ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
414 are being addressed through changes in the carriage design that prevent pinching and x -direction  compressive loads. Flexure pull -out will be addressed by using better surface preparation and high- quality  epoxy that is not past its shelf life.  

Conclusions  

This work presents the development of a compliant suspension for a microspine gripper assembly suitable for use in space as a drill anchor or as part of an asteroid- capture mission. A brief overview of the microspine  architecture has been presented, along with the design details for a compliant parallel -guiding suspension  system. The testing method has been outlined and results summarized.    It has been shown that the p roposed design has potential to provide adequate gripping force in asteroidcapture or micro -gravity  drilling application. The critical issues of tangling, binding, and flexure pull -out  appear solvable and are currently being addressed. With additional des ign, prototyping, and testing, the  microspine architecture could provide a reliable, scalable, space- capable anchoring system.  

Lessons Learned   • The microspine architecture can be effectively translated into space- grade materials.   • The rock surface- microspine interaction is complex and stochastic, making modeling difficult.  Therefore, extensive prototyping and testing is necessary to understand performance.   • Proper use of inexpensive prototypes can speed development compared to purely analytic  or  numeric models   • Proper consideration should be given to all stages of manufacturing and assembly to produce  meaningful test specimens.  

Acknowledgements  

The research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a  contract with the National Aeronautics and Space Administration. This work was supported in part by a  NASA Office of the Chief Technologist's Space Technology Research Fellowship.  

References  

[1]  A. Parness, M. Frost, N. Thatte and J. P. King, "Gravity -Independent Mobility and Drilling on Natural  Rock Using Microspines," in IEEE International Conference on Robotics and Automation , Saint Paul,  Minnesota, USA, 2012.   [2]  A. Parness, M. Frost, N. Th atte, J. P. King, K. Witkoe, M. Nevarez, M. Garrett, H. Aghazarian and B.  Kennedy, "Gravity -independent Rock -climbing Robot and a Sample Acquisition Tool with Microspine  Grippers," Journal of Field Robotics, vol. 30, no. 6, pp. 897 -915, 2013.   [3]  A. T. Asbeck, S. Kim, M. R. Cutkosky, W. R. Provancher and M. Lanzetta, "Scaling Hard Vertical," The  International Journal of Robotics Research, vol. 25, no. 12, pp. 1165 -1179, 2006.   [4]  L. Howell, Compliant Mechanisms, John Wiley Sons, Inc, 2001.
417 and as a consequence occupies a lot of volume,  limiting the depth of penetrat ion to the length of the  penetrating rod (the drive unit is kept above the surface) . The remaining qualities are just advantages li ke  simplicity and reliability of  the system as well as the possibility to apply different energy levels.  There exist s  a prototype of an electromagnetic mole -type penetrator, where the capacitor was removed outside the outer  casing and a stock of 5 electromagnets was used;  it is the recently developed EMOLE within ESA  PECS  project [ 12].  

System Overview  

The Hammering Mechanism, as specifically mentioned in this paper, is located inside the Outer Casing and  consists of the Hammer and the Suppressor  Mass assemblies, together with Drive Springs, a Brake Spring  and a Wire H elix (see Figure 2). From the point of view of integration,  the HM is divided into:  Hammer Lock  Assembly  (HLA) , Axis Bearing Assembly , and Motor Assembly  (MA) . HM is guided against Outer Casing  with a so- called Tongue Assembly, which is also important for the launch lock feature of the device.  The  actual details and components of the design are shown in Figure 2.  

Figure 2.  Components of HM. top : pre -PFM parts, bottom right corner: Wire H elix  The HLA consists specifically of the Hammer mounted with the Cam located inside the Hammer Housing.  Two drive springs (inner and outer) are used with opposed coil turns  and are located freely inside the  Hammer H ousing. They are protected against falling off by a Hammer Nut (screwed and pinned at the tip  of the Hammer ). The HLA is fixed w ith the MA through the Bearing Housing that is a part of  the Axis Bearing  Assembly . The HLA and  the MA are counter torqued against each other on the Bearing Housing’s thread.  The pair of  angular bearings  located in the Bearing H ousing provide axial rotation for the Roller Axis . The  Axis is coupled with a gear shaft through a Clutch E lement , which provides 40° of angular deadband  in the  movement of the axis . This angle is important for the phase of operation when the Roller (mounted at the  end of the Roller Axis) falls off the C am’s edge and rotates  freely the Axis with respect to the C am to allow  for the unconstrained movement of the H ammer.  

