ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Actuator Chronoloay  The complete development of the actuator is beyond the scope of this paper but several important  -  -I ..  milestones should be noted  1997 Fine stage flexure developed‘: Large axial input results in small axial output due to compound  flexure configuration.  1999 First Actuator built? 1 0-mm motor, dry film lubrication on all gears and bearings, tested at  cryogenic temperatures (30 K), demonstrated fine resolution of less than 10 nanometers.  2000 AMSD Actuator built3: %-inch motor, more robust, twin counter-rotating coarse drive screws,  three monopods per mirror, first mirror phasing demonstrated.  2002 IR&D Actuator: %-inch motor, more modular to reduce fabrication & assembly costs, large  coarse drive screw to accommodate launch loads. Never tested.  2003 Test Bed Telescope Actuator4: 1 0-mm motor, low cost, 150 units built, hexapod configuration,  smaller size, flight-quality positioning, ambient conditions, new fine stage flexure design.  2004 Flight Actuator: %-inch motor, ball screw for improved axial load capability, dry lube on all  bearings & gears, new fine stage flexure.  Figure 7 shows an actual collection  of data from the first fine range of  motion test. The graph shows  absolute height vs. motor steps and . the distorted sine wave is clearly  visible. Note that the fine range here  is = 10.9 microns (0.0109 mm).  Subsequent adjustment of the fine  stage flexure resulted ir, a fine range  of 10.5 microns. Fine Staae lmwovement  Figure 6 shows the simplified fine  stage flexure. The shape is generally  that of the capital letter “A”. Like the  original fine-stage flexure, movement  of the cross-beam deflects the side  beams, which, in turn change the  overall height of the flexure. The  cross-beam is attached to an eccentric  cam shaft, which is driven by a  gearmotor. As the cam shaft rotates,  the cross-beam is driven up and down  resulting in a sinusoidal displacement  pattern. The sinusoid is distorted due  to the compound nature of the  geometry. The fine range of motion  can be easily adjusted by changing out  the pair of shims under the feet of the  fine stage flexure. A change in shim  thickness of about 0.1 mm (.004 in)  results in a change of fine motion of  about 1 micron. Large movement of cross  beam results in small overall  Eccentric Bearing drives  cross-beam motion  Shims under feet are  adjustable to modify fine  range of motion  Figure 6. Simplified Compound Flexure  3  Figure 7. Fine Stage performance  244
Actuator Mechanical Description  The best way to describe the functioning of this  mechanism is to follow the drive train. The major  components in the actuator are shown in Figure 8 and in  the diagram in Figure 9. All major components attach  directly to the main housing.  Gearmotor  The drive train of the Actuator begins with a stepper  motor. This type of motor is often used for positioning  mechanisms because the rotation is divided into discrete  steps. The motor for this application has 24 steps per  revolution or 15 degrees per step. The stepper motor is  attached to a 60:l gear head and a resolver to form an  integral gearmotor assembly. All bearings and gears are  coated with a Ball proprietary dry film lube to enable  operation at 30K.  First Pass to Cam Shaft  The output from the gearmotor uses a simple 3:l spur-  gear pass to drive the cam shaft. The cam shaft  incorporates an eccentric bearing in the middle that drives  the fine stage flexure shown in Figure 8. The shaft is  supported by two simple bearings that are preloaded so  that the shaft is always pulled away from the gear end.  The cantilevered mounting of the shaft enables the use of  1:l right angle bevel gears to change the drive axis from  horizontal to vertical.  Second Pass to Coupling  The bevel gear pass connects to the coarse drive  shaft through the coarse drive coupling as shown in  Figure 5 described previously. Both sides of the  coupling are supported by preloaded bearing pairs.  Except for the gears, both sides of the coupling are  identical to take advantage of commonality in  fabrication. The drive side has a bevel gear and the  driven side has a spur gear pinion attached.  Third Pass to Coarse Drive  The spur gear pinion drives a large ring gear  resulting in an 8:l ratio. The coarse drive shaft is an  8-mm ball screw with a 2-mm pitch that is mounted  as a cantilever with two preloaded bearings at one  end to attach the shaft to the main housing.  Other Components  The remaining actuator components are discussed  later in the paper and include:  0 Friction brake  0 Torsional stabilizer  LVDT position sensor  0 Dry film lubrication Figure 8. Actuator on Test Stand  Fine Position 0.01 mm  Fine Range  Compound  flexure  1 :3 Spur gear pass  I 1 : 1 Bevel gear  A  Geai  Ball screw & nut  Torsional  Stabilizer 21 mm Coarse Range  Figure 9. Schematic Diagram  245
