液壓與氣壓系統(tǒng)

1、弟揪閭捍季蘸蘿曠腧狴弧引談豪Hydraulic System剞撬氚魷刻莪扈浦龐蟛水湓苴挺 There are only three basic methods of transmitting power：Electrical，mechanicaland fluid powerMost applications actually use a combination of the three methods to obtain the most efficient overall systemTo properly determine which principle method to use。i

2、t is important to know the salient features of each typeFor example，fluid systems call transmit power more economically Over greater distances than Can mechanical typesHowever。fluid systems are淬霪熊錆敫邪酮甾滯尼嚷拂叮呸r(nóng)estricted to shorter distances than are electrical systems呱白斫銷噌犯愛穸緋喔郇灝鏨岫Hydraulic power tran

3、smission system ale concerned with the generation, modulation, and control of pressure and flow and ,and in general such systems include: 灸枯春案廢菀等沙隍鶼穗萬鍇鸛1Pumps which convert available power from the prime mover to hydraulic power at the actuator暄信枰廩榷蕪鹿俁汀襁烤附躋旎 2Valves which control the direction of pu

4、mp-flow，the level of power produced，and the amount of fluid一一flow to the actuatorsThe power level is determined by controlling both the flow and pressure level諞薜紅萌饔嗵瞪楹褸劍幟葫矜塞 3Actuators which convert hydraulic power to usable mechanical power Output at the point required鞔楚茌刷燉兵觥硤女氙糝躑湃吶 4The medium，whi

5、ch is a liquid，provides rigid transmission and control as well as 1ubrication of component s，sealing in valvesand cooling of the system攮桐姚液裂途礙創(chuàng)汜齪醯剩狁夾 5Connectors which link the various system components，provide power conductors for the fluid under pressure，and fluid flow return to tank(reservoir) 柚杠

6、吞審喟徹唼表殘燈岬汩促銑6、Fluid storage and conditioning equipment which ensure sufficient quality and quantity as well as cooling of the fluid蓄諱梟侶胎下程摧懵涅瓏泛極壇7、pneumatics systems required a lubricator to inject。a very fine mist of oil into the air discharging from the pressure regulatorThis prevents wear of the

7、closely fitting moving parts of pneumatic縱滟印篩?；偷稊U(kuò)阻韁鼠姆Hydraulic systems ale used in industrial applications such as stamping presses，steel mills，and general manufacturing，agricultural machines，mining industry，aviation，space technology，deepsea exploration, transportation，marine technology，and offsho

8、re gas and petroleum explorationIn short，very few people get through a day of their 1ives without somehow benefiting from the technology of hydraulics2閫暑繃荽春溶腺刮韶瞟矸瘼噘靈The principle of electrical-discharge machining also called electro is or spark-erosion machining, is based on the erosion of metals by

9、 spark discharges. We know that when two current-conduct in wires are allowed to touch each other, an arc is produced. If we look closely at the point of contact between the two wires, we note that a small portion of the metal has been eroded away, leaving a small crater.儕頌瀲祁介稚哚腧躉倘粥號(hào)姚蔗The basic EDM

10、system consists of a shape tool and the workpiece, connected to a dc power supply and placed in a dielectric fluid this is one of the most widely used machining processes, particularly for die-sinking operations when the potential difference between the tool and the work piece is sufficiently high,

11、a transient spark discharges through the fluid, removing a very small amount of metal from the work piece surface.忮偕鄆炬縷暗瓶態(tài)罵仍癟蚍滯秤The capacitor discharge is repeated at rates of between 50,with voltages usually ranging between 50vand 380v and currents from 0.1A to 500A.瘴庥頁喇醉垡茬軛避熄貰攀回早Mechanical control

12、 includes cams and governors. Although they have been used for the control of very complex machines, to be cost effectively, today they are used for simple and fixed-cycle task control. Some automated machines, such as screw machines, still use cam-based control. Mechanical control is difficult to m

13、anufacture and is subject to wear.屹嗄蕩嫁辟扛碗背脖似弗杏炕蛺Pneumatic control is still very popular for certain applications. It uses compressed air, valves, and switchs to construct simple control logic, but is easily slow. Because standard compaonents are used to construct the logic, it is easier to build tha

14、n a mechanical control . Pneumatic control parts are subject to wear.披塵拄僭肛?fù)p廠曦塊町耥光脬冊(cè)As does a mechanical control, an electromechanical control uses switches, relays, times counters, and so on, to construct logic, it is faster and more flexible. The controllers using electromechanical control are call

15、ed relay devices.董訂媾鄶鯽扦莎魁固敝芭玢松瞿The values in the express the relative tool distance from the home position. This distance is shown in the relative or incremental coordinates, U and W. 蠡尼炭毋下蕆咤履盎鸕桑榴乜祭when reading the values in the not possible to know directly how far the tool is from the part origin.

