ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
TheAzimuth Ringis4metersindiameter andcanbedisassembled intofourquarter arcsections; each quarter section weighs 10.4kg(23Ib).Fourleveling jackscrews areprovided toprevent rocking ofthe SFGonuneven terrain. Toallowforassembly bytwopeople, theZenithArcisattached totheAzimuth RingSideSledsusingtwopinnedconnections onaclevisassembly. Thisallowsforquickassembly by oneperson, whiletheotherholdsthetrussinposition. DriveSystem Theinstrument sledthatcarriestheGER3700,andtheAzimuth basering,aredrivenwithidentical 0.4HPbrushless DCmotorsshowninFigures 6&7.Themotorshavearatedspeedof3,900RPM,0.8N-m (7in-lb)continuous torqueandapeaktorqueof3.4N-m(30in-lb).Eachmotoriscoupled tothetiming beltdrivepulleythrough adirectcoupled 30:1planetary gearhead. Eachendofanopen-ended polyurethane timingbeltisfixedateachendoftravelforbothzenithandazimuth drives. Thetimingbelt selected is30mmwide,hassteelreinforcement cables, andhasanAT5toothdesign, 5mmpitch.The toothed drivepulleyhasidlerpulleysoneachsidetomaintain agreater than180°raparound thedrive pulleyandprovide therequired toothengagement (Figure 8).Theidlersalsokeepthebeltclosetoits fixedposition andbelowthebottomofeachdrivesled.Oneendofeachbelt-end attachments hasan adjustable pretensioning latchtopretension eachbelttothere(uiredloadafterassembl, Figure 6.Instrument SledDriveMotor Figure7.Azimuth BaseRingDriveSled Figure8.Installation ofBeltDrive 171
Theuseofguiderollersfortheinstrumentsledandazimuthbaseringwasselectedovertheuseofan off-the-shelf THKstainlesssteelguidetrackandcarriage.Thelead-timeassociatedwithfabricatinga curvedtrackwasthreemonths.Inaddition,thenetcostforthestructureandinstrumentsledwouldbe 50%greaterthanfabricatingcomponents andeachtrusshalfsectionwouldhaveaddedanextra5kgto thestructure.TheSFGisintendedtobefielddeployable inareaswheredustanddirtcouldseriously affecttheperformance ofaballbearingcarriageassembly. Oneproblemthatoccurredduringthe operationoftheSFGwastrackingoftheazimuthbelt.Tensionfromthebelttotheazimuthbasering sledwoulddeflectthedriveandidlerpulleyscausingthebelttotrackverticallydownward. Toalleviate theproblem,acamfolloweronthesledwasrepositioned tocompensate forthetensiononthebelt.In addition,beltguideswereaddedtothebaseringtokeepthebeltcenteredwiththedrivepulley. MotorDrives Thecurrent controlandcommutation ofeachmotorisprovided byaVariable Frequency Drive.Each motorisequipped witharesolver forabsolute position feedback ofthemotorrotor.TheVFDusesa20kHzPulseWidthModulated converter stagetoconvert theDCpowersourcetoa3-phase variable magnitude andfrequency current supplyforeachmotor. Thisdrivestage,commonly calleda6-pulse converter, ismadeupof6Insulated GateBipolar Transistors and6freewheeling diodes. TheVFDuses theresolver feedback tocommutate the3-phase rotating currentsource inphasewiththefixedmagnetic polesofthemotor. Themagnitude ofthemotorcurrent isalsocontrolled bythepulseduration ofthe PWMconverter. Acurrent sensorintheVFDprovides feedback forclosed-loop motorcurrent control. Thebrushless DCmotorandPWMdriveproduce ahighbandwidth torquecontrolsystem withaclosedloopmotorcurrent (torque) bandwidth inexcessof900Hz. Figureg.TheControl System Control System Thecontrolsystem hardware showninFigure9includes anultra-rugged portable PCwithanembedded GalilPC104 motioncontroller card.ThePC104motioncontroller isa2-axiscontroller withadequate input/output channels toaccommodate theinstrument's operation andcontrol. EachVFDcontains an encoder emulator forconverting themotorresolver dataintoaquadrature encoder output. Theemulated encoder signals areinputtothePC104cardforclosed-loop velocity andposition controlofthezenithsled andazimuth carriage. Additionally, thePC104motioncontroller performs axishoming, end-of-travel limiting, jogging functions, reference targetcontrol, VFDpowerupandenabling, andsystem fault monitoring andcontrol. Withit'sownprocessor, thePC104motioncontroller executes themotioncontrol 172
