Questions on choosing a rotary stage 7

[brdf]

Hi...

Do you guys happen to know any good rotary stages that would work in the vertical plane? I searched Physics Instrument, Zaber and New Port etc. but mostly they only specify a maximum load weight so I assume they would only work well in the horizontal plane.

I am designing an automated "goniometer" to make optical scattering measurement. The key part is an aluminum BAR1 carrying a small optical tube assembly (telescope) pointing at ground to collect scattered light. Let X and Y be Cartesian coordinate in horizontal and Z along the vertical up (X cross Y = Z), then BAR1 will rotate around axis-Y in the X-Z plane and my telescope will always point to X=Y=Z=0. Let Theta be the angle the BAR1 makes with axis-Z, and my measurement would require Theta ranges from (-80, 80) deg., with angular resolution about 0.05 deg. Such a configuration would require a rotary stage working in the vertical plane (X-Z) with a load up to ~80Nm (I can add some counter-weight to reduce the torque caused by BAR1's weight and its telescope).

I would be very grateful for your suggestions/recommendations on the followings:
(1) a rotary stage working in vertical plane with angular resolution ~0.05 deg. and a torque load of ~80 Nm;
my BAR1 rotating speed doesn't need to be too fast (b/c I need to record scattering at each desired annular position), e.g., 0.1 deg/s; so worm gear is a good idea?
(2) as the whole optical system would be sitting on one whole bench, for the motor the quieter the better. Should I choose a DC servo or a stepper?
(3) to prevent BAR1 from hitting my incident optics (BAR2 fixed at another angle between (-80, 80) deg), what possible mechanism would be best?

Many thanks!

 

[brdf]

yes Ellipsometer! That's almost exactly what I want to build but with longer arms and finer angular viewing steps. I guess if I could google out some good ellipsometer designs that would make my life simpler...

Harold: IRstuff already answered the fixed position question, here are something more; indeed some designs of the BRDF instrument do use fixed viewing positions; for example, if we can fix many viewing fibers (on a dome for example) all pointing to the sample surface collecting the scattered radiance, no moving parts would be needed (isn't that nice?); an example instrument can be found here:

http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-39-33-6197

However, such a design is usually for faster field instrument when higher angular resolution is not needed (remember the angular resolution is determined by the ratio of the aperture stop diameter to the distance to sample surface); if one wants to look at some subtle angular structures such as the rainbow (by transparent and spherical grains), a much finer angular step would be desired.

As for why a horizontal sample surface: I will be mostly dealing with particulate samples: sand, soil, volcanic ashes.... i.e., a packed surface will be measured. If only air-suspended particles (e.g., aerosol jet) are desired, a horizontal gonio layout would suffice, see e.g.:
1.

http://www.opticsinfobase.org/ao/abstract.cfm?id=67710

2. "Experimental determination of scattering matrices of dust particles at visible wavelengths: The IAA light scattering apparatus
Munoz et al
Journal of Quantitative Spectroscopy and Radiative Transfer
Volume 111, Issue 1, January 2010, Pages 187-196

Cheers!

 

[IRstuff]

This Woollam brochure has a nice picture of the version that Harold envisioned on page 6:

http://www.jawoollam.com/pdf/VASEBrochure2007.pdf

But, you can see how that might work with the sample horizontal, and you would need to have the stationary bases of the rotary stages on either side of the sample, and the viewer and source outboard on their arms.

TTFN

FAQ731-376