ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
were perfo rmed in this con dition, re sulting  in on ly a slight i ncrease in t he required force  and no  comp romise in velocity smoothness.    Design De tails  Unpowere d Holding Fo rce  Vespel SP3  Spheri cal Rol ler  Steel Pin with Dicronite  Dry Film Lub ricant  (Sliding Cont act) Rolling Conta ct Point  Piezo Moto r  Finge rs  Figure 12.  Spherical Roll er Cros s Sec tion The piezo m otor m oves the o utput stage th rough an oscillation of the pi ezo fingers th rough a  friction  interface. Wh en the motor is n ot powered, the pi ezo fingers are still prelo aded again st the moving sled.   This stati c interface betwe en the  piezo fingers and the sled gives the b enefit of unpo wered holding  force .  Under ambie nt con ditions the current prototype has a holdin g force of a pproximately 13  N, which is  directly pro portional  to th e preload  of the finge rs and the numb er of el emen ts used i n the motor. T he  mech anism can however, be readily  backdriven  by si mply overco ming th e frictional holdi ng force withou t  any da mage  to the  moto r or friction interface. Thi s holding force i s likely not en ough to cage  the  mech anism for launch conditions, but will hold  the mechanism during orbital maneuvers of th e spa cecraft  after the laun ch lo ck me chanism h as been rele ased.   

Mech anical H ardstops  Two me chanical ha rdstops are incorp orated into the mecha nism, one at either end of travel.  These   hardstops protect the me chanism  and the optics from overtravel, b ut also all ow for positional  calibratio n of  the me chanism at sta rtup. Since th e piezo fingers slip on th e ceramic d rive strip when th e stall force of  the moto r is excee ded, th ere is no damage done to the m echanism when th e moving  sled encounters a  hardstop. To calibrate  the me chanism it is drive n in one direction  until a position error th reshold is  excee ded. T he po sition t racking software i s then re-zeroed to create a hom e position in  the co ntrolle r,  which elimin ates the nee d for an ab solute feedba ck device.   

Powe r Consumption   The fou r-element pie zo motor itself consumes approximately 3.25 watts of p ower un der normal ope rating  conditions on Earth. Po wer consumption will be slightly reduced (although ex actly how much has yet to  be quantified ) on orbit due to the d ecrease in the coefficient of fri ction of th e Vespel rollers i n vacuum  and  the corre sponding  reduction in th e force ne cessary t o move th e cube corner sled. The  drive ele ctronics  used in the prototype are not desi gned for efficien cy as they are f or industrial application s, and co nsum e  approximatel y 4 watts giving a total of 7.25 watts tot al power con sumptio n for the me chanism. The pi ezo  element s require a sinusoidal voltag e of 120 volts fo r excitation. T he control electronics currently run  off  of a 24 or 48  volt DC bus and a majo rity of the drive electro nics’ power con sumption is u sed for voltage   conve rsion.   257
Feedb ack an d Control    The p rototyp e currently u ses a vacuum  rated, Renishaw 0.1-mi cron linea r encoder for positional feedback  to control the velocity profile. A standard servo controller running a cascaded velocity/position control loop  is used to control the motion prof ile. The interferometer’ s referenc e laser will eventual ly replace the  encode r as the me chanism’s fee dback device. The  zero crossings of the sinusoidal laser interference  pattern can be counted  in much  the same was a s a tradition al encoder allo wing a standard controll er to  be imple mented. Usi ng th e laser a s feedba ck shoul d increa se the ro bustness of the m echani sm by   decreasing the number of subsystem s. It is also expected that this will increase the perform ance of the  mech anisms due to  the high resolution of the la ser int erferomete r and the  fact th at the control system  will  feedba ck dire ctly on the op tical path differen ce, which is the varia ble of intere st.   