Design Discussion  Figure 10 is a cut away view of the actuator showing the preloaded bearing pairs and gear passes.  Standard recommended fits and tolerances were used. These are all standard mechanical configurations  derived from catalog information.  DW Lube  Operation at 30K prevents the use of liquid  lubrication. Instead, dry film lubrication was applied  to the moving surfaces of all bearings and gears.  This Ball proprietary process as been used  successfully on other cryogenic programs such as  SIRTF and Hubble. Moving components can  therefore be operated at ambient as well as  cryogenic temperatures.  Gearmotor Life  The life requirement for the gearmotor was  estimated using expected operational cycles for the  life of the unit. A total of 1.7 million motor  revolutions were estimated. The dry film lubrication  in the gearmotor has been analyzed to last at least  3 million cycles.  The gearmotor has been noted as a life limited item  and motor revolutions must be recorded. Factor = spec/total = 1.75  Margin = spechotal -1 = 0.75  Toruue Marain  The motor is a stepper type that rotates a precise  amount for each step command. Torque 'margin  calculations were generated to compare the output  torque of the motor to all of the resistance torques  including friction, inertia, coulomb drag and  operational loads. Appropriate safety factors were  placed on the various loads including cryogenic  operation. The motor shows a positive margin under  all conditions.  Friction Brake  A small friction brake was added to the actuator to  prevent the coarse drive screw from back-driving  operation. The axial force on the ball nut applies a Geajmotor  w all Screw Shaft  Figure 10. Section View  torsional component to the coarse drive shaft. The coarse drive gear was chosen for the brake location  because it is the largest torsional element on the coarse drive shaft thereby requiring the least force to  constrain. The brake uses a double cantilevered beam to support and apply force to two Vespel buttons.  The buttons slide along a raised surface on the coarse drive gear.  Torsional Stabilizer  In order for the actuator to apply pure axial motion, the nut on the ball screw must be constrained to the  main housing in such a way as to resist torsional loads but to allow axial movement. The torsional  stabilizer provides this constraint by incorporating a thin flexible shear panel that resists the torque applied  to the shaft while allowing the ball nut to translate. As the nut moves up and down the shaft, the flexure  forms an "S" shape. A pivot flexure that is opposite the panel flexure minimizes the radial loading on the  ball nut from the stabilizer.  246
Power Train Capabilities  Because of the numerous gear passes, it was convenient to summarize the load at each step of the power  train. Starting with the gearhead output torque, Table 2 lists the load at each step. The input torque is  converted to a tangential force by dividing by the radius of the pitch diameter of the gear. The Pitch Angle  is also factored in as well as the resulting load on the bearings. The tangential force is then multiplied by  the radius of the driven gear to obtain the torque on the driven shaft. The torque on the shaft is then used  as the input torque of the next pass. The calculations shown are for the 1 g operational load.  Table 2. JWST Power Train Calculations  First Pass Calculations  Gearhead Input Torque  Shaft Radius  Tangential Tooth Load  Camshaft Gear Radius  Efficiency  Torque to Cam Shaft  Second Pass Calculations  Cam Shaft Input Torque  Bevel Gear Radius  Tangential Tooth Load  Bevel Gear Radius  Efficiency  Torque to Coupling  Third Pass Calculations  Coupling Input Torque  Pinion Radius  Tangential Tooth Load  Coarse Gear Radius  Efficiency  Torque to Lead Screw  Lead Screw Calculations  Lead Screw Input Torque  Brake Drag  Lead Screw Radius  Ball Screw Ramp  Axial Force 0.200 in-lb 0.02 N-m  0.166 in 4.22 mm  1.205 Ib 5.36 N  0.500 in 12.70 mm  0.950 0.950  0.572 in-lb 0.065 N-m  0.572 in-lb 0.065 N-m  0.166 in 4.22 mm  3.448 Ib 15.33 N  0.166 in 4.22 mm  0.950 0.95  0.544 in-lb 0.061 N-m  0.544 in-lb 0.061 N-m  0.156 in 3.97 mm  3.481 Ib 15.48 N  1.250 in 31.75 mm  0.950 0.95  4.133 in-lb 0.467 N-m  4.133 in-lb 0.467 N-m  3.000 in-lb 0.34 N-m  0.164 in 4.17 mm  0.077 in 1.95 mm  90.09 Ib 400.7 N  248
