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外文翻译--数字控制的发展及数控用传感器.doc

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外文翻译--数字控制的发展及数控用传感器.doc

英文原文ThedevelopmentofNCandTransducersforNCmachineToolsThefirstNCmachinesusedvacuuintubes,electricalrelays,andcomplicatedmachinecontrolinterfaces.Theseciondgenerationofmachinesutilizedimprovedminiatureelectronictubes,andlatersolidstatecircuits.Ascomputertechonologyimproved,NCunderwentoneofthemostrapidchangesknowninhistory.Thethirdgenerationusedmuchimprovedintegratedcircuits.ComputerhardwarebecameprogressicelulessexpensiveandmorereliableandNCcontrolbuildersintroducedforthefirsttimeReadOnlymemoryROMtechnology.ROMwastypicallyusedforprogramstorageinspecialpurposeapplications,leadingtotheappearanceofthecomputernumericalcontrolCNCsystem,CNCwassuccessfullyintroducedtopracticallyeverymanufacturingprocess.Drilling,millingandturningwereperformedonmachingingcentersandturningcenters.CNCtookoverglasscutting,patternmaking,electricaldischargemaching,steelmillrollgrinding,coordinatemeasuring,electronbeamwelding,tubebending,drafting,printedcircuitmanufacturing,coilwinding,functionaltesting,robots,andmanyotherprocesses.Asetofpreprogrammedsubroutines,namedcannedcycles,weredevelopedforyseinroutineoperations.TheywererecordedintotheROMsandremainedthereevenafterpowerwasshutoff.Forthefirsttime,thisconceptmadeitpossibletoreadthemachingingprogramintomemoryandtooperatethemachinefrommemory.Inadditiontotheadvantagesofediting,theproblemscausedbyerroneoustapereadingdisappeared.Alongwiththemanycannedcycleoptions,CNCbuildersintrodyceddisplaysforvisualeditingofpartprogramsinmemiry.Variousincycleproblemsgeneratedalarmsandhundredsofdiafnosticmessageswhichcouldbedisplayedasapplicable.Practicallyeveryfunctionofthemachinewastiedintothesystemandmonitoredduringoperation.Aconstantsurfacespeedcontrolwasincorporatedandcontinuouslyanticipatedthemostefficientspindlespeedofthenextcuttominimizetimelostforspindleacceleratin.Theconventionallinearandcircularinterpolationincartesiaretangularcoordinatesweresupplementedbypolarcoordinatesandhelicalinterpolation.Safezones,whichcouldbesetthroughprogrammedcodesorinternalparameters,createanelectroniccrashbarriertopreventtoolcollisionmanufacturinginmetalcuttingindustry.Theimprovementindriveswasasimportantforthesystemasthecontributionofthemicroprocessorortheminicomputer.Thefeeddrives,usuallyknownasservodrives,consistofamotoranditscontrolwhichreceivesitsmotioninstructionsfromtheCNC.theirperformanceisessentialtotheaccuracy,reliability,andflexibilityoftheCNCsystem.Theopenloopsystemisnormallyusedinsimplepointtopoint,orpositioningsystems,althoughimprovementsintechnologyhavemadeitpossibletoinstallthesystemincontiuringsystemsaswell.Theclosedloopconfigurationismoreaccurateandreliable,asreflectedbyitshighercost.AlthoughmanyCNCsystemstillusehydraulicorpulesmotors,theDCdriveshavegaineddominanceonamuchlargerscale.Inmostcases,thedrivepackagesarepurchasedfromspecializeddrivesystembuilders.ThesedirectcurrentDCpermanentmagnetwoundfieldserviomatorsrangefrom3,000revolutionsperminutetolessthan1rpmwethoutstalling.Theydeveloppeaktorquecapabilitieswithhighslideaccelerationandlowinertiaforoptimizedsystemresponse.Mostdrivesystemsofferachoicebetweentransistorizedsiliconecontrolledrectigiersandpulsewidthmodulationoverthefullrangeofamplifiedvoltages.Thesedrivescannowdrivevirtuallyanyleadscrew.Theirhighresponseinnercurrentloopsprovidereliableregulationoftorqueloaddisturbances,Theycanalsobebuiltwithhighgainpreamplofierstoclosehighbandwidthvelocityoops.TheDCdrivesprovidetheanswertithemostessentialneedsofacceleration,deceleration,stopping,andconstantvelocity,withinherentshaftstiffnessforsuccessfuloperationoftheCNCsystem.Thesamedrivesystemsactuaterobots,transferlines.flifhtsimulators,graphicplotters,ect.Asthesedivesareinfinitelyvariableandfullyregenerative,theycanprovidefirmaximumperformanceandcontroloverthewholerangeofthemotor.Byeliminatinggearboxesandclutches,thecostocdrivesforthethirdgenerationCNCsystemswasreducedsubstantiallyThefourthgenerationmicroprocessorCNCincorporatedinmanycasesthecontroversialbiblememory.Thebiblesaremagneticgarnetcrystalsgrownonnonvolatiledatastorage.Althoughatthisstageitisnotcompetitiveinthelargecomputers,thebiblememoryisclosingthecostgapwithdiskstoragedevices.Insensitivetoadversetemperaturechanges,dust,andvebration,thebubblememoryhasdemonstratedsuperioereliabilityinshopenveronment.GeneralNumericsintroduceditsfourthgenerationCNCusingbubblememoryhoweverHitachi,anotherelectronicgiant,believesthatbubblememorywillprovidetheeconomicalanswertodirectnumericalcontrolDNC.AmongthestrengthsofthefourthgenerationmecroprocessorCNCMCNCareaddedpartprogrammemorystorage