As a drive unit , a customized Maxon DC Motor Unit DCX22 with Planetary Gearhead GP 22 HP  is used,  which was installed inside the Motor Housing by screws and using 3M Scotch Weld Epoxy Adhesive 2216  B/A G ray as a filler . Near the front part of the gear box and outside of the Motor Housing,  a heater was  Tip  Tongue Assy.   Hammer Lock Assy.   Axis Bearing Assy.   Motor Assy.   Drive Springs   Hammer   Roller Axis   Clutch   Heater (DLR)   PT-1000 (DLR)   Wire Helix   Cam  Roller   Angular   Bearings   DC motor+gearbox (DLR)   Brake Spring
419 a)   b)   Figure 3. a) Hammer Lock Assembly, b) Cam loading Drive Springs compression sequence inside  the Hammer Housing  (Cam -Roller engagement, disengagement, travel of Hammer)  

Cam optimization   Resignation from the spring preload, prompted the requirement to use higher cam inclination to provide  higher spring compression and increase accumulated energy. A new approach to the cam design was  undertaken with the following assumptions:  the torque characteristics should be constant for most of the  cycle time, the over all angular width of the cam is 280 °, maximum reasonable angle at which the roller can  roll in is 30 ° and allowable cam height is 15 mm (in contrast  to the previous 7.8 mm).  Eventually , the Cam  starts with 30 ° angle inclination and continues until the pl ateau of constant torque is reached (which is at  about 78°  of Cam angle, this corresponds to 0.2 Nm of constant  torque), then the inclination of the cam  smoothly decreases to keep the resulting torque at the same level together with the increasing force of the  drive springs. The actual cam profile and expected torque characteristics  together with corresponding  equations  are shown i n Figure 4 and Figure 5 (friction losses are assumed to be negligible) . The s ymbols ’  meanings  are:  φ – angle of the Cam; φ 0 – angle of the Cam at which the inclination starts to change from  30°; h(φ) – height of the Cam; T(φ) – expected torque on the gear shaft ; R – radius from the rotational axis   to the working point of the Roller  at the Cam ; k – stiffness of the Drive S prings. Additional advant age of  higher cam is that when Roller disengages from the Cam losses are expected, and partially the actual few  millimeters of the height of the cam is not 100%  effective. Hence, i t is much better to have higher cam since  this transition phase (between rol ling and falling)  has twice smaller relative contribution to the dist urbance  of the movement of the H ammer . It has also much more travel distance to accelerate and provide effective  impact on the Outer C asing.  

    Figure 4.  Theo retic al shape of the Cam (symbols for equation described in the text)
421 Additional tests for this type of tribological pair can be found in [13].  Figure 8 shows  wear traces of the  tested samples  clearly showing higher wear resistance for nitrided titanium and tungsten with MoS 2  sputtered . 

Figure 6. Materials and coatings of the Hammering Mechanism  

Figure 7.  Friction coefficient changes as a function of friction distance of used materials after   different surface treatments (“ ball on disc” test against Al 2O3 ball under 10 -N load) in air  

a)   b)  c)   d)   Figure 8.  Wear traces of Ti6Al4V (a), nitrided Ti6Al4V (b) and tungsten alloy (d) coated by MoS 2 in  comparison to uncoated tungsten alloy (c); pictures are in  the same scale  

IMI 318   1.4310   HE395/HE3925   440C  Marval X12   other  TiN + Pb   Pb  Nitrided + MoS 2  TiN + MoS 2  TiN + Pb   Pb  Nitrided + MoS2   MoS2
422 Worth mentioning is that the m echanism was required to be tested also in air and room temperature and  some wear of the coatings  was expected. For this reason,  all sliding and rolling surfaces (previously coated)  were additionally lubricated with Braycote 601EF. The deposition of the Braycote was done by application  of the excess of Braycote on the desired surfaces and its removal with a dust -free wipe until a film of it was  left. The typical method of grease plating  could not be used because of assembly complexity and multiple  bonding steps interchanged with the lubrication process. Often masking had to be used, especially for  deposition of the coatings (MoS 2 and lead)  as shown in Figure 9ab. Unfortunately, MoS 2 did tend to wear  from the Hammer Lock Pins ( Ti6Al4V nitrided + MoS 2) during mechanism inspection runs  that were done  yet before Braycote application , see Figure 9c.  

 a)  b)    c)   Figure 9. Appearance of different coatings and surface treatments ; a) Hammer (MoS 2),   b) Cam (TiN+ Pb), c)  wear of MoS 2 on Hammer Lock Pin (TiN + MoS 2) 

Bearings   Together with tribological coatings the bearings were implemented to take over loads induced by drive  spring tensioning  and cam torqueing. Angular bearings ( 440C, PEEK cage, O -configuration) were  implemented to support rotational movement of the Roller Axis. The actual design is shown in  Figure 10.  The bearings  are inserted on the Roller A xis part with a slip fit, they are separated from each other by the  mean of the Bearing Housing where slip fit is used as well. The bearings are loaded from the side of the  Motor Clutch E lement, through the Outer  Clutch Element that is screwed into the Roller Axis and stops on  a distance washer and inner ring of one of the bearings . The washer  is adjusted to the height which provides  cancellation of the clearances in the bearings  and stops on it after the locking torque is applied.  The Outer   Clutch Element has a left hand thread which corresponds to the direction of rotation of the gear shaft. This   is an additional means  of locking the connection (besides  glue and torque applied).  

a)  b)   Figure 10. a) Half-section of Axis Bearing Assembly, b) Picture of Axis Bearing Assembly  

The bearings are not sealed and external lubrication was applied. This is a low velocity application (15 rpm) and again the Braycote 601EF was used. As shown in Figure 11, six drops of Braycote were applied on the  bearings balls with the total mass of about 0.03g (which is about 20% of  the maximum volume of bearing  that can be filled) . Then the lubricant was s pread around by rotating the bearing.    Additionally, an individual design of the bearings for the Roller Assembly was implemented (Figure 12) that  significantly improved the Drive Springs loading process . To provide better load characteristics , it is  MoS2 (PVD)   Pb (PVD)   TiN
423 mounted on the R oller Axis at 60°  angle to the main axis (see Figure 10a and Figure 12a), so not only radial  but also axial forces are introduced to the assem bly. As an assembly, it has 34 rotating parts (12 balls  and  22 rollers), compacted into a Ø9.2x14.9  mm envelope and undergoes  87 N of radial and 50  N of axial  periodic  load from the Drive S prings . The design of the R oller is interesting itself and evolved a few times  until it reached the presented design . It consists  of the Roller Shaft which has to be a single part to ensure  coaxial surface for the rotating parts . The R oller part has a  press fit with Roller Shaft. The back of the Roller  is closed with a Roller W asher , which does not take loads except for holding needles from escapement  and  it is joint to the assembly  by a Roller R ivet made of 1H18N9T (EN 1.4541) stainless steel. The balls take  over the axial loads. All parts , with the exception of the rivet , are 440C  stainless steel  hardened to 58 HRC.  The interior of the Roller A ssembly is lubricated with Braycote  601EF , which was applied by injection after  the actual assembly – the lubricant was pressed into the Roller Assembly to fill 1 00% of the roller v olume  (which is about 0.15g). Then the R oller was rotated with 50- 100 rpm for 60 seconds to remove the excess  of lubricant. This resulted in 66% of lubricant remaining in the volume of the R oller ( about 0.10g). T he  measured drag torque of the R oller with the Braycote in room temperature was c.a. 0.5 N-mm, which would  have marginal influence on the gear shaft torque (close or less than 1%). One of the tests , with the prePFM model , revealed that even the blocked Roller can still be successfully elevated on the Cam with the  provided motor, therefore increase of drag torque in lower temperatures is not critical for the mechanism.  The large amount of Braycote plays an important role in sealing the Roller from unwanted debris.  

