Hydrauliccylindervibratestoa400Hzsine.
(DYNA-MESSGmbh)andHänchenreachnewheightsofperformance
[attach]46537[/attach]Modernqualitystandardsmeanthatcomponentsarenowfacingmorevariedandusefulteststhanatanytimebefore.DYNA-MESSTestingSystemsspecialisesintestingmachinesfordynamiccomponentandmaterialtesting.Withitsbroadandvariedrangeofstandardandspecialtestmachines,theAachen-basedcompanyexploitsthepossibilitiesofmodernfluidtechnologytothebestadvantage.Itspiècederesistanceisaspecialtestingmachineforelastomerswhich,withthehelpofstandardhydrauliccylindersfromHänchen,realisescontrolledvibrationsof400Hzinorder,forinstance,totestthedampingofbearingelementsmadeofrubber-metalcompositesfortheautomotiveindustry.
[attach]46538[/attach]Hydraulicsiscutting-edgetechnology
AccordingtoDr.MarcusJarchow,ManagingDirectorofDYNA-MESS,"thesetestunitsareexposedtoextremestresseswithanominalforceof10kNandafrequencyofanythingfrom0to400Hz.Ithasbeenextremelydifficulttofindasuitablyhigh-performancehydrauliccylinderonthehydraulicsmarket",becausethetestdevicedependsontheperfectstick-slipbehaviourofthehydraulicsystem.Cylinderswithhydrostaticallysupportedpistonrodguidesarenormallyusedforthistypeofapplication,butthetechnicalexpenditureforthissolutionisenormous."Wehaveneverthelesskeptourearstothegroundtotryandfindoutwhocanoffersomehelpwithfindingasolution"statedtheManagingDirectorofDYNA-MESS."Everybodyhesitatedwhenwementionedthetechnicalrequirements,withtheexceptionofHänchenHydraulik.Afurtherargumentintheirfavourwasthattheyhadtheirowntestequipmentandwouldbeabletobasetheirresultsonextensiveexperience.Ultimately,thehydraulicspecialistsfromOstfildern,nearStuttgart,offeredastandardcylinderwithpatented,floatingannulargapsealwhichisconsiderablymorecost-effectivethandriveswithhydrostaticallysupportedpistonrodguides".ThePZLassemblyseriesfromHänchen,however,alsoprovidesthesehigh-endcylinders.
[attach]46539[/attach]ThePZRfloatingannulargapseal
Thepatented,floatingannulargapsealfromHänchenpermitstheuseofcost-effectivePZRhigh-endtestcylinders,inwhichasteelsleeveispositionedthroughachokegapandtherebycreatesacontact-freesealinggapofjustafew1/100mm.Thisprocesscan,however,onlyfunctioncorrectlywithaproductionaccuracyofonlyafewµm,asleakswouldotherwiseleadtoanunacceptablelossofhydraulicfluid.ThisPZRassemblydiffersonlybytheslightlylesserabsorptionofthelateralforcesfromacylinderwithhydrostaticallysupportedpistonrodguide,butyieldsaconsiderablecostadvantage.Thankstotheirnegligiblefriction,however,PZRcylindersoffermaximumpositioningandrepeataccuracyandarestick-slipfree,makingthemideallysuitableforextremelyslowaswellasfastmovementsandminimumtraveloverrangesofaveryfewµm.Aslateralforcesarenotexperiencedinthis400HzDYNA-MESStestequipment,thedecisionwasmadeinfavourofthesecylinders.
High-qualityperipherals
Thecylinderisequippedwithaspecialinductivepositionmeasuringsystemandaforcetransducerwithanextremelylownaturalfrequencyandyieldmeasuringstrips.Bothsensorssupplyanalogoutputsignalswhicharedigitalisedwitharesolutionof16Bitandtestedwithmorethan20kHz.Theysupplythecontrolwiththenecessarydata,whichmustbeconvertedpracticallyinrealtimebyacontrolcardwithitsownhigh-performanceprocessor.Tried-and-testedDYNA-MESSsoftwaremoduleswereadaptedtothespecialconditionstofacilitateprogramming.APCformsthebasisfortheWindowsuserinterface.Thevalvesrepresentedyetanothertechnicalchallenge,astheyhavetoworkwithacontrolfrequencyof16kHz.Thefluidcircuithasbeendesignedfor300barandoperatesat40l/min.Thishighpowerdensityenabledalowdesignsize,becauseahighfrequencywithawidefrequencyspectrumplacesextremelyhighdemandsonthemechanicalconstruction:theframemustnothaveanynaturalresonanceoverthewholeofthefrequencyrange.
Commissioning
Commissioningprovedtobeatime-consumingexercise,particularlyduetotheneedtotuneintothevariousfrequencyranges.Thefrequencywasincreasedinstepsof10,20,30…upto400Hz,withtheresonancehavingtobeminimisedateverystage.Thecompletecontrolwasalsotunedduringthistime,inthattheruntimedelaysbetweenthereactionoftheprocessoranditsexecutionbythehydraulicsystemarecapturedandincludedinthecontrol.Finallythecontrolqualityandcurveformwereoptimised,thisoperationbeingfollowedbyfinetuningwiththehelpofafriction-freeandloss-freespring,whichmeasuresthedynamicwithoutphasedisplacementandsoenablesmaterialteststobecarriedoutunderclearlydefinedconditions.Afterupto400Hzhadbeenreached,Dr.Jarchow’steamcarriedoutfurthertestsuptoafrequencyof1,000Hz."Weweresurprisedatwhatoutputswerepossible,uptodoublethenominaloutputat800Hz",saidthehydraulicspecialist."Itwasonlyabovethisfrequencythatthelimitsofwhatistechnicallyfeasibleatthemomentwereclearlyreached.Thehydrauliccylinderhasmorethanmatchedtherequirementsplacedonit,andthatwaswiththeuseofacataloguecylinderandataveryattractiveprice”.Thefinishedsystemwasthencommissionedduringthefirstquarterof2002.
Practicalapplication
Hänchen’sPZRhydrauliccylindersarenowbeingusedbyaDaimler-Chryslersuppliertotestvibrationdampersforengineandgearboxsuspensionsforloadcarryingability,dampingbehaviourandservicelife.Thesecomponentsaremadefromrubber-metalcompositematerialwithembeddedpassivehydraulicdamping.Thesealedglycolcircuitinthiscomponentisusedtodampenthevibrations.Anewtestbenchenablesthedeveloperstooptimisethedampingcharacteristics.Sweeptestswithapre-selectedloadwhichcorrespondstotheengineorgearboxweightareusedtodetermineatwhichfrequencydampingismosteffective.Forthistestthefrequencyissuperimposedoverthestaticloadwiththeaimofachievinganoptimiseddampingoverthewholefrequencyrangeofupto400Hz."
Ourengineeringcompetence,theexperienceandevaluationofoursuppliersaswellastheabilitytodeveloptestsolutionstogetherwithourcustomerswerethedecidingfactors",explainedDr.Jarchow,whoseteamperformsallcalculations,isresponsiblefordesign,software,electronicdevelopment,control,configurationaswellasinstallationandrealisesthecompletesysteminco-operationwiththesuppliers."Supplierswhoseproductsconformtoourownhighstandardsplayacriticalrole.ThatiswhyweareworkingtogetherwithHänchenHydraulik".