机械专业英语文章中英文对照.pdf

英语原文

NUMERICALCONTROL

Numericalcontrol(N/C)isaformofprogrammableautomationinwhichtheprocessing
equipmentiscontrolledbymeansofnumbers,letters,andothersymbols,Thenumbers,letters,
andsymbolsarecodedinanappropriateformattodefineaprogramofinstructionsfora
particularworkpartorjob.Whenthejobchanges,theprogramofinstructionsischanged.The
capabilitytochangetheprogramiswhatmakesN/Csuitableforlow-andmedium-volume
production.Itismucheasiertowriteprogramsthantomakemajoralterationsoftheprocessing
equipment.
Therearetwobasictypesofnumericallycontrolledmachinetools：point—to—pointand
continuous—path(alsocalledcontouring).Point—to—pointmachinesuseunsynchronized
motors,withtheresultthatthepositionofthemachiningheadCanbeassuredonlyupon
completionofamovement,orwhileonlyonemotorisrunning.Machinesofthistypeare
principallyusedforstraight—linecutsorfordrillingorboring.
TheN/Csystemconsistsofthefollowingcomponents：datainput,thetapereaderwiththe
controlunit,feedbackdevices,andthemetal—cuttingmachinetoolorothertypeofN/C
equipment.
Datainput,alsocalled“man—to—controllink”,maybeprovidedtothemachinetool
manually,orentirelybyautomaticmeans.Manualmethodswhenusedasthesolesourceof
inputdataarerestrictedtoarelativelysmallnumberofinputs.Examplesofmanuallyoperated
devicesarekeyboarddials,pushbuttons,switches,orthumbwheelselectors.Thesearelocatedon
aconsolenearthemachine.Dialsaleanalogdevicesusuallyconnectedtoasyn-chro-type
resolverorpotentiometer.Inmostcases,pushbuttons,switches,andothersimilartypesof
selectorsaredigitalinputdevices.Manualinputrequiresthattheoperatorsetthecontrolsfor
eachoperation.Itisaslowandtediousprocessandisseldomjustifiedexceptinelementary
machiningapplicationsorinspecialcases.
Inpracticallyallcases,informationisautomaticallysuppliedtothecontrolunitandthe
machinetoolbycards,punchedtapes,orbymagnetictape.Eight—channelpunchedpapertape
isthemostcommonlyusedformofdatainputforconventionalN/Csystems.Thecoded
instructionsonthetapeconsistofsectionsofpunchedholescalledblocks.Eachblockrep