ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
397 Appendix A:  Consolidated Specific Details for RWA IV Dataset Values   Table A -1.  Computed Values f or RWA Axial Force Principal Direction Key Harmonics (4)   Data Set  1.0 Harm onic 2.0 Harm onic 2.8 Harm onic 5.2 Harmonic   RWA S/N -  Set 2nd-O Coe f  (mlb/RPM2)* Eq.  GE  (µin) 2nd-O Coe f  (mlb/RPM2)* Eq.  GE  (µin) 2nd-O Coe f  (mlb/RPM2)* Eq.  GE  (µin) 2nd-O Coe f  (mlb/RPM2)* Eq. GE   (µin)  1001 – 1 (P)  1001 – 2 (P)  1001 – 3 (P)  1001 – 4 (F) 9.22  7.99  6.65  6.73 7.58  6.56  5.46  5.53 7.40  9.17  9.13  8.86 1.52  1.88  1.87  1.82 19.53  23.44  16.83  16.14  2.02  2.42  1.74  1.67 28.80  31.86  35.68  34.49  0.88  0.98  1.09  1.06  1001 – ave. 7.65 6.28 8.64 1.77 18.98  1.96 32.71  1.00  1002 – 1 (P)  1002 – 2 (P)  1002 – 3 (F)  1.11  0.74  2.26 0.91 0.61  1.85 1.97 6.17  6.78 0.40 1.27  1.39 15.33 19.39  18.18  1.58 2.00  1.88 26.71 33.31  37.68  0.82 1.02  1.15  1002 – ave.  1.37 1.12 4.97 1.02 17.64  1.82 32.57  1.00  1003 – 1 (P)  1003 – 2 (P)  1003 – 3 (P)  4.07  3.50  2.91 3.35 2.87  2.39 3.45  10.40  8.12 0.71 2.14  1.67 6.91  24.16  16.50  0.71 2.50  1.70 16.79 18.92  6.21 0.51 0.58  0.19  1003 – ave. 3.49 2.87 7.32 1.50 15.86  1.64 13.98  0.43  1004 – 1 (F)  1004 – 2 (F)  1004 – 3 (P)  1004 – 4 (F)  1004 – 5 (P)  1004 – 6 (P)  1.57  2.09  2.35  2.48 4.22  2.29 1.29 1.72  1.93  2.03 3.47  1.88 2.73 0.11  0.74  0.43 0.21  0.13 0.56 0.02  0.15  0.09 0.04  0.03 17.60  9.00  16.36 15.10 26.38  15.51  1.82 0.93  1.69  1.56 2.73  1.60 17.77 15.43  19.92  22.38 37.47  18.62  0.54 0.47  0.61  0.69 1.15  0.57  1004 – ave. 2.50 2.05 0.72 0.15 16.66  1.72 21.93  0.67  1005 – 1 (P)  1005 – 2 (P)  1005 – 3 (F)  1005 – 4 (P)  3.46 4.32 4.02  4.16 2.84 3.55 3.30  3.42 13.65  8.53 8.17  6.82 2.80 1.75 1.68  1.40 21.13 29.91 30.92  27.74  2.18 3.09 3.19  2.87 19.29 20.72 19.69  21.57  0.59 0.63 0.60  0.66  1005 – ave. 3.99 3.28 9.29 1.91 27.43  2.83 20.32  0.62   ALL  – ave. 3.81 3.13 5.65 1.16 19.30  1.99 24.17  0.74  * Note : all milli-pound/RPM2 values shown are 106 times actual values  for tabulation clarity .  Table A -2: Computed Values f or RWA Radial Force Principal Direction Key Harmonics (4)   Data Set  1.0 Harm onic 2.0 Harm onic 2.8 Harm onic 5.2 Harmonic   RWA S/N -  Set 2nd-O Coef  (mlb/RPM 2)* Eq.  GE  (µin) 2nd-O Coe f  (mlb/RPM2)* Eq. GE   (µin) 2nd-O Coe f  (mlb/RPM2) * Eq.  GE  (µin) 2nd-O Coe f  (mlb/RPM2)* Eq.  GE  (µin)  1001 – 1 (P)  1001 – 2 (P)  1001 – 3 (P)  1001 – 4 (F)  8.56 7.96 9.73  9.11 7.04 6.54 8.00  7.48 7.67 2.42 5.65  4.11 1.57 0.50 1.16  0.84 13.89  9.78  12.41  10.81  1.43 1.01 1.28  1.12 7.90 3.31  10.07  7.89 0.24 0.10 0.31  0.24  1001 – ave. 8.84 7.26 4.96 1.02 11.72  1.21 7.29 0.22  1002 – 1 (P)  1002 – 2 (P)  1002 – 3 (F)  4.23 5.76  11.59  3.47 4.73  9.52 3.69 4.58  3.94 0.76 0.94  0.81 7.52 5.93  6.28 0.78 0.61  0.65 6.76 6.26  6.40 0.21 0.19  0.20  1002 – ave.  7.19 5.91 4.07 0.84 6.58 0.68 6.48 0.20  1003 – 1 (P)  14.43  11.86  5.59 1.15 9.26 0.96 3.66 0.11
