UFDC Home  myUFDC Home  Help 



Full Text  
REVERSE KINEMATIC ANALYSIS AND UNCERTAINTY ANALYSIS OF THE SPACE SHUTTLE AFT PROPULSION SYSTEM (APS) POD LIFTING FIXTURE By JEFFREY S. BRINK A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ENGINEERING UNIVERSITY OF FLORIDA 2005 Copyright 2005 by Jeffrey S. Brink This thesis is dedicated to the Kennedy Space Center workers who have done their best to help this effort succeed, in hopes of making operations better and safer. ACKNOWLEDGMENTS I would like to thank NASA Orbiter Handling's Rob Summers and United Space Alliance (USA) Orbiter Handling's Glenn Roberts for their invaluable help. As the experts on this hardware and installation process, they responded promptly and patiently to my constant barrage of questions. Their willingness to do anything they can to make operations safer is commendable. They shoot a pretty good game of pool, too. Boeing Orbiter Handling's Will Judd was also very helpful. He answered several technical questions and verified the accuracy of some information I had found on my own. NASA Payload Mechanical Engineering's Doug Lenhardt and NASA Mechanical Design Engineer Paul Schwindt were instrumental in the Pro/E portion of this study. Doug and Paul answered questions that helped my knowledge of Pro/E grow from beginner level to intermediate. After I experienced quite a bit of difficulty getting the integrated C program to run, NASA Senior Software Engineer Dan Nieten was kind enough to teach me several very helpful debugging techniques. These techniques enabled me to figure out what was wrong, and how to make it work. NASA Thermal Protection Systems' Lisa Huddleston provided guidance on performing my literature review and gave tips on how to use numerical methods to reduce error in the integrated program. I also frequently consulted Lisa about details of this study and (even though robotics is not her field of expertise) she never seemed to run out of good questions. I would also like to thank my supervisory committee for their contribution. Dr. Carl Crane III (my supervisory chair) was particularly helpful. The concepts taught in his textbook formed the backbone to this solution method. Dr. John Scheuller and Dr. Ashok Kumar provided good insight as this thesis reached its conclusion. NASA Launch Accessories' Kristina Morace and NASA Orbiter Handling's Ryan Holmes checked the technical content of this thesis and helped make it more clear and understandable. TABLE OF CONTENTS page A C K N O W L E D G M E N T S ................................................................................................. iv LIST OF TABLES ......... .. .. ....................................... .... .... .............. viii LIST OF FIGURES ............................... ... ...... ... ................. .x LIST OF ABBREVIATIONS ............................................................. .............. xi A B S T R A C T .............................................. ..........................................x iii CHAPTER 1 B A C K G R O U N D ................................................................ ....... ................ . In tro du ctio n ............................................ ...................... ... .................... . H ardw are F am iliarization ................................................................... ......... ...........2 Installation Procedure and M ethodology ................................................. ............... 4 2 PROPOSED ALIGNMENT METHOD ...............................................................10 O v erv iew ............... ........ ..... ... ........... ... ....................................... 10 Determination of Desired Joint Angles ................................................. ................. 10 Alignment of APS Pod Attach Points with Orbiter Attach Points....................11 Adjustment Mechanism Reverse Kinematic Analysis .....................................17 Adjustm ent mechanism parameters .................................. ............... 17 Closetheloop variable calculations ........... ... ............... ... ............ 18 Reverse kinematic analysis of a PPPS mechanism .....................................19 Rotator B ar Length Calculation...................................... ......................... 26 N om in al S solution .......... ............................................................................. . ....... 2 7 3 UNCERTAINTY ANALYSIS ........................................................ ............. 31 OffNominal Conditions within Tolerance.............................................31 Adjustment Mechanism Spherical Joint Socket Locations .............. ...............31 Orbiter Attach Point Locations..... ................................31 The APS Pod Fitting Locations.......................... .......... ..................... 32 Lifting Fixture Attach Point 3 Location....... ..........................................32 Lifting Fixture Adjustment at Attach Point 3........................... .............32 U uncertainty of Input V alues............................................... ............................. 33 C alculationR elated U ncertainties.................................... ......................... .. ......... 33 H ardw are Positioning U uncertainty ........................................ ........................ 34 Uphill/Downhill Joint Offset Measurement ................ ............... ........34 OfftheDeck/OntheDeck Joint Offset Measurement.................................. 35 Forward/Aft Joint Offset M easurem ent............................................................35 Rotator Bar Joint Offset Measurement.....................................................35 C om pliance in Joints .................................................... ........ ....... ............36 Total Uncertainty Calculation.......................................................... 36 One Hundred Percent Covariance Method........................................................36 R oot Sum Squared M ethod ........................................ ........................... 37 4 EVALUATION OF PROPOSED ALIGNMENT METHOD...............................52 D iscu ssion of R results ........ .. ...... .. ............ ....................... ....................52 Recommendations........ ........ ....... ... .................. ........ 53 Summary of Recommendations................. .......... .......................... 56 C o n c lu sio n s........................................................................................................... 5 6 APPENDIX A SHUTTLE COORDINATE SYSTEMS................................. ...................... 58 B REVERSE KINEMATIC ANALYSIS NOTATION......................................63 L IST O F R E F E R E N C E S ........................................................................ .....................65 B IO G R A PH IC A L SK E TCH ..................................................................... ..................66 LIST OF TABLES Table page 21 Adjustment mechanism parameters. ............................................. ............... 30 22 Comparison of joint offsets calculated by the program to measured using the C A D m odel. ..................................................................30 31 Forward spherical joint socket tolerances. ............................... ..... ...........38 32 Aft spherical joint socket tolerances. .................................................................... 38 33 Orbiter Attach Point 1 tolerances. ........................................ ......................... 39 34 Orbiter Attach Point 2 tolerances. ........................................ ......................... 39 35 Orbiter Attach Point 3 tolerances. ........................................ ......................... 40 36 APS pod Attach Point 1 tolerances. .............................................. ............... 40 37 APS pod Attach Point 2 tolerances. .............................................. ............... 41 38 APS pod Attach Point 3 tolerances. .............................................. ............... 41 39 Lifting fixture Attach Point 3 tolerances ....................................... ............... 42 310 Lifting fixture Attach Point 3 adjustment. .................................... .................42 311 M isalignm ent of the rotator bar base .................................................. .. .. ............ 43 312 Com puter program uncertainty. ........................................ ......................... 43 313 Forward adjustment mechanism uphill measurement uncertainty.........................44 314 Aft adjustment mechanism uphill measurement uncertainty ................................45 315 Forward adjustment mechanism offthedeck measurement uncertainty ...............45 316 Aft adjustment mechanism offthedeck measurement uncertainty.......................46 317 Fwd and aft adjustment mechanism measurement uncertainty in the forward direction ................................................... .................. ..............46 318 Rotator bar length measurement uncertainty. .................................. .................47 319 Joint com pliance uncertainty ................................ ...................... ............... 47 320 Summary of Attach Point 1 uncertainty sources............................................... 48 321 Summary of Attach Point 2 uncertainty sources ................................................49 322 Summary of Attach Point 3 uncertainty sources............................................... 50 323 Total uncertainty using the 100% covariance method. .........................................50 324 Total uncertainty using the root sum squared method. .........................................51 LIST OF FIGURES Figure pge 11 A left APS pod is being removed from the space shuttle orbiter Atlantis ...............7 12 The twelve APS pod attach point locations, left pod shown (right pod m irror) ................................................ .................. 7 13 G SE used to install an APS pod. ........................................ ........................... 8 14 Forward and aft adjustment mechanisms allow motion in forward/aft, uphill/downhill, and offthedeck/onthedeck directions ........................................ 8 15 R otator bar joint axes. ............................................................. ................ .9 16 A left APS pod is transported by crane to Atlantis for installation .......................9 21 Joint offset calculation procedure....................................... .......................... 28 22 Three points are needed to determine each adjustment mechanism's position and orientation (aft adjustment mechanism shown, typical of all adjustment m mechanism s)......... ... .................................................. ............... ... 29 23 Adjustment mechanism joint axis vectors and link vectors ................................29 31 Adjustment mechanism joint axis vectors and link vectors.............. .......... 44 A i O rbiter coordinate system ............................................. .............................. 