TASS [shutter]

[Tom Droege <droege@FNAL.GOV>]

I spent a good part of the weekend working on the shutter for the 
Mark IV.  The little model airplane servo really works great.  Easy
to control from digital logic.  The scheme is to have a long plate 
with a hole in it.  Move hole from left to right over the CCD to
open.  Continue moving right to close and end the exposure.  Next 
exposure make similar moves left.  This has the advantage that all
areas of the window are equally exposed.  

I found a nice linkage to couple the rotary motion of the servo to
the linear motion of the shutter.  Works very freely (if I keep away
from aluminum to aluminum sliding contact).

The problem is the inertia of the shutter.  That little servo really
gets the shutter moving and it wants to stay moving.  I am presently
using a brass (0.012") shutter because aluminum likes to stick when
it runs on aluminum.  Sigh!  I will end up doing materials research
before I am done.  My next try will probably be a brass foam 
sandwich.  Hmmmm!  I think I will try a brass (say 0.001" brass)
balsa wood sandwich.

The alternative is to just slow it down with software.  Little steps
work fine.  Arne, I know how your camera works, but it takes two motors
(or solenoids) to drive it.  Still trying to do it with one.

This scheme takes a lot of space.  I my yet go back to the parlor door
scheme since it is compact, and give up on the uniformity for short 
exposures. 

Tom Droege