ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
The cross support arms support the Sample Carousel Disk via a set of 4 wheels rolling in a v-groove in  the Sample Carousel Disk. Each Cross Support Arm wheel contains a set of preloaded angular pair  bearings in the back-to-back configuration. The Cross Support Arm wheels roll in the Sample Carousel  Disk groove when the Sample Carousel Disk is locked to the Ground Ring, Figure 3.  Due to the tight positioning requirements of the Sample Cups, the Sample Carousel Disk was required to  be concentric with respect to the center hub axis of rotation. To accomplish this in the presence of  significant manufacturing tolerance stack-up, the radial position of the cross support rollers was adjusted  during assembly to ensure the Sample Carousel Disk was concentric to within 0.05 mm. Shims were  independently precision ground to desired thicknesses at the assembly level, Figure 6.  Shim adjusts the radial  position of the Cross  Support Arm Roller. Wheel/Carousel V-Groove  Interface  Cross Support Arm  Figure 6 - Radial Adjustment Shim for Carousel Disk Concentricity  Using a single actuator to position both the Rotating Elevator Frame and the Sample Carousel Disk  required more than 360° of rotation of the center hub. A twist capsule carries power and signals to the  elevator actuator and feedback switches on the Rotating Elevator Frame. To prevent damage to the twist capsule in the event of actuator run-off, hard stops were implemented in the Center Hub. To allow for  greater than 1 revolution of travel, an intermediate hard-stop ring travels bet ween the ground and the  output of the center hub, Figure 7. This design allows for 693 ° of rotation, hard stop to hard stop.   Fixed Hard-stop Intermediate Ring  Rotating Hard-stop  Twist Capsule  Figure 7 - Top Section View of Center Hub Twist Capsule and Hard-stops  Rotating Elevator Frame The Rotating Elevator Frame consists of a linear actuator to raise and lower cup s, a parallel spring  flexure, and a launch lock for the elevator subassembly, Figure 8. The parallel spring flexure allows the  307
Elevator launch lock cleats to de-mate when there is no load applied to the elevator lift via a sample cup.  This system allows for a re-usable launch lock mechanism and a reduction in structural mass required to  deliver a seal force to a sample cup or the contamination seal. The 1350 Newtons that the elevator  delivers is all reacted locally, Figure 9. The load path does not trace back through the center hub assembly, which would have required significantly more structural mass to accommodate.                                Launch  Lock Cleats Motor &  Planetary  Gearbox  Elevator Lift Parallel Springs Figure 8 – Elevator Actuator & Rotating Elevator Frame            Pyrolysis  Oven Cleats Load Path Contained Locally  Launch Lock,  Cleats MatedElevator not  loaded, Cleats  De-mated  Figure 9 - Rotating Elevator Frame Launch/Seal Lock   Elevator Actuator The linear actuator for the Elevator consists of a hal l commutated brushless  DC motor, 80:1 planetary  gearbox, 2.4:1 spur gear arrangement, and a pair of 5/16-12 ACME lead screws, resulting in resolution of 1088 hall counts per millimeter. The two lead scre ws are mechanically coupled via Custom 455 H1000  Stainless Steel spur gearing in the bottom of the Elevator Assembly. The two lead screws are Nitronic 60,  50% Cold Worked Stainless Steel and the ACME nuts are 15-5PH H1025 Stainless Steel. The ACME screw is non-backdriveable for coefficient of friction > 0.09. A magnetic detent brake on the motor rotor is  sufficient to hold the elevator preloaded  in the event there is no friction  in the leadscre w nut. The lead  screws rotate in Nitronic 60, 20% Cold Worked Stainless Steel journal bearings and 440C needle roller thrust bearings. The screws, nuts, bearings and gears are grease plated with Braycote 600 EF Micronic.  Reservoirs in the journal bearings and the root of the ACME screws were also packed with the same  grease.   308
Elevator Seal Force The elevator actuator is required to deliver 1350-N force to a sample cup to an accuracy of ±10% of the  commanded force. The force delivered by the actuator must be commandable to allow for multiple uses of  a single sample cup. An appropriately sized load cell could not be found that could withstand the temperature range (-55 to 110°C). A desire to reduce the burden on the control electronics and the added  cost of development and qualification of a load cell led to an alternate solution custom tailored to the SMS  design.   