ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Thus,  we h ave de monstrated that MEM S devices ca n fun ction fo r many (>1 010) cycle s in vacuum and that  their motio n is actually im proved, requiring less voltage, in some appli cation s. We have d esigned, built,  and tested th e first fully fu nction al vacu um micropro be test facility specifically intended to optimize th e  developm ent of MEMS device s for space appli cations and have embarked on the adventure of  developin g and ultimately  flying MEM S-based scie ntific instruments and  spacecraft systems on future  space missions. 

Ackn owledgements 

We g ratefully  ackno wledge contributio ns to d eveloping o ur ME MS device s and va cuum  test facility b y  Troy Di az, Ray Gold stein,  Heath er Hanson, Yvette  Tyler, and Martin Wüest. The MUMPs fab ricate d  resonato rs were provided cou rtesy of  Dr. Steven Hudak. T his work was fun ded by a P residential Intern al  Research an d Develo pment Grant from  the Southwe st Research Institute. 

Referen ces 

1M. Mehreg any and S. Roy, Introductio n to MEMS in Micro engineering Ae rospace System s, edited by H.  Helvajian (The Aero space Press an d Ameri can In stitut e of Aerona utics a nd Astronauti cs, 19 99), pp. 1-2 8.  2J. Lyke and G. Forma n, Space ele ctronics packaging rese arch a nd engine ering in Microen gineerin g  Aerospace Systems, edite d by H. Helva jian (Th e Aerosp ace Pr ess and Ameri can Institute of Aeron autics  and Astrona utics, 199 9), pp. 259-3 46.  3H. Helvajian and S.W. Ja nson, Mi croengineering space system s in Micro engineering Ae rospace  Systems, edit ed by H. Helv ajian (T he Ae rospa ce Press and Ame rican Institute of Aerona utics and  Astron autics, 1999 ), pp. 29 -72.  4 McCom as, D.J., G.P. Miller, J.N. Mitch ell, S.E. Pope, P.W. Valek, Space a pplications of ME MS: The  SwRI® vacuu m micro probe facility and initial vacuum test re sults, Rev. Sci. Instruments., 74(8),  38743878, 20 03  4S.L. Miller, et al., Friction in surfa ce mi croma chined mi croengine s in Proceedings, SPIE Smart  Electro nics and MEMS , Vol. 12722, 19 96, pp.197 -204.  5D. Koester, R. Mahad evan, B. Hardy, and K. Markus, MUMPsTM Desig n Handbook: Revi sion 6.0,  (Cron os, Research T riangl e Park, 20 01). Lates t versi on at http://www.memsru s.com/mu mps. pdf  6S. Kota, et al., Synthesizin g high-pe rformance co mpliant stro ke amplification systems for M EMS, The  Thirtee nth Annual Intern ational Confere nce on Micro Electro Me chanical Syste ms, IEEE, 20 00), pp. 164 - 169. 

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the su spension had to b e desig ned to give the rove r a rid e somewhere between a luxury v ehicle and a   truck. The suspension system st iffness target was one that wo uld produce a tra nslatio nal im pact lo ad no  greate r than 6 G’s and not let the rover bo dy d eflect bel ow a 20 cm g round h eight. The resulting   suspension structu ral members were fabricated from tapered, welded, titaniu m box b eams tuned  to me et  these requirements. Th e design of th ese eleme nts also p rovides exce ptional be nding and torsio nal  capability whi le minimizi ng the volume and mass impact to the spacecraft. 

Figure 1 .  Mars Exploratio n Rov er with a Deplo yed Suspension  

The la st an d most difficul t desig n requ ireme nt was to create a susp ension th at woul d sto w withi n the  tetrahed ral la nder, u nfold and latch into  a deployed configuratio n, and provide the rover with the gro und  clearance and stability necessary to navigate the Martian surface.  This task required signifi cant  coordination with oth er rover and lande r subsystems in order to p roduce a deployment sequ ence fre e of  static o r dyna mic interfe rences (see Fig ure 2 & 3). 