16、 Just how far it is from the home position. mounted on exhaust ports of air valves and actuators to reduce noise and prevent operating personnel from possible injury resulting not only from exposure to noise but also from highspeed airborne particles.The sign of the coordinates is zero or negative b

17、ecause the tool cannot move farther than the machine origin . thus at present , the values are zero so the tool is at the home position. The values in the are normally used when setting up the tools in order to find the real tool distances from the part origin.賻噻阿腡羲瓔捍妲繒霜巫懾亭筆The values in the absolut

18、e position express the absolute tool distance from the part origin. This distance is shown in shown in absolute coordinates, x and z .the sign may be positive or negative, depending on the quadrants in which the tool is moving. because of the compressibility of air，春鍛讜獅濾鉞遺影枷地好蛐豹廠it is impossible to

19、obtain precise controlled actuator velocities with pneumatic systemsalso，precise positioning control is not obtainableWhile pneumatic pressures are quite so far is to good. This is an important piece of information for the operator when maching, since any value in the absolute position is directly r

20、elated to the part.煅迤圮躬簋粵怙炮徹樹櫞謎倚鵝The secret of hydraulic systems SUCCESS and widespread use is its versatility and manageabilityFluid power is not hindered by the geometry operations when the potential difference between the tool and the work piece is sufficiently high, a transient spark discharges

21、through the fluid, removing a very small amount of metal from the work piece of the machine as is the ease in mechanical systemsAlso，power can be transmitted in almost limitless quantities because fluid systems are not so limited by the physical 1imitations of materials as are the electrical systems

22、For example，the performance of an electromagnet is limited by The saturation limit of steelOn the other hand，the power limit of fluid systems is 1imited only by the strength capacity of the material胙舄嗔室艿宜碳廬罡鏝瘡嗾糗嗚In the express the relative tool distance from the home position. This distance is shown

23、 in the relative or incremental coordinates, U and W. when reading the values in the not possible to know directly how far the tool is from the part origin. 葑港砰月廬訥模嘗贊位眍借渴互Just how far it is from the home position. The sign of the coordinates is zero or negative because the tool cannot move farther t

24、han the machine origin . thus at present , the values are zero so the tool is at the home position. The values in the are normally used when setting up the tools in order to find the real tool distances from the part origin.萊肼絡(luò)菥粽簍蝦歐純幅懔渚酃攄Industry is going to depend more and more on automation in ord

25、er to increase productivityThis includes remote and direct control of production operations，manufacturing processes。and materials handling鋱墀蓊麼壢虱淚雩疰漆傘太挺睢Fluid power is the muscle of automation because of advantages in the following four major categories豆疊忖仞岫轉(zhuǎn)凡窒饋發(fā)鏢揖櫻簪 1Ease and accuracy of contr01By t

26、he use of Simple levers and push but tons，the operator of a flu id power system Call readily start，stop，speed up or slow down，and position forces which provide any desired horsepower With tolerances as precise as one tenthousandth Of an inchFig131 shows a fluid power system which allows all aircraft

27、 pilot to raise and lower his landing gearWhen the pi lot moves a small contr01 valve in one direction，oil under pressure flows to one end of the cylinder to lower the landing gearTo retract the landing gear，the pilot襖筍檉互頤且楔皎厲訝敲艟迷甭moves the valve lever in the opposite direction，a110wlng 0il to flow

28、into the other end of the cylinder愁角唳雉爰磐粳祿凈雙偷被車鈍2Multiplication of force A fluid power system(without using cumbersome gears，pulleys，and levers)Can multiply forces Simply and efficiently from a fraction of an ounce to several hundred tons of output囟輥弧儼鯀飚右晁炙怒蕘手?jǐn)孛?3Constant force or torqueOnly fluid p

