ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Its performance has been thoroughly checked during a extensive qualification tests during 2003 that  covered mostly functional, environmental and lifetime tests. The investigation performed has allowed  control of the state of the new har monic drive. Four flight models have already been delivered to our first  customer ALCATEL SPACE for a scheduled launch date in 2004. 

The SARA®21 function, design, performances and qualificati on test results are discussed more in detail  hereafter. 

Design Description  SARA®21 rotary actuator is intended for space mec hanisms orientation as well as providing the  associated positioning signal with extreme precis ion to the spacecraft on-board electronics. The  SARA®21 main functions are:  • sustaining the mechanism:  the actuator is abl e to withstand high loads and can absorb important  environments throughout all lifetime phases, and in  particular throughout orbit transfer phases  • rotating the mechanism:  the actuator can rotate eit her in forward or reverse directions, and motion is  not limited to a restricted angular zone. Rotation is  also regular and highly precise, each step being  equal to 0.00625°. Finally, it can operate over a great speed range.  • measuring the mechanism position:  measurement  is ensured by potentiometers that detect each  motor step. 

While fulfilling those required functions of the rotary  actuator, providing low weight and compactness has  been one of the major guidelines for designing the SARA®21. On the bas is of its  experienc e on SEPTA  mechanisms, SNECMA MOTEURS has therefore c hosen the CSD 20-160 Harmonic Drive as one of the  key components of the rotary actuator. This  element manufactured by Harmonic Drive is composed of: 

  circular spline short flexspline  wave generator

Figure 2.  SARA®21 CSD 20-160 Super Flat Harmonic Driv e 

• a wave generator:  a thin-raced ball bearing fitted out an elliptic plug serving as a high efficiency  torque converter  • a circular spline:  a solid steel ring with internal teeth  • a short flexspline:  a flexible cylinder with external teeth and a flanged mounting ring 

The complete element is a super-flat (type-20) harm onic drive gear box allowing a 160-reduction ratio. Its  very small dimensions and high performances have allowed SNECMA MOTEURS to develop an  optimized design for the SARA®21 in its entirety. 

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• a two-phase permanent-magnet stepper motor with redundant stator windings  that provides 360  steps of 1° per turn under 76 Ω. It is commanded simply by step- to-step mode, voltage-regulated ( ±  26 V) or current-regulated modes.  • duplex bearings that are lubricated and rigidly prel oaded in order to give the SARA a great tolerance  both to thermal gradients and vibration loads  • two fine and two coarse potentiometers (mai n and redundant) that provides a instantaneous  measurement of the output flange angular position. The fine potentiometers are able to detect each  motor steps, while the coarse potentiometers give  non-ambiguous indication of which revolution the  associated fine is on. Both fine and coarse have a full course of 357° (3° dead zone only).  • a housing that is composed of an aluminum alloy sate llite interface, a titanium part that is glued the  stator motor, an aluminum flange that the wires go through  • a titanium reflector interface 

All are reliable components and some have even proven their efficiency on previous SEPTA® SNECMA  MOTEURS mechanisms with very close configur ations, such as the stepper motor (in its 285 Ω form),  super duplex bearings and potentiometers. 

Performance  The most important performance requirements for which the SARA®21 has been designed are: 

Table 1.  SARA®21 Performance  

SPECIFICATION UNIT BASIS DATA  Motor step angle ° standard 1  Harmonic drive ratio - standard 160  Output step angle ° standard 0.00625  Steps / revolution - standard 57600  step/s maximal 200 Output shaft speed °/s maximal 1.25  Axial stiffness 106 N/m maximal 300  Radial stiffness 106 N/m maximal 150  Bending angular stiffness m.N/rad maximal 50000  Torsion stiffness m.N/rad min / max 13000 /  25000  Axial load capability N maximal 10000  Radial load capability N maximal 8000  Flexion load capability m.N maximal 200  Power consumption (under 26 V) W nominal 10  Inertia capability Kg.m² maximal 200  Output torque m.N nominal 45  Holding torque m.N nominal 70  Detente torque m.N nominal 8  Non operating temperature °C min / max -100 / + 100  Turn-on temperature °C min / max -65 / + 95  Operating temperature °C min / max -50 / + 85  Total mass kg nominal 1.8 

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Qualification Campaign  The SARA®21 has recently achieved an ex tensive qualification campaign during which the performances  detailed above were verified and associated margins established with regards to our first customer  ALCATEL SPACE operational requirements and specified environment conditions. 

