专业英语第10单元作业.docx

专业英语第10单元作业.docx

《专业英语第10单元作业.docx》由会员分享，可在线阅读，更多相关《专业英语第10单元作业.docx（15页珍藏版）》请在冰豆网上搜索。

专业英语第10单元作业

10IntroductionofProgrammableControllers

Fromasimpleheritage,theseremarkablesystemshaveevolvedtonotonlyreplaceelectromechanicaldevices,buttosolveanever-increasingarrayofcontrolproblemsinbothprocessandnonprocess.Byallindications,thesemicroprocessorpoweredgiantswillcontinuetobreaknewground开辟新天地intheautomatedfactoryintothe1990s.

10.1HISTORY

Inthe1960s,electromechancaldevicesweretheorderoftheday风尚asfarascontrolwasconcerned.Thesedevices,commonlyknownasrelays,werebeingusedbythethousandstocontrolmanysequential-typemanufacturingprocessandstand-alonemachines.Manyoftheserelayswereinuseinthetransportationindustry,morespecifically,theautomotiveindustry.Theserelaysusedhundredsofwiresandtheirinterconnectionstoeffectacontrolsolution.Theperformanceofarelaywasbasicallyreliable—atleastasasingledevice.Butthecommonapplicationsforrelaypanels（继电器盘，配电盘）calledfor要求300to500ormorerelays,andthereliabilityandmaintenanceissuesassociatedwithsupportingthesepanelsbecameaverygreatchallenge.Costbecameanotherissue,forinspiteofthelowcostoftherelayitself,theinstalledcostofthepanelcouldbequitehigh.Thetotalcostincludingpurchasedparts,wiring,andinstallationlabor,couldrangefrom$30~$50perrelay.Tomakemattesworse,theconstantlychangingneedsofaprocesscalledforrecurringmodificationsofacontrolpanel.Withrelays,thiswasacostlyprospect,asitwasaccomplishedbyamajorrewiringeffortonthepanel.Inaddition,thesechangesweresometimespoorlydocumented（验证）,causingasecond-shiftmaintenancenightmaremonthslater.Inlightof（按照）this,itwasnotuncommontodiscard（放弃）anentirecontrolpanelinfavorofanewonewiththeappropriatecomponentswiredinamannersuitedforthenewprocess.Addtothistheunpredictable,andpotentiallyhigh,costofmaintainingthesesystemsasonhigh-volumemotorvehicleproductionlines,anditbecameclearthatsomethingwasneededtoimprovethecontrolprocess-tomakeitmorereliable,easiertotroubleshoot故障检修,andmoreadaptabletochangingcontrolneeds.

以上女生完成

Thatsomething,inthelate1960s,wasthefirstprogrammablecontroller.Thisfirst‘revolutionary’systemwasdevelopedasaspecificresponsetotheneedsofthemajorautomotivemanufacturersintheUnitedStates.Theseearlycontrollers,orprogrammablelogiccontrollers（PLC）,representedthefirstsystemsthat①couldbeusedonthefactoryfloor场地,②couldhavethere‘logic’changedwithoutextensiverewiringorcomponentchanges,and③wereeasytodiagnoseandrepairwhenproblemsoccurred.

Itisinterestingtoobservetheprogressthathasbeenmadeinthepast15yearsintheprogrammablecontrollerarea.Thepioneerproductsofthelate1960smusthavebeenconfusingandfrighteningtoagreatnumberofpeople.Forexample,whathappenedtothehardwired硬接线andelectromechanicaldevicesthatmaintenancepersonnelwereusedtorepairingwithhandtools?

Theywerereplacedwith‘computers’disguised（伪装）aselectronicsdesignedtoreplacerelays.Eventheprogrammingtoolsweredesignedtoappearasrelayequivalentpresentations.Wehavetheopportunitynowtoexaminethepromise,inretrospect回顾,thattheprogrammablecontrollerbroughtmanufacturing.

以上719完成

10.2BASICCONCEPTS

AllprogrammablecontrollersconsistofthebasicfunctionalblocksshowninFig.10.1.We’llexamineeachblocktounderstandtherelationshiptothecontrolsystem.Firstwelookatthecenter,asitistheheart（oratleastthebrain）ofthesystem.Itconsistsofamicroprocessor,logicmemoryforthestorage存储oftheactualcontrollogic,storageorvariablememory（变量存储器）forusewithdatethatwillordinarilychangeasafunctionofthecontrolprogramexecution执行,andapowersupplytoprovideelectricalpowerfortheprocessorandmemory.NextcomestheI/Oblock.ThisfunctiontakesthecontrollevelsignalsfortheCPUandconvertsthemtovoltageandcurrentlevelssuitableforconnectionwithfactorygradesensorsandactuators.TheI/Otypecanrangefromdigital（discreteoron/off）,analog（continuouslyvariable）,oravarietyofspecialpurpose‘smart’I/Owhicharededicatedtoacertainapplicationtask.Theprogrammer编程器isshownhere,butitisnormallyusedonlytoinitiallyconfigureandprogramasystemandisnotrequiredforthesystemtooperate.Itisalsousedintroubleshootingasystem,andcanprovetobeavaluabletoolinpinpointingtheexactcauseofaproblem.ThefielddevicesshownhererepresentthevarioussensorsandactuatorsconnectedtotheI/O.Thesearethearms,legs,eyes,andearsofthesystem,includingpushbuttons,limitswitches,proximityswitches,photosensors,thermocouples热电偶,RTDs电阻式温度传感器,positionsensingdevices,andbarcodereader条形码阅读器asinput;andpilotlights指示灯,displaydevices,motorstarters,DCandACdrives,solenoids螺线管,andprintersasoutputs.