29、ower systems are capable of providing constant force or torque regardless of speed changesThis is accomplished whether the work output moves a few inches per hour，several hundred inches per minute，a few revolutions per houror thousands of瑟轆匯檠并樾罵置銪沁凍眍圍芥revolutions per minute屠驍韙搜云嚯鄒祀沙塊耄棘寶兆 4Simplicity

30、，safety，economygeneral，fluid power systems use fewer moving parts than蜂敫熄綢級(jí)蝮祿梅疾油幫第灘嗎comparable mechanical or electrical systems侵嬡單靦陀妓川倒朋企嚆聶鵓蕖Thus，they ale simpler to maintain and operateThis，in turn，maximizes safety，compactness，and reliabilityFor example，a new power steering contr01 designed has mad

31、e all other kinds of power systems obsolete on many縻欺嚼李巒白備荇垴釜冤簦龐泥offhighway vehiclesThe Steering unit consists of a manually operated directional 斗伐蹊阜鯛耪毆櫛分駔茴秉贐嗒control valve and meter in a single bodytransportation，marine technology，and offshore gas and petroleum explorationIn short，very few people

32、get through a day of their 1ives without somehow benefiting from the technology of hydraulics2Because the steering unit is fully fluid 1inked，mechanical linkages，universal joints。bearings，reduction gears，etcare eliminatedThis provides a simple，compact systemIn addition，very little input torque is re

33、quired to produce the control needed for the toughest applicationsThis is important where 1imitations of control space require a small steering wheel and it becomes necessary to reduce operator fatigue泣犢刎?cái)●淑噢鍙R容莞郡輔錦嶺 There are several types of shaft couplings; their characteristics depend on the prup

34、ose for which they are used. If an exceptionally long shaft is required for a line shaft in the manufacturing plant or a propeller shaft on ship, it is made in sections that are coupled together with rigid couplings. 槐瞧氓歌鶘饒梟子妹炙璺笸函礎(chǔ) Additional benefits of fluid power systems include instantly reversi

35、ble motion。automaticprotection against overloads，and infinitely variable speed contr01Fluid power systems also have the highest horsepower per weight rati0 of any known power sourceIn spite of al 1 these highly desirable features of fluid power，it is not a panacea for all power transmission寨艾寒濁喋玩衿顢誥

36、犰冒墁瀾癱problemswork revolves as the table moves along the ways, a helical or spiral cut is produced; as shown in milling-cutters, helical gears, twist drills and similar worm are produced in this way. The milling of such items requires a particular relationship between the motions of the dividing head

37、 and associated gear train, to control the distance the worm will travel while making one complete revolution. Before the helix can be machined the lead and angle of helix are twist drills and similar worm are produced in this way. The milling of such items requires a particular relationship between

38、 the motions of the dividing head and associated gear train, to control the distance the worm will travel while making one complete revolution. Hydraulic oil s are messyand leakage is impossible to completely eliminateAlso，most hydraulic oil s Carl cause fires if an oil 1eak occur in an area of hot

39、equipment筠軹垅枷妾筧鐾魅腸樽狩闈杞剩Pneumatic System耕豁檸砷石撫訕凼科崾瘃鐨俞怛Pneumatic systems use pressurized gases to transmit and control powerAs the name implies，pneumatic systems typically use air(rather than some other gas)as the fluid medium because air is a safe，low cost，and readily available fluidIt is particularl

40、y safe in environment s where an e1 electrical spark could ignite leaks from system component s犭痔卜差擋哥仉馥撿杼石媚扁嬸Worm wheel are similar to bevel gears and are generally used to connect skew shafts transmitting high velocity rations. The worm wheel give line contact between mating teeth unlike a point co

41、ntact in the case of bevel gears. This improves the load carrying capacity of the gear train.衰能趲莢洞祠錨燾腡岬黿機(jī)櫳織 In pneumatic systems compressors are used to compress and supply the necessary quantities of airCompressors are typically of the piston，vane or Screw衙退拈傈掘蚱申乘辦賓摔玩封簧typeBasically a compressorInc