399 **   Note: a physical interpretation/meaning of Equivalent Geometry Error (EGE) for radial moments is vague.   *** Note : abbreviated test series obtained only axial and radial force IV data; no radial moment data   Table A -5: Computed EGE Coefficients f or All Detected IV Radial Force Harmonic Ratios   Harm. Ratio ↓\RWA → 1001  1002  1003  1004  1005  Ave.    0.35    1.00    2.00    2.82    3.00   1.67**     8.84**     4.96**   11.72**     1.16*    1.70**     7.19**     4.07**     6.58**      --   1.83**   12.67**     7.98**     9.29**     1.39   1.20**     4.65**     4.01**     9.15**     2.07   1.63**   16.16**     4.66**   15.53**     1.49   1.61    9.38   4.94  10.58    1.53    3.12    3.25   3.60    3.84    4.00    4.14    4.55    4.74    5.00   2.27*     3.84*     1.81*     4.47*     2.86*     8.33**     5.26*     3.61*     2.85*     --    --    --     --     --    6.37**      --    --     --   2.23   2.98   1.95    5.13    1.77    8.10**     3.54   3.63    1.95   1.31   1.62   0.59    1.14    2.69    3.91**     1.05   1.39    0.93   1.70   4.74   1.49    6.31    2.95    5.64**     3.07   3.07    1.75   1.88   3.30   1.46    4.26    2.57    6.47    3.03    2.93    1.87    5.18    5.60    5.76    6.00    7.50    8.28    8.50    8.70    9.00  10.20  10.44 10.80  11.22  11.88    7.29**   14.39**     3.16*   16.05*   10.37**   11.45*   12.04**      --  10.90*      --    8.13*     7.22*   18.25*   13.80*    6.48**     8.46**      --     --    7.26**      --  10.01**      --     --     --     --    --     --     --   3.69**     5.99**     2.01 13.50    7.67**     5.32  11.96**      --    1.04     --    7.01   8.07  22.00  18.10    3.71**     7.49**     2.51 12.20    3.48**   11.90  11.49**      --    4.00    6.59    4.85   3.34  19.30  11.70    6.18**   13.71**   14.50  13.80    3.27**     7.72    8.00**   11.80  14.00 10.50  10.10  17.10 29.50  27.70   5.34  10.00   5.55  13.89    6.41    9.10  10.70  11.80   7.49    8.54   7.52   8.93  22.26  17.83   Note: all values shown are 106 times actual computed values.   Note: underlined plus bold items are 4 key harmonic ratios; underlined-only are next 4 secondary ratios.   --   Harmonic ratio value is below reliable detectability for this RWA’s IV data.   *    Average value for 2 data sets for this particular RWA.   ** Average value for all data sets for this particular RWA.
402 This concept was originally developed to provide the ability to climb porous and dusty vertical walls. It also  has applications in exploring rocky or icy space  environments . Since the microspine gripper does not rely  on reaction forces from the surroundings to provide preload, it can be used in micro -gravity  to provide  reaction forces for other operations. For example, microspine grippers could be used in conjunction with a  percussive impact drill, providing the necessary reaction force to hold the drill agains t a surface. Such  a  gripping mechanism could be used to retrieve a boulder from an asteroid.  

