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Unit9NCMachines第9单元数控机床MachinemaybeclassifiedaccordingtothenumberofaxesofnumericallycontrolledmovementswithrespecttoCartesianX-Y-Zcoordinates.Theremaybeothermovementnotnumericallycontrolled.Atwo-axismachinewouldhavethetablemovedlengthwiseandcrosswiseinahorizontalplane;athree-axismachinewouldhaveanadditionalverticalmovementofthespindle,forexample,Four-,five-,orsix-axismachinesprovideadditionallinearorrotarymovements.机器根据多轴数控运动方面笛卡尔某某坐标可分为多种。有可能是其他运动的数字控制。一种双轴机将表的纵向和横向移动在水平面；三轴机将有额外的主轴垂直运动，例如，四-，五-，或提供额外的线性轴机或旋转运动。ThreeclassesofNCsystemsarecommonlyrecognized.Oneoftheseiscalledpoint-to-pointorpositioningNC,whereacuttingtoolandworkpiecearepositionedwithrespecttoeachotherbeforeacutistaken,asexemplifiedbyanNCdrillpress~.Thepathbetweenpointsisoflittleconcernandisnotparticularlycontrolled.Anotherclass,knownasastraight-cutNCsystem,involvesmovementsbetweenpointslikepoint-to-pointNCbutalongstraightorcurvedpathsdeterminedbythemachinewaysorslides.AnNCturretlathemaybeofthesecondclass.Athirdclassiscontinuous-pathNC,ormoreformallycontinuoustoolpathcontrol,whichdoescontouringorprofilingoflines,curves,orsurfaces,ofallshapes.OnewayofachievingcontinuouspathNCistomovetheworkpieceorcutterfrompointtopointalongastraightlineorcurve(aparabolicpathbetweenpointsisusedonsomemachines)withmanypointsspacedcloselyenoughtogethersothatthecompositionpathofthecutapproximatesadesiredcurvewithinlimitsrequired~.Anotherwayistodrivemachinemembers,sayasaddleandthetableonit,alongcoordinateaxesatvaryingvelocitiescontrolledsothattheresultantmotionisalongaparticularlineorcurve.在三类数控系统中。其中一类被称为逐点或位置调节数控，在这类数控系统中，进行切削之前，切削刀具和工件彼此之间的位置就被确定了，数控钻床就是一个例子。点之间的路径不太重要，不是特别控制。另一类，称为数控纵切系统，涉及运动点像点位数控但沿直线或曲线路径决定的方式或过程。数控转塔车床可能是二类。三分之一类是连续轨迹数控，或更正式的连续轨迹控制，其轮廓或轮廓线，曲线，或表面，各种形状。得到数控连续路径的一种方式是使工件或刀具沿一直线或曲线做点到点的运动（在某些机床上，点之间采用抛物线路径）许多点的间隔足够小，一边在要求的限度内使切削组合的路径接近一预想的曲线。。另一种方法是驱动机器的成员，说一个鞍状结构，沿坐标轴以不同的速度控制，由此产生的运动是在一个特定的直线或曲线。AnNCmachinemaybecontrolledthroughanopen-looporclosed-loopcircuitasdepictedinFig.9.1.Theopen-loopsystemisthesimplestandcheapestbutdoesnotassureaccuracy.Asignalthatisanorderforacertainaction(suchastoturnonthecoolant,startthespindle,ormovethetabletoacertainposition)isissuedbythecontrolunit.Thistravelsthroughthedrivemechanismwhichimposestheactionuponthecontrolledmemberofthemachine.Thebasicdrivemechanismforatableorothermachinememberinanopen-loopsystemisasteppingmotor,alsocalledadigitalorpulsemotor.Ithas,forexample,49polesaroundthearmatureinsideof50polesaroundthestator.Twopolesarealwaysaligned.Polesareenergizedtoalignthenexttwopolesandturnthearmaturethroughadefinitesmallangleeachtimeapulseofelectricityisreceived.Themotorturnstheleadscrew,whichmovesthetableacorrespondingdistance.If,forexample,apulsestandsfora0.001mmmovement,andamovementof0.05mmisdesired,thecontrolunitissues50pulses;themotorturnsthrough50stepsandturnstheleadscrew,andthetable(orothermember)isdriventhe0.05mmrequired.Therateatwhichthepulsesareissueddeterminestherateoffeed.Thepowerofasteppingmotorislimited,andiftheresistancetomovementislarge,themotormayjuststallandmisssteps.Thereisnofeedbacktoreporttheomission,andaccuracyislost.Directdrivewithasteppingmotorisconfinedtolightserviceatfractionalhorsepower.Formorepowerandheavyservice,asteppingmotorismatchedwithahydraulicmotorthroughaservovalvefortabledrivesupto7.5kW(10hp)andmore.数控机床可控制通过一个开环或闭环电路如图9.1所。开环系统是最简单和便宜但不保证准确性。一个信号,表明是一个为了一个特定操作(例如打开冷却剂,启动主轴,或的表移动到某一个位置)发出控制单元。这个过程,通过驱动机制规定行为控制机器的成员。在开口回路系统中，一工作台或其他机器构件的基本的驱动机制是步进电动机，,也称为数字或脉冲发动机。比如,它在电枢内部49波兰人在定子的50波兰人。两个极点总是一致的。波兰人有足够的精力来调整下两个极点,将通过一个明确的小角度电枢每次收到的脉冲电。马达转动的有,移动表对应的距离。比如说,如果一个脉冲代表一个0。001毫米的运动,和一个运动的0.05毫米是很明显的，控制单元50脉冲，;马达转动到50步和将有和表(或其他)是0.05毫米驱动所需的。脉冲的速率决定的速度进给。步进电机的力量是有限的,如果抵抗运动是大型汽车可能只是停滞,错过的步骤。没有反馈报告遗漏,和失去了准确性。与步进电机直接驱动仅限于光服务在分马力。更多的力和沉重的服务,一个步进电机配个通过伺服阀液压马达为表驱动7.5千瓦(10点)和更多。Itiscommoninclosed-loopsystemsforthepulsedcommandsignalforthemovementofthetable(orothermember)ofthemachinetobeconvertedtoasteadyanalogsignal.Thatsignalturnsonthepowertothedrivemechanism.HydraulicandacbutmostlydcelectricmotorsareallusedforNCmachinedrives.Theintensityofthesignalisdeterminedbythefeedvelocityordered.Forahigherfeed,pulsesareissuedatafasterrateand/ortheanalogsignalislarger,whichturnsonmorepowertothemotortodrivethetablefaster.Atachometerinthemotordrivesendsbackasignalthatiscomparedtothefeedrateordertoassurethattherequiredfeedrateisbeingdeliveredandtomakecorrectionsifitisnot.Commonly,aresolverisdrivenbytheleadscrewandreturnsasignalshowinghowfarthetablemoves.Moreaccuracyforalongerperiodoftimeisobtainedwiththefeedbackdeviceattacheddirectlytothetable,butsuchdevicesaremorecostly.Thefeedbacksignaliscomparedtotheorder,andwherethefeedbackequalstheorderandsignifiestherequiredmovementhasbeencompleted,thepowerisshutoff,andthemovementstops.Sincetheyarecontrolledthroughseparatechannels,allmovementsmayactatthesametime.Indeed,itisnecessarythattheyactsimultaneouslyandbesynchronizedaccuratelyforcontouring.这是常见的闭环系统的脉冲信号指挥运动（或其他）的机器转换到一个稳定的模拟信号。信号打开电源的驱动机制。液压，但大多都是采用直流电机驱动的数控机床。发出脉冲的频率确定进给的频率。一个较高的进给，脉冲发出以更快的速度和/或模拟信号较大，这将