ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
actuatorevenwhenthegloveisclosed.Aslongasthisforceislessthantheinherentstaticfrictioninthe glovejoint,nouncommanded motionwilloccur. Withfixedgloveparameters, slackoccurrence depends onactuator inertia. Giventheminimum cable tension (thebiasforcereferred toabove)T,thegloveinertiaMG,andmaximum expected operator input forceF,amaximum actuator inertiaMAcanbecalculated toavoidslackinthecable: I JT°MGI Thismodelalsoillustrates thatwhenthesystem isoperating nominally (noslack),theaugmented glove behaves withtheinertiaofthegloveplustheinertiaoftheactuator. Glove"feel"couldthusbeimproved byreducing actuator inertia. Apractical limittoimprovement wouldoccurwhenthelevelofactuator inertiafellbelowtheinherent gloveinertia. Whenthesecalculations wereperformed ontheMkIactuator (aftertestinghadbegunandthegloveinertiahadbeendetermined) itsinertiawasfoundtoberoughly fourtimesthatoftheglove,clearlyleaving roomforimprovement intheMkIIdesign. Examination oftherelationships described abovereveals abasicdesigntradeoff inthisapplication. For anygivenmotor,decreasing powerdissipation andincreasing maximum forcecapability byadjusting the effective spoolradiusRisinconflictwithreducing theinertiaandfrictionoftheactuator. Figure4 illustrates thistradeoff forthemotorusedintheMkIactuator. D IT100 9O 8O 70 60 5O 40 30 20 10 0 0.0'\\_  -20 _"'---,.._ 115 :10 i5 .... I. I.... I.... "0 0.5 1.0 1.5 2.0 Equivalent Inertia(normalized toMk i--Maximum Force.- --Power Dissipation at451tI /:5O 14s ::4o ::35 !3o ::2s! Figure4.Maximum ForceandPowerDissipation vs.InertiaforQT-1106 Motor Sinceitwasdesired todecrease powerdissipation, inertia,andfrictionsimultaneously fortheMkII design, clearlythesearchformotorswouldhavetobeexpanded. Giventheseinterests, DCbrushless motorshadseveral promising properties. Theirrotorscarrypermanent magnets instead ofcoils,so typically havelessinertiaforthesameperformance. Sincetheheat-dissipating electromagnets areinthe statortheycontact thehousing directly overalargesurface area,sothermal management iseasier. Theyhavelessinternal friction, sincetherearenobrushes. Brushwearisnolongeramaintenance problem, contamination frombrushdustisavoided, brusharcingandwelding intowpressure anddry-gas environments isnotaconcern, andelectromagnetic interference isreduced. Thedrawbacks arethat 98
several morewiresareneeded (typically eightversus two),moresophisticated electronics isrequired for commutation (typically including Hall-effect sensors insidethemotor), andtheaspect ratiosavailable offthe-shelf tendtoward tallcylinders ratherthan"pancakes," duetotheadded length ofthesensors. Graphs likeFigure 4illustrate thetradeoffs foragivenmotor, buttocompare different motors, eachof whichmightbeconsidered witharangeofeffective spoolradii,adifferent approach wasneeded. Itwas decided tocompare motor/spool combinations onthebasisofequalinertia--so eachcombination compared wouldproduce equivalent "feel"andresistance tocableslack. Thedifferent inertias foragiven motorareobtained withdifferent spoolradii.Table1demonstrates thismethod. Listedontheleftarea number ofCOTS motors fromtheInland Motors Division ofKollmorgen, Inc.,inorderofincreasing diameter. Thenextcolumn ismotorconstant Kin,afigureofmeritwhichindicates themotor's efficiency atturning electrical power intotorque. Thisgenerally increases withmotorsize,whichislistedinthenext twocolumns. Thenperformance figures ofmaximum cableforcecapability andaverage power dissipation aretabulated foreachoffoureffective inertia levels, starting withinertia equivalent totheMkI actuator andreducing byafactoroftwoineachstep. Table 1.Motor Trade Matrix Brushed Km Motor (mN*ml;W) QT-0717D 3.74 QT-1106A 11.09 T-1259A 16.95 NT-1372E 29.31 QT-1401D 26.41 T-1342A 28.60 QT-1906A 32.91 T-2003B 10.45 T-2509C 30.58 Brushless Motor RBE-00510C 7.06 RBE-00710B 15.82 RBE-01210B 28.25 RBE-01510BInertia=MkIInertia=Mk1/2Inertia=Mk114Inertia=Mk118 Diam. Ht.Force Power Force Power Force Power Force Power (cm) 2.86 0.95 3.49 0.98 3.81 1.30 4.92 1.37 4.92 1.37 4.92 2.13 6.03 1.27 6.25 0.78 7.62 0.94 2.67 1.97117.43 2.33 73.40 5.96 58.72 9.32 3.78 2.16 I77.00 1.58 122.54 3.30 88.50 6.32 61.27 13.20 4.92 2.10 189.84 2.72 132.89 5.56 94.92 10.90 44.98 6.03 2.10i164.03 3.19 115.78 6.40 82.01 12.76 Theaverage powerfigures shown werecalculated assuming a1Hzsinusoidal full-range MCPangle trajectory andaforcemodel approximating theexpected second-generation glove. Theshaded areas designate combinations whichwererejected eitherbecause theywoulddissipate morepower thanthe MkIunitontheMkIglove(>17W)orproduce insufficient cableforce(<45N(10Ibf)).Thedouble lines ineachcolumn indicate thelevelabove whichreduction gearing isnecessary toobtain asufficient physical spooldiameter. Tables ofthissortwereusefuldesign tools,enabling manydifferent potential systems tobecompared quickly onanequalfooting. Theconsequences ofchanging anyoneparameter (e.g.package size)could easilybeseen. Onthebasisofthisinformation andsomepackaging exercises, themotorselected fortheMkIIactuator wastheInland RBE-00510C, withagearratioof3.024:1 driving a2.5mm(0.1in)diameter spool,giving halftheeffective inertia oftheMk1actuator. Asthetableshows thisgivesamaximum forcecapability of 99
73.4N(16.5Ibf),aslightincrease overtheMkIvalue(itwasconsidered wisetohavesomemarginover thetarget45N(10Ibf)),andexpected powerdissipation of6W,areduction of65%.Itwasanticipated thatfrictionwoulddecrease alsoduetothelackofmotorbrushes. Motordiameter decreased by23%, though thiswasoffsetbyanincrease inmotorheightof107%. Asubstantial benefitinpackaging wasobtained whenitwasrealized thatthethreeHall-effect sensors incorporated inthemotorforcommutation couldalsobeused(inprinciple) asanincremental position encoder. Thisenabled thedeletion oftheseparate opticalencoder, andacorresponding reduction in wirecount(byfour,toatotalofeight;compared tosixfortheMkIsystem). Thisinnovation entailed somerisk,sincenewelectronics wereneeded andthenetposition resolution woulddecrease from1300 countsovertherangeoftravelto216. DrivenGear-_ /DriveCable Drive---1 _-CableSpool  Motor 11 Figure5.MkIIActuator Figure6.Comparison ofMkIandMkII(onglove)Actuators 100
Thenewdesign(Figures 5and6)placedthecablespooloutside thehousing, making cableinspection andreplacement simple. Ashaftsealwasincorporated toenableunderwater use(although thisactuator, withabrushless motorandnoencoder, couldbeintegrally waterproofed tooperate flooded ifdesired). Allcomponents werecompatible withvacuum operation. Theelectrical requirements wereapeakcurrent of3.6A(anincrease of33%overtheMkI)andamaximum voltage of12VDC(wellunderthe30VDC limitforNBSandthe+42.5VDCneeded bytheMk1actuator). Thepackage sizewas3.4cm(1.33in) wide(43%ofMkI)by5.1cm(2in)long(78%ofMkI)by2.5cm(1in)tall(sameasMkI).Overall volume decreased from114cm3(7in3)to39cm3(2.4in'),areduction of66%fromtheMk1actuator. Results Testing oftheMkIIgloveandactuator followed asimilarsequence tothatoftheMkIsystem. Glove forcecalibration showed thattheILCglovedesigners hadmettheirgoals:45N(10Ibf)cabletension produced thefullrangeofMCPjointtravel. Figure7compares theauto-calibration resultsforthissystem withthecompensation onandoff.TheMkIIactuator lowered peakgloveresistance forcefrom45N (10Ibf)to3.3N(0.75Ibf);areduction ofover90%.Thispercentage wasverysimilartotheMkIvalue, showing thatthenewglovedesignwasequally