Testing 

The prototyp e me chanism was tested using the double pass interferomete r setup shown in Figure 1 3 to  give true out put velocity measurement s. A 633-n m wavelength si ngle-f requency He:Ne reference laser i s  sent th rough a beam splitter with one half of the bea m going to th e station ary cube corne r and the oth er  half of th e beam going to the m oving cube corner. The beams reflect off th e cube corners onto the  retro  reflecto r whe re the beam s then retrace their p aths. The two b eams then recom bine at the b eam splitter  where their overlappi ng waves a dd and subtra ct, depen ding on their relative path differen ce, to produ ce  an interfe rence pattern. If the moving cube corn er trans lates at a co nstant velocity, the interferen ce  pattern i s a consta nt frequ ency si ne wa ve. The wave form pattern in the dete ctor is sampl ed at 1MHz and   the data is an alyzed u sing a cu stom ana lysis tool built  by ASI.  Laser Beam Retro  Reflec torMichel son  Mirro r Beam  Splitter LaserDete ctorStationary Cu be Co rner Movin g Cube Corn er Figure 13.  Laser Inte rferometer Te st Setup 

258
Figure 1 4 shows the  original la ser inte nsity de picte d in the form of a sine wave. The  Hilbert transform o f  this data i s then ta ken to  calculate th e freq uency of the data a t every point.  This  frequ ency is di rectly  proportional to the cube corner linear vel ocity. The  calc ulate d velo city is plotted  in Figu re 15. The F ourier  transfo rm can then be taken of the velocity data to identify the freque ncies at which disturb ances o ccur  and their ma gnitude. Thi s velocity erro r data is sh own in Figu re 16. Usin g this method, th e true velocit y  error of the  cube corner can b e measured and the  freque ncy of the disturban ces can be quantified, whi ch  helps to ident ify and eliminate the sou rces of velocity error. 

Figure 14.  O riginal laser intensity  data ov er 0.1 ms sample per iod  (red circle s are sample p oints) 

Figure 15.  Calculate d velocity (freque ncy) vs. time  over 1 second  sample peri od

259
0.7%  error   100  kHz 

Figure 16.  Velocit y Error  Data for th e PAOS Mech anism  Over 50 0 runs have bee n conducted using the current  prototyp e, cha racterizing it s performance and  robustness. The me chanism is consistantly able to produce le ss than 0.7% cumulative vel ocity erro r at  freque ncies up to 100 kHz. It is anticipat ed that usi ng the refe rence lase r as feed back will furth er imp rove  this error by rejectin g low freque ncy disturba nces that  are within th e servo range of the control  system.    260
Pancam Mast Assembly  on Mars Rover 

Robert M. Warden*, Mike Cross* and Doug Harvison * 

Abstract 

The Pancam Mast Assembly (PMA) for the 2003 Mars Rover is a deploy able structure that provides an  elevated platform for several cameras. The PMA cons ists of several mechanisms that enable it to raise  the cameras as well as point the cameras in all di rections. This paper describes the function of the  various mechanisms as well as a description of  the mechanisms and some test parameters. 

Designing these mechanisms to operate on the surfac e of Mars presented several challenges. Typical  spacecraft mechanisms must operate in zero-gravity and high vacuum. These mechanisms needed to be  designed to operate in Martian gravity and atmosphere.   

Testing conditions were a little easier because the mechanisms are not required to operate in a vacuum.  All of the materials are vacuum compatible, but the mechanisms were tested in a dry nitrogen  atmosphere at various cold temperatures.   Figure 1.  Rover Conf iguration - Deployed UHF  monopole  antenna  High Gain  antenna  (HGA)  Solar arrays Warm  Electronics  Box (WEB)  Mobility System Mobility DifferentialInstrument Depl oyment Device (IDD)Rover Equipment Deck ( RED)MagnetsPancam  Mast  Assembly  (PMA) Low gain antenna  (LGA)Calibration Targ et  Pancam sNavcam s Introduction 

The Pancam Mast Assembly is one of the two main  mechanical systems that mount on the top of the  Rover Equipment Deck (RED); the ot her being the High Gain Antenna System (Figure 1). The mast lays  flat against the RED from launch to landing and is held in place to the RED with a Launch Restraint  Mechanism. After the Rover has landed and the Solar Arrays have deployed, the Launch Restraint is  released. The Mast Deployment Driv e then elevates the mast from horiz ontal to vertical to give the  cameras better visibility. The Azimuth Drive rotate s the upper part of the mast left and right while the  Camera Bar Drive raises and lowers the cameras. The Mini Thermal Emissivity Spectrometer, or MiniTES, is located beneath the RED and looks up through the center of the PMA like a periscope. An                                                         * Ball Aerospace & Technologies Corp., Boulder, CO 

Proceedings of the 37th Aerospace Mechanisms Symposium, Johnson Space Center, May 19-21, 2004   263
adjustable mirror at the top of the mast allows the Mini-TES to  look up and down independently of the  other camera. 

