CRC编码的Simulink仿真实现

CRC编码的Simulink仿真实现CRC编码的Simulink仿真实现第页共17页functionsys=mdlOutputs(t，X，U。m。G)计算输出结果sys=R；付：外文翻译电火花加工电火花加工法对加工超韧性的导电材料（如新的太空合金）特别有价值。这些金属很难用常规方法加工，用常规的切削刀具不可能加工极其复杂的形状，电火花加工使之变得相对简单了。在金属切削工业中，这种加工方法正不断寻找新的应用领域。塑料工业已广泛使用这种方法，如在钢制模具上加工几乎是任何形状的模腔。电火花加工法是一种受控制的金属切削技术，它使用电火花切除（侵蚀）工件上的多余金属，工件在切削后的形状与刀具（电极）相反。切削刀具用导电材料（通常是碳）制造。电极形状与所需型腔想匹配。工件与电极都浸在不导电的液体里，这种液体通常是轻润滑油。它应当是点的不良导体或绝缘体。用伺服机构是电极和工件间的保持0.0005~0.001英寸（0.01~0.02mm）的间隙，以阻止他们相互接触。频率为20000Hz左右的低电压大电流的直流电加到电极上，这些电脉冲引起火花，跳过电极与工件的见的不导电的液体间隙。在火花冲击的局部区域，产生了大量的热量，金属融化了，从工件表面喷出融化金属的小粒子。不断循环着的不导电的液体，将侵蚀下来的金属粒子带走，同时也有助于驱散火花产生的热量。在最近几年，电火花加工的主要进步是降低了它加工后的表面粗糙度。用低的金属切除率时，表面粗糙度可达2—4vin.(0.05—0.10vin)。用高的金属切除率[如高达15in3/h(245.8cm3/h)]时，表面粗糙度为1000vin.(25vm)。需要的表面粗糙度的类型，决定了能使用的安培数,电容,频率和电压值。快速切除金属（粗切削）时，用大电流,低频率,高电容和最小的间隙电压。缓慢切除金属（精切削）和需获得高的表面光洁度时，用小电流,高频率,低电容和最高的间隙电压。与常规机加工方法相比，电火花加工有许多优点。.不论硬度高低，只要是导电材料都能对其进行切削。对用常规方法极难切削的硬质合金和超韧性的太空合金，电火化加工特别有价值。.工件可在淬火状态下加工，因克服了由淬火引起的变形问题。.很容易将断在工件中的丝锥和钻头除。.由于刀具（电极）从未与工件接触过，故工件中不会产生应力。.加工出的零件无毛刺。.薄而脆的工件很容易加工，且无毛刺。.对许多类型的工件，一般不需第二次精加工。.随着金属的切除，伺服机构使电极自动向工件进给。.一个人可同时操作几台电火花加工机床。10.能相对容易地从实心坯料上，加工出常规方法不可能加工出来的极复杂的形状。11.能用较低价格加工出较好的模具。12.可用冲头作电极，在阴模板上复制其形状，并留有必须的间隙。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