸輪軸中心偏心的和根據(jù)從動(dòng)件接觸面的形狀（比如平面、輥?zhàn)印Ⅻc(diǎn)——刀尖式，球面，平面曲線(xiàn)或空間曲面）。
對(duì)于一個(gè)對(duì)心直動(dòng)滾子從動(dòng)件盤(pán)形凸輪，可畫(huà)出的與凸輪表面相切且與輪軸同心的最小圓是基圓。隨動(dòng)件的點(diǎn)就是產(chǎn)生節(jié)線(xiàn)的輥?zhàn)又行牡狞c(diǎn)。壓力角就是輥中心軌跡方向線(xiàn)和通過(guò)輥?zhàn)又行牡墓?jié)線(xiàn)的法線(xiàn)之間的夾角而且是傳動(dòng)角的余角。忽略摩擦影響，這法線(xiàn)方向跟凸輪與從動(dòng)件之間接觸力方向是重合一致的。像在一連桿機(jī)構(gòu)中，壓力角在循環(huán)運(yùn)轉(zhuǎn)過(guò)程中變化且是凸輪把運(yùn)動(dòng)作用力傳遞到從動(dòng)件去的一種量度。大壓力角將產(chǎn)生施加到從動(dòng)件桿上的側(cè)向力，因摩擦力存在，那將勢(shì)必把從動(dòng)件限制在導(dǎo)槽中。在自動(dòng)化機(jī)械中的許多應(yīng)用需要間歇運(yùn)動(dòng)。一個(gè)典型的例子將要求一個(gè)含有上升一停歇一返回和可能另一個(gè)停歇的周期，每階段經(jīng)過(guò)一個(gè)指定的角度，伴隨著一個(gè)所要求的從動(dòng)件的位移，這個(gè)位移以厘米或度來(lái)度量。設(shè)計(jì)者的工作就是相應(yīng)地設(shè)計(jì)出該凸輪。首先要做的決策就是要選擇凸輪從動(dòng)件的類(lèi)型。規(guī)定的應(yīng)用可能要求凸輪和從動(dòng)件相結(jié)合。轉(zhuǎn)化為決策的某些因素有：幾何形狀條件，動(dòng)力條件，環(huán)境條件和經(jīng)濟(jì)因素。一旦凸輪與從動(dòng)件運(yùn)動(dòng)副類(lèi)型被選定，則從動(dòng)件運(yùn)動(dòng)就必定選定。因此，速度、加速度和在某些情況下，從動(dòng)件位移的進(jìn)一步的方案實(shí)屬極端重要。
齒輪是借助于輪齒成功嚙合來(lái)傳遞運(yùn)動(dòng)的機(jī)器零件。齒輪從一根回轉(zhuǎn)軸到另一回轉(zhuǎn)軸傳遞運(yùn)動(dòng)或傳遞運(yùn)動(dòng)到一傳動(dòng)齒條。多數(shù)應(yīng)用中都以恒定角速比（或常定扭矩比）而存在。恒定角速比應(yīng)用中必定是軸向傳動(dòng)。在各種各樣有用的齒輪類(lèi)型基礎(chǔ)上，輸入軸和輸出軸需要在一直線(xiàn)上或需要互相平行都不受什么限制。由于使用非圓齒輪，非線(xiàn)性角速比也是很有用的。為了保持恒定的角速度，各個(gè)齒輪齒廓必須服從齒輪嚙合的基本規(guī)律：為了一對(duì)齒能傳遞恒定角速比，他們接觸齒廓的形狀必須是要這樣：公法線(xiàn)通過(guò)兩齒輪中心連線(xiàn)上的固定點(diǎn)。
滿(mǎn)足嚙合基本規(guī)律的兩嚙合齒廓被稱(chēng)為共軛齒廓。盡管有著許多滿(mǎn)足相嚙合齒的可能齒形能被設(shè)計(jì)出來(lái)，以滿(mǎn)足基本嚙合規(guī)律，但一般僅有兩種在使用：擺線(xiàn)齒廓和漸開(kāi)線(xiàn)齒廓。漸開(kāi)線(xiàn)具有若干重要的優(yōu)點(diǎn)：它易于加工制造和一對(duì)漸開(kāi)線(xiàn)齒輪之間的中心距可以變化而不改變速比，當(dāng)使用漸開(kāi)線(xiàn)齒廓時(shí)，可不要求精密的軸間公差。