PMA Mechanism Overview  (Figure 2)  • Launch Restraint holds the mast to the RED  and releases on command. Allows for Rover  flexibility and thermal expansion.  • Mast Deployment Drive moves mast from the  horizontal position to the vertical position.  Latches into place when deployed. Contains  seals for light and dust.   • Azimuth Drive provides 360 degrees of  rotation. Rotates Pancams, Navcams, and  Mini-TES mirrors in azimuth.  • Camera-bar Elevation Drive rotates Pancams  and Navcams up and down. Hard stop at one  end of travel is used to provide pointing  reference position.    • Mini-TES Elevation Drive rotates the MiniTES mirror up and down independently of the  camera bar. Also rotates the mirror to point at  the internal calibration target. Calibration  position closes the aperture to provide dust  and stray light protection during calibration.  Hard stops provide pointing reference  position.     Figure 2.   PMA in the Deployed C onfiguration Azimuth  Drive  Mast  Depl oyment  Drive Camera  Bar D rive Mini-TES  Elevation  Drive Surog ate  Camera  Bar  Composite Mast 

Stowed Configuration   In the stowed configuration, the PMA lays agains t the equipment deck under the parachute canister as  shown in Figure 3. The deck is covered with sola r cells except for specific areas reserved for  attachments. The Mast Deployment  Drive supports the mast at the base but the “head” of the mast  needed additional support to withstand the launch and landing loads. The launch restraint mechanism  secures the mast-head in two places and when combined wi th the MDD, results in a three point mount. In  addition, the solar panels  fold up against the  parachute canister to form  a pyramid. Threedimensional CAD modeling  was essential for packaging  the PMA in the required  envelope. Note that the  camera bar assembly  is  tilted toward the center to  avoid contact with the solar  panel. This volume is also  shared with the High Gain  Antenna and Low Gain  Antenna. Clearance was  required to prevent damage  to the fragile solar cells  mounted on the inside of  the deployable panels  during launch and landing.     Parachute  Canister Low Gain Antenna  High Ga in Antenna  PMA Launch R estraint Figure 3 -PMA Stowed       264
Launch Restraint Mechanism 

The first mechanism to operate is the Launch Rest raint System. The PMA must be held down to the  Rover deck during launch, flight and landing. After the Rover lands and the solar panels are opened, the  launch restraint must release to allow the PMA to deploy. In addition, the mechanism that raises and  lower the cameras must also be constrained to pr event damage. The customer  directed that redundant,  pyrotechnically actuated pin-pullers would be used to engage (or disengage) the launch restraints. 

The biggest challenge for launch restraint mechanism wa s to provide a launch lock that would not over  constrain the system or be too co mplicated. There is significant differential movement due to the  difference in thermal expansion between the mast and t he Rover deck. Also, the Rover deck is somewhat  flexible. The restraint system must allow movement al ong the axis of the mast ye t provide restrain in the  other two axes. Another constraint is that the top of the rover is a honeycomb panel assembly covered  almost entirely with solar cells. Only a few small ar eas were allocated to support the PMA in the stowed  position. 

Basic Requirements:   • Hold PMA to dec k  • Constrain PMA rotation to protect MDD gear train  • Constrain Camera Bar rotation to pr otect Camera Bar Drive gear train  • Use maximum of 3 pin-pullers (only 2 implemented)  • Accommodate thermal distortion of deck  • Allow PMA conical deployment 

Exit Direction Mono-pod Bi-pod  PinPuller Pin  Clev is PinPullerPin- Puller Figure 4.  PMA Launch Restraint  (Mast-head structure remov ed for clarity ) Mast  Rest raint  The primary launch restraint function is to  secure the mast-head to the Rover deck.  This is accomplished by attaching a bracket  at the top of the mast  that features two  "ears" protruding to the side (Figure 4).  These ears contain self-aligning journals in  the form of spherical bearings. Each  spherical bearings fits into a precision clevis  or yoke, which are then pinned into place  using the above mentioned pin-pullers.  

