平面連桿機(jī)構(gòu)及其設(shè)計(jì)課件

1、Planar coupler linkages mechanism and its design(平面連桿機(jī)構(gòu)及其設(shè)計(jì))8.1 General Description概述 Key points：Definition Characteristics Main study content關(guān)鍵知識(shí)點(diǎn)：平面連桿機(jī)構(gòu)的定義，特性，主要學(xué)習(xí)內(nèi)容 Definition平面連桿機(jī)構(gòu)的定義 Just as the Figure shows, the driving link 1 transfers its movement to output link 3 through a middle link 2 whi

2、ch is named as coupler. Coupler linkage may have many links. Based on the number of links, we can name four-bar, five-bar, six-bar and etc.如圖1所示機(jī)構(gòu)原動(dòng)件1的運(yùn)動(dòng)要經(jīng)過(guò)一個(gè)不直接與機(jī)架相連的中間構(gòu)件2才能將運(yùn)動(dòng)傳遞到輸出件3，這個(gè)不直接與機(jī)架相連構(gòu)件稱(chēng)為連桿。連桿機(jī)構(gòu)可以有多個(gè)構(gòu)件，根據(jù)構(gòu)件數(shù)目可以命名為四桿、五桿、六桿等。第1頁(yè)，共30頁(yè)。圖1 Characteristics平面連桿機(jī)構(gòu)的特點(diǎn)1.Advantages優(yōu)點(diǎn)Can transfer mo

3、vement to long distance可以傳遞較遠(yuǎn)距離的運(yùn)動(dòng)The variety of coupler curve連桿曲線的多樣化The variety of linkage movements構(gòu)件運(yùn)動(dòng)形式多樣化All is low pair都是低副click for the simulation鉸鏈四桿機(jī)構(gòu)第2頁(yè)，共30頁(yè)。click for the simulationclick for the simulation 第3頁(yè)，共30頁(yè)。2.Disadvantages缺點(diǎn)Low efficiency and big error效率低、誤差大Big inertia which is

4、difficult to avoid慣性力大、難以準(zhǔn)確消除Difficult to decide fixed movement (compared with CAM) 難以確定任意的確定運(yùn)動(dòng) Main Study Content主要學(xué)習(xí)內(nèi)容1.The Type and application of Planar Four-bar Linkage平面四桿機(jī)構(gòu)類(lèi)型和應(yīng)用2.The basic knowledge of Planar Four-bar Linkage平面四桿機(jī)構(gòu)的基本知識(shí)3.Design of Planar Four-bar Linkage by scheming method圖解法

5、設(shè)計(jì)四桿機(jī)構(gòu)第4頁(yè)，共30頁(yè)。8.2 The Type and application of Planar Four-bar Linkage用圖解法作機(jī)構(gòu)的動(dòng)態(tài)靜力分析Key points： Several terms Basic Forms Variation of revolute four-bar mechanism關(guān)鍵知識(shí)點(diǎn)：幾個(gè)名詞解釋?zhuān)拘问剑莼问?Several terms幾個(gè)名詞解釋 If all lower pairs in a four-bar mechanism are revolute pairs, the mechanism is called a revolu

6、te four-bar mechanism, which is the basic form of the four-bar mechanism. 如果四桿機(jī)構(gòu)中所有的低副都是轉(zhuǎn)動(dòng)副，我們稱(chēng)之為旋轉(zhuǎn)四桿機(jī)構(gòu)。它是平面四桿機(jī)構(gòu)的基本形式Side links: In a revolute four-bar mechanism, the links connected to the frame are called side links.與機(jī)架相連接的桿稱(chēng)為連架桿第5頁(yè)，共30頁(yè)。Couple: Usually, one of the side links is an input link, and

7、 the other is the output. The floating link couples the input to the output. The floating link is therefore called the coupler.通常，在四桿機(jī)構(gòu)中一個(gè)連架桿作為運(yùn)動(dòng)輸入，另一個(gè)作為運(yùn)動(dòng)輸出。那么連接輸入與輸出的桿件稱(chēng)為連桿Crank: If a side link can rotate continuously through 360 relative to the frame, it is called a crank。在連架桿中能作整周回轉(zhuǎn)的成為曲柄Rocker:

8、If a side link can not rotate continuously through 360 relative to the frame, it is called a rocker.在連架桿中不能作整周回轉(zhuǎn)的成為搖桿 Basic Forms基本形式第6頁(yè)，共30頁(yè)。1.crank-rocker mechanismOne side link can rotate continuously through 360 relative to the frame, while the other side link just rocks. Therefore, the first on

