From: "Tom Krajci" 
To: 
Reply-To: "Tom Krajci" 


From: IAPDK{at}ADMIN.DRAKE.EDU

>I looked over your pages on the 12-point cell and it was very helpful
in
>making me understand how these large-N cells are designed, there is
just
>one aspect that you might consider - the collimation supports.

>In all your designs you identify the three underlying supports as the
>"collimation bolts".  It is not necessary that these three points
co-exist
>with the collimation mechanism.  In the latest incarnation of my 8-inch
>cell I put the collimation bolts outside the mirror circle such that
the
>adjustment thumbscrews are above the cell floor.  The old way with the
>bolts underneath the mirror required the cell to be raised so that the
>bolts could clear the rocker base.  Putting the bolts completely above
>the base and moving the springs out from under the mirror allowed me
>to lower the mirror an inch or so and reduce counterweighting.  The
>effect would be much greater with a large mirror.

Good points!  Got any diagrams of photos of this setup?  I certainly have
not exhausted the possibilities of where to put the collimation bolts.

>Earlier you described mirror slop created by running a bolt through
>a wide hole in the cell.  I drilled two 3/8" acorn nuts, threaded
>them to fit the thumbscrews, and screwed them up to the thumbs.  Now
>the ball of each acorn sits partially down in the hole of the cell
>and there is no slop.

Yes, but there is still stiction/static friction.  I'm leaning toward use
of compliant hinges as much as possible.  I think I know what I want to do
for the hinges in this regard.  Now I need to kick around more ideas on the
collimation/axial motion control issue.  The way I see it there are two
tasks:

1.  Move the cell up/back axially
2.  Constrain the motion to only be axial motion

In the typical amateur cell the threaded rod does both tasks...but with
some slop, so task 2 is not performed very well.  In the compliant cells
from Clement and Owens the compliant hinges constrain the motion very well(
task 2), and the lead screw/micrometer head performs task 1.

Because my design is for an unattended-use CCD imaging system...I need
tighter tolerances than the typical visual-only scope.  I may need to use
two devices to perform the two tasks I've listed above.  I've got some
thinking to do this weekend.

All feedback is appreciated!

Tom Krajci
Tashkent, Uzbekistan


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