ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
126 preloaded track roller bearings support torsion loads and minimize rotations between the slide adapter and  outer housing.  

A lead screw mechanism drives the slide adapt er with the lead screw and actuator assembly mounted to  the outer housing and the nut mounted to the slide adapter . Both the leadscrew and nut are mounted with  gimbals to isolate the lead screw from any bending and radial loads . To limit the travel of the Z -stage, hard   stop tabs are mounted directly to the free end of the lead screw and directly contact tabs on the nut gimbal   when fully extended and tabs in the shoulder when fully retracted.  

The shoulder and elbow joints  provide precise lateral positioning and placement of the EE at all stations  with sufficient torque capability during station interactions , as well as  holding torque during Rover traverse  stow. Both joints are identical in design and utilize the structural  member of the arm as housings for the  joints . The gearmotor directly attaches to the gearmotor housing with the output connected to the wave  generator of the harmonic drive through an Oldham coupling. Downstream of the harmonic drive is the  output shaft t hat is supported by a back -to-back duplex bearing pair separated by a spacer for increased  stiffness and reduction in wobble. To further reduce misalignments, the output shaft is pinned and match  drilled to the flexspline of the harmonic drive . Embedded in the output shaft is the  dual speed resolver from  Ducommun Inc. to provide precise position feedback and knowledge of the joint .   

When stowed for launch, the SHA is restrained by two NEA separation nut mechanisms , similar to the  devices used for the BC door releases . One NEA is used to launch- restrain the Z -stage assembly, while  the other is used to launch- restrain the SHA forearm, located at the end of the arm before the EE  interface.  

Figure 9. SHA Overview  (EE not installed) .
127   Figure 10. SHA Z-Stage Cross -Section  (shown sideways).  

End Effector   The EE is mounted at the end of the SHA and interfaces  with gloves , with sample tubes  via gloves , and  covers to be manipulated and moved throughout the ACA . The EE is comprised of two primary components:   A Tube Gripper Assembly (TGA)  which  secures covers or s ample tubes via gloves during manipulation via  a ball lock interface;  and the Remote Center of Compliance Mechanism (RCCM)  which  provides compliance  for all SHA to station interactions  (Figure 11). A third component, the Lockout System, secures the RCCM  during launch and traverse (Figure 1 2).  

The TGA has a n electronically commutated  gearmotor that is mounted to the angular deflection plate of the  RCCM with the output of the gearmotor directly connected to a ball screw mechanism (Figure 13 ). A pair  of angular contact bearings support the ball screw mechanism as well as the gearmotor . The nut of the ball  screw is attached to a plunger, which when the ball screw rotates either extends or retracts the plunger . In  the retracted state, the ball lock groove of the plunger lines up with the ball sockets of the upper housing,  which puts the ba ll locks in the released state. When the plunger extends, the balls extend out of the upper  housing to allow the EE to grip against a cover or a glove (with sample tube) . The TGA also contains a 6  degree- of-freedom force- torque sensor with the inner diamet er mounted to the TGA upper housing and the  outer diameter mounted to the TGA lower housing. The force/torque sensor protects the SHA, EE, and  stations during operations against inadvertent loading during SHA free space motion and limiting loads  during station interaction.  

The RCCM compliant mechanism is designed to lower the necessary loads  required to align the EE  during  station interactions (Figure 14) . The concept comes from robotic end effectors that use a remote center of  compliance approach to insert a peg into a hole as described in [6] to minimize the chance of jamming in  close toleranced parts. The RCCM compliance is achieved through two sets of ma chined flexures: Lateral  Flexures, which provide the lateral /translational  compliance to the mechanism, and Angular Flexures, which  provide the angular compliance to the mechanism . Both sets of flexures can be twisted about the z -axis for  rotational compli ance.  

To reduce the chances of a fatigue failure, the flexures of the RCCM are locked out during launch as well  as Rover traverse. This is achieved through the Lockout System mechanism internal to the EE  that  interfaces with a cam mounted to the shoulder of the SHA  (Figure 12) . The main structural component of  the Lockout System is the RCCM housing, which has two spring loaded lock ro ds, one bolted and one  floating, that slide into  bushings in the RCCM housing. The cover plate interfaces with the opposite end of
128 the lock rod. Affixed to a clevis directly adjacent to the lock rod and cover plate interface is a roller supported  by a shou lder bolt and locking nut. This roller rides on a clearance- fit bushing and is supported on both  faces by thrust washers . When the roller engages the cam during stow operations, the cover plate  compresses towards the RCCM housing and restrains the RCCM by a series of pins and holes present at  both the lateral and angular stages . These interfaces restrain motion of the RCCM via a load path back to  the primary structure, the RCCM housing.  

