附錄附錄一英文材料MICROPLANETARYREDUCTIONGEARUSINGSURFACE-MICROMACHININGAbstractAmicroplanetarygearmechanismfeaturingahighgearreductionratiowithcompactnessinsizeispresentedinthispaper.SUMMiTVisemployedforthefabricationmethodsothattheredundancyofassemblingpartsiseliminated.Thedesignrulesofwhichhasalsobeenchecked.Tomakefulluseofthebenefitsofthesurface-micro-machining,theplanetaryreductiongearisdesignedtowardusingtheon-chipmicro-engine.Theexpectedgearreductionratioiscalculatedandcomparedwiththeconventionalchaingearmechanism.Themicroplanetarygearmechanismpresentedinthispaperisexpectedtohave162:1reductionratioutilizinglessspaceconsumption.Thisisanorderofmagnitudehigherthanthepreviouslyreporteddesigninasinglereductiongeartrain.Keywords:MEMS,planetarygear,reductiongearsurface-micromachining,SUMMiTVprocessNomenclatureasungearbplanetgearscinternalgear(fixed)dinternalgear(rotary)nthenumberofunitsofgeartrainDdiameterofthepitchcircleNnumberofteethPnumberofplanetsIntroductionThegearmechanismsinmicroelectromechanicalsystems(MEMS)arecommonlyexpectedtogeneratehightorqueintheconfinedmicro-sizesystems.However,itisgenerallydifficultforthemicro-scalesystemstohavesuchahightorquewithouthavingmultiplereductionsystems.Thedesignofthereductiongeardrivebasedonaplanetaryparadoxgearmechanismcanincreasethetorquewithinacompactarea,sincethemicroplanetarygearsystemhasanadvantageofhighreductionratioperunitvolume1.Howeveritsmechanismissocomplicatedthatrelativelyfewattemptshavebeenmadetominiaturizethegearsystems2-3.Suzumorietal.2usedthemechanicalparadoxplanetarygearmechanismtodrivearobotfor1-inpipesforwardorbackward.Theyemployedasinglemotortodrivethegearmechanismswithhighreductionratio.Precisegearfabricationwasenabledbymicrowireelectricaldischargemachining(micro-EDM).Theseparts,however,shouldbeassembledbeforethedrivemotorisattachedtothegearbox.Takeuchiet.al.3alsousedmicro-EDMtofabricatethemicroplanetarygears.TheysuggestedspecialcermetsorHighCarbonSteelforpossiblematerials.Whilethedesigncanachieveareductionratioof200,thegearsshouldalsobeassembledandmotordriven.Toenablethedrivingoftheplanetarygearbyonchipmeans,SandiaUltra-planarMulti-levelMEMSTechnology(SUMMiT-V)process4forplanetarygearfabricationisadoptedinthisstudy.TheSUMMiT-Vprocessistheonlyfoundryprocessavailablewhichutilizesfourlayersofreleasablepolysilicon,foratotaloffivelayers(includingagroundplane)5.Duetothisfact,itisfrequentlyusedincomplicatedgearmechanismsbeingdrivenbyon-chipelectrostaticactuators5.However,inmanycases,themicroenginesmaynotproduceenoughtorquetodrivethedesiredmechanicalload,sincetheirelectrostaticcombdrivestypicallyonlygenerateafewtensofmicronewtonsofforce.Fortunately,theseenginescaneasilybedrivenattensofthousandsofrevolutionsperminutes.Thismakesitveryfeasibletotradespeedfortorque7.Rodgersetal.7proposedtwoduallevelgearswithanoverallgearreductionratioof12:1.Thussixofthesemodulartransmissionassembliescanhavea2,985,984:1reductionratioatthecostofthehugespace.Withthedesireforsizecompactnessandatthesametime,highreductionratios,theplanetarygearsystemispresentedinthispaper.Itwillbethefirstplanetarygearmechanismusingsurfacemicromachining,totheauthorsknowledge.Theprinciplesofoperationsoftheplanetarygearmechanism,fabrication,andtheexpectedperformanceoftheplanetarygearsystemsaredescribedinthispaper.PrinciplesofoperationAnalternativewayofusinggearstotransmittorqueistomakeoneormoregears,i.e.,planetarygears,rotateoutsideofonegear,i.e.sungear