高速双色牙刷植毛机机械结构设计（全套含CAD图纸）
收藏
资源目录
压缩包内文档预览：
编号：10055240
类型：共享资源
大小：35.61MB
格式：ZIP
上传时间：2018-04-28
上传人：机****料
认证信息
个人认证
高**（实名认证）
河南
IP属地：河南
50
积分
- 关 键 词：
-
高速
牙刷
植毛机
机械
结构设计
全套
cad
图纸
- 资源描述：
-
- 内容简介：
-
4FORCESINSTRUCTURESANDFLUIDSOVERVIEWWHENMECHANICALENGINEERSDESIGNPRODUCTS,SYSTEMS,ANDHARDWARE,THEYMUSTAPPLYMATHEMATICSANDPHYSICALPRINCIPLESTOMODEL,ANALYZE,ANDPREDICTSYSTEMBEHAVIORSUCCESSFULDESIGNISSUPPORTEDBYEFFECTIVEENGINEERINGANALYSISEFFECTIVEENGINEERINGANALYSISRELIESONANUNDERSTANDINGOFFORCESINSTRUCTURESANDMACHINESTHISISTHEFOCUSOFTHISCHAPTERANDTHENEXTELEMENTOFMECHANICALENGINEERINGTHISCHAPTERINTRODUCESYOUTOTHESUBJECTOFMECHANICS,ATOPICTHATENCOMPASSESFORCESTHATACTONSTRUCTURESANDMACHINESANDTHEIRTENDENCYEITHERTOREMAINSTATIONARYORMOVETHEFUNDAMENTALPRINCIPLESTHATFORMTHEBASISOFMECHANICSARENEWTONSTHREELAWSOFMOTION1EVERYOBJECTREMAINSINASTATEOFRESTORUNIFORMMOTIONOFCONSTANTVELOCITYUNLESSANEXTERNALUNBALANCEDFORCEACTSUPONIT2ANOBJECTOFMASSM,SUBJECTTOAFORCEF,EXPERIENCESANACCELERATIONINTHESAMEDIRECTIONASTHEFORCEWITHAMAGNITUDEDIRECTLYPROPORTIONALTOTHEMAGNITUDEOFTHEFORCEANDINVERSELYPROPORTIONALTOTHEMASSOFTHEOBJECTTHISRELATIONSHIPCANBEEXPRESSEDASF5MA3THEFORCESOFACTIONANDREACTIONBETWEENTWOOBJECTIVESAREEQUAL,OPPOSITE,ANDCOLLINEAR43MOMENTOFAFORCEWHENYOUARETRYINGTOLOOSENAFROZENBOLT,THEBOLTISMOREEASILYTURNEDWHENAWRENCHWITHALONGHANDLEISUSEDTHETENDENCYOFAFORCEINTHISCASE,APPLIEDTOTHEHANDLESENDTOMAKEANOBJECTROTATEISCALLEDAMOMENTTHEMAGNITUDEOFAMOMENTDEPENDSBOTHONTHEFORCETHATISAPPLIEDANDONTHELEVERARMTHATSEPARATESTHEFORCEFROMAPIVOTPOINTPERPENDICULARLEVERARMTHEMAGNITUDEOFAMOMENTISFOUNDFROMITSDEFINITION48FDMOWHEREMOISTHEMOMENTOFTHEFORCEABOUTPOINTO,FISTHEMAGNITUDEOFTHEFORCE,ANDDISTHEPERPENDICULARLEVERARMDISTANCEFROMTHEFORCESLINEOFACTIONTOPOINTOTHETERMTORQUECANALSOBEUSEDTODESCRIBETHEEFFECTOFAFORCEACTINGOVERALEVERARM,BUTMECHANICALENGINEERSGENERALLYRESERVETORQUETODESCRIBEMOMENTSTHATCAUSEROTATIONOFASHAFTINAMOTOR,ENGINE,ORGEARBOXWEWILLDISCUSSTHOSEAPPLICATIONSINCHAPTER7BASEDONEQUATION48,THEUNITFORMOISTHEPRODUCTOFFORCEAND,DISTANCEINTHEUSCS，THEUNITFORAMOMENTISINLBORFTLBINTHESI,THEUNITNMISUSED,ANDVARIOUSPREFIXESAREAPPLIEDWHENTHENUMERICALVALUEISEITHERVERYLARGEORVERYSMALLFORINSTANCE5000NM5KNMAND0002NM2MNMCONVERSIONFACTORSBETWEENTHETWOSYSTEMSOFUNITSARESHOWNINTABLE42,WHEREYOUCANSEETHAT1FTLB1356NMWORKANDENERGY,WHICHAREOTHERQUANTITIESTHATARISEINMECHANICALENGINEERING,ALSOHAVEUNITSTHATARETHEPRODUCTOFFORCEANDDISTANCEFORINSTANCE,WHENWORKINGINTHESI,AJOULEJISDEFINEDASONENEWTONMETERITISTHEAMOUNTOFWORKPERFORMEDBYA1NEWTONFORCETHATMOVESTHROUGHADISTANCEOF1METERHOWEVER,THEPHYSICALQUANTITIESOFWORKANDENERGYAREQUITEDIFFERENTFROMMOMENTSANDTORQUES,ANDINORDERTOBECLEARWHENDISTINGUISHINGTHEM,THEUNITOFNMANDNOTJSHOULDBEUSEDINTHESIFORMOMENTANDTORQUETHEEXPRESSIONMOFDCANBESTBEUNDERSTOODBYAPPLYINGITTOASPECIFICSTRUCTUREINFIGURE49A,THEFORCEFISDIRECTEDGENERALLYDOWNWARDANDTOTHERIGHTONTHEBRACKETONEMIGHTBEINTERESTEDINTHEMOMENTOFFABOUTTHEBASEOFTHESUPPORTPOST,WHICHISLABELEDINTHEFIGUREASPOINTOTHESTRUCTURECOULDBREAKATTHATLOCATION,ANDANENGINEERWOULDEXAMINETHEPOSTTOMAKESURETHATITCANSUPPORTFTHEMOMENTISCALCULATEDBASEDUPONBOTHTHEMAGNITUDEOFFANDTHEPERPENDICULAROFFSETDISTANCEDBETWEENTHEFORCESLINEOFACTIONANDPOINTOINFACT,FCOULDBEAPPLIEDTOTHEBRACKETATANYPOINTALONGITSLINEOFACTION,ANDTHEMOMENTPRODUCEDABOUTOWOULDREMAINUNCHANGEDBECAUSEDWOULDLIKEWISENOTCHANGETHEDIRECTIONOFTHEMOMENTISCLOCKWISE,BECAUSEFTENDSTOCAUSETHEPOSTTOROTATETHATWAYEVENTHOUGHTHERIGIDMOUNTINGWOULDPREVENTTHEPOSTFROMACTUALLYMOVINGINTHISCASEINFIGURE49BTHEDIRECTIONOFFHASBEENCHANGEDTHEFORCESLINEOFACTIONNOWPASSESDIRECTLYTHROUGHPOINTO,ANDTHEOFFSETDISTANCEBECOMESD0NOMOMENTISPRODUCED,ANDTHEFORCETENDSTOPULLTHEPOSTDIRECTLYOUTOFITSBASEINSHORT,THEORIENTATIONOFAFORCEASWELLASITSMAGNITUDEMUSTBETAKENINTOACCOUNTWHENCALCULATINGAMOMENTEXAMPLE43THEOPENENDWRENCHSHOWNINFIGURE410TIGHTENSAHEXAGONALHEADNUTANDBOLTCALCULATETHEMOMENTSPRODUCEDBYTHE35LBFORCEABOUTTHECENTEROFTHENUTWHENTHEFORCEISAPPLIEDTOTHEWRENCHINTHETWOORIENTATIONSSHOWNTHEOVERALLLENGTHOFTHEHANDLE,WHICHISINCLINEDSLIGHTLYUPWARD,ISINLONGBETWEENCENTERSOFTHEOPENANDCLOSEDENDS16SOLUTIONAINFIGURE410A,THE35LBFORCEACTSVERTICALLYDOWNWARDTHEPERPENDICULARDISTANCEFROMTHECENTEROFTHENUTTOTHEFORCESLINEOFACTIONISD6INTHEINCLINEANDLENGTHOFTHEWRENCHSHANDLEAREIMMATERIALINSOFARASCALCULATINGDISCONCERNEDTHEHANDLESLENGTHISNOTNECESSARILYTHESAMEASTHEPERPENDICULARLEVERARMDISTANCETHEMOMENTHASMAGNITUDE351B6IN210INLB175FTLBWHICHISDIRECTEDCLOCKWISE（CW）BINFIGURE410BTHEFORCEHASSHIFTEDTOANINCLINEDANGLE,ANDITSLINEOFACTIONHASCHANGEDSOTHATDISMEASUREDTOBEIN,THEMOMENTISREDUCEDTO83535LB5375IN188INLB157FTLBWEREPORTTHEANSWERASMO157FTLBCWMOMENTCOMPONENTSJUSTASWECANBREAKAFORCEINTORECTANGULARCOMPONENTSITISSOMETIMESUSEFULTOCALCULATEAMOMENTASTHESUMOFITSCOMPONENTSTHEMOMENTISDETERMINEDASTHESUMOFPORTIONSTHATAREASSOCIATEDWITHTHETWOCOMPONENTSOFTHEFORCE,RATHERTHANTHEFULLRESULTANTVALUEOFTHEFORCEAMOTIVATIONFORCALCULATING,THEMOMENTINTHISMANNERIS,THATITISOFTENEASIERTOFINDTHELEVERARMSFORINDIVIDUALCOMPONENTSTHANFORTHERESULTANTFORCEWHENAPPLYINGTHISTECHNIQUE,ITISNECESSARYTOUSEASIGNCONVENTIONANDKEEPTRACKOFWHETHERTHECONTRIBUTIONMADEBYEACHFORCECOMPONENTISCLOCKWISEORCOUNTERCLOCKWISETOILLUSTRATETHISMETHOD,WECALCULATETHEMOMENTSABOUTPOINTOOFTHEFORCESSHOWNINFIGURE411WEFIRSTCHOOSETHEFOLLOWINGSIGNCONVENTIONAMOMENTTHATISDIRECTEDCLOCKWISEISPOSITIVE,ANDACOUNTERCLOCKWISEMOMENTISNEGATIVETHESIGNCONVENTIONISJUSTABOOKKEEPINGTOOLFORCOMBININGTHEVARIOUSCLOCKWISEANDCOUNTERCLOCKWISEMOMENTCOMPONENTSANYCONTRIBUTIONTOTHEMOMENTABOUTOTHATACTSCLOCKWISEISGIVENAPOSITIVESIGNANDANYCONTRIBUTIONINTHEOTHERDIRECTIONISNEGATIVETHISCHOICEOFPOSITIVEANDNEGATIVEDIRECTIONSISARBITRARYANDWECOULDJUSTASEASILYHAVESELECTEDTHECOUNTERCLOCKWISEDIRECTIONASBEINGPOSITIVEHOWEVER,ONCETHESIGNCONVENTIONISCHOSEN,WESTICKWITHITANDAPPLYITCONSISTENTLYINFIGURE411ATHEFORCEISBROKENDOWNINTOTHECOMPONENTSFXANDFYRATHERTHANDETERMINETHEDISTANCEFROMPOINTOTOTHELINEOFACTIONOFF,WHICHOUGHTINVOLVEAGEOMETRICALCONSTRUCTIONTHATWEWANTTOAVOID,WEINSTEADCALCULATETHEINDIVIDUALLEVERARMDISTANCESFORFXANDFY,WHICHAREMORESTRAIGHTFORWARDKEEPINGTRACKOFTHESIGNCONVENTION,THEMOMENTABOUTOBECOMESEACHCONTRIBUTIONTOMOISPOSITIVEBECAUSEFXANDFYEACHXFYMXOTENDTOCAUSECLOCKWISEROTATIONTHEIREFFECTSCOMBINECONSTRUCTIVELYTHEORIENTATIONOFFHASBEENCHANGEDINFIGURE411BWHILETHECOMPONENTFXCONTINUESTOEXERTAPOSITIVEMOMENT,FYNOWTENDSTOCAUSECOUNTERCLOCKWISEROTATIONABOUTOITTHEREFOREMAKESANEGATIVECONTRIBUTION,ANDTHENETMOMENTBECOMESHERETHETWOYXOCOMPONENTSCOMBINEINADECONSTRUCTIVEMANNERFORTHEPARTICULARORIENTATIONINWHICH,THETWOTERMSPRECISELYCANCELTHEMOMENTINTHATCASEISZEROBECAUSETHEXYFLINEOFACTIONFORFPASSESDIRECTLYTHROUGHO,ASINFIGURE49BINTHEGENERALCASEOFTHEMOMENTCOMPONENTSMETHOD,WEWRITE49XFYMXOANDTHEPOSITIVEANDNEGATIVESIGNSARESELECTEDDEPENDINGONWHETHERTHECOMPONENTTENDSTOCAUSECLOCKWISEORCOUNTERCLOCKWISEROTATIONREGARDLESSOFWHICHMETHODYOUUSETOCALCULATEAMOMENT,WHENREPORTINGANANSWERYOUSHOULDSTATE1THENUMERICALMAGNITUDEOFTHEMOMENT,2THEUNITS,AND3THEDIRECTIONYOUCANINDICATETHEDIRECTIONBYUSINGNOTATIONPROVIDEDTHATYOUHAVEALSOSHOWNTHESIGNCONVENTIONONYOURDRAWINGTHENOTATIONCWORCCWISALSOUSEFULFORDENOTINGWHETHERTHEMOMENTACTSCLOCKWISEORCOUNTERCLOCKWISEEXAMPLE44DETERMINETHEMOMENTABOUTTHECENTEROFTHENUTASTHE250NFORCEISAPPLIEDTOTHEHANDLEOFTHEADJUSTABLEWRENCHINFIGURE412USEATHEPERPENDICULARLEVERARMMETHOD,ANDBTHEMOMENTCOMPONENTSMETHODSOLUTIONAASSHOWNINFIGURE413A,WEDENOTETHECENTEROFTHENUTASPOINTA,ANDTHEPOINTOFAPPLICATIONOFTHEFORCEASPOINTBUSINGTHEDIMENSIONSGIVEN,DISTANCEABISCALCULATEDASALTHOUGHTHISISTHEDISTANCEFROMATOTHELOCATIONATWHICHTHE214M0752FORCEISAPPLIED,ITISNOTTHEPERPENDICULARLEVERARMDISTANCEDFORTHISREASON,WENEEDTOCALCULATETHELENGTHOFSEGMENTACBECAUSETHEAPPLIEDFORCEISTILTED35FROMVERTICAL,ALINEPERPENDICULARTOTHEFORCEISORIENTED35FROMHORIZONTALASDEPICTEDINFIGURE413ALINEABLIESATTHEANGLETAN175/200206BELOWHORIZONTAL,ANDSOITISOFFSETBYFROMACTHECORRECTLEVERARMDISTANCETHEREFOREBECOMES4162035THEWRENCHSMOMENTIS207MCOSD518NM0275AMDIRECTEDCLOCKWISECWBINFIGURE413B,THE250NFORCEISBROKENINTOITSCOMPONENTSTHEHORIZONTALPORTIONIS250NSIN35143N,ANDTHEVERTICALCOMPONENTIS250NCOS35205NTHOSECOMPONENTSAREORIENTEDLEFTWARDANDDOWNWARD,RESPECTIVELY,ANDTHEYEACHEXERTCLOCKWISEMOMENTCONTRIBUTIONSABOUTAINFIGURE413B,WEHAVESHOWNOURPOSITIVESIGNCONVENTIONFORMOMENTSASBEINGCLOCKWISEBYSUMMINGTHEMOMENTOFEACHCOMPONENT,WEHAVEM518N20N75M143AMBECAUSETHENETRESULTISPOSITIVE,THEMOMENTISDIRECTEDCLOCKWISE44EQUILIBRIUMOFFORCESANDMOMENTSWITHGROUNDWORKFORTHEPROPERTIESOFFORCESANDMOMENTSNOWINPLACE,WENEXTTURNTOTHETASKOFCALCULATINGUNKNOWNFORCESTHATACTONSTRUCTURESANDMACHINESINRESPONSETOOTHERKNOWNFORCESTHATAREPRESENTTHISPROCESSINVOLVESAPPLYINGTHEPRINCIPLEOFSTATICEQUILIBRIUMTOSYSTEMSTHATAREEITHERSTATIONARYORMOVINGATCONSTANTVELOCITYINEITHERCASE,NOACCELERATIONISPRESENT,ANDINACCORDANCEWITHTHELAWSOFMOTION,THERESULTANTFORCEONTHESYSTEMISZEROPARTICLESANDRIGIDBODIESAMECHANICALSYSTEMCANINCLUDEEITHERLASINGLEOBJECTFORINSTANCE,ANENGINEPISTONORMULTIPLEOBJECTSTHATARECONNECTEDTOGETHERTHEENTIREENGINEWHENTHEPHYSICALDIMENSIONSOFTHEOBJECTAREUNIMPORTANTINCALCULATINGFORCES,THEOBJECTISCALLEDAPARTICLETHISCONCEPTIDEALIZESANOBJECTASBEINGCONCENTRATEDATASINGLEPOINT,RATHERTHANDISTRIBUTEDOVER,ANEXTENDEDAREAORVOLUMEFORTHEPURPOSESOFPROBLEMSOLVING,APARTICLECANTHEREFOREBETREATEDASHAVINGNEGLIGIBLEDIMENSIONSONTHEOTHERHAND,IFTHELENGTH,WIDTH,ANDBREADTHOFANOBJECTAREIMPORTANTFORTHEPROBLEMATHAND,ITISCALLEDARIGIDBODYWHENLOOKINGATTHEMOTIONOFTHESPACESHUTTLEASITORBITSTHEEARTH,FORINSTANCE,THESPACECRAFTISREGARDEDASAPARTICLEBECAUSEITSDIMENSIONSARESMALLCOMPAREDTOTHESIZEOFTHEORBITHOWEVER,WHENTHESHUTTLEISLANDINGANDENGINEERSAREINTERESTEDINITSAERODYNAMICSANDFLIGHTCHARACTERISTICS,THEVEHICLEWOULDINSTEADBEANALYZEDASARIGIDBODYFIGURE414ILLUSTRATESTHEDISTINCTIONBETWEENFORCESTHATAREAPPLIEDTOAPARTICLEANDTOARIGIDBODYYOUCANSEEHOWAFORCEIMBALANCECOULDCAUSETHERIGIDBODYTOROTATEAPARTICLEISINEQUILIBRIUMIFTHEFORCESACTINGONITBALANCEWITHZERORESULTANTBECAUSEFORCESCOMBINEASVECTORS,THERESULTANTMUSTBEZEROINTWOPERPENDICULARDIRECTIONS,WHICHWELABELXANDYAND4100IXF0IYFFORARIGIDBODYTOBEINEQUILIBRIUM,ITISNECESSARYTHAT1THERESULTANTOFALLFORCESISZERO，AND2THENETMOMENTISALSOZEROWHENTHOSECONDITIONSAREMET,THEREISNOTENDENCYFORTHEOBJECTEITHERTOMOVEINRESPONSETOTHEFORCESORTOROTATEINRESPONSETOTHEMOMENTSTHEREQUIREMENTSFOREQUILIBRIUMOFARIGIDBODYINVOLVEEQUATION410AND4110IOIMTHENOTATIONMOIISUSED,TODENOTETHEITHMOMENTTHATISAPPLIEDABOUTPOINTOINSUMMARY,THETWORELATIONSHIPSINEQUATION410SPECIFYTHATNONETFORCEACTSINEITHERTHEXORYDIRECTIONS,ANDEQUATION411STATESTHATNONETMOMENTTENDSTOCAUSEROTATIONSIGNCONVENTIONSAREABOOKKEEPINGMETHODTODISTINGUISHFORCESACTINGINOPPOSINGDIRECTIONSANDMOMENTSTHATAREORIENTEDCLOCKWISEORCOUNTERCLOCKWISETHESUMMATIONSINTHEEQUILIBRIUMEQUATIONARECONDUCTEDOVERALLFORCESANDMOMENTSPRESENT,WHETHERORNOTTHEIRDIRECTIONSANDMAGNITUDESAREKNOWNINADVANCEFORCESTHATAREUNKNOWNATTHESTARTOFTHEPROBLEMAREALWAYSINCLUDEDINTHESUMMATIONALGEBRAICVARIABLESAREASSIGNEDTOTHEM,ANDTHEEQUILIBRIUMEQUATIONSARETHENAPPLIEDTODETERMINENUMERICALVALUESMATHEMATICALLYSPEAKING,THEEQUILIBRIUMEQUATIONSFORARIGIDBODYCOMPRISEASYSTEMOFTHREELINEAREQUATIONSINVOLVINGTHEUNKNOWNFORCESANDMOMENTSONEIMPLICATIONOFTHISCHARACTERISTICISTHATITISPOSSIBLETODETERMINEATMOSTTHREEUNKNOWN,QUANTITIESWHENEQUATIONS410411AREAPPLIEDTOASINGLERIGIDBODYBYCONTRASTWHENAPPLYINGTHEEQUILIBRIUMREQUIREMENTSTOAPARTICLE,THEMOMENTEQUATIONISNOTUSEDTHEREFORE,ONLYTWOINDEPENDENTEQUATIONSAREPRODUCED,ANDONLYTWOUNKNOWNSCANBEDETERMINEDITISNOTPOSSIBLETOOBTAINMOREINDEPENDENTEQUATIONSOFEQUILIBRIUMBYRESOLVINGMOMENTSABOUTANALTERNATIVEPOINTORBYSUMMINGFORCESINDIFFERENTDIRECTIONSTHEADDITIONALEQUATIONSWILLSTILLBEVALID,BUTTHEYWILLSIMPLYBECOMBINATIONSOFTHEOTHERALREADYDERIVEDONESASSUCH,THEYWILLPROVIDENONEWINFORMATIONWHENYOUSOLVEEQUILIBRIUMPROBLEMS,YOUSHOULDALWAYSCHECKTOBESURETHATYOUDONOTHAVEMOREUNKNOWNQUANTITIESTHANINDEPENDENTEQUATIONSFREEBODYDIAGRAMSFREEBODYDIAGRAMSABBREVIATEDFBDARESKETCHESUSEDTOANALYZETHEFORCESANDMOMENTSTHATACTONSTRUCTURESANDMACHINES,ANDTHEIRCONSTRUCTIONISANIMPORTANTSKILLTHEFBDISUSEDTOIDENTIFYTHEMECHANICALSYSTEMTHATISBEINGEXAMINEDANDTOREPRESENTALLOFTHEKNOWNANDUNKNOWNFORCESTHATAREPRESENTTHREEMAINSTEPSAREFOLLOWEDWHENAFBDISDRAWN1SELECTANOBJECTTHATWILLBEANALYZEDBYUSINGTHEEQUILIBRIUMEQUATIONSIMAGINETHATADOTTEDFINEISDRAWNAROUNDTHEOBJECT,ANDNOTEHOWTHELINEWOULDCUTTHROUGHANDEXPOSEVARIOUSFORCESEVERYTHINGWITHINTHEDOTTEDLINEISISOLATEDFROMTHESURROUNDINGSANDSHOULDAPPEARONTHEDIAGRAM2THECOORDINATESYSTEMISDRAWNNEXTTOINDICATETHEPOSITIVESIGNCONVENTIONSFORFORCESANDMOMENTSITWILLBEMEANINGLESSTOREPORTANANSWEROF,SAY,“25NM“OR“250LB“WITHOUTHAVINGDEFINEDTHEDIRECTIONSASSOCIATEDWITHTHEPOSITIVEANDNEGATIVESIGNS3INTHEFINALSTEP,ALLFORCESANDMOMENTSAREDRAWNANDLABELEDTHESEFORCESMIGHTREPRESENTWEIGHTORCONTACTBETWEENTHEFREEBODYANDOTHEROBJECTSTHATWEREREMOVEDWHENTHEBODYWASISOLATEDWHENAFORCEISKNOWN,ITSDIRECTIONANDMAGNITUDESHOULDBEWRITTENONTHEDIAGRAMFORCESAREINCLUDEDEVENIFTHEIRMAGNITUDESANDDIRECTIONSARENOTKNOWNATTHISSTEPINTHEANALYSISIFTHEDIRECTIONOFAFORCEISUNKNOWNFORINSTANCE,UPWARD/DOWNWARDORLEFTWARD/RIGHTWARD,YOUSHOULDJUSTDRAWITONEWAYORTHEOTHERONTHEFBD,PERHAPSUSINGYOURINTUITIONASAGUIDEAFTERAPPLYINGTHEEQUILIBRIUMEQUATIONSANDCONSISTENTLYUSINGASIGNCONVENTION,THECORRECTDIRECTIONWILLBEDETERMINEDTHROUGHYOURCALCULATIONSIFYOUFINDTHEQUANTITYTOBEPOSITIVE,THENYOUKNOWTHATTHECORRECTDIRECTIONWASCHOSENONTHEOTHERHAND,IFTHENUMERICALVALUETURNSOUTTOBENEGATIVE,THERESULTSIMPLYMEANSTHATTHEFORCEACTSOPPOSITETOTHEASSUMEDDIRECTIONEXAMPLE45DURINGCRASHTESTINGOFANAUTOMOBILE,THELAPANDSHOULDERSEATBELTSEACHBECOMETENSIONEDTO300LB,ASSHOWNINFIGURE415ATREATINGTHEBUCKLEBASAPARTICLE,ADRAWAFREEBODYDIAGRAM,BDETERMINETHETENSIONTINTHEANCHORSTRAPAB,ANDCDETERMINETHEANGLEATWHICHTACTSSOLUTIONATHEFREEBODYDIAGRAMOFTHEBUCKLEISSHOWNINFIGURE415BTHEXYCOORDINATESYSTEMISALSODRAWNTOINDICATEOURSIGNCONVENTIONFORTHEPOSITIVEHORIZONTALANDVERTICALDIRECTIONSTHREEFORCESACTONTHEBUCKLETHETWOGIVEN300LBFORCESANDTHEUNKNOWNFORCEINTHEANCHORSTRAPFORTHEBUCKLETOBEINEQUILIBRIUM,THESETHREEFORCESMUSTBALANCEALTHOUGHBOTHTHEMAGNITUDETANDDIRECTIONOFTHEFORCEINSTRAPABAREUNKNOWN,BOTHQUANTITIESARESHOWNONTHEFREEBODYDIAGRAMFORCOMPLETENESSBWESUMTHETHREEFORCESBYUSINGTHEVECTORPOLYGONAPPROACH,ASSHOWNINFIGURE415CTHEPOLYGONSSTARTANDENDPOINTSARETHESAMEBECAUSETHETHREEFORCESACTINGTOGETHERHAVEZERORESULTANTTHATIS,THEDISTANCEBETWEENTHEPOLYGONSSTARTANDENDPOINTSISZEROTHETENSIONISDETERMINEDBYAPPLYINGTHELAWOFCOSINESEQUATIONSFOROBLIQUETRIANGLESAREREVIEWEDINAPPENDIXBTOTHESIDEANGLESIDETRIANGLEINFIGURE415CLBCOS120L320LB3L022TFROMWHICHWECALCULATE6519CTHEANCHORSTRAPSANGLEISFOUNDFROMTHELAWOFSINESLB6519SINL03IANDEXAMPLE46APAIROFWIRECUTTERSISSHOWNINFIGURE416AMACHINISTAPPLIESTHE70NGRIPPINGFORCETOTHEHANDLESWHATISTHEMAGNITUDEOFTHECUTTINGFORCEONTHEELECTRICALWIREATASOLUTIONTHECOORDINATESYSTEMANDPOSITIVESIGNCONVENTIONFORTHEFORCEANDMOMENTDIRECTIONSARESHOWNINFIGURE417WENEXTDRAWTHEFREEBODYDIAGRAMFORONEJAW/HANDLEASSEMBLY,WHICHISTREATEDASARIGIDBODYBECAUSEITCANROTATEANDTHEDISTANCESBETWEENTHEFORCESARESIGNIFICANTTOTHEPROBLEMWHENABLADEISPRESSEDAGAINSTTHEWIRE,THEWIREINTURNPUSHESBACKWITHTHEUNKNOWNFORCEAONTHEBLADEFORCEBISCARRIEDBYTHEHINGEPIN,WHICHCONNECTSTHETWOJAW/HANDLEPIECESTHE70NGRIPPINGFORCEISGIVENANDSHOWNONTHEFBDACTINGATTHEENDOFTHEHANDLEWITHTHEFREEBODYDIAGRAMCOMPLETEDINFIGURE417,THECUTTINGFORCEAISFOUNDBYAPPLYINGTHEEQUILIBRIUMEQUATIONSFORARIGIDBODYTHEFORCEBALANCEREQUIREMENTINTHEVERTICALDIRECTIONBECOMES0N7BATHEREARETWOUNKNOWNS,AANDB,ANDSOANADDITIONALEQUATIONISNEEDEDBYSUMMINGMOMENTSABOUTPOINTB,WEHAVE0M290N7ATHENEGATIVESIGNISPRESENTBECAUSETHE70NFORCEPRODUCESACOUNTERCLOCKWISEMOMENTABOUTBTHECUTTINGFORCEISFOUNDTOBEA315N,ANDAFTERBACKSUBSTITUTION,B385NBECAUSETHESEAREEACHPOSITIVE,THEDIRECTIONSASSUMEDANDSHOWNONTHEFBDARECORRECTTHESEWIRECUTTERSOPERATEACCORDINGTOTHEPRINCIPLEOFALEVEREACHJAW/HANDLEASSEMBLYROTATESSLIGHTLYABOUTPOINTBTHECUTTINGFORCEATAISPROPORTIONALTOTHEFORCEONTHEHANDLES,ANDITISALSORELATEDTOTHERATIOOFDISTANCESABANDBCTHEMECHANICALADVANTAGEFORAMACHINEISDEFINEDASTHERATIOOFTHEOUTPUTANDINPUTFORCES,ORINTHISCASE,315N/70N45THUS,THEWIRECUTTERSAMPLIFYTHEMACHINISTSGRIPPINGFORCEBYSOME450EXAMPLE47THEFORKLIFTSHOWNINFIGURE418AWEIGHS35001B,ANDCARRIESAN800LBSHIPPINGCONTAINERTHEREARETWOFRONTWHEELSANDTWOREARWHEELSONTHEFORKLIFTADRAWAFREEBODYDIAGRAMOFTHEFORKLIFTBDETERMINETHECONTACTFORCESBETWEENTHEWHEELSANDGROUNDCHOWCANYOUDETERMINETHEFRONTWHEELFORCEWITHOUTHAVINGTOFINDTHEFORCEATTHEREARWHEELSDHOWHEAVYALOADCANBECARRIEDBEFORETHEFORKLIFTWILLSTARTTOTIPABOUTITSFONTWHEELSSOLUTIONATHEFREEBODYDIAGRAMOFTHEFORKLIFTISDRAWNINFIGURE418B,ANDTHEPOSITIVESIGNCONVENTIONSFORTHEFORCESANDMOMENTSAREALSOSHOWNWECHOOSETHEUPWARDDIRECTIONASBEINGPOSITIVEFORFORCESANDTHECLOCKWISEDIRECTIONPOSITIVEFORMOMENTSWEFIRSTDRAWANDLABELTHEKNOWN35001BAND8001BWEIGHTSTHATACTTHROUGHTHEMASSCENTERSOFTHEFORKLIFTANDCONTAINERTHEUNKNOWNFORCEBETWEENAFRONTWHEELANDTHEGROUNDISDENOTEDBYF,ANDTHEUNKNOWNFORCEBETWEENAREARWHEELANDTHEGROUNDISRONTHESIDE,VIEWDRAWINGOFTHEFBD,THENETEFFECTSOFTHOSEFORCESONTHEWHEELHAIRSBECOME2FAND2RBTHEREARETWOUNKNOWNSFANDR,ANDTHEREFORETWOINDEPENDENTEQUILIBRIUMEQUATIONSARENEEDEDTOSOLVETHEPROBLEMWEFIRSTSUMFORCESINTHEVERTICALDIRECTION02LB350L8RFBUTASECONDEQUATIONISREQUIREDTOSOLVETHEPROBLEMSUMMINGFORCESINTHEHORIZONTALDIRECTIONWILLNOTPROVIDEANYUSEFULINFORMATION,SOWEUSEAMOMENTBALANCEANYLOCATIONCANBECHOSENASTHEMOMENTPIVOTPOINTWERECOGNIZETHATBYCHOOSINGTHEMOMENTPOINTTOCOINCIDEWITHTHEFRONTWHEEL,FORCEFWILLBEELIMINATEDFROMTHECALCULATIONTHUS,TAKINGMOMENTSABOUTPOINTA,WEHAVE0IN72LB4I350LB24IN80RFROMWHICHWEFINDR888LBHERE,THE800LBFORCEANDTHEREARWHEELFORCESEXERTCOUNTERCLOCKWISEORNEGATIVEMOMENTSABOUTA,ANDTHEFORKLIFTS3500LBWEIGHTGENERATESAPOSITIVEMOMENTABOUTASUBSTITUTINGTHESOLUTIONFORRINTOTHEFORCEBALANCERETURNSF1262LBCTOFINDTHEFORCEUNDERTHEFRONTWHEELSWITHOUTHAVINGTOFINDR,WECANSUMMOMENTSABOUTTHEREARWHEELATPOINTBTHEUNKNOWNFORCERPASSESTHROUGHTHATPOINTANDTHEMOMENTBALANCENOWREADS0IN72LB30I5LB96IN80FWEOBTAINF1262LBDIRECTLYTHROUGHONLYONEEQUATIONDWHENTHEFORKLIFTISONTHEVERGEOFTIPPINGABOUTTHEFRONTWHEELS,THEREARWHEELHASJUSTLOSTCONTACTWITHTHEGROUNDANDSOR0WEDENOTEASWTHENEWUNKNOWNWEIGHTOFTHESHIPPINGCONTAINERTHATCAUSESTIPPINGTHEMOMENTBALANCEABOUTTHEFRONTWHEELSISNOW0LB42IN35024INWTHEFORKLIFTWILLBEONTHEVERGEOFTIPPINGWHENTHEOPERATORATTEMPTSTOLIFTAW6125LBCONTAINER45BUOYANCY,DRAG,ANDLIFTFORCESINFLUIDSUPTOTHISPOINT,WEHAVECONSIDEREDMECHANICALSYSTEMSWHERETHEFORCESAREASSOCIA
- 温馨提示:
1: 本站所有资源如无特殊说明，都需要本地电脑安装OFFICE2007和PDF阅读器。图纸软件为CAD,CAXA,PROE,UG,SolidWorks等.压缩文件请下载最新的WinRAR软件解压。
2: 本站的文档不包含任何第三方提供的附件图纸等，如果需要附件，请联系上传者。文件的所有权益归上传用户所有。
3.本站RAR压缩包中若带图纸，网页内容里面会有图纸预览，若没有图纸预览就没有图纸。
4. 未经权益所有人同意不得将文件中的内容挪作商业或盈利用途。
5. 人人文库网仅提供信息存储空间，仅对用户上传内容的表现方式做保护处理，对用户上传分享的文档内容本身不做任何修改或编辑，并不能对任何下载内容负责。
6. 下载文件中如有侵权或不适当内容，请与我们联系，我们立即纠正。
7. 本站不保证下载资源的准确性、安全性和完整性, 同时也不承担用户因使用这些下载资源对自己和他人造成任何形式的伤害或损失。
人人文库网所有资源均是用户自行上传分享，仅供网友学习交流，未经上传用户书面授权，请勿作他用。
川公网安备: 51019002004831号