The load path for the seal force is transmitted through the lead screws and thrust bearings to a compliant  flexure arm, Figure 10. The lead screws and lift assembly are allowed to translate along the axis of the applied load. A spherical shoulder on the bottom of each lead screw allows the flexure arm to rotate about  its hinge axis without inducing moments in the spur gearing and the leadscrew/nut interface. Further, the  lift assembly is pinned to each leadscrew nut to allow the lift to flex without induci ng moments in the lead  screws, thereby maximizing the efficien cy of the screw/nut interface. At the end of the flexure arm is a  spring-loaded electromechanical switch. With no load applied, the switch is an open circuit. Once a load is applied to the lift, the switch begins  to close. Once the load reaches 450 Newtons, the switch closes. A  short stroke wave spring provides the repeatable contact force for the switch assembly. Once the switch  closes, the structure becomes a linear spring. The stiffness of the structure, in units of motor counts per Newton, is determined during mechanism calibration. Therefore, once the switch closes at a known force,  all backlash in the load path and drivetrain has been eliminated. Commanding the motor to run a specific  number of hall counts past the switch transition will result in the desired seal force applied to the sample  cup. An integrated bellows assembly keeps the switch contact area free of particulate and Martian dust.                            Applied Load  Pinned Connection LiftFlexure Arm  Hinge Flexure Arm  Spherical Shoulder Figure 10 - Elevator Actuator Break-Out View Spring Loaded  Switch with  Bellows  Incremental Encoder Optical switches reside at the output of the Rotating Elevator Frame and consist of opposed LEDs and  Phototransistors. A pair of LED/PT switches, together with the tooth profile on the Ground Ring act as a  custom incremental encoder  located at the output of the mechanism, Figure 11. The “region of alignment”  indicates the REF is in a position where it is acceptable to actuate the toggle mechanism or raise and  lower a cup. By integrating feedback to the output of the mechanism, motor hall counts can be compared  to optical switch state transitions to detect faults by a prompt, safe, and recoverable me ans. Together with  the hard-stops on the center hub, the SMS is capable of full recovery from an unexpected loss of power  that would result in the loss of position information. The SMS may also operate should either the motor hall sensors or the optical switches fail. It is a redundant control scheme.   309
Figure 11 - REF Incremental Encoder  Sample Carousel Disk The Sample Carousel Disk holds all 74 sample cups, the toggle mechanism, and the Vacuum Seal and  excess sample container, Figure 12. There are 37 sample cups located on each row of the Sample Carousel Disk. The packing density of the Sample Carousel was maximized to provide as many clean  cups as possible within the allotted vol ume. Each sample cup can interfa ce with the puncture station,  pyrolysis oven, and sample inlet on its respective row. Two rows of cups provides for redundancy in the  event of a pyrolysis oven failure.   In the launch position, the vacuum seal is elevated at the solid sample inlet location. O-rings provide a  vacuum tight seal to prevent the sample cups from being contaminated prior to arrival at Mars. Also  integrated into the vacuum seal is a reservoir to collect excess sample flushed through the inlet tubes. When the vacuum seal is in place, the launch lock on the elevator assembly is active. Each sample cup is  constrained to the Sample Carousel Disk by a cantilever spring detent release/restraint device. The  sample cup restraint must hold the sample cups during launch and EDL activities and release when the cup is used for an experiment on Mars.   310
Vacuum Seal and  Excess Sample Bin Dummy  Sample Cups  Toggle  Mechanism  Figure 12 - Sample Carousel Disk  Test Results and Lessons Learned  The SMS Flight Model has recently completed its Flight Model Proto-flight test campaign. An Engineering  Model was also subject to an extended proto-flight test program and 2X life test. Several lessons learned  are reported here as a result.   Sample Cup Launch Restraint The launch restraint for the sample cups required a redesign during Engineering Model Testing. The  initial design utilized a canted coil spring to restrain each cup during launch and EDL events. A canted  coil spring is often used in spring-loaded shaft seals to provide low friction mitigation against dust and  debris on rotating shafts. The canted coil springs can also be used as a detent device for a shaft sliding  through a cylinder. The initial design utilized an Inconel X-750 canted coil spring housed in a Nitronic 60  Stainless Steel bushing, Figure 13. The sample cup stem is Titanium 6AL-4V plated with a Canadize™ coating (Polymer infused Titanium Oxide) from General Magnaplate Corporation. A groove on the  Titanium Sample Cup Stem allowed the sprin g to constrict and conse quently provide a restraint for the  sample cup. When the sample cup is used, the Elevator actuator would apply an axial force to the sample cup stem and cause the canted coil spring to “dilate”, thereby releasing the cup from its restraint.                   Sample Cup Stem  Groove, Bottom  Edge FR Sample Cup Stem  and Spring Detent  X-SectionFA FN Sample Cup  StemCanted Coil  Spring 5 mm  311
