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1、英文原文N/CMachineToolElements———From《EnglishforMachinery》N/Cmachinetoolelementsconsistofdimensioningsystems,controlsystems,servomechanismsandopen-orclosed-loopsystems.Itisimportanttounderstandeachelementpriortoactualprogrammingofanumericallycontrolledport.ThetermmeasuringsysteminN/Creferstot
2、hemethodamachinetoolusestomoveapartfromareferencepointtoatargetpoint.Atargetpointmaybeacertainlocatingfordrillingahole,millingaslot,orothermachineoperation.ThetwomeasuringsystemsusedonN/Cmachinesaretheabsoluteandincremental.Theabsolutemeasuringsystemusesafixedreferencepoint.Itisonthispoin
3、tthatallpositionalinformationisbased.Inotherwords,allthelocationstowhichapartwillbemovedmustbegivendimensionsrelatingtothatoriginalfixedreferencepoint.FigureshowsanabsolutemeasuringsystemwithXandYdimensions,eachbasedontheorigin.Theincrementalmeasuringsystemhasafloatingcoordinatingsystem.W
4、iththeincrementalsystem,thetimethepartismoved.Figure16.2showXandYvaluesusinganincrementalmeasuringsystem.Noticethatwiththissystem,eachnewlocationbasesitsvaluesinXandYfromtheprecedinglocation.Onedisadvantagetothissystemisthatanyerrorsmadewillberepeatedthroughouttheentireprogram,ifnotdetect
5、edandcorrected.TherearetwotypesofcontrolsystemscommonlyusedonN/Cequipment:point-to-pointandcontinuouspath.Apoint-to-pointcontrolledN/Cmachinetool,sometimesreferredtoasapositioningcontroltype,hasthecapabilityofmovingonlyalongastraightline.However,whentwoaxesareprogrammedsimultaneouslywithe
6、qualvaluesa45anglewillbegenerated.Point-to-pointsystemsaregenerallyfoundondrillingandsimplemillingmachinewhereholelocationandstraightmillingjobsareperformed.Point-to-pointsystemscanbeutilizedtogenetatearcsandanglesbyprogrammingthemachinetomoveinaseriesofsmallsteps.Usingthistechnique,howev
7、er,theactualpathmachinedisslightlydifferentfromthecuttingpathspecified.Machinetoolsthathavethecapabilityofmovingsimultaneouslyintwoormoreaxesareclassifiedascontinuous-pathorcontouring.Thesemachinesareusedformachiningarcs,radii,circles,andanglesofanysizeintwoorthered
