ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
The rasp tool is driven by a brushed DC motor. The motor is powered by a current limited on-off circuit,  which provides a maximum of 1.0 Amp, at 24.6 to 29.3 V. Accounting for frictional drag in the system, the  actuator is able to produce 41 mNm of output torque at the rasp cutting bit and bit speeds of  approximately 5300 RPM at room temperature. Torque is transferred from the motor shaft to the rasp  cutting bit through a set of spur gears, and a pair of miter gears yielding an overall speed reduction of  1.25:1 from the motor to the bit. All gears are AGMA Q10, constructed of 15-5 PH stainless steel and age  hardened to condition H1000. Figure 3 shows a cross section of a portion of the ISAD drivetrain. The  cutting bit is supported on the upper end by a back to back angular duplex bearing pair while the lower  end is supported by two shielded radial bearings. Another set of duplex angular bearings support the  pivoting housing while three additional radial bearings support various drive train gears. All bearings are  ABEC 7 and comprised of 440C stainless steel balls and races with phenolic retainers. All bearings and  gears were grease plated with a solution containing 10 wt% Castrol Braycote® Micronic 600EF.   The device includes three resistive strip heaters that warm the mechanism to allowable operational  temperatures. A 2.1-watt heater is attached to the motor, and two additional heaters, 2.7 watts and 1.6  watts are attached to the pivot housing. A temperature sensor on the motor provides ISAD temperature  feedback. All components used to power the rasp cutting bit are thermally isolated from the main scoop  body through the use of vespel as an insulating material. This minimizes heat transfer from the drivetrain  components to the scoop sample transfer surfaces in an effort to reduce icy sample loss due to  sublimation. The cutting tool includes a set of features for producing vibration of the scoop surfaces. This vibration is  essential for moving acquired sample from the rear chamber of the scoop to the front, and for improving  the transfer efficiency from the front funnel to the instrument inlet ports. The vibration mechanism is only  engaged when the rasp cutting bit is in its rest position against the “lower” hard stop. A cam feature  attached to the rasp cutting bit engages a low-friction surface, which is grounded with respect to the  scoop. As the rasp bit rotates at high speed, the cam feature causes the pivot housing to oscillate such  that the spring loaded housing impacts the “lower” hard stop once per revolution, resulting in high  frequency vibration. 

Figure 2. Icy Soil Acquisition Device Flight Unit on Assembly Fixture      The front and rear chambers of the scoop are separated by a sample transfer plate. During digging  operations, this plate prevents the majority of scooped material from filling the rear chamber of the ISAD,  which could result in jamming of the cutting tool. This plate also acts to move sample from the rear  292
chamber to the front chamber so that samples acquired using the rasp cutting tool can be dropped off to  instruments in the same manner as bulk soil. The plate consists of a vertical and a horizontal shelf, with a  slot in the horizontal shelf. This creates a labyrinth through which material can be transferred from rear to  front by rotating the entire scoop about the Robotic Arm wrist axis. The sample transfer plate is made  from 7075-T73 aluminum with a hard coat clear anodize for abrasion and wear resistance.   Once digging reveals hard icy soil, the secondary blade, located on the bottom of the scoop, may be used  to prepare the surface for acquisition by the rasp tool, depending on the surface topography. This flat  edged blade will scrape the icy soil to form a more uniform surface for placement of the ISAD. Once the  surface has been prepared, the RA will place the ISAD such that the rasp tool is in contact with the target  area. The RA will then preload the ISAD with a minimum preload of 40 N. The rasp cutting tool will then  be energized for a period of approximately 30 to 60 seconds, resulting in acquisition of icy soil. The RA  then relieves the preload on the ISAD and retracts it from the surface. Placement and acquisition can be  repeated several times in different locations, depending on the amount of sample desired, and the  spacecraft resources available. After all acquisition operations have been completed, the sample is  transferred to the front of the scoop for imaging by the RAC, and drop-off to the analytical instruments.  