-------- Original Message --------
Subject: Re: Review of Support Structure Design
Date: Wed, 29 Sep 2004 13:19:05 -0400
From: Kevan Hashemi
To: Werner Riegler
References: <99E508F423BD2147B22B2D3044BE3D80412F34@cernxchg18.cern.ch>
Dear Werner,
> In the attachment you find a few spaceframe pictures and a picture of
> the mounting plate. There is also an e-drawing of the baseplate, so
> you can find all dimensions of it.
Thank you for your drawings and specifications. I will see if we can
read the e-drawing with our new Mac OS X drafting program.
> The monitoring system will be installed on the outer Ringe of the
> spaceframe (front and back). The distance between the 'crossing of
> the neutral line' of the bars is 1.3m. The lens of the BCAM is at a
> distance of 20cm from this point, so the distance between the BCAM
> lenses is 90cm.
At which distance the dynamic range in the vertical direction (radial
and azimuthal) is 40 mrad x 0.9 m = 36 mm. In the polar direction it's
30 mrad x 0.9 m = 27 mm.
> For the discussion of the field of view you can use the mini review
> you did already for us.
Thank you for reminding me of that. I just dug it out of my archive.
> When the spaceframe is deformed this distance changes by a maximum of
> 0.1mm, so for our purpose we assume the distance to be constant and
> we just have to measure angles in order to find the absolute position
> of the spacefram points.
So, range is constant, and we have deformations taking place mainly in
directions perpendicular to the line of sight.
> Our goals is to know the position of these points to <0.5mm.
Is this correct:
(1) You survey the frame with cameras and surveying targets. By this
means you get the position of all points to 0.3 mm (I know they claim
better, but Christoph has determined that their actual accuracy is
closer to 0.3 mm).
(2) You record the BCAM measurements from all BCAMs and associate these
measurments with the surveyed point positions.
(3) You track deformations using ARAMYS and changes in BCAM measurements.
(4) You hope to track changes to 0.3 mm, so that your combined surveying
and tracking error comes to 0.5 mm.
> The BCAMs will measure the inner angles of the regular 18gon which
> are 160 degrees nominal.
(5) We can estimate the tracking error by accumulating BCAM relative
angle measurments in the internal angles of the 18-gon.
> For full loading condition of the spaceframe we expect a change of
> +-2mRad, for worst case loading conditions we expect -+4mRad.
This, I believe is in the vertical direction, not in the horizontal.
Please confirm, because if your movements are in both directions, you
need to know the rotation of the CCD with respect to its mounting balls
(as we discussed at CERN).
> So -- that's it in very short -- tell me if you need more details.
It's a good start.
Yours, Kevan