有幾種標(biāo)準(zhǔn)齒輪可供選用。為了在平行軸條件下應(yīng)用，通常使用直齒圓柱齒輪，平行軸斜齒輪或人字齒齒輪。在相交軸的情況下使用直齒錐齒輪或螺旋齒輪。對(duì)于非相交軸和非平行軸齒輪傳動(dòng)，交錯(cuò)軸螺旋齒輪，蝸桿蝸輪，端面齒輪、斜齒圓錐齒輪或準(zhǔn)雙曲面齒輪將被選用。對(duì)于直齒圓柱齒輪，相嚙合齒輪的節(jié)圓是彼此相切的。他們互相滾動(dòng)而無(wú)滑動(dòng)。齒頂高是輪齒伸出超過(guò)節(jié)圓的高度（也是節(jié)圓和齒頂圓之間在徑向的距離）。頂隙是一個(gè)給定齒的齒根高（在節(jié)圓以下的齒高）大于與它相嚙合的齒輪的齒頂高的量（差值）。齒厚是沿著節(jié)圓圓弧上跨齒的距離，而齒間距（齒槽S）是沿著節(jié)圓圓弧上相鄰兩齒間的空間距離。而齒側(cè)間隙是在節(jié)圓上的齒槽寬度大于其相嚙合齒輪在節(jié)圓上的齒厚的差值。
螺紋件、緊固件和聯(lián)接件：
固緊和聯(lián)接零件的典型方法包括利用諸如螺栓、螺帽、有頭螺釘、定位螺釘、鉚釘、鎖緊裝置和鍵。零件也可以用熔焊、銅焊和夾緊連接。在工程圖學(xué)和金屬加工工藝研究中常常包括關(guān)于各種連接方法的說(shuō)明，在工程上對(duì)此很感興趣的，求知欲強(qiáng)的任何人自然會(huì)獲得關(guān)于固緊方法上良好的基礎(chǔ)知識(shí)。
如果讓一個(gè)穿制服的人去選擇他能想象的機(jī)械設(shè)計(jì)方面最枯燥最不感興趣的學(xué)科的話(huà)，那么他就會(huì)選擇緊固件學(xué)科，即螺栓和螺帽。事實(shí)上，術(shù)語(yǔ)“螺栓和螺帽”是與艱苦、單調(diào)的工作同義。但是乏味的工作總是需要的。人們嚴(yán)肅設(shè)想能有一群螺栓螺帽制造者組成一個(gè)協(xié)會(huì)并在一起召開(kāi)年會(huì)嗎？那樣的話(huà)，還有什么學(xué)科不能讓人感興趣呢？
盡管埋怨，但這學(xué)科在機(jī)械設(shè)計(jì)整個(gè)領(lǐng)域中還是最使人感興趣的學(xué)科之一。在緊固件方面新的種類(lèi)變化數(shù)目超過(guò)你能注意到的有巨大變化的任何時(shí)期。多得如潮水般的有用的緊固件可供設(shè)計(jì)者任意選擇使用。尚有一件事，你知道嗎？好的螺栓的材料應(yīng)該是強(qiáng)固而堅(jiān)硬的，而好的螺帽的材料應(yīng)該是軟而有韌性的?；蛘吣阒绬幔咳舸_定在使用的螺栓、螺帽，你應(yīng)該盡可能地把它們旋緊。如果在上緊過(guò)程中，由于旋緊這螺栓過(guò)程中而未發(fā)生失效現(xiàn)象，那么螺栓將有不會(huì)失效的理想的可能性。在材料方面隨后你將發(fā)現(xiàn)這些問(wèn)題的原因。你將掌握螺栓、螺帽為什么會(huì)松動(dòng)和你必須怎樣令它保持旋緊狀態(tài)。連接零件的方法在工程結(jié)構(gòu)質(zhì)量方面是極端重要的。在設(shè)計(jì)和使用的各種情況下，充分了解緊固件和連接件的性能那是必要的。
大型噴氣發(fā)動(dòng)機(jī)客機(jī)像波音747和洛希德1011，需要250萬(wàn)個(gè)緊固件，其中一些每個(gè)要花數(shù)美元。例如波音747，大約需要裝70000個(gè)鈦合金緊固件，全部大約要花150000美元；400000個(gè)具有精密公差的其他緊固件，大約要花250000美元；和30000個(gè)擠壓用鉚釘，價(jià)值每個(gè)50美分。為了保持低成本，波音和洛希德和他們的工程承包人常常重新審查緊固件的設(shè)計(jì)、安裝技術(shù)和加工工具。節(jié)省設(shè)計(jì)和加工工具費(fèi)用將找到一個(gè)預(yù)備市場(chǎng)，那將像Jumbo噴氣發(fā)動(dòng)機(jī)增值那樣而增長(zhǎng)價(jià)值。