Actuator Testing  Assembly stage  Motor only  Motor & gearhead ambient  Motor & gearhead cold  Actuator assembly, ambient  Actuator assembly, cold  Bipod assembly, ambient  Bipod assembly, cold Testina Options  Early in the program it became apparent that the testing of certain properties of the actuator could occur at  several different stages of assembly as shown in Table 3. Because some of the components are life  limited and because of the relatively large quantity of units involved, it was impractical to test every  property at every level. Also, it was desirable to limit cryogenic testing because it is expensive and time  consuming.  Property to be tested  Motor torque  Motor torque, gearmotor torque  Motor torque  Motor torque, fine range of motion, coarse range of  motion, coarse accuracy, Axial stiff ness, Axial  backdriving capability  Motor torque, fine range of motion, fine step size, fine  accuracy, coarse range of motion, coarse step size,  coarse accuracy, LVDT output accuracy  Motor torque, coarse range of motion  None Table 3. Actuator Testing Options  1  Assembly Stage: Motor only, Motor & gearhead ambient, Motor & gearhead  cold, Actuator assembly, ambient, Actuator assembly, cold, Bipod assembly,  ambient, Bipoci assembly, cold, Mirror hexapod assembly, ambient, Mirror  hexapod assembly, cold.  Mirror hexapod assembly, ambient  Mirror hexapod assembly, cold I I  Motor torque,  TBD Property to be tested: Motor torque, Fine range of motion, Fine step size,  Fine accuracy, Coarse range of motion, Coarse step size, Coarse accuracy,  Axial stiffness, Axial backdriving capability, LVDT output accuracy  Test Plan  After much discussion and trades, a testing plan was established to identify those properties that would be  tested, and at what stage. It was desirable to test certain properties early in the process to determine any  potential problems. The final test plan is shown in Table 4.  249
i.  I  11111111111111111-  c  Error in microns  a Actuator Test Results  To date, there have been four major test activities: ambient motor tests,  cryogenic motor tests, ambient actuator tests and cryogenic actuator tests.  Ambient Testinq  Figure 11 shows the combination test stand at the actuator fabricator. The  fixture is used to measure axial stiffness, fine range of motion and coarse ;  accuracy under ambient conditions. To measure the coarse accuracy, the  length of the actuator was measured from stowed to deployed at every cam  shaft revolution. The theoretical position was then subtracted from the  measured position and the results are presented in Fig. 12. Note each  point represents 0.25-mm axial movement. The accuracy requirement is  2% for this level of move, which equals 0.005 mm (5 microns). The test  was performed in both the deploy (CW) and retract direction (CCW). .  Figure 11. Test Stand  111111111111111.  - 5 micron requirement  Crvoaenic testing  After the actuator was delivered to Ball, more accurate tests were performed to verify cryogenic operation  and fine motion characteristics. Nanometer-level measurement testing requires interferometric  instrumentation, vibration compensation and special software. Up to seven actuators can be tested at  once using the special setup shown in Figure 13. One of the fine motion tests is single step repeatability.  The results of this test are shown in Figure 14. The motor was rotated one step clockwise then one step  counter-clockwise several times. The results show  an average step size of about 7 nanometers and a  repeatability of 1 nanometer.  Figure 13. Cryogenic Testing at Ball  250
Conclusion  The design of the Cryogenic Nano-Actuator for JWST is now complete. The EDU units have been  assembled and tested. The actuators will next be assembled into bipods, which will then be integrated into  the primary or secondary mirror hexapod configuration. Long lead component procurement for the flight  actuators is underway. Flight actuator fabrication is scheduled to begin in the last quarter of 2006.  The design of the actuator was extremely challenging but test results show that optical level positioning  can be reliably achieved using simple mechanical components. The unique combination of the patented  fine stage flexure with the coarse coupling proved to be quite effective in achieving fine accuracy over a  long range of travel. Mass production techniques greatly simplified the design and assembly of the  actuator. Reliable operation was achieved by the use of robust components and supporting analysis.  