畢業(yè)設(shè)計(論文)-電動自行車智能控制器的設(shè)計與制作

)式中為占空比。改變ρ，即可改變其平均電壓。2.3.5無刷直流電動機及控制器的保護(hù)如圖2-12所示：圖2-12保護(hù)電路一、電機過流和過熱保護(hù)電機過流保護(hù)和過熱保護(hù)（電機的過載保護(hù)和小電流過載保護(hù)也可以通過過熱保護(hù)來實現(xiàn)），由單片機循環(huán)檢測電機電流樣值信號和電機過熱信號,檢測到任何一種信號,單片機將進(jìn)入保護(hù)方式，令單片機輸出的PWM信號變?yōu)榱忝}寬，使電機失電，同時借助于自行車本身的制動系統(tǒng)，使自行車停止前進(jìn)。如圖所示，此兩種信號由P0.0和P0.1提供。二、蓄電池欠壓保護(hù)系統(tǒng)軟件設(shè)計時,當(dāng)出現(xiàn)欠壓信號時，并不是馬上就切斷主回路，而是在一定時間內(nèi)連續(xù)檢測欠壓信號，如果欠壓信號保持兩秒鐘，系統(tǒng)將進(jìn)入欠壓保護(hù)報警程序，如果欠壓信號持續(xù)不到兩秒鐘，系統(tǒng)就不進(jìn)入保護(hù)報警程序，繼續(xù)正常工作。如圖所示，此種信號從單片機的P0.2口輸入。三、剎車控制剎車控制也采用實時響應(yīng)方式,當(dāng)系統(tǒng)檢測到剎車信號后,立即使單片機輸出的PWM信號變?yōu)榱忝}寬,使電子開關(guān)斷開,電機失電。同時借助于自行車本身的制動系統(tǒng),使自行車停止前進(jìn)。這時單片機系統(tǒng)應(yīng)處于等待狀態(tài),剎車信號消失后,系統(tǒng)恢復(fù)工作，此時PWM信號為零脈寬，騎車人需進(jìn)行加速才能繼續(xù)前進(jìn)。這樣做的好處是，可以防止自行車在剎車信號消失后急速前沖，給騎車人帶來不安全因素。如圖所示，此信號從單片機的P0.3口輸入。四、報警指示報警指示電路由四個發(fā)光二極管和一個蜂鳴器構(gòu)成，由單片機的P0.4-P0.7口和P3.3口控制，四個發(fā)光二極管分別表示電動機過熱、過流、蓄電池欠壓和剎車，當(dāng)電動機過熱、過流或蓄電池欠壓時，相應(yīng)的發(fā)光二極管就被點亮，同時發(fā)出報警聲提醒騎車人，而當(dāng)剎車信號出現(xiàn)時，相應(yīng)的二極管點亮，但不發(fā)出報警聲。為了方便單片機控制，發(fā)光二極管正極接+5V電源，負(fù)極通過限流電阻與單片機相連，驅(qū)動蜂鳴器的三極管采用9015，其電路如圖2-12。第三章系統(tǒng)軟件設(shè)計基于AT89C51單片機的需要，本設(shè)計用匯編語言進(jìn)行編程。由于給直流電動機調(diào)速用的PWM信號由外電路產(chǎn)生，大大減小了程序的復(fù)雜程度，其程序流程如圖3-1。圖3-1程序主流程圖在本系統(tǒng)控制中，欠壓保護(hù)采用多點檢測，當(dāng)出現(xiàn)欠壓信號時，并不是馬上就切斷主回路，而是在一定時間內(nèi)連續(xù)檢測欠壓信號，如果欠壓信號保持兩秒鐘，系統(tǒng)將進(jìn)入欠壓保護(hù)報警程序，如果欠壓信號持續(xù)不到兩秒鐘，系統(tǒng)就不進(jìn)入保護(hù)報警程序，繼續(xù)正常工作。過流、過熱保護(hù)都采用實時響應(yīng)，一旦檢測到過流或過熱保護(hù)，系統(tǒng)就立即進(jìn)入保護(hù)報警程序。在上述保護(hù)方案中,電流保護(hù)和蓄電池欠壓保護(hù)采用非恢復(fù)性保護(hù),一旦進(jìn)入保護(hù)狀態(tài),就必須等排除故障、重新啟動單片機系統(tǒng)后,才能恢復(fù)工作。而過熱保護(hù)采用可恢復(fù)性保護(hù),在軟件保護(hù)過程中,若電動機溫度下降到保護(hù)值以下時,應(yīng)撤消保護(hù),系統(tǒng)恢復(fù)正常工作狀態(tài)。加速、減速控制也采用實時響應(yīng)，一旦檢測到加速或減速信號，單片機就相應(yīng)改變X的值，以達(dá)到加速或減速的效果。另外，為了便于騎車人調(diào)速，系統(tǒng)的加速或減速的幅度和騎車人按加速或減速按鈕的時間成正比，按得越長，改變的速度值就越大，只要按著加速或減速按鈕，系統(tǒng)就一直執(zhí)行加速或減速程序，直到速度達(dá)到最大值或零。剎車控制也采用實時響應(yīng)，一檢測到剎車信號，剎車燈亮，并將速度調(diào)到零。因為目前我國在電動自行車中采用的無刷直流電動機都是低轉(zhuǎn)速的，一般為200轉(zhuǎn)/分，并與車輪整合在一起，不經(jīng)過變速，無刷直流電動機轉(zhuǎn)子的轉(zhuǎn)速就是車輪的轉(zhuǎn)速，而采用12M晶振的單片機系統(tǒng)定時器的最長定時只有60多毫秒，在這么短的時間里，車輪不可能轉(zhuǎn)一周，因此測速只能采用周期法，即多次中斷定時，每次中斷設(shè)為15毫秒，測出車輪轉(zhuǎn)一周所需的中斷次數(shù)，就可以得到車輪每轉(zhuǎn)一周所需的時間，從而算出車子的行進(jìn)速度，在本程序中暫時將車輪的周長定為1米，中斷程序流程圖見圖3-2。圖3-2中斷程序流程圖第四章結(jié)束語電動自行車控制器的性能在很大程度上決定了電動自行車的整車性能。通過單片機AT89C51將各硬件部分有機地組合起來，使系統(tǒng)能及時、有效地檢測到各種控制信號并將轉(zhuǎn)換后的信號反饋給各控制部件，實現(xiàn)了軟硬件的完美組合。此控制器具有節(jié)能、工作可靠等特點，基本符合了人們對電動自行車控制器的要求。