机械毕业设计英文外文翻译244基于制动试验台的虚拟仪器与变频技术 副本Word文件下载.docx
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机械毕业设计英文外文翻译244基于制动试验台的虚拟仪器与变频技术 副本Word文件下载.docx
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Therefore,itisfeasibletousecombinedinertialflywheelstosimulaterotatinginertiaofcranehoistanditstransmissioncomponentstotesttheperformanceandqualityofthebrake.
Accordingtothemomentofmomentumtheorem:
Tb·
t=Ji·
ω
(1)
WhenTbisfixed,tbcanbecontrolledthroughcombinationsbetweenJiandωdifferently.Brakedrumorplate,whichwillbemeasured,andcombinedinertialflywheelsforloadingonaredriventorotatebyACfrequencyconversionmotor(orDCone,whichwillnotbe
dealtwithinthisarticlecarefully).Accordingtotheprinciplesshownintheformula
(1),wecansimulateactualprocessesofbrakesfittedonliftingandtransportmachineries,engineeringones,miningonesandconstructiononesbychangingthetechnicalspecificationdutyJC,theflywheel'
sinertialmomentJiandmotor'
srotationalspeedni.Whendetectedbrakesworkinsimulationcycleandbrakerepeated,infraredthermoscopesandtorquesensors,andothersensorswillrecordbrakingshownintheheat,brakingtorque,brakingtimeandbrakespeedparameters.
2Thecompositionandstructureofthebraketestsystem
Thistestsystemisintendedtoachievetheperformancesofdrumanddiscbrakesandhasfollowingfunctions:
(1)Brakereplacement
Accordingtodifferenttypeofbrakesthecorrespondingbasewillbechosenandbrakepositioncouldbeadjustedusingelectricslidetest-bed;
(2)Multi-levelloading
Wecansimulatetheactualloadingonbrakesinacranewithdifferentcombinedflywheels.Thetestsystemadoptsmanualhydraulicsystemcomposedbyathree-positionfour-wayhand-operateddirectionvalve,areliefoneandtheiraccessories,anditisoperationsavingandconvenienttoreplaceflywheels.
(3)Regulationtherotationalspeedn(orω)
ItcanberealizedbychangingfrequencysuppliedtotheACmotor.Whenbrakingtorqueisverylarge,suchas10000Nm,itshouldbeappropriateforregulatinginitialbrakespeedupward1000r/mintominimizerotatinginertiapossibly.
(4)Brakingfrequencyadjustment
Basedonactualneedsbrakingfrequencycanbeconfinedinarangeof1~4timesperminute.
(5)Brakingtorquemeasurement
Therearethreemethods:
a)Directmeasurementviatorquesensors:
Rotationalspeedandtorquesensorwillbeinstalledbetweenthedetectedbrakedrumorplateandinertialflywheelplates.Dynamicbrakingtorqueofdetectedbrakewillbedirectlymeasured,showninFig.1andFig.2.Accordingtothescopeofbrakingtorqueofdetectedbrakes,twoorthreerotationalspeedandtorquesensorsshouldbepreparedfortestingtorquetomeettheaccuracyrequirements;
b)Indirectparametermeasurement:
Basedontherotatinginertiaandbrakingtimewecangetbraketorqueusingmathematicalrelationshipbetweentheseparameters,asshowninFig.2.
c)Indirectmeasurementbypedestal-force:
Thepressuresensorsareinstalledunderthebasewheredetectedbrakearefixedtofeeltheforcesgivenbybrake,andthentoobtainbraketorque.
Thesecondapproachhassmallinvestment,simplestructureandnotorquesensorswhichmeannotconsideringrelatedtroublesofchangingtorquesensors.Buttheprocedureto
calculatetorqueiscomplex,andaccumulatingtotalerrorswouldbelargerandthentheresultaccuracywillbelow.
Thethirdwayhastheadvantageofthereplacementofsensorsiseasierandnospecialrequirementsforsensorsinstallingprecision.Itisstillanindirectmeasurementbuttheprocedureislessthanthatinthesecondmethodandthatmeansthecumulativeerrorsrelativelyissmaller.Andvisibleshortcomingispoordynamicresponse.
(6)Automaticcontrol
Excepttomanualoperationtestsystemisalsoprogrammedcontrol.
(7)Monitoring
Brakingfrequency,initialbrakingspeed,theaggregatebrakingnumber,moment,timeandsoonwillbeshownautomatically.