Acknowledgements  This paper presents the design of the Cry0 Actuator for JWST. The design of the actuator is the result of  important contributions from numerous people and organizations. I would like to acknowledge the  contributions from those at Ball Aerospace including Robert Slusher, Scott Streetman, Lana Klingemann  (nee Kingsbury), William Schade, Mike Matthes, Bruce Hardy and all the technicians, machinists,  engineers and administrators. I would also like to acknowledge the outstanding work of outside vendors &  suppliers including CDA Intercorp, All American Gear, New Hampshire Ball Bearing, Barden Bearing,  ATK-Able, Next Intent, Schaevitz and Beaver Aerospace. The photographs in Figures 8, 11 & 15 are  courtesy of Able. Finally, I would like to thank our customer, Northrop Grumman Space Technology  (formerly TRW) and NASA Goddard.  References  1. R. Slusher, “Motion Reducing Flexure Structure”, US. Patent Number 5,969,892, Oct. 19, 1999.  2. S. Streetman, L. Kingsbury, “Cry0 Micropositioner”, U.S. Patent Number 6,478,434, Nov. 12, 2002.  3. Scott Streetman, Lana Kingsbury, “Cryogenic Nano-positioner Development and Test for Space  Applications”, in IR Space Telescopes and Instruments, Proceedings of SPlE Vol. 4850, Sep. 2002.  4. Lana Kingsbury, Paul Atcheson, “JWST Testbed Telescope”, in Optical, Infrared and Millimeter Space  Telescopes, Proceedings of SPlE Vol. 5487, June, 2004.  252
Body Flap Actuator Background  The Body Flap actuator is shown in Figure 1. Several failure modes can end the life of the BF actuator  bearings. Fatigue spalling, fretting fatigue, lubricant failure, high temperature oxidation, corrosion pitting,  severe wear or combinations of these mechanisms can cause bearing failure. Corrosion pits or wear  damage accelerate fatigue crack growth that can cause fatigue failure before the bearing reaches the B1  or B10 fatigue life. If the bearing wear life or the Braycote 601 grease life is exceeded, the bearings can  fail. However, because the actuators possess very high driving torques, the worst bearing failure mode  was expected to be a broken ball or bearing race that could jam the actuator as well as the common drive  shaft and cause an actuator performance failure.  The design criteria for the space shuttle (OV) BFA are 100 missions and 10 years. During the 1990s,  excessive BF flutter during launch and excessive BF housing corrosion led to disassembly and inspection  of BF actuators. In October 2002, bearings from the SIN 402 and SIN 405 actuators were cleaned and  microscopically inspected to find out if ball bearings in the BFA assemblies needed to be replaced. As  part of that investigation, shaft bearing PIN 5902050, SIN V6L009, from body flap actuator SIN 402, was  found to possess unusually dark wear surfaces when compared to the rest of the bearings under  examination (Figure 2) [I, 21. NASA's Engineering and Safety Center (NESC) became aware of this issue  and initiate an Independent Technical Assessment to assess this bearing and all other bearings in the  Shuttle's Rudder Brake and Body Flap Actuators [4].  qw aonn D nc~rumn snw~ INTEGRAL BAL BEARINGS  OUTCLW PIANEf OUR  C mnb  OUTPUT HOUSING  (STATOR)  NPUT HOUSING  CmTER HOUSINO (flAl-0 R)  mom R)  Figure 1. Space Shuttle Body Flap Actuator  -  Figure 2. Body Flap Shaft Bearing S\N V6L009
Analysis of BFA Bearing with Black Balls  Visual inspection of P/N 5902050, SIN V6L009, revealed a black, tribological coating on the balls and  race wear tracks (Figure 3). It should be noted that no other bearing in the Body Flap or Rudder/Speed  Brake actuators was found to contain the black, tribological coating on the wear surfaces. Minor corrosion  was noted on the inner and outer raceways. The grease present in the bearing was brown in appearance  due to the tribological decomposition of the Braycote 601 grease and iron oxide wear debris. The  recommendation based on microscopic examination analysis was to replace the bearing since the wear  surfaces were black and it suffered Brinell damage during disassembly.  I  Figure 3. Black bearing after sectioning and cleaning  Note black balls and the dark bands present on the raceways.  Further work performed in 2004 by Hamilton Sundstrand, Inc. reported that the inner ring contained a  black tribological coated band. The black band or wear track possessed a smooth matte finish with a  grain boundary like structure. Outside the black wear track, the original surface was still evident along  with the original finish marks. The outer ring contained a similar black coated wear band (Figure 4). The  wear surface of the outer race was similar in appearance to the wear surfaces present on the balls.  