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CreatingLinearMotionOneStepataTimePrecisionLinearMotionAccomplishedEasilyandEconomically

Part2of2

InPart1,wediscussedthebasicsofasteppermotorbasedlinearactuator,oneofthemosteffectivewaysto

convertrotaryintolinearmotionforawiderangeofapplications. InPart2,wewillexplainhowtoaccuratelysizealinear

actuator.

HowIsaLinearActuatorSized?Sizingalinearactuatorisquiteeasyonceyouunderstandthebasicneedsoftheapplication. Thefollowingistheminimum

informationneededtobeginsizingtheproperdevice.

1.Linearforceneededtomovetheload,expressedinNewtons(N)2.Lineardistancetheloadneedstobemoved,expressedinmeters(M)3.Timerequiredtomovetheload,expressedinseconds(s)4.Table1illustratedbelow5.PerformancecurvesillustratedinHaydonlinearactuatorcatalogs

PowerRequirementsThepowerrequiredtomeettheapplicationisnowcalculatedusingtheparametersabove. Thiswillallowtheuser

toeasilychoosethecorrectmotorframesizeneeded.

Plinear = (distancetraveledinMeters)(forceinNewtons)(TimetotravelthedistanceinSeconds) = watts

Oncethepowerisknowninwatts,choosetheproperframesizeoftheactuatoraslistedinTable1. Allsteppermotor

linearactuatorsrequireadrivetosendthepulsestothemotor. AsseeninTable1,thepowerforbothanL/Rdriveanda

chopperdriveislisted. Mostapplicationstodayuseanelectronicchopperdrive. Unlesstheapplicationisbatterypowered

(asinahandheldportabledevice),achopperdriveishighlyrecommendedtogetmaximumperformancefromthelinear

actuator.

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Table1.FrameSizesandPerformanceBasedOnRequiredOutputPower

HybridSingleStackMax.LinearPower(watts)

Series Size MaxForce(N) rTravelPerStep(mic L/RDrive ChopperDrive21000 8 45 1.5 40 0.3 0.3728000 11 90 3 50 0.27 0.5135000 14 220 1.5 50 0.59 1.543000 17 220 1.5 50 1.02 2.3157000 23 880 4 50 1.47 687000 34 2200 12.7 127 N/A 21.19

HybridDoubleStackMax.LinearPower(watts)

Series Size MaxForce(N) rTravelPerStep(mic L/RDrive ChopperDrive28000 11 133 3 50 N/A 1.1435000 14 220 15.8 127 N/A 2.743000 17 350 15.8 127 N/A 4.6257000 23 880 12.7 127 N/A 10.08

Canstack

Max.LinearPower(watts)

Series Size MaxForce(N) rTravelPerStep(mic L/RDrive ChopperDrive15000 15mm 7 20 0.025 0.0320000 20mm 16 25 100 0.05 0.06

Z20000 20mm 35 25 100 0.09 0.2326000 26mm 50 6 100 0.17 0.18

Z26000 26mm 80 6 100 0.18 0.4836000 36mm 160 3 100 0.23 0.6946000 46mm 260 12.7 400 0.55 1.13

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VelocityAftercalculatingthemechanicalpowerneededtomeettheapplicationrequirements,thelinearvelocityininches

persecondiscalculatedusingthefollowingequation:

Velocitylinear = requiredtraveldistance(in) Timetoachievetravel(s) =in/s

Forcevs.LinearVelocityCurves

Oncetherequiredactuatorframesizeisdeterminedandthelinearvelocityiscalculated,theforcevs.linear

velocitycurveisusedtodeterminetheproperresolutionoftheactuatorleadscrew.

Figure1.Size17Actuator Forcevs.LinearVelocityChart

ActuatorLifeTherearemanyvariablesthatultimatelydeterminelifeoftheactuator. Thebestwaytopredictlifeisthrough

applicationtesting,whichishighlyrecommended. Thereis,however,afirstapproximationtechniquethatcanhelp

estimatethisvalue. Thesteppermotorprimemovercontainsnobrushestowearoutandalsoutilizesprecision,longlife

ballbearings. Themainwearcomponentisthepowernut. Thenumberofcyclescanbesummarizedasafunctionofload,

asillustratedinFigure2below.

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Figure2. CyclesonaStandardStrokeActuatorasaFunctionof%MaxLoadExample#1ApplicationRequirements:

ReqdForce(lbs)= 15lbs

ReqdTravel(in)= 3in

TimeToAchieveTravel(s)= 6s

DesiredCycles= 1,000,000

LinearVelocity(in/s)= 3in/6s=0.5in/s

COMPUTATION:Calculatetheinitialratedforcebasedonrequired#ofcycles:

Step1:

RefertoFigure2anddeterminethecorrectsizingfactorneededinorderfortheactuatortoachievetherequired

1,000,000cycles.ThisisillustratedwiththeyellowlineinFigure3below.