The transfer operation consists of a series of RA wrist motions to move the sample along a number of  panels that divide the front and rear chambers of the scoop. During the transfer operation, the rasp  cutting tool can be energized, inducing vibration to aid in the flow of particles.  Mechanism Design and Test Lessons Learned  High Speed Low Torque Seal Design The Icy Soil Acquisition Device is a high speed, low torque sampling device. The Maxon REØ25 motor,  coupled with a reduction ratio of 1.25 : 1, has a nominal output torque of 0.054 N•m (0.478 in•lb). In order  to transfer the maximum possible amount of torque to the cutting bit, the frictional drag torque of the  drivetrain needs to be minimized. Some sources of frictional drag in the mechanism’s drivetrain include  inefficiencies in spur and miter gear torque transfer, drag due to lubrication of bearings, and preloading of  angular contact bearings. These effects can be minimized by tight tolerances and good assembly  techniques, however the largest variability in a low torque mechanism’s friction drag can come from the  dust seal if not accounted for early in the design process.  Dust Seal Cutting BitPreloaded  Angular Contact  BearingsMiter Gear Set Spur Gear Radial BearingsRadial Bearings

Figure 3. Drivetrain Cross Section Showing Dust Seal Location  293
volatiles or (3) a combination of both effects. For mechanisms that are sensitive to slight increases in drag  torque, it is recommended that mechanism designers experiment with these spring energized seals at the  expected environmental conditions prior to finalization of the design.    Cam Actuated Vibration Mechanism Design The ISAD includes a unique method of producing the vibration necessary for moving particles across  sample transfer plates within the scoop. To the best of the authors’ knowledge, this cam vibration  mechanism is unlike any other flight-qualified device, and the design contains several important features  that contribute to its successful operation. This type of mechanism can be utilized on future planetary  sampling systems where vibration is required to aid the flow of particles.  The cam vibration mechanism utilizes a spring preloaded pivoting assembly to produce an impact force  on the base of the ISAD scoop. Figure 4 shows the “Pivot Housing” in its rest state, with the mechanism  un-powered. In this state, the “Cutting Bit” is in the fully extended position, and the pivot housing is fixed  against the “Lower Hardstop”. As the cutting bit rotates, the “Cam” gradually engages the “Bumper”,  raising the pivot housing off of the lower hardstop, against the direction of torsion spring preload. As the  cam and cutting bit rotate further, a change in the cam geometry causes the cam to suddenly disengage  from the bumper. This releases the preloaded pivot housing, allowing it to impact against the lower  hardstop. This impact is directly coupled with the rotation speed of the cutting bit, and results in an  approximately 90 Hz frequency. Both the cam and the bumper are individual components that can be  changed out without affecting the design of surrounding hardware. This minimizes schedule risk, as cam  and bumper design can proceed without delaying fabrication of mating hardware.  BumperCam Cutting Bit Lower HardstopTorsion Spring Preload DirectionPivot Housing XY XY

Figure 4. Cam Vibration Mechanism Section View  The primary challenge of a cam-actuated vibration mechanism is designing the interface between the  cam and the bumper to function throughout the expected lifetime of the device. Gradual wear of the cam  and bumper will ultimately degrade the ability to produce vibration. Material choices, cam and bumper  geometry and surface treatments all contribute to the functionality of the mechanism as it nears the end of  its required operational life. The cam vibration mechanism on the ISAD was required to function for a total  295
