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1、英文原文CNC machine toolsWhilethespecificintentionandapplicationforCNCmachinesvaryfromonemachinetype toanother,allformsofCNChavecommonbenefits.Herearebutafewofthemoreimportant benefitsofferedbyCNCequipment.ThefirstbenefitofferedbyallformsofCNCmachinetoolsisimprovedautomation. The operatorinterventionrel
2、atedtoproducingworkpiecescanbereducedoreliminated.ManyCNCmachinescanrununattendedduringtheirentiremachiningcycle,freeingtheoperatortodoother tasks.ThisgivestheCNCuserseveralsidebenefitsincludingreducedoperatorfatigue,fewer mistakescausedbyhumanerror,andconsistentandpredictablemachiningtimeforeach wo
3、rkpiece.Sincethemachinewillberunningunderprogramcontrol,theskilllevelrequiredof theCNCoperator(relatedtobasicmachiningpractice)isalsoreducedascomparedtoamachinistproducingworkpieceswithconventionalmachinetools.ThesecondmajorbenefitofCNCtechnologyisconsistentandaccurateworkpieces.TodaysCNCmachinesboa
4、stalmostunbelievableaccuracyandrepeatabilityspecifications.Thismeans thatonceaprogramisverified,two,ten,oronethousandidenticalworkpiecescanbeeasily producedwithprecisionandconsistency.AthirdbenefitofferedbymostformsofCNCmachinetoolsisflexibility.Sincethese machinesarerunfromprograms,runningadifferen
5、tworkpieceisalmostaseasyasloadinga differentprogram.Onceaprogramhasbeenverifiedandexecutedforoneproductionrun,itcan beeasilyrecalledthenexttimetheworkpieceistoberun.Thisleadstoyetanotherbenefit,fast changeover.Sincethesemachinesareveryeasytosetupandrun,andsinceprogramscanbe easilyloaded,theyallowver
6、yshortsetuptime.Thisisimperativewithtodaysjust-in-time(JIT) product requirements.Motioncontrol-theheartofCNCThemostbasicfunctionofanyCNCmachineisautomatic,precise,andconsistentmotion control.Ratherthanapplyingcompletelymechanicaldevicestocausemotionasisrequiredon mostconventionalmachinetools,CNCmach
7、inesallowmotioncontrolinarevolutionarymanner2.AllformsofCNCequipmenthavetwoormoredirectionsofmotion,calledaxes.Theseaxes canbepreciselyandautomaticallypositionedalongtheirlengthsoftravel.Thetwomostcommonaxistypesarelinear(drivenalongastraightpath)androtary(drivenalongacircularpath).Insteadofcausingm
8、otionbyturningcranksandhandwheelsasisrequiredonconventionalmachinetools,CNCmachinesallowmotionstobecommandedthroughprogrammedcommands.Generallyspeaking,themotiontype(rapid,linear,andcircular),theaxestomove,theamountofmotionandthemotionrate(feedrate)areprogrammablewithalmostallCNCmachinetools.ACNCcom
9、mandexecutedwithinthecontroltellsthedrivemotortorotateaprecisenumberoftimes.Therotationofthedrivemotorinturnrotatestheballscrew.Andtheballscrewdrives thelinearaxis(slide).Afeedbackdevice(linearscale)ontheslideallowsthecontroltoconfirm thatthecommandednumberofrotationshastakenplace3. Thougharathercru
10、deanalogy,thesamebasiclinearmotioncanbefoundonacommontablevise.Asyourotatethevisecrank,yourotatealeadscrewthat,inturn,drivesthemovablejawonthevise.Bycomparison,alinearaxisonaCNCmachinetoolisextremelyprecise.Thenumberofrevolutionsoftheaxisdrivemotorpreciselycontrolstheamountoflinearmotionalongtheaxis
11、.Howaxismotioniscommanded-understandingcoordinatesystems.ItwouldbeinfeasiblefortheCNCusertocauseaxismotionbytryingtotelleachaxisdrivemotorhowmanytimestorotateinordertocommandagivenlinearmotionamount4.(Thiswouldbelikehavingtofigureouthowmanyturnsofthehandleonatablevisewillcausethemovable jawtomoveexa
12、ctlyoneinch!)Instead,allCNCcontrolsallowaxismotiontobecommandedinamuchsimplerandmorelogicalwaybyutilizingsomeformofcoordinatesystem.Thetwomost popularcoordinatesystemsusedwithCNCmachinesaretherectangularcoordinatesystemand thepolarcoordinatesystem.Byfar,themorepopularofthesetwoistherectangularcoordi
13、nate system.TheprogramzeropointestablishesthepointofreferenceformotioncommandsinaCNC program.Thisallowstheprogrammertospecifymovementsfromacommonlocation.Ifprogramzeroischosenwisely,usuallycoordinatesneededfortheprogramcanbetakendirectlyfromtheprint.Withthistechnique,iftheprogrammerwishesthetooltobesenttoapositiononeinchtotherightoftheprogramzeropoint,X1.0iscommanded.Iftheprogrammerwishesthetooltomovetoapositiononeinchabovetheprogramzeropoint,Y1.0iscommanded.Thecontrolwill automaticallydeterminehowmanytimestorotatee
