CRC編碼的Simulink仿真實(shí)現(xiàn)

CRC編碼的Simulink仿真實(shí)現(xiàn)CRC編碼的Simulink仿真實(shí)現(xiàn)第頁(yè)共17頁(yè)functionsys=mdlOutputs(t，X，U。m。G)計(jì)算輸出結(jié)果sys=R；付：外文翻譯電火花加工電火花加工法對(duì)加工超韌性的導(dǎo)電材料（如新的太空合金）特別有價(jià)值。這些金屬很難用常規(guī)方法加工，用常規(guī)的切削刀具不可能加工極其復(fù)雜的形狀，電火花加工使之變得相對(duì)簡(jiǎn)單了。在金屬切削工業(yè)中，這種加工方法正不斷尋找新的應(yīng)用領(lǐng)域。塑料工業(yè)已廣泛使用這種方法，如在鋼制模具上加工幾乎是任何形狀的模腔。電火花加工法是一種受控制的金屬切削技術(shù)，它使用電火花切除（侵蝕）工件上的多余金屬，工件在切削后的形狀與刀具（電極）相反。切削刀具用導(dǎo)電材料（通常是碳）制造。電極形狀與所需型腔想匹配。工件與電極都浸在不導(dǎo)電的液體里，這種液體通常是輕潤(rùn)滑油。它應(yīng)當(dāng)是點(diǎn)的不良導(dǎo)體或絕緣體。用伺服機(jī)構(gòu)是電極和工件間的保持0.0005~0.001英寸（0.01~0.02mm）的間隙，以阻止他們相互接觸。頻率為20000Hz左右的低電壓大電流的直流電加到電極上，這些電脈沖引起火花，跳過(guò)電極與工件的見(jiàn)的不導(dǎo)電的液體間隙。在火花沖擊的局部區(qū)域，產(chǎn)生了大量的熱量，金屬融化了，從工件表面噴出融化金屬的小粒子。不斷循環(huán)著的不導(dǎo)電的液體，將侵蝕下來(lái)的金屬粒子帶走，同時(shí)也有助于驅(qū)散火花產(chǎn)生的熱量。在最近幾年，電火花加工的主要進(jìn)步是降低了它加工后的表面粗糙度。用低的金屬切除率時(shí)，表面粗糙度可達(dá)2—4vin.(0.05—0.10vin)。用高的金屬切除率[如高達(dá)15in3/h(245.8cm3/h)]時(shí)，表面粗糙度為1000vin.(25vm)。需要的表面粗糙度的類型，決定了能使用的安培數(shù),電容,頻率和電壓值。快速切除金屬（粗切削）時(shí)，用大電流,低頻率,高電容和最小的間隙電壓。緩慢切除金屬（精切削）和需獲得高的表面光潔度時(shí)，用小電流,高頻率,低電容和最高的間隙電壓。與常規(guī)機(jī)加工方法相比，電火花加工有許多優(yōu)點(diǎn)。.不論硬度高低，只要是導(dǎo)電材料都能對(duì)其進(jìn)行切削。對(duì)用常規(guī)方法極難切削的硬質(zhì)合金和超韌性的太空合金，電火化加工特別有價(jià)值。.工件可在淬火狀態(tài)下加工，因克服了由淬火引起的變形問(wèn)題。.很容易將斷在工件中的絲錐和鉆頭除。.由于刀具（電極）從未與工件接觸過(guò)，故工件中不會(huì)產(chǎn)生應(yīng)力。.加工出的零件無(wú)毛刺。.薄而脆的工件很容易加工，且無(wú)毛刺。.對(duì)許多類型的工件，一般不需第二次精加工。.隨著金屬的切除，伺服機(jī)構(gòu)使電極自動(dòng)向工件進(jìn)給。.一個(gè)人可同時(shí)操作幾臺(tái)電火花加工機(jī)床。10.能相對(duì)容易地從實(shí)心坯料上，加工出常規(guī)方法不可能加工出來(lái)的極復(fù)雜的形狀。11.能用較低價(jià)格加工出較好的模具。12.可用沖頭作電極，在陰模板上復(fù)制其形狀，并留有必須的間隙。ElectricaldischargemachiningElectricaldischargemachininghasprovedespeciallyvaluableinthemachiningofsuper-tough,electricallyconductivematerialssuchasthenewspace-agealloys.Thesemetalswouldhavebeendifficulttomachinebyconventionalmethods,butEDMhasmadeitrelativelysimpletomachineintricateshapesthatwouldbeimpossibletoproducewithconventionalcuttingtools.Thismachiningprocessiscontinuallyfindingfurtherapplicationsinthemetal-cuttingindustry.Itisbeingusedextensivelyintheplasticindustrytoproducecavitiesofalmostanyshapeinthesteelmolds.Electricaldischargemachiningisacontrolledmetalremovaltechniquewherebyanelectricsparkisusedtocut(erode)theworkpiece,whichtakesashapeoppositetothatofthecuttingtoolorelectrode.Thecuttingtool(electrode)ismadefromelectricallyconductivematerial,usuallycarbon.Theelectrode,madetotheshapeofthecavityrequired,andtheworkpiecearebothsubmergedinadielectricfluid,whichisgenerallyalightlubricatingoil.Thisdielectricfluidshouldbeanonconductor(orpoorconductor)ofelectricity.Aservomechanismmaintainsagapofabout0.0005to0.001in.