Following is a brief description of the most important tests the SARA®21 Qualification Model (QM) went  through. 

Functional tests   • Power consumption control  • Electrical controls: potentiometers or  motor winding resistance and insulation  • Accuracy and output step size control + hy steresis / repeatability and linearity control  • Torque capability control  • Stiffness control (axial / radial / bending / torsion measurements) + combined loading tests 

Figure 5.  SARA®21 functional test set-up  

Environmental tests   • Vibration tests:  sine and random vibrations were  performed along all three axes for 6 minutes, as  well as torsion load vibrations along X-axis (Figures  6 and 7). The QM survived the vibrations with all  frequencies superior to 385 Hz when vibrated with a 3-kg yoke mass. 

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Figure 6.  SARA®21 vibration test set-ups  (centered mass for sine and random + deported mass for torsion load)  

Figure 7.  SARA®21 sine and random v ibrations lev els 

• Shock test: Pyrotechnic shocks were simulated along a ll three axes at the levels shown in Figure 8.  The QM survived those shocks without failure; performances were nominal after the tests. 

Figure 8.  SARA®21 shock lev el and test set-up  

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Figure 9.  SARA®21 shock response spectrum along Z-axis  

Thermal tests: Thermal tests were performed in ambi ent and vacuum conditions at the temperature levels  given in Table 1. The QM surviv ed those thermal cycles nominally. Temperature did not over pass 100°C  for the housing and interfaces, nor 120°C for the wi nding. Regular functional tests such as power  consumption controls, motorization margins and moto r capability tests, were performed without detection  of any degradation. 

Figure 10.  SARA®21 thermal v acuum life test set-up  

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Lifetime tes t  Lifetime test were performed in va rious thermal and vacuum conditions: 

• ambient conditions cycles :       75 complete revolutions            75 cycles on 4°        1500 cycles on 0.2°  • vacuum conditions cycles :       20 complete revolutions          750 cycles on   4° (    250 at 85°C,     250 at -50°C,     250 at 20°C)          975 cycles on 18° (    325 at 85°C,     325 at -50°C,     325 at 20°C)      75000 cycles on   0.2° (25000 at  85°C, 25000 at -50°C, 25000 at 20°C)  • additional vacuum cycles :  50000 cycles on   0.2° at 20°C            20 cycles on 13.5° at 20°C 

The second vacuum cycles were performed in addition to the scheduled qualification tests in order to gain  more confidence within the SARA®21 by proving very comfor table lifetime margins. 

Investigation 

After completing the tests, an investigation was initiated to analyze the condition of the various  components of the SARA®21 QM after completing the qualification tests. 

The mechanical parts show very good condition after the qualification tests with only very slight fretting  traces apparent upon some parts because of qualification vibration levels. 

The harmonic drive has been fully disassembled and inspec ted. The lubricant was still present in nominal  quantity without any specific marks, evolutions or loss. The geometry of  the different parts was nominal  without traces of load damage or degradations. 

Figure 11.  SARA®21 QM CSD 20-160 Harmonic Driv e after qualification tests  

This demonstrates the ability of the new CSD 20-160 Harmonic Drive to sustain very high loads with  margin. Therefore, this component is very attractive for space mechanism s with a very precise position of  the three harmonic drive parts (given by  the bearings) and with a good lubricant. 

The stepper motor was controlled and is fully operational with its nominal performance. 

The potentiometers were checked too; only some sli ght marks were present on the tracks due to vibration  loads for coarse potentiometers (local marks)  and due to extended lifetime for fine potentiometers  (circular marks). In each case, wear of the tr ack / cursor was nominal without impact on signal. 

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Conclusion  The SARA®21 ability to sustain and position a reflecto r with extreme precision was demonstrated  throughout a complete qualification test program during which all of a standard mission phases were  taken into account to establish the envir onment conditions and levels of the tests. 

The SARA®21 performance results were as expected and the investigation that followed on the  qualification model has confirmed its small and compact design has been correctly sized. 

Models are now ready to be integrated upon s pacecrafts, and will soon be flight proven. 

