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Integrated Passive and Active Vibration Control of Ultra precision Lathe

Review by : TsingHua
浏览次数: 322
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出版日期: 十二月 30, 2000
0 IntroductionInultraprecisioncuttingprocess ,vibrationisoneofthekeyfactorsaffectingthem achiningquality,therefor,manyscholarsareman agingtodecreaseoreliminatetheinfluenceofvib ration.Besidesenhancingmachiningaccuracyofe verycomponentandreducingeffectsofenvironmen tsuchastemperaturechange,adoptingpassivevib rationcontroloractivevibrationcontrolcandec reasemachinevibrationgreatly.Thepassivevibr ationcontrolhasbeenappliedwidelyduetoitscha racteristicsofsimplestructureandhighreliabi lity,butithasmoredisadvantagessuchasparamet ersunchangingafterthevibrationsystembeingde terminedanddifficultisolationtolowandultral owfrequencyvibration.Itisfortunatethattheac tivevibrationcontrolcanmakereparationforthe sedeficienciesjustrightbecauseofitshighmobi lityandgoodadaptabilitytoenvironment.In1993 ,NeubertbroughtforwardtheconceptIntegratedP assiveandActiveVibrationControlbycombininga ctivevibrationcontrolandpassivevibrationcon trol.InHCMIUltraprecisionLathedevelopedinPr ecisionEngineeringResearchInstituteofHarbin InstituteofTechnology,activevibrationcontro ltechniqueisadoptedonthebasisofpassivevibra tioncontrol,formingintegratedpassiveandacti vevibrationcontrol,thusthevibrationofmachin ewasdecreasedapparently.1 VibrationControlo fCompleteMachineTominimizetheinfluenceofvib rationtransferringfromearth,separateconcret efoundationisadoptedinHCMIUltraprecisionLat he,asshowninFig.1.Concretefoundationisplace dinisolationtrenchinwhichdampingmaterialssu chashandstonesandsandareadded.Asaresult,ama jorityofvibration(about70%)iseliminated.The fourairspringsupportingmachinecanfurtheriso latethevibrationoffoundation.Nowconsiderthe isolationsystemofmachinefromfoundation.Them echanicalmodelofintegratedpassiveandactivev ibrationcontrolisshowninFig.2.InFig.2,x0(t) isdisplacementoffoundation;mismassofmachine ;kisstiffnesscoefficientofairspring;cisdamp ingcoefficientofairspring;fc(t)isactivecont rolforce.Ifonlypassivevibrationcontrolisado pted,themotionofmassmism¨x+c(x-x0)+k(x-x0)= 0(1)andthetransferfunction,relatingdisplace mentofmassmtothatoffoundationisHp(s)=X(s)X0 (s)=cs+kms2+cs+k(2)Becauseusinglargemasslat hebedandlowstiffnessairspring,thesystemnatu refrequencycanbelowtoseveralhertz.Fig.1 HCM IUltraprecisionLatheantivibrationschematicd iagram1.dampingmaterials;2.earth;3.concrete foundation;4.airspring;5.machineFig.2 Physi calsytemoffeedbackcontrolIfactivevibrationc ontrolisadoptedsimultaneouslyonthebasisofpa ssivevibrationcontrol,formingintegratedpass iveandactivevibrationcontrol,themotionofmas smism¨x+c(x-x0)+k(x-x0)=fc(3)Usingdisplacem ent,velocityandaccelerationofmassmasfeedbac kvariables,theactivecontrolforceisfc=(ka¨x+ kv(x+kdx)(4)Sothemotionofmassanddisplacemen ttransferfunctionaregivenrespectivelyby(m+k a)¨x+(c+kv)(x+(k+kd)-(cx0+kx0)=0(5)Hl(s)=X( s)X0(s)=cs+k(m+ka)2+(c+kv)s+k+ks(6)Thefrequ encyresponseofsystemforζ=0.05adoptingdispla cementfeedback,velocityfeedbackandaccelerat ionfeedbackareplottedinFig.3respectively.It canbeseenfromthefigurethatincreasingthedisp lacementfeedbackincreasesthesystemnaturalfr equency,asiteffectivelyincresasesthestiffne ssofthesystem,resultinginanincreaseoflowfre quencyisolationbutadecreaseofhighfrequencyi solation;increasingthevelocityfeedbackeffec tivelyincreasesthesystemdamping,thus,increa singtheisolationeffectintheregionofthesyste mresonancewithlittleeffectatlowandathighfre quencies;increasingtheaccelerationfeedbacki sequivalenttoaddingmasstothesystem,resultin ginamovementoftheresonancefrequencytolowerf requency,thusincreasinghighfrequencyisolati onbutdecreasinglowfrequencyisolation.Fig.3  Frequencyresponseofsystemforζ=0.05(a)Displa cementfeedback;(b)Velocityfeedback;(c)Accel erationfeedbackItisalsocanbeseenfrom(5)and( 6)thatthemass,stiffnessanddampingofthesyste marechanged.Ifthefeedbackgainskd,kvandkaare chosenrationally,excellentisolationeffectca nbeobtained.2 VibrationControlofSlideHCMIUl traprecisionLatheissupportedbyaerostaticfil mthatcannotonlyeliminatethecreepingofslideandenhancestraightlinemotionaccuracybutalsoreducethevibrationlevelofslide.Implementingintegratedpassiveandactivevibrationcontrolby
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