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\begin{center}
\LARGE{ \bf Assembly station}


\hspace{1cm}

\large{ versie 0}
\end{center}

\section{Introduction}
The production of 96 of the largest ATLAS MUON chambers starts at NIKHEF.
Figure~\ref{bol} shows a 
 muon chambers consisting of two panels (multi-layers),
 each with three drift tube layers, 
separated by a  support structure called the spacer. The spacer
 consists of three beams, called crossplates, that run orthogonal to the
 tubes which connect the multilayers. The crossplates are connected by two beams, called longbeams.

  The 'Barrel Outer Large' (BOL) chambers have dimensions 5~m$\times$2~m.
 The drift tubes are 30~mm in diameter
closed by precise end-plugs which center the 50~\um gold-plated tungsten wire.
In ATLAS, the wires run along the magnetic field direction, the chamber $X$ coordinate. The bending of the particle trajectories in the chamber $Z-Y$ plane is then orthogonal to the wires.

Over the past two years the assembly station, based on a granite block,
 has been prepared. Figure~\ref{bolroom} shows the assembly station.
The combs which will position the tubes are visible.
The two outer most combs have to be very precise, since they hold the endplugs and thus determine the wire position, and were constructed by Frascati. The nine central combs are designed and constructed at NIKHEF.

The spacer is supported by six precision towers. Figure~\ref{bolroomtower} displays one precision tower. The removable 'ears' on the spacer accomodate a sphere that is support by the sphere holders on the towers.
Figure~\ref{bolroomtower} displays one precision tower, supporting the ear of the bare spacer.
The towers can be adjusted in heigth by changing the 'stacking blocks' corresponding to thickness of  tube layers that have been attached to the spacer, during the gluing process.
Figure~\ref{bolroomtower} also shows the  alignment system, RASAS, that monitors the position of the ears.

\begin{figure}[b]
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
 \put(0,0){\mbox{\psfig{file=fmmdtch1.epsi,height=110pt,angle=-90}}}
\end{picture}
\label{bol}
\caption{\sl Schematic view of a muon chamber.}
\end{figure}

\begin{figure}[b]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
\put(-1,0){\mbox{\epsfysize=10cm\epsffile{Bol_room_febr2000.ps}}}
\put(14.5,5){\mbox{\epsfysize=2cm\epsffile{frame.eps}}}
\end{picture}
\end{center}
\label{bolroom}
\caption{\sl View of the assembly station. The bare spacer is carried by the six sphere towers. The combs, which will support the tubes are also visible. In 
the background, the tube production can be seen.
The coordinate frame is also displayed in this figure; on the wall the character
 'N' defines the 'North' direction, which coincides with the $X$ direction. }
\end{figure}

\begin{figure}[b]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
\put(0,0){\mbox{\epsfysize=10cm\epsffile{bolroom_1.ps}}}
\end{picture}
\end{center}
\label{bolroomtower}
\caption{\sl The picture show one sphere tower that carries the spacer. The
'removable' ear on the spacer is monitored by the aligment system. }
\end{figure}




We follow the specs given in the ATLAS MUON TDR (page 138). Combining the intrinsic
accuracy and the positioning accuracy we summarize:
\begin{itemize}
\item
The $Y$, $Z$  accuracy of Frascati-combs and towers has to be 10\um.
\item
The $X$ accuracy has a spec of 100\um.
\item  Angles $A_X$, $A_Y$ and $A_Z$ of the Frascatie combs have to be precise to 25~\urad, 0.5~mrad and 0.5~mrad respectively.
\item  The concentricity of the wire in the tubes has to be accurate to 100~\um RMS.
\end{itemize}

These values have been translated into measurable quantities, which will be
described in the following sections.

We aim to align the combs and towers such that the wire positions in the bending plane are controlled
within 20~\um. The wires are centered in the tubes over the full length of the
tubes within 100~\um.

Finally, we mention the importance of the Torque, or, the angular
 difference between the North and South Frascati combs. The calibration procedure of the in-plane system or a certification scan with the X-ray tomograph will not reveal the torque.  Therefore the torques has te be known to sufficent accuracy and aborbed in the in-plane calibration constants.