The launch restraint system is designed so  that the stowed PMA is not over  constrained. This is accomplished by  making one of the clevis supports in the  form of a bi-pod to take lateral and vertical  loads. The other clevis support is a simple  mono-pod that only takes vertical loads. In  this way, the mast-head is prevented from  rotating but allowed to expand as needed.  The pin-pullers are located at the top of the  clevis supports. When deployment is  required, a signal is given to actuate the pin-pulle rs. The securing pins are thereby pulled out of the  spherical bearings and the mast is free to deploy.   

Mast Launch Restraint summary :   • The bi-pod mount constrains in  vertical and horizontal only  • The mono-pod constrains in  vertical axis only  • Together they constrain rotation about the mast axis  • Spherical bearing used for self aligning journal  • Dissimilar metals used for sliding surfaces 

Camera Bar Restraint   265
The second function of the launch restraint is to cons train the camera bar. The camera bar assembly is  discussed in more detail later in the paper. For this se ction, however, it is important to note that the  camera bar imparts a significant load to the drive motor  during launch and landing. The packaging is very tight as  shown in Figure 5. Any appreciable movement of the  camera bar while the solar panels are folded up would  damage the solar cells. 

The customer requested that the quantity of pin-pullers  be minimized to help reduce complexity and mass so  one of the design goals was to avoid the use of any pinpullers with the camera bar restraint. The design goal,  therefore, was to combine the function of securing the  mast to the deck with the function of securing the  camera bar drive.   

The camera bar features two small protrusions or "tabs";  one on each end as shown in Figure 6. These tabs  rotate with the camera bar. The mast-head also features  two tabs, but these are fixed to t he mast-head. In the stowed position, the rotating tabs on the camera bar  contact the fixed tabs on the mast- head. A floating clevis captures eac h tab pair, thereby  preventing the  camera bar from rotating with respect to the came ra head. Each clevis is mounted on a compliant support  so that the tab pairs can move with respect to the Rover deck but are still captured with respect to each  other. As the mast deploys, the t ab pairs are no longer captured allowing movement of the Camera Bar  Drive. Note that after the mast starts to deploy , the camera bar no longer needs to be secured. This  design uses the action of lifting the mast off of the Rover desk to release the camera bar. 

Stowed Solar  Panel Parachute   Canister  Tab & Cl evis Location Stowed Camer a Bar 

Figure 5.  Stow ed Configuration  Follower Side Driven Side Exit  DirectionClevisMast head  tab Camera bar  tab  Figure 6.  Camera Bar Restraint Components  The clevis surfaces have a slight spherical profile to allow relative rotation and have a slight amount of  clearance to avoid binding. As the ma st deploys, the tabs pull out of the clevises, which are attached to  the deck. The tabs are then free to separate and the ca mera bar drive then controls the rotation of the  camera bar. The materials are carefully chosen and t he surfaces are coated to limit the possibility of  galling and binding. Mockups of this system were built  early in the design to verify the performance.  Vibration testing of the final hardware resulted in scuffing of the coated surfaces but no failure of the  coatings or galling of the surfaces. 

Camera Bar Restraint summary :  • Constrains Camera Bar only in rotation relative to mast-head  • Only engaged in stowed configuration  • Flexible support eliminates  over-constrained condition  • Imparts slight friction during deployment  266
Mast Deploy ment Driv e (MDD) 

The second mechanism to operate is the Mast Deployment Drive (MDD). This  mechanism drives the  mast from horizontal to vertical. The mast is st owed against the Rover Equipment Deck in the horizontal  position from launch to landing. On command, the MDD mo ves the mast into the vertical position where it  is latched in place. The MDD also handles the lar ge bundle of wires that are required to operate the  cameras and other mechanisms. 

