ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Operational Improvements ofaPyrotechnic UltraLowShockSeparation Nut Alexander Luna* Abstract Thedesign requirements andimprovements insatellite platform construction haveoutpaced thedesign evolution ofpyrotechnic separation devices. Demands oftheaerospace industry havequickly moved toward smaller separation devices thatcancarrylargerpreloads andproduce shockoutputlevelsthat canbetolerated bysensitive electronic andopticalpayloads. Hi-Shear Technology ,Corporation's product enhancement effortshavesuccessfully brought itsSN9400 seriesLowShockseparation nuttechnology inlinewithindustry demands bydeveloping theSN9500 seriesUltraLowShock(ULS)separation nut. Thisproduct enhancement hasyielded anewgeneration ofseparation nutswithshockoutputs reduced 75-85% belowtheSN9400 seriesseparation nuts. Introduction Inaddition totherequirements ofhighloadcarrying capacity andlowshockoutput, theaerospace industry strives toretaintheuseofthehighlyreliable design heritage associated withstandard pyro initiator systems, suchassystem leveluseoffiveampere twenty-five voltpulsedpower. Thesesimple powerallocations havebeenthemostwidelyaccepted foractuation ofseparation devices. Twomethods canbeemployed inmeeting thedemands forreduced shockseparation devices, 1) developing alternative methods ofactuation andseparation, 2)Improving theoperation characteristics of current pyrotechnic actuated separation devices. Hi-Shear product enhancement effortsusedthelatterin developing theUltraLowShockseparation nut.ThispaperwillreviewthedesignoftheSN9400 series separation nutfocusing ontheareasthatweremostfruitfulforreducing shockoutputandthesuccessful resultsthatwereachieved. SN9400 SeriesLowShockSeparation Nut BasicDesiqn Parameters Thebasicmechanism construction fortheSN9400 isshowninFigure1.Thedesignparameters areas follows: •ShockOutput: 29,430m/s2(3,000g)-98,100 m/s2(10,000 g) •Leakage: qualified to1x10.4cc/second through theinternal seals •Release Mechanism: piston/cylinder •Actuation Time:lessthan10milliseconds •Initiation Device: NASAStandard Initiator, singleordualcartridge •PowerRequirements: 5ampere, 25voltspulsedpower •Mounting: flangemount •MatingFastener: boltorstud Theory ofOperation 1.Application ofapreload totheseparation nutviaastudorboltproduces aradialloadbetween three threaded segments andthestud/bolt. 2.Thethreethreaded segments andtheradialloadarecontained byalocking ring,whichisfastened to acylinder. Thethreethreaded segments aremounted overahard-mounted keyedbase.Thesekeys lockthesegments andprevent rotation. Hi-Shear Technology Corporation, Torrance, CA Proceedings ofthe3_hAerospace Mechanisms Symposium, GlennResearch Center,May15-17,2002 NASA/CP--2002-211506 131
m_ z__r'c DATE/TIME:ThuSep06Ol04:36TESTENGINEER :A.Luna TESTITEM :HSTCP/Ng364594-1 TESTTYPE:ShockResponse IMPACT LOC. :g400SeriesSepNut TEST MACHINE : iiiiiiiiiiill iiiiiii++i+i...........iiiii!iii......iiii Iiii!i!i?iiiiiii?iiiiiiii_iiiiiiiii_i_ii_!i?5!?!!.._:'i!!_?i!?!_?i!i!?i?i_.i!i?!ii_i??i!i?ii_iiiii_iiiii}ii?i}ii_ii_i_?: _?ii?_f! .:-:,.i?iiiiil?iiiii_:iii!_iiii!:i?_ii_i_!i .................. ;............__'_}IN_ .................. i...........}ii__ ".....i;...........I!.................... }-i_i_ .................. _...........,::_...--.+-..-_..-+..!-..i..._-i ................... _..........._..-,.-+-...-i.... -/................................... _--.i...!..-,-+ _?!!!?)!!!!?!!!!!!!!!!!!!i!!)! !!!)!)?!!?!!!!!!!!!!)14!?!!!!?!!!!!!?!!! .................. _.....!...