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Figure 1:  Rolamite Joint 

Backgrou nd 

As the relativ e mass prop erties of mechani cally c onnecte d subsystems increa ses, the vibra tion-in duced  jitter also increases (deg rading poi nting accu racy), while host agili ty (slew rate ) decrea ses [1]. The need  for an isolatio n system was identifi ed du ring the de sign of a spa cecraft with agg ressive pointin g and agility  as well a s high sola r-generated power requi reme nts. T he initial po wer requi rement of the solar array wa s  100 kW. The pre dicted mass prope rties of the array and perfo rman ce req uireme nts of the ho st were the   impetu s behi nd develo pment of  the isol ation syste m.   Host Subs ystem Isolation s ystem Figure 2.  Isolation Sy stem Hinge Ar rangeme nt 

In orde r to minimize the co mplexity of th e isolat ion system and b urden on the h ost, a passive system was   desired. Active system s requi re significant en gineering effort a nd necessa rily expensive and co mplex  components i ncluding fa st cont rol alg orithms, sen sors and moto rs. The novel approach devel oped i n [1]  has be en predicte d to meet isolatio n requi rements for the point desi gn and has p otentially wid e  appli cability for any sub system with hi gh mass prope rties relative to the host. 

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Figure 3.  T wo Turn Enga gement M echanism Dual  Driv e Mechanism 

In order to engage the high  torque mode  of the drive mechani sm, the motor become s directly couple d (in  the driven di rection) to the drive d rum after ±2 revolution s from the sp ring free state. A passive   mechani sm, simila r to a car o domete r consists of several in dependent pa wls mounted on a common shaft  betwe en the motor and drive drum. Each pa wl ena bles almo st one full revolution before enga ging the  next adja cent pawl. T wo revolutions f rom the free state is sufficient  to eliminate buckling sta bility concerns  of the spiral sprin g, which i s typically limited to ±3 revo lution s. After two revolutions in either dire ction, the  motor pa wl has rotated e ach ind ependent pawl an d engag es the drive dru m pawl in the directio n of  revolutio n thereby providin g a dire ct loa d path. Dithe ring (reversin g) torqu es are applie d at a rate multiple   times lo wer t han the an gular spee d capability of the motor. 

Safe Mode 

In the event of the host sp acecraft entering safe mo de, each Rola mite hinge m ust have the ability to lock  and with stand very significant mome nt loads, estim ated to be 27 Nm for a 25-kW sola r arra y. In order to   achieve this, a mechani sm was required which wa s capabl e of rea cting the se loads a s well a s remaining  in either the  locke d or unlo cked sta te without ex ternal po wer. A conventional frictio n brake wa s  considered, but packagi ng and mass requireme nts elimi nated this possibilit y. The final config uration  consists of d ual cam driv en pa wls, wh ich e ngage a large i nternal splin e with a tapered to oth profile to   preve nt bindi ng. The cam profile h as been de signed such that any  radial lo ads while in the lo cked po sition   will be rea cted throu gh the  cente r of rot ation of the cam, redu cing the possibilit y of torque o n the spli ne  counter rotati ng the cam a nd unintentio nally disen gaging the mechani sm. The cam is a ctuated with a bistable rotary solenoid coupled throug h a torsi on spri ng to  allow ful l motion of the sole noid in case the pa wl  teeth do not initially line up with a spli ne. An exter nal detent sp ring hol ds th e sole noid o utput shaft at  either extre me to meet the power-off req uirement. Fi gure 4 illu strates the safe m ode me chanism con cept. 

Figure 4.  Safe Mode M echanism Con cept 

Conclu sions  and Lesso ns Learn ed 

The Rol amite approa ch has proven to be a soun d fundame ntal mech anism for this application an d  prelimi nary hard ware testing ha s valid ated this a s well. Scal ability and available volum e for additio nal  mechani sm p ackagi ng are  just as impo rtant as f undamental me chani cal ope ration when considering an  approach for a develo pmental appli cation. Several re lated le sson s have be en le arned so far; components  norm ally re garded a s sources of lo w friction can prove to be othe rwise and n ormally accepta ble  manufa cturing techni ques and toleran ce can also prov e to sign ificantly influence system  perform ance  167
The lesso ns learned from  the enginee ring unit hav e been incorporated into the current d esign of the  Rolamite joint . A compreh ensive testin g pro gram has begu n at the com ponent level and will culminate in   the characte rization of a fully articul ated two-di mensional isol ation system  on a n airbearing floo r.  Amplitude a nd freq uency sweep s will be cond ucted on the 2-D isolation system in the  ope ration al  envelope wit h resultant tr ansmitted force at the simulated host re corded. The data will then be correlated   to the analytical mod el. Joint perform ance will be  evaluated both from the system as well as fro m  component le vel testing. 