Below, we start with a description of the non-standard measurement tools.
 Then we present the results on the intrinic precision of the mechanics,
 followed by the results on the positioning accuracy. 
We devote a full section on the aligment monitoring system before we discuss some additional checks. The appendix gives a brief overview of all the measurements.

\clearpage

\section{Measurement tools}
In this section we describe the home-made and other not so common tools to measre the mechanics and to align the assembly station. 

\subsection{The Slof}
The 'Slof' is a commercial instrument to measure relative heights. It has an intrisic accuracy of 1\um.

\subsection{The malmonitor}
The malmonitor is a homemade instrument to monitor the distance between NIKHEF sub- combs before and during gluing. A NIKHEF comb consists of four sub-combs.

The malmonitor consists of two parts which are placed on the two adjacent sub-combs. Two
RASNIK systems are used to measure the possible shifts and also rotation between these parts with an accuracy of about 5~\um.


\subsection{Laser optics}
We use a Hewlett Packard laser with small (hardly visible) divergence over the 
relevant distance up to 6~m. Several optical instruments are used to measure
angles, distance and straigthness to high accuracy. Instincically, the distance and straigthness measurement is accurate to a few micron; the angular measurement is accurate to 10 urad.

However, The obtained accuracy of the measurements is limited by the flatness of the contact surface of the mechanics and instruments and other reproduction errors.

% Most notably is the  use of the laser optics in the measurement of the parallelity of the Frascati combs. The laser is pointed along the X axis op the assebly station. A penta prism is used to reflect the beam by 90 degrees with an accuracy of 10 urad. 
% Then, the Frascati combs are alinged with respect to this beam with an
% accuracy of about 100~\um. As reference contact we used the feet of the combs, but we also performed measurents on the body of the combs. Note that his procedure defines the X axis of the assembly station.

\subsection{Bal-monitor}
\label{sbalmon}
The 'Bal-monitor' is a home made instrument originally designed to measure the Z distance between
the sphere towers and combs. This tool also checks the Y distance between the  combs and the towers. Furthermore, it can be used to measure the orientation of the towers.

The Bal-monitor can be desribed as a cross-plate, equipped with RASNIK-lenses near the outer ends. A 'fork' with RASNIK-camera and mask is put on the combs. The lenses
fall in between this fork. The whole setup has to be positioned above the north and south Frascati comb (and optionally, above the central NIKHEF comb) and measures the relevant difference in Z and Y. After calibrated of the optical axis, defined by camera and mask, it is accurate to 5um.

\subsection{Calibration tower}
\input{caltower.tex}
\subsubsection{Calibration tower for In-Plane masks}
To calibrate the orientation of the in-plane masks we equipped a tower of the appropriate heigth with a RASNIK lense and CCD. The intrinsic orientation of the CCD was calibrated using the calibration tower and found to amount 11.7~$\pm$0.11~mrad.

\section{The intrinsic accuracy of the mechanics}
In this section we  present the results on the  intrinsic accuracy of the several components. 
The Fracati comb and sphere tower determine the position of the wires and therefore have to be accurate in the Z and Y coordinate to 10um. The NIKHEF combs determine the concentricity of the wire in the tubes and have be accurate to about 100um in Z and Y.
Our measurements show that the intrinsic accuracy is high and even below the specifications.

\subsection{Frascati combs intrinsic}
The Frascati combs are measured on a 3D coordinate machine at NIKHEF and found to be very accurate with an RMS of a few microns in the Y and Z coordinate.
However, the combs are too low (Y) by about 20um.
 The combs are shimmed using foil with a precise thickniss of 20um. The measurements are repeated and show that this approach is accurate to a few micron.

\subsection{Sphere towers intrinsic}
Measurements with 3D machine indicate that Y of the towers is
accurate whitin 10um. By selecting optimal combinations of
block, spacer and holder the Y and Z accuracy is  about 5um.

\subsection{NIKHEF combs intrinsic}
The combs are glued together with help of MAl-Monitor. 
Y, Z combs measured with 3D machine. Largest intrinsic deviation is found to be only 30um. 




\section{The positioning of the mechanics}
The accuracy of the $Y$ position of the mechanics is limited by the flatness of the granite table. Over short distances (one meter) this accuracy is about
 10~\um. Over longer distances, temperature gradients start to play a role, which make the table bend and can lead to a sagitta of 20~\um over five meter.