Figure 2 .  Stowed MER Rocker -Bogie Suspension on Assembly  Fixture   186
Figure 3.  Sto wed MER Rover on Lan der Ba sepe tal 

Folding and Unfolding the MER Mobilit y 

Determinatio n of how the  rocke r-bogie suspen sion could be “b roken” to ena ble it to stow within th e  allotted sp ace wa s the first challen ge fa ced in th e design of the sub-system. As the name would su ggest,  the two pri mary com ponents of this type of su spension a re the rocker and b ogie (see Fi gure 4). Th ese  two stru ctural elements a re conn ected via a free rotating pivot dubbed the Bog ie Pivot. The right and left   sets of rocke r-bogie assemblies a re conne cted to each oth er via the ve hicle’s differential,  a passive,   motion-reve rsal joint that constrain s the two sid es of the mobility system to eq ual and o pposite motion.   Three uni que break point s we re selected: the Rocker-B ridge Joi nt, a mid-sp an rocker foldi ng joint; the   Rocker De ployment Actuat or (RDA) Join t, a moto r driven deployme nt joint o n the forward rocker arm, and  a tele scopin g prismatic joint on th e bogie mem ber. Thus, a total of s ix joint s mus t be reliably locked and  latche d into p lace d uring deployment to provide the rover with a saf e and sta ble platform for d riving.  

Figure 4.  MER Suspen sion Nomen clature (Deplo yed Configuration )  187
Deployment of the rove r takes place d uring the Sta ndup and Deployment  phase of th e lan ded mi ssion,  after critical  systems li ke the sola r arra y and ima ging ma st have been deployed and the ve hicle’ s health   has been confirmed. T he first step in  deploying the m obility is to rotate  and lock the Ro cker-B ridge Joint  into place. The MER me chani cal de sign team had determi ned e arly on that a lande r-based Rove r Lift  Mech anism, or RLM, woul d be need ed to lift the rover from its sto wed po sition. A rover-b ased RLM wo uld  have re sulted  in significant  rover sca r mass, as there wo uld likel y be a need for two actu ators, one o n  each sid e of the rover, rather tha n one centralized device. As de signed, the RL M utilize s portions of the   suspension subsy stem to create a four bar linkage  that guid es the  rove r body up into its ground clearing  stance. By u sing the  Bogie /Basepetal  (Labele d 1 in Step 1) an d the Aft Ro cker (Labeled 2) as two lin ks in  a four ba r linkage, the  RLM needs only t o provide th e two remai ning links and  the exten sion force to raise  the rover into it’s standi ng position [4]. 

Step 1: Rover Lift 

Once the b ody of the rover is lifted to its pea k hei ght, just beyo nd it’s nomin al driving height, t he second  phase of rover stand -up begins. At the compl etion of Step 1, the forward ro cker arm and  the attach ed  rocke r wheel  are still in their “u p-side -down” stowed orientation. By activating the RDA on  each rocke r  arm, the forward po rtion of  the rocke rs is rotate d 180 degre es into  its full stance positio n. A mid-d eploysequence steering motio n was added to avoid  interfe rence of the  wheels with  the solar arrays. On ce the  RDA  deployment i s complete, the steering actuators a re rotated  to thei r forward  drivin g orientation (see  Step 2). 

Step 2: Rocker De ployme nt (inclu des Steering A ctuator rotation to  clear Sol ar Arrays) 

The third step in the stan d-up sequence is the retraction of the RLM. On ce the RDAs a re deployed  and l atched into pla ce, the rove r is capable of supporting itself in it s upri ght confi guratio n. At this point  in the deploy ment pro cess, the rover is supporting itself on all six whe els (se e Step 3).   

Step 3: Rover Lift Mechani sm Ret raction 

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Figure 5.  Open Box/Plate  & C-Cha nnel Options  

After the selection of the  fabri cation  process, a set of torsion  tests were perfo rmed on 30 mm by 3 0 mm  article s that were re prese ntative of the base of the forwa rd rocker weldme nt.  The torsion al load in th at  locatio n was 421 N-m (3725 in-l b). Th e test results in dicate d that t he failu res began n ear the corne r of the   weldm ent rat her tha n the weld seam. Test result s also d emonstrated the b ox beam’ s tend ency to yield  rathe r than b reak at load s far in ex cess of its desi gn capacity. Thi s type of failu re me ant a driving impa ct  case greater than the d esign loa d woul d result in “graceful degradation”, allo wing the surfa ce mission t o  contin ue in stead of ca using a cata strop hic system fai lure.   

