ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Alternatively, thediaphragms havenothadachance to'bite'theshaftandaresusceptible tobeginsliding motionprematurely. Thistypeofgeometry maycausedifficulty gettingthediaphragms toinvert,andin theextreme, nodiaphragm inversion occurs, andtheloadtocollapse theenergy absorber fallsfarbelow specification. Therefore, forbothreliable inversion andreliable reset,thespringelement mustbecarefully placedwith respect tothediaphragms. Boththeinitialcontact position withthediaphragms andthespringratemust becontrolled. Control PhaseOperation Afterslidingmotionhasbegun,thedragthatthediaphragms produce ontheshaftdepends onthe position ofthediaphragms. Because theshaftisbiggerthanthe'hole'inthediaphragms, maximum interference occursattheflatposition. Ifthediaphragms canbekeptattheflatposition, maximum interference resultsinmaximum forcesattheshaft/diaphragm interface, whichproduces maximum drag. Thedragisleastwhenthediaphragms arefullyinverted, andthereisminimal forcebetween theshaft anddiaphragms. Thisisillustrated inFigure10,wherethecalculated mechanical interference between theshaftandthediaphragms isplottedalongside theforcerequired topushtheshaftthrough agivenset ofdiaphragms. Thenormalforcegenerated bythediaphragms isproportional totheinterference, and thefrictiongenerated isproportional tothenormalforce. 1200 0i  1000 0.08 c 800.-.. 0r06 -: ,oo 0.04 400IL_ 0.02 200 0 ,,0 0 0,5 1 !,5 2 Diaphragm Position fromFlat(ram) Figure 10.ShaftSliding Through FixedDiaphragms Indetermining theconfiguration ofanenergyabsorber foragivenapplication, thenumber ofdiaphragms mustbechosen suchthatthefrictional loadofthediaphragm stackinthefiatposition isgreater thanthe loaddesired. Toaccount forwear,theCETAenergyabsorber isinitiallysetuptooperate atabout1/3 thepeakloadthatthediaphragm stackcanproduce whenflat. Because theshaftdragisproportional tothenormalforce,itdoesnotmatterifthediaphragms areonone sideofflatortheother,orwhichdirection theshaftismoving, tfthedragontheshaftshowninFigure10 isexpanded tobothsidesoftheflatposition, aroughly symmetric curveresults. Iftheconditions arethen changed, suchastodecrease thecoefficient offriction, asecond curvewouldresult.Thepointsatwhich theloadiszerowouldremainthesame,sincethisisaresultofgeometry. Itisatthesetwodiaphragm deflections wherethediaphragms ceasetomakecontact withtheshaft.Thepeakloadwouldstillbeat 108
theflatposition.Varyingthenumberofdiaphragms, thesurfacefinishoftheshaft,theamountorquality oflubrication, oranynumberofotherfactorsaffectingthecoefficientoffrictionallchangethecurveinthe sameway.Figure11illustratessuchafamilyofcurves. ..._a# Force Typ_.,_hm_ofcurves /I\ foragiven_Jo_/_...t_ Mixload.....//_/__,_//_'_ .....1_Desiredoperating rangeof MInload-/_/4-,_:---- _- ---_, Energy Absorber -_.Diaphragm Position Umltofcontact 0(_t) Figure 11.Sliding Frictional DragBetween ShaftandDiaphragms Figure11alsoillustrates thedesired operating rangefortheenergy absorber. Notethatallcurvesexcept theonelabeled 'a'and'b'passthrough thedesired operating range. Curve'a'represents conditions that aretoo'slick'.Iftheseconditions arepresent, thedesired loadwillneverbereached. Itisimportant to notethattheenergyabsorber shouldbedesigned toallowthefulldeflection ofthediaphragms. Inthis way,anycondition thattendstoincrease coefficient offrictionwillbeaddressed. Theonlycondition that wouldthenbeofconcern istheslickest condition thatcanoccur.Curve'b'represents areduced interference between theshaftanddiaphragms, aswouldbeexpected duetowearordifferential thermal expansion. Aslongastheslickest, leastinterference condition hasapeakthatisabovetheminimum load,allothersareaccommodated. Thiscanbeassured byspecifying aminimum surface finish,by addingdiaphragms, orbyincreasing theinterference between thediaphragms andtheshaft. Design Development Theenergy absorber asitexisted inJune1999,isshowninFigure12.Theprimary