9、e is a crank while the second is a rocker. This mechanism is called a crank-rocker mechanism. The input link may be the crank or the rocker.當(dāng)一個(gè)連架桿（搖桿）做往復(fù)運(yùn)動(dòng)，另一個(gè)（曲柄）可以繞機(jī)架整周旋轉(zhuǎn)。這種平面四桿機(jī)構(gòu)稱(chēng)為曲柄搖桿機(jī)構(gòu)。曲柄或者搖桿都可以作為運(yùn)動(dòng)輸入部件。such as Rader antenna pitching linkage雷達(dá)機(jī)構(gòu)演示動(dòng)畫(huà)曲柄搖桿機(jī)構(gòu)第7頁(yè)，共30頁(yè)。Both of the side links can make

10、 complete revolution relative to the frame. Thus, both of them are cranks. This mechanism is called a double-crank mechanism. If one crank rotates at a constant speed, the other crank will rotate in the same direction at a varying speed.兩個(gè)連架桿都能?chē)@機(jī)架做整周運(yùn)轉(zhuǎn)，這兩個(gè)連架桿統(tǒng)稱(chēng)為曲柄，這樣的平面四桿機(jī)構(gòu)稱(chēng)為雙曲柄機(jī)構(gòu)。如果一個(gè)曲柄以一定的角速度轉(zhuǎn)動(dòng)，另

11、一個(gè)在同樣的方向上進(jìn)行轉(zhuǎn)動(dòng)。2.double-crank mechanism雙曲柄機(jī)構(gòu)第8頁(yè)，共30頁(yè)。parallelogram mechanism：平行四邊形機(jī)構(gòu)Such as locomotive linkage and seeding-machine seed feeding linkageReverse parallelogram mechanism：逆平行四邊形機(jī)構(gòu)Bus door linkage第9頁(yè)，共30頁(yè)。3.doublerocker mechanismBoth of the side links can only rock through a limited angle

12、relative to the frame. Therefore, both of them are rockers. This mechanism is called a double-rocker mechanism. 兩個(gè)連架桿都只能在有限的角度范圍內(nèi)繞機(jī)架轉(zhuǎn)動(dòng)，這兩個(gè)連架桿都叫搖桿，這樣的平面四桿機(jī)構(gòu)被稱(chēng)為雙搖桿機(jī)構(gòu)。Such as Fan rotating head Such as motorcar雙搖桿機(jī)構(gòu)第10頁(yè)，共30頁(yè)。 Variation of revolute four-bar mechanism演化形式1.Change the shape and size of the

13、 linkages1改變構(gòu)件的形狀和運(yùn)動(dòng)尺寸的演化方法第11頁(yè)，共30頁(yè)。2. Change the size of a revolute pair改變運(yùn)動(dòng)副尺寸的演化方法第12頁(yè)，共30頁(yè)。3. Choose different elements to the frame 選用不同的構(gòu)件做機(jī)構(gòu)演化鉸鏈四桿機(jī)構(gòu)第13頁(yè)，共30頁(yè)。8.3 The basic knowledge of Planar Four-bar Linkage用圖解法作機(jī)構(gòu)的動(dòng)態(tài)靜力分析Key points： Conditions for crank existence Four-bar Quick-Return Trans

14、mission angle & Pressure angle Dead-points關(guān)鍵知識(shí)點(diǎn)：曲柄存在的條件，四桿急回機(jī)構(gòu)，傳動(dòng)角和壓力角,死點(diǎn) Conditions for crank existence曲柄存在的條件1.Conditions with rotating pair有周轉(zhuǎn)副的條件(1)Conditions of the link length: the sum of shortest link and longest link is less than that of the remaining links. 桿長(zhǎng)條件 最短桿長(zhǎng)度與最長(zhǎng)桿長(zhǎng)度小于其余兩桿長(zhǎng)度之和。(2)One

15、 of the two links which form rotating pair must be the shortest link. 組成該周轉(zhuǎn)副的兩桿中必有一桿為最短桿。第14頁(yè)，共30頁(yè)。第15頁(yè)，共30頁(yè)。2.Judge the mechanism form判斷機(jī)構(gòu)形式(1)If the length of the links is satisfied,and if the shortest link is ground, then it is crank rocker. 若滿足桿長(zhǎng)條件，且最短桿為連架桿是曲柄搖桿機(jī)構(gòu)play the simulation第16頁(yè)，共30頁(yè)。(2)

16、If the length of the links is satisfied, and if the shortest link is XX, then it is double crank-rocker.若滿足桿長(zhǎng)條件，若最短桿為機(jī)架,是雙曲柄機(jī)構(gòu)。play the simulation 第17頁(yè)，共30頁(yè)。(3)If the length of the links is satisfied, and if the shortest link is the opposite XX, then it is double-rocker.若滿足桿長(zhǎng)條件，最短桿的對(duì)邊為機(jī)架時(shí),是雙搖桿機(jī)構(gòu)play