\subsection{ Frascati comb positioning}
The Frascati comb is shimmed and positioned with low accuracy. The high precision is reached by adjustments and many remeasurements in a iterative way.

The first check is performed with the 'slof', which measures the comb-heigth relative to the table.
All these accurate measurements as listed in Table~\ref{combh} indicate values below 10~\um deviation from nominal. 
This implies that the angle Az is sufficently low. The thickness of the Frascatie comb is about 2cm. When there would be a rotation over the z-axis, it would lead to a heigth problem.

\begin{table}[thb]
\begin{center}
\begin{tabular}{|lcccccccc|} \hline
Comb. &  \multicolumn{8}{c}{$\Delta_Y$}   \\ \hline
Frascati South  &  +2&   +2&   -2&   -2&    0&   -2&   +6 &  -1 \\
NIKHEF9         & +6 &  +5 &   0 &   0 & +12 &  +8 &   0  & +6 \\
NIKHEF1         & +5 & +12 &  +3 &  +1 &  +8 & +13 &  +4  & +3 \\
Frascati North  &  +4&   +8&   +2&   +3&    0&   +7&    0 &  +3 \\ \hline
\end{tabular}
\caption{\sl Comb heigth deviation from nominal for the Frascati and most outewr NIKHEF combs. The results are obtained from measurements
 with the 'Slof' at eigth equidistant $Z$ positions. }
\label{combh}
\end{center}
\end{table}



The X distance was based on a test-TUBE with known length
and rechecked by tape-measure. The X-distance between the tube supports is
 stable within 500~\um, dominated by the low precision of the X coordinate of these supports themselves.

Most important is the angle between the two Frascati combs, related to $A_Y$.
Therefore a laser beam in the $X$ direction is used, aligned by the silicon sensor on the first wedges of the Frascati combs. 
Using a penta prism, accurate to 10~\urad, the laserbeam is reflected over
 an angle of 90 degrees into the $Z$ direction.
The Frascati combs are aligned with respect to this beam, leading to a
 straigthness in $X$ whithin 100~\um as listed in Tabel~\ref{xdev}. 
Thus, seen in the $X$-$Z$ plane, the Frascatie combs describe a rectangular 
shape with angular deviations of about 100~\urad.

\begin{table}[thb]
\begin{center}
\begin{tabular}{|lccccccc|} \hline
            &  \multicolumn{7}{c}{$\Delta_X$ (\um)}   \\
            & Z1 & Z2 & Z3 & Z4 & Z5 & Z6 & Z7  \\ \hline
Frascati North &-11.3 & -21.3 & -13.4 & 2.4 &   35.3 &  36.8 &  22.7 \\ \hline
NIKHEF 1    & 15  &  50     & 125  & 160   &  228  & 225   & 340 \\
NIKHEF 2    & 12  &   14    & 50   &  30   &  80   &  70   &  130 \\
NIKHEF 3    & 13  &   27    & 64   &  47   &  183  &  209  &  228 \\
NIKHEF 4    & 66  &   37    & 131  &  109  &  254  &  218  &  257 \\
NIKHEF 5    & 1   &   -112  & 59   &  -113 &  153  &  -102 &  113 \\
NIKHEF 6    & 81  &   85    & 161  &  192  &  260  &  316  &  293 \\
NIKHEF 7    & 14  &   27    & -33  &  -7   &  -46  &  -55  &  -59 \\
NIKHEF 8    & 118 &   113   & 186  &  214  &  229  &  276  &  339 \\
NIKHEF 9    & 80  &   117   & 172  &  194  &  217  &  258  &  338 \\ \hline
Frascati South & -2.9  & -4.8 &  -19.3 & -35.3 & -49.1 & -83.6 & -90.6 \\ \hline
\end{tabular}
\caption{\sl The $X$ deviations at seven equidistant positions in $Z$ along the  combs. For the Frascati combs a mean value is quoted for several measurments. The uncertainty on the mean value is about 50~\um. For the NIKHEF combs a typical measurement is listed with an uncertainty of about 100~\um.
The NIKHEF comb numbering starts at the North side,
 the wedge numbering starts from East,
 $\Delta_X>0$ means a shift in the South direction. }
\label{xdev}
\end{center}
\end{table}



The relative torque of the frascatie combs is measured by using tiltmeters. Despite the high intrinsic precision precison of these tiltmeters,
 a measurement better than than 10~\urad seems impossible. We measured the
torque to be zero whithin the scatter of the measurements.