,reductionofprintedcircuitboards,programmableinterface,fastermemoryaccess,parametricsubroutines,andmacrocapabilities.Thesystemusercannowwritespecificcannedcyclesdirectedtoparticularapplicationsusermacros,farmoreeconomicalandefficientthanconventionalcannedcycles.Mathematicalcalculationswithdoloopsubroutinesusingvariablescannowbeincorporatedinthepartprogram.Themicroprocessorcontrolsbothcomputationsandmotioncommands.Thus,followinganinprocessgaging,anoutoftoleranceconditionwillbefedback,andthetooloffsetwillbeautomaticallymodifiedtoachievethedesiredpartdimensions.PositioningfeedbackdevicesforNCcanbeclassifiedintotwogroups,viz.rotaryandlineartransducers.Rotarytransducersmaybeconnectedtotheleadscreweithyerdirectlyorthroughprecisiongearing.ThisfeedbackdevicemeasuresindirectlythepositionoftheslideasitmeasuressomeangleandthefeedtrainratiorelatestheSametothelinearmovementoftheslide.Ontheotherhand,lineartransducersindicatethepositionoftheslidedirectly.Inthiscaseonepartofthetransducerisfixedtothemachinetoolstructure.Theotherpartisattachedtoaslidewhichmovesoverthestationarypart.RotaryTransducersRotarytransducersarequitepopularwithNCmachinemanufacturersbecauseoftheircompactsizeandtheflexibilitywithwhichthesecanbeused.Therearetwoprimarytypesofrotarytransducersresolversandencoderstheresolverisananalogdevicewhoseoutputisconvertedtodigitalform,whereastheencoderisanumericaldevicethatoutputsdigitaldatadirectly.ResolverResolverslikesynchrosaresimple,small,cylindricalacmotorsinconstruction.Thestatorofasimplesynchrocontainsthreewindings120apartwhilethatofaresolverhastwowindings90apart.Astherotorturns,synchrosandresolversbehaveasrotatingtransformersandaninductivecouplingexistsbetweenthestatorandrotor.Typically,byexcitingtherotorwindingsavoltageisinducedinthestatorwindings.Themagnitudeoftheinducedvoltageisproportionaltothecosineoftheanglebetweentherotorcoilaxisandthestatorcoilaxis.RotaryInductosynItislikearesolverwithalargenumberofpolessay144or360polesandwithonerotorcoil.Duetoalargenumberofpoles,theoutputsignalcyclesperrevolutionincreasemanifold,viz.halfthenumberofpolesaswasmentionedearlierinthecaseofresolver.RotaryEncodersRotaryencodersarewidelyusedwidelyusedinNCmachinetoolsaspositionandmotionsensors.Thesecanbeclassifiedaseitherincrementalencodersorabsoluteencoders.IncrementalencodersPulseGeneratingEncodersTheopticalincrementalencoderconsistsofaglassdiscwithaccuratelyetchedlinesatregularintervals.Typicallythediameterofthediscsmayvaryfrom60mmto150mmwithlines10to2500.Thediscrotatesbetweenalightsourceandoneormoreofphotodiodes.Thelinesmakeandbreakthisphotoelectricbeamandthegeneratedpulsesignalisamplifiedtogiveasquarewaveoutput.Anencoderwith360linesaccordinglygives360pulsesperrevolutionAccordingly,ifanencoderwith2500linesisdirectlyconnectedtoaleadscrewof25mmpitchthenapulsewillbegeneratedforevery0.01mmmovementoftheslide.Thisresolutioncouldbefurtherimprovedbymechanicalamplification,vizrackandpinion,precisiongearingandtimingbeltstecifsodesired.Thedirectionofrotationmaybetypicallysensedbyusingtwotracksoflinesandthereforeemployingsystemreadingthesamedisc.Inthiscasethetwosetsoflinesarephaseshiftedby90.Thesignalsfromboththesetracksarefedtodirectionsensinglogiccircuitwhichdifferentiateseachedgeofthetwosignalsandcheckstheirinterrelationship.Anindexpulseoneperrevolutioncanbeusedtoserveasazeroreferencepositionfromwhichangularincrementsoftheshaftaretobecounted.LinearTransducersTheprinciplesinvolvedinthepoerationofthesetransducersarequitesimilartothosediscussedforrotarytransducers.Asthesemeasurethepositionoftheslidedirectly,thesedonotneedhighlypreciseintermediatemembersnamelyscrewandnut,andgearing.Further,theerrorsduetothisinterposingfeedtrainaresent.MaintypesaredescribedbelowGlassScaleswithLineGrationgThetransparentindexgratingsensingdeviceandtheglassscalesinthiscasehavesimilarlinegraduation.Therelativemovementbetweenthetwoscalesresultsinalternatetransparentandopaqueregions.Typicalwidthofthelinesandspacesis20micronseach.Thelightpassingthroughtheseregionsissensedbyphotodiodes.Theresistanceofthesephotodiodeschangeswiththeintensityoffallinglightresultingintoelectricalpulses.Theperiodicsignalsareprocessedwithinthecounterinsuchamannerthatasingleforwardcountingpulseisproducedevery5to10micronsofscaledisplacement.Thetotaltravelisdeterminedbycountingthesepulses.LinearInductosynItconsistsofascaleusuallyfixedtothemachinetoolbedandaslider.Thescaleismadefromsteeloraluminiumsectionsofabout250mmlength.Aninsulatinglayercoversthisbasematerial.Thecoil,inacontinuousrectanguglarwaveformpatternwithatypicalcyclicpitchof2mmisbondedtothescale.Thesliderabout100mmlonghastwoseparatebutidenticalcoiltracks

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