--.-+..-.._.-+.-_..-!.._..i ................... ;.........,_--'.._-.,_....-.i.... _.._..;.-_.............................. I........... _!!__ •__-.-:--t-_---.T- >--;-_-?--_--?_"_! ............................... ............. ___?t 18-_-:-:...-.:_,...',.:::i..._.:; ...... .......... ........................ _........._.............. -,,_L,,.:_:_..,:_.:::.....,:_..:.:::::,:c::,:::_::.:.:::.._::_..-.: '.;.:._:!!:.!!:.!!!!L!!: ,:.................... _:_.,_:_.-.._-,_. .................. ...........;.......'...,,...>...._._..._..3._, .................. L.........._,...-..L.....'L...3......3..L, r................... ;................. _......L...'..._..L..L °_.:............_.........._.;''......._.._.._...!.._.i ..................._..........!......._....i...!.."+..._..i..l ............................. i.......l.-._:..!...i...i...i • 18 188 1888 _ooo 18B_ Pre_em_ (_) C_II.III_| l_.r=3' WO_| =_ler&t|o'rl ] _mpt_ =8.8_ Plot -6t_Oct. NaxT_e-Moxf-14ax Som_les fronMenn_ Figure4.SN9400 ShockResponse Spectrum fora89kN(20kIbf)preload GHISXSTEh_,II_C.CAT$VS_I_ DATE/TIME:ThuSep060104:36TESTENGINEER:A.Luna TESTITEM:HSTCP/Ng364694-1 TESTTYPE:ShockResponse IMPACT LOC. :g400Series _epNut TESTMACHINE : S_nsitivity: .Ch.1_14188.45 9's/Dlv Ch.2=_L449.2B g'_Lv ,._.3:t694,9_ g',s_DIv•4:2,8_v,'Oiv 3 Filter: Ctl TIldECUR_ PERI(_ 1STTill2N_INITll_../_IP •It31.31_S126.58 B'¢ -182.89 9"_7.84hv¢ 12.8_S 213.31_235.74 9%239.28 0%S_.44Iw'a 12.8nS 3.13.31mS46.839% 78.86g's 45.28 l_v_ 12.8e_S 4z3,__s--e.__,--_.1_7v e _..s •,_,_,_ Figure 5.SN9400 TimeDomain Shock Response, 89kN(20kIbf) NASA/CP--2002-211506 135
'£"estReport. _i5VSTr."_, I_C._T5YS'T,E:_ DATE /TIME:Mon Aug270123:16 TESTENGINEER :A.LUNA TEST ITEM :I/2 INCH bq.s TEST TYPE :_OCK RESPONSE IMPACT LOC. :20K PRELOAD TEST _b_CHINE : !!!!!!_!!!!!!!:i!!!N!!!!!!!!!!!!!!!!!!!!! _!_!!!_i!!!_!!!!!_!!!!!_!!!!!!!!!!_!_!!!:!!!!!!!!i!!!!i!!K!_ _!!!!!_!_i_!!!!!!!!! .............................2.......................................i...........I..........................i............iiiiiii......iiii_o •,........ _20o0 ,I !:!!:!:!!:!:!!:!::i!!:!:i:!!:!::!:!i!:!!::S_!I;!_!!!::!:!i!i!!:!i!:!!:!i!!:!!:i!::i!:!:i!:!i!:!!:!_!::!:!:!:!:!:!!!:!!!!:!:!!!:!:I!:!:!:!:!:i:i!:!:!:!!:i!!:!S!:!!!: !_??iii ii}ii!?!.........1..........l!iii1'118 ..... _ ........ I a(_oooo_o ,_ Pr'ec_euct 3(H_) C]_nne| Nuezber= 3 Node| =Rccelez'atio_ I l_.ping -8.85 Plot =6tbDct. I Figure6.SN9500 ULSShockResponse Spectrum, 89kN(20kIbf)preload W,=vefoz_= &"eet. ]P,epO_;: DATE /TIHE :MortAug270123:15 TEST ENGINEER :A.LUHA I:EST ITEM :!/2I_CH UL$ IEST TYPE :_HOr.K RESPONSE IMPACT LOC. :20KPRELOAD TEST V_kCHINE: 5_-nsit iuit_ : C_.1:1_.45 Sl's/l)|v Ch.2:144fl.28 9'_,l)iv Ch. 3:1694.92 9"s._Div :Ch.4:2._ v/Bfv. 3 lrig. Cb.:2 Potartt_ :141ndeu Leve!:11_9._9g"s Pretr i_er :1B.}...aa_-_. :-:.....-;:..:-::_-.-._::----.--::: |,m'_"- .......... :..... :..... :..... :..... :..... :..... _..... :....  III(E _ _ P?/I( _ B! lET 113.31 mS-31.38 g's-_-_9'_5.91lcu's 213.31_ 188.1_8g's -_l.t_l] g's_(.21 In/s u313.31 _E;-12.16 9's -?II].RE] fl's-lfl.5l Inls  13.31 nS 1_.83v 8._v 02HI)IHT 12.8 12.8mS 12.B_-S 12.8_E; Figure7.SN9500 ULSTimeDomain ShockResponse, 89kN(20kIbf) NASA/CP--2002-211506 136