\subsection{ NIKHEF comb positioning}
The NIKHEF combs are fixed at the reference side and adjusted such that they are aligned in $Z$ better than 50~\um

The accuracy of the $Y$ and $Z$ position of the NIKHEF combs is measured  with
respect to the Frascati combs using the silicon sensor. This measurement was performed at several wedges.

\begin{table}[thb]
\begin{center}
\begin{tabular}{|ccccccccccc|} \hline
            &  \multicolumn{10}{c}{$\Delta_Z$ (\um)}   \\ 
            & 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9  & <average> \\ \hline
wedge20     &+10& +9&-16& +1&-26&+12& +5& -2& -8 &  -2 +- 12 \\
wedge62     & +3&+10&-24& +4&-30& +8&+11& -1& +4 &  -2 +- 14 \\
wedge68     & -7 &-2&-36& -3&-50&-11&  0&-20& -5 & -15 +- 16 \\ hline
<average>   & +2 &+6&-25& +1&-35& +3& +5& -8& -3 &  -6 +- 14 \\hline
\end{tabular}
\caption{\sl The NIKHEF comb deviations, for several wedges, from a line defined by the corresponding Frascati wedges.
The NIKHEF comb numbering starts at the North side, the wedge numbering starts from East, $\Delta_Z>0$ means a shift in the West direction.  }
\label{ncombz}
\end{center}
\end{table}

\begin{table}[thb]
\begin{center}
\begin{tabular}{|ccccccccccc|} \hline
            &  \multicolumn{10}{c}{$\Delta_Y$ (\um)}   \\
            & 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9  & <average> \\ \hline
wedge20     & -2&-13& -6& -3&-11&-11&-12&-12&-14 &  -9 +- 4 \\ 
wedge62     & +8& +5& -3& +2& +1& +3&-10&-14&-11 &  -2 +- 7 \\ 
wedge68     &-24&-14& +3&-22& -5&-10& -1&-23&-18 & -13 +- 9 \\ \hline
<average>   &-6 &-7 &-2 &-8 &-5 &-6 &-8&-16&-14  & -8 +- 4 \\ \hline
\end{tabular}
\caption{\sl The NIKHEF comb deviations, for several wedges, from a line defined
 by the corresponding Frascati wedges.
The NIKHEF comb numbering starts at the North side, the wedge numbering starts f
rom East, $\Delta_Y>0$ means a shift up. }
\label{ncomby}
\end{center}
\end{table}

The largest deviation in $Z$ is 50~\um and in $Y$ we observed 24~\um. 

The heigth of the most outer NIKHEF combs with respect to the  granite table was also checked
with the slof. The results are listed in Table~\ref{combh}.
 The observed deviations are smaller than 20~\um.

The angle $A_Y$ is checked using laser optics and accurate within 500~\urad.
 The small deviations in $Y$ imply that the angle $A_Z$ is sufficiently small
 and needs no further check.


\subsection{ Sphere tower positioning}
The sphere towers will support the spacer during the gluing procedure and
so determine the wire positions between the several tube layers.
The towers are initially positioned  with an accuracy in the $Z$ direction of about 100~\um using standard optical tools. 

The alignement in $Y$ of the three refence towers is checked with
 the silicon sensor.
The results indicate that the middle tower with respect
 to a line defined by the $Y$ of the outer towers deviates by 
 -25~$\pm$~10~\um. The non
 reference side is checked in a similar way, which reveals the same deviation.
The intrinsic accuracy of these towers is does not allow such deviation,
 leading to the conclusion that the surface of the granite table, 
at the position of the towers, has deviations of the same order. We tried
to find more evidence, but to measure with this accuracy over 5~m is far from
trivial. However, (re)measurements with standard optical tools indeed
 suggest a negative deviation in heigth of the central towers.