There were several issues with thi s not sufficient to hold the cups  in place with sufficient margin can see responses peaks as high as 130 Gs during random ove diameter was reduced to  radially compress the spri ll the parts were precision  cleaned in ultrasonic cleaners en, 1 Acetone), the coefficient of friction between the  The resulting spring deflection was  also getting close to the solid straint/release device  behaved differently in the cle bsequent testing on the Engineering Model in the clean oved to be very difficult to pair  prings with sample cups. Eventually a point was reached where the Carousel was fully populated with  e sharp corner on the groove and thereby reducing  Figure 14 - Post Random Debris in Cup Stem Restraint Device  Six of the modified cup stems were then integrated into the sample carousel disk for vibration testing. The  lateral X and Y tests were performed first, in which the in-axis was normal to the center axis of the sample  cup. The Z-axis test aligned with the cup’s major axis. On the full level random test, 5 of the 6 modified Figure 13 - Initial Sample Cup Restraint  s design. Initially the restraint force wa during launch. The Sample Carousel Disk   vibe. To address this issue, the bushing gro ng more, resulting in a higher detent force. Once a through multiple baths (3 IPA, 1 Simple Gre spring and the sample cup stem increased. “height” of the spring. Thus, the behavio Canted Coil Spring fully  compressed in groove Canted Coil Spring under  Magnification  r of the re an room than in the pre-cleaned state. Su  room showed signs of erratic behavior. It pr s cups exhibiting “acceptable ” performance.   The Engineering Unit was then subject to a vacuum bake-out at 90°C for 24 hours. Following the bakeout, the cup stems exhibited stick-slip behavior, which was not entirely unexpected given the performance in clean room bench testing. Most of the cup stems would only release after a much higher load was  applied by the Elevator actuator than was previously necessary. Some did not release at all. It was  determined that the combination of increased compression on the canted coil spring, precision cleaned components lacking surface lubricants (particularly after the vacuum bake-out), and a sharp corner on the  bottom edge of the sample cup groove (Figure 13) resulted in high contact stresses at the spring/stem  interface which caused the intermittent and unreliable behavior of the restraint/release device. Some cup  stems were then modified with a radius on the bottom edge of the groove in the sample cup stem.  reliminary testing showed promise that eliminating thP the contact stress at the interface would allow the cup stem to release in a predictable and reliable  manner.          312
cup stems released from their restraint. None of the remaining 68-cup stems released during the test.  However, in post-test performance testing, the unmodified (sharp groove corner) cup stems did not  release. Inspection identified the cause as significant debris generation due to the  random vibration  environment. The debris lodged in between the coils of the spring and seized the release mechanism entirely, Figure 14.  The design that worked in T/V testing did not pass Random Vibe and vice versa. The proposed solution  was to add another spring to the top end of the sample cup bushing in an attempt to stabilize the cup  stem and prevent it from rattling and generating s in vibration. The compression of g was  lso reduced to keep contact stresses as low as possible. Several variations utilizing two springs were  tried. A component level random vibration test was then performed based on the response seen on the  Carousel Disk dur on the two-spring   rattle during random vibration and contact forces between the beams and the cup debri  the sprin a ing the system test. There were no candidate solutions based  concept as a result of the test. The springs were not sufficient to prevent the sample cup stem from  rattling in the bushing and generating significant debris.   