61 A2 Right APS pod coordinate system .......... ................. ....... ................ ..... .......... 62 LIST OF ABBREVIATIONS Term or acronym Adjustment mechanisms APS APS pod Cylinder joint FEA GSE Definition Two PPPS manipulators used for OMS pod alignment. Aft Propulsion System Orbiter component that houses the Orbital Maneuvering System and the aft Reaction Control System. A joint that allows rotational and translational motion about the same axis. Finite Element Analysis Ground Support Equipment Hydraulic jack Hypergol KSC Lifting fixture Move director NASA Nominal solution OMS OPF A forceoutput device used to overcome the binding condition experienced by the aft adjustment mechanism and cause forward/aft motion along a prismatic joint axis. A rocket fuel that spontaneously ignites when mixed with an oxidizer. Monomethyl hydrazine is the hypergol used by the OMS. Kennedy Space Center A large structure that attaches to the OMS pod and is manipulated by the adjustment mechanisms and rotator bar. The USA technician that uses information from technicians and engineers to determine the next manipulation. National Aeronautics and Space Administration The joint offsets required to align the lifting fixture. Orbiter Maneuvering System, propulsion system that provides thrust for orbital insertion, orbit circularization, orbit transfer, rendezvous, and deorbit. [1] Orbiter Processing Facility Term or acronym Orbiter Orbiter deck Plucker coordinates Prismatic joint Pro/E RCS Revolute joint Rotator bar Space shuttle Spherical joint USA The Orbiter is a doubledelta winged reentry vehicle capable of carrying both passengers and cargo to lowearth orbit and back to a controlled gliding landing. [1] The Orbiter is the only Space Shuttle element to reach orbit. NASA's Space Shuttle fleet consists of three orbiters: Atlantis, Endeavour, and Discovery. The orbiter surface that mates to the OMS pod. Homogeneous coordinates used to describe points, lines, or planes. Plticker coordinates can be used to simplify equations so that calculations can be performed more efficiently. A joint that allows translational motion only (also known as a slider joint). Pro/ENGINEER, a CAD software package used for modeling and finite element analysis. Reaction Control System, propulsion system used as the primary flight control at altitudes greater than 70,000 feet. [1] A joint that allows rotational motion only (also known as a hinge joint). A RRPRRR manipulator used for OMS pod alignment. NASA's only manned spaceflight vehicle. The Space Shuttle is comprised of an orbiter, external tank, and two solid rocket boosters. A joint that allows rotational motion in x, y, and z directions (also known as a ballandsocket joint). United Space Alliance, a Boeing and Lockheed Martin joint venture. USA is the prime contractor for space shuttle operations. Definition Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Engineering REVERSE KINEMATIC ANALYSIS AND UNCERTAINTY ANALYSIS OF THE SPACE SHUTTLE AFT PROPULSION SYSTEM (APS) POD LIFTING FIXTURE By Jeffrey S. Brink May 2005 Chair: Carl D. Crane III Major Department: Mechanical and Aerospace Engineering The space shuttle Aft Propulsion System (APS) pod requires precision alignment to be installed onto the orbiter deck. The Ground Support Equipment (GSE) used to perform this task cannot be manipulated along a single Cartesian axis without causing motion along the other Cartesian axes. As a result, manipulations required to achieve a desired motion are not intuitive. My study calculated the joint angles required to align the APS pod, using reverse kinematic analysis techniques. Knowledge of these joint angles will allow the ground support team to align the APS pod more safely and efficiently. An uncertainty analysis was also performed to estimate the accuracy associated with this approach and to determine whether any inexpensive modifications can be made to further improve accuracy. CHAPTER 1 BACKGROUND Introduction The Kennedy Space Center (KSC) is NASA's operations center for the space shuttle. This role includes mission configuration and deconfiguration, vehicle modifications, repair, and routine maintenance (essentially everything that happens to a space shuttle orbiter, from landing through launch). The installation of an Aft Propulsion System (APS) pod onto an orbiter is one example of a KSC operation. My study aimed to improve the APS pod installation operation by calculating the joint offsets required to align the APS pod with the orbiter deck. These calculations can be performed before the operation begins, which will reduce the operational time spent performing the alignment. APS pod installation is classified as a hazardous operation, which makes reducing the operational time particularly desirable. Throughout the operation, the potential exists for a hypergol leak to develop, which could be lethal to nearby personnel. The Ground Support Equipment (GSE) used to perform an APS pod installation consists of a lifting fixture, two adjustment mechanisms, and rotator bar. There are a total of 13 joints that change position during the operation. My analysis showed that they can be considered as three separate manipulators connected by a large structure. After the desired position of the large structure has been ascertained, the end effector position and orientation of each manipulator is found. A reverse kinematic analysis is then performed for each manipulator, to determine joint angles. An uncertainty analysis was then conducted. Both 100% covariance and root sum squared methods were used to quantify alignment accuracy. This analysis was used to determine whether the solution method described above is accurate enough to aid APS podinstallation operations; and to determine which of the error sources can be eliminated for significant improvements in accuracy. Hardware Familiarization Each space shuttle orbiter has two APS pods, one on each side of the vertical tail. Each APS pod houses the Orbital Maneuvering System (OMS) and the aft Reaction Control System (RCS). OMS is the propulsion system that provides thrust for orbital insertion, orbit circularization, orbit transfer, rendezvous, and deorbit [1]. The RCS propulsion system is used as the primary flight control at altitudes greater than 70,000 feet [1]. An APS pod is shown in Figure 11. The APS pods were not designed to be maintenance while installed on an orbiter. As a result, APS pods must be removed for inspections and repairs, generally after every three or four flights. On completion of these tasks, the APS pod is installed onto the orbiter. The APS pod is attached to the orbiter deck at 12 locations (called attach points). During the installation operation, all efforts are focused on aligning attach points 1, 2, and 3. If those three attach points are aligned, then attach bolts can be installed at all twelve attachpoint locations. Attach Point 1 is the forward inboard attach point, Attach Point 2 is the forward outboard attach point, and Attach Point 3 is the aft outboard attach point (Figure 12). The APS pod Attach Point 3 fitting must be aligned within 0.0033" (+/ 0.0018" depending on tolerances) of the orbiter bushing or else the attach bolt cannot be installed. The APS pod Attach Point 2 bushing resides in a slotted hole, which prevents podtopod variation and other factors from making an APS pod "not fit" onto an orbiter. The APS pod Attach Point 2 fitting must be aligned within 0.0063" +/ 0.0048" in the non slotted direction. Since attach points 2 and 3 are 12' 3.3" apart, this accuracy requirement is equivalent to positioning Attach Point 3 within 0.0033" on the orbiter deck and then orienting the APS pod to within 0.00250 of the desired position. The orbiter Attach Point 1 bushing can accommodate misalignments of up to 0.2231" along the orbiter deck plane. The alignment process is made significantly more challenging by the presence of a bulb seal on the bottom surface of the APS pod. The bulb seal is basically a hollow flexible tube that forms an environmental seal when compressed against the orbiter deck. When the bulb seal is compressed, the APS pod cannot be moved along the orbiter deck plane without risking damage to the bulb seal (the bulb seal is more likely to tear than slide along the deck). As a result, if the APS pod is lowered onto the orbiter deck and discovered to be misaligned, then it cannot simply be adjusted until it is aligned. Instead, it must be raised off the deck (until the bulb seal is no longer compressed) before it can be adjusted and then lowered onto the orbiter deck. The ground support equipment used to install APS pods is a lifting fixture, forward adjustment mechanism, aft adjustment mechanism, and rotator bar (Figure 13). The lifting fixture is a large structure that connects to the APS pod at APS pod Attach Point 1, 2, 3, and 4 fittings. The lifting fixture can be adjusted at attach points 1, 2, 3 and 4 to accommodate podtopod dimensional variation. As a result of this adjustment capability, not every APS pod will have the exact same position and orientation relative to the lifting fixture. The forward and aft adjustment mechanisms structurally support the lifting fixture and allow its position to be adjusted. Forward and aft adjustment mechanisms are nearly identical. Temporary supports are mounted to the orbiter and the adjustment mechanisms each form a spherical joint with a support. Adjustment mechanisms have three orthogonal prismatic joints that allow motion in the forward/aft, uphill/downhill, and off thedeck/onthedeck directions. The lifting fixture is connected to the adjustment mechanisms by the forward/aft prismatic joint. Figure 14 shows adjustment mechanism prismatic joint axis directions. The center of gravity of the lifting fixture and APS pod is not directly above the spherical joints for the duration of APS pod installation. As a result, the rotator bar is used to control the rotation of the lifting fixture about the two adjustment mechanism spherical joints (the two spherical joints essentially form a hinge). One end of the rotator bar is rigidly attached to the lifting fixture and the other end is mounted to a large stationary beam. Revolute joints are used to ensure the rotator bar does not restrict the lifting fixture motion. Figure 15 shows the rotator bar's revolute joint axes. It should be noted that none of the revolute and spherical joints can be actuated. Their role in the alignment process is purely passive. Installation Procedure and Methodology The APS pod installation operation begins with the APS pod in the Orbiter Processing Facility (OPF) transfer aisle. The lifting fixture, forward adjustment mechanism, and aft adjustment mechanism assembly have already been attached to the APS pod. A bridge crane lifts the APS pod and GSE to a location near the orbiter (Figure 16). Adjustment mechanism prismatic joints have been adjusted to provide maximum clearance to the orbiter as the spherical joints are connected. The crane transfers the weight of the APS pod, lifting fixture, and adjustment mechanisms to the spherical joints. The rotator