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外文翻译--在内部复杂机械荷载下的负荷传感系统动态特性 英文版【优秀】.pdf

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外文翻译--在内部复杂机械荷载下的负荷传感系统动态特性 英文版【优秀】.pdf

BirgittaLanttoPetterKrusJanOvePalmbergDivisionofFluidPowerTechnology,DepartmentofMechanicalEngineering,LinkdpingUniversity,S58183Linkoping,SwedenDynamicPropertiesofLoadSensingSystemsWithInteractingComplexMechanicalLoadsAloadsensingfluidpowersystemisafeedbacksystemwithseveraltypesofinstabilitymodes.Thispaperdealswithoneofthem,whereloadinteractionthroughamechanicalstructureandthefluidpowersystemmaycauseinstability,e.g.inalorrycrane.Criteriaforinstabilityareevaluated.Thispaperalsoproposessomemethodshowtoavoidthistypeofinstability.IntroductionThehighenergysavingpotentialofloadsensingsystemsisaspecialadvantage,especiallywhentheconfigurationincludesavariablepump.ControllabilityofsuchsystemsmaybeenhancedbypressurecompensatedcontrolvalvessinceinteractionbetweentheactivatedloadscanbeavoidedseeFig.1.However,thistypeofsystemisafeedbacksystemand,unfortunately,alsoextremelyundamped.Therefore,itisnotunlikelythatinstabilitytakesplaceinsuchsystems.Generally,themostriskyfeedbackisthepumppressureandhighestloadpressurefeedbackscontrollingthepumpregulatorwhichcouldleadtothesocalledpumpandpumploadinstabilities,seeKrus1989.Thereisalsoariskofinstabilityattheloadifafeedbackcomponentsuchasanovercentrevalvecontrolstheactuator.AthirdtypeofinstabilityisdiscussedinLantto1992.Whenseveralactuatorscontrolthesamemechanicalstructure,e.g.acranearm,theyinteractthroughthestructureandthefluidpowersystem.Then,afeedbackcouldbecreatedasinFig.2whereamovementoftheactuatorwiththelowestloadchangesthehighestloadpressureandthereforetheloadsensingpumppressurewhichchangestheflowtothelowestload.Suchdestabilizinginteractionhasearlierbeenanalyzedbye.g.Ramachandran1982andPannala1985.Thispapergivesadeeperdiscussionaboutthisthirdtypeofinstabilityrisk,mainlyfoundinloadsensingsystems.ThestabilityanalysisinthispaperisbasedonKrus1988,Krus1989,Palmbergetal.1985,andLantto1992andconcernsmainlysystemswithnoncompensatedcontrolvalves.Onlysystemswithanunsaturatedloadsensingpumparediscussedhere.Moreover,onlypositivemassandinertialoadsareconsidered.InstabilityBecauseofLoadInteractionThroughtheMechanicalStructureInthissection,wewillshowhowinstabilitycanbeevaluatedforastructurecontrolledbyanidealloadsensingsystem.ThisContributedbytheDynamicSystemsandControlDivisionforpublicationintheJOURNALOFDYNAMICSYSTEMS,MEASUREMENT,ANDCONTROL.ManuscriptreceivedbytheDynamicSystemsandControlDivisionMarch25,1991revisedmanuscriptreceivedJuly1992.AssociateTechnicalEditorA.Akers.sectionwillalsodiscusswhenanormallorrycranereachesinstability.Sincethistypeofinstabilityisdependentonboththefluidpowersystemandthegeometryofthemechanicalstructure,thedesignofthestructureandthefluidpowersystemwillbediscussed.Theanalysiswillshowthatthisinstabilitygenerallymayoccurif1apositiveornegativemovementofthelowestloadwillcauseanegativeapositive,respectivelymovementofthehighestloadthroughthemechanicalstructureand2ifafeedbackcomponentcontrolsthesystemsothatanincreaseofthehighestloadpressurewillcauseanincreaseoftheloadflowtothelowestloadthroughthefluidpowersystem.InstabilityinaLoadSensingSystem.ThesimplestructureinFig.3,controlledbytwocylindersinaloadsensingsystemwithnoncompensatedcontrolvalves,hasthefollowingequaFig.1Loadsensingsystemincludingcontrolvalveswithconventionalpressurecompensatorspools////.vHighestloadLoadflowfrLowestload\4Loadsensingpressure4Fig.2FeedbackthroughthemechanicalstructureJournalofDynamicSystems,Measurement,andControlSEPTEMBER1993,Vol.115/525Copyright©1993byASMEDownloaded22Mar2009to202.198.46.187.RedistributionsubjecttoASMElicenseorcopyrightseehttp//www.asme.org/terms/Terms_Use.cfmFig.3Loadsensingsystemwithloadinteractionthroughasimplifiedmechanicalstructuretionsofmotion,describingthesmallmovementsofthetwopistonsinthefrequencydomains2/AXLj\AXL2,00B2\AXi2,ALl£JLlAolUPolAL2APL2A02AP01TheyformthetransferfunctionsGmAandG„h2ofthemechanicalloadinAppendixwhereMmlm2,Bibi,M2m2andB2b2,whileMfi1MKi2m2formsthetransferfunctionsofthemechanicalcouplingasG«,GK2AL1AL2m2sALxALlm2s23TheseequationsandtheAppendixformtheblockdiagraminFig.4whichdescribesageneralloadsensingsystemwithloadinteractionthroughthemechanicalstructureblocksGKilandGKi2andthefluidpowersystem.rfFKEFig.4BlockdiagramofaloadsensingsystemwithloadinteractionThenextstepistoanalyzethisfeedbacksystembyreducingtheblockdiagramintoclosedlooptransferfunctionswheretheoutputsignalsAXLiandAXL,2arefunctionsofAXViiandAA,seeLantto1992.Then,thecharacteristicequationisfoundas1H,iiG,ni1GGmlHmGnFLSCGmxGvHL2GmirtC/j.2j/pumpGm2G„\FLSGn1HL\GKj1HL2GK1G„G„.HmHmGPlFLsGpGmiG„GmiHmH,,lHspGnG„2Gp045AB,bCdPDLFsGsHsJkKcarea,m2viscousdampingcoefficientofactuator,Ns/mvolumecapacitanceV7/3e,m3/Pavolumetricgradientofpumpdisplacement,mVrevmotorloaddisplacement,mVrevfiltertransferfunctiontransferfunctionwhereoutputisnormallyflowwhileinputispressure.Theflowisoutputandvalvedisplacementinputwhenthesubscriptisx.transferfunctionwhereoutputispressurewhileinputisflow.inertia,kgmspringcoefficient,N/mflowpressurecoeff.oforificedq/dpmPOM,m3/sPaKqL,lM,mnPqsVXHe6APe01flowgainofvalveorifice3/dxvalve,m2/slength,mmass,kgpumpspeed,rev/spressure,Paflow,m3/sLaplacetransformoperator,rad/svolume,m3displacement,meffectivebulkmodulus,Padampingratiosmallvariationinalinearizedvariable.density,kg/m3angle,radfrequency,subscriptindicatesabreakfrequency,rad/s.CapitalletterofavariablemayindicateaLaplacetransformedvariable.SubscriptLLSm0PregTVK12Jmeterinsideofcylinderloadsensinglinemechanicalloadmeteroutsideofcylinderpumppumpregulatorpumpsupplyvolumetankcontrolvalveorvalvepackageloadwhichcouplestheactuatorsthroughthestructurethehighestloadthesecondhighestloadshortnoteinsubscript,e.g.,L,Imeansu526/Vol.115,SEPTEMBER1993TransactionsoftheASMEDownloaded22Mar2009to202.198.46.187.RedistributionsubjecttoASMElicenseorcopyrightseehttp//www.asme.org/terms/Terms_Use.cfmAfirstglanceatthisequationusingthefollowingsimplifications9Aninfinitelyfastpumppressurecontrolwithoutleakagemodelledasaninductance,Gpl/LpSoowhichleadstopumP1/Gp,andconsequentlyAPsAPLii.9Noorificeintheloadsensingline,FLS1.8Constantpressureonthemeteroutsideofthepistons,AP0il0otAoA0leadingtoG„,A«Gm1respectivelyAP0i20orAOi20leadingtoG™,2Gm,2.8OnlymassloadswithoutspringforcesandwiththeonlyviscousfrictionappearinginthecylindersareanalyzedwhichleadtoGKAALAALa/MK2sandGK1ALAALB.Assumethat«\\825il«L,KcBxj«1Then,uAandwfiwillbeachievedfromEqs.6and7as9uAiDL2.Thehighestloadstartsat0s,theotherat5sec.KCnM2MKlALli40LhWA2iA12UBKCn\M,ALlA72M2\21£dl2WB13TheequationshowsonstabilityonlywhenM212L22ALlAL2BiCLjKc2UA20LXB2CL2Kr...2A214Assumingnoviscousfrictioninthecylinder,B20,andnt\0inthesimplifiedcaseinFig.3,whereMKAM2m2,leadsustothefollowingcrudecriterionsincewAwLAandoBooIfinstabilityshalloccurinthesystem,thepistonareaAL,2ofthelowestloadmustbelargerthanthepistonareaALAofthehighestload.ThismeansthatforthemechanicalstructureinFig.3,instabilitywillalwaysoccursincetheactuatorwiththehighestpressurehasthesmallestpistonarea,seeFig.5.Inreality,thismaynotalwayshappensincethesimplificationsprecedingEq.6normallyarenotfulfilledwhichincreasesthedampingandconsequentlythestabilitymarginofthesystem.DesignAspectsofAvoidingInstability.Thisinstabilitytypehasitsoriginineffectivenegativedampingratioofthelowestloadinthetwoloadsituation.Toincreasethedampingratiooftheactuatorisconsequentlystabilizinge.g.withthemeteroutorifice.Asmentionedearlier,thefeedbacknormallypassesbetweentheactuatorsthroughthemechanicalstructure,butalsothroughtheloadsensinglinetothepumpandpumppressurevolume.Thebestwaytoreducetheinstabilityriskshouldthereforebetodesignthemechanicalstructureproperly.Thisrequiresthatalargemassorinertiaofthedynamiccouplingfromthelowestloadtothehighest,MKUmustbeavoided.Howtocalculatethismassandothersisgivenasanexampleinthenextchapterforalorrycranearm.AflexiblestructureJournalofDynamicSystems,Measurement,andControlSEPTEMBER1993,Vol.115/527Downloaded22Mar2009to202.198.46.187.RedistributionsubjecttoASMElicenseorcopyrightseehttp//www.asme.org/terms/Terms_Use.cfmFig.6ModelofalorrycranestructureTotallengthofcylinder1mhighesthadmaxTotallengthofcylinder2mHighriskFig.7Variousvaluesof2bAlvAA\jmKcv2asafunctionofthepistondisplacementsofthelorrycrane.Negativevaluesindicatedestabilizationoftheoscillations,whilepositivevaluesindicatestabilization.isalsostabilizingcomparedwithastiffone.Thefeedbacksignalthroughaloadsensingpumpisalsostoppedbyalowpassfilter,thatisanorifice,intheloadsensinglinesinceithastopassthisline.Italsoseemsasifafastpumppressurecontrolintheloadsensingsystemmayeasetheinteractionbetweentheactuatorsthroughthefluidpowersystemandincreasetheriskofinstability.TopressurecompensatethecontrolvalveofthelowestloadsintheloadsensingsystemreducestheinstabilityrisksinceKC„2isclosetozeroofavalvepackagewithafastandidealpressurecompensatorspoolsuchasinFig.1.AnExampleInstabilityofaLorryCraneArm.Will2hA/wAinEq.13bepositiveforthelorrycranestructureinFig.6AroughcriterionofacranearmisachievedifthefollowingassumptionsaremadeThestructureisstiffThemassofthestructureislumpedintotheloadmassm9TheboomisthehighestloadOnlypositiveloadsarediscussed,9290deg.TheLagrangeequationdescribesthemovementsofthestructure.TisthekineticenergyandMejthetorquefortheangle0,.ddf\dT,jt{wwMe,12mkleue2y2meue215TLlcosdlL2cos62jLisinOZsin1617TimesecTimesecFig.8Measurementsonthelorrycrane.Thecranepositionintheleftdiagramgaveinstability.M0Mr,ALiAPLiA0lAPolBlSAXLlh\AL2APL2A02AP02B2sAXL218Foracranestructure,the0,«0,termsijcanbeneglectedcomparedtotheaccelerationtermsij.Then,thefollowingdynamicequationsofmotionyieldinthefrequencydomainZ.,L2cos0,02/,h0l2iAX,L{L2cosdid2L\A0,A62iA0lAP0lBtsAXLlAL2APLlA02AP02B2sAXL2ALlAPLliiAX,i2,/,0hhA0,A01920Equations18and19canbereducedtothesameformasinEq.1whereM\mLiLl2LlL2coseid2M2mMKXMK2mL1L2cos6162LJ212223Todescribetheinstabilityrisk,onecontourplotof2bA/uAA\i2/mKCyV2havebeenmade,implementedonafullsizelorrycrane,HIAB070fromHIABFoco.Thisplot,inFig.7,hasbeendrawnforacasewhenthereisnoviscousfrictionintheactuators,BXQandB20.KCV2hasaconstantvalue.Thediagramsaredrawnwiththepositionofthecranearmcylinderonthexaxis,whilethepositionoftheboomcylinderisonthe.yaxis.Theleft,lowercornerofthediagramshowsnovalues,sincethecranearmcylinderhasanegativeloadthere.Thediagramsaredrawnfordifferentvaluesof5wherenegativevaluesindicatearangewhereinstabilitymayoccur.ThediscussionaboveexplainsthelaboratoryexperimentofthelorrycraneinFig.8.Asituationwherethecranearmisfoldedupwiththeboomcylinderpointingintotheskyseemstobepronetoinstability.Inthetests,theboomcylinderhadalowspeedwhilethecranearmcylinderhadahigherspeed.ConclusionsThedesignofafluidpowerfeedbacksystemmustaddressnotonlythehydraulicsystembutalsothestructureitiscontrolling.Thispapershowsclearlythatinstabilitycausedbyloadinteractionthroughamechanicalstructureisreality,atleastinloadsensingsystems.Thistypeofinstabilityriskishighlydependentonthegeometryofthemechanicalstructure.Therefore,aproperdesignofthestructurewouldeliminatethisproblem.Suggestionshave528/Vol.115,SEPTEMBER1993TransactionsoftheASMEDownloaded22Mar2009to202.198.46.187.RedistributionsubjecttoASMElicenseorcopyrightseehttp//www.asme.org/terms/Terms_Use.cfm

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