elements ofthe deviceare:theshaft,thediaphragms, andthespringelement, whichinthisdesignisasinglebelleville spring. Duringassembly andtestoftheflightunitsinthespringof1999,therewasgreatdifficulty in obtaining andmaintaining theproperloadsettingofthedevices. Thefirstproblem discovered wasinthe areaofmanufacturing ofthebelleville springs. Theprecise loadneeded fromthebelleville, combined withasensitivity totheinitialheightofthespringforreliable resetmadeitextremely difficult to manufacture. Additionally, duetothefactthatthebelleville canbepressed completely flatbythe diaphragms, theloadofagivenbelleville couldonlybedetermined after'scragging' ofthepart.This involves pressing itflat,whichchanges thepeakloadofthewasher, butdoesnotsubstantially change thespringconstant. Atrialanderrorapproach wastherefore necessary, withtestingrequired beforethe bellevilles couldbeaccepted fromthemanufacturer. Asecond problem, uncovered duringlifecycletesting, wassideloading oftheshaft.Ascanbeseen fromFigure12,theshaftisconstrained simplybyaholeinthehousing. Deposits ofaluminum fromthe housing andsteelfromabushing (notshowninthisfigure)inthecoverwereobserved. Adding Vespel bushings tobothendsofthehousing tosupport theshafteliminated thissituation. 109
Whiletheaboveproblems maybeovercome byadetermined designeffort,themostsignificant problem encountered wouldprovetobeunpredictable, andultimately fataltotheproduction ofarepeatable controlload. Housing ,_ _-_-.......:_-......Y_ -;,:.;.7//////_/2_x.,', Return/ Belleville --"- Spring spring_ Cover  r\,hl,t_ Diaphragms Figure12. 1994energyabsorber usingasinglebelleville washertocontroldiaphragm deflection Referring toFigure5,itcanbeseenthatthediaphragm element contacts theshaftin3locations viathree beamelements, whichwecallblades.Whileeachdiaphragm generally centralizes itselfaroundthe shaft,onceplacedinastack,frictional forcesbetween diaphragms duringoperation keepthemfrom movingperpendicular totheshafttobalance theloadbetween thethreeblades.Thispositional freezing ofthediaphragms iscombined withshaftmotionduetotheallowedclearances aroundtheshaft,the possibility ofoff-axisloadingcases,andthepossible variation offrictioncoefficient atpositions aroundthe shaftitself.Thisallowstheloadofeachbladetovarydramatically. Itisthisasymmetrical loadingwhich isbothunpredictable andirreversibly damaging tothebelleville springelement. Believille springsthat havebeensubjected tothistypeofloadingtypically nolongerhaveaconsistent height,duetolocalized yielding. Inthemostdramatic examples seen,thebelleville iscompletely flattened byonesetof diaphragm blades,andlightlyloadedbytheothertwosetsofblades. Changes insetpointloadof25% havebeenobserved tooccurintwosuccessive cycles.Astheasymmetric conditions mayeasilybe foundonorbitduetoatomicoxygenfluxpreferentially affecting onesideoftheshaft,thisaspectofthe designhadtobeavoided. Inordertomaintain theproperloadingconditions forthespringelement, designmodifications were necessary andnewcomponents wereadded.Oneliesbetween thediaphragm stackandthespring element, anditridesalongtheshaftlikeacollar.Thespringelement thenseesonlyuniformaxial compression fromthecollarandisimmune toasymmetrical diaphragm loading. Attacking theproblem ofmanufacture andsensitivity topositionandspringrateofthespringelement, the authorsdiscarded thesinglebelleville washerinfavorofaspringcartridge. Thespringcartridge contains anumberofbelleville washers whicharemodified fromreadilyavailable stocksizes.Thestackis preloaded onassembly. Byadjusting thenumberofbelleville washers andthepreloadviashims,the necessary performance maybeobtained withoutrequiring tightlycontrolled manufacturing. Also,much largerdiaphragm displacements maybeaccommodated thanwerepossible withasinglebelleville, which allowshighercoefficients offrictiontobeaccommodated. 110
