外文翻譯--數(shù)字控制的發(fā)展及數(shù)控用傳感器.doc

英文原文：ThedevelopmentofNCandTransducersforNCmachineToolsThefirstNCmachinesusedvacuuintubes,electricalrelays,andcomplicatedmachine-controlinterfaces.Theseciondgenerationofmachinesutilizedimprovedminiatureelectronictubes,andlatersolid-statecircuits.Ascomputertechonologyimproved,NCunderwentoneofthemostrapidchangesknowninhistory.Thethirdgenerationusedmuchimprovedintegratedcircuits.ComputerhardwarebecameprogressicelulessexpensiveandmorereliableandNCcontrolbuildersintroducedforthefirsttimeReadOnlymemory(ROM)technology.ROMwastypicallyusedforprogramstorageinspecial-purposeapplications,leadingtotheappearanceofthecomputernumericalcontrol(CNC)system,CNCwassuccessfullyintroducedtopracticallyeverymanufacturingprocess.Drilling,millingandturningwereperformedonmachingingcentersandturningcenters.CNCtookoverglasscutting,patternmaking,electricaldischargemaching,steel-millrollgrinding,coordinatemeasuring,electronbeamwelding,tubebending,drafting,printedcircuitmanufacturing,coilwinding,functionaltesting,robots,andmanyotherprocesses.Asetofpreprogrammedsubroutines,namedcannedcycles,weredevelopedforyseinroutineoperations.TheywererecordedintotheROMsandremainedthereevenafterpowerwasshutoff.Forthefirsttime,thisconceptmadeitpossibletoreadthemachingingprogramintomemoryandtooperatethemachinefrommemory.Inadditiontotheadvantagesofediting,theproblemscausedbyerroneoustapereadingdisappeared.Alongwiththemanycannedcycleoptions,CNCbuildersintrodyceddisplaysforvisualeditingofpartprogramsinmemiry.Variousin-cycleproblemsgeneratedalarmsandhundredsofdiafnosticmessageswhichcouldbedisplayedasapplicable.Practicallyeveryfunctionofthemachinewastiedintothesystemandmonitoredduringoperation.Aconstantsurfacespeedcontrolwasincorporatedandcontinuouslyanticipatedthemostefficientspindlespeedofthenextcuttominimizetimelostforspindleacceleratin.Theconventionallinearandcircularinterpolationincartesia(retangular)coordinatesweresupplementedbypolarcoordinatesandhelicalinterpolation.Safezones,whichcouldbesetthroughprogrammedcodesorinternalparameters,createanelectroniccrashbarriertopreventtoolcollisionmanufacturinginmetalcuttingindustry.Theimprovementindriveswasasimportantforthesystemasthecontributionofthemicroprocessorortheminicomputer.Thefeeddrives,usuallyknownasservodrives,consistofamotoranditscontrolwhichreceivesitsmotioninstructionsfromtheCNC.theirperformanceisessentialtotheaccuracy,reliability,andflexibilityoftheCNCsystem.Theopen-loopsystemisnormallyusedinsimplepoint-to-point,orpositioningsystems,althoughimprovementsintechnologyhavemadeitpossibletoinstallthesystemincontiuringsystemsaswell.Theclosed-loopconfigurationismoreaccurateandreliable,asreflectedbyitshighercost.AlthoughmanyCNCsystemstillusehydraulicorpulesmotors,theDCdriveshavegaineddominanceonamuchlargerscale.Inmostcases,thedrivepackagesarepurchasedfromspecializeddrivesystembuilders.Thesedirectcurrent(DC)permanent-magnetwoundfieldserviomatorsrangefrom3,000revolutionsperminutetolessthan1rpmwethoutstalling.Theydeveloppeaktorquecapabilitieswithhighslideaccelerationandlowinertiaforoptimizedsystemresponse.Mostdrivesystemsofferachoicebetweentransistorizedsilicone-controlledrectigiersandpulsewidthmodulationoverthefullrangeofamplifiedvoltages.Thesedrivescannowdrivevirtuallyanyleadscrew.Theirhigh-responseinnercurrentloopsprovidereliableregulationoftorque-loaddisturbances,Theycanalsobebuiltwithhigh-gainpreamplofierstoclosehigh-band-widthvelocityoops.TheDCdrivesprovidetheanswertithemostessentialneedsofacceleration,deceleration,stopping,andconstantvelocity,withinherentshaftstiffnessforsuccessfuloperationoftheCNCsystem.Thesamedrivesystemsactuaterobots,transferlines.flifhtsimulators,graphicplotters,ect.Asthesedivesareinfinitelyvariableandfullyregenerative,theycanprovidefirmaximumperformanceandcontroloverthewholerangeofthemotor.Byeliminatinggearboxesandclutches,thecostocdrivesforthethird-generationCNCsystemswasreducedsubstantiallyThefourth-generationmicroprocessorCNCincorporatedinmanycasesthecontroversialbiblememory.Thebiblesaremagneticgarnetcrystalsgrownonnonvolatiledatastorage.Althoughatthisstageitisnotcompetitiveinthelargecomputers,thebiblememoryisclosingthecostgapwithdiskstoragedevices.Insensitivetoadversetemperaturechanges,dust,andvebration,thebubblememoryhasdemonstratedsuperioereliabilityinshopenveronment.GeneralNumericsintroduceditsfourth-generationCNCusingbubblememory；howeverHitachi,anotherelectronicgiant,believesthatbubblememorywillprovidetheeconomicalanswertodirectnumericalcontrol(DNC).Amongthestrengthsofthefourth-generationmecroprocessorCNC(MCNC)areaddedpartprogrammemorystorage,reductionofprintedcircuitboards,programmableinterface,fastermemoryaccess,parametricsubroutines,andmacrocapabilities.Thesystemusercannowwritespecificcannedcyclesdirectedtoparticularapplications(usermacros),farmoreeconomicalandefficientthanconventionalcannedcycles.Mathematicalcalculationswithdo-loopsubroutinesusingvariablescannowbeincorporatedinthepartprogram.Themicroprocessorcontrolsbothcomputationsandmotioncommands.Thus,followinganin-processgaging,anout-oftoleranceconditionwillbefedback,andthetooloffsetwillbeautomaticallymodifiedtoachievethedesiredpartdimensions.PositioningfeedbackdevicesforNCcanbeclassifiedintotwogroups,viz.rotaryandlineartransducers.Rotarytransducersmaybeconnectedtotheleadscreweithyerdirectlyorthroughprecisiongearing.ThisfeedbackdevicemeasuresindirectlythepositionoftheslideasitmeasuressomeangleandthefeedtrainratiorelatestheSametothelinearmovementoftheslide.Ontheotherhand,lineartransducersindicatethepositionoftheslidedirectly.Inthiscaseonepartofthetransducerisfixedtothemachinetoolstructure.Theotherpartisattachedtoaslidewhichmovesoverthestationarypart.RotaryTransducersRotarytransducersarequitepopularwithNCmachinemanufacturersbecauseoftheircompactsizeandtheflexibilitywithwhichthesecanbeused.Therearetwoprimarytypesofrotarytransducers:resolversandencoderstheresolverisananalogdevicewhoseoutputisconvertedtodigitalform,whereastheencoderisanumericaldevicethatoutputsdigitaldatadirectly.Resolver:Resolverslikesynchrosaresimple,small,cylindricalacmotorsinconstruction.Thestatorofasimplesynchrocontainsthreewindings120apartwhilethatofaresolverhastwowindings90apart.Astherotorturns,synchrosandresolversbehaveasrotatingtransformersandaninductivecouplingexistsbetweenthestatorandrotor.Typically,byexcitingtherotorwindingsavoltageisinducedinthestatorwindings.Themagnitudeoftheinducedvoltageisproportionaltothecosineoftheanglebetweentherotor-coilaxisandthestator-coilaxis.RotaryInductosyn:Itislikearesolverwithalargenumberofpoles(say144or360poles)andwithonerotorcoil.Duetoalargenumberofpoles,theoutputsignalcyclesperrevolutionincreasemanifold,viz.halfthenumberofpolesaswasmentionedearlierinthecaseofresolver.RotaryEncoders:RotaryencodersarewidelyusedwidelyusedinNCmachinetoolsaspositionandmotionsensors.Thesecanbeclassifiedaseitherincrementalencodersorabsoluteencoders.Incrementalencoders(PulseGeneratingEncoders)Theopticalincrementalencoderconsistsofaglassdiscwithaccuratelyetchedlinesatregularintervals.Typicallythediameterofthediscsmayvaryfrom60mmto150mmwithlines10to2500.Thediscrotatesbetweenalightsourceandoneormoreofphotodiodes.Thelinesmakeandbreakthisphotoelectricbeamandthegeneratedpulsesignalisamplifiedtogiveasquarewaveoutput.Anencoderwith360linesaccordinglygives360pulsesperrevolutionAccordingly,ifanencoderwith2500linesisdirectlyconnectedtoaleadscrewof25mmpitchthenapulsewillbegeneratedforevery0.01mmmovementoftheslide.Thisresolutioncouldbefurtherimprovedbymechanicalamplification,vizrackandpinion,precisiongearingandtimingbeltstecifsodesired.Thedirectionofrotationmaybetypicallysensedbyusingtwotracksoflinesandthereforeemployingsystemreadingthesamedisc.Inthiscasethetwosetsoflinesarephaseshiftedby90.Thesignalsfromboththesetracksarefedtodirectionsensinglogiccircuitwhichdifferentiateseachedgeofthetwosignalsandcheckstheirinterrelationship.Anindexpulse(oneperrevolution)canbeusedtoserveasazeroreferencepositionfromwhichangularincrementsoftheshaftaretobecounted.LinearTransducersTheprinciplesinvolvedinthepoerationofthesetransducersarequitesimilartothosediscussedforrotarytransducers.Asthesemeasurethepositionoftheslidedirectly,thesedonotneedhighlypreciseintermediatemembersnamelyscrewandnut,andgearing.Further,theerrorsduetothisinterposingfeedtrainaresent.Maintypesaredescribedbelow；GlassSca