successful atisolating MCPmotion. i,45, / 40-]- 35-130+ 25"1" 2O-I15÷ 10+ 0,,_s.D TT.]T_...... I......... I......... I......... I......... I........ 0.0 0.5 1.0 1.5 20 2.5 3.0 3.5 CableContraction (cm) I....Force(Closing) _Force(Opening) II ! Figure7.MkIIGloveForceWithandWithout Compensation Thenewactuator exhibited afactoroffourdecrease ininternal staticfriction. This,combined withthe factoroftworeduction ininertia,provided muchsmoother operation thantheMkIsystem. The anticipated reduction inpowerconsumption byafactorofthreewasconfirmed, although actualvaluesfor eithersystem inheavygloveuseexceeded thedesign-phase estimates by66%,givinganactualaverage consumption of10WfortheMkIIunit,withpeaksto25W.Thelowerpowerconsumption andbetter heatconduction ofthenewactuator madeadramatic improvement inoperating temperature. TheMkII unitcouldrunindefinitely inthelaboratory without exceeding 54°C(130°F). Noneofthemechanical problems associated withoverheating wereobserved withtheMkIIunit. Theuseofcommutation sensors forencoding worked reliably. Thereduction inencoder position resolution to0.15mm(0.006in)stepsdidnotperceptibly degrade smoothness. Theimprovement in massandbulkovertheMkIactuator thatthisinnovation allowed wasquitenoticeable totheoperator in theglovebox(l-g)environment. Insummary, alloftheengineering goalsoftheMkIIdevelopment weremet.Further physiological testing isplanned, toquantify thepotential benefits toEVAcrew. 101
Conclusion Thisprojectrepresents asignificant stepforward inpoweraugmentation technology forspace applications. TheMkIIactuator fitseasilyonthebackofagloveandcanreduce MCPtorqueby90%. Theseresultsdemonstrate thataverysimplesystem withnointrusive sensors orcomplicated feedback lawscanperform verywell.Packaging andpowerrequirements aremodest enough toallowmultiple degrees offreedom onthespacesuit tobeassisted; asmanyasthreeonthegloveitself.Suchsystems couldbeanenabling technology forfuturedevelopments suchasthe55kPa(8psi)spacesuit and planetary exploration suits. Inaddition totechnology validation, several procedural lessons werelearned inthecourseofthisproject. Ourtwo-stage process wasgood:thefirstdesigniteration toproveoutconcepts andvalidate hypotheses, thesecond toexplore designtradeoffs andoptimize performance. Concurrent development withtwoteamsinvolving industry/academic cooperation worked surprisingly well;concepts evolved that wouldneverhaveoccurred toeithergroupalone.Keyelements wereearlybrainstorming sessions to cross-fertilize ideasandmakesureeveryone startedonthesametrack,frequent communication, trustin theexpertise oftheothergroup,earlyagreed-upon interfaces, andgenerous designmargins. Acknowledgements Thisworkwassupported underthe1996and1997NASAResearch Announcements onAdvanced Human Support Technology. Whiletheauthorwasresponsible fortheactuator designworkdescribed here,thatwasonlyoneaspectofanexceptional teameffort.Particular noticeshouldbetakenofthe contributions ofDavidCadogan andRobertLingoofILCDover,Inc.forglovedesignandfabrication, the development ofpoweranddatasystems andphysiological testingbyElizabeth Sorenson, control software byDr.RobertSanner, andafinejobofprincipal investigating byDr.DavidAkinoftheUniversity ofMaryland SSL. References 1.Callaway, R."Advanced EVASystems Program Plan,"NASA,Washington, D.C.,1994. 2.Cleland, J.,andWinfield, D.,"NASAWorkshop Proceedings: Extravehicular Activity Gloves," Research Triangle Institute, 1985. 3.Eppter,D.,andCallaway, R.,"Managing EVATechnology: thePresent andtheFuture," Space Programs andTechnologies Conference, Huntsville, AL,1994. 4.Kosmo, J.,"Rolling Convolute JointforPressurized Glove," NASATechBriefMSC-21628, 1995. 