Detailed De scription of S uspen sion Mechanisms 

Rocker Brid ge Joint an d Latch Desi gn  The rocke r-bridge joint i s essentially a y oke and clevis design. Each sin gle-use j oint pivots o n two (2 ) 52  mm diam eter Torl on 7130 thrust/radial  bushings. Bray cote 601EF grease is appli ed to the  bushing s as an  adde d me asure of fri ction reduction.  Once deployed, the rocker-b ridge joi nt nee ds to  with stand  a  maximum 7 14 N-m (6325 in-lb ) bending load generated when the center whe el falls into a 20-cm  hole.  The joint also simultan eously se es a 506 N-m (447 5 in-lb) torsion  load created by the 12 cm lateral off set  betwe en the rocker-b ridge joint and the mobility whee ls (see Fig ure 6). 

           Figure  6.  Rocker -Bridge Joint i n Stowed & Deplo yed States  

The ro cker-b ridge latch consists of a pa wl that falls into place on ce the aft rocke r has rotated 39 deg rees  from its stowed po sition. A small appe ndag e on th e forwar d side of the pa wl was included in the p awl  design to  engage  the microswitch  lever arm to i ndicate the joi nt has su ccessfully bee n locked. An   interme diate step was al so adde d to the latch d esign in  order t o isolate the latch from RLM stall load s.  The interm ediate latch po sition allowe d the latch pa wl to travel past its final position, cau sing the RLM to  stall a gainst its own intern al ha rd stop rather than  against th e latch, whi ch avoi ds unnecessary lat ch and  suspensi on loading. Instead, once t he RLM has stal led at the top of li ft, it then lowers the rover and the  latch pa wl fall s into its final latche d position (see Fig ure 7).  190
Figure 7.  Ro cker-Bridg e Latc h Pa wl Actio n durin g the RL M Lift and Lo wer 

Rocker Deplo yment Actuator and L atch Design  The tri angular shape of the lan der b asepetal was a strong motiv ator to  stow the front wheels directly in   front of th e rover. Foll owing thi s motivation, a j oint called th e rocker d eploy ment a ctuato r (RDA) was  adde d to the suspension to pe rmit the  front wheels to be stowe d directly in f ront of the  rover. During  deployme nt, the RDA deploys the  front  wheels into  a position  that maintain s the ne cessary rover pitch   and roll stabil ity. Once dep loyed, the RDA is requi red to with stand  390 N-m (34 50 in -lb) be nding and 421  N-m (372 5 in-lb) torsio nal load s. The RDA is a 100 -mm long, 80-mm diameter cylindri cal body. A Maxo n  REO20  DC b rushed  moto r with i ntegral 5 sta ge planetary ge arhead is em ploye d to create th e RDA' s 20  N-m (175 in-lb) torque capability. The maximum p redict ed flight  deployme nt load i s 2.8 N-m (25 in -lb),  giving the act uator con siderable m argin over its re quired task. Two pairs of 57.2-mm (2.25 i n) diam eter  MPB angul ar conta ct bearings are utilized a s the RDA 's rolling elements (see Fi gure 8). T he latch d esign  chosen was based on a latch used on the M agella n spa cecraft to latch  the spacecraft’s solar pan els in  place. The RDA latch can best be d escrib ed as a va riation on th e comm on door lat ch. Th e two pri mary  comp onents of a door latch are the sp ring-lo aded pawl in the door and a fixed strikepl ate attache d to the  doorf rame. T he RDA latch inverts the d ynamic and  static roles in t his latch design by fixing  a pawl on the  stator h ousing and all owing the roto r mounted strikeplate to pivot. In an effort to minimize th e latch lo ad,  the diameter of the RDA was ma de as large a s possibl e, the primar y restriction s being the RDA’ s  proximity to the land er side and ba se petals, rove r body, and scie nce h ardware. 

                   Figure 8.  Ro cker Deplo yment Ac tuator  

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Bogie De ployment and Lat ch Desi gn  The original design of the  MER suspension was one with a  bogie of fixed  length. A s the MER rover  design beg an to mature, its cent er of gravity began to ri se. The fli ght system h eld a firm req uirement that  the rove r wou ld be stable t o at lea st 45 degree s in ve hicle pitch and roll. Th e increase in rover c.g. me ant  that the d riving position  of the aft b ogie wheel neede d to m ove backwards in order to meet the 4 5 degree  stability requi rement. Due to the volum e constraints placed on the mobility in the stowed configuration,  the bo gie design needed to b e modified to  depl oy, allowin g an increase of the b ogie length by a n  addition al 17 cm. 

