differencebetween_pneumatichydraulicelectricalactuators
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WhatstheDifferencebetweenPneumatic,Hydraulic,andElectricalActuators?MachineDesignCarlosGonzalezThu,2015041611:51
Alinearactuatormovesaload,whichcanbeanassembly,components,orafinishedproduct,inastraightline.Itconvertsenergyintoamotionorforceandcanbepoweredbypressurizedfluidorair,aswellaselectricity.
Hereisabreakdownofcommonlinearactuators,theiradvantagesandtheirdisadvantages.
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HowTheyWork
Pneumaticlinearactuatorsconsistofapistoninsideahollowcylinder.Pressurefromanexternalcompressorormanualpumpmovesthepistoninsidethecylinder.Aspressureincreases,thecylindermovesalongtheaxisofthepiston,creatingalinearforce.Thepistonreturnstoitsoriginalpositionbyeitheraspringbackforceorfluidbeingsuppliedtotheothersideofthepiston.
Hydrauliclinearactuatorsoperatesimilarlytopneumaticactuators,butanincompressibleliquidfromapumpratherthanpressurizedairmovesthecylinder.
Anelectriclinearactuatorconvertselectricalenergyintotorque.Anelectricmotormechanicallyconnectedturnsaleadscrew.Athreadedleadorballnutwithcorrespondingthreadsthatmatchthoseofthescrewispreventedfromrotatingwiththescrew.Whenthescrewrotates,thenutgetsdrivenalongthethreads.Thedirectionthenutmovesdependsonwhichdirectionthescrewrotatesandalsoreturnstheactuatortoitsoriginalposition.
PneumaticActuators
Advantages
Thebenefitsofpneumaticactuatorscomefromtheirsimplicity.Mostpneumaticaluminumactuatorshaveamaximumpressureratingof150psiwithboresizesrangingfromto8in.,whichtranslateintoapproximately30to7,500lb.offorce.Steelactuatorshaveamaximumpressureratingof250psiwithbore
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sizesrangingfromto14in.,andtheygenerateforcesrangingfrom50to38,465lbf.
Pneumaticactuatorsgeneratepreciselinearmotionbyprovidingaccuracy,forexample,within0.1inchesandrepeatabilitywithin.001inches.
Pneumaticactuatorstypicalapplicationsinvolveareasofextremetemperatures.Atypicaltemperaturerangeis40Fto250F.Intermsofsafetyandinspection,byusingair,pneumaticactuatorsavoidusinghazardousmaterials.Theymeetexplosionprotectionandmachinesafetyrequirementsbecausetheycreatenomagneticinterferenceduetotheirlackofmotors.
Inrecentyears,pneumaticshasseenmanyadvancesinminiaturization,materials,andintegrationwithelectronicsandconditionmonitoring.Thecostofpneumaticactuatorsislowcomparedtootheractuators.AccordingtoBimbaManufacturing,forexample,theaveragepneumaticactuatorcosts$50to$150.Pneumaticactuatorsarealsolightweight,requireminimalmaintenance,andhavedurablecomponentsthatmakepneumaticsacosteffectivemethodoflinearmotion.
Disadvantages
Pressurelossesandairscompressibilitymakepneumaticslessefficientthanotherlinearmotionmethods.Compressorandairdeliverylimitationsmeanthatoperationsatlowerpressureswillhavelowerforcesandslowerspeeds.Acompressormustruncontinuallyoperatingpressureevenifnothingismoving.
Tobetrulyefficient,pneumaticactuatorsmustbesizedforaspecificjob.Hence,theycannotbeusedforotherapplications.Accuratecontrolandefficiencyrequiresproportionalregulatorsandvalves,butthisraisesthecostsandcomplexity.
Eventhoughtheairiseasilyavailable,itcanbecontaminatedbyoilorlubrication,leadingtodowntimeandmaintenance.Companiesstillhavetopayforcompressedair,makingitaconsumable,andthecompressorandlinesareanothermaintenanceissue.
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HydraulicActuators
Advantages
Hydraulicactuatorsareruggedandsuitedforhighforceapplications.Theycanproduceforces25timesgreaterthanpneumaticcylindersofequalsize.Theyalsooperateinpressuresofupto4,000psi.
Hydraulicmotorshavehighhorsepowertoweightratioby1to2hp/lbgreaterthanapneumaticmotor.
Ahydraulicactuatorcanholdforceandtorqueconstantwithoutthepumpsupplyingmorefluidorpressureduetotheincompressibilityoffluids
Hydraulicactuatorscanhavetheirpumpsandmotorslocatedaconsiderabledistanceawaywithminimallossofpower.
Disadvantages
Hydraulicswillleakfluid.Likepneumaticactuators,lossoffluidleadstolessefficiency.However,hydraulicfluidleaksleadtocleanlinessproblemsandpotentialdamagetosurroundingcomponentsandareas.
Hydraulicactuatorsrequiremanycompanionparts,includingafluidreservoir,motors,pumps,releasevalves,andheatexchangers,alongwithnoisereductionequipment.Thismakesforlinearmotionssystemsthatarelargeanddifficulttoaccommodate.
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ElectricalActuators
Advantages
Electricalactuatorsofferthehighestprecisioncontrolpositioning.Anexampleoftherangeofaccuracyis+/0.000315in.andarepeatabilityoflessthan0.0000394in.Theirsetupsarescalableforanypurposeorforcerequirement,andarequiet,smooth,andrepeatable.
Electricactuatorscanbenetworkedandreprogrammedquickly.Theyofferimmediatefeedbackfordiagnosticsandmaintenance.
Theyprovidecompletecontrolofmotionprofilesandcanincludeencoderstocontrolvelocity,position,torque,andappliedforce.
Intermsofnoise,theyarequieterthanpneumaticandhydraulicactuators
Becausetherearenofluidsleaksandenvironmentalhazardsareeliminated.
Disadvantages
Theinitialunitcostofanelectricalactuatorishigherthanthatofpneumaticandhydraulicactuators.AccordingtotheexamplefromBimbaManufacturing,anelectricalactuatorcanrangefrom$150togreaterthan$2,000dependingonitsdesignandelectronics.
Electricalactuatorsarenotsuitedforallenvironments,unlikepneumaticactuators,whicharesafeinhazardousandflammableareas
Acontinuouslyrunningmotorwilloverheat,increasingwearandtearonthereductiongear.Themotorcanalsobelargeandcreateinstallationproblems.
Themotorchosenlocksintheactuatorsforce,thrust,andspeedlimitstoafixedsetting.Ifadifferentsetofvaluesforforce,thrust,andspeedaredesired,themotormustbechanged.
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