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1、TEXTREADINGMATERIALUnit22TEXTFundamentalsofNumericalControlControllingamachinetoolbymeansofapreparedprogramisknownasnumericalcontrol,orNC.NCequipmenthasbeendefinedtheElectronicIndustriesAssociation(EIA)as“Asysteminwhichactionsarecontrolledbythedirectinsertionofnumericaldataatsomepoint.Thes
2、ystemmustautomaticallyinterpretatleastsomeportionofthisdata”.InatypicalNCsystemthenumericaldatawhichisrequiredforproducingapartismaintainedonapunchedtapeandiscalledthepartprogram.Thepartprogramisarrangedintheformofblocksofinformation,whereeachblockcontainsthenumericaldatarequiredtoproduceo
3、nesegmentofthework-piece.Thepunchedtapeismovedforwardbyoneblockeachtimethecuttingofasegmentiscompleted.Theblockcontains,incodedform,alltheinformationneededforprocessingasegmentofthework-piece:thesegmentlength,itscuttingspeed,feed,etc.Dimensionalinformation(length,width,andradiiofcircles)an
4、dthecontourform(linear,circular,orother)aretakenfromanengineeringdrawing.Dimensionsaregivenseparatelyforeachaxisofmotion(x,y,etc.).Cuttingspeed,feed-rate,andauxiliaryfunction(coolantonandoff,spindledirection,clamp,gearchanges,etc.)areprogrammedaccordingtosurfacefinishandtolerancerequiremen
5、ts.PreparingthepartprogramforaNCmachinetoolrequiresapartprogrammer.Thepartprogrammermustpossessknowledgeandexperiencesinmechanicalengineering.PartProgrammersmustbefamiliarwiththefunctionofNCmachinetoolsandmachiningprocessandhavetodecideontheoptimalsequenceofoperations.InNCmachinetools,each
6、axisofmotionisequippedwithaseparatedrivingdevicewhichreplacesthehand-wheeloftheconventionalmachine.ThedrivingdevicemaybeaDCmotor,ahydraulicactuator,orasteppingmotor.Thetypeselectedisdeterminedmainlybythepowerrequirementsofthemachine.TheNCmachinetoolsystemcontainsthemachinecontrolunit(MCU)a
7、ndthemachinetoolitself.TheMCUhastoreadanddecodethepartprogram,toprovidethedecodedinstructionstothecontrolloopsofthemachineaxesofmotion,andtocontrolthemachinetooloperation.TheMCUconsistsoftwomainunits:thedataprocessingunit(DPU)andthecontrolloopsunit(CLU).Thefun