algorithmsuninterrupted bytaskexecuted bythePC.TheGalildevelopmental software running under Windows N_ontheportable PCprovided command levelprogramming ofthemotioncontrolalgorithms. Thezenithaxisalsoincorporates twoservoinclinometers, onemounted onthebaseandoneonthe zenithsled,forabsolute zenithanglefeedback. Theinclinometers werenotusedforclosed-loop control, butwereusedfordisplay purposes only.Itwasfoundthatwiththemotorresolver, coupled tothetiming beltthrough thegearhead, itwaspossible toachieve precise position controlofthezenithsledand azimuth carriage. Oncethedriveswerehomed, eachaxiscouldbepositioned tobetterthan1/loofa degree. Onceproperly tunedthemotioncontroller produced averysmooth acceleration, repositioning anddeceleration downtothenewposition setpoint. Theportable PCprovides theoperator interface foroperation andcontroloftheinstrument's positioning system. Theoperator interface formonitoring andcontrolwasdeveloped usingVisualBasic.Windows foroperation andcontrolinclude achecklist forstartup, motioncontrol, alarmsandmessages, andstation editor. Thismotioncontrolwindow allowstheoperator toinitiatehoming, axisjogging, andexercise and scanreference target. Thealarmsandmessages window displays system faultsandmessages generated inthePC104motioncontroller. Thestationeditorgenerates andstoresazimuth andzenith positioning matrices. Therequirements specify thatthepositioning matrixwithrepeating 15°increments alongthezenitharcevery30degrees ofazimuth baseangleforatotalof66measurements. Thestation editorallowsanycombination ofazimuth andzenithanglestobeentered, eithermanually or automatically byentering rangeofmotionandpositioning increment foreachaxis.Anygenerated position matrixcanbesavedandreloaded forrepeated use. Sinceitisdesirable totakeahemisphere ofdatawiththesuninoneposition thespeedofinstrument positioning anddataacquisition weredefined askeyrequirements. Toautomate theprocess of instrument positioning anddataacquisition, themotioncontroller PCcommunicates withthe spectroradiometer PCthrough anRS232seriallink.Parameters arepassed between thetwoPCsto initiatemotionanddataacquisition. Also,theseparameters contain information aboutreference target position anddata.Themotionsystemforeitheraxiscanreposition overa15°arcislessthan1sec. Dataacquisition bythespectroradiometer takesapproximately 3sec.,dependent onthenumber of integrations bytheinstrument. Theexisting system isabletoexceed thespecified requirements, taking thedefaultmatrixof66measurements inlessthan5minutes. AutoCalibration System Sincethesun'sposition isalwaysinmotionandchanges intheatmosphere canoccur,theSFGdesign incorporates anautomated calibration devicethatusesaSpectralon targetthatrotatesintoviewofthe spectroradiometer (Figure 10).Thespectroradiometer iscalibrated everytimeitpasses theNadir position ontheZenithArc.TheSpectralon targetisplaced28cm(11in)fromtheinstrument's foreoptic lens,allowing calibration without shadowing whenusedatlatitude greater than16degrees. Figure 10.Calibration Arm 173