bar is then extended until it can be connected to the lifting fixture and the alignment portion of this operation begins. According to the APS pod operations and maintenance manual, the rotator bar is extended until the APS pod mating surface is approximately 2.5" above the orbiter deck and the surfaces are parallel. The lifting fixture is moved forward or aft to the "install position" (a marking on the lifting fixture structure). Additional adjustments are made to align attach points 2 and 3. The APS pod is then lowered to 1/8" above the orbiter deck with mating surfaces parallel. The bulb seal is now contacting the orbiter deck but it is not compressed. Adjustments are made again to align attach points 2 and 3. Once aligned, the APS pod is lowered onto the orbiter deck and observers check to make sure the inboard side of the APS pod is also seated. If the APS pod is misaligned, it must be raised off the deck 1/8" or more, adjusted as required, and lowered back onto the deck. Attach point bolts are installed upon successful completion of the APS pod alignment procedure [2]. APS pod alignment is not accomplished as easily as the operations and maintenance manual describes. It is not possible to adjust the position of one attach point without affecting the position of the other attach points. This is particularly evident when either Attach Point 2 or 3 has been alignedadjustments intended to align one attach point usually misalign the other. The person who determines the next manipulation and commands that it be executed is known as the move director. Different move directors have differing philosophies about whether Attach Point 2 or Attach Point 3 should be aligned first. Move directors also use different techniques to align an APS pod. One technique is to align the APS pod 1/8" above the orbiter deck, then simultaneously retract the rotator bar and actuate both adjustment mechanisms in the onthedeck direction. Another technique is to slightly misalign the APS pod, then allow the rotator bar to correct the misalignment as both adjustment mechanisms are simultaneously adjusted in onthedeck direction. It should be noted that simultaneous motion is accomplished by manual start/stop and velocity control. Additionally, not all equipment operates as designed. Field experience has shown that the forward/aft install position does not necessarily align the APS pod. The aft adjustment mechanism's forward/aft prismatic joint was not designed with an actuator  it was designed to "follow" the motion of the forward adjustment mechanism. However, it binds rather than follows so a hydraulic jack is used to force it to follow. Figure 11. A left APS pod is being removed from the space shuttle orbiter Atlantis [3]. VHAPTOO Figure 12. The twelve APS pod attach point locations, left pod shown (right pod mirror) [2]. Mechanism Forward Adluslment Mecnanism Rotator Ba. Figure 13. GSE used to install an APS pod. Forward Uphill Offthedeck Onthedeck downhill A Figure 14. Forward and aft adjustment mechanisms allow motion in forward/aft, uphill/downhill, and offthedeck/onthedeck directions [3]. ~~i~ii~t'F~a~uP Revolute Joint Axis S Revolute Joint Axis Figure 15. Rotator bar joint axes. Figure 16. A left APS pod is transported by crane to Atlantis for installation [3]. CHAPTER 2 PROPOSED ALIGNMENT METHOD Overview The geometry of all relevant hardware and the desired position and orientation of the APS pod is known. As a result, a reverse kinematic analysis was conducted to determine sets of joint angles that would align the APS pod with the orbiter. Due to the large number of joints associated with this hardware, the rotator bar and adjustment mechanisms were treated as three independent robots connected by a large rigid structure. Since the large structure (lifting fixture) has adjustment capability to attach to the APS pod, it is assumed that these adjustments will be measured before the operation begins and is incorporated into the analysis. The lifting fixture CAD model (Figure 13) shows it in the position required to align the APS pod. As discussed previously, the displayed alignment position does not necessarily align the APS pod with the orbiter. The coordinates given in the CAD model were used as a starting point in this analysis. They were used to determine the position and orientation of the three robot end effectors. End effector position and orientation, partnered with known geometry, was used to perform reverse kinematic analyses. The output of these analyses was the joint angles required to align the APS pod. Figure 21 shows the process used to determine the manipulator joint offsets. Determination of Desired Joint Angles An existing Pro/E model of the lifting fixture, rotator bar, and adjustment mechanisms was refined for this analysis. The location of each end effector and APS pod attach point, in orbiter coordinates, was ascertained from the model and input into a C program. The C program translated and rotated the input points until the APS pod attach points were aligned with orbiter attach points. The resulting end effector points were used in reverse kinematic analyses to calculate joint angles. These joint angles can be described as the joint angles required to align the APS pod with the orbiter attach points. The orbiter coordinate system and APS pod coordinate systems are discussed in detail in Appendix A. Alignment of APS Pod Attach Points with Orbiter Attach Points The initial position and orientation of the lifting fixture in the CAD model is arbitrary. The lifting fixture's adjustments at attach points 1, 2, 3 and 4 have been physically measured and incorporated into the CAD model. The CAD model also contains seven points on the lifting fixture needed to describe end effector positions and orientations. Attach points 1, 2, and 3 are located in the CAD model of the left APS pod and their desired locations on the orbiter are also included in the model. Adjustment mechanism points can be seen in Figure 22. Attach Point 3 has the most stringent accuracy requirements so it is aligned first. The alignment algorithm begins by calculating the misalignment of APS pod Attach Point 3, PPod, relative to orbiter Attach Point 3, pOrbte p pOrbte pPod (2.1) Translate AttachPt3 AttachPt3 The APS pod and lifting fixture can be translated such that APS pod Attach Point 3 is aligned by adding PTram,,,, to all points located on either object 12 pPod pPod + p AttachPtI A=ttachPtl Translate pPod = pPod P AttachPt2 AttachPt2 Translate pPod = PPod + p AttachPt3 AttachPt3 Translate pLftrngFzxture pLfhngFzxture + P RotatorBar RotatorBar Translate pLfrngFzxture _= pLfhngFxture + P FwdAdjMechOng FwdAdjMechOng Translate pLftrngFxture pLfhngFixture + (2.2) Fwd4djMechX Fwd4djMechK Translate pLftIngFixture p PLftIngFixture +, FwdAdjMechZ FwdAdjMechZ Translate pLfthngFzxture p_ PLngFzxture +P AftAdjMechOng AftAdMechOng Translate plLftrngFzxture PLfhngFzxture + PT AfAdjMechX AfAdMechX Translate pLzftrngFxture pLfhngFixture + AftAdjMechZ AftAdjMechZ Translate Attach Point 2 has the next most stringent accuracy requirements and therefore is aligned second. The unit vectors from pod Attach Point 3 to pod Attach Point 2 and pod Attach Point 3 to orbiter Attach Point 2 are described as pPod _PPod V AttachPt2 AttachPt3 32 Pod pPod _PPod AttachPt2 AttachPt3 (2.3) pOrbiter PPod V AttachPt2 AttachPt3 32 Orb POrbiter PPod AttachPt2 AttachPt3 The unit vector mi perpendicular to both V32 pod and V2 Orb can be calculated as 3m V32 Pod XV32 Orb (2.4) min =  (2.4) 32 Pod 32Orb and the angle 02 between V2 pod and V32 Orb is the unique solution to Equations 2.5 and 2.6. 2 =cos 1 32 Orb (2.5) 2 \~32 Pod 32 Orb) 25 0 =sin 1 2 Pod 32 Orb (2.6) Pod Attach Point 2 will become aligned and pod Attach Point 3 will remain aligned if lifting fixture and APS pod points are rotated by angle 02 about an axis containing vector mi and passing through pod Attach Point 3. This transformation matrix T, is then calculated. [4] mIxmlxn1 + cos 02 minmxl in, sin n2 minxmliz + il sin 02 T m imnIl + mlZ sin 02 mnmilyv + cos 02 mymny, mI sin 02 mmz1u, n ly sin 02 inmin, + mix sin 02 minz i + cos 02 O 0 0 pPod AttachPt3,X pPod AttachPt3,Y (2.7) pPod AttachPt3,Z 01 cos02 This rotation is then performed on all APS pod and lifting fixture points. pPod PPod pPod AttachPtL 2 AttachPt2 AttachPt3 1 1 pPod 7 Pod pPod SAttachPt3 = T AttachPt3 AttachPt3 pLfngFxture pLifingFxture pPod 1 1 pLfhngFxture pLfhngFxture pPod FwdAdjMechOng T FwdAdjMechOng AttachPt3 1 1 1 pLifhngFixture pLfhngFixture pPod FwdAdjMechX FwdAdjMechX AttachPt3 1 L 1 pLifngmFxture pLfnngFtxture pPod FwdAdMech T FwdAdjMechZ AttachPt3 1 1 1 pLfngFixture pLfngFixture pPod AAdMechng T AfAdMechng AttachPt3 1 1 pLifngFixture pLifngFixture pPod LAftAdjMechX I T AftA djMechX AttachPt3 1 1 1 pLfhngFixture pLfhngFixture PPod SAfAdjMechZ T AfAdjMechZ AttachPt3 1 1 1 (2.8) Another rotation must be performed to align pod Attach Point 1. The axis of rotation must pass through pod Attach Point 2 and pod Attach Point 3 so that these points do not become misaligned. The Plicker coordinates of this line are {S2; SOL2} {32 Orb, AttachPt3 32 Orb} (2.9) and the parallel line passing through pod Attach Point 1 is given as {S; SOL } = 2 OrP X 2 O} (2.10) {S1;SOL1} { Orb' AttachPtl 32 Orb (2.10) Vectors p, and p, are perpendicular to each line and originate at the orbiter coordinate system origin. P = S SOL1 (2.11) P2 = S2 x SOL2 When aligned, pod Attach Point 1 will reside on the ypod=100 plane. The ypod coordinate of pod Attach Point 1 can be calculated using part of the LefPdT transformation matrix: 0.0526981625 0.7183402679 pPod y .4AttachPt1 (212 pod 0.6936931332 1( 194.96530381 The required angle of rotation 01 can now be calculated. = sin pod 100 (2.13) 2P2 p I _) 2 od100)2 0, = cos1 2 A (Ypod l) (2.14) P2 P The transformation matrix equation can be used again to calculate transformation matrix T,. [4] V32 Pod,x 32 Pod,xU2 + COS 1 V32 Pod,x 32 Pod,y 2 32 Pod,zin T 3 P 32 Pod,x32 Pod,y 2 32 Pod,z sin 1 32 Pod,y~3,2 Pody 2+cos 1 32 Pod,x 32 Podz odsin 2 od, 32 od, 2 + V32 odxsin 0 0 SVPodx 2Pod,z2 2T Pod, S Vin 2 P ht3x(2.15) (2.15) V32 Pod,r 32 Pod 32 Pod,y sin 01 PAhPt3x 1Pod V32Pod, y 32Podzt)2 32_ Pod,x sin 1 01  V32 Pod,zv32 Pod,.U2 + COS 1 PAttachPt3,y 0 1 16 where v2 1 cos 01 Transformation matrix T2 is then used to perform the rotation of all points about the line passing through pod Attach Point 2 and pod Attach Point 3. pPod pPod pPod AttachPt1 T AttachPt1 AttachPt3 I 1 1 1 pPod P Pod pPod AttachPt2 T AttachPt2 AttachPt3 1 1 P Pod pPod pPod 1 1 pLifngFixture pLifngFixture p PPod RotatorBar T RotatorBar AttachPt3 1 ] 1 PliFFngFMxture pLifngFixture p Pod LFwdAdMechOng FwdAdjMechOng AttachPt3 1 1 pfng Fxture 7 pLIfngFxture pPod LFwdAdMechX _T 2 FwdAdjMechX AttachPt3 1 1 PLftlngFmxture 7 pLffingFixture PPod LFwdAdjMechZ T 2 FwdAdjMechZ AttachPt3 1 1 PLftngFmxture PLftngFxture PPod 1 1 AftAdjMechX T AftAdjMechX AttachPt3 1 1 pLftngFixture 7 pLftngFxture PPod AftAdMechZ AdMechZ A AttachPt3 1 1 (2.16) APS pod attach points 1, 2, and 3 have been aligned. A reverse kinematic analysis will now be conducted to determine the adjustment mechanism joint