Re: [ATM] LWT setup questions

["Don Clement" <clement.focuser@verizon.net>]

Nils,



> I have tried the LWT test with a remote-controlled setup:
> http://web.telia.com/~u41105032/tester/tester.htm
> and with a manually controled one - a 200 mm arm moved by a micrometer,
and
> a 20 mm arm from the pivot (ball bearings from a butchered hard disk) to
the
> "wire" (a thin scratch on plexiglass).
> The latter failed entirely to give reproducible meaningful results, and I
am
> convinced it is because with my setup it was impossible to adjust the
> micrometer manually, without inadvertently moving the whole tester some
> microns each time I touched it.

I would suggest replacing ball bearings with stiction-free flexure pivots
and using a bowed flexure for moving the "wire". Compliant flexure type
mechanisms will give higher precision and the more reproducible results than
ball bearing type mechanisms.

 I received this message from a customer for whom I made a moving mirror
focuser for recently:

" Don,
The focuser arrived. I have completed measurements of its performance and am
pleased to report that I need an interferometer to measure the errors. The
tilt over the entire 1.4" travel is on the order of 50 fringes over 10".
This is absolutely exceptional! ."

All bearings for the moving mirror focuser were flexural hinges with a
single manually controlled, compliantly mounted non-rotating leadscrew
(micrometer) for positioning.



Don Clement

Running Springs, California



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