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1、附錄英文原文N/CMachineToolElements———From《EnglishforMachinery》N/Cmachinetoolelementsconsistofdimensioningsystems,controlsystems,servomechanismsandopen-orclosed-loopsystems.Itisimportanttounderstandeachelementpriortoactualprogrammingofanumericallycontrolledport.ThetermmeasuringsysteminN/Cr
2、eferstothemethodamachinetoolusestomoveapartfromareferencepointtoatargetpoint.Atargetpointmaybeacertainlocatingfordrillingahole,millingaslot,orothermachineoperation.ThetwomeasuringsystemsusedonN/Cmachinesaretheabsoluteandincremental.Theabsolutemeasuringsystemusesafixedreferencepoint.
3、Itisonthispointthatallpositionalinformationisbased.Inotherwords,allthelocationstowhichapartwillbemovedmustbegivendimensionsrelatingtothatoriginalfixedreferencepoint.FigureshowsanabsolutemeasuringsystemwithXandYdimensions,eachbasedontheorigin.Theincrementalmeasuringsystemhasafloating
4、coordinatingsystem.Withtheincrementalsystem,thetimethepartismoved.Figure16.2showXandYvaluesusinganincrementalmeasuringsystem.Noticethatwiththissystem,eachnewlocationbasesitsvaluesinXandYfromtheprecedinglocation.Onedisadvantagetothissystemisthatanyerrorsmadewillberepeatedthroughoutth
5、eentireprogram,ifnotdetectedandcorrected.TherearetwotypesofcontrolsystemscommonlyusedonN/Cequipment:point-to-pointandcontinuouspath.Apoint-to-pointcontrolledN/Cmachinetool,sometimesreferredtoasapositioningcontroltype,hasthecapabilityofmovingonlyalongastraightline.However,whentwoaxes
6、areprogrammedsimultaneouslywithequalvaluesa45anglewillbegenerated.Point-to-pointsystemsaregenerallyfoundondrillingandsimplemillingmachinewhereholelocationandstraightmillingjobsareperformed.Point-to-pointsystemscanbeutilizedtogenetatearcsandanglesbyprogrammingthemachinetomoveinaserie
7、sofsmallsteps.Usingthistechnique,however,theactualpathmachinedisslightlydifferentfromthecuttingpathspecified.Machinetoolsthathavethecapabilityofmovingsimultaneouslyintwoormoreaxesareclassifiedascontinuous-pathorcontouring.Thesemachinesareusedformachiningarcs,radii,circles,andangleso
8、fanysizeintwoorther
