The survey and alignment of SLAC's B-factory injector and high energy ring will be complete in March 1997. Modern digital electronic surveying tools are contributing to new, efficient alignment procedures. A laser tracker was used to fiducialize almost 300 quadrupole magnets. Digital levels were used to pre-set base plate elevations. Theodolites with very accurate co-axial distance meters were used for everything from layout to 3D magnet positioning to network surveys, all in free stationing mode. A number of procedures and measurement results are outlined

Gaydosh, Michael L.

Pietryka, Matthew J.

UNT Digital Library

SURVEY AND ALIGNMENT OF SLAC'S B-FACTORYM. Pietryka, M. Gaydosh; Stanford Linear Accelerator Center, Stanford, CA 94309, USA.AbstractThe survey and alignment of SLAC’s B-factory injectorand high energy ring will be complete in March 1997.Modern digital electronic surveying tools are contributingto new, efficient alignment procedures.  A laser trackerwas used to fiducialize almost 300 quadrupole magnets.Digital levels were used to pre-set base plate elevations.Theodolites with very accurate co-axial distance meterswere used for everything from layout to 3D magnetpositioning to network surveys, all in free stationingmode.  A number of procedures and measurement resultsare outlined.1 FREE STATIONINGLaser trackers and a new breed of “total station” aredesigned specifically for industrial metrology.  They bothcombine arc-second angle accuracy with better than 100micron distance accuracy in a package with co-axialoptics.  They are, essentially, portable coordinatemeasuring machines and have changed the face ofsurveying at SLAC.  While the laser tracker’s power andversatility is now familiar, most B-factory work wasperformed with the Leica TC2002 total station.  TheTC2002 is much more robust and portable, much lessexpensive, and ideally suited to discrete pointmeasurements.Total station technology was introduced by HPtwenty years ago.  The key to metrology application wasimprovement of distance meter technology.  Unlike thelaser tracker, which uses interferometry, this class ofdistance meter emits a modulated infrared signal that isreflected back to the instrument by a retro-reflectivetarget.  The differential phase angle between the exitingand returning signals yields a distance equal to a fractionof the modulation wavelength.  The additional integernumber of wavelengths comprising the distance is thendetermined by switching to a lower frequency to repeatthe measurement.  A few years ago the most accuratetotal station distance meters, after extensive calibration,could approach 1mm.  Today, certain Leica total stationsachieve 0.1mm right out of the box.  Figure 1 showsdifferences between distances measured with fourTC2002s and SLAC’s interferometer. Distances from 1 to30 meters were measured at one-meter intervals.  Figure 2shows a Fourier model of the differences betweenTC2002 and interferometer distances measured atintervals of 0.1 meter over 6 meters.  The model reducedthe measurement standard deviation from 73 to 52microns.[1]Figure 1  TC2002 vs. InterferometerThe total station allows dramatic changes in routinesurveying procedures.  Formerly, special forced-centering hardware was erected and centered over floormonuments to receive separate angle and distancemeasuring instruments.  Distance measurements werevery slow, many minutes per observation, and differentialleveling was required to deliver the third dimension.With the total station, activities ranging from networkdata collection to bolt pattern layout are conducted in“free stationing” mode.  Free stationing means that theinstrument is not force-centered over a monument, butlocated in a general area where all points of interest arevisible.  Monuments are no longer confined to the floor,but more conveniently located on walls and even ceilings.Monument designs vary, but all are some form of cupmade to accept sphere-mountedFigure 2  Fourier Cyclic Error Model-0.25-0.20-0.15-0.10-0.050.000.050.100.150.200.250.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0 26.0 28.0 30.0 32.0TC2002 Distance (meters)Difference (mm)TC1 sn358471 TC2 sn359471 TC3 sn359904 TC4 sn359906SLAC-PUB-7446Work supported in part by US Department of Energy contract DE-AC02-76SF00515.targets(SMT) and retro-reflectors(SMR).  Trackers andtotal stations both use commercially available 1.5 inchsphere targeting.  The reference point is the center of thesphere in the monument.  A much denser monumentpattern can be installed since distances require only a fewseconds each and measurements are taken in 3D.  Theinstrument measures 3D vectors, horizontal angle,vertical angle, and distance, from its center of optics toeach point of interest.  