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单词复习:surfaceroughnessgageDictate决定;对…有决定性影响GrounddownToolandcuttergrindersPitchdiameterBore上一课回顾1整理pptLesson11NumericalControl
数控
重点词汇:codedinstructionsPatentn.专利factoryfloor工厂车间MassachusettsInstituteof
TechnologyMIT麻省理工学院CartesiancoordinatesystemCounterclockwise2整理pptParagraph1Numericalcontrol(NC)canbedefinedasthecontrolofoperationofmachinetoolsbyaseriesofcodedinstructionscalledtheprogram,whichconsistsmainlyofalphanumericcharacters(numbersandletters数字和字母).数字控制是指称为程序的一系列编码指令对机床操作的控制,该程序主要由字母和数字符号组成。3整理pptParagraph2:Wecanseefromthisdefinitionthatthesequenceofeventsisbothpreplannedandpredicable.Inotherwords,anydesiredsequenceofeventscanbeobtainedbycodingtheappropriateinstructionsandcanalsobechangedbychangingthosecodedinstructions(编码指令).Therefore,NCsystemsareconsideredtobethetypicalformofprogrammableautomation.从定义中我们可以看到:这一系列的事情可以预先计划也可以预报。换句话说,一系列任何想要做的事情都可以通过编写适当的指令来实现,也可以通过修改编码指令来修正。4整理pptParagraph3:
ThebasicconceptofNCisnotnewatallanddatesbacktotheearlyyearsoftheIndustrialRevolution,whenJosephJacquarddevelopedamethodtocontroltextileloomsbyusingpunchedcards.数控的基本概念并不新鲜,时间可以追溯到工业革命早期—约瑟夫·捷克尔德开发出一种通过穿孔卡片控制织布机的方法。5整理pptButwhenheappliedforapatentforhisinvention,hewasdeniedthatrightbytheQueenofEngland,becauseshebelievedthatitwouldhaveputpoorworkersoutofwork(noticethesimilaritywithrobotsnowadays).Infact,thisoldinventioncanbeconsideredsimple,crudeformsofmechanicalNC.然而当他为自己的发明申请专利时,由于女王认为它会造成工人失业(与今天的机器人很相似)而被否定。事实上,这些古老的发明是简单的、机械式数控的雏形。6整理pptParagraph4:
AmodernversionofNCemergedin1947attheParsonsEngineeringCompanyofTraverseCity(帕森斯特拉弗斯城的工程公司),Michigan,asaresultoftheneedofJohnC.Parsons(theownerofthecompany)tomanufacturehelicopterrotorbladesfastenoughtomeet(如期完成)hiscontracts.现代数控1947年出现在密歇根州的帕森斯特拉弗斯城的工程公司,当时公司主人约翰·帕森斯根据合同要求尽快生产飞机螺旋桨叶片。7整理pptLater,ParsonsEngineeringwasawardedastudycontractbytheU.S.AirForceMaterialCommandtospeedupproductionanddevelopcontinuous-pathmachining,withthesubcontractorbeingtheMassachusettsInstituteof
Technology(MIT麻省理工学院).后来帕森斯工程公司得到了与美国空军装备司令部签订的研究合同,来提高生产率和开发连续轨迹加工,后来二次转包给麻省理工学院。8整理pptThewholetaskwasafterwardgiventoMIT,andthemachinetheydevelopedwassuccessfullydemonstratedin1952.Betweentheyearsof1953and1960,therate(速度)ofbuildingandsellingNCmachinesintheUnitedStateswasveryslow.