(8)Automaticallydataacquisitionandprocessing
Thecurvedescribingbrakingtorque,timeandspeedcouldbedrawnautomaticallybymeansofcomputersoftwarewhiledetectedbrakeismeasuredindutycycleoperation.Therefore,inresponsetothewaytotestbrakingtorquethesystemcanbedividedintothreeonesofthatwithtorquesensorsuchasFig.1and2above,thatwithouttorquesensorsuchasshowninFig.3andthatofpedestal-powermeasurementwithouttorquesensor,asshowninFig.4.ThetestsystemismainlycomposedofACfrequencyconversiontransmissionsystem,flywheelsloadingsystem,rotationalspeedandtorquesensors,basewhichtofixdrumorplatebrakes,adjustableDCpowersupply,detectedbrakesandtestandcontrolsystem.
Inadditiontotheabovefunctions,thesystemcouldtestfollowingperformancesofthebrakes:
a)Releaseperformance:
Thisistestedundertheconditionsof85%Veandratedload,adjustingvoltageviaboosterdevices;
b)Closeperformance:
ThisistestedundertheconditionsofratedvoltageVeand50%ofratedloading;
Otherwise,thefollowingperformancescouldalsobetested:
1)Structuralperformances:
a)Abilityofbrakeshoe'
spositionfollowingdrum;
b)Assemblyforkeepinggapsbetweendrumandshoesequalling;
c)Lubricating.
2)Otheritems:
a)Contactarea;
b)Springtesting;
c)Brakingliningsandshoesgap;
d)Pin'
shardness.
3ACfrequencyconversionadjustingspeedsystem
ComparedwithDCmotor,theACmotorhassimpleandcompactstructure,littlemaintenanceworkload,highefficiency,smallrotatinginertiaandquickdynamicresponse,anditcouldbemadeofhigh-voltage,largecapacityandhighspeed.Currently,ACmotorhastrendtoreplaceDConeinthefieldofadjustingspeedtransmission.Generallyspeaking,therearemanykindsofmotorswhichcouldbeappliedtodiversetypesofconverter-driven,andwhichareroughlydividedintoordinaryACmotor,specialoneanddedicatedone.Thefrequencyconversionadjustingspeedingsystemiscomposedoffrequencyconverterand
dedicatedliftmotor.
Totheordinaryasynchronousmotor,thefollowingfactorsshouldbeconsideredwhiletodeterminetheircapacity:
(1)Chosenmotorcapabilityshouldbegreaterthanthepowerloadneeded;
(2)Comparedwithneededloadpull-intorquethegreatesttorquethatmotorexportsshouldhavesufficientlysurplusvolume;
(3)Evensupplyvoltageislower10%thanratedvalue,motorscanexportneededtorquealso;
(4)Consideringthelifelengthofmotoritshouldrunninginthespecifiedtemperaturescope;
(5)Becauseoftransmissionrateofthetransmissionsystem,efficiencyandloadfluctuation,themotorpowershouldhaveenoughsurplusvolume;
(6)Againstloadnature,itisnecessarytochoiceasuitable
motorsoperatingmodessuchascontinuousservicesystem,short-termoperationandduplicationsystem.
IntheACadjustingspeedcontrolsystemwithfrequencyconvertermotor'
sslowdownisachievedbyreducingtheoutputfrequencyoftheconverter.Whenmotorsneedslowdownfasterthantherateoffreedeceleration,underspeedofconverteroutputfrequencymightberan-upandthespeedwhichiscorrespondingtothatfrequencyislowerthantheactualrotationalspeedofmotor,andmotorwillberegenerativebraking.Insuchcases,asynchronousmotorwillbeanasynchronousgenerator,andloadmechanicalenergywillbeconvertedtoelectricalenergyandthenfeedbacktotheconverter.However,whenthebackfeedisoverload,overvoltageprotectioncircuitofconverterwillworktocutconverter'
soutputandmotorswillbefreelyslowdowninsteadarapidspeed-down.Toavoidabovephenomenon,thatis,toconsumetheenergyinotherpartsoftheDCcircuitwithoutcausingvoltageriseinthevoltage-fedconverter,regeneratingbrakingcircuits(brakingresistors)arenormallyusedandtheenergyfedbacktotheDCcircuitwillconsumedintheformofheat.Forthetestsystem,itisapparentlythatbrakingresistancesarenotnecessarybecauseoftheusageofbrakeforbrakingdeceleration.Itisnecessarytodefinesurpluscapacityofmotororconverteronthebasisofpracticalsituation.Andonthecaseofensuringtomeetrequirementsofdrivingsystemperformance,energyconsumptionoreconomicfactorsshouldbeconsidered,andoveral
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