number of output revolutions of 383,000. Due to the unique nature of the device, a demonstration of two  times life was required to prove flight worthiness.  The geometry of the cam was an important consideration in the design. Figure 5 shows the wear of an  early prototype cam made from 17-4 PH Stainless Steel age hardened to condition H900 with no surface  treatment. This cam interfaced with a bumper made from 50% cold worked Nitronic 60. These parts were  designed for simplicity of fabrication in a short amount of time, and minimal consideration was given to  the cam geometry. The wear shown in the images occurred after one hour of operation at 5300 RPM  (approximately 318,000 output revolutions). These tests were performed in a vacuum chamber at Mars  ambient conditions on a test fixture with similar geometry and rotational speed as the flight ISAD design.  The vibration produced at the end of the test was insufficient to fluidize even dry particles. These images  show the importance of geometry and material selection to the overall success of a cam-actuated  vibration mechanism. The combination of 17-4 PH and Nitronic 60 is typically used to minimize galling  and wear in sliding friction applications. In this application, the high speed and abrupt impact quickly  deteriorated both materials.  Before Testing After 1.0 Hour Test Cam Geometry Figure 5. 17-4 PH Prototype Cam Wear and Geometry As shown in Figure 5, the geometry of the prototype cam was not optimized to deliver a smooth transition  between the minor diameter of the cam and the major diameter. The transition was abrupt, and occurred  in the final quarter rotation of the cam. The flight cam design utilizes a cycloidal cam profile to gradually  transition from the minor diameter to the major diameter through three quarters of a rotation. Cycloidal  cam geometry is used in cam design where a sinusoidal acceleration profile is desired to minimize  reaction loads. Equation 1 shows the desired cam acceleration profile. The displacement profile can be determined through integration and application of boundary conditions. The formula for the radius of the  cycloidal cam profile is shown by Equation 2.   /g7/g8/g6/g4/g5/g3=TCa/g2/g12sin     Equation 1 /g14/g15/g13 /g8/g9/g7/g11 /g12/g10/g5 /g6/g4/g11 /g12/g10/g5 /g6/g4/g1/g14/g15/g13 /g8/g9/g7/g11 /g12/g10/g5 /g6/g4+ =Th Thr rROOT/g2/g3 /g2/g3 2sin2   Equation 2  r = Cam radius ,  r ROOT = Minor radius of cam,  h = Distance between major and minor radius of cam  T = Period of cam  Age-hardened Vascomax C-300 Stainless Steel was chosen as the material for both the cam and the  bumper due to its superior strength and hardness (52 Rockwell “C”). In addition, a low-friction electroless  nickel coating from General Magnaplate (Magnaplate HMF) was used as a surface treatment on both the  cam and bumper to reduce frictional effects, and improve surface hardness at the contact interface.  296
Figure 7 illustrates a prototype braze joint which was fabricated and load tested. Due to packaging  constraints, it was necessary to reduce the diameter of the carbide bit to fit into the stainless steel shank.  Three grooves in the bit provide for mounting of gold-nickel alloy wire to act as filler metal for the braze  joint, but also decrease the overall strength of the tungsten carbide bit. The dimensions of these preform  grooves is dependent on the amount of filler metal required to coat the surface of the braze joint. A loose  radial clearance in this region between the bit shaft and the shank allows for braze filler metal to flow. The  joint also includes an alignment feature near the base of the cutting bit teeth which controls shaft runout,  but does not allow a sufficient gap for braze filler metal to reinforce the connection. Figure 8 shows the  completed braze joint after having performed load testing. The joint was sectioned in order to view the  internal braze penetration. Cracks at each of the three preform grooves are evident in the figure. Whether  load testing, or the act of sectioning the joint was the cause for these cracks is unknown, however it is  clear that the aspect ratio of depth to height of the preform grooves resulted in a high stress concentration  at the base of these features, and failure of the brittle tungsten carbide shaft.  Alignment Feature to  Control Shaft Runout. No  Braze Filler Metal Tungsten Carbide Cutting Bit Braze Lap Joint SurfaceLoose Fit For Flow  of Braze Filler MetalPreform Grooves for Gold Filler Rings

Figure 7. Prototype Cutting Bit Braze Joint Design  Preform Grooves for  Gold Filler Rings Crack in Cutting Bit Shaft