Tosimultaneously achievethegoalofareliablereset,thespringelement isdividedintotwoparts.The mainloaddetermination isdonewithaspringcartridge, whichhasalargetravel,andanadjustable initial loadandspringrate.Theinversion andresetting isdonewithasecond'resetspring',inthiscaseanother belleville washer,whichhasaneasilycontrolled initialposition. Thisarrangement isshowninFigure13. Housing --_X.'_'/mm_z+_r 7/,+_:_]-'--__/_/_ ..,,...._Cover Figure13.SprlngCartrldge Implementatlon Asubtlebutimportant effectistheloadatwhichthediaphragm inversion occurs. Theinversion eventis characterized byalargechangeinthehousingreaction force,asshowninTable1andFigure9.Ifthis eventoccursatornearthesetpointofthespringcartridge, itcancausethespringcartridge tooscillate. Figure14illustrates oneexample ofanoscillating springcartridge, Figure15showshowtheeffectscan beminimized byforcingthediaphragm inversion tooccurwellbelowthesetpoint.Thisisaccomplished bytheuseoftheresetspring,sodiaphragm inversion occursduringitstravel,beforethepreloadofthe springcartridge isreached. IntheCETAenergyabsorber, theseeventsoccurwithinthefirst3mm (0.125in)ofstroke,andtheloadtocompress theshaftstabilizes afterabout6.4mm(0.25in). 1200 t_O0' =_=o0 t4+sO =0oInlUa!Iz_on: Prololype  _DC-phraorn tnvlmlon )" De'mequlredstIl<}'Iz o_ 0 0:2 0-4 0.41 OJl I 1,2 Dllpllceanlnl (mill) Figure14.Oscillating SpringCartridget.4+o0o ts0o _tO00 1IooIdlallZ¢_ -Flgh_Unit o 0,0.-j---,r,+_,..+.',.""_' ..,.++,.,++,_.+ '_I,,.+ _,_ Olmphragm Inversion,,, / DetosquiredatIKHZ 0,5 1,0 Ollp_l¢imlnl (am) Figure15.Oscillations Controlledt.5 Mostimportantly, theforcesupplied bythespringelement mustbecloselycontrolled, astheforce neededtocollapse theshaftisthesimplesumofthespringforceandthehousing reaction. Therefore, thespringrateofthespringcartridge shouldbechosensuchthatthesumofthesetwoisasconstant as possible, whichwillyieldaconstant shaftloadduringoperation. Figure16illustrates thecumulative effectoftheseforces.Itshowshowthenetforceinthenominaloperating positionofthediaphragms is determined. Figure16describes theenergyabsorber performance withrespecttodiaphragm deflection, 111
beforeandafterslidingmotionhasbegun. Itshouldbenotedthattheforce!displacement curveofthe energyabsorber shaftwillonlyfollowthiscurveuntilslidingbegins, because thediaphragm deflection andtheshaftposition onlycoincide uptothatpoint.Thedeparture fromtheinitialization phasetothe controlphasewilloccurwhereindicated inFigure16.Further shaftcompression willresultinsomeshaft loadvariations, butagenerally constant loadistheresult,asillustrated byFigures 3and15. z O !13000 2500 2000 1500 1000 500 0 -500 -1000iit .... Springca_idge__...._ ._, ca_k_eand__ /_ T _housing reacl:ion)_2_,_ _D_leddon el"cliaphragms f _',4/__ _Diaphragm ,rr_erslon must .... /'_,/"coincidewithresetspring 1 2 3 4 Displacement [mm) Figure16.Initialization PhaseSummary Figure17showstheinteraction oftheenergyabsorber system ofFigure16withthevariable friction conditions asshowninFigure11.Theloadtocompress theshaftwillfollowtheenergyabsorber curve, untilitintersects theloadlimitofthediaphragm/shaft frictioninterface, whichisrepresented byaseriesof curves. Theshaftloadwillthenremainessentially constant, because ofthestartofaslidingmotion between thediaphragms andshaft.Asthecoefficient offrictionvaries,theloadtocompress theenergy absorber shaftisgivenbytheintersection oftheenergy absorber curvewiththeappropriate friction coefficient curve.Thisdefines thepredicted rangeofoperating loadslabeled inthefigure. Twoimpediments existtoachieving aperfectly flatforce/displacement curveinthecontrolregion. The firstisthatthehousing reaction curvechanges withtime.Asthediaphragms wear,boththemagnitude andshapeofthecurvechanges. Thematerial attheedgesofthediaphragms isdisplaced, 'smeared' intotheadjacent diaphragms, physically connecting them.Therefore, theslopeofthespringcartridge force-deflection curvemaybechosen tomatchthehousing reaction initially, butthismaychange with wear.TheCETAenergyabsorber usesnon-aged C17200 