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外文翻译--数字控制.doc

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外文翻译--数字控制.doc

1NumericalControlWithChinabeingfasttobecomeglobalmanufacturingcenter,ofourcountrymanufacturingindustryinrecentyearsdevelopswiftandviolent,numericalcontrolisitbecomemarketcompetitionandenterprisedevelopmentnewandonalreadytoprocess,CADandmanufactureCAD/CAMbecomeahotissueofthemechanicalmanufacturingindustry.OneofthemostfundamentalconceptsintheareaofadvancedmanufacturingtechnologiesisnumericalcontrolNC.PriortotheadventofNC,allmachinetoolsweremanuallyoperatedandcontrolled.Amongthemanylimitationsassociatedwithmanualcontrolmachinetools,perhapsnoneismoreprominentthanthelimitationofoperatorskills.Withmanualcontrol,thequalityoftheproductisdirectlyrelatedtoandlimitedtotheskillsoftheoperator.Numericalcontrolrepresentsthefirstmajorstepawayfromhumancontrolofmachinetools.Numericalcontrolofmachinetoolsisreportedtohavebeenfirstdevelopedbetween1947and1952attheMassachusettsinstituteofTechnology,inconjunctionwiththeParsonsAircraftCorporation.Thedevelopmentofnumericalcontroltechniquesisaccreditedtotheneedforproducingveryaccuratelysizedandintricatelyshapedpartsforaircraft,principallyspacevehicles.Becauseofthecomplexshapes,considerabletimeswasbeingspentinensuringthatthework/toolrelationshipwascorrectbeforemachiningtookplacethisledtolongmanufacturingtimesandhencehighcosts.Inordertoreducecosts,attemptsweremadetocontrolautomaticallythework/toolrelationship.ThisresultedinthedevelopmentofpositionalcontrolusingnumericalprinciplesonaCincinnatiHydrotelverticalmill.Numericalcontrolmeansthecontrolofmachinetoolsandothermanufacturingsystemsthroughtheuseofprerecorded,writtensymbolicinstructions.Ratherthanoperatingamachinetool,anNCtechnicianwritesaprogramthatissuesoperationalinstructionstothemachinetool.Foramachinetooltobenumericallycontrolled,itmustbeinterfacedwithadeviceforacceptinganddecodingtheprogrammedinstructions,knownasareaderNumericalcontrolwasdevelopedtoovercomethelimitationofhumanoperators,andithasdoneso.Numericalcontrolmachinesaremoreaccuratethanmanuallyoperatedmachines,theycanproducepartsmoreuniformly,theyarefaster,andthelongruntoolingcostsarelower.ThedevelopmentofNCledtothedevelopmentof2severalotherinnovationsinmanufacturingtechnologyElectricaldischargemachining.Lasercutting.Electronbeamwelding.Numericalcontrolhasalsomademachinetoolsmoreversatilethantheirmanuallyoperatedpredecessors.anNCmachinetoolcanautomaticallyproduceawidevarietyofparts,eachinvolvingancontrolhasallowedmanufacturerstoundertaketheproductionofproductsthatwouldnothavebeenfeasiblefromaneconomicperspectiveusingmanuallycontrolledmachinetoolsandprocesses.Likesomanyadvancedtechnologies,NCwasborninthelaboratoriesoftheMassachusettsInstituteofTechnology.TheconceptofNCwasdevelopedintheearly1950swithfundingprovidedbytheU.S.AirForce.Initsearlieststages,NCmachinesereabletomakestraightcutsefficientlyandeffectively.However,curvedpathswereaproblembecausethemachinetoolhadtobeprogrammedtoundertakeaseriesofhorizontalandverticalstepstoproduceacurve.theshorterthestraightlinesmakingupthesteps,thesmootheristhecurve.Eachlinesegmentinthestepshadtobecalculated.Thisproblemledtothedevelopmentin1959oftheAutomaticallyProgrammedToolsAPTlanguage.ThisisaspecialprogramminglanguageforNCthatusesstatementssimilartoEnglishlanguagetodefinethepartgeometry,describethecuttingtoolconfiguration,andspecifythenecessarymotions.ThedevelopmentoftheAPTlanguagewasamajorstepforwardinthefurtherdevelopmentofNCtechnology.TheoriginalNCsystemswerevastlydifferentformthoseusedtoday.Themachineshadhardwiredlogiccircuits.Theinstructionalprogramswerewrittenonpunchedpaper,whichwaslatertobereplacedbymagneticplastictape.Atapereaderwasusedtointerprettheinstructionswrittenonthetapeforthemachine.Together,allofthisrepresentedagiantstepforwardinthecontrolofmachinetools.However,therewereanumberofproblemswithNCatthispointinitsdevelopment.Amajorproblemwasthefragilityofthepunchedpapertapemedium.Itwascommonforthepapertapecontainingtheprogrammedinstructionstobreakortearduringamachiningprocess.Thisproblemwasexacerbatedbythefactthateachsuccessivetimeapartwasproducedonamachinetool,thepapertapecarryingtheprogrammedinstructionshadtobererunthroughthereader.Ifitwasnecessarytoproduce100copiesofagivenpart,Ifitwasalsonecessarytorunthepapertapethroughthereader100separatetimes.Fragilepapertapessimplycouldnotwithstand3therigorsofashopfloorenvironmentandthiskindofrepeateduse.Thisledtothedevelopmentofaspecialmagneticplastictape.Whereasthepapertapecarriedtheprogrammedinstructionsasaseriesofholespunchedinthetape,theplastictapecarriedtheinstructionsasaseriesofmagneticdots.Theplastictapewasmuchstrongerthanthepapertape,whichsolvedtheproblemoffrequenttearingandbreakage.However,itstilllefttwootherproblems.Themostimportantofthesewasthatitwasdifficultorimpossibletochangetheinstructionsenteredonthetape.Tomakeeventhemostminoradjustmentsinaprogramofinstructions,itwasnecessarytointerruptmachiningoperationsandmakeanewtape.Itwasalsostillnecessarytorunthetapethroughthereaderasmanytimesastherewerepartstobeproduced,fortunately,computertechnologybecamearealityandsoonsolvedtheofNCassociatedwithpunchedpaperandplastictape.ThedevelopmentofaconceptknownasdirectnumericalcontrolDNCsolvedthepaperandplastictapeproblemsassociatedwithnumericalcontrolbyeliminatingtapeasthemediumforcarryingtheprogrammedinstructions.Indirectnumericalcontrol,machinetoolsaretied,viaadatatransmissionlink,toahostcomputer.Programsforoperatingthemachinetollsarestoredinthehostcomputerandfedtothemachinetoolasneededviathedatatransmissionlinkage.Directnumericalcontrolrepresentedamajorstepforwardoverpunchedtapeandplastictape.However,itissubjecttothesamelimitationsasalltechnologiesthatdependonahostcomputer.Whenthehostcomputergoesdown,themachinetoolsalsoexperiencedowntime.Thisproblemledtothedevelopmentofcomputernumericalcontrol.ThedevelopmentofthemicroprocessorallowedforthedevelopmentofprogrammablelogiccontrollersPLCsandmicrocomputers.ThesetwotechnologiesallowedforthedevelopmentofcomputernumericalcontrolCNC.WithCNC,eachmachinetoolhasaPLCoramicrocomputerthatservesthesamepurpose.Thisallowsprogramstobeinputandstoredateachindividualmachinetool.Italsoallowsprogramstobedevelopedofflineanddownloadedattheindividualmachinetool.CNCsolvedtheproblemsassociatedwithdowntimeofthehostcomputer,butitintroducedanotherproblemknownasdatamanagement.Thesameprogrammightbeloadedontendifferentmicrocomputerswithnocommunicationamongthem.Thisproblemisintheprocessofbeingsolvedbylocalareanetworksthatconnectmicrocomputersforbetterdatamanagement.Asapplicationthatnumericalcontrolisprocessedbeingextensivewithdeepeningdaybyday,CADandmanufactureCAD/CAMbecomeahotissueofthe4mechanicalmanufacturingindustry.MakebyBeijingInstituteofAeronauticsCAXAthatHaierdevelopengineerrelyoncharacteristiconfunctioncomplete,easytolearnandusetheiruseextensively.CAXAisusedinnumericalcontrolmillingmachine,numericalcontrollathe,wirecuttingmachinetoolandmachiningcenter,etc.mainly.ThistextdiscussesapplicationonthemachiningcenterofCAD/CAMsystem,itsessenceisthatCAXAmakestheengineerXPapplicationonmachiningcenter.Atthisstage,manyplantscommonlyusedtwodimensionaldesignsoftwarefor2Ddesignpartsoftheplans,andthecraftspersonnel/programmerat3DconceptdirectlytoGcodeoraptlanguageofNCprogramming.Thisapproachappliestosimplegraphicprocessingcomponents,linearprocessing,turnaroundprocessinghardwareprocessingandpointspaces.Itsprogrammingisfastercodeconcise.Forcomplexgeometricshapes,jigassemblycomplex,especiallyfornonYuancamberprocessing,theprogrammingmethodwasverydifficult.Asatrajectoryofspacegeometricfigureandthemathematicalcalculationofhandlinglarge,complexprocess,noteasilygraspandprogrammingprocess,theconstituentelementsoftheenvironmentcannotbeprocessedgeometricspacerelationsbetweeninspections.Aknifespacestargetcoordinatestothegeometricfiguretoinspectprocessing,precisionlow,notvisual,andtherefore,theneeddebuggingprocedures,occupancydigitalmachinehours,technicalpreparationsforthecyclelonger.

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