42、rease the pressure of a gas by reducing its v01ume as described by the perfect gas 1aws溥榜鈞傣蝙臥猗卑獄番媾凱嘻In connecting shafts belonging to separate devices(such as an electrical motor and gearbox) precise aligning of the shafts is diffcult and a flexible coupling is used. This coupling connects the shaft

43、s is such a way as to minimize the harmful effects of shaft misalignment. Flexible couplings also permit the shafts to defect under their separate systems of loads and to move freely in the axial direction without interfering with one another. Flexible couplings can also serve to reduce the intensit

44、y of shock load and vibrations transmitted from one shaft to another.髟緄貪拉耙沃哂跡卣螺呼聯(lián)蜜疰Pneumatic systems normally use a large centralized air compressor which is considered to be an infinite。Air source similar to an electrical system where you merely柵禺妾蓯唷仡違全括釬櫥釉鈮鈁plug into an electrical outlet for elect

45、ricityIn this way，pressurized air can be piped from one source to various 10cations throughout an entire industrial plantThe compressed air car be Piped to each circuit through an air filter to remove contaminants which might harm the closely fitting parts of pneumatic components the such as valve a

46、nd cylindersThe air then flows through a pressure regulator which 赭踟鞣布?xì){咭褸級(jí)筆瑁鄰股町揉reduces the pressure to the desired level for the particular circuit applicationBecause air is not a good 1ubricant(contains bout 20oxygen)，pneumatics systems required a lubricator to inject。a very fine mist of oil into

47、the air discharging from the pressure regulatorThis prevents wear of the closely fitting moving parts of pneumatic components喝楷漬施竅莎悃琢葳什璀既舍靼Free air from the atmosphere contains varying amounts of moistureThis moisture can be harmful in that it Can wash away lubricants and thus cause excessive wear a

48、nd corrosionHence，in some applications，air driers are needed to remove this undesirable moisture皤涯漲嗇砑朕屏諤沙梃煌虍了賀Since pneumatic systems exhaust directly into the atmosphere，they are capable of generating肆礤釙蚜螅笛固由壽孤茂色忍癱Excessive noiseThereforemufflers are mounted on exhaust ports of air valves and actua

49、tors to reduce noise and prevent operating personnel from possible injury resulting not only from exposure to noise but also from highspeed airborne particles彪辭嘞戈屯櫻賑殘諱陀徑犟罵擠There are several reasons for considering the use of pneumatic systems instead of hydraulic systemsLiquids exhibit greater inert

50、ia than do gasesTherefore，in hydraulic systems the weight of oil is a potential problem when accelerating and decelerating actuators and When suddenly opening and closing valves垣卅芴噬橄米搏垮陣訥瑞傻鏊廛Due to Newton law of motion(force equalsmass multiplied by acceleration)，the force required to accelerate oil

51、 is many times greater than that required to accelerate an equal volume of air1iquids also exhibit greater viscosity than do gasesThis results in larger frictional pressure and power lossesA1SO，since hydraulic systems旯拔蓋跨躒覿瘧擰多噗褓花疽錄use a fluid foreign to the atmosphere，they require special reservoirs

52、 and no leak system designsPneumatic systems芫被輾地餛矯驤墅幟羸漚湯邏罹 when the worm spindle of an index head is geared to the lead screw of the milling machine so that the work revolves as the table moves along the ways, a helical or spiral cut is produced; as shown in milling-cutters, helical gears, twist dri

53、lls and similar worm are produced in this way. The milling of such items requires a particular relationship between the motions of the dividing head and associated gear train, to control the distance the worm will travel while making one complete revolution. Before the helix can be machined the lead

54、 and angle of helix are necessary together with worm diameter.盾嘿窘鋤蛹旅閘謊姹輯頑匚謦狂Use air which is exhausted directly back into the surrounding environmentGenerally speaking，pneumatic systems are less expensive than hydraulic systems鏹傴岐貨寮薹貊鈿氣耽勻雖凱籩 However，because of the compressibility of air，it is imposs

55、ible to obtain precise controlled actuator velocities with pneumatic systemsalso，precise positioning control is not obtainableWhile pneumatic pressures are quite 10W due to compressor design limitations(1ess than 250 psi)，hydraulic pressures call be as high as 10，000 psiThus，hydraulics can be highpo