5.Lapham, B.,andLacey,D.,"Astronaut EVASymposium," Johnson SpaceCenter, 1994. 6.Main,J.,Peterson, S.andStrauss, A.,"Power AssistEVAGloveDevelopment," 22ndInternational Conference onEnvironmental Systems, Seattle, WA,1992. 7.Sorenson, E.A.,Sanner, R.M.,Howard, R.D.,Akin,D.L.,Lingo,B.,andCadogan, D.,"Development ofaPower-Assisted SpaceSuitGloveJoint,"27_hInternational Conference onEnvironmental Systems, Tahoe, NV,1997. 8.Sorenson, E.A.,Sanner, R.M.andRanniger, C.U.,"Evaluation ofaPower-Assisted SpaceSuit GloveJoint,"Proc.IEEESMCConference, Orlando, FL,I997. 9.NASA-STD-3000, Rev.B,"Man-Systems Integration Standards," July1995. 102
AnEnergyAbsorber fortheInternational SpaceStation BobWilkes"andLoraLaurence" Abstract Theenergyabsorber described hereinissimilarinsizeandshapetoanautomotive shockabsorber, requiring aconstant, highloadtocompress overthestroke,andself-resetting withasmallload.The differences intheseloadsoverthestrokerepresent theenergyabsorbed bythedevice,whichis dissipated asfriction. Thispaperdescribes theevolution oftheenergyabsorber, presents theresultsof testingperformed, andshowsthesensitivity ofthisdevicetoseveralkeydesignvariables. Introduction Theenergyabsorber described inthispaperwillbeusedontheCrewEquipment Translation Aid(CETA), ontheInternational SpaceStation(ISS).TheCETAwillbeusedbyextravehicular crewmembers to movelargeormassive piecesofequipment neededforrepairormaintenance alongtheISStruss.The CETAisahuman-propelled trolley,confined toridealongthetrussrailsystem,whichextends thelength ofthestation. Crewmembers willinserttheirfeetintofootrestraints ontheCETA,andpullthemselves andtheircargoalongthetrusswithahandoverhandmotion. TheCETA,showninFigure1,canweigh upto9,790N(2200Ibf)whenfullyloadedwithcrewmember andcargo,andtravelatupto0.91m/s(3 ft/s). Figure1.CETA,unloaded andwithout crew Thepurpose oftheenergyabsorber istoprotecttheCETAfrominadvertent collisions withISSrailstops bykeepingcontactloadstoadefinedmaximum. Itwillfunction asabumper, collapsing uponcontact, andre-extending itselfafteracollision. Itmustbeapassivedevice,operatefor15yearsofvacuum, atomicoxygenandultraviolet radiation exposure, andrequirenomaintenance. Additionally, theloads neededtocollapse theenergyabsorber mustbeconstant andpredictable overalargethermalrangeand iLockheed MartinSpaceOperations, Houston, TX NASAJohnson SpaceCenter,Houston, TX Proceedings ofthe34_Aerospace Mechanisms Symposium, GoddardSpaceFlightCenter,May10-12,2000 103
thelifeofthedevice. Theloadof2535N(570Ibf)mustneverbeexceeded, andaminimum of420N-m (308ft-lbf)ofenergy mustbedissipated. Background Thisdeviceistheculmination oftwoindependent designanddevelopment effortsperformed by Lockheed MartinSpaceOperations (LMSO) underthesupervision ofCrewandThermal Systems Division atNASAJohnson SpaceCenter. Theenergyabsorber development effortthatthispaperdocuments beganinMay1999,andresulted inISScertification ofthedesigninDecember 1999.Theprevious development effortandinitialconcept generation waslargelytheworkofClarence Wesselski, which culminated inUSPatent5,423,400 filedonJuly29,1993andwasdescribed ataprevious Aerospace Mechanisms Symposium asaposterpaper[1].Thispaper,however, willdescribe thechanges madeto thedesign, discuss testingofthemechanism, andexplain whyeachchange wasnecessary. ,, 71.7cm(28.5in) _i _1 _i_| _LlnconelShaf t 8.3cm(3.25in)diameter _ 27cm(10.9in) - strokelength Figure2.CETAEnergy Absorber Envelope Theenergyabsorber ispictured inFigure2.Itconsists ofatelescoping shaft,whichaxiallycollapses due toanapplied external loadaboveapre-defined threshold. Theapplied loadisfurtherlimitedfrom increasing aboveanupperbound,overthelengthofthestroke. 2000 1800 1800 t400 t2004000 800 6O0 400 20OiiIT 0 5 1D 15 20 25 30 ShaftDisplacement (cml Figure3.CETAEnergy Absorber Performance 104
