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1、Design,FabricationandControlofMicro-ActuatorsforDual-StageServoSystemsinMagneticDiskFilesRobertoHorowitz,Tsung-LinChen,KennOldham,andYunfengLiComputerMechanicsLaboratory(CML)DepartmentofMechanicalEngineeringUniversityofCaliforniaatBerkeley,CA94720-17401IntroductionS
2、incetherstharddiskdrive(HDD)wasinventedinthe1950sbyIBM,diskdrives'storagedensityhasbeenfollowingMoore'slaw,doublingroughlyevery18months.Thecurrentstoragedensityis10milliontimeslargerthanthatoftherstHDD(Yamaguchi,2001).Historically,increasesinstoragedensityhavebeen
3、achievedbyalmostequalincreasesintrackdensity,thenumberoftracksencirclingthedisk,andbitdensity,thenumberofbitsineachtrack.However,becauseofsuperparamagnetismlimitations,itispredictedthatfuturearealstoragedensityincreasesinHDDswillbeachievedmainlythroughanincreaseintr
4、ackdensity(Howelletal.,1999).ResearchoftheHDDindustryisnowtargetinganarealdensityofoneterabitpersquareinch.Forapredictedbitaspectratioof4:1,thistranslatestoalinearbitdensityof2Mbitsperinch(BPI),andaradialtrackdensityof500Ktracksperinch(TPI),whichinturnimpliesatrackw
5、idthof50nm.AsimpleruleofthumbforservodesigninHDDsisthatthreetimesthestatisticalstandarddeviationofthepositionerrorbetweentheheadandthecenterofthedatatrackshouldbelessthan1/10ofthetrackwidth.Thus,nanometer-levelprecisionoftheservosystemwillberequiredtoachievesuchasto
6、ragedensity.Adiskdrivestoresdataasmagneticpatterns,formingbits,ononeormoredisks.Thepolarityofeachbitisdetected(read)orset(written)byanelectromagneticdeviceknownastheread/writehead.Thejobofadiskdrive'sservosystemistopositiontheread/writeheadoverthebitstobereadorwritt
7、enastheyspinbyonthedisk.Inaconventionaldiskdrive,thisisdonebysweepingoverthediskalongarmconsistingofavoicecoilmotor(VCM),anE-block,suspensions,andsliders,asshowninFigs.1and2.Aread/writeheadisfabricatedontheedgeofeachslider(oneforeachdisksurface).Eachsliderissupporte
8、dbyasuspensionandysoverthesurfaceofdiskonanair-bearing.TheVCMactuatesthesuspensionsandslidersaboutapivotinthecenteroftheE-block.Thisopera