Alternatives toPyrotechnics -Nitinol Release Mechanisms Andrew Tuszynski* Abstract HiShearTechnology Corporation hasbeenproducing theSN9400seriesofseparation nutssincethe early1970's. Itisoneofourmostpopular products, andisstillthelowestshockoutputpyrotechnically actuated nutavailable onthemarkettoday.Thereisastrongdemand inthemarket, especially inEurope, foraseparation nutwhichproduces virtually noshock, produces nogaswhichmaycontaminate the payload, andiseasilyresettable. Toachieve thesegoals,Hi-Shear hasdeveloped andpatented 1(pat.no. 5,248,233) aseparation nutthatreleases theboltpreload usinganelectrically heatedNitinolcolumn. Introduction Ourstandard SN9400separation nutisbasedonthreethreaded segments heldtogether byaring.The preload ontheboltpushes thesesegments outwards against thering.Friction between theringandthe segments holdsthecomponents inplace.Torelease thenut,thepyrotechnic initiators ontopofthenut arefired,generating ahigh-pressure gas.Thisgaspressure ishigherthanthefrictional forceandpullsthe ringoffthesegments thusreleasing thebolt. Theshock,vibration, andthermal cycling loadsencountered bythenutsareverysevere. TheSN9400 seriesseparation nutshavealonghistoryofsuccess inwithstanding theseenvironments andfunctioning asrequired. ThenewNitinolseparation nutstillusesthepedigreed segment andringarrangement, but theboltpreload isrelieved inamuchdifferent way. ThenameNitinolstandsforNickel,Titanium, NavalOrdnance Laboratory. ItisknownasaShapeMemory Alloy,andhastheuniqueabilitytoreturntoacertainshapewhenheated. Inourapplication, theNitinolis taughttoshrinkwhenheated, relieving thetension onthepreloaded bolt.Theringisthenpushed offthe segments withaspringandtheboltissetfree(Figure 1).Sincetherearenopyrotechnics involved, the system isverycleanandeasilyresettable andre-useable. Eachseparation nutcanbetestedandreset beforeshipment, ratherthandestructively testing 10%ofthelotasisthecasewithpyrotechnic nuts.The Nitinolnutscanbeusedoverandoverbythecustomer duringground system tests,ratherthanhavingto shipthembacktothefactorytoberebuilt. Separation NutShockOutput Thethreemainsources ofshockoutputduringseparation nutactuation 2are1)Pyrotechnic Shock, 2) Release ofBoltStrainEnergy, and3)Mechanical Impactoftheinternal components. TheNitinolSN9600 seriesnuthasnopyrotechnics andreleases theboltstrainrelatively slowly,inseconds, notmilliseconds. Themechanical impacts aredrivenbyaspringandaremuchlowerthanthosedrivenbypyrotechnic activation. Sincetheboltpreload hasalready beenrelieved bytheshrinking oftheNitinol,therequired forcetomovetheringistwoordersofmagnitude lowerthanwhatisneeded tomovetheringina standard pyrotechnic device. Theshockoutputofastandard SN9400,9.5-mm (3/8")LowShockSepNut,witha30,000Newton (6,750 Ib)preload isapproximately 4,500g'satabout7,000Hz(Figure 2).ASN9600NitinolNutofthesame size,withthesamepreload, putsoutamaximum of500g's(Figure 3).Thisshocklevelisroughly equivalent totheshockobtained bydropping asmallboltontoanaluminum platefromaheightof20cm (8"). Hi-Shear Technology Corporation, Torrance, CA Proceedings ofthe3_hAerospace Mechanisms Symposium, GlennResearch Center,May15-17,2002 NASA/CP--2002-211506 137
NitinolTraining Acolumn oftheNitinolalloyisattheheartofthisseparation nutdesign. Although itisusedinthewire forminthemedical field,finding asupply ofthesizeneeded inastructural application hasbeen challenging. Therehavebeenmanypaperswrittenaboutthevarious alloysintheacademic community, butusefulengineering dataforanavailable product isalsoveryhardtocomeby. Mostapplications oftheShapeMemory Alloyrequirethematerial toreturntoitsinitialshapewhenheated. Auni-axial lengthrecovery ofapproximately 7.5%iseasilyachievable. Inourapplication, theNitinolis