經(jīng)過這次畢業(yè)設(shè)計，我覺得自己學(xué)到了不少東西。學(xué)會了更好地查閱資料和利用工具書。當(dāng)在設(shè)計過程中需要用一些不曾學(xué)過的東西時，就要去有針對性地查找資料，然后加以吸收利用，以提高自己的應(yīng)用能力，而且還能增長自己見識，補充最新的專業(yè)知識，并且加強了PROTEL軟件的應(yīng)用設(shè)計，最主要的是，使我對編程有了一定的提高，我是最怕編程的，因為在以前學(xué)習(xí)中，編程就是我最大的弱點，所以真的很感謝這次畢業(yè)設(shè)計。同時在這里，我要感謝我的導(dǎo)師石炳存老師和畢業(yè)設(shè)計過程中所有給我真誠幫助的老師和同學(xué)。參考文獻(xiàn)：[1]沈卓群,劉電霆,蔣存波。電動自行車智能控制器研制[J],桂林工學(xué)院學(xué)報。2002，4(22):406～408。[2]張毅坤，陳善久，裘雪紅。單片微型計算機原理及應(yīng)用[M]，西安電子科技大學(xué)出版社。1998年9月。[3]邵富春。怎樣保護(hù)電動機[M],中國農(nóng)業(yè)機械出版社。1984年6月.[4]葉金虎,徐思海,張頡明,崔海大,施民生。無刷直流電動機[M],科學(xué)出版社。1982年1月[5]邱丹,王東,高振東。直流電機PWM閉環(huán)調(diào)速系統(tǒng)[J]，青島大學(xué)學(xué)報。2000，1(15):10～12.[6]韓志榮,黃鄉(xiāng)生,李躍忠。AT89C51單片機在直流電機閉環(huán)調(diào)速系統(tǒng)中的應(yīng)用[J],華東地質(zhì)學(xué)院學(xué)報.2002,1(15):70～74。[7]楊素行。模擬電子技術(shù)基礎(chǔ)簡明教程[M],高等教育出版社.1998年10月.[8]盧靜,陳非凡,張高飛,施涌潮.基于單片機的無刷直流電動機控制系統(tǒng)設(shè)計[J]，北京機械工業(yè)學(xué)院學(xué)報。2002,4(17):44～49.[9]王曉明，電動機的單片機控制，北京航空航天大學(xué)出版社.2002[10]馬家辰，孫玉德，張穎。MCS-51單片機原理及接口技術(shù)。[11]吳金戌。8051單片機實踐與應(yīng)用[M]，清華大學(xué)出版社。ComputerAidedDesignGoodengineeringdesignisnecessarytoguaranteetatapartormechanismfunctionscorrectlyandlastsforareasonablylongtime.Functionalconsiderationsduringdesigninvolve,amongotherthings,weight,strength,thermalproperties,kinematics,anddynamics.Theperformanceofadesigncanbeevaluatedbycomparingitsperformancemeasurementswiththerequiredspecifications.Asimportantassatisfactoryperformanceis,thereareotherareaspartshouldbedesignedeconomically.Thisimpliesthatthefinishedpartshouldbedesignedasclosetothespecificationsaspossible.Ifthefunctionofasupportingmemberofastructurerequiresthemembertowithstand10,000psiofcompressivestress,thendesigningthemembertowithstand30,000psiisunnecessaryandwillprobablybemoreexpensivethantherequireddesign.Engineeringdesign,thereforeshouldaddressfunctionalityandeconomics,Functionalityisdeterminedbyapart’sgeometry,materialproperties,andenvironment.Theeconomicfactorsincludematerials,processingcosts,andmarketingdetails.Asmuchas70%oftheproductioncostsofamanufacturedpartaredeterminedduringtheengineeringdesignprocess.Thismeansthatbythetimetheparthasleftthedesigner’shandsthelargemajorityofitsproductioncostshavebeenestablished.Theyaredefinedimplicitlybythematerials,dimensions,tolerances,surfacefinishes,andotherparameterswhichdetermineprocessingcosts.Therefore,only30%ofthepart’scostissubjecttomoney-savingeffortsduringthemanufacturingplanningstage.This70/30ratioemphasizestheimportantofthedesigncanbeamajorhelpinassuringproperfunctionandreasonableproductioncosts.Computer-aideddesign(CAD)isatermwhichmeansmanythingstomanypeople.Tosome,itmeanscomputer-aideddraftingordrawing.Toothers,itmeanscompute-aidedanalysis.Andtostillothers,itsuggeststotallyautomateddesignwheretheengineerneedspecifyonlythefunctionofapartandthecomputerarrivesatasatisfactoryorevenoptimaldesign.CADisalloftheabove,aimingmostlyforthefastdescriptionthroughtechniquesinartificialintelligence.CAD,however,stillexistsseparatelyineachofthestagesmentioned.ProbablythemostcommonandsimplestCADsystemsarelimitedtoautomateddraftingcapabilities.Moreadvancedsystemscanperformanalysesandevenhelpguidetheengineertotheequationsnecessarytodeterminetheeffectivenessofthedesign.BecauseoftheavailabilityofawidevarietyofCADsystemswithdifferentcharacteristicssuppliedbydifferentvendors,propercommunicationandexchangeofdatabetweenthesesystemshavebecomeasignificantproblem.TheneedforasingleneutralformatforbettercompatibilityispresentlyfilledlargelybytheInitialGraphicsExchangeSpecificaton(IGES).Vendorsneedonlyprovidetranslatorsfortheirownsystemstopreprocessthedataintotheneutralformatintotheirsystem.IGESisusedfortranslationintwodirections(intooroutofasystem)andisalsousedwidelyfortranslationof3-Dlineandsurfacedata.Amorerecentdevelopmentisasolid-model-basedstandardcalledProductDataExchangeSpecification(PDES),whichisbasedonIGES.AlthoughIGESisadequatefromostrequirement,PDEShaslessmemorysize,requireslesstimeforexecution,andislesserrorprone.Becauseoftheexistenceofvariousstandardsinothercountriesaswell,itisexpectedthatinthenearfuturethesestandardswillculminateinaninternationalstandard,calledtheStandardfortheExchangeofProductModelData(STEP).HardwareandSoftwareHardwarevariesagreatdealbetweenCADsystems.MainframeshavelongbeenusedforCADsystems.TherapidincreasesinprocessingspeedshavemademicroandminicomputersviableCADstations.Networksgenerallyareusedsothatdesignscanbestoredcentrallyanddatacanbesharedamongdesigners.Manyinputdevicesareused.CommonI/Odevicesincludekeyboard,mouse,trackball,digitizingpad,joystick,keypad,andlightpens.Outputdevicesaretypicallyscreen,plotter,printer,andharddrivesanddisksforstorage.ThereisawidevarietyofCADsoftwareavailableformainframesengineeringstationsandmicrocomputers.Thepackagesvarytosomedegreeininformationintheformofdrawingexchangefiles.Thesefilescanbeimportedintoothersoftwaretoassistinprogrammingthemachinetool.ElementsofCADSystemsThedesignprocessinaCADsystemconsistsoffourstages,asdescribedbelow.Geometricmodeling.Ingeometricmodeling,aphysicalobjectoranyofitspartsisdescribedmathematicallyoranalytically.Thedesignerfirstconstructsageometricmodelbygivingcommandsthatcreateormodifylines,surfaces,solids,dimensions,andtextthattogetherareandaccurateandcompletetwo-orthree-dimensionalrepresentationoftheobject.Themodelscanbepresentedinthreedifferentways.Inthelinerepresentation(wire-frame;Figure10.ld),alledgesarevisibleassolidlines.Thisimagecanbeambiguous,particularlyforcomplexshapes.However,variouscolorsaregenerallyusedfordifferentpartoftheobject,thusmakingtheobjecteasiervisualize.Inthesurfacemodel,allvisiblesurfaceareshowninthemodel,andinthesolidmodel,allsurfacesareshown,butthedatadescribetheinteriorvolume(Figure10.1e,f)Designanalysisandoptimization.Afterthedesign’sgeometricfeatureshavemayconsistofanalyzingstresses,strains,deflection,vibrations.Thisphasetemperaturedistribution,ortolerance.Varioussophisticatedsoftwarepackagescapableofcomputingthesequantitiesaccuratelyandrapidlyareavailable.Designreviewandevaluation.Animportantdesignstageisreviewandevaluationtocheckforanyinterferencebetweenvariouscomponentsinordertoavoiddifficultiesduringassemblyoruseofthepart,andwhethermovingmembers,suchaslinkages,aregoingtooperateasintended.Softwareisnowavailablewithanimationcapabilitiestoidentifypotentialwithmovingmembersandotherdynamicsituations.Duringthedesignreviewandevaluationstage,thepartispreciselydimensionedandtolerance,asrequiredformanufacturingit.Documentationanddrafting.Aftertheprecedingstageshavebeencompleted,thedesignisreproducedbyautomateddraftingmachinesfordocumentationandreference.Detailandworkingdrawingsarealsodevelopedandprinted.TheCADsystemiscapableofdevelopingdraftingsectionalviewsofthepart,scalingthedrawings,andperformingtransformationtopresentvariousviewofthepart.InCADsystems,muchofthedesignprocesswasformerlycarriedoutonworkstationconnectedtoamainframecomputer,butthetrendhaschangedrapidlytopowerful,high-performance,andmuchlessexpensivestand-alonedesktop32-bitUnixworkstation;64-bitprocessorswithevenbetterperformancearealsobecomingavailable.TheDesignProcessBeforedelvingintoCAD,itisimportanttounderstandthedesignprocessitself.Computertechniquesarenomorevaluablethanthetheoryonwhichtheyarebased.Afterashortdiscussionofdesigningeneral,wewillexplorehowthecomputercanhelpwitheachofthedesignstages.Shigleydefinesthedesignprocessasaniterativeprocedureconsistingofsixphase:RecognitionofneedDefinitionofproblemSynthesisAnalysisandoptimizationEvaluationPresentationThefirststep,recognitionofneed,arisesfromanidentifiedproblem.Suppose,forexample,thatanew,moreefficientjetengineisrequiredbecauseofafuelshortage.Step2,definitionoftheproblemismorespecific.Definingthespecificsofthejetengineinvolvesknowingthethrust,horsepower,allowableweight,etc.Someofthesespecificationsareconstraints;I.e.,theyarerequirementsthatmustbemetforthedesigntobefeasible.Thejetengineweightlimitmaybeoneconstraintontheavailableliftoftheplanewings.Amaximumweight,then,wouldbeaconstraint.Constraintsareusuallyexpressedasamaximumorminimumvalueorrageofvalues.Otherspecification,however,aretermedcriteria,i.e.,measuresofthegoodnessorqualityofthedesign.Criteriaareusedtomeasureadesignandcomparedesignsagainstoneanother,asoccursduringtheoptimizationstage.Onecriterionofthejetenginemaybegallonsoffuelburnedperhourorpermileoftravel.Criteriahavenomaximumorminimumlimitsonvalues.Asatisfactorydesignisoneinwhichalltheconstraintsaremet.Thisbestdesign,Iadditiontomeetingtheconstraints,willhavethebestcombinationofcriteriavalues.Selectionofconstraintsandcriteriaisanintegralpartofstep2,definitionoftheproblem.Followingdefinitionoftheproblem,thenextthreesteps(synthesis,analysis/optimization,andevaluation)areiterative.Synthesisandanalysisareperformedinconjunctionwithoneanother.Severaltypesofproblemscanariseduringthedesignprocess.Synthesisrequiresdeterminingtheotakestheformofengineeringdrawingsincludinggeometry,tolerances,materialtypes,andcomponentparnumbers.Analysismayrangefromasimpleestheticevaluationtothesolutionofasetofcomplexdifferentialequationswhichdescribetheperformanceofthepartorassembly.Theresultsofanalysescanbeexpressedintabularorgraphicalform.Itisthejobofthedesignertoevaluatetheanalysisdataandtoperformanyredesign.Evaluationsalsoatypeofanalysis,butusuallyrequiresanexpensiveprototypeandracksofinstrumentation.Thedesignprocesscanbeverycostlyandinvolvemanypeople.Designcostmaybelowed,however,byreducingthenumberofpeopleandtheprototypingprocessitself.AnalysisTheanalysisisthecornerstoneofCAD.Theresultsgeneratedbyanalysismodulesareusedbytheengineertodeterminethefeasibilityofadesignortooptimizeorredesigntheobject.Fundamentaltoanalysisisdevelopedtoaccuratelypredicttheperformancebasedonthedesignvariablevalues.Typically,sophisticatedanalysisprogramsaretheperformancemodelsofthedesign.Theuserdoesnotneedtoformulateequationswhichdescribetheperformanceorfunctionality.Whattheusermustdoinsteadistomodeltheobjectgeometryinanappropriateformat.Usuallytieengineerwhoisdesigningacommonlyanalyzedpartorassemblycanpurchaseanalysissoftwaretoevaluatethedesign.Itisonlyinthecaseofanunusualdesignorperformancerequirement,whereoff-the-shelfsoftwareisnotavailable,thattheengineermustformulateauniquemodel.Inthiscase,theengineerwillusuallyderiveamathematicalmodelintheformofequationsusinghelawsofphysicsandwriteaprogramtoreadthedesigndescriptionandcalculateteperformanceparameters.Thesecommonlyavailableanalysismodulesreadthedesigndescriptionandgenerateperformanceresultintheformofnumbers,graphs,charts,etc.AnExampleofUsingCADCAD,normallyusedinengineeringdepartments,hasdrasticallychangedthesedepartments.Drawingusedtobemadeonpaperwithpencilorpenanddrawinginstruments.Theywerethencopied,andthecopiesweresenttothefloorforproduction.Theoriginalswerestoredinlargedrawers.Evenasmallenterprisecouldhavethousandsoflargeblueprintsonfile.Ifchangeswerenecessary,theengineerwouldgettheoriginaloutofthefiledrawer,maketheneedforallofthephysicalstorageofprints.Thecomputeralsoallowedforrapidandeasyprintmodifications.Theengineerordesignerfirstdrawsthepartonthescreenthispartdrawingistheactualpartgeometry.Thesizesandlocationareallcorrectsothattheinformationcanbeusedlatertocreateaprogramtomachinethepart.Theengineerordesignerfirstdrawsthepartonthescreen.Thispartdrawingistheactualpartgeometry.Thesizesandlocationsareallcorrectsothattheinformationcanbeusedlatertocreateaprogramtomachinethepart.Thedesignermustworkcloselywiththemanufacturingpeopletoestablishsomestandardsfordesign.CADallowsdifferentlayers(orlevels)tobecreated.Thisallowsthedesignertoputdifferentpotionsofthepartgeometryondifferentlayers.Forexample,imagineasimplepartthathasa1/2-inchslotmilledinitandfourholesdrilledthroughit.Thedesignerwouldputtheslotononelayerofthedrawingandtheholesonanotherlayer.Thiswillallowothersoftwaretotakethepartgeometryformeachlayerandassigndifferenttoolstoit.Thinkofdifferentlayersasdifferentmachiningoperationthatwouldhavedifferenttoolassignedtothem.Layersareliketransparency.Ifweputallofthetotaltransparenciesontopofeachother,weseethetotalpart.Butwecanstilltakeanyonetransparencyandisolatesomeofthepartgeometry.TheCADsystemwillprinttheblueprintsoitappearsthereisonlyonelayer,orindividuallayerscanbeprinted.Thedesigneralsodimensionsthepart.Thisisquiteautomatic.Thedesignerchooseswherehe