数控技术-外文翻译-外文文献-英文文献.doc

外文翻译NUMERICALCONTROLNumericalcontrol(N／C)isaformofprogrammableautomationinwhichtheprocessingequipmentiscontrolledbymeansofnumbers，letters，andothersymbols．Thenumbers，letters，andsymbolsarecodedinanappropriateformattodefineaprogramofinstructionsforaparticularworkpartorjob．Whenthejobchanges，theprogramofinstructionsischanged．ThecapabilitytochangetheprogramiswhatmakesN／Csuitableforlow-andmedium-volumeproduction．Itismucheasiertowriteprogramsthantomakemajoralterationsoftheprocessingequipment．Therearetwobasictypesofnumericallycontrolledmachinetools：point—to—pointandcontinuous—path(alsocalledcontouring)．Point—to—pointmachinesuseunsynchronizedmotors，withtheresultthatthepositionofthemachiningheadCanbeassuredonlyuponcompletionofamovement，orwhileonlyonemotorisrunning．Machinesofthistypeareprincipallyusedforstraight—linecutsorfordrillingorboring．TheN／Csystemconsistsofthefollowingcomponents：datainput，thetapereaderwiththecontrolunit，feedbackdevices，andthemetal—cuttingmachinetoolorothertypeofN／Cequipment．Datainput，alsocalled“man—to—controllink”，maybeprovidedtothemachinetoolmanually，orentirelybyautomaticmeans．Manualmethodswhenusedasthesolesourceofinputdataarerestrictedtoarelativelysmallnumberofinputs．Examplesofmanuallyoperateddevicesarekeyboarddials，pushbuttons，switches，orthumbwheelselectors．Thesearelocatedonaconsolenearthemachine．Dialsaleanalogdevicesusuallyconnectedtoasyn-chro-typeresolverorpotentiometer．Inmostcases，pushbuttons，switches，andothersimilartypesofselectorsayedigitalinputdevices．Manualinputrequiresthattheoperatorsetthecontrolsforeachoperation．Itisaslowandtediousprocessandisseldomjustifiedexceptinelementarymachiningapplicationsorinspecialcases．Inpracticallyallcases，informationisautomaticallysuppliedtothecontrolunitandthemachinetoolbycards，punchedtapes，orbymagnetictape．Eight—channelpunchedpapertapeisthemostcommonlyusedformofdatainputforconventionalN／Csystems．Thecodedinstructionsonthetapeconsistofsectionsofpunchedholescalledblocks．Eachblockrepresentsamachinefunction，amachinin