(0.01to0.02mm)betweentheelectrodeandthework,preventingthemfromcomingintocontactwitheachother.Adirectcurrentoflowvoltageandhighamperageisdeliveredtotheelectrodeattherateofapproximately20000hertz(Hz).Theseelectricalenergyimpulsesbecomesparkswhichjumpthedielectricfluid.Intenseheatiscreatedinthelocalizedareaoftheparkimpact,themetalmeltsandasmallparticleofmoltenmetalisexpelledfromthesurfaceoftheworkpiece.Thedielectricfluid,whichisconstantlybeingcirculated,carriesawaytheerodedparticlesofmetalandalsoassistsindissipatingtheheatcausedbythespark.Inthelastfewyears,majoradvanceshavebeenmadewithregardtothesurfacefinishesthatcanbeproduced.Withthelowmetalremovalrates,surfacefinishesof2to4um.(0.05to0.10um)arepossible.Withhighmetalremovalratesfinishesof1000uin.(25um)areproduced.Thetypeoffinishrequireddeterminesthenumberofampereswhichcanbeused,thecapacitance,frequency,andthevoltagesetting.Forfastmetalremoval(roughingcuts),highamperage,lowfrequency,highcapacitance,andminimumgapvoltagearerequired.Forslowmetalremoval(finishcut)andgoodsurfacefinish,lowamperage,highfrequency,lowcapacitance,andthehighestgapvoltagearerequired.Electricaldischargemachininghasmanyadvantagesoverconventionalmachiningprocesses.Anymaterialthatiselectricallyconductivecanbecut,regardlessofitshardness.Itisespeciallyvaluableforcementedcarbidesandthenewsupertoughspace-agealloysthatareextremelydifficulttocutbyconventionalmeans.Workcanbemachinedinahardenedstate,therebyovercomingthedeformationcausedbythehardeningprocess.Brokentapsordrillscanreadilyberemovedfromworkpieces.Itdoesnotcreatestressesintheworkmaterialsincethetool(electrode)nevercomesincontactwiththework.Theprocessisburr-free.Thin,fragilesectionscanbeeasilymachinedwithoutdeforming.Secondaryfinishingoperationsaregenerallyeliminatedformanytypesofwork.Theprocessisautomaticinthattheservomechanismadvancestheelectrodeintotheworkasthemetalisremoved.OnepersoncanoperateseveralEDMmachinesatonetime.Intricateshapes,impossibletoproduce