/shewantsdimensionsplacedandthecomputerplacestheactualdimensions.Dimensionswouldbeonadifferentlayerthanpartgeometry.Thecomputerallowsdesignstobeviewedandtestedbeforetheactualpartisevenmanufactured.Thepartcanbetestedmakesureitfitswithanymatingpars.CADsystemcancheckforinterferenceofparts,whichcansavealotofwastedmachininganddevelopmenttime.CADsystemscanstress-testparttoseeiftheywillmeetthestrengthrequirementsoftheapplication.ThegraphicsabilitiesofCADsystemalsoallow3-Dviewingofpartfromanyangle.IntegratedCADTheemphasisofthechapterisintegratedCAD/CAM.Theintegrationaspectisaccomplishedwhenthedesignandanalysismodulesareunitedintoonepackage.Thedesigngeometryenteredbythedesignercanbeusedbytheanalysisprogramsandbythemanufacturing,inspection,inventory,andotheraspectsoftheproductliftcycle.Themanifestationofintegratingsoftwareisrecognizedwhentheusercansitdownatacomputerterminal,designapart,viewitonthescreen,analyzeitfordesignrequirements,andhittheproverbialmanufacturingbuttonthekeyboardtohavethepartautomaticallymanufactured,inspected,anddelivered.Variousstagesofintegrationdoexist,butnoneisascompleteastheexamplejustmentioned.Integrationimpliesautomation.AutomationimpliesthatthehardwareandsoftwarecancreateaCADdatabaseanduseittoanalyzeandmanufacturetheparttotallyautomatically,withlittleornohumanintervention.Thequestionastowhetherhumaninterventionisadvisableisstillopen.Certainlyhumanintelligenceisvaluableindevelopingadesigningeometryandfunctionality,recognizingcertainpatternsandshortcomingsofproducts,andformulatingmanufacturingplans.Ithasbeensuggestedthatartificialintelligence(AI)techniquescansubstituteformuchofthehumandesign/manufacturinginput.AIresearchhashadsuccessintheareasofpatternrecognition,planning,naturallanguageunderstanding,roboticcontrol,faultdiagnosis,andotherapplications.ThemostwellrecognizeareaofAIisthedevelopmentofexpertsystem.Expertsystemssimulatehumanexpertisebystoringaknowledgebaseofdataaboutaspecificdomain.ThearchitectureofanexpertsystemisshowninFigure10.2.Theknowledgebasecontainsknowledgeaboutaspecificproblemdomainandfactsstatingtheproblem.Theinferenceengineistheprogramcontrolwhichsearchestefactsabouttheproblemtosatisfytheknowledgebaseadabovetheproblem計算機輔助設(shè)計一個好的機械設(shè)計產(chǎn)品必須保證產(chǎn)品的部分或全部功能在產(chǎn)品壽命中能夠正確有效地實現(xiàn)。在設(shè)計中產(chǎn)品功能的研究包括：重力、強度、熱、溫度特性、運動學(xué)和動力學(xué)。評價設(shè)計的好壞與否可以通過比較產(chǎn)品的實際性能與設(shè)計要求的差距來衡量。設(shè)計除了功能達(dá)到設(shè)計要求之外，其它方面的實際同樣也十分重要。比如說經(jīng)濟(jì)性方面的要求。