differencebetween_pneumatichydraulicelectricalactuators

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 print | close What’s the Difference between Pneumatic, Hydraulic, and Electrical Actuators? Machine Design Carlos Gonzalez Thu, 2015-04-16 11:51  A linear actuator moves a lo ad, which can be an assembly, components, or a finished product, in a str aight line. It converts energy into a motion or force and can be powered by pressurized fluid or air, as well as electricity. Here is a breakdown of common linear actuators, their advantages and their disadvantages. Related  A Comparison of DC Linear Actu ators with DC Linear Motors Stepper Motor Linear Actuators 101 Screw Drive Survival and Actuator Life How They Work •Pneumatic linear actuators consist of a piston inside a hollow cylinder. Pressure from an external compressor or manual pump moves the piston inside the cylinder. As pressure increases, the cylinder moves along the axis of  the piston, creating a linear force. The piston returns to its original position by either a spring-bac k for ce or fluid being supplied to the other side of the piston. Hydraulic linear actuators operate similarly to pneumatic actuators, but an incompressible liquid from a pump rather than pressurized air moves the cylinder.  An electric linear actuator converts electrical energy into tor que. An electric motor mechan ically conn ected turns a lead screw. A threaded lead or ball nut with corresponding threads that match those of the screw is prevented from rotating with the screw. When the screw rotates, the nut gets driven along the threads. The direction the nut moves depends on which direction the screw rotates and also returns the actuator to its original position. Pneumatic Actuators  Advantages The benefits of pneumatic actuators come from their simplicity. Most pneumatic aluminum actuators have a maximum pressure rating of 150 psi with bore sizes ranging from ½ to 8 in., which translate into approximately 30 to 7,500 lb. of force. Steel actuators have a maximum pressure rating of 250 psi with bore

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    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