a)  b)   Figure 11. Angular baring lubrication : a) Bray cote application area, b) close- up 

a)  b)   c)   Figure 12. a) Roller loading, b) Half- section of the Roller , c) Roller hold in fingers to show the scale  

Launch Lock system   Functionality of the launch lock system was improved in the scope of the project. The final design allows  for multipl e locking and unlocking of the Hammer against the Suppressor Mass and the S uppressor  Mass  against the Outer C asing (i.e. , Tongue  Assembly) without the necessity to disassemble the whole mole  mechanism ( particularly important for planetary protection procedures) . The Hammer Housing possesses   dedicated slots  (axially symmetrical on both side of the Hammer H ousing)  in its walls to al low for proper  guidance of Hammer Lock Pins and T ongue Assembly Lock P ins an d constraints the vertical movement of  the traveling  masses in its normal operation mode. Besides  the guidance slots , it also possesses the  dedicated lock notches, that are used in the locking and releas ing modes of operation , see Figure 13 and  Figure 14 for details .
424   A reverse operation of the motor  is used to lock the mechanism. The motor starts to turn counter -clockwise  and eventually the Roller pushes the Cam and as a result the whole H ammer Assembly . While the Hammer  rotates inside the Hammer Housing, the Hammer Lock Pins encounter slope of the lock notches  and slide  up about 1.5 mm upwards . Eventually , they cross maximum elevation of the notch and drop into the final  position in the launch lock pocket slightly loaded in that position by the D rive Springs. The motor still  continues to rotate and the Hammer L ock Pins stop on the T ongue assembly  fork-shaped features, see  Figure 13. As a result , it is now the Suppressor  Mass to start rotating in the opposite direction with respect  to the T ongue A ssembly. While it rotates , the cut -outs on the bottom of the Suppressor  Mass change their  position until the T ongue Assembly Lock Pins are positioned in the launch lock pocket of the Suppressor   Mass, see Figure 14. Both pairs of the Launch Lock P ins are located in little local pocket s that keep the  assemblies in place during vibrations. They are not likely to freely jump out of this position because the  gear shaft would have to start rotating , which requires multiple rotations of DC  motor, but this is not  happening during the l aunch.    The unlocking is just a matter of powering the motor in the operational (hammering) mode. The R oller Axis  would start then to rotate clockwise and eventually the Roller encounters the  Cam. The Hammer Assembly  now elevates and as a result t he Hammer Lock P ins are released from the launch lock pocket s in the  Hammer Housing.  Consequently the Hammer A ssembly is turned with respect to the S uppressor  Mass (in  the Hammer Housing) towards the normal operation guidance slots . Eventually the Hammer Lock Pins  reach the opposite fork -shaped feature of  the T ongue Assembly and resist against it , which allows  now the  Suppressor Mass assembly to start rotating backwards  with respect to  the Tongue Lock Pins and eventually  position all the assemblies and their l ock pins in corresponding guidance slots of  the Hammer H ousing.  

a)    b)   Figure 13. Launch lock design details; a) Hammer Lock Assembly with Tongue Assembly in  locked position, b) Hammer locking on Suppressor Mass  (right pictures without Tongue Assy.)  