angles with the APS pod aligned. Adjustment Mechanism Reverse Kinematic Analysis Adjustment mechanism parameters Joint axis vectors S, and link vectors aY must be chosen for the adjustment mechanisms. These selections are shown in Figure 23. It should be noted that the spherical joints are treated as "three noncoplanar cointersecting revolute joints". [4] Joint angle Oj is defined as the angle from a to ajk about the vector S Similarly, twist angle aij is defined as the angle from S to S about the vector a . S, sin O = a x ak (2.17) a sin a =S x S Joint offset SJ is the distance from aY to ajk along S Link length ay is the distance from S to S, along a The first joint angle, (i, describes the angle from fixed coordinate system X axis and vector a2 . S, sin 1 = XFxed xa12 (2.18) Adjustment mechanism joint angles, twist angles, joint offsets, and link lengths are defined in Table 21. The constant parameters are exactly the same for both forward and aft adjustment mechanisms. Parameters marked as 'variable' are not necessarily the same for both adjustment mechanisms because adjustment mechanism end effector positions are not identical. Closetheloop variables are created by the hypothetical closure link. [4] a67 and a67 are userspecified values (rather than a function of manipulator geometry) since the seventh joint is hypothetical. Closetheloop variable calculations Closetheloop variables can be calculated using the constant mechanism parameters listed in Table 21. Flxed is defined as [0 0 1] since the vector S is exactly aligned with the fixed coordinate system Z axis. Fixed S is given by the expression Fixed 7Fixed I Fxd g (2.19) Unit vectors Fixed a and Fixed are the X axis and Z axis of the adjustment mechanism 6th coordinate system, respectively. They can be calculated as Fixed pLifhngFixture PLifhngFixture a67 FwdAdjMechX AdjMechOng Fixeds = pLifhngFixture pLifhngFixture 6 FwdAdjMechZ AdjMechOng These definitions allow the unit vector Fixeda71 to be determined from Fixed So Fixed o a7e 1 Fixed S Fixed The closetheloop variables can now be calculated. A unique value for the twist angle a71 between vectors S7 and S, is given by cos(a71) =Fixed S7 *Fxed S si* n(71) (Fixed s Fixed Fixed (2.22) sin(al) = S x S, 7 al Similarly, the joint angle 07 can be found cos(07) Fixed a7 *Fxed a1 sin(,) =Fixed > Fixed ) F7xed s (2.23) sin(07) ( r a67 x^ a71^ 7 The angle yi is defined as the angle between a7 and the X axis of the fixed coordinate system. cos(,)=Fixed a7 .[1 0 0]O sin(y) = (Fx ed 0 )Fxed (2.24) The joint offset S7 along the S, vector can be calculated by (Fixed S X j pLfhngFixture Fixed Z1 AdjMechOng 71 S7 = echo (2.25) sin(al) The link length a71 along the a71 vector is given by (pLLfhingFixture Fixed S *Fixed S 'AdjMechOng X7 a71  (2.26) sin(a71) Joint offset S1 along the S, vector is (pLifhngFixture Fixed S *Fixed  S AdjMechOng a7 71 S,= =.(2.27) sin(a'7) The closetheloop variables a71, 07, yi, S7, a71, and Si will be used in the reverse kinematic analysis of this PPPS mechanism. Reverse kinematic analysis of a PPPS mechanism As previously stated, the adjustment mechanisms are RPPPS spatial mechanisms but will be analyzed as an equivalent RPPPRRR mechanism. They are categorized as group 1 mechanisms since the spatial mechanisms and equivalent spherical mechanisms have a single degreeoffreedom. Spherical equations generally contain a high number of terms. However, these terms exist in patterns that allow a shorthand notation to describe the equation more concisely. Notation variables are defined in Appendix B. 01 is the first unknown joint angle that will be calculated. The fundamental spherical heptagon equation Z45671 = 23 (2.28) can be expanded to S12 (X4567S1 + Y4567C )+ 12Z4567 = 23 (2.29) X4567 and Y4567 are defined by notation variables X456 and Y456 X4567 X456C7 456S7 Y4567 =71 (X456S7 + Y456c7 S71Z456 (2.30) Z4567 = S71 (X456S7 + g456C7 )+ C71456 07 and a71 are closetheloop variables that have already been calculated, so X456, Y456, and Z456 are the only unknown terms that must be calculated. They can be defined as X456 X45C6 45S6 Y456 C67 (X45S6 45c6) S67Z45 (2.31) Z456 S= 67 (X45S6 + 45C6) + C67Z45 06 is a constant mechanism parameter and a67 is a userspecified value, so both are known quantities. X45, Y45, and Z45 must now be defined. X45 X4c5 Y45 Y45 C56 (X4S5 + Y ) S56Z4 (2.32) Z45 S56 (X4S5 Y4C5 +56Z4 05 and a56 are constant mechanism parameters. X4, Y4, and Z4 are defined as X4 S S34S4 4 (S45C34 + C45S34C4) (2.33) Z4 C45C34S45S34C4 04, a34 and a45 are constant mechanism parameters so X4, Y4, and Z4 can be calculated. Using substitution, X4567 and Y4567 can now be calculated. This results in an equation of the form Ac, + Bs, + D = 0. Using the trigonometric solution method [4], 01 can be calculated S= cos1 C23 124567 + (2.34) 1 1 (s12Y4567)2 +(s12X4567)2 where y is the unique solution of sin 1 S12X4567 s124567)2 +(s12X4567)2 (2.35) (2.35) 1 S12Y4567 7/ = Cco s __ _ J(s12Y4567) +(s12X4567)2 It should be noted that 01 has two solutions, designated as 01A and 01B. Other joint angles are a function of 01, so it is necessary to solve each joint angle using 01A and 01B. There are two sets of joint angles, solution set A and solution set B, that satisfy the input end effector position and orientation for the specified manipulator geometry. Unknown joint angle 62 can now be calculated using O1A and O1B. The fundamental spherical heptagon equations X45671 = 23S236) Y45671 = S23C2 will be used. Since X4567 Y4567, and Z4567 were determined in the 01 derivation, X45671 and Y4671 can be calculated immediately using O1A and O1B. X45671 X4567C1 4567S1 ( Y45671 C12 (X4567S1 + Y45671 )S12Z4567 02 is the unique solution to equation 2.38 for the solution set containing OlA and the set containing O1B. 02 = sin'1 X45671 S s23 (2.38) 02 = cos1 45671 The reverse kinematic analysis continues with the calculation of unknown joint angle 63. The fundamental spherical heptagon equations X56712 34(2.39) Y56712 = S34C3 can be used because O1A, O1B, 02A and 62B have been calculated. X56712 and Y56712 are defined as X56712 X5671C2 5671S2 . Y56712 C23 (X5671S2 Y5671c2)S23Z5671 Similar to the solution for 01, the solution for 63 proceeds by solving for the notation variables that comprise X56712 and Y6712. X5671 X567 1 567S1 S671 = c12 (X5671 + Y567C1) 12Z567 Z5671 12 (X567s1 + Y567C) + C12Z567 X567 X56 6 56S6 567 71 (X56S7 + 56C7 ) 71Z56 Z567 71 (X56S7 + 56C7 ) + ) 71Z56 X56 X56 C 5S6 56 = 67 (X5s6 + Y6) S67Z5 Z56 S67 (X5 + Y56)+ 67Z5 X, 5 45S5 (56C 5 C56S45C5) Z5 c56c45 s56S45C5 (2.41) A unique solution for joint angle 63 can now be calculated for solution set A and solution set B using their associated joint angles. 03= sin 1 X56712 (2.42) 03= cos1 Y5712 SS34 Joint offset S4 will be calculated using the vector loop equation. The vector loop equation is given by S S + 2 a 2 + S2S2 + a23a23 +S3S3 +a34 a34 + S4S4 a45 a45 (2.43) +S5 S + a56 a, + S6 + a67 a + S, S7 + 6 a71a = 0 Since several of these offsets are zero, the vector loop equation can be reduced to S SI + a34 34 +S4 S4 + 67 67 +S7S7 + a71a71 = 0 (2.44) Using spatial heptagon direction cosines set 5, the vector loop equation [4] becomes SX76 + a34W45 + S4X5 + a676 + S7X6 aW76 = 0 (2.45) Several notation terms in Equation 2.45 must be calculated X76 X7C6 Y7S6 W45 5 4 S5S4c45 W76 = 6C7 S6S7C67 (2.46) X6 6766 X7 71S 7 Y7 (S67C71 + C67S7IC7) Unknown joint offset S4 can now be calculated by solving Equation 2.45 for S4. S4 S1X76 34W45 a676 a7176 (2.47) X5 Joint offset S6 is calculated by substituting spatial heptagon direction cosines set 4 into the vector loop equation. Equation 2.44 then reduces to SX765 +344 + S6 X5 + a67W65 + 7X65 a71W765 = 0 (2.48) Equation 2.48 can be further reduced by noting that c4=0. S,X765 + S6 X, + a67W65 + SX65 + a7,W765 = 0 (2.49) The unknown notation variables can be calculated from X765 = X76 5 76S5 Y76 56 (X7s6 +7C6) S56 Z7 Z7 C67c71 S71c7 X5 = s56S5 X65 X6C5 65 (2.50) Y6 (S56C67 + C56S67C6) W65 C5C6 S5S656 W765 S5 (U76S56 + 76 56)+ 5W76 U76 S S767 V76 (S67 + C6SC67) Solving Equation 2.49 for S6 yields S SX765 67W65 65 71765 (2.51) S6 = (2.51) X5 The only joint offset that has not yet been calculated is S5. Spatial heptagon direction cosines set 3 are substituted into the vector loop equation given in Equation 2.44. SX23 34 + S5 X4 67654 + SX654 +7123 = 0 (2.52) Once again, notation variables must be calculated before the unknown joint offset can be determined. X23 Xc, Ys X2 s 12s2 Y2 (12C12 + C12S12C2) X4 S 45S4 X54 Xc4 YS4 X654 X65C4 65S4 (2.53) 65 C45 X6S5 +Y C5 S 45Z6(2.53) z6 56C67 s 56S67C6 W123 3 (U12z23 + V23)+) +W2 V12 =( C1 + CS1C12 W, 2 C2cI ss 2,S Finally, joint offset S5 can be calculated SSX23 a34 S6X54 S7X654 71 23 .54) S5 = (2.54) X4 Both solution sets have now been calculated. In the case of the adjustment mechanism, all three joint offsets are the same in both solution sets. These joint offsets will be used to orient the lifting fixture so that a finite element analysis can be performed. Rotator Bar Length Calculation The rotator bar can be described as a RRRCRR mechanism. A reverse kinematic analysis could be conducted to ascertain joint angles and joint offsets that result in the APS pod being aligned. To conduct this analysis, the position and orientation of the end effector relative to the base must be input. The position of the rotator bar 6th coordinate system origin has been previously defined as P,'TauB The orientation of the end effector can be determined by also inputting points on the a67 and S6 axes and subtracting PLngFd e from each to determine the unit vectors a7 and Sg Before conducting a reverse kinematic analysis of the rotator bar, it was noted that unique geometry makes it possible to calculate the joint offset of the cylinder joint. With the exception of the cylinder joint offset, all rotator bar link lengths and joint offsets are zero. As a result, the cylinder joint offset can be calculated using the distance equation LifhngFxture LifngFiF~xre LfngFxture LfngFxture 2 S\ RotatorBarX RotatorBarBaseX I PRotatorBarY RotatorBarBaseY (2.55) S, (2.55) +p PLfngFmxture PLft,,ngFxture SRotatorBarZ RotatorBarBaseZ Although unknown joint angles could be calculated using S3, they are not needed for this analysis. Nominal Solution A program was written to perform pod alignment and subsequent joint offset calculations as described in this chapter. The mechanism parameters specified in Table 21 and the input coordinates of points pPod PP o PPod pRfngFxture pLzh ngFzxture pLzh ngFzxture pLzhngFzxture pLiftngFixture pLingFxture pLand pLngFxture w FwdA4djMechOng FwdA4djMechX > FwdAdjMechZ AftAdjMechOng > AftAdjMechX ,> AftAdjMechZ were used. Table 22 compares the joint offsets calculated by the program to the joint offsets measured using a perfectly aligned APS pod CAD model. The similar results show that the program is able to accurately calculate joint offsets for a known lifting fixture location. The two solutions, solution A and solution B, have nearly identical joint offsets but differing joint angles (not shown). The program is also able to perform a reverse kinematic analysis for right APS pods. This is accomplished by inverting the sign of the input Yorbiter coordinates then proceeding with the rest of the solution method. Right APS pods, lifting fixtures and orbiter attach points are mirror images of left APS pods, lifting fixtures, and orbiter deck attach points. The CAD model of the lifting fixture is positioned and oriented arbitrarily. The APS pod attach point and end effector positions are input into an alignment algorithm. Figure 21. Joint offset calculation procedure. The algorithm aligns APS pod attach points with orbiter attach points and calculates the resulting end effector position and orientation for each manipulator. The rotator bar length is calculated and a reverse kinematic analysis is performed on both adjustment mechanisms. Figure 22. Three points are needed to determine each adjustment mechanism's position and orientation (aft adjustment mechanism shown, typical of all adjustment mechanisms).   