Beryllium Copper diaphragms, whichare significantly softerthantheInconel 718shaft.Pairsofdiaphragms werefoundstucktogether post-test duetomaterial displacement alongtheshaftinterface. Although thismaterial choiceprevented any significant shaftwear,itistheauthors' expectation thattheagedcondition wouldbothreducediaphragm sticking andincrease overallwearlife. Useofahardermaterial toimprove thewearproperties mayalsoreducehysteresis byreducing or eliminating material transport between diaphragms attheshaftinterface. Because thediaphragms move dynamically duringthecontrolphasetoaccommodate variations inconditions, hysteresis influences the degree ofcontrolthatcanbeexpected fromthissystem. Figure18showsanexaggerated illustration of thepossible effectsofhysteresis ontheshaftload.Theactualeffectispoorlyunderstood atthistime, sincetheamount ofdiaphragm movement thatoccursduringoperation hasnotbeenaccurately 112
measured. Whether sufficient diaphragm motionoccurstoallowthefullrangeofhousing reaction hysteresis toberealized isunknown. 3no0 2500 2000 151)0 iJ _ooo 5OO 0 -500PredickKl__ loodvar_io_n 0/ ! 2 3 4 D_placeme__nm) Figure 17.Predicting System Performance zv ,b O M.3O00 2500 2_00 1500 1000 500 0 -500 -1000SpdngelementF_ _ _. ExI:_Ct ._1IOadvad,_on _._,.-.-_..,,_"f Io.d  t[.,J"Co_IbuUon.,,,/("Opemttonei ofh_risiS /y _ hysted_s .3, .2 -1 0 I 2 D_placement (ram) Figure 18.EffectofHysterisis Thesecond impediment tomoreuniform loadcontrolishysteresis. Thespringcartridge consists ofa belleville washer stackwhichdoesnottouchthehousing ortheshaftoneitherinsidediameter oroutside diameter. The304stainless steelsleeveatthetopofthebelleville stack,showninFigure13,slides alongahardanodized aluminum borewithnolubricant. Thisarrangement hasabout130N(30Ibf)less returnforcethanduringcompression. Thehousing reaction hysteresis canbedetermined fromFigure3. 113
Theratioofthehousing reaction atinitialization tothehousing reaction atresetisinthiscase83%,which istypicalfortheCETAenergyabsorber. Aprobable causeofthisdifference isthatanymotionofastack ofdiaphragms resultsinasmallbutsignificant slidingmotionbetween everydiaphragm inthestack.This canbemitigated somewhat byproviding lubrication between diaphragms, although noworkhasbeen donetodatetofindanacceptable lubricant, andnoneisusedontheCETAenergyabsorber. Testing Aspartofflighthardware certification, theenergyabsorbers aresubjected to3tests:vibration, thermal extreme, andlifecycle.Additionally, theCETAenergyabsorber wassubjected toimpacttestingtoverify thatitrequired aconstant loadtocompress despitevariations incompression velocity. Thissectionshall describe thetests,andpresenthowtheenergyabsorber performance wasaffected byeach. Vibratiort I;_l;inq TheCETAenergyabsorbers areonlysubjecttosignificant vibration duringlaunchaboardthespace shuttle. TheCETAitselfislaunched onISStrusssegment $1,withapairofenergyabsorbers. The vibration testingproduced nodistinguishable effectonperformance. Thermal extreme testinq Thenominal operating rangeoftheCETAenergyabsorbers is-73°Cto+88°C(-100°Fto+190°F). Oneunitwasdesignated thecertification unit,anditwassubjected tooperation from-79°Cto+93°C(- 110°Fto+200°F).Figure19illustrates thechangeintheoperating setpointofthedeviceduetothese temperatures. Table2summarizes theaverage loadsateachtemperature, overtherangefrom0.6cm (0.25in)to26.7cm(10.5in)oftheavailable stroke.Figure19showstheseaverage loadsasdashed lines,andtheverticalbarsdelineate theportionofthestrokeusedforthedatainTable2. =.oo-[11 col, I -79,c(-!lo, 2000 1500 1000 500 0I 0 5 10 15 20 25 30 Displacement (cm) Figure19.Performance vs.Temperature 114