這就是說最終的產(chǎn)品要近可能地接近設(shè)計要求。如果要求支撐設(shè)計能承受1000N/min的能力，然而設(shè)計成能承受2000N/min，則沒有必要也不經(jīng)濟(jì)。因此機械設(shè)計必須處理好產(chǎn)品的功能與其經(jīng)濟(jì)性之間的矛盾。產(chǎn)品的性能受零部件的結(jié)構(gòu)、材料屬性和人機環(huán)境的影響；產(chǎn)品的經(jīng)濟(jì)性則和材料的成本以及市場因素有關(guān)。在機械設(shè)計過程中70%的制造成本已經(jīng)決定了。這就是說設(shè)計者把產(chǎn)品交給制造之前，絕大部分主要的成本已經(jīng)決定。比如：材料尺寸、公差、表賣弄粗糙度及過程成本的其它參數(shù)。因此，在加工過程中，我們在制造過程中再努力也只能減少%30的花費。這個比例說明設(shè)計過程起著置關(guān)重要的作用。我們應(yīng)該清楚計算機能夠幫上很大的忙。計算機輔助設(shè)計對不同的人意味著不同的意思。對一些人來說，它意味著計算機輔助繪圖和草繪，對另外一些人來說，他則意味著完全自動化設(shè)計，設(shè)計者只要規(guī)定設(shè)計的功能，則計算機能設(shè)計出滿足要求的產(chǎn)品，甚至經(jīng)過優(yōu)化的設(shè)計。以上則是計算機輔助設(shè)計。他的目標(biāo)就是通過人類的智慧實現(xiàn)后面敘述的一種情形。計算機輔助設(shè)計仍停留在計算機輔助繪圖階段。大多數(shù)簡單的CAD只能進(jìn)行自動草繪功能。更高級的系統(tǒng)呢功能進(jìn)行分析引導(dǎo)工程師得到必須平衡的關(guān)系。因為不同的賣主提供具有不同特點的計算機輔助設(shè)計系統(tǒng)，這些系統(tǒng)之間具有各自不同的數(shù)據(jù)標(biāo)準(zhǔn)。他們之間的交流和數(shù)據(jù)轉(zhuǎn)化變得非常有意義。IGES在不同系統(tǒng)之間數(shù)據(jù)格式轉(zhuǎn)換中扮演了中間者的角色。不同軟件廠商只要提供與IGES格式相互轉(zhuǎn)換的模塊系統(tǒng)，各種計算機輔助設(shè)計軟件能導(dǎo)入和導(dǎo)出IGES格式的文件，同時這種格式的文件在3D圖形轉(zhuǎn)換種也有根廣泛的應(yīng)用。目前一種基于IGES格式的實體建模技術(shù)的數(shù)據(jù)格式（PDES）也得到很大的發(fā)展。這種格式的文件占用系統(tǒng)空間小、速度快、可靠性高。由于國外也有各種不同的標(biāo)準(zhǔn)存在，預(yù)計不久這些標(biāo)準(zhǔn)將導(dǎo)致一個國際標(biāo)準(zhǔn)規(guī)格，叫產(chǎn)品模型數(shù)據(jù)(STEP)的交換的標(biāo)準(zhǔn)。硬件和軟件硬件在計算機輔助設(shè)計系統(tǒng)之間存在很大的差別。服務(wù)器早就用于計算機輔助設(shè)計系統(tǒng)。處理速度迅速增加的微型和小型計算機也可以進(jìn)行的計算機輔助設(shè)計系統(tǒng)的運行。網(wǎng)絡(luò)一般被使用以便設(shè)計可以被中心儲存，數(shù)據(jù)可以被分給設(shè)計者。很多輸入裝置使用的非常廣泛。普通I/O設(shè)備包括：鍵盤，鼠標(biāo)，跟蹤球，數(shù)子化儀，控制桿，輔助鍵盤和光筆數(shù)字化儀。典型的輸出裝置通常是屏幕，繪圖儀，打印機、移動硬盤和軟盤。有多種計算機輔助設(shè)計軟件提供給工作站和微型計算機。數(shù)據(jù)包在某種程度上以繪圖信息形式的交換文件變化。這些文件可以被輸入到其他軟件中幫助可編程的機床。計算機輔助設(shè)計系統(tǒng)的要素計算機輔助設(shè)計系統(tǒng)的設(shè)計過程由四級組成，如下描述。幾何學(xué)模型化。在幾何學(xué)模型化過程中，將一個物體或者它的任何部分進(jìn)行分析后用數(shù)字描述。首先設(shè)計者給出命令建立或者修改能夠完成二維或三維的線條、表面、實體、尺寸和正文構(gòu)造幾何學(xué)模型。幾何學(xué)模型可以用三種不同的方式呈現(xiàn)。如下圖(線框內(nèi)；圖10.ld)，全部邊緣都象固體的線一樣可見。這幅圖像可能是含糊的，特別是復(fù)雜的形狀。不過，各種各樣的顏色一般用于物體的不同的部分，因此使物體更容易想象。在表面模型里，全部可見的表面被用模型顯示，并且在實體模型里，全部表面被顯示，但是內(nèi)部以數(shù)據(jù)的形式描述(數(shù)字10.1e，f)設(shè)計分析和最優(yōu)化。設(shè)計幾何學(xué)特征有可能由分析壓力、疲勞、撓度、振動組成。這階段溫度分布或者容忍。各種各樣復(fù)雜軟件包能計算出質(zhì)量的準(zhǔn)確并且快速的變化。設(shè)計評論和評估。設(shè)計過程忠一個重要的設(shè)計階段是檢查在各種各樣的組成部分之間是否存在任何干涉，是否有自由度，例如將要作為運動構(gòu)件的連桿。計算機軟件能利用動畫模擬運動的構(gòu)件及其它運動狀態(tài)。在設(shè)計過程的評論和評估階段，零件已經(jīng)具有制造需要的準(zhǔn)確尺寸和公差。文檔編制和草繪。在那些先前階段完成之后，那些設(shè)計被自動化草繪儀復(fù)制作為文檔編制和參考用，細(xì)節(jié)和圖紙也被沖印。計算機輔助設(shè)計系統(tǒng)能繪制零件的剖視圖、局部視圖，并且能提取零件的各種各樣的視圖。以前