i i i i i 23 Figure 23. Adjustment mechanism joint axis vectors and link vectors. Table 21. Adjustment mechanism parameters. Link length, inches Twist angle, degrees Joint offset, inches Joint angle, degrees a12 = 0.000 a12 = 270.0 S1 = Closetheloop (p = variable variable a23 = 0.000 a23 = 270.0 S2 = 0.000 02 = variable a34 = 4.147 a34 = 270.0 S3 = 0.000 03 = variable a45 = 0.000 a45 = 270.0 S4 = variable 04 = 270.0 a56 = 0.000 a56 = 90.0 S5 = variable 05 = 270.0 a67 = 0.000 a67 = 90.0 S6 = variable 06 = 180.0 a71 = Closetheloop a7l = Closetheloop S7 = Closetheloop 07 = Closethe variable variable variable loop variable Table 22. Comparison of joint offsets calculated by the program to measured using the CAD model. Forward adjustment Aft adjustment mechanism Rotator ,echs .Aft adjustment mechanism , mechanism bar Measurement 4 S method S4 s5 S6 S4 s5 S6 S3 CAD model 13.6655" 14.5243" 8.7968" 12.3174" 14.8512" 8.8823" 94.5707" Programodel 13.6655" 14.5244" 8.7968" 12.3174" 14.8512" 8.8823" 94.5707" so tonram 13.6655" 14.5244" 8.7968" 12.3174" 14.8512" 8.8824" solution A 94.5706" 94.5706" Program 13.6655" 14.5243" 8.7968" 12.3174" 14.8512" 8.8824" solution B CHAPTER 3 UNCERTAINTY ANALYSIS Due to the stringent accuracy requirements associated with the APS pod installation operation, an uncertainty analysis was conducted to assess the validity of the proposed solution method. Two different uncertainty calculation methods were used to create an upper and lower bound for total uncertainty. The 100% covariance method produces very conservative results since it assumes all errors are at their maximum value. The root sum squared method provides more optimistic results. The 100% covariance and root sum squared uncertainty calculations provide an upper and lower bound respectively for the total error that can be reasonably expected. OffNominal Conditions within Tolerance Manufacturing tolerances can have a significant effect on the overall accuracy of a manipulator. As a result, precision manipulators are often manufactured with very tight tolerances. Adjustment Mechanism Spherical Joint Socket Locations There are manufacturing tolerances associated with the spherical joint sockets and the position of their mounting holes on the orbiter. These tolerances yield an uncertainty of +0.0349" in the position of each spherical joint (both Xorbiter and Zorbiter directions). The resulting misalignment of the APS pod can be seen in Tables 31 and 32. Orbiter Attach Point Locations There is also uncertainty associated with the position of the orbiter attach points on the orbiter. According to drawing tolerances, the orbiter attach points are located within 0.010" of their intended position in the Xpod, Ypod, and Zpod directions. The effect of a 0.0104" attach point misalignment in all directions on the alignment of an APS pod can be seen for each attach point individually in Tables 33, 34, and 35. The APS Pod Fitting Locations There is also uncertainty about the locations of the fittings on the APS pod. As with the orbiter attach point locations, the tolerance associated with the APS pod fitting locations is 0.010". Therefore, an uncertainty of 0.0104" in all directions is associated with each pod fitting location. The APS pod misalignment caused by this uncertainty is given in Tables 36, 37, and 38. Lifting Fixture Attach Point 3 Location The position of the APS pod relative to the lifting fixture is largely determined by the location of the lifting fixture's attachment to the APS pod Attach Point 3 fitting. Drawing tolerances affect the position of the lifting fixture's attachment location relative to the adjustment mechanism end effectors. According to drawing tolerances, the lifting fixture Attach Point 3 location can be up to (0.0349", 0.0698", 0.0349") from the intended position in (Xpod, Ypod, Zpod). It may be surprising to note that this tolerance singlehandedly prevents the Attach Point 3 accuracy requirement from being met. However, it is probable that engineers did not expect to apply robot kinematics to the lifting fixture when it was designed in 1977. The pod misalignment resulting from this uncertainty can be simply calculated. Results are presented in Table 39. Lifting Fixture Adjustment at Attach Point 3 There also exists the capability to adjust the position of the APS pod at the Attach Point 3 location. The magnitude of this adjustment capability is 0.418" in the +Xpod directions. Since this adjustment potentially shifts the entire APS pod, all three attach points are affected by this source of uncertainty as shown in Table 310. Uncertainty of Input Values Location of rotator bar base. At first glance, it might appear that the base of the rotator bar can be considered "ground" at a known position relative to the spherical joint sockets and orbiter attach points. Unfortunately, this is not the case. One factor is the dimensional variance between each of the three OPFs. The rotator bar base is mounted to a beam in each OPF and the location of that beam might not be identical in each OPF. A much more significant factor is that the position of the orbiter relative to the OPF is not always the same. After each mission, the orbiter is towed into the OPF and jacked off the floor. Per specification, the orbiter must be towed to +1" forward/aft, 1.5" port/starboard, and +0.25" up/down of a specified nominal position. Therefore, the position of the rotator bar base can be significantly different from nominal. As a result, the position of the rotator bar base relative to the spherical joint sockets must be measured before each APS pod installation. Preliminary indications are that this position can be measured to a total accuracy of 0.010" or better. The uncertainty can be determined by positioning the rotator bar base 0.0104" from the nominal position and using nominal joint offsets. The effect of this measurement error is greatest if it occurs along the prismatic joint axis. Table 311 shows the effect of this error on attach point alignment. CalculationRelated Uncertainties Computer program uncertainty. Ideally, the computer program calculates the exact joint offsets required to position the lifting fixture as desired. However, roundoff errors can propagate and potentially become a significant error source. To determine error associated with the program, the lifting fixture CAD model was positioned in a known location. Using Pro/E's mechanism application, connections between components were defined as joints rather than rigid connections. This automatically positioned the adjustment mechanisms and rotator bar joints as needed to properly connect to the lifting fixture and mechanism base. The position of specific points in the model was then input into the program. The program calculated the joint offsets required to align the lifting fixture. These offsets were compared to the joint offsets measured in the CAD model. Inaccuracies were initially experienced due to errors in the CAD model. Additionally, using only three decimal places for input values caused significant errors. After these problems had been remedied, numerical methods were not required to further refine the calculations. Results can be viewed in Table 312. Hardware Positioning Uncertainty Although joint offsets can be accurately calculated to several decimal places, the ability of the pod installation team to adjust the rotator bar and adjustment mechanisms is limited. These limitations are largely due to measurement device uncertainty, mounting inaccuracies, and the tolerances of the components being measured. Adjustment mechanism measurement directions are shown in Figure 31. Uphill/Downhill Joint Offset Measurement The joint offset S4 has been previously defined as the distance along the S4 vector between the a34 and a45 vectors. The pod installation team can adjust this joint offset to match the value calculated by the alignment program. The desired joint offset reading on the measurement device can be achieved. However, the accuracy of this measurement is affected by factors such as measurement device uncertainty, mounting inaccuracies, and hardware tolerances. A preliminary assessment of these factors suggests that an accuracy of +0.010" can be achieved. This uncertainty analysis will determine the alignment error resulting from a misalignment of 0.0104" uphill for the forward and aft adjustment mechanism. The results of this analysis are stated below in Tables 313 and 314. OfftheDeck/OntheDeck Joint Offset Measurement The accuracy of the S5 joint offset measurement is also affected by measurement device uncertainty, mounting inaccuracies, and hardware tolerances. The total measurement uncertainty is approximated as 0.010". An analysis has been performed to ascertain attach point misalignment due to a 0.0104" misalignment in the offthedeck direction for each adjustment mechanism. The results of this analysis can be found in Tables 315 and 316. Forward/Aft Joint Offset Measurement As with the measurement uncertainties for joint offsets S4 and S5, it is assumed that measurements of joint offset S6 are accurate to within 0.010". The effect of a 0.0104" misalignment in the forward direction was studied. In order for this misalignment to occur, the entire lifting fixture must be 0.0104" forward which means both the forward and aft S6 are misaligned by the same value. The resulting misalignment of attach points is listed in Table 317. Rotator Bar Joint Offset Measurement The rotator bar S3 prismatic joint offset is affected by the same uncertainty sources as the adjustment mechanism joint offsets. Measurement uncertainty is also approximately 0.010". The misalignment of a rotator bar that is extended 0.0104" more than the measurement indicates is shown in Table 318. Compliance in Joints It is stated that "80% of the flexibility of industrial robots comes from the joint." [5] Quantifying this compliance is a difficult task. It will be estimated by considering each joint on an individual basis. Joints exist where two components are attached. The dimensional difference between those two components was first identified. Loading was then considered while determining the relative position of the components under the assumption they are in contact. One component is