Thevelocityoftheshaftcompression wasaconstant 46cm/s(18in/s)foreachofthesethreetests.As evidenced bythedata,variations inloadduetochanges inconditions alongthelengthoftheshaftare somewhat exacerbated bythereduced temperature condition. FromFigure19,eachcycleincreases loadslightlyduringthestroke,withawavelikevariation from20cmto25cmthatislargerinmagnitude atcoldtemperatures. Table2.Performance atThermal Extreme 93_C !703N 47N1760/1390 N (383Ibf) (11Ibf)(3961312 Ibf) 23°C 1877N 33N1940/1770 N (422Ibt) (7.5lbf)(435/397 Ibf) -79°C 2104N 48N2210/2020 N (473Ibt) (I1Ibf) (498/455 Ibf) Performance Incontrolphase,0.6to26.8crnsboke Therearetwomainchanges duetotemperature thatcouldberesponsible forthechanges observed in average load;differential thermalexpansion, andlubricant viscosity change. Initially,thelubricant was thoughttobethemostlikelycause.Brayco815Zoilisusedtolubricate theshaft,whichexperiences significant changes inviscosity overthistemperature range,particularly at-70°Candbelow.Informal testshavebeenconducted downto-86°C(-122°F),withnosignificant differences observed from-79°C. Thechanges inloadduetotemperature arealmostlinear,whichstronglysuggest thatdifferential expansion effectsaremorelikelytobethecause.Thecoefficient ofthermalexpansion forberyllium copperisabout25%higherthanthatofInconel718,resulting in0.1mmgreaterinterference atcoldthan atambient. Thehottemperature caseresultsin0.07mmlessinterference. Whilethesechanges appear tolooselymatchtheratioofchangeobserved intheload,additional workshouldbeperformed toverify thishypothesis, suchaschanging theshaftmaterial toadifferent thermalexpansion coefficient. 2500 2000 _..1500 Q o u_1000 500 5 10 15 20 25 3O Oisl_¢acemenl (crn} Figure20.LifeCycleSummary 115
Lifecycletestina Thelifecycletestingrequirement oftheCETAenergyabsorber is120cycles. Theactualnumber ofonorbitcyclesisonly60.Asummary ofthecertification lifecycletestingispresented inFigure20.Itis interesting tonotethatnotrendisevident fromthisdata,whichsuggests thatsubstantially morethan120 cyclescouldbeaccommodated. Themaximum number offullstrokecyclestestedbytheauthors is240. After240cycles,thedevicedemonstrated agreater variation inloadalongthestroke,butnosignificant change intheaverage load. Duringanengineering evaluation test,anenergy absorber wascycledwithout anylubricant. Thefirst60 cyclesshowed littledegradation inload.Ataround 70cycles,theloadthattheenergy absorber would requiretocompress theshaftbegandropping witheachsuccessive stroke,suchthatvirtually noload carrying capacity existed bycycle80.Subsequent measurement ofthediaphragms showed thatthere wasvirtually nointerference withtheshaftduetomaterial lossonthediaphragm insidediameter. The lnconel shaftwasvisiblycoatedwithberyllium copper. Conclusion Anenergy-absorbing deviceispresented, planned foruseontheInternational SpaceStation, offering collision protection forthelargetranslating massoftheCETA. Thedevicerequires approximately 1800N (400Ibf)tocompress overastrokeof27.6cm(10.9in),andwillself-reset withanaverage oflessthan67 N(15Ibf)overthestroke. Thekeyelement intherecentdevelopment hasbeentheuseofaspring cartridge toisolateandcontrolthisfrictionbasedenergy dissipation system. Withtheuseofaspring cartridge, aconsistent, knownspringloadcanbeusedtocontrolafrictionbasedinteraction whichmay varyenormously duetomanyvariables suchastemperature, wear,surface finishorlubrication. References 1.Wesselski, Clarence. "Energy Absorber fortheCETA", Proceedings ofthe28thAerospace Mechanisms Symposium, 1994,pp141-146. 2.Boyer,Howard &Gall,Timothy, editors. "Metals Handbook deskedition", American Society forMetals (1985) 3.MIL-HDBK-5F, "Metallic Materials andElements forAerospace Vehicle Structures", (1990) 116