The final design eliminated the canted coil spring entirely, Figure 15. The springs were replaced by  integrated cantilevered beams that snap into the same groove in the sample cup stems that the spring  used. The cantilever beam bushing is Brush Wellma n Alloy 25 Copper Beryllium in the TH-04 condition.  The bushing was also electro-polished to reduce surface roughness and contact stresses. A much more  repeatable and reliable restraint and release mechanism has been evident with this design. It does not  llow the cup stem toa stem are easier to predict and control.     Figure 15 - Final Sample Cup Restrain r lessons learned from the sample cup restraint exercise ar re of lab test results that involve friction. Always precision  ricants that can collect in a lab environment. Precisio eaned parts.  Do not rely on components that are difficult to analyze and deb The form factor of the canted coil spring and its release behavior  rrors. The spring interaction with the cup stem wa If a canted coil spring is used to provide a detent for a compo understood and excessive debris will not result. The cante for light detent applications if used in a conservative manner.    re of the lap joint in the spring where the wire is welded add to non-linearities/asymmetry at the interface between tt Design  The majo e as follows.  1. Bewa clean parts to eliminate any oils or  other lub n cleaned parts behave differently than  pre-cl 2. ug for a critical restraint application.  made analytical predictions prone to  large e s difficult to model and hidden from view.     3. nent, ensure the vibration environment  is well d coil spring can be a good solution  4. Be awa . If not considered, the weld can also  wo components. If hig  contact  stresses exist, the weld may be problematic. he t h 313
Contamination Another lesson learned in the development of the SMS pertains to contamination. When designing an   third party  placcos k not tinstrument with extremely stringent outgassing and contamination requirements, work with all suppliers early and often on the contamination front. Expensive bake-outs resulted because assembled components such as motors were manufactured without additional contamination control guidelines in  e. Once components are assembled, the vent path for all outgassing molecules becomes long and  tortuous. The SMS motors required a 6-week bake-out before they were acceptable to use. Eliminating excessive polymeric harness staking and connector potting can also drastically reduce bake-out time and  t. Integrate metallic features in parts to tie harnesses down to rather than staking with polymerics.  Avoid thick layers of polymerics. The thicker the layer, the longer it takes to diffuse and the longer the  ba e-outs become. The science return of the mission would have been comp romised had the bake-outs  been sufficient.  Op ical Switches ical switch thresholds will change with temperature. Be mindful when using optical switches to zero  ition counters in mechanisms. If position counteOpt os rs are reset with an optical switch transition, ensure   that switch has been characterized through its temperature range, particularly if a fine p the behavior of aperture is not implemented. Testing on the LED/PT switches used in the SMS demonstrated a shift with temperature in the threshold voltage of the optical switch, Figure 16. The SMS implemented a differential  switch scheme with the custom incremental encoder that cancelled out the temperature shift. Optical  switches on the elevator mechanism did not require fine positioning that counter resets would affect.   Change in Transition Over Temperature 56 04 - 2 02468 1 0 1 2 Displacement (x .025 mm)e 123Phototransistor Vc0 deg C -20 deg C -40 deg C -55 deg C 20 deg C 40 deg C 60 deg C 80 deg C Figure 16 - Optical Switch Performance Vs Temperature  Seal Force Feedback The performance of the Load Cell replacement in the Elevator Actuator mechanism was sufficient to  satisfy SMS requirements. Paramount to the success of the design was a reliable switch closing force. So  long as the force at which the switch closed remained consistent and was sufficient to remove any  structural or electromechanical play in the load path and drive train, the stiffness of the structure can be  utilized to apply a given force. Take care to tune the structural stiffness to the accuracy requirements and ensure the actuator feedback device has sufficient resolution to stay well within the required force  accuracy, Figure 17. This is an effective method for applying a known force to a large number of distinct  components of varying geometries.   314
