1M.SukD.GillisEffectofmechanicaldesignofthesuspensionondynamicloadingprocessReceived:2July2003/Accepted:24February2004/Publishedonline:3August2005_Springer-Verlag2005Abstract:Indesigningaload/unloadsystemutilizedinharddiskdrives,necessarycareneedstobetakentoensurethatthesliderdoesnotdamagethedisksurfaceduringloadingandunloadingprocesses.However,asmalldeviationinthedesignpointofthepreloadbetweentheload-domeandflexurecanleadtoundesirableloadingprocessesresultinginanadversenumberofslider/diskcontacts.Inthisstudy,weshowthatifthepreloadbetweentheload-domeandflexureistoolow,theslidercanoscillatecausingthecornersoftheslidertocontactthediskmultipletimeseventhoughthesliderisafewmicronsawayfromthedisk.Inaddition,theslidercanbesuckeddowntowardsthediskresultinginacompleteseparationoftheload-domefromtheflexureassemblyleadingtouncontrolledloadingconditions.Thisseparationoccurswhilethesuspensionisstillontheramp,andthusnopreloadisexertedonthesliderimmediatelyfollowingtheseparation.Consequently,thesliderfliesataflyingheighthigherthanthedesignpointuntilthegapbetweentheload-domeandflexurecloses.Hence,thesuspensionmustbecarefullydesignedtosuppressslideroscillationandtoensurethattheloaddomedoesnotseparateduringtheloadingprocess.1IntroductionOneoftherequirementsindesigningaload/unloadsystemutilizedinharddiskdrivesisensuringthatthesliderdoesnotdamagethedisksurfaceduringloadingandunloadingprocesses.Sinceitisdifficulttoavoidslider/diskcontactsinentirety,however,thesystemisdesignedtominimizethenumberofslider/diskcontacteventsandtolessentheconsequenceswhencontactsdooccur.Thelikelihoodofslider/diskcontactsdependsontheloadingspeed,diskspeed,staticattitudeoftheslider,air-bearingroughness,slidergeometry,etc.Forexample,sliderswithalargeradiusofcurvatureatitscornerscaneliminatediskdamagebyreducingthecontactstressbetweentheslideranddisksurface(SukandGillis1998).Manyrecentstudieshaveconsideredtheeffectofsuspension,limiter,andair-bearingdesignsontherobustnessoftheloadingandunloadingprocesses(B2ogyandZeng2000；Huaetal.2001；LiuandZhu2001；ZengandBogy2000).However,mostofthesestudieshaveprimarilyfocusedontheunloadingprocesssincethispartofthesequenceusuallyrevealsinterestingdynamicprocessesduetotheeffectsofnegativepressureairbearingdesigns.Thenegativepressureregionoftheairbearingresiststheunloadingactionresultinginstorageofpotentialenergyintheflexureandsuspensionassembly.Whenthesliderisfinallypulledawayfromthediskandthepotentialenergyisreleased,theslidercanoscillateviolently(Fig.1).Ontheotherhand,forareasonablywell-designedsystem,theloadingprocessdoesnotexhibitsuchabehavior.Hence,mosthaveprimarilyinvestigatedtheunloadingprocessgivingonlacursoryattentiontothemorecriticalloadingprocess.Mostdesignersofload/unloadsystemswillfindthattheloadingprocesscanbemoretroublesomecomparedtotheunloadingprocess.Besidespotentiallycausingdamagetothedisk,otherproblemscanbeencounteredduringtheloadingprocess.Forexample,insomeinstances,theslidermayneverloadtothedesignedflyingheight,butrather,loadatflyingheightsontheorderof1lm(Suketal.2004).Inthispaper,weshowhowasmalldeviationinthemechanicaldesignoftheflexure/suspensionassemblycanincreasetheprobabilityofslider/diskcontactsthatcanleadtoasignificantnumberofdiskcontactsinonesingleloadcycle.Specifically,weshowthatasuspensionsystemwithlowpreloadbetweentheflexureandloaddomecanleadtoloadingoftheslideratanuncontrolledstaticattitudeandvelocity.Theproblemsassociatedwiththisparticularaspectofdesigncanbeeasilyidentifiedbymeasuringthefull-bodycapacitanceduringtheloadingprocess.2DescriptionofexperimentThesliderloadingdynamicswasinvestigatedusingalaser-Dopplervibrometer(LDV),62kHzframeratehigh-speedcamera,andfull-bodycapacitance.Theexperimentalsetupconsistsofastandardload/unloadtester.Thecapacitancemetermeasuresthefull-bodycapacitancebetweentheslideranddiskwhilethesliderisloadingontothedisk,similartotheoneusedin(Suketal.2004).Thesliderwasloadedontoan3dunloadedfromthediskusingamovingrampwhilekeepingtheslider/suspensionassemblyfixedovertheODregionofthedisk.TheverticalmotionofthetrailingedgeofthesliderwasmeasuredusinganLDV.Alltestswerecarriedoutusingan84mmglassdiskandanegativepressurebobsledtypesliderwiththediskrotatingat10krpm.Thepitch-staticattitude(PSA)oftheslidersusedintheexperimentwasbetween1and2_.Toshowtheeffectoflackofpreloadbetweentheflexureandload-dome,wechosetwosuspensionassembliesthatareessentiallyidenticalwiththeexceptionofthepreload.Sincethedifferenceinthemagnitudeofthepreloadisdifficulttomeasure,onlytheexistenceofsubstantialdifferenceisverified.Todothis,wemounttheheadsuspensionassemblywithnormalpreload(NPHSA)ontotheramp.Asmallweight,thatissufficienttocauseload-domeseparationfromtheflexure,isthenattachedtotheflexure.TheamountofseparationismeasuredwithaproperlypositionedCCDcamera.Similarmeasurementismadeforaheadsuspensionassemblywithlowpreload(LP-HSA).Figures2and3showopticalimagesoftheload-domeandflexuretakenunderthesameconditionsforbothNP-HSAandLPHSA,respectively.Agreaterload-domeseparationfromtheflexureisobservedforLP-HSAthantheNP-HSA,confirmingthatLP-HSAhaslowerpreloadthanNPHSA.3ResultsanddiscussionnegativepressureslidersT4hesliderloadsontothediskandthenfollowstherunoutofthediskasexpected.ThebottomplotinFig.3isthecorrespondingfull-bodycapacitancemeasurement,whichshowsasinglejumpinthecapacitanceatthemomentthesliderloadsontothedisk.AsimilarmeasurementforLP-HSAisshowninFig.5.Inthiscase,theslideroscillatesbeforeloadingontothediskunlikethecasewithahigherpreloadbetweentheload-domeandflexure.Furthermore,theslidersverticalloadingvelocitysuddenlyincreaseswhenthesliderisabout50lmawayfromthedisk.Associatedwiththissuddenincreaseinthevelocity,thecapacitancemeasurementrevealsmultiplesharptransitions.Followingthetransitions,thecapacitancedoesnotreachthemaximumvalueforanother1msorso.Theseobservationsindicateaproblem,butitisdifficulttoascertaintheprecisedynamicsduetothelowmeasurementbandwidth.Higherresolutionmeasurementrevealsthattheslidercontactsthediskmultipletimes(Fig.6)notethatthisexactbehaviordoesnotoccurforeverysuspensionassembly,butvariesfromonesuspensiontoanother.Figure6showssimultaneousmeasurementoffull-bodycapacitanceandLDVduringloadingforLP-HASimmediatelybeforefullyloadingontothedisksurface.Capacitancemeasurementshowssomeoscillationabout2msbeforeastep-likejumpisobserved.Notethattheaverageheightofthesliderduringtheseoscillationsisontheorderofafewmicrons.Atthisheight,thesuspensionpreload(notthepreloadbetweentheflexureandload-dome)isstillsupportedbytheramp.TheLDVmeasurementshowsthattheslideractuallycontactsthediskandbounceson-and-offthediskoscillatingatthesamefrequencyasthatofthemeasurementmadewiththecapacitancemet