The de cision on how to deploy the b ogie wa s reached relativel y quickly. Th e aft bogie whe el drive   actuato r was the logi cal mechanism to  pull the  bogie into its final  configuration. The aft bogi e wheel drive,   as designed for pe rformi ng its p rimary rover t raverse functio n, is able to supply up to 33 3 N (75 lbf ) of  deployme nt force. The addition of this capability bro ught with it b oth ma ss and compl exity impact s to the   design of the  rover and th e land er. On the rove r, the  bogi e was split into two d istinct structural ele ments,  each having t o house a po rtion of the mecha nical com pone nts ne cessary to allow the bogie to deploy an d  latch into  its final po sition. On the l ander, a small, co gged platform wa s added to ea ch of the aft wh eel  restraints, designed specifically to engage th e wheel cleats an d gua rante e maximum tra ction during  deployme nt. 

The me chanism by whi ch the aft bogie membe r mov ed within the  forwa rd bogie wa s originally slated to  be skid s to reduce system mass.  The final desi gn, h oweve r, wa s a system of roller a ssembli es suppo rted  by spri ng ele ments. The basis of this d ecision was the de sire to decrea se the friction in th e desi gn an d  increa se the bogie’ s ability to tolerate thermal di storti on. In additio n, it was felt that rolling el ements would   be more tole rant to deb ris that co uld be inge sted into the moving com ponents du ring deployme nt.  Whereas a sliding motion could sei ze due to a smal l amount of d ebris, a rollin g system would be mo re  forgiving, resulting in a robust ove rall design a pproach. Th e increase in bogie mass was con sidered  accepta ble in orde r to increas e the depl oyment’s reli ability. 

The design goal of th e bogie roller assemblie s was to su spend the aft b ogie within th e forward b ogie.   Four pai rs of rolle r assem blies suppo rt the aft bo gie and remove 5 of 6  degrees of free dom. By placi ng  the two forward p airs a s far away from the aft p air, rolle r loads are mini mized and t he roll er size  corre spondin gly redu ced. This i s particularly impo rtant in the b ogie, whi ch is locate d in a n area of the   rover where space was at a premi um.  The statio n distance bet ween the pai rs of roller asse mblies i s 10  cm (see Fi gure 9). 

Figure 9 .  Bogie Deplo yment Dia gram  

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A roller a ssembly con sists of a roller pin with two n eedle bea rings, one on each end of the pin . The rolle rs  are po sition ed over the vertical po rtion of the aft bogi e to allow lo ad tran sfer th rough a stro nger po rtion o f  the bogie cross-se ction. This roller placem ent al so provide s an efficient m echanical ad vantage for  managi ng torsion al load s applie d to the aft bogie. Even with  these considerations put into pl ace, the wall   thickne ss of t he deploye d aft bogie  in th e location  where the roller reste d had to  be increased from 1 mm   to 3 mm to  withstand  the roller point lo ads. T he roller pin assemblies are n ested bet ween  the aft bogi e  and a pai r of belleville wa shers stacks.  These stacks are n eeded to counte ract any thermal or de bris  pertu rbatio ns that could arise on the M artian surface durin g bogie deployme nt. A combinatio n of wa shers  in both parallel and se ries enabl ed the roller a ssembl y to have a “ soft” co nditio n durin g the lightly loade d  deployme nt phase and a “stiff” con dition duri ng the driving p hase. The “soft” condition, en gaged d uring  deployme nt loadin g, was desired in order to redu ce the dr ag in the roll er needle bea rings. Final an alysis  eventually re quire d the a ddition of a stiffness pha se to the rol ler de sign. Analysi s of po tential rover  egress/drivin g “drop” cases indicate d that the roller pins wo uld fa il in be nding, despite b eing fabri cated  from MP35N high strength  steel. Based  on the result s of this anal ysis, a deci sion wa s made  to by-pass  the belleville washer stacks du ring this large inte rmittent load and  transmit it directly thro ugh the 440 C  steel roll er sleeve and into  the roller cover (see Fig ure 10). 

Figure 10 .  Cross-sec tion of Bogie Ro ller Assembl ies 

The n ominal  applie d loa d to the aft b ogie wheel during bogie deployme nt is about 1 5% of the rover  weight, or 97 N (22 lb) on  Mars. Thi s load i ncreases as the rover i s pitched up or sideways. A set of  thermal te sts were pe rformed at ro om temperatu re and –7 0 oC to determin e the assem bly deployme nt  margi ns. Th e tests sho wed a relatively small differen ce in the fo rce req uired to deploy the b ogie up to a  150% nomi nal applied lo ad. Past this point the deploy ment fo rce in creases sharply. T he wo rst-case  deployme nt force of 2 24 N whe n a 222 N loa d was applied remained withi n acceptable li mits of the wheel   drive actu ator’s 333 N capability (see Fig ure 11 ). 

