

\section{The 'Frascati' Jigs}


   The precision jigs holding the tubeplugs at the HV and RO ends
during the glueing of a tubelayer were assembled at Frascati.
They consist of 4 aluminum pieces with glued steel precision rods
to position the plugs.
These pieces were produced using a master jig
as descibed in [ref.Frascati], and then glued together to
make one 72 tube BOL jig.
  The assembled jigs were measured on a CNC machine at NIKHEF.
The analysis of the measurements showed :

   . the average z-pitch of the two complete jigs is 35.0350mm  at 20.0degC
     and devitations of < 0.1 \mum from this value  
     for the average z-pitch of the original jig pieces. 

     The  rms of the individual positions  in z
     and the rms of the  y-deviations from a straight line 
     are less than  2\mum.
     No significant systematic shifts in z or y were found
     at the glue joints of the 4 pieces.


----
                             Pitch        rmsZ    rmsY
      CombFitFix : Frasc1   30.0355mm      2mu     4mu(inclStav)  20.8deg?
                   Fracs2      "            "      3mu  "

             20.8 -> 20.0 ?     -0.8*0.7=0.56  ->   30.0350 at 20.deg ?
---




\section{The Tube Jigs}


The jigs supporting the tubes inbetween the precision jigs,
at ~0.5m intervals ,have been machined at Nikhef as solid aluminum pieces
with a width corresponding to 18 tubes.A total of 50 pieces were produced
en measured on the CNC.

 To assemble the 9 full width jigs (72 tubes) 
the 36 best pieces were selected, taking into account
the precision of the wedges and the connecting surfaces.
The assembled jigs were again measured on the CNC and the results were 
compared with the nominal height and Frascati pitch.
The  RMS deviations of the tube positions  are <15\mum in z and y.



\section{Jigs on the Assembly table}



   On one side of the table the precision jigs are fixed to 
the corresponding assembly stacking towers . In order to assure
that the two multilayers are glued to the spacer without a 
significant stereo angle between them, the distance between the wedges
and the spacer fixation in z must differ by less than 10\mum
for the two precision jigs. This is because the HV and RO
ends of a chamber are interchanged with respect to the two
precision jigs for glueing either of the two multilayers
(see [Assembly.intro])
 For the QA/QC of this requirement we use an auxiliary device
called the BOL-monitor. This consists of a cross-plate
with two small lenses attached to one of the flanges
 approximately 1.5m away from each other.
at positions corresponding to two precision wedges in the jigs.
This cross-plate is positionned on the stacking towers in the
same way it is done for glueing tube layers. The relative
position of each of the lenses is measured with an LED/Mask/CCD-camera
combination  mounted on a brass fork with steel positionning inserts.
 This fork is placed on two precise steel rods 
lying in the jig wedges such that
the cross plate lens is  hanging aproximately in the middle between the
Mask and the CCD. With the thus created RASNIK system the 
the lens position in Z and Y is read out , while varying
the fork position by +-2mm in the optical axis direction (X)
along the supporting rods. These measurements are done 
at both precision jigs, using the same fork/rods combination.
Comparison of the measurements yields the difference in Y
and Y of the jig and reference assembly tower combination.
The use of two lenses on the cross-plate 
provides two independent measurements. In addition
the whole procedure is repeated with the cross-plate rotated
180 degrees around the vertical axis, thereby interchanging
the lens/fork combinations and yielding additional redundancy.

  The BOL-monitor was used to fix the initial position of
the jigs and these measurements are ment to be repeated regularly as part of
the QA/QC procedures.

  An recent example of such a measurement is shown in fig [xyzbol11.ps].
 Here we plot the difference in Z and Y position of the cross plate
 lenses with respect to the two precision jigs, as measured on the North 
 and South side of the assembly table. The position difference is plotted
 as function of the X position of the forks; X=0 corresponding to the
 lens being exactly in the middle between the mask and the CCD of
 of the Rasnik system. ( Niet echt waar maar ja , bijna ).
 The X values are derived from magnification of the mask image
 on the CCD.
  Straight lines are fit through the two corresponding sets of data 
 at the North and South side respectively. 
 The points show the deviations of the measurements on the North side
 from the line fit throught the measurements on the South side, and
 vice versa.
 The two colors differentiate between the two orientations of 
 the monitor cross-plate, which in principle
 should lead to the same result. The corresponding lens positions are
 indicated by Reference side and NonReference side. 
 For the DZ measurement the the Reference side data are the most reliable,
 as the distance between the reference tower and the lens is short (30 cm)
 and temperature effects can be neglected. For the Non-Ref Z measurements
 the lens is at 210 cm from the reference tower and its position is thus
 subject to temperature differences of the cross-plate between North
 and South data sets, which are not corrected for.