References 

1. T. Murphey, M. Botk e, R. Blankens hip, N. Hag ue, “A n Articulate d Motion an d Vibratio n Isolat or for  Spacecraft”, AIAA-2003 -1829, May 200 3 

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the lifecycle cost of an airborne line-of-sight TCDL data-link and incr ease the range of the data link to be  limited only by the UAV altitude, up to a distance of 322 km (200 mi)." A bi-product of this contract is the  new plastic Omni-Wrist III shown her e. Benefits expected to arise fr om the SBIR include: high capacity  multimedia data exchange, jam-resist ant communication, small transmit/receive aperture, low power and  weight and resistance to EMI and co-site interference. 

The test and evaluation Omni-Wrist III unit (Figure 2) addresses technology gaps in existing approaches  to sensor pointing. Typical precision solutions have in volved the use of either a distributed axis system or  a gimbal. Both of these types of conventional azimuth/elevation mounts su ffer from slowed response  times and/or limited range of motion, or from singularit ies (voids in the work envelope). The first type of  design has a sensor mounted on a fork for elevation (p itch) that in turn is mounted on a rotating base for  azimuth (yaw). Such a design requires the posit ioning of two independent syst ems, which increases  response time by introducing unnecessary path optimizati on calculations into every pointing operation.   

Figure 1.  Adv anced UAV Antenna Pointing Sy stem

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Figure 2.  Omni-Wrist III Pointer  Linear Actuators Support Colum n Wrist Head Sensor Mount  Plate  Presently two forms of precision antenna pointi ng systems dominate the ground-based and space-based  markets (Figure 3). Schaeffer Magnetic , Inc., Chatsworth, California “Biaxial Drive” represents the most  common design, also know as an azimuth and elevation or yaw-pitch type drive [6]. Schaeffer’s system is  173
Table II shows the positions used in  the tests. Figures 6 and 7 plot  the test results. Each value repr esents the average of at least three  repetitions. Figure 8 is a plot  of the resultant [SQRT(x2  + y2)] pointing  error. The median pointing error was 60.84 arc seconds.  176  

       Table II 

Figure 5.  Omni-Wrist III Test  Setup  

 Home Position  Dec = 89; Az = 180  Home Position:  Dec = 0;  Az = 0 

Test  #  DEC AZ    Test #   DEC AZ              1  0 0    1  89 0  2  45 90    2  89 45  3  45 270    3  89 90  4  45 0    4  89 135  5  75 180    5  89 180  6  75 45    6  89 225  7  80 170    7  89 270  8  89 90    8  89 315  9  89 270    9  45 0  10  45 45    10  45 90  11  80 0    11  45 45  12  89 135    12  45 135  13  89 225    13  45 180  14  15 315    14  45 225  15  30 315    15  45 270  16  89 45    16  45 315  17  35 315    16  45 315  18  40 315     19  50 315     20  60 315     21  70 315     22  80 315
Pointing Error from Home Position - Dec 89 ; Az 180 -250.00-200.00-150.00-100.00-50.000.0050.00100.00150.00200.00250.00 0 5 10 15 20 25 Test NumberPointing Error (Arcsec)Az Error Dec Error

Figure 6.  Azimuth and Declination Pointing Errors for the Omni-Wrist Sensor Mount 

Pointing E rror from Home Posi tion - Dec 0;  Az 0 -200.00-150.00-100.00-50.000.0050.00100.00150.00200.00 02468 10 12 14 16 Test NumberPointing Error (Arcsec)Az Error Dec Error

Figure 7.  Azimuth and Declination Pointing Errors for the Omni-Wrist Sensor Mount  177
Resultant Pointing Error 0.0050.00100.00150.00200.00250.00 0 5 10 15 20 25 Test NumberResu ltant Error - [S QR(x^2 +y^2)]  Arcsec Home (89,180) Home (0,0) Median Error = 60.84 Arcsec

Figure 8.  Resultant Pointing Error for Omni-Wrist Sensor Mount  

Conclusions 

A background on the pointer problem was presented with a discussion of desired capabilities. These  capabilities include (1) full hemispherical range that is singularity free, (2) ease of control through single  computation, (3) high slew rate, and (4) low cost. Histor ical sensor mount designs that persist to this day  were related. The Omni-Wrist III Sensor Mount wa s presented as a candidate with advanced horizon-tohorizon  tracking capability. The value of singularity-fr ee motion was presented with test results. 