trainedtobothshrinkinlengthwhenheated, thentogrowbackwhencooled, givingita"TwoWayShape Memory" 3of+2%.Thisisachieved bydeforming thebartoformamosaic of"Stress BasedMartensite crystals". Thematerial returns toitsparentshapewhenheated pastitstransition temperature, butwith training, remembers thesecrystals, andreturnstotheshapeitwasgivenwhencooled. ThetermTransition Temperature describes thetemperature atwhichtheNitinolalloychanges statefrom Martensite toAustenite. Thetransition temperature ofthealloyusedforspacecraft applications is90°C. Whilethebarisunderload,thetransition temperature risesupto125°C.Theabilitytotrainthematerial in twodirections givesustheabilitytoverifythequalityofeachcolumn usedineachseparation nutwithin eachproduction lot.Italsogivesourcustomers theabilitytoreusetheseseparation nutsinground tests asneeded. Required Length A9.5-mm (3/8inch)diameter boltandseparation nutsystem istypically expected tocarryamaximum of 45,000 N(10,000 Ib).A75-mm boltlengthisexpected tostretch approximately 0.23mm(0.009") under thatload.TheNitinolcolumn issizedinbothlengthanddiameter toshrinkandrelieveallthepreload. In thiscasetheNitinolcolumn is2.54cm(1.00inch)longandwillgiveup0.51mm(0.02"). Summary Engineering designalwaysinvolves balancing tradeoffs.TheSN9600NitinolNutdoesnotproduce any gasandhasvirtually noshockoutput. Itwillnotcontaminate norjartheopticsofasensitive satellite. However, theamount ofelectrical energy required toactuate theNitinolnutismuchhigher. Pyrotechnic nutstypically use25wattspercartridge overa10millisecond timespan.Alltheenergytorelease thenut isstoredinthepyrotechnic charge. TheNitinolnutrequires 125wattsfor15to30seconds. Sincethe actuation timecycleissolong,simultaneity isnotachievable. Ontheotherhand,forapplications where lowshockoutput,orcleanliness, isofhigherimportance thanpoweruseandtime,thisistheseparation nutofchoice. Atthistime,theengineering development isnearing completion andwehavecustomers interested inqualification andflightofthisproduct asanalternative topyrotechnics. References Patent Number 5,248,233, "No-Shock Separation Mechanism", Richard G.Webster, (Hi-Shear Technology Corporation) September 28,1993 2.AlexLuna,"Operational Improvements ofaPyrotechnic UltraLowShockSeparation Nut"Proceedings ofthe36thAerospace Mechanisms Symposium, GlennResearch Center, May,2002 3.Duerig, T.W.,Melton, K.N.,Stockel, D.,andWayman, C.M."Engineering Aspects ofShapeMemory Alloys", Butterworth-Heinemann, 1990,pp201 NASA/CP--2002-211506 138
j..-.._.-.-.-4 _--Threaded Segments __I_I _Ring  !ILJ_L__ ..... NitinolColumn •...........,........°.°%. ,,...o...Oo........%.... F_////////////Z _!__;___'///////_',///__\\\\\\\\\\\"_,,\._ ._'%_\\\.N\\\\x.\\N_I I t f I_\\\\\\\\\\\\\\\N'tm Figure1.SN9600Separation NutSchematic NASA/CP--2002-211506 139
m_t_ux_-t .':.'__,:'_;E_.', :::3._.'.T."/,_T'_':; OATE/TIRE :03nov2000;14:00 TESTITEM :3/8ntttnol $epnut IMPACT LOC. :shockoutputTESTENGINEER :krb&at, TESTTYPE TESTI_CH[NE :24x24xl elptate E c_ime! _ 3 iPe_l_lt_l -B.B5 kTram -Maxl-Nmx................... :..........:........:.....:.....:'"7":"':': ................... "........... '........".......:"?""'":"7"_ ................... i........... "......._......_"'_'-?-7 "." .................... ?..........-........i.....i.....?'-'i'--?'i"}................... _...........i......._......i""i"")--?i--i ................... _...........).......i......i.....!'"?i"-_"_600 •,;__._.......... ,................... _........... ;........ ;...._....;,_..i.. ;._..; ............... -;......... ,...... .:......_...;_,.:.. _.;,_..,._._..a ......... _.....  •. ._ ..... _,,,- ::•;: :--3;: 111 11_ F_ (Hz) NodeII -nccelerat to. Pill -6tkOct. SMIpt_frmXwmr_ _,u.o..e ,.'v_. ............ 24V4,.50 PRELE)AD: 30000 NE/'/TON]; Figure2,SN9600Nitinol Separation Nut ShockResponse Spectrum, 30kN(6,750Ib)Preload NASA/CP--2002-211506 140
System Characterization andMotorStepVerification through Rotary Acceleration Signals ScottStarinandFredCrosno* Abstract Stepper motortorqueoutput, resonant frequency determination, andpulsestepverification havealways beenquestions oftheperformance andreliability ofstepper motoractuators. Traditionally, stepper motors havebeencharacterized byopenloopstepcounting. Insomeinstances, loadposition information (hence stepintegrity) hasbeendetermined through theuseofbrush-type potentiometers orthrough brushless resolvers. Thedisadvantage ofpotsistheconcern ofreliability andparticulate wearofthebrushes, and resolvers requires excitation andadditional circuitry toprocess theinformation toananalog ordigital format. TheabilitytouseaDCtransducer signaltocharacterize motorstepperformance andintegrity isa majoradvantage inpermanent magnet stepper motorapplications. Introduction Forbackground andconsistency purposes, wewilldiscuss stepper motortorquecharacteristics, define keyterms, andestablish relationships onloadinertiaandfriction onstepper motorperformance. Additionally, wewillpresent aclassical stepper motorposition versustimeprofile,anditscorresponding acceleration versus time.Withthisbackground information, wewilldemonstrate thataDCsignalin proportion totherotaryacceleration maybeusedtodetermine anumber ofparameters suchasload inertia,resonant frequency, overshoot, torquemargin, settling time,andchange infriction overtime.In addition tothecharacteristic andperformance criteria, wewilldiscuss several ofthemanyoptions of usingtherotaryacceleration information todetermine stepintegrity, aswellasdirection ofrotation ofa stepper motoractuator. Stepper MotorDynamic Performance Figure1showsatypicalPulseRateversusTorque forapermanent magnet stepper motor.Keyterms andperformance pointsarehighlighted here.Therehasbeenanunfortunate lackofconsistency inthe industry forthedefinition ofsomekeyterms.Thisgraphically showstermsweuseinourdiscussions of stepper motorperformance. Figure1-StepperMotorPerformance lewR_te ,S  Pull)utTorque / PulseR_t R=( Hold_gTorque PlInTorqu_ / 0 5 10 15 20 25 30 35 40 4.5 Torque (mNm) Figure1.Typical Dynamic Stepper MotorPerformance underLowLoadInertia *CDAInterCorp, Deerfield, FL Proceedings ofthe36thAerospace Mechanisms Symposium, GlennResearch Center,May15-17,2002 NASA/CP--2002-211506 141
Pull-inandPull-Out Torque: Itisnotsufficient tosimplyspecify running torqueataparticular pulserate forastepper motor. Pull-In andPull-Out Torque should beunderstood andcharacterized when designating astepper motor.Pull-InTorque isafairlylinearrelationship thatfallsonalinefromtheNo LoadResponse RatetotheTorque atLowPulseRate.ThePull-InTorque isthemaximum frictional load youmay"pull-in" fromrest,orchange direction ofrotation without missing pulses. Oncesynchronous angular velocity hasbeenachieved, ittakesmoretorquetoPull-Out amotorfromdynamic operation. The Pull-Out torquefallsalongalinefromtheSlewRatetotheTorque atLowPulseRate. LoadInertiaandResonant Frequency: Theperformance ofastepper motorissignificantly affected bythe introduction ofloadinertia.Energy thatwasgoingintoaccelerating anddecelerating themotorrotormust