The distance between the Frascati comb and its
corresponding reference tower is of large importance.
The difference between North and Sourth in this distance leads to an undesired
angle between the wires in the two multilayers.
The measurement of the relative distance is performed using the 'balmonitor', see Sec.~\ref{sbalmon}.
After initial measurements, showing large deviations, the distance is adjusted
by rotating the North sphere tower over its $Y$ axis. This adjusts effectively
the distance between tower and comb.

However, when the tower is rotated a problem may arise,
 The sphere holder on top of the tower is designed such that
it moves freely in the $X$ direction to absorb temperature expansions of the
spacer. We have to be sure that this movement over several millimeters
has no effect on the $Z$ (and $Y$) position. 

Figure~\ref{balmon} shows the result for the two lenses, in two orientations,
combined with the two forks.
We observe a deviation in $Z$ of about 10~\um. Deviation of the same order
are found in $Y$. The results for $Y$ are checked by measurements with the
slof.
The RASNIK-scale can vary 10\%, 
from the free movement of the sphere holders alone.  bla bla bla


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




All the measurements above convince us that the mechanics are
 positioned to high accuracy wrt to the granite table.
 The observed deviation using the silicon sensor indicate a 
(local) non-flatness of the granite table.

\section{RASAS calibration}
The RASAS system monitors the spacer position during the gluing procedure.
The specification for the accuracy is 10um, we aim at maximal 5um deviations for manipulations with the bare spacer. 
This leaves some space for other error sources during the gluing procedure.

To translate the RASNIK coordinates into our Global Coordinate System we have
to know the relative tranlation and rotation of the coordinate frames.
The RASAS towers accomodate the camera and lense, while the mask is housed in the ears of the outer xross plates. The optical axis points roughly into the
global X direction, RASNIK X and RASNIK Y point roughly in the global Z and Y direction respectively.
The rotation around the optical axis of the mask, $A_M$, has to be known with an accuracy such that $\sigma_{angle} arm = \sigma_{position}$. When we aim for a calibration error of 5um, with  the $arm$ to be the largest step size of 26mm, we obtain $\sigma_{angle} arm =5um/26mm=200urad$.
Other rotations are ignored; these effect the results only at the second order level. The construction of the RASAS towers and ears, guarantee that these rotations are comfortably small (<<25mrad).
The angle of the optical axis with respect to the global X axis in the global X-Y plane, $A_XY$, and X-Z plane, $A_XY$, has to be known to $\sigma_{angle}$ = 5\um/10mm=0.5mrad.
The coordinate transformation is now simplyfied and expressed in measurable quantities:
\begin{eqnarray}
 Z_G= X_R + Z_R A_XY +  Y_R A_M - X_offset \\
 Y_G= Y_R + Z_R A_XZ -  X_R A_M - Y_offset
\end{eqnarray}
where the suffix R and G represent the coordinate systems RASNIK and Global respectively.
Note that the CCD is treated as a point when the RASNIK X, Y coordinates are extracted. The CCD rotation has not entered these equations.

\subsection{Pre-calibration CCD rotation}
The rotation of the RASAS CCDs around the optical axis are measured using the special precalibration tower.
The RASAS- and precalibration tower is are put on a granite table such that the mask image is nicely projected on the CCD. The angle is measured by RASNIK to a high statistical accuracy. However, we observed that small  movements of the towers lead to large fluctuations of the measured angle. These systematic effects are not properly understood and therefore we assign an uncertainty to the precalibration of maximal 200urad corresponding to the size of these fluctuations.

\subsection{From RASNIK to Global coordinates}
To translate the RASNIK coordinates into our Global Coordinate System we 
have to determine the direction of the optical axis

The spacer is positioned in the central three stacking position and the RASAS system is read out. It provides the X, Y, Z=1/scale and rotation of the mask, relative to the CCD en lense system.  Note that the rotaion of the masks $A_M$ is now known to about 200urad (for the moment we ignore the positioning error of the RASAS towers on the granite table).
The direction of the optical axis, represented by the angles $A_XY$ and $A_XZ$, are determined by moving the masks in the RASNIK Z (Global X) direction. The uncertainty on $A_XY$ and $A_XZ$ is dominated by the uncertainty in the sphere tower orietation, see above.
In the relevant region the RASAS measurements, expressed in Global Coordinates, are precise to 10um.