Figure 8. Prototype Cutting Bit Braze Joint Section Showing Cracks in Bit  The braze joint implemented on the flight ISAD unit utilizes the same cutting bit as the prototype design,  but includes a number of improved geometric featur es for decreasing stress and controlling shaft runout.  Figure 9 shows the final design of the braze joint. The material selected for the bit shank was 15-5 PH  Stainless Steel. The material selected for the braze alloy was 82% gold and 18% nickel. Following the  completion of the braze operation, the entire assembly was precipitation hardened to Condition H1000 to  harden and strengthen the shank.   Compared to the prototype design, the aspect ratio of the preform grooves was changed to minimize  stress concentrations at the base of the groove. Gold bands were used rather than gold rings, resulting in  298
shallower and wider grooves while maintaining the necessary volume of filler metal. This significantly  reduces the stress concentration at the grooves. This design also incorporates a tapered transition  between the outer diameter of the bit and the reduced diameter at the braze joint. This provides for ease  of assembly while minimizing the stress concentration due to the change in geometry. To further  strengthen the joint, a shallow recess in the tapered region allows braze filler metal to flow into the  tapered region. To control runout of the bit, a tightly toleranced region at the base of the cutting bit allows  the bit to maintain concentricity with the stainless steel shank during assembly and throughout the braze  cycle.   These minor changes in geometry help to increase the load capacity of the brazed joint. The brazed joint  survived a lateral load of 50 N applied at the tip of the cutting bit, with a proof load factor of 1.2. Highresolution X-Ray images of the joint confirmed that no cracks formed as a result of load testing, and that  braze filler material penetrated all lap joint connections, including the tapered region. It should be noted  that during the brazing process, the cutting bit was facing up with respect to gravity, demonstrating that  capillary action alone allowed braze filler metal to flow into the tapered recess area, further strengthening  the joint. Running the bit at its peak speed of approximately 5300 RPM and visually observing the runout  confirmed that concentricity between the cutting bit and the shank had been maintained. Figure 10 shows  the brazed assembly.  Tight Fit Tapered  ConnectionTungsten Carbide  Cutting Bit Braze Lap Joint SurfaceLoose Fit For Flow of Braze  Filler MetalPreform Grooves for  Gold Filler Rings Tight Fit to Control Shaft Runout Recessed Tapered  Section for Braze Filler   Figure 9. Flight ISAD Cutting Bit Design  When designing small form factor braze joints exposed to high load conditions and consisting of one or  more brittle materials, it is important to minimize stress concentrations around geometry transitions, and  to reinforce these transition areas with braze metal whenever possible. This braze joint is optimized for  the geometry and material constraints imposed by the ISAD design. Had these factors, in addition to  budget and schedule limitations not been present, the design may have taken a less involved approach,  possibly utilizing a solid tungsten carbide shaft rather than a braze connection, or a less brittle material for  the cutting bit.  Figure 10. Flight ISAD Braze Joint  299
between the spring, the housing and the shaft. Significant torque margin should be applied to the spring  design to account for these effects.  Acknowledgments  The authors would like to thank all of the ISAD program technicians, machinists, designers, engineers  and managers at Honeybee Robotics and JPL for their commitment to developing this device.  Specifically, the authors would like to thank Mark Balzer, Don Lewis, Don Noon and Greg Peters all of  JPL for their time and technical insights.  This work was performed under a contract with Jet Propulsion Laboratory, California Institute of  Technology, for the National Aeronautics and Space Administration. References herein to any specific  commercial product, process or service by trade name, trademark, manufacturer, or otherwise does   not constitute or imply its endorsement by the United States Government or the Jet Propulsion  Laboratory.  302