整个任务给了MIT,机器成功开发是在1952年。在美国1953-1960年数控机床的生产与销售量很小。9整理pptThistypeofmachinetoollatergainedwidespreadindustrialapplicationbecauseoftheneedforconsistencyofdimensionsandtightertolerances.由于(零件)尺寸一致接近公差的需要,这种机床后来被广泛应用于工业生产。10整理pptParagraph5Aswithanyengineeringapplication,NCprogrammingisbasedontheCartesiancoordinatesystem(笛卡儿坐标系).Accordingtothatcoordinatesystem,anypointwithinaplanecanbedefinedwithitsdistancesfromtheY-axisandtheX-axis(i.e.theXandtheYcoordinates,respectively).11整理pptAlso,thepointofintersection(相交)ofthesetwoperpendicularaxesiscalledtheorigin,orzeropoint.Thecoordinatesofapointcanbothbepositive,bothbenegative,oronebenegativeandtheotherpositive,dependinguponthelocationofthatpoint.12整理pptInfact,thosetwoperpendicularintersectingaxesdividetheplaneintofourquadrants,whicharenumberedcounterclockwise.AllvaluesofXandYarepositiveinthefirstquadrantandnegativeinthethirdquadrant.13整理pptInthesecondquadrant,allvaluesofXarenegative,andallvaluesofYarepositive,contrarytosignsinthefourthquadrant,whereitistheotherwayaround.14整理pptInotherwords,whenapointfallstotherightoftheYaxis,itsXcoordinateispositive,butwhenitistotheleftofthataxis,itsXcoordinateisnegative,whereastheYcoordinateofapointispositivewhenitisabovetheXaxisandnegativewhenthepointislocatedbelowthataxis.15整理pptTheCartesiancoordinatesystemcanbeextendedtodescribeapointinspacebyaddingathirddimensionalongtheZaxis,whichisperpendiculartotheplaneoftheXandYaxes.Paragraph616整理pptParagraph7TherearethreebasictypesofcontrolsystemsforNCmachinetools,point-to-point,straightcut,andcontouring.数控机床有三种基本类型的控制系统——点对点、直线切削、轮廓切削。17整理pptPoint-to-Pointsystem点位系统.Thepoint-to-pointsystemisusuallyusedinNCdrillingmachinesthatareemployedindrillingprecisionpatternsofholes(孔系).点位系统常用于数控钻床来加工精密布置的孔。Paragraph818整理pptThefunctionoftheNCsystemis,therefore,tomovethespindle(ormachinetable)totheexactlocation,asgivenbyatapecommand,sothataholecanbedrilled.Assoonasthedesiredholeisdrilled,thesystemmovesthespindletothenextprogrammedlocationtodrillanotherhole,andsoon.19整理pptThespindle(ormachinetable)movementfromoneholelocationtothenextmustbedoneasfastaspossibletobringtoaminimumthenonproductivetime(非生产时间)spentinmovement.Accordingly,speedsofmorethan2500mm/minarequitecommon.20整理pptParagraph9Straight-cutsystem直线切削系统.Thestraight-cutsystemisquitesimilartotheprevioussystem,exceptthatthefeedrateofthespindlealongeachmachineaxisiscontrolledsoasto(为了)besuitableformachining(e.g.,amillingoperationonaverticalmill).21整理pptAgain,thespindlecannotbecontrolledsuchthatitmovesalongalineinclinedtotheX-andY-axesofthemachine,sincethemotionalongeachaxisisindependentfromthatalongtheotheraxis,becauseitiscontrolledbyaseparateNCcircuit(orsubsystem).22整理pptNevertheless,motionsalonglinescoincidingwithorparalleltoeithertheXortheY-axiscanbeaccuratelycontrolled.23整理pptParagraph10
Contouringsystem轮廓系统.Inordertomakeangularcutsontheworkpiece,thetwodrivingservomotors(onefortheX-axismotionandtheotherfortheY-axismotion)havetorunatunequalspeeds.24整理ppt
Infact,therateoftravelalongtheYdirectionbythatalongtheXdirectionmustbeequaltotanθ,whereθistheanglethattheangularcutmakeswiththeXdirection.Thecapabilityofacontrolsystemtoregulatetherateofspindle(ortable)travelalongtwoaxesofmotionatthesametimeiscalledlinearinterpolation.25整理pptAcontrolsystemofthecontouringtypecanalsoproducecurvestoveryclosetolerances.Therefore,itissometimesreferredtoasthecontinuous-pathsystem.Paragraph11
26整理pptThemethodofemployinglinearinterpolationtoproducecurvesinvolvesbreakingdowncurveoranarcintoalargenumberofstraightlinesinsuchamanner(于是,如此)thattheendofeachlineisthebeginningofthenextone(tip-to-tailfashion).27整理pptEachandeverylinesegmentmust,therefore,beprogrammedinorderforthepathtoconformtothedesiredcurve.Wecanobviouslyseethatthelargerthenumberofsegmentstaken,thesmallereachofthesegmentlinesbecomesandthesmootherthemachinedcurvebecomes.28整理pptParagraph12TheadvantagesofNCmachinetoolsarefeltnotonlyonthefactoryfloorbutalsoinmanyotherdepartmentsofthebusinesscorporation.Followingaresomeofthoseadvantages,whichcanbeusedasjustificationforemployingNCmachinetools:29整理ppt①ThedesignandconstructionofNCmachinetools,togetherwiththefactthatthesemachinesarecontrolledbynumericalvalues,ensurepositioningaccuracyandrepeatability.
Inotherwords,ifthesameprogramisemployedtoproduceanumberofparts,theyhaveexactlyidenticaldimensions.
数控机床的结构与设计及机床利用数字控制的事实,保证了它的定位精度和重复加工能力。换句话说,同一程序加工同一批零件,它们有完全相同的尺寸。30整理ppt②Complex-shapedcomponentscanbeproducedautomatically,withclosertolerancesandveryhighdegreesofreliability.This,indeed,providesthedesignerwithgreatdegreeofflexibilityandfreedomwhenpreparingdesigns.31整理ppt③Highdimensionalaccuracyandrepeatabilityenablethemanufactureofpartsthatrequirelong
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