\subsection{Grand fit and final Mask angles}
We can position the spacer in all orientations, such that all four RASAS-masks are viewed by the four RASAS towers. This provides information on the intercalibration of the mask angles.
In addition,  data obtained in all the stacking positions of the spacer contains information on the possible stacking block deviations  and provides information on the absolute calibration of the mask angles. 
We attempt to extract this information in a fit procedure using the RASAS X,Y and Z readings.

In the free parameters in the fit procedure are:
\begin{itemize}
\item the mask angles (4 param.),
\item the $Y$ deviations of the layer one and three stacking blocks ( 8 param.)
\item the $Z$ deviations of these blocks at the reference side (4 param.)
\end{itemize}

The residuals, see Table~\ref{gfit}, amount only a few microns, 
consistent with the expected stacking reproduction errors. 
\begin{table}[b]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
\put(0,0){\mbox{\epsfysize=10cm\epsffile{gfit.ps}}}
\end{picture}
\end{center}
\label{gfit}
\caption{\sl Results of the Grand Fit}
\end{table}

\begin{table}[b]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
\put(0,0){\mbox{\epsfysize=10cm\epsffile{amask.ps}}}
\end{picture}
\end{center}
\label{amask}
\caption{\sl Results of the Grand Fit}
\end{table}

\begin{table}[b]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
\put(0,0){\mbox{\epsfysize=10cm\epsffile{block.ps}}}
\end{picture}
\end{center}
\label{block}
\caption{\sl Results of the Grand Fit}
\end{table}

 





The resulting mask angles are lited in Table~\ref{amask}. The mask angles, determined in the fitting procedure, are compared to the initial angles determined from the
relative CCD-MASK angles provided by the RASAS systems and the precalibration of
the CCD angles.
We observe deviations, consistent with the systematic uncertainties of 200urad.

The block deviations are displayed in Table~\ref{block}. These deviations are below 10um as expected from the CNC measurements desribed in Section ??.



\section{Tubes on the combs}
The most relevant measurements concerning the combs,....tubes+silicon sensor

Guido laser









\begin{table}[thb]
\begin{center}
\begin{tabular}{|ccccc|} \hline
Component & X & Y & Z & Tool \\ \hline
Sphere towers & & 10um & 10um & CNC machine \\
Frascatie combs & 500um & 2um & 2um & CNC machine \\
NIKHEF combs & 500um & 20um & 20um & CNC machine \\
Granite &  & -25um &  & Silicon sensor\\ \hline
\end{tabular}
\caption{\sl }
\label{app}
\end{center}
\end{table}

Overview of the intrinsic deviations of the components of the alignement station.  The tool used in the measurmeent is also listed.

\begin{table}[thb]
\begin{center}
\begin{tabular}{|cccccc|} \hline
Component & With respect to & dX & dY & dZ & Tool \\ \hline
Middle Sphere tower & Outer towers & 1mm & 25+-10um & 50um & Silicon sensor \\
outer ref sphere towers & Frascati Combs & 500um & 10um & 10um & Balmonitor \\
 sphere towers & granite table &  & 10um &  & Slof \\
 sphere towers & combs &  & 10um &  & Slof \\
 Frascati combs & granite table &  & 10um &  & Slof \\
 outer NIKHEF combs & granite table &  & 10um &  & Slof \\
Fracati comb N & Frascati comb S& 500um & & & tape-measure, tube \\ 
Fracati comb & Global Z &  & &10um & Silicon sensor \\ 
Fracati comb & Global X & 100um & & & Laser+optics \\
NIKHEF combs & Frascati combs &  & 50um & 50um & Silicon sensor \\
NIKHEF combs & Global X & 200 &  &  & Laser optics \\
orientation sphere towers & Combs & (5mm)  & 10um & 10um & Balmonitor \\
Torque sphere towers & & & $<$20um & & Tilt-meter \\
Torque Frascati combs & & & $<$20um & & Tilt-meter \\ \hline
\end{tabular}
\caption{\sl }
\label{proc}
\end{center}
\end{table}


Overview of the alignement of the assembly station. All possible angular deviations have been transormed into the corresponding translations in X,Y or Z. The tool used in the measurmeent is also listed.

\input{jigs.tex}
\input{guido.tex}
\input{layer.tex}


\end{document}



 