緊固件是根據(jù)計(jì)劃并以如何使用他們來(lái)命名的，而不是根據(jù)其在具體例子中實(shí)際的應(yīng)用。如果記住了這個(gè)基本事實(shí)，就將不難區(qū)別螺釘和螺栓。如果所設(shè)計(jì)的產(chǎn)品其主要目的是把它裝入到已攻絲的螺紋孔中，那就是螺釘。這樣螺釘是要在螺釘頭上施加扭矩來(lái)旋緊的。如果所設(shè)計(jì)的產(chǎn)品打算跟螺母配合使用，那就是螺栓。螺栓是靠在螺母上施加扭矩來(lái)旋緊的。雙頭螺栓就像刻了螺紋的桿，一端旋入螺紋孔中，另一端再裝上螺帽，那就是確定產(chǎn)品名稱(chēng)的意義，并不是其實(shí)際使用。這樣，在各種場(chǎng)合用鉆頭去鉆孔穿過(guò)兩塊鋼板，人們就會(huì)用螺栓和螺帽來(lái)連接它們，這可能是人們所希望的。有四種形式的螺釘頭，最普遍使用四種帶帽螺釘是：六角頭螺釘，槽頭螺釘，平頭螺釘和內(nèi)六角沉頭螺釘。
當(dāng)想要一個(gè)可以被拆開(kāi)又不破壞被聯(lián)接零件的聯(lián)接時(shí)，而且這個(gè)聯(lián)接又要有足夠的強(qiáng)度以承受外拉力和剪力或這兩種力的結(jié)合，使用淬火墊圈的簡(jiǎn)單螺栓聯(lián)結(jié)是一個(gè)很好的方法。在這種連接中，首先把螺栓上緊以產(chǎn)生一預(yù)緊載荷初拉力，而后施加外拉力載荷和剪切載荷。預(yù)載荷的作用是使被聯(lián)接零件處于壓應(yīng)力狀態(tài)以便更好地抵抗剪切載荷。螺栓預(yù)加載荷的重要性不能被過(guò)高地估計(jì)。較高預(yù)載荷能提高螺栓聯(lián)結(jié)的抗疲勞能力和改善鎖緊作用。
已經(jīng)知道：高預(yù)載荷在重要的螺栓聯(lián)接中是非常希望的。下一步我們必須考慮，當(dāng)要裝配零件時(shí)，實(shí)際研制預(yù)載的保險(xiǎn)的辦法。
如果具有橫截面積為A的螺栓總長(zhǎng)度為L(zhǎng)，當(dāng)它被裝配時(shí)，實(shí)際上是可以用千分表來(lái)測(cè)量的。由于預(yù)載力F而使螺栓伸長(zhǎng)為d,d可以利用公式d＝FL/AE來(lái)計(jì)算。式中E是螺栓材料的彈性模量。那么簡(jiǎn)便地旋緊螺母直至使螺栓伸長(zhǎng)達(dá)到d。這就保證了所希望的預(yù)緊載荷已經(jīng)達(dá)到。
然而螺釘?shù)纳扉L(zhǎng)通常是不可能被測(cè)量的。因?yàn)槁葆敹瞬靠赡苁敲た?。在許多情況下，去測(cè)量螺栓的伸長(zhǎng)也是不實(shí)際的。在這樣情況下，要求能產(chǎn)生具體預(yù)載荷的扭矩扳手必須加以測(cè)定。因?yàn)榕ぞ匕馐?，氣?dòng)沖擊扳手，或螺帽旋動(dòng)圈數(shù)扳手等方法，可能被使用。
扭矩扳手具有內(nèi)裝指示盤(pán)，以便指示正確的扭矩。用沖擊扳手時(shí)，要調(diào)節(jié)空氣壓力，當(dāng)獲得正確扭矩時(shí)，扳手即停止轉(zhuǎn)動(dòng)?；蛘哂心承┌馐?，當(dāng)達(dá)到希望的扭矩時(shí)，壓縮空氣被自動(dòng)關(guān)掉。要使用螺母轉(zhuǎn)動(dòng)圈數(shù)法扳手首先要求我們確定適度緊的意義。適度緊的狀態(tài)就是借助于沖擊扳手沖擊若干次所達(dá)到的緊度的意思。已經(jīng)達(dá)到適度緊狀態(tài)時(shí)候，所有的附加旋動(dòng)會(huì)在螺栓中產(chǎn)生有益張緊力。旋動(dòng)螺母圈數(shù)法要求：必須先旋動(dòng)零點(diǎn)幾轉(zhuǎn)以便產(chǎn)生在適度緊基礎(chǔ)上所要求的預(yù)緊載荷。例如對(duì)于重型的六角頭螺栓的旋轉(zhuǎn)螺母圈數(shù)法的技術(shù)說(shuō)明書(shū)稱(chēng)：螺母應(yīng)從適度緊狀態(tài)出發(fā)最少被旋動(dòng)到180°。注意這也是關(guān)于客車(chē)輪子螺母預(yù)緊的大體合適的轉(zhuǎn)數(shù)。