Theshaftpushesthroughasetofberylliumcopperdiaphragmelementslocatedwithinthehousingthat mechanically interferewiththeshaft,producingtheresistancetomovementthatdissipatesenergyas friction.Theshaftismadefromlnconel718,anditiscoatedwithaverythinfilmofBrayco815Zoil.The diaphragms areC17200BerylliumCopper,whichhavenotbeenaged(precipitation hardened). Onthe compression stroke,aspringelementthatwillbedescribedlatercontrolsthedeflectedpositionofthe diaphragms, whichwilldeterminetheloadnecessarytopushtheshaftthroughthem.Thereturnstroke allowsthediaphragms toflexfreely.Asaresult,theyprovidelittleresistancetomotioninthisdirection. Figure3illustratestheCETAenergyabsorberperformance. Thethreephasesofoperationare:initiation, control,andreset.Theforcerequiredtoinitiateshaftmotionrisessharplytotheoperatingloadofthe device.Itthenremainsfairlyconstantoverthestroketobothlimitcontactloadsandabsorbtheminimum energyrequiredtoeffectacompletestopoftheCETA.Theresetoftheenergyabsorberoccurs automatically. Theareacircumscribed bythecurveshowninFigure3representstheenergyabsorbed bythedevice.Figure4showsthepredictedstoppingdistancesforvariousCETAweightsduringan energyabsorberimpact. 35 3O tlv ,=2+ +1t2O 2 g o: IlO g _5 0 O0.9+,m+C+++)"/ -o.-. (1100lift')! I, 0,2 04 08 0,8 1,0 VelO<itty PriortOCoI!siOll (m/i)I-'Hole' forshaft-,015to .023mminterference (.oc_-+o_) Diaphragm, withthreesymmetrical beam elernents (blades) which interfere withtheshaft. Typical thickness is0.5turn(0.020 in).Astack ofI0isusedfortheCETA energy absorber. Figure4.Stopping Distances fora 1780N(400Ibf)Energy AbsorberFigure 5.Diaphragm Theoperation oftheenergyabsorber isbestexplained bydeconstructing theinteraction between the threeelements (shaft,diaphragms, andspring) ineachofthesethreeoperational phases. Thefollowing section willshowtheindependent effectsofeachelement ineachofthethreephases ofoperation. Energy Absorber Theory Shaft/DiaDhraam Interaction Thediaphragms, showninFigure5,consist of3symmetrical bladesthathavea'hole'smaller thanthe shaftdiameter. Thediaphragms arestableineitherdirection ofshafttravelbecause thebladescanbe deflected ineitherdirection. Changes inshaftdirection resultinthediaphragms 'popping through' theflat position, whichismeta-stable, andinverting. Thiseffectissimilartothatwhichcanbeobserved onfast fooddrive-through sodalids.Typically, thelidwillhaveaseriesofdomeshaped buttons thatindicate whattypeofdrinkisinthecup.Thedomesarestableintwopositions, theup'asmolded' position, and theinverted position thatoccurswhenitispushed. Theflatposition isunstable, andthedomewill'pop through' thisposition, infavoroftheothertwo. 105
Figure6illustrates theinterference fitofthediaphragms ontheshaftandshowstheforcesactingonthe diaphragms. Fromthefigure,itcanbeseenthatmotionfromrighttoleftcanoccurrelatively easily,as theshaftmotionisinthedirection ofthedeflected diaphragms, andslidingcanbeginatalowshaftload. Shaftmotionfromlefttorightwillcausethediaphragms topinchtheshaft,asthediaphragm bladesgo intocompression, andcreatealargenormalforceontheshaft.Iftheshaftforceislargeenoughto overcome theresistance tomotioncausedbythediaphragms, theywillpassthroughtheneutralposition andinvert.Itisonlyafterthediaphragms haveinverted thatanyslidingmotionoccurs. Whenthe configuration showninFigure6ismeasured intest,theforcevs.displacement curveofFigure7results. Figure7showstheforcesthatthediaphragms exertontheshaftpriortoinversion, whichareequaltothe housing reaction. Intheinitialization phasethereisessentially norelativemotionbetween thediaphragm insidediameter andshaft,andthereisnosignificant sliding.Thediaphragm edgesrollontheshaftas theydeflectandchangeposition. Itisimportant tonotethatthereaction fromthehousingchanges direction whenthediaphragms invert,andthattheonlyforceresisting motionoftheshaftisthecoefficient offrictiontimesthenormalforce(IJN).TheshaftforcecannotexceedIJN.Beforeslidingbegins,the shaftforcewillalwaysbelessthanpN. co.tadpo_on-0 (deflect) I/.