Tongue   Assy.  Hammer   Lock Pin   Fork-shaped   features   Locked   Unlocked   1-1.5mm
425 a)   b)  c)   Figure 14.  Launch lock design details: a) Tongue Assembly with visible one of Lock Pins, b)  Hammer Housing slot for SM guidance, c) Suppressor -Mass locking on Tongue Assembly   

Lessons Learned  

The implemented changes allowed to achieve relatively high energy penetration strokes  as for the given  constraints of mass and C am height , with much improved efficiency. The resulting average power  consumption was 0.6 W (0.33/0.72 W peak values). As a result, the overall efficiency of the system is 30%.   The average work cycle of the Hammering Mechanism is about 4s. Figure 15 shows  the motor’s current  record from the first two strokes of the HM -4 unit ( FM). Spring loads and release phases can be seen on  this plot. When compared to the previous Figure 5, it can be clearly seen that the cam profile optimization  works as expected: the uniform  increase of current represents the 30 ° inclination slope, then the current  keeps constant value (and motor constant load) until the Roller reaches the edge of the C am. 

Figure 15. Current record o f first two strokes of HM -4 (FM) 

Beside s satisfactory results that have been achieved, there were few sensitive  issues encountered that are  worth mentioning here.    One of such issues was connected with T ungsten alloy that was used for the Hammer and Motor Housing   parts . Initially , only HE 395 alloy was  used, with which CBK already had experience during development of  KRET penetrator. Eventually a few cases in which this material revealed its brittle  nature occurred. This  happened in the Hammer parts in the area of Hammer Lock Pin location . The crack appeared in the notch  Locked   Unlocked   Power ON    Power OFF   Roller -Cam   engagement   Roller -Cam   disengagement   Cycle of work
426 area as shown in Figure 16a  and propagated . It could appear either at the moment of assembly or  manufacturing. It was decide d to change the material of the Hammer to HE  3925 alloy , which is more  ductile.  In fact the cracks in T ungsten alloy  are hard to detect by direct visual inspection, also its surface  features and specific reflection  capabilities  very often look like crack which appears not to be in the end   (example shown in Figure 16b) . Beside s a very detailed visual inspection (microscopic with magnification  over x20) of all tungsten parts, also a scanning electron microscope was used and in some cases even X - ray computer tomography (which was limited just to single millimeters  of penetration due to high densit y of  tungsten). Eddy current detection method was also investigated but due to complex shapes of the  investigated parts the interpretations of measurements was not unequivocal . Starting from HM- 3 model a  new material was used and also all notch areas signi ficantly modified to limit all the possible stress  concentration areas.  It is important to mention that no cracking was recorded for the Hammer  parts during  their operation and qualification tests, both for HE 395 (in HM- 1 and HM -2) or HE 3925 material (for HM- 3,  HM-4 and HM- 5).  

a)    b) c)      Figure 16.  a) Hammer crack in the Hammer Lock Pin area (view to the interior of Hammer part),    b) Motor Housing Scratch (not a crack), c) magnification of Tungsten alloy HE 3925 inspected  surface (SEM, x250, inspected scratch inside the contour)   Beside s tungsten alloy issues, a fatigue cracking was experienced. Models HM-1 and HM- 2 have  been  implemented in a Clutch S pring in a form of two symmetrical 0.2-mm bands of 1.4310 steel that connected  the Inner Clutch  Element with the Outer  Clutch Element. The purpose of the Clutch S pring was to provide  the additional accumulat ion o f energy which was used during Cam -Roller disengagement . The C lutch  Spring was to kick off the Roller  from the edge of the C am and eventually reduce the losses of energy  connected with rolling out . Due to the schedule constraints, t he actual laboratory test s that were performed  after the HM -1 and HM- 2 development shown  a fatigue failure of the spring after 15000 strokes (whereas  qualification level was 45000 strokes). The actual e ffect of kicked -off rolling  out can be noticed on the highspeed  camera videos, but in the end the actual change of the mechanism’s overall performance (stroke  energy)  was unnoticeable. In further models (HM- 3, HM- 4 and HM- 5) the Clutch Spring was removed from  the design. In other words, if properly designed the Clutch Spring could bring benefits to this type of the  mechanism, but is not obligatory.  

a)     b)     c)  

Figure 17. a) Clutch Spring location in Axis Bearing Assembly, b) T he actual appearance of Clutch  Spring, c) Broken Clutch Spring during the tests   Clutch   Spring