Design Refinements   Development of this design is targeted on the objective of increasing the load capacity of the microspine  gripping device. This follows two av enues :  increase the number of microspines engaged in a given surface,  and eliminate failure modes observed in the suspension. These failure modes include flexure pull -out and  tangling. Subtle geometric changes in the suspension and gripper are being explored to increase the  number of spines engaged with the surface. Alternative manufacturing methods may be able to mitigate the flexure pull -out, while more accurate manufacturing may reduce the tendency of the suspension to  tangle with adjacent suspensions.  

Gripper Design    This section gives an overview of gripper concept of operations (CONOPS) and summarizes some historical variations.  

Gripper C ONOPS   The microspine grippers that have been constructed at the Jet Propulsion Laboratory  include a variety of  architectures, but share several essential features.  They all are used to provide reaction forces based on a  rough surface. Operations proceed along a similar outline (see Figure 1).   .  1. The gripper is placed in contact with a surface and aligned with the surface normal .  2. The microspines are dropped so that they make contact with the surface.   3. The mechanism applies tension to the microspines, so that all of the spines are dragged in towards a central axis.    4. The tool is now in the “gripped” state, and can be used to support various activities, including  drilling, crew activity, towing or similar  tasks .  5. Tension is unloaded in the system, bringing the tool to a “released” state.   6. The gripper tool can now be lifted aw ay from the surface.  

Historical Variations   This technology has been applied in many different configurations. Figure 2 shows a sampling of some of  these designs .   Figure 1.  Illustration of gripper function, broken into three steps: alignment with  the surface, deploying the microspine carriages, and gripping of the surface.
404    Figure 2.  Examples of previous incarnations of microspine grippers. Top: NEEMO anchors. Upper  middle: Lemur IIB  climbing robot. Lower middle : Hand -actuated climbing paddles. (Parness and  Discovery Channel,  2009)  Bottom: Test grippers with elastomer flexures (left) and aluminum hoop   flexures (right).  

The following sub- sections describe functional elements common to all microspine gripper designs.  

Spines   The spines on each gripper provide the surface interface. A variety of sizes and profiles have been investigated, but most systems have used #6 fish hooks, cut off to an appropriate length. Sizes from #4 to #26 have been used in various configurations. These hooks get mounted in the next assembly by pressing into a cavity, then potting with epoxy. The primary selection criteria for a given application are strength to
405 support the estimated loads, and slenderness and sharpness appropriate to intrude into asperities expected  to be present in the gripping surface. That is, smaller hooks can take advantage of finer asperities, larger  ones can support more load on each hook.  

Surface Conformance   The spines describe d above are mounted into a flexible element that provides a degree of conformance to  the surface. This flexibility enables  the hook to make contact with the surface while allowing other spines  to continue moving towards the surface. The design goal is to m aximize the number  of hooks that  make  contact with the surface and establish a firm grip.    For cases where the microspines are grouped into “cassettes” or “carriages”, a roll degree of freedom was implemented to allow the group to conform to the bulk surf ace angle.  

Load- Sharing   Similarly, as a groups of spines is dragged across the surface, some spines will catch in asperities before others. It is desirable that the spines that have not yet caught continue to move along the surface until they catch, or th e mechanism end of travel is reached.  However, compliance in this degree of freedom  must  produce high forces to provide grip.  

Movement across surface/Application of Tension   Grippers have used a variety of sources for the primary tension that drags the spines across the surface. Some handheld units use the grip force of a hand to actuate. The ARM gripper will use a motor ized tool  drive on the  spacecraft to drive a lead screw, producing motion across the surface.    This movement has also been transferred in a variety of ways  among the historical examples shown in  Figure 2. The Lemur and NEEMO grippers used a straight shaft pulled through a rotating barrel joint.  The  “Alien Wire Gripper” used compliant wires sliding through a 3D -printed channel.  

Motion Takeup   The gripper is designed so that a single actuator applies the inward (x -direction) pulling force. However, the  individual carriages may not all move inward the same amount. To absorb these differences in motion, the carriages are cable actuated with springs in series with the actuating cables. When a single carriage has a sufficient number of its microspines engaged with the rock surface, the cable spring will  begin to deflect.  This allow s the actuator to continue to move or apply increasing force to the other carriages without over - actuating fully -engaged carriages.     Each stage of the system is designed to share load among an uncertain number of elements that are  engaged with an unknown surface.  

Microspine Suspension D esign  

Design Requirements   Design requirements were derived from previous experience us ing microspines in climbing and grasping  robots. Approximately optimal stiffness values were found from prototypes using elastomer flexure  elements; one key challenge was designing a metal suspension system that could match the low stiffness of the elastom eric versions. These design requirements are listed in Table 1. Z is the direction orthogonal  to the surface to be gripped, and x is the radial direction.
406 Table 1.  Key design requirements for stiffness and motion of the compliant suspension.   Metric  Value   kz 0.005 N/mm   kx 0.5 N/mm   Δz 0.010 m  Δx 0.012 m   Maximum rotation  15°  Maximum envelope  0.075 m x 0.075 m x 0.002 m  Factor of safety  on material failure  1.25 

In addition to the quantifiable design requirements listed above, several requirements were proposed that cannot easily be reduced to a singl e number. These are listed here:   • The mechanism should be simple to build in desired quantities   • The mechanism’s x -direction stiffness should sharply increase at the extreme limit of travel   • The mechanism should be capable of nesting with itself to enable greater density of microspine placement   • The mechanism should, as much as possible, isolate x and z displacements  