.Mostplanetaryreductiongears,atconventionalsize,areusedaswell-knowncompactmechanicalpowertransmissionsystems1.TheschematicoftheplanetarygearsystememployedisshowninFigureSinceSUMMiTVdesignsarelaidoutusingAutoCAD2000,theFigure1isgeneratedautomaticallyfromthelayoutmasks(Appendix1).Oneunitoftheplanetarygearsystemiscomposedofsixgears:onesungear,a,threeplanetarygears,b,onefixedringgear,c,onerotatingringgear,d,andoneoutputgear.Thenumberofteethforeachgearisdifferentfromoneanotherexceptamongtheplanetarygears.Aninputgearisthesungear,a,drivenbythearmconnectedtothemicro-engine.Therotatingringgear,d,isservedasanoutputgear.Forexample,ifthearmdrivesthesungearintheclockwisedirection,theplanetarygears,b,willrotatecounter-clockwiseattheirownaxisandatthesametime,thosewillrotateaboutthesungearinclockwisedirectionresultinginplanetarymotion.Duetotherelativemotionbetweentheplanetarygears,b,andthefixedringgear,c,therotatingringgear,d,willrotatecounterclockwisedirection.Thisissocalleda3Kmechanicalparadoxplanetarygear1.FabricationprocedureandteststructuresThefeaturesoftheSUMMiTVprocessofferfourlevelsofstructuralpolysiliconlayersandanelectricalpolylevel,andalsoemploytraditionalintegratedcircuitprocessingtechniques4.TheSUMMiTVtechnologyisespeciallysuitableforthegearmechanism.Theplanetarygearmechanismcanbedrivenbytheon-chipengineandthusisanotherreasonofusingtheSUMMiTVprocess.SincetheSandiaprocessissuchawell-knownprocedure5-7,onlybriefexplanationispresented.Figure2representsthecross-sectionalviewofFigure1,andalsowasgeneratedfromtheAutoCADlayoutmasks(Appendix1).Thediscontinuityinthecross-sectionisfortheetchholes.Thepoly1(gray)isusedforthehubsandalsopatternedtomakethefixedringgear,i.e.,c,thesungear,i.e.,a,therotatingringgear,i.e.,c,andtheoutputgearispatternedinthepoly2.Sincetheplanetarygearneedstocontactboththefixedringandrotatingringgear,poly2isaddedtopoly3,wherethegearteethareactuallyformed.Thepoly4layerisusedforthearmthatdrivesthesungear.Afterthereleaseetch,theplanetarygearswillfalldownsothatthosewillengageboththeringgears.ThefiguresfortheteststructuresarepresentedinAppendix2.Sincetheaimofthispaperistosuggestagearreductionmechanism,theplanetarygearsystemisdecomposedtoseveralgearunitstoverifyitsperformance.Thefirstteststructureisaboutthearm,whichrotatesthesungear,connectedtotheon-chipengine.Theangularvelocityofthearmdependsontheengineoutputspeed.Thesecondteststructuredescribesthepointatwhichthesungearandplanetarygearsareengagedtothefixedringgear.Becauseofthefactthattheringgearisfixed,theplanetarygearisjusttransmittingthetorquefromthesungeartothefixedringgearwithoutplanetmotion,e.g.,rotatingitsownaxisnotaroundthesungear.Whentherotatingringgearismountedontopofthefixedringgear,i.e.,thethirdteststructure,theplanetarygearsbegintorotatearoundthesungearsothattheplanetmotionareenabled.Therefore,onceoneoutputgearisattachedtotherotatingringgear,i.e.,thefinalteststructure,thewholereductionunitiscompleted.Dismantlingtheplanetarygearintothreeteststructuresallowsthepinpointingofpossibleerrorsinthegearsystem.SolutionsprocedureandexpectedperformanceThereductionratioisdefinedastheratiobetweentheangularvelocityofthedrivergearandthatofthedrivengear.Highreductionratiosindicatetradingspeedfortorque.Forexample,a10:1gearreductionunitcouldincreasetorqueanorderofmagnitude.Sincethegearsintheplanetarysystemshouldbemeshedtooneanother,thedesignofgearmoduleshouldfollowarestriction.Forexample,thenumberofteethfo