Figure 4. Magnified views of the black wear tracks in the inner race (left) and outer race (right)  are shown. Note the false brinelling marks. The dark brown color is an optical  aberration of the black color.  Scannina Electron MicroscoDv GEM)  Scanning electron microscopy was performed on segments of the black ball bearing by various groups  [5]. The segments examined included the balls, inner raceway and outer raceway. Analysis of the balls by  energy dispersive spectroscopy (EDS) revealed that the black tribological coating was composed of  carbon and iron oxide. The coating was porous and appeared to be uniform over the entire ball surface. A  few skid marks were noted (Figure 5). In addition, each ball possessed a moon-shaped spot that  appeared to have penetrated the burnished coating. The spot was probable caused by a drop of rain  255
water absorbing corrosive chemical from the degraded grease and dissolving the black coating during  Shuttle storage.  Figure 5. Scanning electron micrograph of black ball showing spot (left) and skid marks (right)  Figure 6. Scanning electron micrographs of the black ball (left) and magnification of particle  present on the ball surface (right)  Higher magnification of the ball revealed some particles present on the ball (Figure 6). The presence of  aluminum and silicon, in addition to other elements detected by EDS on these particles, were likely  attributed to the bentonite clay additive present in the Braycote 601 grease and not contamination as was  originally proposed. Analysis of the inner and outer raceways showed surfaces similar to the black ball.  EDS performed on those surfaces detected the carbon iron oxide coating found on the black balls.  Examination of the inner raceway away from the burnished band showed the original finishing marks  which gradually translated into a smoother region as the burnished area was approached (Figure 7).  Figure 8 shows the surface for the coating present on the black ball obtained by surface profilometry.  Figure 7. Scanning electron micrograph of the outer raceway in the region above the burnished  band (left), and within the burnished band (right) I 256
1 ---  3 3311  , , , frnl7l  000 mm 0 361  Figure 8. Surface profilometry trace showing the coating present on the black ball including a  segment of the grain boundary-like structure in the center  Raman SpectroscoDy  Raman spectroscopy of the black balls showed carbonaceous peaks from the carbon coating on the  surface of the complex iron oxide, black, tribological coating [6]. Specifically, the diamond, D, and  graphitic, G, peaks were observed confirming the presence of amorphous carbon (Figure 9).  Figure 9. Raman spectrum for black ball showing the graphitic (G) and diamond (D) peaks  associated with amorphous carbon.  X-rav Photoelectron Spectroscopv [XPS)  XPS was performed on the black ball at three different locations and on the inner race. Following the  initial scans, depth profiling was performed by application of fifteen sputtering cycles, each lasting ten  seconds, and a total sputter time of 450 seconds per location. The results show a carbon-rich coating on  top of an iron oxide-rich surface. The carbon-rich top surface forms during the tribological decomposition  of Braycote 601 grease and contains fluorine and sodium from the grease [7, 81. The Raman spectrum of  the carbon-rich coating is reported in the Raman spectroscopy section. Below the carbon-rich coating is  the black tribological iron oxide-rich coating that also contains fluorine from the grease. At the end of the  sputtering cycles, sodium was no longer present and chromium was observed in both locations in addition  to carbon oxygen, fluorine, and iron (Figure 10).  Metalloaraphv  A black ball and a segment of the race from the blackened bearing, S/N V6L009, were metallographic  cross sectioned and the tempered martensitic 521 00 steel and black tribological coating examined  (Figure 10 and 11) [5]. The microstructure of the black ball was consistent with properly processed 52100  temper martensite with finely dispersed carbides with a hardness of R, 64-65 from the surface into the  ball. Tapered sections showed no evidence of annealing below the black tribological coating therefore the  257
temperature of the ball did not go above 204°C during the formation of the black tribological coating. The  black coating appears to be a micron or two thick. Pits present on the cross-section were very shallow.  11K  10%  1M  9%  LI.(  0.x  BK  7.5K  7K  6.W  5w U  6 5.W  BW 5  4%  4n  3s  jn  23  w  I.€#  1H  5a:  11 6 1-6 -6 EYE6 7W6 8p8.6 5-6 A986 3986 -6 lW6 W6  mw harw lev1  Figure 10. An XPS spectrum for black ball I  Figure 11 a. Metallographic section of black bearing  258