References 

1.  Honeywell, 1996. M597B/CLR. “Rotary Actuator  Characteristics.” Specifications sheet on  Honeywell’s space qualified rotary actuator.   2.  Rosheim, M., Sauter, G. 2002. "New High- Angulation Omni-Directional Sensor Mount." SPIE  Conference Proceedings. Seattle, Washington, 8-11 July 2002, 482163.  3.  Rosheim, M. 2000. U.S. Pat ent 6,105,455. “Robotic Manipulator.” Filed Sept. 14, 1999; issued Aug.  22, 2000.  4.  Rosheim, M. 1999. U.S. Pat ent 5,979,264. “Robotic Manipulator.” Filed Oct. 16, 1997; issued Nov. 9,  1999.  5.  Rosheim, M. 1999a. U.S. Pat ent 5,893,296. “Multiple Rotatable Li nks Robotic Manipulator.” Filed  Mar. 13, 1997 and issued Apr. 13, 1999.   6.  Schaeffer, E. 1991. “Application of Harmonic Drive in Space.” Presented at the International  Harmonic Drive Symposium. Mats umoto, Japan. May 23, 1991.  

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Figure 1.  The S wRI MEMS de velopment and test facilit y. The v acuum  microprobe station,  mounted o n pneuma tic dampers, and  nitrogen -purged storag e cabinet ar e inside the d own flow  clean te nt while the con trol computer , ARBs, A RB signal amplifiers, and hi gh resolutio n directfeed monitor  are on the a djacen t workbench.   The station is contain ed within a HEPA-filtered, down flow environment, al ong with a nitrogen -purged  cabinet whe re we  store MEMS device s not presently in use.  In this way, the ME MS chip s can be removed  from their tra nsport contai ners an d inserted into th e vacuum mi croprobe stati on entirely wi thin a cle an  environ ment.  Continuo us real-time im aging of the test device s is accompli shed through a very thin (1.6  mm) si ngle crystal sa pphire wind ow. Be cause of the l arge dista nce throug h the window a nd down to the  test su rface, we h ave dev elope d an i maging syste m that incorp orates o ne of t wo very long  focal le ngth  prima ry obje ctives, followe d by a CCD came ra and image captu re system. Thi s provides coarse imag es  that are ~1 280 x 960 µm, with ~2 µm resol ution and  ~320 x 240 µm, with ~ 0.5 µm res olution, for c oarse  and fine imag ing, respe ctively.  A more thor ough d escription of the facility is give n in 4. 

Initial Vacuum Testing and Results 

These tests were set up to answe r two  fundamental  question s about MEMS operatio n in vacu um. First,  we sought to determi ne how important air dam ping is for the m otion of MEMS d evices. Seco nd, we  were  very co ncern ed that the air mol ecules in gen eral, and the water vap or in the ai r, in pa rticula r were  providin g critical lubrication. Thu s, it was importa nt to dete rmine if MEMS wo uld work i n vacuum at all. If  they do fun ction in va cuum, then it is crit ical to determine ho w their operational  chara cteristics vary from   those o bserved at atmosp heric pres sure and wheth er their fun ctional lifetimes are ade quate for typical  appli cation s. 

We tested six separate size/type combinations of m echani cal oscillators that are pa rt of a material s test  packa ge d evelope d at S wRI a nd fab ricated using the Ch ronos MUMPS p rocess.6 These oscillators  consist of a  simply su pported beam with  a mass at the distal e nd. The edge  of the ma ss supports comb - drive fingers for actuatio n. Figure 3 sho ws a ph oto o f one of our medium -sized oscillator d evices. When   operated at reso nance, th e end m ass oscillates with a larg e displaceme nt. The device s were  operated in   181