Sealing Station   The Sealing Station supports  two functions within the ACA :  to activate a hermetic seal within a sample  tube, and to drop -off a sample tube from the Rover for retrieval by a potential future sample return mission.  To accomplish these functions, t he Sealing Station consists of two mechanis m assemblies , a ram  mechanism to conduct seal activation, and a gripper mechani sm to support the sample tube during seal  activation as well as perform sample tube drop- off, as described in [ 7]. The ram mechanism is capable of   generat ing more than 20 kN with a stroke of approximately 16 mm (Figure 15). To achieve this, a gear  motor drives  a gear train that connects to a planetary roller screw from SKF, Inc. that provides the  linear  Tube  Gripper  Assembly   EE Harness   Tube Gripper  Plunger   Force -Torque  Sensor   Remote  Center of  Compliance  Mechanism  (RCCM) –  within  housing   End Effector  Structure and  Interface to  SHA  RCCM Cover Plate  & Lockout Rods  (shown locked out)   Compression  Spring   Bolted Lockout  Rod  Cover Plate   Cam  Roller   Floating  Lockout  Rod  Lower Housing   Plunger   Upper Housing   Force -Torque  Sensor   Gearmotor   Lead 

Nut  Angular  Contact  Bearing  Pair  Angular Deflection  Plate  RCCM Housing   Angular Flexure   Lateral Flexure   Lateral Deflection  Plate  Lower Cover  Figure 11. End Effector Assembly . Figure 12. End Effector Lock -out System.   Figure 13. Tube Gripper  Assembly  Cross -Section . Figure 14. RCCM Cross -Section.
129 motion necessary to mechanically  activate a hermetic seal within a sample tube, within a small package.  The gripper mechanism is actuated via a gear motor connected through a gear train to the gripper, which  opens and closes to “grip” or release a sample tube within the station . A kicker is attached to the gripper  mechanism, which rotates with the actuated gripper, to enforce a sample tube to release from the station  during the drop- off sequence. Figure 16 shows a cross -section of the Sealing Station with the ram in contact  with a hermetic seal  at the start of the seal  activa tion sequence within a sample tube, and the kicker in a  retracted position. The ram will travel approximately 3.5 mm from this position until the ram hard stops on  the gripper at which point the hermetic seal has been fully activated within the sample tube. Full activa tion  occurs when the hermetic seal knife- edge feature has fully expanded into the sample tube wall, thereby  creating a seal. 

Figure 15. Sealing Station Ram and Gripper  

Figure 16. Cross -Section of Sealing Station with  Sample Tube in Position for Hermetic Seal  Activation.  

Sample Tube Storage Assembly   The STSA houses thirty -nine flight sample tube assemblies within storage sheaths (Figure 17 ). Within each  sheath is a sampl e tube and a glove. Figure 1 9 shows a cross -section of an empty sample tube with glove  attached in a sheath. A glove serves  two purposes:  1) Prevents contamination from entering a sheath to  maintain sample tube cleanliness, and 2) Provides an interface between the SHA and sample tube for  manipulation within the ACA . Due to cleanliness concerns, a sample tube is not to directl y contact the EE  of the SHA.  

The sample tube consists of a passive ball lock mechanism with two states, engaged or disengaged . The  engaged state has the balls pushed outward into a groove to “lock” the sample tube into a sheath or bit .  The disengaged stat e allows the balls to retract to support sample tube removal from a sheath or bit  via the  SHA. With the  glove attached to a sample tube, a multi -stage ball -lock activation process is required for  sample tube manipulation. To manipulate a sample tube, the E E tube gripper first extends its plunger into  a glove which ball locks the two together . With the tube gripper and glove locked together, the tube gripper  plunger continues to extend, which pushes on the glove plunger . Depending on the amount of tube gripper  plunger travel, the glove can be engaged or disengaged from a sample tube. Continued extension of the  tube gripper plunger eventually results in the glove plunger pushing on the sample tube plunger, thereby  disengaging the sample tube ball lock all owing for sample tube removal from a sheath or bit . Retraction of  the tube gripper plunger provides the opposite effect and allows for sample tube ball lock engagement into  a sheath or bit.  