Operational Considerations TheSFGcanbeeasilymovedonhardsurfaces usingthebuiltincasterassembly. UsingC-channel rails, theSFGcanbemovedtodifferent locations onuneven surfaces. Allcomponents havebeendesigned to minimize weighttoallowforassembly inremotelocations. TheSFGcanrunon120VACoronsupplied DCGelCellbattery packs. Conclusion Manufacture oftheSFGcommenced inOctober 1998andcompleted inMay1999.TheSFGwas delivered toStennis SpaceCenterandiscurrently operational. TheGoniometer hasbeensuccessfully deployed withrepeatable resultsafterbeingassembled anddisassembled overseveral dozencycles. A testofthepointing accuracy wasperformed usingalasertoseehowwellthespectroradiometer could trackthecenteroftheSFG.Thepointing accuracy wasmeasured at+1.2cm,whichiswellwithinthe required rangeof+3.5cm.Assembly timeforthegoniometer istypically under30minutes. Once assembled, theSFGisabletoperform itsdefaultsetof66measurements inundersixminutes whichis fasterthanthetargetgoalof8minutes. Wearontherubberrollerslocated ontheinstrument sledhas occurred fasterthananticipated. Thereisalsoconcern regarding overheating ofthecomputer sincethe instrument isusedindirectsunlight forprolonged periods oftime. Asample ofdataobtained fromtheGER3700isshowninFigure11.Thisdatashowsthereflectance of lightat2307nmforvarious angles. Thereflectance dataobtained creates aspectral fingerprint thatcan beusedtoground truthhyperspectral images takenfromaircraftorsatellites andcorrectdistortions caused byBRDF. 2:SD7nrn 2.0 1-'5 "_1.2 OFigure 11.Spectral Fingerprint ofgrassat2307nm References 1.Sandmeier FieldGoniometer Project Management Plan,Doc#A92C-9801-X100 2.Requirements Document ForSandmeier FieldGoniometer, Doc#A92C-9801-X101 3.Sandmeier, Stefan, et.al."Acquisition ofBi-directional Reflectance DataUsingtheSwiss FieldGoniometer System (FIGOS) in:Proc.ofEARSeL Symposium, Basel,Switzerland, 1996.Balkema Publ.NL,pp.55-61. 4.Sandmeier, St.,andK.I.Itten,AFieldGoniometer System (FIGOS) forAcquisition of Hyperspectral BRDFData,IEEETrans.Geoscience andRemote Sens.,accepted. 174
MotorRedundancy Concepts: Efficient orReliable? EricFavre" Abstract Whenaredundant electric motorisrequired toactivate amechanism, atrade-off ismadeinorderto determine whichtypeofredundancy toimplement. Thispaperpresents thefivedifferent designoptions available forthemotorredundancy, withanemphasis ontheirrespective andrelative performances and comparing boththeiradvantages anddisadvantages. Theimpactofconsidering aredundant motoratsubsystem level(mechanism) isalsoaddressed. Introduction Whentrading-off theredundancy concepts forelectric motor-driven mechanisms, twobasicoptions are possible: tohaveeithertwoseparate motorsonthesameshaftortohaveonlyonemotormechanical and magnetic element withbuilt-inelectrically redundant windings. Forthesetwooptions, fivedifferent designs canbeconsidered, eachhavingdifferent impacts onthefollowing motorperformances: Theriskofhavingafailurethatsimultaneously damages themainandtheredundant parts(singlepoint failure); _,Aglobalperformance degradation whenafailureoccursinthemainwinding, theredundant winding beingusedasthesparepart; Themotor's nominal performances (i.e.,torquecapability, powerbudget) whenonlyonewinding is energized (mainorredundant winding); >.Themotor's performances whenthetwowindings aresimultaneously energized (mainandredundant windings foranemergency over-torque scenario). Thefollowing mainpointsareaddressed inthispaper: Apresentation ofthedifferent available redundancy options; Adiscussion oftheirrespective performances; :_Acomparison oftheirrelativeperformances; :_Ananalysis oftheimpactatsub-system level(mechanism) ofconsidering aredundant design(i.e., cost,mass,packaging). Theseinputsshallprovide therationale behindtheselection ofagivenmotorredundancy concept, enabling themechanism designer toselectthebestoptionforgivenprojectneeds. Lessons Arising fromaMotorFMECA Agoodintroduction tothedefinition ofthepossible redundancy concepts isprovided bytheanalysis ofthe potential causesoffailures observed onelectric motors. Tableisthesummary ofafailuremodeandeffects criticality analysis (FMECA) performed onaframeless motor(electric /magnetic parts). Aredundant brushless two-phase motorisconsidered, usingpermanent magnets (i.e.hybridstepper orpermanent *ETELAerospace Inc.,Boulder, CO Proceedings ofthe34_Aerospace Mechanisms Symposium, Goddard SpaceFlightCenter,May10-12,2000 175