1.2減（耐）摩擦軸承:
減摩擦（滾動(dòng)）軸承這個(gè)術(shù)語(yǔ)被用于描述一類(lèi)軸承，其主要載荷是通過(guò)滾動(dòng)接觸而不是滑動(dòng)接觸的元件傳遞的。在滾動(dòng)軸承中起動(dòng)摩擦和運(yùn)行摩擦大體上是相同的，有關(guān)摩擦的有效載荷、速度和溫度變化是小的。把滾動(dòng)軸承說(shuō)是“減摩擦軸承”可能是錯(cuò)的，因?yàn)槟承┹S承的摩擦不存在，但是這一術(shù)語(yǔ)已普遍地徹底地用于工業(yè)上了。從機(jī)械設(shè)計(jì)者的觀點(diǎn)出發(fā)：研究減摩擦軸承當(dāng)與所研究的課題相比較時(shí)，可提供幾方面的思考。減摩擦軸承方面的專(zhuān)家面臨著設(shè)計(jì)一組組成滾動(dòng)軸承的元件，這些元件必須設(shè)計(jì)得能裝入所規(guī)定的尺寸空間，它們必須設(shè)計(jì)成能承受具有某種特性的載荷而最后這些元件必須設(shè)計(jì)成當(dāng)規(guī)定條件下運(yùn)轉(zhuǎn)時(shí)具有令人滿(mǎn)意的壽命。因此軸承專(zhuān)家必須考慮這些事項(xiàng)：破壞荷載、摩擦力、熱、抗腐蝕、運(yùn)動(dòng)學(xué)問(wèn)題，材料性質(zhì)、潤(rùn)滑、加工公差、裝配、使用和費(fèi)用。從所有這些因素的考慮出發(fā)，在判斷中他要達(dá)到一種妥協(xié)方案。這一方案就是所陳述問(wèn)題的最佳答案。
減摩擦軸承制造者已經(jīng)做出了有用的幾乎是無(wú)數(shù)規(guī)格和形式的滾動(dòng)軸承。他們已經(jīng)將這些規(guī)格和類(lèi)型連同所建議的載荷和速度一起在手冊(cè)中列表顯示。這樣機(jī)械設(shè)計(jì)專(zhuān)家的任務(wù)就不是如何去設(shè)計(jì)滾動(dòng)軸承而是如何去選擇滾動(dòng)軸承的問(wèn)題了。
然而我們不能如此簡(jiǎn)單地討論這一課題。至少，簡(jiǎn)短地研討減摩擦軸承的內(nèi)容應(yīng)該是關(guān)于機(jī)械設(shè)計(jì)文獻(xiàn)的一部分，進(jìn)而，如果我們考察過(guò)多種機(jī)械元件，例如齒輪、軸承、緊固件、離合器和類(lèi)似元件，減摩擦軸承代表著關(guān)于機(jī)械壽命精確度，荷載能力和可靠性的完美的頂峰，那可能就是真的了。這完美程度未曾有過(guò)靠偶然的因素來(lái)實(shí)現(xiàn)。那是一個(gè)最佳工程實(shí)踐的例子，并可將所掌握知識(shí)在別處運(yùn)用。
制造出的軸承承受純徑向載荷、純軸向載荷或者承擔(dān)上述二者相結(jié)合的載荷。球軸承的術(shù)語(yǔ)在圖1中有說(shuō)明（在這未表示出來(lái)），該圖表示了軸承的四個(gè)主要零件。這些零件就是外圈、內(nèi)圈、鋼球即滾動(dòng)元件，和分隔器。在便宜的軸承中分隔器是被省略的，但它具有重要的分隔鋼球的作用，因之將不會(huì)發(fā)生擦傷接觸。
單列深溝軸承將承受徑向載荷和一些軸向載荷?？繉?nèi)圈移偏到一定位置，然后將鋼球塞入溝槽中，加載后鋼球被分開(kāi)，而分隔器是后來(lái)再裝配上去的。
利用內(nèi)外圈上的裝填缺口，能讓較多的鋼球被填塞進(jìn)去，這樣來(lái)增加承載能力。然而要注意減小軸向載荷，因?yàn)楫?dāng)軸向的載荷出現(xiàn)在鋼球正對(duì)準(zhǔn)圈上缺口時(shí)，鋼球?qū)l(fā)生振擺擦傷，以致跳出。
角接觸軸承會(huì)產(chǎn)生較大的軸向推力。所有這些軸承都可以在一邊或兩邊用擋板防護(hù)。這些擋板并不是完全密閉的但對(duì)灰塵污物提供防護(hù)措施。許多軸承制造時(shí)在一端或兩端予以密封。當(dāng)兩端都進(jìn)行密封時(shí)，軸承在制造廠就已潤(rùn)滑。盡管密閉軸承假定為了提高壽命已被潤(rùn)滑過(guò)，但有時(shí)還是要規(guī)定潤(rùn)滑的方法。