translated and, in some cases also rotated, to the determined position. The resulting APS pod misalignment is calculated from these translations and rotations. The total uncertainty related to compliance is documented in Table 319. Total Uncertainty Calculation There are different methods for calculating total system uncertainty for a specified set of individual uncertainties. Individual uncertainties at each attach point are summarized in Tables 320, 321, and 322. This information will be used to calculate total uncertainty using the 100% covariance method and the least squared method. The total uncertainty will then be compared to the accuracy requirements for APS pod alignment. One Hundred Percent Covariance Method The 100% covariance method assumes that each individual uncertainty is at a maximum at the same time. Assuming that all significant sources of uncertainty have been found and reasonably approximated, the 100% covariance method provides the "worst case scenario". The total uncertainty is calculated by summing all individual uncertainties. The Xpod and Zpod accuracy requirements at attach points 1 and 3 are not specified individually. Since it is desired to compare total uncertainty to accuracy requirements, the Xpod and Zpod total uncertainty has been combined for attach points 1 and 3. Table 3 23 allows the uncertainty calculated using the 100% covariance method to be compared to the accuracy requirement. Root Sum Squared Method The root sum squared method provides the lower bound for total uncertainty projections. The root sum squared uncertainty is calculated by U ot = = ,2 (3.1) where UTotal is the total uncertainty and the individual uncertainties are given by Ui through Un. The Xpod and Zpod uncertainties at attach points 1 and 3 have been combined for comparison to accuracy requirements. This comparison is presented in Table 324. Table 31. Forward spherical joint socket tolerances. dine N in Fwd socket misaligned Resulting Coordinate Nominal . Attach point solution by 0.0349" in the +Xorbiter attach point axis solution and +Zorbiter directions misalignment Xpod 106.5000" 106.5335" 0.0335" Attach Point 1 Ypod 100.0000" 100.0353" 0.0353" Zpod 152.3460" 152.3745" 0.0285" Xpod 106.5000" 106.5181" 0.0181" Attach Point 2 Ypod 100.0000" 100.0224" 0.0224" Zpod 49.1790" 49.2075" 0.0285" Xpod 253.5000" 253.5167" 0.0167" Attach Point 3 Ypod 100.0000" 100.0078" 0.0078" Zpod 39.7680" 39.7747" 0.0067" Table 32. Aft spherical joint socket tolerances. Aft socket misaligned by Resulting attach Coordinate Nominal . Attach point ai option 0.0349" in the +Xorbiter point axis solution and +Zorbiter directions misalignment Xpod 106.5000" 106.5016" 0.0016" Attach Point 1 Ypod 100.0000" 100.0062" 0.0062" Zpod 152.3460" 152.3440" 0.0020" Xpod 106.5000" 106.5141" 0.0141" Attach Point 2 Ypod 100.0000" 99.9962" 0.0038" Zpod 49.1790" 49.1770" 0.0020" Xpod 253.5000" 253.5153" 0.0153" Attach Point 3 Ypod 100.0000" 100.0155" 0.0155" Zpod 39.7680" 39.7839" 0.0159" Table 33. Orbiter Attach Point 1 tolerances. Attach Point 1 Nominal misalignment of Resulting attach .Nominal misalignment of Attach point Coordinate axis 1 point A h p t solution 0.0104" in all point misalignment three directions mis Xpod 106.5000" 106.5104" 0.0104" Attach Point 1 Ypod 100.0000" 100.0104" 0.0104" Zpod 152.3460" 152.3564" 0.0104" Xpod 106.5000" 106.5000" 0.0000" Attach Point 2 Ypod 100.0000" 100.0000" 0.0000" Zpod 49.1790" 49.1790" 0.0000" Xpod 253.5000" 253.5000" 0.0000" Attach Point 3 Ypod 100.0000" 100.0000" 0.0000" Zpod 39.7680" 39.7680" 0.0000" Table 34. Orbiter Attach Point 2 tolerances. Attach Point 2 *Resulting attach Nominal misalignment of Attach point Coordinate axis nominal mialinnt of point solution 0.0104" in all poi three directions misalignment Xpod 106.5000" 106.5000" 0.0000" Attach Point 1 Ypod 100.0000" 100.0000" 0.0000" Zpod 152.3460" 152.3460" 0.0000" Xpod 106.5000" 106.5104" 0.0104" Attach Point 2 Ypod 100.0000" 100.0104" 0.0104" Zpod 49.1790" 49.1894" 0.0104" Xpod 253.5000" 253.5000" 0.0000" Attach Point 3 Ypod 100.0000" 100.0000" 0.0000" Zpod 39.7680" 39.7680" 0.0000" Table 35. Orbiter Attach Point 3 tolerances. Attach Point 3 Nominal misalignment of Resulting attach .Nominal misalignment of Attach point Coordinate axis 1 point A h p t solution 0.0104" in all point misalignment three directions mis Xpod 106.5000" 106.5000" 0.0000" Attach Point 1 Ypod 100.0000" 100.0000" 0.0000" Zpod 152.3460" 152.3460" 0.0000" Xpod 106.5000" 106.5000" 0.0000" Attach Point 2 Ypod 100.0000" 100.0000" 0.0000" Zpod 49.1790" 49.1790" 0.0000" Xpod 253.5000" 253.5104" 0.0104" Attach Point 3 Ypod 100.0000" 100.0104" 0.0104" _Zpod 39.7680" 39.7784" 0.0104" Table 36. APS pod Attach Point 1 tolerances. Attach Point 1 Fitting Resulting iResulting Nominal misalignment of Attach point Coordinate axis Nominal misalignment of attach point solution 0.0104" in all three n directions misalignment directions Xpod 106.5000" 106.5104" 0.0104" Attach Point 1 Ypod 100.0000" 100.0104" 0.0104" Zpod 152.3460" 152.3564" 0.0104" Xpod 106.5000" 106.5000" 0.0000" Attach Point 2 Ypod 100.0000" 100.0000" 0.0000" Zpod 49.1790" 49.1790" 0.0000" Xpod 253.5000" 253.5000" 0.0000" Attach Point 3 Ypod 100.0000" 100.0000" 0.0000" Zpod 39.7680" 39.7680" 0.0000" Table 37. APS pod Attach Point 2 tolerances. Attach Point 2 Fitting Resulting N.T i Resulting Nominal misalignment of Attach point Coordinate axis Nominal misalignment of attach point Attah p t solution 0.0104" in all three atah pint directions misalignment directions Xpod 106.5000" 106.5000" 0.0000" Attach Point 1 Ypod 100.0000" 100.0000" 0.0000" Zpod 152.3460" 152.3460" 0.0000" Xpod 106.5000" 106.5104" 0.0104" Attach Point 2 Ypod 100.0000" 100.0104" 0.0104" Zpod 49.1790" 49.1894" 0.0104" Xpod 253.5000" 253.5000" 0.0000" Attach Point 3 Ypod 100.0000" 100.0000" 0.0000" Zpod 39.7680" 39.7680" 0.0000" Table 38. APS pod Attach Point 3 tolerances. Attach Point 3 Fitting Re N.T i Resulting Attach point Coordinate axis Nominal misalignment of attach point solution 0.0104" in all three n directions misalignment directions Xpod 106.5000" 106.5000" 0.0000" Attach Point 1 Ypod 100.0000" 100.0000" 0.0000" Zpod 152.3460" 152.3460" 0.0000" Xpod 106.5000" 106.5000" 0.0000" Attach Point 2 Ypod 100.0000" 100.0000" 0.0000" Zpod 49.1790" 49.1790" 0.0000" Xpod 253.5000" 253.5104" 0.0104" Attach Point 3 Ypod 100.0000" 100.0104" 0.0104" Zpod 39.7680" 39.7784" 0.0104" Table 39. Lifting fixture Attach Point 3 tolerances. Coordinate Nominal Lifting fixture Attach Resulting Attach point axis solution Point 3 misalignment due attach point axis solution . to tolerances misalignment Xpod 106.5000" 106.5349" 0.0349" Attach Point 1 Ypod 100.0000" 100.0698" 0.0698" Zpod 152.3460" 152.3809" 0.0349" Xpod 106.5000" 106.5349" 0.0349" Attach Point 2 Ypod 100.0000" 100.0698" 0.0698" Zpod 49.1790" 49.2139" 0.0349" Xpod 253.5000" 253.5349" 0.0349" Attach Point 3 Ypod 100.0000" 100.0698" 0.0698" Zpod 39.7680" 39.8029" 0.0349" Table 310. Lifting fixture Attach Point 3 adjustment. Maximum Adjustment of Resulting h p Coordinate Nominal 0.4184" in the +Xpod resulting Attach point attach point axis solution direction at Attach Point aah int 3 misalignment Xpod 106.5000" 106.9184" 0.4184" Attach Point 1 Ypod 100.0000" 100.0000" 0.0000" Zpod 152.3460" 152.3460" 0.0000" Xpod 106.5000" 106.9184" 0.4184" Attach Point 2 Ypod 100.0000" 100.0000" 0.0000" Zpod 49.1790" 49.1790" 0.0000" Xpod 253.5000" 253.9184" 0.4184" Attach Point 3 Ypod 100.0000" 100.0000" 0.0000" Zpod 39.7680" 39.7680" 0.0000" Table 311. Misalignment of the rotator bar base. 0.0104" rotator Resulting attach Nominal Attach point Coordinate axis olion base point solution misalignment misalignment Xpod 106.5000" 106.4989" 0.0011" Attach Point 1 Ypod 100.0000" 99.9836" 0.0164" Zpod 152.3460" 152.3563" 0.0103" Xpod 106.5000" 106.5001" 0.0001" Attach Point 2 Ypod 100.0000" 99.9974" 0.0026" Zpod 49.1790" 49.1893" 0.0103" Xpod 253.5000" 253.5002" 0.0002" Attach Point 3 Ypod 100.0000" 99.9983" 0.0017" _Zpod 39.7680" 39.7800" 0.0120" Table 312. Computer program uncertainty. Joint offsets Joint offs Joint offsets from Resulting Coordinate from the CAD Attach point iae om e the program are attach point axis model are S d input into the model misalignment used Xpod 106.5000" 106.5000" 0.0000" Attach Point 1 Ypod 100.0000" 100.0000" 0.0000" Zpod 152.3460" 152.3460" 0.0000" Xpod 106.5000" 106.5000" 0.0000" Attach Point 2 Ypod 100.0000" 100.0000" 0.0000" Zpod 49.1790" 49.1790" 0.0000" Xpod 253.5000" 253.5000" 0.0000" Attach Point 3 Ypod 100.0000" 100.0000" 0.0000" Zpod 39.7680" 39.7680" 0.0000"   Figure 31. Adjustment mechanism joint axis vectors and link vectors. Table 313. Forward adjustment mechanism uphill measurement uncertainty. Nominal Misalignment of the Resulting Attach point Coordinate axis olion Fwd S4 0.0104" attach point solution Uphill misalignment Xpod 106.5000" 106.5071" 0.0071" Attach Point 1 Ypod 100.0000" 100.0080" 0.0080" Zpod 152.3460" 152.3686" 0.0226" Xpod 106.5000" 106.5011" 0.0011" Attach Point 2 Ypod 100.0000" 100.0005" 0.0005" Zpod 49.1790" 49.2015" 0.0225" Xpod 253.5000" 253.5005" 0.0005" Attach Point 3 Ypod 100.0000" 99.9996" 0.0004" Zpod 39.7680" 39.7819" 0.0139" Table 314. Aft adjustment mechanism uphill measurement uncertainty. Nominal Misalignment of the Resulting Attach point Coordinate axis olion Aft S4 0.0104" attach point solution Uphill misalignment Xpod 106.5000" 106.4929" 0.0071" Attach Point 1 Ypod 100.0000" 100.0058" 0.0058" Zpod 152.3460" 152.3550" 0.0090" Xpod 106.5000" 106.4992" 0.0008" Attach Point 2 Ypod 100.0000" 100.0003" 0.0003" Zpod 49.1790" 49.1880" 0.0090" Xpod 253.5000" 253.4999" 0.0001" Attach Point 3 Ypod 100.0000" 99.9994" 0.0006" Zpod 39.7680" 39.7860" 0.0180" Table 315. Forward adjustment mechanism offthedeck measurement uncertainty. Nominal Misalignment of the Resulting Attach point Coordinate axis olion Fwd S5 0.0104" attach point solution OfftheDeck misalignment Xpod 106.5000" 106.5002" 0.0002" Attach Point 1 Ypod 100.0000" 100.0103" 0.0103" Zpod 152.3460" 152.3566" 0.0106" Xpod 106.5000" 106.5006" 0.0006" Attach Point 2 Ypod 100.0000" 100.0113" 0.0113" Zpod 49.1790" 49.1895" 0.0105" Xpod 253.5000" 253.5007" 0.0007" Attach Point 3 Ypod 100.0000" 100.0023" 0.0023" _Zpod 39.7680" 39.7792" 0.0112" Table 316. Aft adjustment mechanism offthedeck measurement uncertainty. Nomil Misalignment of the Resulting Attach point Coordinate axis solution Aft S5 0.0104" Off attach point solution theDeck misalignment Xpod 106.5000" 106.4993" 0.0007" Attach Point 1 Ypod 100.0000" 99.9961" 0.0039" Zpod 152.3460" 152.3570" 0.0110" Xpod 106.5000" 106.4996" 0.0004" Attach Point 2 Ypod 100.0000" 99.9978" 0.0022" Zpod 49.1790" 49.1900" 0.0110" Xpod 253.5000" 253.4996" 0.0004" Attach Point 3 Ypod 100.0000" 100.0063" 0.0063" _Zpod 39.7680" 39.7795" 0.0115" Table 317. Fwd and aft adjustment mechanism measurement uncertainty in the forward direction. Misalignment of the Resulting T AResulting Nominal Fwd S6 and Aft S6 Attach point Coordinate axis nominal Fd 6 ad At S6 attach point solution by 0.0104" in the misalignment Forward Direction mis Xpod 106.5000" 106.4997" 0.0003" Attach Point 1 Ypod 