For network or mapping surveys,the measurements are simply stored on the data collectorfor processing in the office.  For alignment work, thesurveyor first takes observations to several monuments, adata collector program solves for the instrument positionand orientation, then component positioning proceeds.2  HER QUAD FIDUCIALIZATIONThe fiducialization measurements were performedwith SLAC’s CMS 3000 laser tracker.  The liabilities ofthe tracker’s 80-pound weight, large power supply, bulkycabling, and delicate nature are mitigated when it can beset up in a laboratory environment for gross datacollection.  An area in the magnet warehouse was clearedso that the tracker could be rolled on its stand all the wayaround the magnets.  Monuments were installed in thefloor around the perimeter of the cleared space.  Sixfiducial bushings were welded onto each magnet, four onthe top and two on the aisle side, to accept removablemagnetic mounts for 1.5 inch sphere targeting.  Themagnet engineer designed a one-meter-long mandrel thatregistered on two pole tips, projected through the magnet,and held a magnetic sphere mount on axis on each end.The magnets were measured six at a time.  Theywere arranged in a line, in three groups of two tofacilitate mandrel handling, as shown in Figure 3.  Thetracker was situated adjacent to the first pair, on the“aisle” side, and measurements were recorded to all floormonuments, the fiducials and exposed lamination edgeson magnets 1 and 2, and the mandrel in magnets 1and 2in four different positions each.  With bungy cords andshims the mandrel was forced into contact with each pairof pole tips for four different positions.  In turn, thetracker was moved into position next to the aisle side ofeach magnet pair and then measurements were taken tothe monuments, fiducials, and the mandrel positions.Then the tracker was rolled to the “wall” side and anotherdata set was recorded next to each magnet pair.  Onesurveyor in one shift measured this large, six-magnet dataset.  On the swing shift, another six magnets were movedinto position to be measured the next day.The day’s measurements were processed in one bigadjustment.  The common monument observations madefor a very redundant, geometrically strong network.  Theresulting coordinates were parsed into individual magnetdata sets for further processing.  Each magnet data setwas used to generate magnet-centered fiducialcoordinates.  The beamline axis was defined by the axisof a best-fit cylinder through the mandrel coordinates,magnet center by the average of magnet end positions,and remaining coordinate axis orientation by a best-fitplane through lamination edge coordinates.Figure 3  Six magnets ganged for fiducialization3  TOTAL STATION WORKTo do alignment work with the total station, whetherbolt pattern marking or component positioning, thesurveyor arrives on scene with the instrument and a datacollector loaded with surveyed monument coordinatesand component ideal coordinates.[2]  The instrument isset up on a portable tripod where several monuments andthe area to be worked are visible.  The monumentpositions are considered known and are used to solve forthe instrument position.  Distances and angles aremeasured to a number of monuments, some upstream andsome downstream.  While two monuments would give aunique solution for the instrument position, it is goodpractice to observe four or five monuments.  This isenough data to identify possible problems with themonument coordinates and provide a redundant solution.SLAC’s software displays measurement residuals andcalculated standard deviations to help evaluate the qualityof the solution.  With a good solution in hand, alignmentbegins.3.1  Layout and Stand AlignmentSome simple custom hardware facilitates layout andstand alignment.  A layout block is a piece of steel 3 by 5by 1 inches with a through-hole in its center.  Pressedflush into one end of the hole is a drill bushing, while theother end is beveled to form a cup for the 1.5 inch SMR.The floor is marked by removing the SMR and inserting acenter punch sized for the bushing. For stand alignment,special magnetic SMR cups were built to occupy criticalcomponent/stand interface positions.  The surveyor entersthe point name in the data collector and the position ofthe SMR in the block or cup is observed with the totalstation.  For low precision work, it is adequate to aim theinstrument at the apparent SMR apex and record a singlemeasurement.  The software computes a position andreturns the difference between the observed and idealpositions.  The difference cab be displayed in the beam-following coordinate system or in a system oriented to theline between the point and the instrument.  