magnetsynchronous motors),whilefailureslinkedtotheeventualuseofDCbrushesareexcluded.The failurecausesareidentifiedandclassifiedintothefollowingtwocategories: .Feilures Causes tobeSecured byD._sign, Manufacturinq Pro(;_sse._ &Procedures _,Statorlaminations freetomovewithinthemotorhousing Motorrotorpartsfreetomovewithrespect tothesub-system rotating parts _,Looseorbrokenmagnets Inadequate cabledesign/handling (transport, integration, tests)atmotororsystem level Mechanical shock/stressonthewinding(s) Failure._that couldRequire theImplementation ofaRedundant Path _,Failureonawinding solderjoint(opencircuit) Awinding's dielectric insulation failure(short-cut) _,Thermal stressonthewinding(s) _,Magnets demagnetized byover-temperature Inputproblems totheelectronic driver Theimplementation ofaredundant winding pathisareliableoptionincaseof(1)havinganopencircuitin themainwinding and(2)forelectronic driverfailures corresponding toanopencircuit. Forthefailuremodesleading toapartialortotalmainwinding short-circuit andformotorswitha continuously activepoleexcitation (i.e.created bymagnets, asgenerally considered forhybridstepper motorsandsmallsizebrushandbrushless DCmotors), abraking torqueoccurswhentherotormoves. Thisbraking torqueisduetoinduced eddycurrents intotheshort-circuited coils,theshaftmotionbeing eithercreated by(1)theuseoftheredundant pathor,simply,(2)byanapplied external shaftload.The valueofthisbraking torquedepends onboththespeedandthefailedwinding electrical characteristics and isnotnecessarily greatest atthehighest speeds. Inanycase,theresultofashort-circuit failureisreduced motortorquewhentheredundant pathisused,duetothisbraking torquecomponent fromthefailedwinding path.Ifthisbraking torqueisnotnegligible /manageable, theefforttoeliminate theriskassociated with thisdegraded performance wouldnecessitate lessefficient motortechnologies [1],avoiding theuseof permanent magnets. Electronic driverfailures thatleadtoawinding short-circuit alsocreatethedegraded performance duetothe short-circuited winding's braking torque. Theriskofhavingsuchafailuremustbemitigated asmuchas possible byanadequate electronic design. Generally, however, otherreliability concerns prevailatagiven stageandasmallriskofhavingsuchafailurestillremains. Athermal over-stress hastwomajorconsequences: (1)todamage thewinding and(2)todemagnetize the motormagnets, ifany.Intermsofaredundancy concept, themajorconcern istohaveadesignwhich avoidstheriskofhavingacommon failuremode(simultaneously damaging themainandtheredundant paths)orsinglepointfailure. Afrequently considered alternative istosecurethedesignbyhavingsufficient designmargins withrespect totemperature. Inshort,intermsofaredundancy concept, thefollowing guidelines shouldideallybeconsidered: suppression ofcommon thermal pathsbetween bothmainandredundant motorparts;andprohibiting the useofpermanent magnets if(1)thebraking torqueintheshort-circuited mainwinding(s) cannotbe managed bytheredundant pathand(2)themagnet(s) maximum temperature isnotsecured bydesign margins. 176
Sub-System Constraints Atsub-system levelandintermsofmotorselection, thegiventorque/speedworking conditions mustbe fulfilledwiththefollowing specified ortargeted constraints: Tohavealimitedpowerallocation _,Tohavelimitedmassanddimension budgets _,Tohaveacceptable sub-system reliability figures Tolimitthemechanical complexity Tohavealimitedprojectcost Disregarding thesub-system reliability, theredundancy concept worksagainst everyotherpointlisted above. Anexample isshowninFigure1,demonstrating thevoluminous cablingneeded foraredundant three-phase brushless