100.0000" 99.9992" 0.0008" Zpod 152.3460" 152.3565" 0.0105" Xpod 106.5000" 106.5002" 0.0002" Attach Point 2 Ypod 100.0000" 99.9995" 0.0005" Zpod 49.1790" 49.1895" 0.0105" Xpod 253.5000" 253.5002" 0.0002" Attach Point 3 Ypod 100.0000" 99.9992" 0.0008" Zpod 39.7680" 39.7792" 0.0112" Table 318. Rotator bar length measurement uncertainty. Nomil Misalignment of the Resulting Attach point Coordinate axis olion Rotator bar S3 attach point solution 0.0104" Extend misalignment Xpod 106.5000" 106.4989" 0.0011" Attach Point 1 Ypod 100.0000" 99.9836" 0.0164" Zpod 152.3460" 152.3563" 0.0103" Xpod 106.5000" 106.5001" 0.0001" Attach Point 2 Ypod 100.0000" 99.9974" 0.0026" Zpod 49.1790" 49.1893" 0.0103" Xpod 253.5000" 253.5002" 0.0002" Attach Point 3 Ypod 100.0000" 99.9983" 0.0017" _Zpod 39.7680" 39.7800" 0.0120" Table 319. Joint compliance uncertainty. Nominal Attach point Attach point Coordinate axis nominal ta ont solution misalignment Xpod 106.5000" 0.0022" Attach Point 1 Ypod 100.0000" 0.3914" Zpod 152.3460" 0.1172" Xpod 106.5000" 0.0002" Attach Point 2 Ypod 100.0000" 0.0886" Zpod 49.1790" 0.0628" Xpod 253.5000" 0.0004" Attach Point 3 Ypod 100.0000" 0.0955" Zpod 39.7680" 0.0620" Table 320. Summary of Attach Point 1 uncertainty sources. Attach Point 1 Uncertainty Description ich. P (inches) Xpod gpod Zpod Fwd spherical joint socket location 0.0335 0.0353 0.0285 Aft spherical joint socket location 0.0016 0.0062 0.0020 Orbiter Attach Point 1 location 0.0104 0.0104 0.0104 Orbiter Attach Point 2 location 0.0000 0.0000 0.0000 Orbiter Attach Point 3 location 0.0000 0.0000 0.0000 APS pod Attach Point 1 location 0.0104 0.0104 0.0104 APS pod Attach Point 2 location 0.0000 0.0000 0.0000 APS pod Attach Point 3 location 0.0000 0.0000 0.0000 Lifting fixture nominal Attach Point 3 location 0.0349 0.0698 0.0349 Adjustment capability of Attach Point 3 0.4184 0.0000 0.0000 Measurement of rotator bar base location 0.0011 0.0164 0.0103 Calculations by computer program 0.0000 0.0000 0.0000 Iterative process acceptance criteria 0.0005 0.0005 0.0004 Measurement of fwd adjustment mechanism uphill/downhill 0.0071 0.0080 0.0226 0.0071 0.0080 0.0226 position Measurement of aft adjustment mechanism uphill/downhill 0.0071 0.0058 0.0090 position Measurement of fwd adjustment mechanism offthedeck/on 0.0002 0.0103 0.0106 0.0002 0.0103 0.0106 thedeck position Measurement of aft adjustment mechanism offthedeck/on 0.0007 0.0039 0.0110 thedeck position Measurement of adjustment mechanism forward/aft position 0.0003 0.0008 0.0105 Measurement of rotator bar joint offset 0.0011 0.0164 0.0103 Compliance in joints 0.0022 0.3914 0.1172 Table 321. Summary of Attach Point 2 uncertainty sources. Attach Point 2 Uncertainty Description ich. P (inches) Xpod gpod Zpod Fwd spherical joint socket location 0.0181 0.0224 0.0285 Aft spherical joint socket location 0.0141 0.0038 0.0020 Orbiter Attach Point 1 location 0.0000 0.0000 0.0000 Orbiter Attach Point 2 location 0.0104 0.0104 0.0104 Orbiter Attach Point 3 location 0.0000 0.0000 0.0000 APS pod Attach Point 1 location 0.0000 0.0000 0.0000 APS pod Attach Point 2 location 0.0104 0.0104 0.0104 APS pod Attach Point 3 location 0.0000 0.0000 0.0000 Lifting fixture nominal Attach Point 3 location 0.0349 0.0698 0.0349 Adjustment capability of Attach Point 3 0.4184 0.0000 0.0000 Measurement of rotator bar base location 0.0001 0.0026 0.0103 Computer program roundoff error 0.0000 0.0000 0.0000 Iterative process acceptance criteria 0.0001 0.0005 0.0004 Measurement of fwd adjustment mechanism uphill/downhill 0.0011 0.0005 0.0225 position Measurement of aft adjustment mechanism uphill/downhill 0.0008 0.0003 0.0090 position Measurement of fwd adjustment mechanism offthedeck/on 0.0006 0.0113 0.0105 0.0006 0.0113 0.0105 thedeck position Measurement of aft adjustment mechanism offthedeck/on 0.0004 0.0022 0.0110 thedeck position Measurement of adjustment mechanism forward/aft position 0.0002 0.0005 0.0105 Measurement of rotator bar joint offset 0.0001 0.0026 0.0103 Compliance in joints 0.0002 0.0886 0.0628 Table 322. Summary of Attach Point 3 uncertainty sources. Attach Point 3 Uncertainty Description ich. P (inches) Xpod gpod Zpod Fwd spherical joint socket location 0.0167 0.0078 0.0067 Aft spherical joint socket location 0.0153 0.0155 0.0159 Orbiter Attach Point 1 location 0.0000 0.0000 0.0000 Orbiter Attach Point 2 location 0.0000 0.0000 0.0000 Orbiter Attach Point 3 location 0.0104 0.0104 0.0104 APS pod Attach Point 1 location 0.0000 0.0000 0.0000 APS pod Attach Point 2 location 0.0000 0.0000 0.0000 APS pod Attach Point 3 location 0.0104 0.0104 0.0104 Lifting fixture nominal Attach Point 3 location 0.0349 0.0698 0.0349 Adjustment capability of Attach Point 3 0.4184 0.0000 0.0000 Measurement of rotator bar base location 0.0002 0.0017 0.0120 Computer program roundoff error 0.0000 0.0000 0.0000 Iterative process acceptance criteria 0.0001 0.0005 0.0001 Measurement of fwd adjustment mechanism uphill/downhill 0.0005 0.0004 0.0139 position Measurement of aft adjustment mechanism uphill/downhill 0.0001 0.0006 0.0180 position Measurement of fwd adjustment mechanism offthedeck/on 0.0007 0.0023 0.0112 thedeck position Measurement of aft adjustment mechanism offthedeck/on 0.0004 0.0063 0.0115 thedeck position Measurement of adjustment mechanism forward/aft position 0.0002 0.0008 0.0112 Measurement of rotator bar joint offset 0.0002 0.0017 0.0120 Compliance in joints 0.0004 0.0955 0.0620 Table 323. Total uncertainty using the 100% covariance method. Attach Point 1 Attach Point 2 Attach Point 3 (inches) (inches) (inches) Description Xpod/Zpod Ypod Xpod Ypod Zpod Xpod/Zpod Ypod Total otal 0.6028 0.5856 0.5099 0.2259 0.2335 0.5585 0.2237 Uncertainty Accuracy Accuracy 0.2231 0.0010 2.0000 0.0010 0.0063 0.0033 0.0010 Requirement Remaining 0.3797 0.5846 1.4901 0.2249 0.2272 0.5552 0.2227 Margin 51 Table 324. Total uncertainty using the root sum squared method. Attach Point 1 Attach Point 2 Attach Point 3 (inches) (inches) (inches) Description Xpod/Zpod Ypod Xpod Ypod Zpod Xpod/Zpod Ypod Total otal 0.4414 0.4004 0.4207 0.1166 0.0856 0.4287 0.1207 Uncertainty Accuracy 0.2231 0.0010 2.0000 0.0010 0.0063 0.0033 0.0010 Requirement Remaining 0.2183 0.3994 1.5793 0.1156 0.0763 0.4254 0.1197 Margin CHAPTER 4 EVALUATION OF PROPOSED ALIGNMENT METHOD Both uncertainty calculation methods used in Chapter 3 indicate that the proposed solution method is not as accurate as desired. If used, it would not be able to align the APS pod with the orbiter deck accurately enough to eliminate the need for additional manipulations. The additional manipulations required for alignment can not be calculated before the operation because the direction and magnitude of the misalignment can not be predicted. Additional manipulations are highly undesirable because the motion resulting from mechanism adjustments is not intuitive. As a result, the uncertainty analysis will be further examined and recommendations will be made to reduce total uncertainty. Discussion of Results Uncertainty due to tolerances can be significantly reduced by measuring "asbuilt" dimensions. The uncertainty associated with those measurements is significantly less than the uncertainty due to tolerances, in some cases by more than one order of magnitude. Measurements of specific points on the lifting fixture, APS pod, and orbiter can be taken before APS pod installation. Uncertainty can be further reduced by more accurately measuring rotator bar joint offset S5 and adjustment mechanism joint offsets S4, S5, and S6. Improvements to reduce uncertainty might require significant modifications to rotator bar and adjustment mechanism hardware. However, these modifications are highly desirable because the uncertainty associated with each joint offset measurement exceeds the total allowable uncertainty at Attach Point 3 by one order of magnitude. The estimated uncertainty due to compliance in rotator bar and adjustment mechanism joints is one of the most significant error sources studied. Although joint compliance can not be reduced without significant modifications to hardware, its effect can be minimized. There are only two lifting fixtures, one for right APS pods and one for left APS pods, and those lifting fixtures are in approximately the same position and orientation during each APS pod installation. The geometry of the lifting fixture configuration indicates that each joint is under load during this operation and those loads determine the direction affected by compliance. As a result, joint compliance has only a minimal effect on precision. To obtain accurate results, a correction factor can be used to compensate for joint compliance error. A correction factor might also be used to compensate for uncertainties related to lifting fixture, APS pod, and orbiter geometry. For a given lifting fixture, APS pod, and orbiter it might be discovered that the calculated solution results in a misalignment that is consistent in magnitude and direction. This precise solution could be made more accurate by implementing a correction factor. Since there are only two lifting fixtures, three orbiters, and a small number of APS pods, a database could be created relatively quickly to facilitate the calculation of a correction factor for each scenario. Recommendations The lifting fixture, adjustment mechanisms, and rotator bar are not currently outfitted with a means of measuring joint offsets. Therefore, it is suggested that measurement devices for each joint offset be installed. Laser rangefinders should be considered because they provide high accuracy and can be installed without modifying loadbearing components. The proposed solution method will allow the ground support team to align the APS pod by manipulating joints to precalculated positions. Without measurement devices, the ground support team will not know when the precalculated positions have been reached. Based on an uncertainty analysis, an accuracy of +0.010" is insufficient for measurement devices. Overall system accuracy would be greatly improved if measurement device accuracy approached 0.001". Crude measurement techniques such a rulers or tape measures would provide highly inaccurate results. The lifting fixture design includes adjustment capability at all attach points to accommodate APS pod dimensional variation. This adjustment capability is large enough that it must be accounted for when considering the location of the APS pod relative to reference points on the lifting fixture. The simplest and most accurate method of determining the position of the APS pod relative to the lifting fixture is to make high accuracy measurements before each APS pod is installed. APS pod attach points 1, 2, and 3 must be measured and the rotator bar and adjustment mechanism end effector locations. Since the orientation of the adjustment mechanism end effectors must be known, a second point along each adjustment mechanism S6 and a6 vectors must also be measured. Total uncertainty can be further reduced by making additional highaccuracy measurements of the rotator bar base and spherical joint socket locations. Orbiter attach point positions can be similarly determined. These measurements yield