Nosingleattemptcouldcoveritsrapidlychangingscope,butthreebasiccharacteristicscanbeexaminedtogiveclassifyanindustrialcontroldeviceasaprogrammablecontroller.

（1）Itsbasicinternaloperationistosolvelogicfromthebeginningofmemorytosomespecifiedpoint,suchasendofmemoryorendofprogram.Oncetheendisreached,theoperationbeginsagainatthebeginningofmemory.Thisscanning扫描processcontinuesfromthetimepowerissuppliedtothetimeitisremoved.

（2）Theprogramminglogicisaformofarelayladderdiagram梯形图.Normallyopen,normallyclosedcontacts,andrelaycoilsareusedwithinaformatutilizingaleftandarightverticalrail（左母线和右母线）.Powerflow能流（symbolicpositiveelectronflow）isusedtodeterminewhichcoilsoroutputsareenergizedordeenergized.

（3）Themachineisdesignedfortheindustrialenvironmentfromitsbasicconcept;thisprotectionisnotaddedatalaterdate.TheindustrialenvironmentincludesunreliableACpower,hightemperatures（0to60degreeCelsius）,extremesofhumidity,vibrations,RF（RadioFrequency射频）noise,andothersimilarparameters.

10.3GENERALAPPLICATIONAREAS

Theprogrammablecontrollerisusedinawidevarietyofcontrolapplicationstoday,manyofwhichwerenoteconomicallypossiblejustafewyearsago.Thisistruefortwogeneralreasons:

①theircosteffectiveness费效比（thatis,thecostperI/Opoint）hasimproveddramaticallywiththefallingpricesofmicroprocessorsandrelatedcomponents,and②theabilityofthecontrollertosolvecomplexcomputationandcommunicationtaskshasmadeitpossibletouseitwhereadedicatedcomputer专用计算机waspreviouslyused.

以上718完成

Applicationsforprogrammablecontrollerscanbecategorizedinanumberofdifferentways,includinggeneralandindustrialapplicationcategories.Butitisimportanttounderstandtheframeworkinwhichcontrollersarepresentlyunderstoodandusedsothatthefullscopeofpresentandfutureevolutioncanbeexamined.Itisthroughthepowerofapplicationsthatcontrollerscanbeseenintheirfulllight角度.Industrialapplicationsincludemanyinbothdiscretemanufacturing独立制造andprocessindustries过程工业.Automotiveindustryapplications,thegenesisoftheprogrammablecontrollers,continuetoprovidethelargestbaseofopportunity.Otherindustries,suchasfoodprocessing食品加工andutilities,providecurrentdevelopmentopportunities.

Therearefivegeneralapplicationareasinwhichprogrammablecontrollersareused.Atypicalinstallationwilluseoneormoreoftheseintegratedtoformacompletesolutiontothecontrolsystemproblem.Thefivegeneralareasareexplainedbrieflybelow.

10.3.1Sequencecontrol

Thisisthelargestandmostcommonapplicationforprogrammablecontrollerstoday,andistheclosesttotraditionalrelaycontrolinits‘sequential’nature.Becauseoftheverygeneralnatureofthiscategory,itissometimesdifficulttounderstandthebreadth宽度ofpowerthatitbringstosomanyapplications.Fromanapplicationsstandpoint,sequencecontrolisfoundonindividualmachinesormachinelines,onconveyorandpackagingmachinery,andevenonmodernelevatorcontrolsystems.

10.3.2MotionControl

Thisistheintegrationoflinearorrotarymotioncontrolintheprogrammablecontroller.Thiscouldbeasingleormultipleaxisdrive多轴驱动systemcontrol,andcanbeusedwithservo伺服,stepper步进,orhydraulic液压drives.Inearlysystems,astand-aloneservodrivewouldbeconnectedtotheprogrammablecontrollerwithaseriesofindividualconductorstodiscreteinputsandoutputs.NewersystemsintegratethisfunctionalitydirectlyintotheI/Oracks机架throughtheuseofspecialI/Oboardsdedicatedtomotioncontrol.Thiseliminates消除theneedtointerface接口thetwodevicestogetherwithdiscreteI/O.Programmablecontrollermotioncontrolapplicationsincludeanunendingvarietyofmachinery;metalcutting金属切割（grinders磨床）,metalforming金属成形（pressbrake碾压成型）,assemblymachines机器组装,andmultipleaxesofmotioncanbecoordinatedforbothdiscretepartandprocessindustryapplications.ExamplesofthesewouldincludeCartesianrobots笛卡尔坐标机器人,andmanywebrelatedprocessesthatis,film涂膜,rubber橡胶,andnonwoven非纺织的textile纺织品（即无纺布）systems.

10.3.3Processcontrol

Thisistheabilityoftheprogrammablecontrollertocontrolanumberofphysicalparameterssuchastemperature,pressure,velocity,andflow.Thisinvolvestheuseofanalog（continuouslyvariable）I/Otoachievea（PID）,softwarealwaysallowtheprogrammablecontroller,retainingthebestfeaturesofeach.Typicalexamplesofapplicationsincludeplasticinjectionmolding注射成型machines,extrusionprocess挤出成型machines,heattreatfurnaces热处理炉,andmanyotherbatch-type分批式controlapplications.

10.3.4DataManagement数据管理