DCmotor,builtwithanintegrated Hallsensorcommutation device. Thispicture emphasizes asomewhat obvious conclusion: apriceispaidfortheredundant pathandthelimitwillbe givenbythetrade-off between overallperformance andreliability issues. Figure 1.European Robotic ArmFrameless Motor(ETEL) Amoremarginal sub-system concern isthepotential increase ofthemotortorquedemand duetothe implementation oftheredundancy itself.Atypicalcaseistheincrease ofthemotor's internal magnetic friction(bothdetentandhysteresis torques) duetothefactthataredundantly woundmotorislarger.This aspectshould, atafirstglance, drivethepreference ofmotortechnologies awayfrompermanent magnets, butthelargerefficiency ofthelattermakesitpreferred. Considered MotorTechnologies Theanalysis ofthepotential motorfailuremodeshasshownthatoneshouldconsider notusingpermanent magnets. Ashorttrade-off ofmotortechnologies ismadehereafter. Readers requiring moredetailed information shouldreferto[1].Threedifferent motorcategories areconsidered here:oneusingpermanent magnets tocreateaDCexcitation field;onenotusingit;andthetechnologies notworthconsidering further duetootherreasons. Thetargeted motorperformances typically rangefrombelow1N-m!50Wand marginally upto5N-m/1,000W(or150in-oz/50W&700in-oz/1,000W). Technoloqies Excluding theUseofMaqnets _,Variable reluctance motors (Figure2).Thistechnology isonlyusedinverycoldconditions (typically below-200°C) whereitsinherent veryhighcopperlossesaresignificantly reduced duetothedropofthe copperresistance. Thisistypically aregularcandidate forcryogenic applications. _,Induction motors. Forspaceapplications, itspoorefficiency makesthesignificantly moreefficient brushless DCmotorapreferred solution. Bothtechnologies workinsimilartorque-speed rangesand requireasimilarelectronic driver.Indeed, thekeyadvantage ofinduction motorsonEarthisthe availability ofa60-Hz/AC powersupply, unavailable onmostspacecraft. 177
Technolo0ies UsinQMaqnets Forperformance reasons, thefollowing technologies areconsidered inmostspaceapplications. Theymust beselected onacase-by-case basis,depending uponthespecific mechanism's performance [1]. _,Hybridstepper motors(Figure3),withadesignoftenreferred toas"pancake", combining magnetic yokesandaxiallymagnetized magnets ontherotor.Thisdesignisconsidered furtherinthispaper whenperformance comparisons aremade.Itisdescribed indetailin[2]. Permanent magnet synchronous motors, oftencalled"brushless DCmotors" (Figure4). _,BrushDCmotors. Unsuitable Technoloaies Thefollowing technologies arenotconsidered inthispaper,eitherbecause theyareoutofscopeordueto theirmarginal usetnspaceprograms forperformance, heritage orindustrial maturity reasons. >SalientpolebrushDCandsynchronous motors. Thistechnology avoidstheuseofpermanent magnets forthemotorDCexcitation forbothbrushandbrushless technologies yetisonlyusedonrelatively large sizemotors. Commercial unitswithsizesgenerally required forspaceprograms arenormally made withpermanent magnets. >Single-phase motors >Hysteresis andHomopolar synchronous motor >Electrostatic, Piezoelectric, Paraffin orShapeMemory Alloy-actuated motors. Conclusion onMotorTechnoloaies Inshort,forperformance reasons, motortechnologies prohibiting theuseofpermanent magnets arerarely usedinspaceprograms. Theselection oftheredundancy concept must,consequently, manage this practical reality. Figure2.Reluctance Stepper Motor Figure 3." !iA Hybrid Stepper Motor 178