( In addition the relative angle of the cross-plate   
 wrt the jigs may add cosine  effect in the Z measurements, which  
 but ...  +-4mm over 2meter -> +-4mu ? )

 For the DY measurements the temperature effects can be neglected .

    From the plot one can see that with both orientations of the cross-plate
 we measure at the Ref side a difference  in Z of  6\mum,
 which is within the 10\mum tolerance.
  This value has remained the same within $\pm$2\mum over the  2 years that the
 assembly jigs have been used.
 
  The Y differences are much less critical for the chamber assembly,
 since the glueing procedure assures that the distance between the two
 multilayers remains the same on both ends of a chamber and only the
 relative position of the cross-plates glued between them is affected.
 Nevertheless the measurements show that Y differences are smaller than
 20\mum on both Ref and NonRef side of the jigs.

 ( Daarentegen is <DY> ref/nonref wel belangrijk : 

          'a+b=c+d' , niet alleen voor een wigvormige kamer
           maar ook voor een shift in Z tussen multilayers

           DZ ~ HCP/DBALLEN * <DY=DYN+DYS,incl signs)
                 ~1/4       *  ""

      iets over zeggen ? 





 In order to properly combine the Frascati jigs with tube jigs
  a 20\mum steel foil was used to shim the height
 of the Frascati jigs on the assembly table. This was needed
 due to a small change in the tube and plug geometry after
 the jigs were already machined. 

 The relative angle ( deviation from a rectangular geometry )
 and distance of the two precision jigs which are ~5m apart
 were measured using a laser interferometer and a pentaprism.
 The fixation of the jigs on the table was adjusted such that
 this angle is smaller than xxx \murad and the distance is within
 yyy mm with respect to the nominal length of an assembled tube. 


 The tube jigs are positionned on the assembly table with one side fixed
to a reference bar. Each jig position is adjusted in z such that
the tube positions of the 9 jigs deviate less than 50\mum from straight lines 
connecting the two precision jigs at each end of the table.

 For this we used a laser and silicon-sensor combination [ref SiSens/Munich]
 The laser beam defines a straight line between the two precison jigs 
 roughly along path of  a tube. The relative beam position
 in z and y is measured by placing a silicon sensor with strips in
 both directions with a pitch of 400\mum in the beam. The sensor
 is mounted on a brass support with steel inserts which are positionned
 on small steel rods lying in the wedges of the jigs. The sensor
 is placed succesively on each of the 11 jigs along the beam.
 The centre of gravity of the beam profile is determined in both
 z and y for each measurement. A line is defined by the two measurements
 of the precision jigs and the deviations from that line are calculated
 for the tube jigs inbetween. These measurements are repeated at 
 several positions along the precision jigs.
  In fig [sisens] we show the distribution of the deviations for
 some of the measurements. The rms of the deviations is typically
 xx \mum in z and yy \mum in y, thus amply fulfilling the requirement
 of 100 \mum rms for the centrisity of the wire with respect to
 the tube centre. These measurements will be  repeated regularly
 as part of the QA/QC procedure.


Both the precision and tube jigs are positionned on the table
with a sliding fixation  such that 
they are allowed to expand freely in the direction away 
from the reference bar in case of temperature variations.
This was checked with laser interferometer measurements
and local heating of some jigs with approximately +5 deg
temperature increase.

   The relative height  above the table surface  of the precision wedges
was checked several times before and during chamber construction
with SLOF measurements. Average deviations from the nominal value
were found to be less than 5\mum with an rms of < 4\mum 
for different positions along the jigs. 
  Simular deviations were found for the relative height of
the precision wedges and the corresponding wedges in tube jigs
next to the precision jigs.

\begin{figure}[b]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,14)
\put(0,0){\mbox{\epsfysize=14cm\epsffile{xyzbol11.ps}}}
\end{picture}
\end{center}
\label{balmon}
\caption{\sl Result of ... waarom bol11?}
\end{figure}

 



