單列軸承會(huì)經(jīng)受小量的軸向偏移或撓曲，但這里是個(gè)嚴(yán)重的問(wèn)題，可能要用自動(dòng)調(diào)心軸承。雙列軸承做成多種類(lèi)型和規(guī)格。雖然雙列軸承一般需要較少的零件，占有較小的空間，但為了同樣的使用目的，有時(shí)兩個(gè)單列軸承一起使用。
大量的標(biāo)準(zhǔn)的滾子軸承也是很有用的。圓柱滾子軸承比同樣規(guī)格的球軸承將承受較大的載荷，因?yàn)橛休^大的接觸面。然而他們也有缺點(diǎn)，那就是其滾道和滾子幾乎都要求有精密的幾何形狀。圓形滾子推力軸承、滾針軸承，圓錐滾子軸承各自都用于不同的用途。
當(dāng)減摩擦軸承中的鋼球或滾子進(jìn)入載荷區(qū)中滾動(dòng)時(shí)，在內(nèi)圈、滾動(dòng)元件和外圈上產(chǎn)生Hertzian應(yīng)力，因?yàn)榻佑|元件在軸向的曲率與徑向的曲率是不同的。為了計(jì)算這些應(yīng)力的公式比起Hertzian方程要復(fù)雜得多。如果軸承清潔并得到合適的潤(rùn)滑和安裝，對(duì)灰塵和污物入口處作了密封，并在這種狀況下還作了維護(hù)且在合理的溫度下運(yùn)轉(zhuǎn)，那么金屬的疲勞將僅僅是由于受到損壞時(shí)才會(huì)發(fā)生。由于這應(yīng)力的作用將是數(shù)以萬(wàn)計(jì)，因此，軸承壽命這術(shù)語(yǔ)就非常普遍地使用。
在疲勞損傷首次發(fā)生之前，單個(gè)軸承的壽命是以軸承運(yùn)轉(zhuǎn)的總轉(zhuǎn)數(shù)來(lái)定義或以軸承在給定的常速下運(yùn)轉(zhuǎn)的小時(shí)數(shù)來(lái)定義。當(dāng)然疲勞具有統(tǒng)計(jì)學(xué)上的本質(zhì)意義，因此如果試驗(yàn)大量的軸承，某些離中趨勢(shì)是可以預(yù)料到的。一組看起來(lái)相同的球軸承的額定壽命被定義為：其百分之九十的軸承在沒(méi)有出現(xiàn)疲勞損傷前能夠完成或者超額完成運(yùn)行的轉(zhuǎn)數(shù)，或當(dāng)這組軸承以某個(gè)給定的恒定速度運(yùn)行時(shí)的小時(shí)數(shù)。
減摩軸承在大量的機(jī)械產(chǎn)品中使用，例如玩具、家居用品，制冷設(shè)備、輥?zhàn)拥准?、?chē)庫(kù)門(mén)、卡車(chē)、工業(yè)機(jī)械、牙科設(shè)備和引導(dǎo)導(dǎo)彈發(fā)射的裝置等等。這些應(yīng)用中的某些用途需要精密軸承，但對(duì)于其他場(chǎng)合，由于使用精密軸承成本高而被禁止使用。
MECHANISMS AND MACHINE THEORY
Aurelian Vadean ?, Dimitri Leray , Jean Guillot
Adeapartment of Mechanical Engineering, Ecole Polytechnique de Montreal, P.O. Box 6079, Station Centre-Ville,Montreal, Québec, Canada H3C 3A7
bLaboratoire de Genie Mecanique de Toulouse - COSAM, INSA Toulouse, 135 Avenue de Rangueil,Toulouse Cedex 4,
Automotive sub-actuators tooth side clearance adjustment optimization techniques
1.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.