gointoaccelerating anddecelerating theloadinertiaandfrictiontorque. Itisimportant toestablish the system resonant frequency intheseapplications, sothosemotoroperational pulseratesmaybereviewed toavoidstepping ataresonant frequency orsympathetic harmonics. Asaruleofthumb, itisdesirable to keeptheratioofloadinertiatomotorinertiadownbelow5:1.Thisminimizes thepossibilities of resonance andunstable performance. However, whileitispossible tosafelyoperate withsignificantly higherinertiafactors, itisdifficult topredict resonant frequencies andtorque performance maybe significantly compromised whentryingtodriveatornearresonant frequencies. Intheseapplications, prototypes shouldbebuilttocharacterize system performance atthedesired operational pulserate.We willdiscuss inertiaanditsaffectonstepper motorperformance laterinthispaper. StepCharacteristics: Figure2showsanactualscopetraceofposition versustime(topcurve)andthe corresponding acceleration versustime(bottom curve)oftwostepsofanunloaded stepper motor.The overshoot, settling time,andgeneral stepcharacteristics areclearlyillustrated here.Withthisillustration, wecandetermine afewcharacteristics ofthestepper motor.Thepeakacceleration happens shortlyafter theinitial"pulse". Thisisduetothe"risetime"ofthecurrent intothemotor. Alsonotehowthe acceleration crosses zeroattheinstantthemotorcrosses thestablestepposition ofthemotor.Thisis referred toasthe"crossover time".Fromthispoint,aclearindication oftheovershoot andbounce region, andsettling timeareclearlyvisibleintheacceleration signal.Ifthepowerwereincreased ordecreased forthissamemotor,fundamental changes wouldoccurintheacceleration profile. Figure2.Position andAcceleration versus TimeforUnloaded Stepper Motor Introduction ofloadsonstepper motorcharacteristics: Whenastepper motoriscoupled toaninertiaor frictional load,thecharacteristic plotshowninFigure2willbealtered. Withtheintroduction ofloadinertia, thepeakacceleration willbeattenuated because torqueisbeingconsumed intoaccelerating theload inertia. Thenumber ofovershoots andthesettling timewillincrease, duetoanincrease inangular momentum. Tocompare performance withandwithout inertialloads,wepresent thefollowing curves. Figure3Aisa stepper motorwiththefollowing characteristics: Holding Torque (TH)=0.115Nm NASA/Cpi2002-211506 142
Motor+Accelerometer Inertia(JM)=1.4E-06 kgm2 Accelerometer ScaleFactor(KVo0=26mV/krad/sec 2 MotorCoulomb Friction (FM)=0.005Nm Attheratedholding torque, thisstepper motor willproduce 78krad/sec 2 acceleration, whichcorresponds to2.0 Vdcpeak;veryclosetotheactual recorded acceleration signalshown in Figure3A.Themaximum acceleration of astepper motormaybecalculated by Equation 1.Note:Thisequation isvalid onlyatlowpulserates.Asvelocity increases, backemfandviscous frictions and damping affect thepeak acceleration. (_M=(TH-(FM+FLM))/(JM+JIM) Eq.1CH] :M_× ].S3U Fiin -].32U i "'""'T' ......."........................ ]........ ;......."......._................ ;iDRTE:Jan 92/92 T]FIE :]?:59:42 CH]:].G@U :29ms /- / 'L4--.j.....,....................... 1-............... ,........,................ "--_................................... _........