   Ram  Gripper  (Closed)   Hermetic Seal in  Sample Tube   Kicker
130 Dispense, Volume, Tube Assembly   The DVT assembly consists of hermetic seal dispensers (D), a volume station (VS), sample tubes (ST) with  gloves in a sheath, and a sample tube parking lot (STPL), all integrated to a single mounting plate (Figure   18). 

There are seven hermetic seal dispensers, with each dispenser contai ning seven seals in a stack protected  by a cover when not in use (Figure 20) . A cover is only removed when a sample tube, with an acquired  sample inside, is ready to retrieve a hermetic seal from a dispenser. Covers remain installed otherwise to  minimize h ermetic seal exposure to the environment and maintain cleanliness . The seal dispenser uses a  two-stage passive ball lock mechanism to allow for the advancement of a single hermetic seal for  dispensing into a sample tube, while also preventing the remaining  seals in a stack from falling out . The  SHA brings a sample tube into a dispenser which activates the ball -lock mechanism, and results in release  of a hermetic seal into a sample tube. Once a seal is dispensed into a sample tube, refer to [8] for seal  activation details at the sealing station .  

Volume assessment is conducted via the SHA bringing a sample tube into contact with the volume probe  to a prescribed load limit . From this operation, the amount of sample material collected can be determined,  while minimizing potential damage to a sample. A cover protects the volume probe when not in use (Figure  21). Covers utilize a passive ball lock mechanism to lock and unlock from the dispensers, volume station,  and the cover parking lots .  

Three sample tube storage locations exist on the DVT similar to those on the STSA . A Sample Tube Parking  Lot (STPL) is a modified sample tube storage sheath that allows for a sample tube to be stored without a  glove. This capability allows for standalone glove operations in the ACA.            

Figure 17. STSA Assembly (bottom view with  glove bottom flanges visible).  

Figure 18. DVT Assembly
137 Sealing Station Mechanisms for the Mars 2020 Rover Sample Caching Subsystem  

Jesse Grimes -York* and Sean O’Brien ** 

Abstract  

The Sealing Station is composed of two mechanisms: the Gripper Mechanism,  for orientation and support  of the Sample Tube during the Hermetic Seal activation activity,  as well as ejecting Sample Tubes out of  the Rover, and  the Ram Mechanism, which produces  and applies  a high force for seal activation. The Ram  Mechanism is a compact high for ce linear actuator that uses a planetary roller s crew (PRS) as the output  linear stage , tapered roller bearings (TRB) to support the PRS at  the high loads , a set of spur gears   supported by cylinder roller bearings , and a brushless motor with a planetary gearhead  and magnetic detent  brake. This paper describes the role of these mechanisms  in the Mars 2020 Rover mission as a part of the  Sample Caching Subsystem (SCS) and Adaptive Caching Assembly (ACA)  and their interactions with the  Hermetic Seal a nd Sample Tube hardware. We report on development testing performed with the PRS that  show it has capability of supporting cross -moment loads, something manufacturer s of these components  do not rate. Also discussed is the interaction of the passive holding torque from magnetic detent brakes  and hardstop preload, setting of a very light preload in the TRB , and the complex linear dyno test equipment  used,  and how that testing could have been improved.  

Introduction  

The Mars 2020 Rover will gather rock core and regolith samples from the surface of Mars for  a potential  return to Earth via the Mars Sample Return mission. Samples are collected into tubes that are hermetically  sealed in- situ to capture both solid material and any volatiles that would otherwise evaporate and exit the  sample during the long journey to Earth. The Sealing Station, pictured in Figure 2, is a two-mechanism  assembly with the duty of activating th ese hermetic seal s and dropping the filled and sealed Sample Tubes  out of the Rover and onto the surface of Mars. Sample Tubes are moved into position within the station by  the Sample Handling Assembly (SHA), having already placed the Hermetic Seal onto the tube. The Sealing  Station is a subcomponent  of the Adaptive Caching Assembly  (ACA)  described in [1] and pictured in  Figure 1 which  is in turn a part of the larger Sample Caching Subsystem (SCS) .  