Friction DriveCharacteristics fortheSpaceStationMobileTransporter RichardC.Hughes', DanielE.Hoyt',andJuanL.Carreras" Abstract Africtiondrivesystemfortranslation alongthetrussstructure oftheInternational SpaceStationisdescribed. Alldevelopment, qualification andacceptance testingofthedesignhasbeencompleted andthe flightarticleisundergoing integrated element testinginpreparation foralaunchin2001.Adiscussion of themechanical design,materials selection andtestprogram ispresented alongwithlessonslearned. Introduction TheMobileTransporter (MT)isaroboticelement, whichmovesalongrailsontheexteriortrussofthe International SpaceStation(seeFigure1).TheroleoftheMTistosupportthebuildingandmaintenance ofthespacestation,overits15-yearnominal life,bytranslating payloads androboticmanipulators between fixedworksites onthestationtruss.Ataworksite theMTsupports operation ofalargemanipulatorarmandatwo-armed robot(bothprovided byCanada) bylatchingdowntohardpointsonthetruss andbyplugging intostationpower. Likemostpartsofthespace station,theMTismaintainable on-orbit byastronauts through theremoval andreplacement ofOrbitalReplaceable Units (ORUs). Alltheavionics and majormechanisms ontheMT aredesigned, developed and testedasseparate ORUs. Whenparkedataworksite for operation oftheroboticmanipulator, theMTisfirmly attached tothetrussbyfour LoadTransfer Unit(LTU) ORUs.Whiletranslating payloads between worksites, theMTissupported bytwo RollerSuspension Unit(RSU) ORUsononesideanda LinearDriveUnit(LDU)ORU ontheotherside.TheLDU provides theforceneededtoFigure 1.Mobile Transporter. accelerate ordecelerate theMTpluspayloads andtopullagainsttheTrailingUmbilical System(TUS) whichprovides powerandcommunication totheMT. •TRWAstroAerospace, Carpinteria, CA ""TheBoeingCompany, Huntington Beach,CA Proceedings ofthe34thAerospace Mechanisms Symposium, GoddardSpaceFlightCenter,May10-12,2000 117
TheLinearDriveUnitisafullyredundant device,whichcontains twoindependent frictiondrivesystems plussensorstoprovidestatusandtodetectworksites onthetruss.Theweightallocation oftheLDUwas 116kgandtheactualweightis111kg.Frictiondriveswerechosenbecause theMTneedstonavigate gaps,offsetsandmisalignments intherailsections. Thesubjectmatterofthispaperisthedesignand development oftheLDU,focusing onthechallenges associated withdeveloping thefrictiondrive. ProjectStatus ThebasicMobileTransporter wasdesigned, developed andtestedbyTRWAstroAerospace under contract toTheBoeingCompany. Astheprimecontractor toNASA,Boeingprovides additional components(suchastheTUS)andintegrates theMTtothespacestation. ThebasicMThascompleted acceptance testingandwasdelivered totheKennedy SpaceCenteron 15July1999inpreparation forintegration withthestationtrusssegment onwhichitislaunched. TheMT istobelaunched inmid2001.Thequalification program ofthevariouscomponents oftheMT,suchas theLDU,hasbeencompleted, although openissuesarestillbeingaddressed. LinearDriveUnitDescription Overview Theprimefunction oftheLDUistoprovidethetranslation forcetomovetheMTalongtheexteriorrailson theSpaceStationtruss.TheLDU,depicted inFigures2and3,comprises primaryandredundant translation drivesystems, primaryandredundant engagement/disengagement (E/D)drivesystems, a bogieassembly, aboosterfootassembly, astructure assembly, Extravehicular Activity(EVA)cams,EVA ORUboltsandEVAlaunchlocks.Thetranslation drivemovestheMTalongthelengthofthetrussviaa pinch-wheel systemthatgripsaflangeonatrussrail.Theflangeispinched between aspring-loaded, highfriction,drivewheelononesideandapairofidlerwheelsattached tothebogieassembly onthe otherside.Onlyonedrivewheelisengaged atatimefortranslation. TheE/Ddrivemechanism is usedtoengageanddisengage thetranslation drivewheelwith thetrussflangeusingageardrivencamassembly. Itis necessary toliftthedrivewheel fromtherailtoeliminate any compression setofthewheel whiletheMTislatchedata worksite. TheE/Ddrivealso performs change-over, cam reset,anddoubleengagement functions. Thechange-over function engages thesecondary translation driveanddisengagesafailedtranslation drive fromthetrussrailtoallow continued MToperation. Acam resetfunction isusedtorepositiontheE/Ddrivecamsafter launchandtorestorethecams toknownpositions afterany failurescenario thatleavestheAssembly Translation Launch Drive Locks Bogie IMCAs AssemblyEngagement] Disengagement DrivetMCAsMT2774 Assembly r--Swingarm Assembly Assembly o0 ^OOIg Figure2.LDUFrontIsometric View. 118