print|close

WhatstheDifferencebetweenPneumatic,Hydraulic,andElectricalActuators?MachineDesignCarlosGonzalezThu,2015041611:51

Alinearactuatormovesaload,whichcanbeanassembly,components,orafinishedproduct,inastraightline.Itconvertsenergyintoamotionorforceandcanbepoweredbypressurizedfluidorair,aswellaselectricity.

Hereisabreakdownofcommonlinearactuators,theiradvantagesandtheirdisadvantages.

Related

AComparisonofDCLinearActuatorswithDCLinearMotors

StepperMotorLinearActuators101

ScrewDriveSurvivalandActuatorLife

HowTheyWork

Pneumaticlinearactuatorsconsistofapistoninsideahollowcylinder.Pressurefromanexternalcompressorormanualpumpmovesthepistoninsidethecylinder.Aspressureincreases,thecylindermovesalongtheaxisofthepiston,creatingalinearforce.Thepistonreturnstoitsoriginalpositionbyeitheraspringbackforceorfluidbeingsuppliedtotheothersideofthepiston.

Hydrauliclinearactuatorsoperatesimilarlytopneumaticactuators,butanincompressibleliquidfromapumpratherthanpressurizedairmovesthecylinder.

Anelectriclinearactuatorconvertselectricalenergyintotorque.Anelectricmotormechanicallyconnectedturnsaleadscrew.Athreadedleadorballnutwithcorrespondingthreadsthatmatchthoseofthescrewispreventedfromrotatingwiththescrew.Whenthescrewrotates,thenutgetsdrivenalongthethreads.Thedirectionthenutmovesdependsonwhichdirectionthescrewrotatesandalsoreturnstheactuatortoitsoriginalposition.

PneumaticActuators

Advantages

Thebenefitsofpneumaticactuatorscomefromtheirsimplicity.Mostpneumaticaluminumactuatorshaveamaximumpressureratingof150psiwithboresizesrangingfromto8in.,whichtranslateintoapproximately30to7,500lb.offorce.Steelactuatorshaveamaximumpressureratingof250psiwithbore

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.

HydraulicActuators

Advantages

Hydraulicactuatorsareruggedandsuitedforhighforceapplications.Theycanproduceforces25timesgreaterthanpneumaticcylindersofequalsize.Theyalsooperateinpressuresofupto4,000psi.

Hydraulicmotorshavehighhorsepowertoweightratioby1to2hp/lbgreaterthanapneumaticmotor.

Ahydraulicactuatorcanholdforceandtorqueconstantwithoutthepumpsupplyingmorefluidorpressureduetotheincompressibilityoffluids

Hydraulicactuatorscanhavetheirpumpsandmotorslocatedaconsiderabledistanceawaywithminimallossofpower.

Disadvantages

Hydraulicswillleakfluid.Likepneumaticactuators,lossoffluidleadstolessefficiency.However,hydraulicfluidleaksleadtocleanlinessproblemsandpotentialdamagetosurroundingcomponentsandareas.

Hydraulicactuatorsrequiremanycompanionparts,includingafluidreservoir,motors,pumps,releasevalves,andheatexchangers,alongwithnoisereductionequipment.Thismakesforlinearmotionssystemsthatarelargeanddifficulttoaccommodate.

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.

SourceURL:http://machinedesign.com/linearmotion/whatsdifferencebetweenpneumatichydraulicandelectricalactuators