Requirement Summary:  • Drive mast from horizontal to vertical  • Provide optical path when deployed  • High stiffness  • Control & support electrical cabling  • “Reasonable” deployment time  • Keep dust out   Interfac es:  • Base bolts  to RED  • 5 Electrical cables & connectors to RED  • Top bolts to Azimuth Drive  • 4 Electrical cables  & to Az  Drive   • 1 Electrical cable to motors 

Early in the program, a need was established for a stiffer deployment mechanism for the PMA. The first  part of the design effort was to step back and look at how large, thin-walled, tubular structures can be  bent. Elastic structures such as a garden hose are i nherently flexible but need a secondary structure for  stiffness. A bellows structure is very stiff in torsion but flexible in all other directions so it would also need  a secondary support structure. The desire was to keep the design simple and to combine the structural  function with the optical requirements.   

The solution was found on top of a water heater. The  flue pipe that carries away the hot gasses is made up of  several angled couplings that enable the pipe to be bent  as needed while maintaining structural integrity and  internal clearance. This was the approach taken for the  new deployment drive. 

Unlike the flue pipe, however, the MDD uses only a  single angled coupling in the form of a bearing mounted  at an angle. The mast travels from horizontal to vertical  in a conical path (Figure 7). The inclined bearing design  is a simple and effective way to rotate the mast and keep  the Martian dust out while maintaining structural  integrity. Although the two main housings are fairly  complicated, the overall design is quite simple and  robust. There are very few parts and the mechanism is  easy to assemble and test. 

The single large diameter, small cross section bearing is  an X-type that is internally preloaded. The large  diameter of the bearing results in good strength and  stiffness while the internal preload eliminates the need  for a second bearing. This type of bearing does have  limited life, but in this application the required  operational cycles were well wi thin the life of the bearing.  Axis of  rotation

Figure 7.  Conical deploy ment path 

This conical deployment path also proved to have an advantage in allowing the mast-head to easily exit  the launch restraint. The mast-head leaves the deck at  about a 40-degree angle so that the vertical vector  is about the same as the horizontal vector. The angle of the inclined bearing was made as large as  possible to maximize the vertical vector.  267
MDD Components   Figure 8 show the five main  structural components in the  Mast Deployment Drive. The  Inner Housing is bolted to the  Rover Equipment Deck and  remains fixed. The inner ring  of the bearing is clamped to  the Inner Housing with the  Inner Clamp. The outer ring  of the bearing is clamped to  the outer housing with the  outer clamp. The Outer  Housing and Clamp are thus  free to rotate on the bearing.  The inside of the fixed inner  clamp features a large  diameter internal tooth ring  gear. The gear-motor is  attached to the Outer  Housing by means of an adapter. The Pinion Shaft coming off the Gear-motor engages the ring gear to  drive the outer housing. Note that the gear-motor rotates with the out er housing. This was done so that  the gear-motors for the MDD and the Az imuth Drive (see next section) c ould share the same wire path.  The Outer Clamp features a protrusion that engages a hard stop at full deployment. 

Design Trade   One of the first design trades to be made with this  mechanism was whether or not to have a separate  latch to hold the mast in place in the deployed posit ion. The detent in the motor through the gear train  was enough to hold the mast in place under most conditi ons. The benefit of not havi ng a latch is that the  mast can be remotely deployed and retracted as often as needed. The benefit of havi ng a latch is that the  gear-motor is not in the load path so the gear  teeth and bearings do not need to be as  strong. The disadvantage of having a latch is  that once the latch falls into place, it must be  manually unlatched in order to stow the mast.  The mass for the stronger bearings and  gears was about the same as for the latch  components. It was finally decided that the  ability to remotely stow the mast was not as  important as the guar antee that the mast  would not creep out of alignment so the latch  was added to the mechanism. 

The hard stop was made adjustable in order  to adjust the final deployed position of the  mast. Materials were chosen so as not to  have similar metals in contact with each  other. The outer flange and tang are made of  hardened Titanium. The latch and hard stop  are made of hardened Nitronic 60. Published  data shows that Titanium against Nitronic has  very good resistance to galling. Gear-Motor AdapterOute r Housing Inner Clamp & Ring GearX-Bearing Oute r Clamp Inner HousingSeal Pinion Shaft

Figure 8:  Exploded v iew of the Mast Deploy ment Driv e 

Oute r flange with ta ng &  pinion r otateFixed Ring Ge ar  LatchHard Stop 

Figure 9.  Latch Detail  268