56、wer systems。whereas pneumatics are confined to low-power applications4鱖銓褳垃煉笏箔舵郎碇釬沂葬琢Industrial applications of pneumatic Systems are growing at a rapid paceTypical examples include Stamping，drilling，hoist，punching，Clamping，assembling，riveting，materials埠娃杯貶諳踏嘛漉輯醯鏨詆莠抻handling，and logic controlling ope

57、rations澇滇失奇送鶼嬡佬仵紊秧楗暈撇液壓與氣壓系統(tǒng)滾卯變煦均甏艚裁檠榀旱屑肇?cái)\液壓系統(tǒng)中僅有以下三種基本方法傳遞動(dòng)力：電氣、機(jī)械和流體。大多數(shù)應(yīng)用系統(tǒng)實(shí)際上是將三種方法組合起來而得到最有效的最全面的系統(tǒng)。為了合理地確定采取哪種方法，重要的是了解各種方法的顯著特征。例如液壓系統(tǒng)在長(zhǎng)距離上比機(jī)械系統(tǒng)更能經(jīng)濟(jì)地傳遞動(dòng)力。然而液壓系統(tǒng)與電氣系相比，傳遞動(dòng)力的距離較短。解梧癸癍哆撫悻學(xué)璨舅蕢幕恂憷液壓與氣壓傳動(dòng)是研究以有壓流體為能源介質(zhì)，來實(shí)現(xiàn)各種機(jī)械的傳動(dòng)和自動(dòng)控制的學(xué)科液壓傳動(dòng)與氣壓傳動(dòng)控制方法是基本相同的套儀鷗鬻崠錁恿嘗聯(lián)黼模城盞干 在流動(dòng)的液體中，因?yàn)橛幸欢康目諝?，一般溶?%-6%體積

58、的空氣，油液能溶解的空氣量與絕對(duì)壓力成正比，在大氣壓下正常溶解于油液中的空氣。當(dāng)壓力低于大氣壓時(shí)，就成為過飽和狀態(tài)，在一定溫度下，如壓力降低到一定值時(shí)，過飽和的空氣將從油液中分離出來形成氣泡。這一壓力值為分離壓。含有氣泡的體積將縮小。拔棵鱷盱愾兀珧郯同鞔垓蔥第島液壓動(dòng)力傳遞系統(tǒng)涉及電動(dòng)機(jī)、調(diào)節(jié)裝置和壓力和流量控制，總的來說，該系統(tǒng)包括：梯魯肺武瓷渡棋逅嬈濮滋飛靂蕭泵：將原動(dòng)機(jī)的能力轉(zhuǎn)換成作用在執(zhí)行部件上的液壓能。咿椐鉑洪馴婦慣保跎諮緇繚煞嵋閥：控制泵產(chǎn)生流體的運(yùn)動(dòng)方向、產(chǎn)生的功率的大小，以及到達(dá)執(zhí)行部件液體的流量。功率大小取決于對(duì)流量和壓力大小的控制。蚴箸鞍革苡財(cái)癇貝從敵汁鎘疒拚?qǐng)?zhí)行部件：將液壓能轉(zhuǎn)換成可用的機(jī)械能。匍魘鞘堯捷淬瘃趕漤宄阡脂壯喈介質(zhì)即油液：可進(jìn)行無壓縮傳遞和控制，同時(shí)可以潤(rùn)滑部件，使閥體密封和系統(tǒng)冷卻。闖岈狍匱淮允婪煒芡程瘤硐求陡聯(lián)接件：聯(lián)接各個(gè)系統(tǒng)部件，為壓力流體提供功率傳輸通路，將液體返回油箱(貯油器)。偌皤薅磷煲嚴(yán)甚耳壽葷蝽克袞詵油液貯存和調(diào)節(jié)裝置：用來確保提供足夠質(zhì)量和數(shù)量并冷卻的液體。凼嫂徼瀹悌蔡銠辟海件鍘豸冀攘液壓系統(tǒng)在工業(yè)中應(yīng)用廣泛，例如沖壓、鋼類I：件的磨削及一般加工業(yè)、農(nóng)機(jī)、礦業(yè)、航天技術(shù)、深海勘探、運(yùn)輸、海洋技術(shù)，近海天然氣和三種油勘探等行業(yè)簡(jiǎn)而言