sample inlet device, foil puncture stations for the metal cups, and a pyrolysis oven on each row of the  SMS Sample Carousel Disk.   To allow SAM to re-use sample cups in an extended missi on scenario, the SMS must deliver up to 1350  Newtons with an accuracy of ±10% of the commanded seal force. A seal is created with the Pyrolysis  Ovens via an annealed copper disk brazed to the sample cup and a titanium knife-edge on the oven.  Each successive use of a sample cu p requires a larger seal force.  Contamination control played a significant role in SMS development. The spectrometers aboard the SAM  suite have the capability to detect molecules in th e parts-per-billion range. Thus, the SMS must be  extremely clean, free of particles, and exhibit a very low outgassing rate. The outgassing rate of the SMS  was required to be less than 4.2E-14 g/cm2/sec as measured by a Qua rtz Crystal Microbalance. This  ultimately corresponded to a delta/delta frequency reading on a TQCM of 1 Hz/hour/hour during bake-out.  The SMS must move the sample from the inlet location and seal it in the pyrolysis oven in five minutes or  less. This requirement is driven by the extreme contamination sensitivity. A given sample cup, once  preconditioned in the pyrolysis oven, must not be exposed to the interior of the SMS for an extended time  to prevent contaminating the measurement on the solid sample. Contamination concerns required the SMS to provide a vacuum seal to prevent contamination of the interior of the SMS during Assembly, Test,  and Launch operations.  The SMS must be capable of recovering from an unexpected power loss. Feedback devices and a robust  high level control architecture combined to provide full fault detectio n and correction capability.   High Level Architecture The four main subsystems of the SMS are identified in Figure 1. Not shown is a contamination cover that  fully encases the SMS within SAM. The SMS is not exposed to the exterior of SAM or the Rover, except when the Sample Inlet Tube (~ Ø4.3 mm) is open to deliver a sample.     Sample Carousel  Disk (normally locked  to Ground Rin g)153 mm Sample Cup  Center Hub Rotating Elevator  FrameSAM Mid-Plate  Ground Ring Mass: 3.0 Kg  (Mid-Plate not included)  Ø 279 mm Figure 1 - SMS Main Subsystems  The SMS is an under-actuated 3 Degree-Of-Freedom robotic system. Two rotational degrees of freedom  are provided by the Center Hub Actuator. A toggle mechanism on the Sample Carousel Disk either couples the Sample Carousel Disk to the Ground Ring or the Rotating Elevator Frame (REF). When the  304
Sample Carousel Disk is coupled to the REF, the Center Hub Actuator positions a given sample cup at an  oven, inlet, or puncture station. When the Sample Carousel Disk is coupled to the Ground Ring, the REF  rotates independently of the Sample Carousel Disk and positions the Elevator subassembly beneath a  given sample cup. At that point, the Elevator actuator (3rd DOF) can raise and lower the sample cup to its  interface. Figure 2 through Figure 4 demonstrate the sequence of operations involved in decoupling the  Sample Carousel Disk from the Ground Ring and moving a cup via the Carousel actuator to another  position.            Carousel Actuator  Figure 2 – Center Hub Actuator Moves Rotating Elevator Frame to Toggle Mechanism, Sample  Carousel Disk is Stationary                       Elevator Actuator  Toggle Unlocks Sample  Carousel From Ground  Elevator Lift Couples  Sample Carousel To REF  Figure 3 - Elevator Actuator Raises Lift to Unlock Toggle Mechanism from Ground Ring and  Couple with Rotating Elevator Frame  305
Figure 4 – Center Hub Actuator Moves Rotating Elevator Frame and Sample Carousel Disk to  Position a Sample Cup  Center Hub Actuator The center hub actuator is comprised of a hall commutated brushless dc motor, 25:1 planetary gearbox,  and 100:1 cup style harmonic drive for an overall gear reduction of 2500:1 and 30000 counts per  revolution, Figure 5. All components are grease-pla ted with Braycote 600 EF Micronic. The maximum  speed at the output of the harmonic drive is 2 RPM. The maximum continuous torque output is 3.4 N-m.  The Carousel Motor is current limited by the motor control board so as not to exceed output torque limits.  Actual running torque of the Center Hub Actuator is only ~.05 N-m at the output of the 25:1 planetary stage. External loads are not significant during operation.   A duplexed pair of angular bearings in the face-to-face configuration is located near the harmonic drive  output. A Conrad bearing is located at the interface of the cross-support arms to the center hub. The  Center Hub bearings support approximately 70% of the system mass during launch and EDL, including the Sample Carousel Disk.     Mounting Interface  to SAM Conrad Bearing/Cross  Support Frame Interface  Motor & 25:1 Planetary  Gearbox  Output of Actuator 100:1 Cup Style Harmonic  Drive  Face-to-Face Angular  Contact Bearings  Figure 5 – Center Hub Actuator & Center Hub Assembly  306