The block orstand is moved toward the ideal position, perhaps aidedby a pocket tape, and another observation is made.  Thisprocess is repeated until the difference between observedand ideal is within tolerance, typically 1 or 2mm. If doinglayout, the SMR is removed, and the center punch isinserted to mark the point.  For stand alignment, theremay be several points to check to verify stand orientationand special spirit levels can be very handy as well.The HER quad raft installation required a secondlayout step.  The hole patterns were drilled, the threadedanchor studs and steel mounting plates were installed, thesurveyors leveled the plates, and the plates were grouted.The second layout was for mating pins in the mountingplates.  The same procedure was used, but with a 0.5mmtolerance.  After the surveyors punch-marked the steelplates the ironworkers followed with a magnetic base drillto make the mating holes.  The mating pins controlled aquad raft’s position and orientation.  Table 1 displayshow effective this scheme proved to be.  The left sideshows the surveyed positions of quads in region fivebefore alignment.  The residuals represent the sum oferrors resulting from mating hole marking and drilling,and quad raft assembly.Quad DZmm DXmm Dymm DXmm DYmm1 -0.15 -0.31 -0.29 -0.03 -0.122 -0.40 -0.27 -0.03 0.01 0.063 -0.18 -0.52 -0.36 0.10 0.144 -0.45 -0.47 -0.02 0.10 0.015 -0.19 -0.62 -0.11 0.04 0.046 -0.01 -0.38 -0.73 -0.39 0.207 -0.99 -0.37 -0.13 -0.18 0.138 -1.01 -0.36 -0.43 -0.10 -0.049 -0.43 -0.55 0.13 -0.22 0.1110 -0.10 -0.65 -0.12 -0.23 -0.0211 -0.62 -1.07 -0.37 0.07 -0.1512 -0.79 -0.35 -0.23 -0.10 0.0413 -0.61 -0.37 -0.18 0.02 0.0314 -0.31 -0.53 -0.21 0.19 -0.1315 -0.15 -0.19 -0.01 0.11 0.0816 -0.78 -0.68 -0.04 0.07 0.2017 -0.33 -0.99 -0.15 0.13 0.0818 -0.47 0.07 -0.77 0.10 0.1119 0.09 0.0720 -1.06 -0.62 -0.06 0.24 -0.0421 0.19 0.0822 -0.21 0.05 0.37 -0.01 0.0123 -1.07 -0.51 0.30 0.04 0.0024 -0.94 -0.28 -0.13 -0.01 0.0225 -0.62 -0.16 -0.02 0.02 0.0226 -0.79 -0.38 -0.04 0.03 0.0127 -0.33 -0.02 0.41 -0.14 -0.1028 -0.25 -0.52 0.48 -0.07 -0.0129 -1.34 0.00 0.25 -0.03 -0.0130 -0.16 -0.16 0.09 0.07 -0.0831 0.05 -0.0132 -0.06 0.06std. dev.= 0.36 0.28 0.30 0.13 0.093.2  Magnet  AlignmentAt a glance, the magnet alignment procedure looksthe same as that for layout or stands.  The tightertolerances dictate a few refinements, however.  First, thesingle set of monument observations is replaced by twoor three sets to better determine the optical center. Thisyields benefits not only statistically, but alsomechanically by compensating for instrumental errors.Second, it is more accurate to aim at a separate sphere-mounted SMT and then switch to the SMR for distancemeasurement. Finally, the light hardwood tripod isreplaced by a heavy optical tooling-style stand, which isrolled from place to place.Magnet fiducial observations started with singlepointings to SMRs; no sense looking for microns until themillimeters were worked out.  In the HER, the surveyorsshot the four top fiducials first to get a look at magnetorientation.  They adjusted pitch and roll to zero to de-couple orientation and translation, then worked Z, Y, andX struts to bring the magnet into position.  Typically, thistook several iterations of survey and alignment.  TheSMT and reverse pointings were not brought into playuntil the magnet was very close to its ideal position, say100 to 200 microns.After all HER quads were aligned, the tracker wasused to map the quads and BPMs.  This was another greatapplication for the tracker; gross data collection in aprotected environment where it could be rolled frommagnet to magnet all around the ring.  The right side ofTable 1 shows results of that map.  The residuals are froma smooth curve fit through the differences betweensurveyed and ideal magnet centers.[3]  They represent thesum of errors from the monument network and the totalstation measurement procedure.4 ACKNOWLEDGEMENTSThe authors recognize that they are reporting theaccumulated knowledge and experience of the entireSLAC alignment team.Work supported by the U.S. Department of Energy undercontract number DE-AC03-768F00515.REFERENCES[1] B.C. Fuss: ‘FOURIER: A Harmonic AnalysisProgram to Model Periodic Data’, SLAC, 1994.[2] W.A. Oren: ‘Ideal Coordinate Calculations’, SLAC.[3] H. Friedsam, W. Oren: ‘The Application of thePrincipal Curve Analysis Technique to SmoothBeamlines’, Proceedings of the First IWAA, SLAC,1989.Table 1  Region 5 Residuals Before and After FirstAlignment

Survey and Alignment of SLAC's B Factory

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Survey and Alignment of SLAC's B Factory

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