Design Overview   The key  feature of the proposed design (shown in Figure 3) is that it achieves the required low -stiffness  performance by utilizing metal ribbon flexures arranged to form two orthogonal parallel -guiding  mechanisms. This serves the function of isolating the x and z  stiffness values, allowing them to be  independently tailored. Additionally, displacement is partially decoupled. Finally, the rotation of the end  stage is in herently small .    By mounting ribbons in a parent material instead of using the parent material itself, the combined mass is reduced and the target stiffness for each degree of freedom can be achieved more reliably. The slenderness of the metal ribbon prov ides the desired compliance while the parallel -guiding nature of the mechanism  restricts its motion to the desired directions.  

Runners   z-flexures   x-flexures   Hook attaches here   Figure 3.  Rendering of CAD assembly model of microspine suspension indicating  key design elements.   x-direction   z-direction
407 The x -flexures and z -flexures provide motion in the x - and z -direction, respectively. The stiffness of these  two flexure systems  must be dramatically different –  by two orders of magnitude. This stiffness difference  is accomplished using two strategies. First, the x -flexures are much thic ker than the z -flexures. Second, as  the upper limit of thickness was approached in the x -flexur es, more flexures were added. This addition of  flexures increased stiffness without increasing maximum stress.  

The proposed parallel -guiding design was initially analyzed using the pseudo- rigid-body model  approximation [4], and then the design was analyzed using finite element analysis in the commercial  package ANSYS. The finite element model is shown in Figure 4. For simplicity, these models only analyze  the flexures; the rigid sections are neglected.  

    Figure 4.  Finite element models of the x -direction flexures (left) and z -direction flexures (right).   Green elements are the displaced state; outlines show the initial state.    It was found that neither wire electro -discharge machining (EDM)  nor water -jet cutting would be able to  fabricate extremely slender flexures. If these manufacturing methods were used, thicker flexures would  have to be employed. With thicker flexures, the flexure would need to be unacceptably long to avoid material  failure  and would violate the envelope restrictions. Thus, the complexity of affixing metal ribbon flexures   was deemed ac ceptable due to the significant performance advantage.  

Design Details   Refer to Figure 3 during the following explanation of design features.  Two candidate materials were  considered for the flexures. 1095 spring steel at a full hard temper is available in a range of standard  thicknesses and has a high yield strength. Alternatively, the class of alloys known as metallic glass offers high performance, but alloys availabl e in ribbon or sheet form are limited, and low -quantity production of  custom alloys is expensive. However, metallic glass is a superior choice for the flexure material because of its high S y/E ratio. Finite element models and preliminary testing showed that the steel flexures would  yield slightly if taken to the full displacements in the x - or z- directions. The low cost of steel made it  acceptable for prototyping, but superior performance is predicted if the challenges of procuring metallic glass ribbon can be overcome.    To simplify  fabrication, the rigid three  sections are all cut from the parent material as one piece. C onnected  by runners, these sections are to remain together until the flexures are fixed in place. Then the runners can  be severed,  allowin g the mechanism to move freely . 

The hook attachment is accomplished first by harvesting the tips off of commercially fishhooks, then  pressing the hook into the hook attachment geometry. The gaps are then filled with aerospace epoxy, which
408 is allowed to cure. When the design enters production, it is intended that hook tips can be specially ordered  to eliminate the harvesting step.  

Prototype Fabrication   While much information on the stiffness and displacement behavior of the compliant suspension can be discovered from finite element modeling, the gripping behavior and interactions with neighboring  microspines is difficult to model. Therefore, several rounds of prototyping were employed to investigate the  behavior of the suspension.    To lower costs and reduce  lead time, initial pro totypes were laser cut from 1.6- mm-thick acrylic sheets.   They were built at 1:1 scale. Flexures were cut from steel shim stock of the appropriate thickness using hand shears. The shearing operation imparted significant curvature to t he flexures, which was removed by  plastically deforming the flexures to straighten them. The flexures were then cut to length and fixed to the acrylic cut -outs with cyanoacrylate.  These prototypes  are shown in Figure 5. In early versions, the fishhook  was omitted to decrease prototyping time and improve safety .     Figure 5.  Acrylic -steel  prototypes in two stages of production. On the left is the acrylic  suspension  body  before the addition of steel  flexures. Note that the three independent sections  are held together with runners. On the right is the completed prototype with steel flexures  embedded and runners removed.  