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Figure3. SafetyFactorNeededToMeet1,000,000CyclesStep2:

Asindicatedinthechart,inordertoget1,000,000cycles,afactorof0.5mustbeusedwhensizingtheactuator.

Theinitialratedforcerequiredinordertomeettheloadafter1,000,000cyclesistherefore

15lbs/0.5=30lbs

Step3:

ConvertlbstoNewtons(N)

30lbs/(0.225lbs/N)=133N

COMPUTATION:Determinerequiredtravelinmeters

3inx(0.0254M/in)=0.0762M

COMPUTATION:Choosetheproperframesizeactuatorusingtheselectorchart

Step1:

Determinetherequiredlinearmechanicalpowerinwatts

Plinear=(133Nx0.0762M)/6s=1.7NM/s=1.7wattsStep2:

Use

Table

1

to

determine

the

correct

frame

size

actuator.

As

discussed

earlier

in

the

aticle,

most

applications

will

useachopperdrivetosupplytherequiredinputpulsestothesteppermotor. The43000(Size17Hybrid)waschosenfor

thisapplication,ashighlightedintheHybridSingleStacksectionofTable1.

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Hybrid SingleStackMax.Power;watts

Series Size MaxForce(N) earTravel/Step(micro L/R Chopper21000 8 45 1.5 40 0.3 0.3728000 11 90 3 50 0.27 0.5135000 14 220 1.5 50 0.59 1.543000 17 220 1.5 50 1.02 2.3157000 23 880 4 50 1.47 687000 34 2200 12.7 127 N/A 21.19

COMPUTATION:DeterminetheproperresolutionusingtheForcevsLinearVelocitychart

Asdeterminedbythelifecalculationperformedabove,aninitialloadof30lbsistobemovedatavelocityof0.5in/s.

TheresultingleadscrewresolutionrequiredintheSize17hybridmotoris0.00048(Jresolution),asindicatedinFigure4

below.

Figure4. LeadscrewresolutionrequiredintheSize17hybridmotoris0.00048(Jresolution),asindicated.

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COMPUTATION:Verifyselectionbycheckingforceattherequiredsteprate

Earlierinthepaper,itwasdiscussedthattheleadscrewadvancesbasedonthenumberofinputstepstothe

motor. Haydonperformancecurvesareexpressedinbothin/sec(asillustratedinFigure4)andalsoinsteps/sec(Figure

5). Asaneffectivecheck,verifytheselectionbycheckingtheforceattherequiredsteprate.

Resolutionchosen 0.00048in/step(Jscrew)

Reqdlinearvelocity 0.5in/s

Reqdsteprate (0.5in/s)/(0.00048in/step)=1041steps/s

Figure5.

Figures4and5aregoodillustrationsofhowthepulsestothesteppermotortranslateintolinearmotionthrough

theleadscrew.

ConclusionThroughtheuseofsteppermotorbasedlinearactuators,rotarytolinearmotiontakesplaceinsidethemotor

itself. Thismethodoffersuniqueadvantagesoveralternativeapproaches,suchasfewercomponents,smalleroverall

footprintsize,highforceoutput,andlongstrokelengths. Whatsmore,thehighprecision,repeatability,longcomponent

areespeciallyattractive,asarethehighresolutionspossible.

Inaddition,theuseofthesteppermotortranslatestoaloweroverallcostforOEMequipmentbuildersintermsof

developmentandproduction. Mostimportantly,thismethodcanbeutilizedinavarietyofverticalmarkets,including

medical,laboratoryinstrumentation,semiconductor,aerospace,andvirtuallyanyotherapplicationwhereprecisionlinear

motionisrequired.

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AboutHaydonKerkMotionSolutions

HaydonKerkMotionSolutionsisthejoiningoftwoworldclassbrandsinthefieldoflinearmotion;Haydonand

Kerk. Together,thecompanynowoffersabroadrangeofprecisionlinearmotionproducts. Recognizedasaleading

manufacturerofsteppermotorbasedlinearactuators,rotarymotors,leadscrewassemblies,andlinearrailandguide

systemsusedinnichemarketapplications,HaydonKerkMotionSolutionsoffershighperformancewithitsrangeofreliable,

precisedesigns. HaydonKerkMotionSolutionshasdevelopedindustryrenownedbrandsbuiltuponitstechnical

innovation,versatility,customization,productdurability,anddedicatedcustomerservice. Formoreinformation,please

visitourwebsiteathttp://www.HaydonKerk.com.