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Figure 11 .  Results o f Deploying Bogie at Cold Ex treme  

The bogie  latch is a vari ation o n the same  basic latch de sign philo sophy  of the ro cker-b ridge  latch:   introdu ce an object that wil l not pe rmit th e furthe r motion of the m echani sm in any dire ction. Near th e end  of bogie depl oyment, an aft bogie-mo unted latch p awl rotate s upward into a n openin g in the forward   bogie.  A 12 degree d eployment pawl angle was utilized to  transfer the p awl load into the f orward bogi e  with the additi on of little mass. 

Problems an d Resolu tions 

Bogie Latch Pawl De sign   During seve ral of the  most extreme  rover m echani cal validation  and ve rificatio n stand-up tests, the  bogie  pawl fail ed to  fully rotate i nto its lat ched position. T he failu re was dete rmined to be the  result of the  aft  bogie rotatin g relative to the forward bogie along the deployme nt axis. The intentionally l ow stiffness  designed into  the bogie for reduced depl oyment load s was all owing the aft bogie to rotate up to 6 deg rees  unde r earth gravity, enou gh rotatio n to cau se the la tch pawl to h it the edge of  the latch op ening in the   forwa rd bogie, keepin g it from fully latching. 

A new bogie latch pa wl was de signed that had tape red edge s tha t eliminated the previo us interferen ce.  Fortun ately, the ori ginal b ogie pa wl ha d sufficie nt marg in to tole rate a red uction in cro ss-section (Figu re  12). 

Figure 12 .  Original and Final Bogie L atch Pa wl Design  

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Lesso n Learned: Te st the  hardware  under extreme  conditions as soon as possible i n the developme nt  phase. T esting will  expo se oversi ghts in  designs such as in this case whe re the non-lin ear stiffness of the   mech anism was un deresti mated and resulted in a lat ch fun ctional failure. 

Implementati on of Microswitch es  The three p rimary component s of th e micro switch asse mblie s are the microswitch bracket, the  microswitch, and the mi croswitch exten sion a ctuato r (Figu re 13). Each of the three uniqu e latches utilize   Honeywell 9 HM30-REL-P GM micro switches to in dicate if their re spective latch h ad succe ssfully engag ed.  The placement of the  microswitch es was such that the lever arm o f the microswi tch woul d be trigge red by   the latch pa wl pushi ng on t he arm. Due t o limited sp ace and the fe ar that the mi croswitch l ever arm might  be ove rexten ded, mi croswitch a ctuato rs Hon eywell JS-151 and JS -152 were used to exten d the range of  the microswit ches. 

The features by which ea ch micro switch was atta ched to its respective joint were intentio nal desi gned  with la rge clearance holes. The th ought behin d this highly a djustable i nterface was to ensure that the   microswitch could easily be p ositioned to register if a successful lat ch action ha d been achieve d.  However, thi s type of interface m eant th ere was sig nificant varia bility between the rove rs in microswitch  actuatio n. In addition, th e interface left the micro switch susceptibl e to small change s in position du e to  dynamic lo ading or the rmal gradie nts. 

Figure 13.  Bogie Micros witch Assem bly  

Testing  of th e rover standup phase yiel ded i nconsistent results f rom the  deployment micro switch es. As a  result, a detai led adj ustme nt proto col was e stablished for each of the micro switch assembli es that yielde d  consistent re sults. A new latch verification seq uence was devel oped as an a dded mea sure to increa se  the und ersta nding of the mobility latch  state s for use during rover sta ndup and d eploym ent. A post - latchin g command was added  to e ach of the  deployment sequ ences that d rove the  joint  in the  stow  direction. The  resultin g stall  of this motion wa s clear indicatio n that a joint had su ccessfully latche d. 

Lesso n Learned: The use of microswitches to  verify a latch ed condition shoul d not be e ntered into lightly.   The prope r impleme ntation of micro switches req uires a con sistent method by whi ch the mi croswitch i s  positio ned with respe ct to t he relevant  compon ents.  An alternate method  such  as d riving th e joint i n the  oppo site dire ction and  monitorin g current can produce telemet ry that  is le ss dependent on th e fine   adjustments asso ciated wi th micro switches.  

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