Figure 4.Space-Rated Brushless DCMotor(ETEL) Design Options fortheMotorRedundancy Thefollowing twobasicoptions areavailable foraredundant motorandeachoptioncanbedesigned in different ways.Thesearediscussed indetailinthischapter :havingtwoseparate motorsonthesameshaft (mechanical redundancy); and,havingonlyonemotormechanical /magnetic part,withbuilt-inelectrically redundant windings (electrical redundancy). Mechanical Redundancy Thefirstideaissimplytousetwoseparate motors: oneforthemainandtheotherfortheredundancy (Figure5-fullmechanical redundancY). Everything isimplemented twice,inparticular themagnetic / electric parts,themechanical housing, andbearings. Foragiventorque-to-power ratio,thebudgets forthe motormass,volume andrecurring costsareroughly twicethosecompared tonon-redundant units.Incase ofthermal failureduetotheheatrejection ofthemotoritself,thisredundancy concept isveryreliable. This reliability advantage is,consequently, lostforthermal failuresduetoanenvironmental thermal overload, likelytosimultaneously heating boththemainandredundant motors. Asimplified optioncouldalsobeconsidered inthiscasebyusingthesamemechanical pieces(housing andshaft)forbothmainandredundant electric/magnetic parts(Figure6-partialmechaniqal redundancy). Itis,nevertheless, notalwayspossible toreducethenumber andsizeofthebearings inthiscasesincethe mechanical loadstobesupported undervibration aresimilartothoseencountered inthefirstoption(Figure 5).Thisdesignsimplifies, however, themechanical interface withthesub-system byreducing thenumber ofmechanical partsandlimitingthemanufacturing recurring costs.Theriskofhavingboththemainand redundant partssimultaneously damaged whenathermal stressoccursis,however, difficulttoavoid. Electrical Redundancy Theelectrical redundancy consists ofwinding twoseparate setsofcoils(the"main"andthe"redundant") uponasinglemagnetic lamination stack.Itcangenerally beimplemented inthreedifferent ways,as described hereafter: Thetwosectorelectrical redundancy (Figure7).Thisoptionlimitsthe"physical contact" between both "main"and"redundant" coils,withamaximum "maintoredundant mechanical interference" occurring in zero,twoorafewmotorslotsdepending uponthemotortypeandsize.Asadrawback, oncethemotor ismagnetically saturated, thisdesignlimitsthemotorpeaktorquecapability andrequires morepower foragiventorque. _'Thetwowiresinparallel electrical redundancy (Figure8).Themotoriswoundwithtwowiresatatime (oneforthe"main"coilandtheotherforthe"redundant"). Athermal failurehererepresents asingle 179
pointfailure.Nevertheless, itisregularlyusedinspaceapplications wherethereisminimal inherent riskofcurrent-induced overheating ofthewindings (integrated thermal sensororlowavailable power). Oncethemotorismagnetically saturated, theadvantage ofthissolution isasignificantly highermotor peaktorquecapability andreduced powerconsumption. Thisredundancy concept shouldalsobe considered forapplications havingshorttorqueoverloads (involving currents likelytodemagnetize the magnets). Thisoptionstillsafeguards onewinding incaseofanelectronic orwire-soldering failure. Thesharedslotelectrical redundancy (Figure9).The"main"and"redundant" coilsarewoundallaround themotor,sharing thecoil'sslot,thereby limitingthephysical contact compared tothe"twowiresin parallel" option. Performances areidentical totheprevious option. Itisagoodcompromise between thefirsttwoelectrical redundancy options. Depending uponthespecific motortypeandsize,oneofthesedifferent redundancy options mightnot feasibly beimplemented duetoparticular manufacturing constraints• Themechanical partsareidentical to theoptionconsidered inthepartialmechanical redundancy concept (Figure6),exceptthatthebearing loads inthiscasemaybeslightlylowerduetopossible shortening ofthemotoraxiallength. Finally, electrical redundancy options onlyconsider onesetofmagnets, whichrepresents asinglepoint failureandmustbemanaged viadesignmargins asanyothermechanical parts. m  REDMOTOR- ....... MOTOR --[_ -_ECHANtSM Figure 5.FullMechanical Redundancy. I "\ i IIlllllll V I iiiiii!ii /%I Figure6.Partial Mechanical Redundancy. 180