17、 the simulation(4)If the length of the links is not satisfied, then it is double-rocker 若不滿足桿長(zhǎng)條件，是雙搖桿機(jī)構(gòu)第18頁(yè)，共30頁(yè)。 Four-bar Quick-Return四桿急回機(jī)構(gòu)Definition: when point B on crank moves from B1 to B2, point C on rocker moves from C1 to C2, when point B on crank moves from B2 to B1, point C on rocker move

18、s from C2 to C1. During this process, crank rotates at constant speed, C1C2=C2C1, but B1B2B2B1當(dāng)曲柄上B點(diǎn)從B1點(diǎn)到B2點(diǎn),搖桿上C點(diǎn)從C1點(diǎn)到C2點(diǎn),當(dāng)曲柄上B點(diǎn)從B2點(diǎn)到B1點(diǎn), 搖桿上C點(diǎn)從C2點(diǎn)到C1點(diǎn),在此過(guò)程中,曲柄以勻角速度轉(zhuǎn)動(dòng),C1C2=C2C1,但B1B2B2B1.即t1t2,v2v1.急回運(yùn)動(dòng)第19頁(yè)，共30頁(yè)。 coefficient of travel speed variationDefinition: the ratio of the faster average angu

19、lar velocity to the slower one is called the coefficient of travel speed variation, denoted as K. So從動(dòng)件快行程與慢行程速度之比稱(chēng)為形成速比系數(shù): Toggle positions angle極位夾角第20頁(yè)，共30頁(yè)。 Transmission angle & Pressure angle傳動(dòng)角和壓力角Pressure angle：The acute angle a between the directions of the force and the velocity of the poin

20、t receiving the force on the follower. 壓力角a ：如圖從動(dòng)件上某點(diǎn)的受力方向與從動(dòng)件上該點(diǎn)速度方向的所夾的銳角a 。Transmission angle: Defined as the anglebetween the output link and coupler.壓力角及傳動(dòng)角第21頁(yè)，共30頁(yè)。For smooth operation of any mechanism without jerky movement, the maximum value of pressure angle should be less than or equal to

21、 the allowable pressure angle ,and generally the value of the allowable pressure is less then 80.在機(jī)構(gòu)的平滑運(yùn)動(dòng)過(guò)程中，要求壓力角應(yīng)該小于或者等于許用壓力角，通常情況下，許用壓力角取值小于80Or the minimum value of transmission should be larger than the allowable transmission angle which is larger then or equal to 40 generally.在機(jī)構(gòu)的平滑運(yùn)動(dòng)過(guò)程中，要求傳動(dòng)角

22、應(yīng)該大于或者等于許用傳動(dòng)角，通常情況下，許用傳動(dòng)角取值大于40第22頁(yè)，共30頁(yè)。 Dead-pointsWhen the rocker is the driver, the follower (crank) is collinear with the coupler, the transmission angle equals to 0 or 180. The force applied to the follower passes through the fixed pivot of the follower. In this situation, the mechanism cannot

23、 move by a torque on the driving rocker. In this sense, these positions are called dead-points.曲柄搖桿機(jī)構(gòu)中，搖桿CD為主動(dòng)件。當(dāng)機(jī)構(gòu)處于連桿與從動(dòng)曲柄共線的兩個(gè)位置時(shí)，出現(xiàn)了傳動(dòng)角=0o，壓力角=90o的情況。主動(dòng)件CD通過(guò)連桿作用于從動(dòng)件AB的力恰好通過(guò)其回轉(zhuǎn)中心，不能使AB桿轉(zhuǎn)動(dòng)，機(jī)構(gòu)此位置稱(chēng)為死點(diǎn)。死點(diǎn)-曲柄搖桿機(jī)構(gòu)第23頁(yè)，共30頁(yè)。 The way to avoid dead-points避免死點(diǎn)的方式 By inertia to pass through the dead-point利

24、用慣性通過(guò)死點(diǎn)Air-plane undercarriage mechanism飛機(jī)起落架動(dòng)畫(huà)第24頁(yè)，共30頁(yè)。Linkage alternate arrangement機(jī)構(gòu)錯(cuò)位排列such as Rader antenna pitching linkage雷達(dá)機(jī)構(gòu)演示動(dòng)畫(huà)第25頁(yè)，共30頁(yè)。8.4 Design of Four-bar linkage作圖法設(shè)計(jì)四桿機(jī)構(gòu)Key points： Basic question Classification of design requirements Design methods An example to apply scheming method關(guān)鍵知識(shí)點(diǎn)：基本問(wèn)題，常用的設(shè)計(jì)要求，設(shè)計(jì)方法，實(shí)際應(yīng)用 Basic question基本問(wèn)題 According to given requirements, the type and specification of the linkage must be decided to meet the conditions of structure, dynami