Electrome(;hanical designandoperation Across-section oftheIRACshutterisshowninFigure4andanexploded viewisincluded asFigure5. Tofacilitate thedescription ofthecomponent partsoftheshutter mechanism, theywillnotnecessarily be discussed inorderoftheirassembly withtheunit.Thedescription willstartwiththesuspension system of themechanism, movetotheactuation system, continue ontothestructure andstresslimiting components, andconclude withthesensory components. Suspension System Theshaftassembly (Figure 6)provides thesuspension system forthemirrorpanel.Theshaft,itself,is fabricated ofAluminum 6061-T651. Thecentralhub,themostrobustportionoftheshaft,isdesigned to holdthemirrorandcounterweight. Themirrorpanelisaluminum andhastwodiamond-turned surfaces coatedwithgold.Anarmextends fromthispanelandmatestoafiatsurface machined intotheshaft's hub.Opposite themirror,a0.1058-kg tantalum counterweight isattached totheshaft.This counterweight minimizes theCGoffsetoftheshaft,whichminimizes moments under1Gandvibration. Theshaftalsosupports thetworotorsoftheactuators andtwoA286steelbushings. Asquare holeinthe centerofeachrotorslidesaxiallyovertheshaftandmateswithamatching square profile. Asaresult, eachrotorisfixedinrotation suchthatrelative motionbetween thepartsisnotpossible. Therotorsare fixedaxiallybyanutonathreaded portionoftheshaftateitherend.Thisthreaded portionalsosupports steelbushings thatprovide bearing surfaces forrotation andactastheradialcentering deviceforthe shaft.Thebushings fitintoholesintheendcapsofthemechanism suchthatthereisonly38.1Ilm (0.0015 in)clearance radially. Thematingsurfaces intheendcapsareplatedwithTeflon-impregnated anodize tominimize friction. Finally, theshaftismachined toallowaBeryllium Copper torsionflexuretorundownthecentralaxis. Thiscomponent provides theaxialstiffness required tolocatetheshaftassembly andprovides the restoring torquetoreopen theshutterwhenpoweristerminated. Theflexureischemically etchedoutof 0.66mm(0.026in)thickBeCu25ATsheetandisheat-treated at315.6°C (600°F) for3hourstoobtain thefollowing strength andfatigueproperties at4K:ault/q,yielO/_fatigue=220/190/110 ksi.Ithastwoactive portions, 0.66-mm (0.026in)square and52.1-mm (2.05in)long,andthreeflanges forattachment to othercomponents. Themiddleflangeisattached tothecentralhuboftheshaft.Twoaluminum end piecesareboltedtotheendflanges suchthatthetwoendsoftheflexurecanbefixedinrotation tothe endcapsofthemechanism. Astheshaftrotateswiththeendsfixed,restoring torqueisgenerated in bothsidesoftheflexuretofightthismotion. Thisrestoring torquereopens theshutterwhenthepoweris off. A(;:tuators Theshuttercontains twoactuators builtaroundeachoftherotorsontheshaft(Figure 7).These actuators areelectromagnetic variable reluctance rotarydevices capable ofproviding 45degrees of angular motion, thoughtheshutteronlyrequires 38degrees ofrotation. Theyarecylindrical indesign andconsist ofarotor,twostators, anelectromagnetic coil,andamagnetic "closeout" cylinder. These devices contain noi_ermanent magnets. Hiperco 50A,heattreated toallowhighmagnetic fluxdensity withlittlehysteresis, provides aclosedpathformagnetic fieldsgenerated byanelectromagnetic coil.All components oftheactuator exceptthebobbinandthecoilitself,aremachined ofthismaterial. The activeportions ofthestatorsareradially contained withinthebobbin. Thecoilis99.99% pure38AWG, HAPTZ insulated copperwireprecision woundonablackanodized aluminum 6061-T651 bobbinto 11,000+ turns.Passing current through thecoilgenerates amagnetic fieldthatisfocussed bythestators andflowsthrough therotor.Thecoilwassizedbyanalysis toprovide anNIvaluegreater than600with 60mA.Tocomplete themagnetic circuit,acloseout cylinder coversthecoilandconnects thetwo stators. Themoving portionoftheactuator, therotor,ispositioned between thetwostatorsandisrigidly affixedtoashaftthatrunsdownthecentralaxisofthedevice. Thisshaftmaintains theradialposition of therotorswithintheactuators andtransfers rotarymotiontothemirror. 3