//j i i Fs<IJN Fs"RH4_00 I-k_Reod_on 70. R. eo. 500 . 200 too Nof_liF_ o_.... ? Diaphragms _m!_t Figure6.Shaft/Diaphragm Interaction Figure7.Housing Reaction Duringthefunctioning oftheenergyabsorber, thediaphragm deflection iscontrolled bythespring element. Figure8illustrates theinteraction ofthespring,shaftanddiaphragms. Whentheshaftisbeing pushedpasttheflatposition, thediaphragms 'want'tofullyinverttowards thedirection oftravel.They thenhitthespringelement, whichprovides resistance tofurthermotion. Thespringelement will compress andallowthediaphragms todeflectfartheriftheshaftforceishigherthanthespringelement force.Thusly,anequilibrium positionisreached. TSeI_hragms havelessnormalforceontheshaft thefarthertheydeflectfromthefiatpositionduetoreduced interference withtheshaft.Thespring element compresses, increasing resistance asthediaphragms deflectit.Thediaphragms willdeflectto thelocationwheretheseforcesandahousingreaction forcebalance. Table1summarizes theequations thatareusedtomodeltheCETAenergyabsorber. Figure9shows typicalcurvesforthehousing reactionandthespringelement, andhowtheydetermine theshaftforce. Notethatthereisasmalloffsetbetween theshaftforceandthespringelement force,whichproduces a moment thatisnotaccounted for.Thiscontribution hasbeenneglected forsimplicity, sincetheoffsetis only0.5mm(0.020in).Asaresult,thehousing reactionforcereported hereinislowbyabout6%. Because ofthemanyvariables thataffectthedragalongtheshaft,suchastheamountorpresence of lubrication, thesurfacefinishoftheshaft,thetemperature, orthetolerance variations oftheshaft/ diaphragm interface, thespringelement Isneededtoallowthediaphragms tovarytheirangletotheshaft dynamically duringoperation oftheenergyabsorber. Thespringelement canbethoughtofas 106
determining the'setpoint'ofenergyabsorberoperation,sothatanydiaphragmdeflectionthatisneeded tomatchthespringforcecanbeaccommodated. C_'da¢lp_ibon-0 Heullng Readlon -RH  I1 ( Fs<&JN F.-F.-R.4SpringElement 7I_'rmdForceN _.....Diaphragmsr2soo Fu.,.,..__ '°°°/,oooI /" o .logo, ,_,m,__ I_ 0 1 3 4 2 I_pi_ merit(mm) Figure8.Interaction ofthe3Elements Figure9.Initialization Model Table1.Govemlng Equations !,Bef(xediamraom inwwsiom &mdMcx)ntact Fs=I_ 2.Beforedlaphraam Inversion. literS.lPfl.rmcontact Fs:Fie+R. 3,Afterdlaphnmm Inversion &smlnacoetKt Fs=F_-R. RefertoFigures6and8fordefinition ofvariables Itisalsothefunction ofthespringtoassurethattheenergyabsorber resetsitselfafteracollision. To fulfillthisfunction, thespringmustbecapable ofdrivingthediaphragms backtotheirodginaldirection. Testinghasdemonstrated thatthediaphragms mustbedisplaced 0.76mm(0.030in)beyondtheflat positiontoassurethattheywillenergetically continue toinvert.Asmallzoneexistsaboutthefiatposition thatisstableduetofrictionwithinthesystem. Even0.25mm(0.010in)lessthanthisdisplacement may resultinlossofreliablereset,withtheshaftpotentially poisedina'hairtrigger'configuration, collapsed, butrequiring onlyasmalldisturbance tosuddenly extend. Thepointatwhichthediaphragm deflection contacts thespringandsubstantial springforcealsocannotoccurtoofarfromtheflatposition. Increasing theinitialcontactdistance substantially to1.5mm(0.060in)allowsthediaphragms tocontact thespringbeforetheyhavedeveloped asubstantial interference withtheshaft.FromTable1: Fs<IJN Fs=FSE+RH Therefore, FSE+RH<pN 107