only marginal accuracy improvements but are desirable nonetheless. In general, highaccuracy measurements can be used to compensate for insufficiently loose tolerances. As previously mentioned, a hydraulic jack is used to ensure the aft adjustment mechanism "follows" the forward adjustment mechanism during forward/aft motion of the lifting fixture. The hydraulic jack is not a precise method for positioning the aft adjustment mechanism. The adjustment mechanisms could be more accurately positioned in the forward/aft direction before they are installed in the sockets. Since the adjustment mechanisms will not be supporting the weight of the lifting fixture or APS pod at that point, they can be adjusted to the precalculated solution position without experiencing binding. If the S6 joint offset calculations are correct, the adjustment mechanisms will not need to be adjusted in the forward/aft direction during operations. One advantage of the proposed solution method is that joint offset adjustments do not need to be made in any particular sequence. Therefore, it is not imperative that motions be simultaneous with one exception. As the APS pod is lowered to the orbiter deck, the bottom of the APS pod should be approximately parallel to the orbiter deck surface. If one bulb seal compresses before the others make contact, then the resulting frictional force might cause a slight misalignment. To minimize this effect, a reverse kinematic analysis should also be performed to position the APS pod at a waypoint 1/8" above the orbiter deck and aligned in Xpod and Zpod. The APS pod can be slowly lowered onto the deck from that waypoint by simultaneously adjusting the rotator bar and adjustment mechanisms. It would also be beneficial to calculate the joint angle adjustments needed to move the APS pod in small increments along each axis. If the lifting fixture is manipulated to the precalculated joint angles and found to be misaligned, the ground support team will know how to manipulate the lifting fixture to align the APS pod rather than rely on intuition. A Finite Element Analysis (FEA) should be performed on the lifting fixture with the APS pod in the installed position. This will allow the rigid body assumption to be validated. If the FEA shows that lifting fixture deflection is significant, then the deflected lifting fixture shape will be used throughout reverse kinematic analysis calculations. Summary of Recommendations The following recommendations should be implemented to ensure success of the proposed alignment method: * Install measurement devices to measure all variable joint offsets. * Make highaccuracy measurements (+0.001") of all critical relative positions. * Position the adjustment mechanisms in the forward/aft direction per S6 joint offset solutions before they begin supporting lifting fixture and APS pod weight. * Position the APS pod at a waypoint 1/8" above the orbiter deck and aligned along the plane of the orbiter deck. The joint offsets needed to position the pod at the waypoint are calculated by reverse kinematic analysis. * Use joint angle adjustments for small misalignments along each pod coordinate axis. * Perform FEA to validate the rigid body assumption. Conclusions It should be evident at this point that the design of the lifting fixture, adjustment mechanisms, and rotator bar is not adequate for the precision positioning task it is required to perform. Given the shuttle program's limited resources, it is highly unlikely that this GSE will be redesigned to improve operations in lieu of upgrades to flight hardware. The reverse kinematic analysis presented in my study does not add the desired 57 level of accuracy to the APS pod alignment operation. However, the level of accuracy it does provide is a substantial improvement to the current process. Implementation of this solution method adds a relatively small amount of manpower and cost to operations compared to the projected benefit. This solution method is a viable aid to APS pod alignment during installation onto the orbiter. APPENDIX A SHUTTLE COORDINATE SYSTEMS Several different coordinate systems are commonly used to describe locations on the space shuttle. Two of these coordinate systems are the orbiter coordinate system and the APS pod coordinate system. The orbiter coordinate system is essentially the orbiter's version of a bodyfixed coordinate system. The origin is located forward of the orbiter's nose. The positive X direction is aft, positive Y direction is outboard through the starboard wing, and positive Z direction is out through the vertical tail. The location and orientation of the orbiter coordinate system can be seen in Figure A1. Orbiter coordinates are used throughout this analysis except when the location of the orbiter deck is specifically needed. The APS pod coordinate systems are local coordinate systems used to describe orbiter locations relative to the orbiter deck planes. In both right APS pod coordinates and left APS pod coordinates, the plane of the appropriate orbiter deck can be described by the equation Ypod = 100. The origin is located forward of the APS pod and below the orbiter deck. The positive X direction is aft and slightly outboard, positive Y direction is perpendicular to the orbiter deck and includes an outboard component, and positive Z direction is angled inboard along the plane of the orbiter deck. The right APS pod coordinate system can be seen in Figure A2. The transformation matrices between orbiter coordinates and right APS pod coordinates are documented as 0.9986104865 0.0526981625 0 1212.4087676 Orbiter 0.0379078857 0.7183402679 0.6946583705 59.30094352 RightPod T 0.0366072197 0.6936931332 0.7193398003 311.74989638 0 0 0 1 0.9986104865 0.0379078857 0.0366072197 1224.3843795 (A RightPod 0.0526981625 0.7183402679 0.6936931332 194.96530381 Orbiter 0 0.6946583705 0.7193398003 183.06021143 0 0 0 1 Drawings containing the APS pod and its ground support equipment show hardware associated with the left APS pod. The CAD model is based on these drawings and therefore also shows left APS pod hardware. Unfortunately, transformation matrices for the left APS pod coordinate system are not documented. The location and orientation of the APS pod coordinate systems are symmetric about the orbiter coordinate XZ plane. Using this fact, transformation matrices for the left APS pod coordinate system can be calculated. It should be noted that the left APS pod coordinate system does not obey the right hand rule. In the interest of avoiding calculation errors due to the use of a left hand coordinate system, the derived left APS pod coordinate system will be made to obey the right hand rule by inverting its Z axis. First, the rotation angle 0 about unknown unit vector m can be calculated from S= cos ll r22 3 = 44.0984373537 (A.2) where rj, r22, and r33 are the first three diagonal terms in oRit d T. The unit vector m can be determined from mn =+ cos = +0.997532008229 1 cos my = 2m1 +r2 = +0.026302324052 2y m (1cosO) r, +r, m = 13 = 3 +0.065100540004 2m ( cos0) The sign of mx and subsequent signs of my and mz are determined from m = 0.997532008229 2sin m = 0.026302324052 (A.3) (A.4) m = 0.065100540004 To calculate the left APS pod coordinate system, a rotation of 0 about the mirror of vector m will be conducted. The resulting transformation matrix is mnxnu + cos 0 Orbiter my + m sin 0 LeftPod T LeflPod mxu + m sin 0 mnmugm sin8 mymyU + cos 0 mymu + m sin 0 mm u m sin mym U mx sin 0 n mmu + cos 0 194.965 183.060 (A.5) 1 v cos = 0.2818547227 After altering the matrix to invert the Z axis, the result is 0.9986104865 0.0526981625 0 0 0.0379078857 0.7183402679 0.6946583705 0 0.0366072197 0.6936931333 0.7193398003 0 1224.380 194.965 (A.6) 183.060 1 The inverse of this matrix is 0.9986104864 0.0379078857 0.0366072197 0 0.0526981625 0.7183402680 0.6936931333 0 0 0.6946583705 0.7193398003 0 1212.40876751 59.3009435119 (A.7) 311.749896399 1 Orbiter T = LeftPod Orbiter T = LeftPod T In retrospect, the simplest solution would have been to have the program invert all negative orbiter Y coordinates input into the program. This would have eliminated the need for the left APS pod coordinate derivation because the right APS pod coordinate system could be used instead. Y. Figure A1. Orbiter coordinate system. Figure A2. Right APS pod coordinate system. [2] APPENDIX B REVERSE KINEMATIC ANALYSIS NOTATION The reverse kinematic analysis notation used in my study is defined as follows. Subscripts h, i, j, k, and 1 are used where f=i3, g=i2, h=i1, j=i+l, k=i+2, and l=i+3. cos O sin 8 SCOS a'  sin a  S1 jS S( SjkCj + Cjk SCj )  CjkCj SjkS1jCj Sk S jk  SCjk + CjSjkCj )  CjCjk SjSjkCj SXc YS ^ Ck j + c) kZ i Sjk (X sj + cj + CkZ, XkC kS c (XkSJ +YkC) S Zk Ss(xk, X YkC )+ CZk  Xck Sk SCkI ( Xsk + Ck) SklZU =Sk (Xsk +Ck k)+ CklZ  XkC Y kS Ch, (Xch S + S kC,) Sh Zk S=, (XkS, + Y, C)+ ChZ (B.1) (B.2) (B.3) (B.4) (B.5) (B.6) (B.7) Xhjk Xh jk h Sk Yhu(k Ckl (Xhjsk +YhCk) SklZhj (B.8) ZhUk Skl ( XhUSk + YiCk )+ CklZhy Xk7zh Xk C h Aki Sh Yk1,h Cgh (X +Ysh + i h) SghZk (B.9) ZIgth Sgh (Xk Sh + YCh) + CghZk7, XhjUki XhujkCI hjkSl Yhuki Cim (XhukSl + YhUkCI Sl)lZhuk (B. 10) ZhUikl sIm (XhjkS, + YhzijkcI ) + clmZhUk Xllekh ~ Xllki Ch Iji, Sh Ylk'h Cgh (xlksh +Y ch) SghZlkJ, (B.11) ZlIkzh Sgh (XlkgrSh + I,Ch ) + CghZilkl u, s s V =(sc +csc^) (B.12) Wl Cc S C'O U CC S Si Vi s (c +cs c J) (B.13) W cci S, s C U Uk U c k jSk = U,, Vik Ck (UU+Sk cJ ) Sk = Vkz (B.14) WKk Sk (Usjk + Jcjk)+ Ckj Wi,, UhUk Uhc jk VhoSjk = Uk7,h Vhk hCk (UhSVk + VhJk SkWh= Vkjh (B.15) WhiSkSk (UhijSk + VhUJsCk U CkWhj W~,kh Ughjk Ughi jk VghjSjk = Ulkhg Vghk Ck (UghzSJk + VghUJk) SkWghz =Vjlhg (B.16) Wghik Sk (UghUSJyk + VghUCJk) k+ CkWghj kWihg Ufghjk UfghU jk fghuSjk = Ukjghgf VfgJhk Ck (UfghUSYk +Vfgh k SkWfghj VA,,hgf (B.17) Wfghjk Sk (UfghiSJk +Vfghj Ck )CkWfghj kjWhgf LIST OF REFERENCES [1] D. R. Jenkins, The History of the National Space Transportation System: The First 100 Missions, 3rd ed. Stillwater, MN: Voyageur Press, 2001. [2] Rockwell International, "Lifting Fixture SetOMS/RCS Pod," National Aeronautics and Space Administration, Houston, TX H700679, 1978. [3] D. Armstrong, "John F. Kennedy Space Center Multimedia Gallery," n.d.; http://mediaarchive.ksc.nasa.gov/index.cfm, 23 Oct. 2004. [4] C. D. Crane III and J. Duffy, Kinematic Analysis of Robot Manipulators. New York: Cambridge University Press, 1998. [5] W. H. ElMaraghy, H. A. ElMaraghy, A. Zaki, and A. Massoud, "Design and Control of Robots with Flexibilities," Annals of the CIRP, vol. 43, pp. 359362, 1994. BIOGRAPHICAL SKETCH Jeff Brink graduated from the University of Michigan in December 2000 with Bachelor of Science degrees in aerospace engineering and mechanical engineering. Jeff started work at NASA in February 2001 as a systems engineer in shuttle processing at the Kennedy Space Center in Florida. In September 2001, he enrolled parttime in graduate school at the University of Central Florida. One year later, Jeff transferred to the University of Florida to study robotics. With the help of the University of Florida's distance learning program, FEEDS, Jeff will graduate in May 2005 with a Master of Engineering degree. 