Figure 1. ACA with SHA pictured holding Sample Tube near Sealing Station  

* Formerly of the Jet Propulsion Laboratory, currently at  NASA Johnson Space Center, Houston,  TX  ** Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA  

Proceedings of the 45th Aerospace Mechanisms Symposium, NASA Johnson Space Center, 2020
138 The primary  mechanism of the Sealing Station is the Ram Mechanism, which is responsible for pushing the  Hermetic Seal’s ferrule into the ‘sealed’ position. The Ram Mechanism is composed of a Planetary Roller  Screw ( PRS), as the output linear stage, supported by a Tapered Roller Bearing ( TRB) pair and driven by  spur gears and a brushless motor. The second ary mechanism is the Gripper, which orients and supports  the Samp le Tube during the high force seal activation, alleviating the Sample Handling Assembly (SHA) of  these requirements. The Gripper additionally performs the Sample Tube drop -off function, to eject the  Sample Tube from the Rover. The Gripper has a rotational joint that moves half of the Sample Tube support  structure, allowing ingress/egress of the Sample Tube. Figure 2 shows steps in this sequence.  

The Ram Mechanism is a high force density device tested to a capability of ~21 kN for a stroke of 16 mm  in a 3. 3-kg package (Ram Mechanism only; total station mass is 5.5 kg). In this paper we will show the  method for setting preload in the tapered roller bearings, development testing of the PRS linear -to-rotary  component, for compatibility with this application and for a loading scenario past the vendor’s recommended  limit for these components . Additionally, dyno testing to these high forces across warm and cold  temperatures is presented with recommendations for how this could be performed more simply  for future  applications.  

An Engineering Model, a Qualification Unit, and Flight Unit have all been designed, assembled, tested, and  integrated into their respective higher -levels of assembly, the ACA. The Mars 2020 Rover is scheduled for  launch in July of 2020 and landing on the surface of Mars in February of 2021. The hardware described in  this paper will be used during the surface mission portion of the mission.  

Figure 2. (left) Sealing Station with Sample Tube during Seal Activation (upper right) prior to seal  activation Ram motion the ferrule is shown in the un- activated position. (lower right) end of seal activation  Ram motion the ferrule has been pushed into final position.
139   Figure 3. The Hermetic Seal assembly shown separate from the Sample Tube and prior to seal activation.  The ferrule expands the knife edge outward as it is pushed through the smaller diameter of the ramp  profile in the seal cup.  Ferrule shown in staring position.  

Hermetic Seal & Sample Tube Design   The Hermetic S eal is compos ed of two major components : the seal c up and the f errule, held together by  the ferrule retainer,  shown in  Figure 3. A retaining spring holds the Hermetic Seal in place inside the Sample  Tube. The spring washer permits the f errule to only move deeper into  the Seal Cup, thus retaining the  ferrule after assembly  and throughout launch. The seal cup has a knife e dge feature that, upon activation,  is pressed against the inner wall of the Sample Tube creating a hermetic seal ( <1×10−8 cc He/sec). The  knife edge i s coated with gold,  which acts to fill in scratches in the interior wall of the Sample Tube caused  by the rock core as it is ingested duri ng coring. The interior of the seal c up has a ramp profile opposite the  exterior knife edge, which is sized and shaped to expand the k nife edge out radially, into the t ube wall. The  geometry of this ramp profile,  ferrule to seal cup to tube  interference, lubricant and materials selection was  a considerable challenge but  is not the focus of this paper. The notable aspects of this seal for the purposes  of seal activation and the Ram Mechanism is that the f errule must be pushed 3.5 mm further into the seal  cup r amp after insertion into the sample tube in order to create the hermetic seal , a task that requires up to  7300 N. Also of note,  this load must be reacted within the Sealing Station as the SHA , the robotic arm   moving the Sample Tube from station to station within the ACA, cannot  support loads of this magnitude.   Figure 4 shows a successful seal activation performed by the SCS during ground testing.  

