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Unit2NumericalControlofProductionEquipment1NumericalControl(NC)isaformofprogrammableautomationinwhichtheprocessingequipmentiscontrolledbymeansofnumbers,letters,andothersymbols.Thenumbers,letters,andsymbolsarecodedinanappropriateformattodefineaprogramofinstructionsforaparticularworkpartorjob.Whenthejobchanges,theprogramofinstructionsischanged.ThecapabilitytochangetheprogramiswhatmakesNCsuitableforlow-andmedium-volumeproduction.Itismucheasiertowritenewprogramsthantomakemajoralterationsoftheprocessingequipment.（1）数控是程序控制的自动化，在数字控制系统中，设备通过数字，字母和符号来编码，以一种合适的格式为每一个特定的零件或工件定义一个程序指令集。当工件变化时，程序也变化，改变程序的能力也就是适合中小批量生产。写一个新程序比改变大量生产设备要容易的多。BasicComponentsofNCAnumericalcontrolsystemconsistsofthefollowingthreebasiccomponents:.programofinstructions.Machinecontrolunit.Processingequipment基本结构：数控系统由下面三部分组成：1.控制程序；2.机器控制单元；3.加工设备。ThegeneralrelationshipamongthethreecomponentsisillustratedinFig.2.1Theprogramisfedintothecontrolunit,whichdirectstheprocessingequipmentaccordingly.三部分的基本关系，由图2.1所示。程序输入到控制单元由送入的程序来引导加工设备控制。Theprogramofinstructionsisthedetailedstep-by-stepcommandsthatdirecttheprocessingequipment.Initsmostcommonform,thecommandsrefertopositionsofmachinetoolspindlewithrespecttotheworktableonwhichthepartisfixture.Moreadvancedinstructionsincludeselectionofspindlespeeds,cuttingtools,andotherfunctions.Theprogramiscodedonasuitablemediumforsubmissiontothemachinecontrolunit.Themostcommonmediuminsueoverthelastseveraldecadeshasbeen1-in.-widepunchedtape.Becauseofthewidespreadsueofthepunchedtape,NCissometimescalled“tapecontrol”.However,thisisamisnomerinmodernusageofnumericalcontrol.Comingintousemorerecentlyhavebeenmagnetictapecassettesandfloppydiskettes.指导程序是一步步详细的指导加工设备的指令。通常指令把主轴上刀具相对于安装工具的工作台定位。更多先进的说明包括主轴的转速，加工工具的选择及其功能。程序刻在合适的介质中，提交到机器控制单元中，在过去几十年中，最常用的介质是一英寸宽的打孔纸带。由于打孔纸带的广泛使用，NC有时也叫纸带控制，然而这是现代数控使用的误称。现在进入使用更多的是磁带和软盘。Themachinecontrolunit(MCU)consistsoftheelectronicsandcontrolhardwarethatreadandinterprettheprogramofinstructionandconvertitintomechanicalactionsofthemachinetoolorotherprocessingequipment.机器控制单元（MUC）由电子和控制硬件组成，机器控制单元可以读出和执行指令程序，可以自动改变加工工具和其他加工设备。TheprocessingequipmentisthethirdbasiccomponentofanNCsystem.Itisthecomponentthatperformsusefulwork.Inthemostcommonexampleofnumericalcontrol,onethatperformsmachiningoperations,theprocessingequipmentconsistsoftheworktableandspindleaswellasthemotorsandcontrolsneededtodrivethem.执行单元是数控系统的第三基础部分，执行原件是有效执行工作的原件，最常见的数控例子其中的一个加工操作，加工设备由工作台和主轴组成，就像用电动机来驱动一样。加工设备由控制单元来驱动控制系统的类型。TypesofControlSystems控制系统的类型Therearetwobasictypesofcontrolsystemsinnumericalcontrol:point-to-pointandcontouring.Inthepoint-to-pointsystem,alsocalledpositioning,eachaxisofthemachineisdrivenseparatelybyleadscrewsand,dependingonthetypeofoperation,atdifferentvelocities.数控有2种基本类型，点对点式和轮廓式控制，点对点式控制也称定位控制，每个轴都是通过丝杠单独驱动，根据加工类型不同，加工速度也不一样。Themachinemovesinitiallyatmaximumvelocityinordertoreducenonproductivetimebutdeceleratesasthetoolreachesitsnumericallydefinedposition.机器开始以最大速度运行来减少非加工时间，但当他达到数据定义的位置时，机器开始减速。Thusinanoperationsuchasdrillingorpunching,thepositioningandcuttingtakeplacesequentially.因此在一个操作中，如钻或冲孔操作先定位再加工。Aftertheholeisdrilledofpunched,thetoolretracts,movesrapidlytoanotherposition,andrepeatstheoperation.在钻或冲孔之后，迅速收起工具移动到另一个位置重复此操作。Thepathfollowedfromonepositiontoanotherisimportantinonlyoneaspect:Thetimerequiredshouldbeminimizedforefficiency.从一个位置移到另一个位置是非常重要的，要遵循一个原则，从效率上考虑只要时间最短即可。Point-to–pointsystemsareusedmainlyindrilling,punching,andstraightmillingoperations.点对点系统主要用于钻，冲孔，直铣操作中。Inthecontouringsystem,alsoknownasthecontinuouspathsystem,positioningandcuttingoperationsarebothalongcontrolledpathsbutatdifferentvelocities.Becausethetoolcutsasittravelsalongaprescribedpath,accuratecontrolandsynchronizationofvelocitiesandmovementsareimportant.轮廓式也就是连续路径式系统，定位和切削同时按不同速度来控制，由于刀具在指定路线运动同时切削，因此速度和运动的同步控制是非常重要的。Thecontouringsystemisusedonlathes,millingmachines,grinders,weldingmachinery,andmachiningcenters.轮廓式系统常用于车床铣床磨床焊接设备和加工中心。Movementalongthepath,orinterpolation,occursincrementally,byoneofseveralbasicmethods.Inallcontouringinterpolations,thepathcontrolledisthatofthecenterofrotationofthetool.Compensationfordifferenttools,differentdiametertools,ortoolwearduringmachining,canbemadeintheNCprogram.沿着路径的运动或以增量差补是几个基本方式的一个，在所有的差补中，要控制刀具的回转中心定位，补偿可以以不同直径及刀具磨损，在数控程序中进行改写。Thereareanumberofinterpolationschemesthathavebeendevelopedtodealwiththevariousproblemsthatareencounteredingeneratingasmoothcontinuouspathwithacontouring-typeNCsystem.Theyinclude:.Linearinterpolation.Circularinterpolation.Helicalinterpolation.Parabolicinterpolation.Cubicinterpolation有一些已形成差补方案来处理数控系统中连续路径和加工系统产生的问题包括：1.线性差补；2.圆弧差补；3.螺旋线差补；4.抛物线差补；5.立体差补Eachoftheseinterpolationprocedurespermitstheprogrammer(oroperator)togeneratemachineinstructionsforlinearorcurvilinearpaths,usingarelativelyfewinputparameters.TheinterpolationmoduleintheMCUperformsthecalculationsanddirectsthetoolalongthepath.每一种差补程序都允许程序源产生加工指令，适用于相对少的输入参数的直线或曲线路径。储存在数控单元中的模块预算指引工具沿计算出的路径运动。Linearinterpolationisthemostbasicandisusedwhenastraight-linepathistobegeneratedincontinuous-pathNC.线性差补