Switch Closed 0.72 Counts per Newton  Eliminate Backlash and  “stretch” load  path com ponents  Figure 17 - Elevator Stiffness Calibration  General Test Data Figure 18 plots the motor current versus time of the SMS during a complete Pyrolysis Experiment  sequence. The sequence includes two sample cup seals, four Sample Carousel Disk re-orientations, and  one vacuum seal/launch lock o peration. Only the profile at -55C is shown. The SMS motor currents were  approximately 30% less at the maximum operating qualification temperature (70° C).  315
Unload Vacuum Seal Move Carousel/Cup to  Pyrolysis Oven Move Carousel/Cup to  Sample Inlet Move Carousel/Cup  back to Pyrolysis Oven Return to Home  Position 1st Pyrolysis Seal 2nd Pyrolysis  Seal Final Vacuum Seal  Fig ile omponents prior to  ssembly. The problems encountered with using canted coil spring detents were a design oversight and  should not be construed as a recom mendation against using them for oth er applications. The debris  generated inside the sample cup bushing demonstrated that another method for positive retention of the  sample cup was necessary. The canted coil springs proved to be effective when used as a light detent  device. Optical switches will drift with temperature. If a fine aperture is not implemented, the voltage threshold on the Phototransistor will occur at different degrees of LED obscuration. Lastly, the compliance  of a structure can be an effective means of delivering a commandable force via an electromechanical  actuator. All structural and drivetrain backlash must me eliminated prior to initiating the position move to a desired force. One means of doing so is implementing a repeatable spring-loaded switch to put the  mechanism at a known point on the stiffness calibration curve.  Acknowledgments  The authors would like to thank all of the SMS prog ram technicians, machinists, designers, engineers and  managers at Honeybee Robotics and GSFC for their commitment and expertise. Specifically, the authors would like to thank Oren Sheinman and Rodger Farley of GSFC and Tom Myrick for their time and  technical insights.  This work was performed under a contract with NASA Goddard Space Flight Center, Greenbelt,  Maryland. References herein to any specific commercial product, process or service by trade name,  trademark, manufacturer, or otherwis e does not constitute or imply its endorsement by the United States  Government or the Goddard Space Flight Center. ure 18 - Pyrolysis Experiment Current Prof Conclusions  The Sample Manipulation System provided many challenge s to the design t eam. Keys to designing  mechanisms for very sensitive science experiments are to get involved with third party vendors as early as possible in the manufacturing stage. Assess the feasibility to bake-out sub-c a 316
Figure 1 shows the payloads  supported from above by a total  of 14 suspension devices. The  red objects are called active/passive (Type A) devices  since they have the facility for  real-time adjustment of their uplift force to maintain the  payload ride height and attitude.  The blue symbols are passive-only (Type P) devices, which  have greater lifting capacity but  have no real-time trim capability.  The green symbols are passive  dashpots, which damp the pendulum modes of the  payload. The next two sections  explain the design and fabrication of these hardware  elements.  Figure 1  Schematic of the isolation system and payload. Operating Principles       Figure 2 shows the operating  principle of a Type A suspension device.  The uplift force on the payload is provided by a special type of air spring  composed of a frictionless piston  moving inside a cylinder with the  pressurized volume under the piston  ported to a much larger external volume. The piston rod shown extending through  the lower end of the cylinder is only for  illustration. The real configuration is explained in the next section. Pressure  in the external volume (and thus in the  cylinder) is controlled by a precision mechanical regulator, which also  provides make-up air.  In Type A devices, a voice coil actuator  (actually several in parallel) act in  parallel with the air spring to provide real-time fine trim of the uplift force.  The  primary feedback sensor is a highresolution pressure transducer. It senses the very small, slow, random  pressure variations that occur in the air  spring. A central controller receives this information from all 14 devices. It then calculates the trim force  required from the voice coils of each of the eight Type A devices in order to maintain the initial ride height  and attitude. The controller then calculates the requi red actuator currents and sends digital commands to PayloadControllerPower amp  Voice-coil   actuator External TankAir in CableFrictionless PistonLoad, pressure, & position sensorsActive electro-  magnetic system Passive pneumatic system Precision Regulator      Figure 2  Operating principle of passive plus active       suspension device.  318