1.1The 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.
Other method is the instantaneous center law, namely the instantaneous center law, this method is extremely useful moreover is frequently when the complex link motion gear analysis quick method. The instantaneous center is a spot, this spot in that flash, on between the organization two components does not have the relative motion. In order to discover known organization certain instantaneous centers the position, Kennedy the (Kennedy) three center theories extremely are useful. It is said that,Each other relative motion three object three instantaneous centers are surely in a straight line.
The organization various components acceleration is makes one be interested, because it affects the force of inertia, subsequently affects the machine part the stress, the bearing load, the vibration and the noise. Because the final goal is the machine and the organization force of inertia analysis, the all acceleration various components all should the disposable picture - - in the organization fixed component inertial coordinate system express in the identical coordinate system.
Should pay attention: Is opposite in rotates on the vice-rotation rigid body an acceleration component usually to have two fixedly. A force component direction cuts in this path, its direction is same with this object angle acceleration direction, and is called the tangential acceleration. Its existence is completely because the angular speed rate of change causes.
Another component, always aims at the object the center of rotation, is called the standard the centripetal acceleration, because this component the velocity vector direction has the change to exist. The movement comprehensive
Ganization is forms many mechanisms the basic geometry structural units, these mechanisms including automatic packaging, printer, mechanical toy, textile machinery and other machineries and so on. The typical organization must design causes the movement which the rigid component relative datum component produces hoped. The organization movement design is the movement synthesis, first step frequently designs the entire machine first. When consideration stress, must ask dynamics aspect question, the bearing load, the stress, the lubrication and so on the similar question, but the major problem is the machine structure question..
The movement scientist defines the kinematics as “the development facility movement and the foundation organization method”. This definition first part involves the kinematic analysis. The known organization, its constitution state of motion determined by the kinematic analysis. The narration movement analysis duty contains the organization between the main dimension, the component links mutually with the input movement technical characteristic or the actuation method. The goal is must discover the displacement, the speed, the acceleration, the impact or the beat (two step accelerations), with various components higher order acceleration which possibly occurs as well as describes the diameter mark and the movement which realizes by certain components. The definition second part of available following two aspect explained ：
1. research produces with the aid of the organization assigns the movement the method.
2. research construction to be able to produce assigns the motion the method, but in two plans, the movement is assigns the organization is the foundation. This is the movement synthesis essence. Such movement synthesis involves to for assigns the performance the organization system design. The movement synthesis aspect may sum up as following two kinds:
1. types are comprehensive. The stipulation requests the performance, how is one kind of type organization appropriate? (Tooth gear train, link motion gear? Cam gear?)How many components but should the organization have? How many degrees of freedom needs? How outline structure is hoped? . About the member number and the degree of freedom consideration was usually considered is in the type synthesis is been called as for a quantity synthesis branch domain.
2. sizes are comprehensive. The movement synthesis second predominant type is the best method which determined through the goal law. The size synthesis attempts to determine the organization the important size and the starting position, this organization is conceives beforehand for the realization stipulation duty and the anticipated performance.
Of the so-called important size meanings are refer about two poles, three poles and so on between the length or the pole are away from, angle between number of articles and spool thread, cam contour size, cam follower diameter, eccentricity, gear quota and so on. Expected the organization type possibly is the crank slide organization, four pole organizations, the tape reel from the moving parts cam gear, but or is non-has some kind of structure shape more complex link motion gear because by the analysis situs method which the inferior analytic method determined. Is comprehensive regarding the movement, in the convention has three duties: Function production, path production and movement production..
Inputs and outputs the component in the function production organization the rotation or the migration must be the interdependence. Regarding arbitrary function y=f(x), a movement synthesis duty possibly is designs a link motion gear to cause the input and the output establishes the relations in order to cause in the xo
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