_'";'--'T ......., Figure3A-Stepper MotorAcceleration underNoLoad whereFLMistheloadfriction, reflected to themotor. Figure 3Bshows the acceleration ofastepper motorwitha directly coupled inertiaof2.0E-6 kgm2. Thisincreased inertia reduces the maximum acceleration to30.6krad/sec 2, andhencethesignalto0.87Vdc.Notice theincrease incrossover timeand settling time.Itisinteresting toevaluate thischaracteristic profile whenmotor powerlevelsarechanged. Forinstance, youmayexperience aresonance ina highloadinertiaapplication thatmaybe eliminated bydecreasing thepower input,because ofthereduction ofthe percentage overshoot andundamped resonant frequency.CH]:_ax 925mU I"l;n-638mU  ::::::--i....................i.......i.......i........i.....i--i........i.......i........i.......,_............i........i......i........ .......i.......:.......i......._.......i.......i......!........i.....;iii_ii:: ______ .... ,: [ , _'--" ......:...../13O#[E:.l_n 62/02 TJilE :14:38 :_0 CH]:I.t3_b :29Jms /- / Figure3B-Stepper MotorAcceleration underInertialLoad Introduction offriction onstepper motor characteristics: Friction hasadifferent affect onstepper motors, when compared toinertial loads. Increased friction alsoattenuates theacceleration signal,butsomeenergy thatwasbeing usedtodisplace theloadisnowbeing dissipated intheformofheatintheload friction. Theovershoot andsettling time arealsoreduced, asonewouldexpect. If thefriction increases significantly, the motorcannot reachthenextstablestep point,andcannot continue todrivethe load.Figure3Cshowsascopetraceof thesamemotorusedinFigures 3A, underapurefrictional load,(theauthor'sCH]:M_,x ],41_U M;n -].r_2u --v;I"""_P""[.......]........?.......:.......]........r......._.......].......:........ !_iiii_i!ii!----<-i.......i.......i.......i.......i.......:'.......!.......i........i....... _iliiii!_'i.....![l].................... , ._.':..........._........................ _............... ,......................... ,DRTE:J_n g2.'82 TIME :15:54:56 CH] :].9(3U :2Elms F/ / / / / Figure3C-Stepper MotorAcceleration underFrictional Load NASAJC P--2002-211506 143
8.00Figure 6-Acceleration Signal &BiasVoltage / Acceleration Signal 6.00 __ ................... _4.00.... _- _'Vb.......  2°°1j,\ ..... o0.00-_--" ....i....\................ _ _-- $0.100 0.202 0.204X0.206 0.208 _ 0.212 0.214 0.216 0.218 0.i20  iiiit...................Time(sec) Figure6showstheacceleration voltage signal(aftersomegain)andtheBiasVoltage (Vb)tothe comparitor, forasinglestepofastepper motor.Whiletheamplified acceleration signalisgreater thanthe Vbvoltage, thecomparitor outputwilllatchhigh,indicating asuccessful pulse.Sincethereisaseparate comparitor foreachphaseoftheacceleration signal,direction ofrotation information isalsoprovided. The pulseoutputs maygotodigitalcounters ordigitallogiccircuits todetermine actualpulsecounting. Since thedirection ofrotation information isavailable, ifthemotorstepsopposite tothedesired direction of rotation onthefirstpulse,theinformation ismaintained. Conclusion Wehaveshownmanypractical applications fortheuseofrotaryaccelerometers toanalyze permanent magnet stepper motors. Acceleration information isveryusefulindetermining performance andload characteristics. Wehaveshownthatitispossible todetermine theactualtorqueproduced ofastepper motorwhiledynamically operated. Additionally, withsomeknown parameters, wecanalsodetermine loadinertia, loadfriction, operational torque margin, andsystem natural circular resonant frequencies, simplybyanalyzing anacceleration signal.Stepverification, stepcounting, anddirection ofrotation may alsobeobtained bysimpledigitaloranalogsignalprocessing. Referen ces 1.CDAInterCorp: "Stepper MotorEngineering Reference Data",@2000 2.CDAInterCorp: "Controllable DriveActuator andRotaryTransducer Engineering Reference Data", @2000 NASA/CP--2002-211506 146