Figure 4. CT scan image of Sample Tube with Rock Core Sample and activated Hermetic S eal. The  Hermetic Seal was successfully activated by the EM Sealing Station integrated to the EM SCS .
140 Mechanism Designs  

Ram Mechanism   The output function of  this mechanism is to push the f errule of the Hermetic Seal into the s eal cup; a stroke  distance of ~3.5 mm with a load of up to 7300 N. Additional stroke length, 16 mm total, is required to retract  the Ram away from the Sample Tube and Hermetic Seal to allow for ingress/egress  of the tube. Ferrule  depth in the c up upon seal a ctivation is determined  by the Ram contacting its extension hardstop. The Ram  Tip geometry is designed to control this depth, targeting the middle of a ~2- mm positional band,  where any  position within this range results  in a successful Hermetic Seal activation. This stroke range allows for  variation in piece part dimensional variation between the 45 Sample Tubes flown on the mission, and dust  accumulation.  

Figure 5. Cross Section view of Ram/Sealing Mechanism showing details of the gear transmission.  

Output force is produced by a PRS where the screw is the translating element and the PRS nut is driven in  rotation. The screw is a 15- mm pitch diameter with a 5- mm pit ch and a 5- start thread, a catalog item that is  only modified to replace steels with stainless steels . The screw  rotation is restricted by two cam follower  bearings running in tracks, see Figure 5. The PRS nut is driven and supported by a spur gear that is in turn  supported by a pair of tapered roller bearings. The output gear is driven by an idler gear supported on a  cylinder roller bearing, which is in t urn driven by a pinion gear mounted to a gear motor.  The gear motor is  described in [2].  The Ram mechanism has been shown, in test, to be capable of producing ~21 kN , for an  input torque of about 7.8 Nm at the pinion gear,  across its qualification t emperat ure range of - 70 to +70° C.  Lubrication throughout the geartrain is accomplished with Braycote 600 EF grease applied by greaseplating, at a  10% grease- to-solvent level, with additional grease, 30% void- volume fill, applied directly  to  the rollers of the TR B and cylinder roller bearing. All geartrain elements are CRES except for t he roller  cages in the TRB and cylinder roller bearing which are silver plated 4340 steel.  

Sensing of Ram position is accomplished by Hall sensors at the motor. The only other telemetry available  for this mechanism, and the station as a whole, is motor current. An example of this telemetry can be seen  in Figure 6 where the distinct Hermetic Seal activation force profile is plainly visible . The mechanism is  designed to be robust to contacting hardstops in either direction at full force and uses the retract hardstop  for position zeroing. Stowing of the Ram for launch and rover traversing is accomplished by pressing the  Ram against the extension hardstop, up against the Gripper , where it has the added benefit of restraining
141 the flexurized portion of the gripper  output , refer to Figure 7 for the gripper flexure. A holding force of 2900 N  is maintained by a passive magnetic detent brake located at the motor . 

The R am Mechanism is not required to produce high output load while simultaneously overcoming startup  drag, especially at low temperatures. The first motion of the mechanism is to un- stow and retract , unloaded,   to allow the tube ingress  prior to any high force actuation. Test data shows that b y this time any start -up  drag from cold grease is overcome. If  the mechanism is ever required to begin operation where high load  is required immediately , it can move backwards away from the load, “warming up” the mechanism before  proceeding forward under high load.  

Figure 6. Telemetry of Hermetic Seal Activation on the FM1 Sealing Station during ground testing at 20° C 

Gripper Mechanism   The Gripper is a much lower force mechanism compared to the Ram but serves the important role of  supporting and locating the Sample Tube during the high force seal activation activity. The SHA is incapable  of supporting loads much higher than about 300 N while seal activation can require as much as 7300 N.  The actuated motion of the Gripper  allows the Sample Tube to be brought into,  and out of the Sealing  Station . The Gripper ’s second primary function is to eject  the tube out of the r over to the Martian surface.  The ACA can return a sealed sample tube to storage and eject it  later as mission operators choose.  The  Sample Tube interface design is highly constrained as it must interact with a large variety of hardware  throughout the SCS on the Mars 2020 miss ion in addition to interacting with the Mars Sample Return  mission . The seal activation function differs from all others in the mission,  giving rise to different design  constraints  for ingress/egress than for  Sample Tube insertion into a Coring Bit , Sample Tube Storage  Sheath,  or Seal Dispenser .  

Figure 7. View of Gripper Mechanism showing details of the gear transmission and flexurized  output .