These acrylic -steel prototypes were subjected to the stiffness testing described in the next section. Once  the accuracy of the finite element model was established, additional prototypes were fabricated to observe  their behav ior as an array. In this iteration, steel hooks were included to facilitate initial tests of grasping  ability.    The behavior of these acrylic -steel prototypes was sufficient to warrant further investigation and aluminum - steel prototypes were built . The aluminum was cut from 1.6- mm (1/16 th-inch) 6061 aluminum sheet material  on a waterjet cutter. Future versions could be cut using a wire EDM to improve machining precision, or using waterjet to do most of the cutting and then using EDM to cut the finer details such as the channels where the fl exures attach. A waterjet -cut blank is shown in Figure 7.
409    Figure 6.  An array of acrylic- steel prototypes.  

Figure 7.  An aluminum blank into which steel flexures will be bonded.  

After cutting on the water -jet, the blanks were de- burred. Because of the large kerf of the water -jet, the  flexures were  fixed  in place with adhesive tape prior to bonding. The tape was arranged to form pockets  into which epoxy was injected, bonding the flexure to the aluminum. This process was labor intensive; future iterations will be altered to avoid the painstaking application and removal of the tape. A lternatively, Teflon  fixtures could be designed to contain the epoxy and hold the flexures during cur ing. In all, 24 aluminum - steel prototypes were built and tested. These were assembled into the test gripper and loaded. Testing is  further described in the following section.  

Testing    At this point the design is currently undergoing testing and design refinement. Initial testing separately measured stiffness of the suspension along each desired motion direction. Then a sufficient number of  prototypes were built to allow for a gripping capacity test to be conducted on natural rock surfaces using a  test stand. The maximum load supported by eighteen microspine suspensions and spines in a test gripper was measured; results indicate that the design merits further testing and refinement.
410 Stiffness Testing  To confirm that the new suspension design met stiffness targets, individual suspensions were tested in a  force- displacement jig. A known displacement was applied and the resulting force was measured.  This  testin g is shown in Figure 8. 

Grip testing   Figure 9 shows the test equipment used to obtain data on the gripping capabilities of the micros pine  flexures.  

Figure 9.  Testing on the microspine gripper in a test fixture.  Top: The entire test fixture, with  independent x - and z - stages to test gripping force in each direction (the rock is scoria). Bottom:  Close- up view of microspines during testing (the rock is rhyolite) . 

The purpose of grip testing is to quantify the forc e a given microspine design can support. The rig shown  in the top half of Figure 9 is able to measure the forces in the x - and z - directions independent of one  another. Although the x -direction force may not seem to contribute to the vertical load capacity, there is a  relationship between the load capacities in the x - and z - directions. This test setup gives more repeatable  Figure 8.  Stiffness testing of the x -direction suspension. This prototype was construc ted  from laser -cut acrylic (1.6 -mm thick), with steel shim stock for the flexures.   carriage  

suspension   microspine
411 results more rapidly and requires fewer microspine specimens than other testing techniques that consist of  attempting to lift large rocks.  

Results    The most important design function is to provide a large reaction force. Therefore, the gripping force in the x and z directions was measured as the critical performance metric. Figure 10 shows a plot of force testing  data with x -direction force plotted on the x -axis and z -direction force plotted on the y -axis. This single  carriage of microspines is generating nearly twenty newtons of vertical reaction force. Used in an array , as  is typical for this architecture, the total vertical reaction force could reach hundreds of newtons.  

Figure 10.  Representative plot of x - and z - directional forces.    In these early stages of testing, we discovered many design issues that must be addressed. Figure 11  shows several of the most common or serious issues that arose.
412    The original test gripper experienced interference  with the rock sample, necessitating a redesign that  provided adequate clearance.  If an x -direction compression load is exerted on the  z-direction flexures, this crimping failure can result,  indicating t he need to protect the flexures from  compressive loads.      The flexure arrays being bolted too tightly into their  carriages caused this binding/tangling failure. Here,  the flexures are only undergoing elastic deformation  and can be untangled without los s of performance.  This photo shows a hook that has shifted in its  mounting epoxy due to a high transverse load.
413    Another binding/tangling failure. Layering thin  Teflon sheets between the microspines has been  proposed as a solution to the tangling problem, and  it may also alleviate the binding issue.  Pullout failure of the z -direction flexure due to  overload in the x -direction. This failure must be  guarded against with better surface preparation of  the flexure material.  

Test run incorporating divider sheets to reduce tangling.  

Figure 11.  Several design issues that came to our attention during testing.  

Design Changes   One of the most important shortcomings in the suspension design was the susceptibility to tangling. To remedy this, divider sheets were included between neighboring microspines. Other problems revealed included susceptibili ty to binding, flexure pull -out, and flexure crimping. The binding and crimping problems