Re: [CAD_CAM_EDM_DRO] a tiny servo motor and re: killing those darn germs

Elliot Burke wrote:

>
> What the heck, mercury itself was used as a germicidal agent for centuries.
> Probably best to keep it way from cutting fluids.

Yeah, the old style "Bag Balm" had a Hg comp'd as the active ingredient.
Hg in cutting fluids would definitely be a no no for legally disposing of the used fluid.

>
>
> There was a technology described a few years ago where a TiO2 layer
> (powder?) would be "activiated" by UV and be germicidal for long periods of
> time. Has anyone heard anything about this?

Cute if it works. Had not heard of this but I don't keep up with the literature.

>
>
> The tiny motor is from a hard drive. The motor is a voice coil sort of
> thing, with a ball bearing to constrain motion to an arc. I'm going to use
> it to drive the reference mirror in an interferometer.
>
> The problem is, my desired sensitivity of motion is 0.05 micron, and the
> range of motion desired is about 5 mm. Since the motor position will be
> linearly related to the current, current needs to be controled to about 10
> ppm. Bandwidth can be pretty small, 100 Hz is OK. This is close to what a
> 16 bit DAC can theoretically do (2^-16 = 15 ppm), so that's where I'll
> probably start.

The dac's on Jon's ppmc board are 16 bit. BTW - are you familiar with LM12's ( I think that is the right part # )
Nice low voltage linear amps. 25 V 10 A. Good distortion figures.

>
>
> Has anyone tried to use all the bits of a 16 bit DAC?
> Can I use a cheap DAC card to get this sort of precision?

Good, fast, cheap....pick any two. :-)

>
> A really off the wall technique would be to synchronously modulate both
> stereo outputs from a computer, run them into a differential amplifier to
> drive the voice coil. If perfectly balanced the difference should be zero.
> The degree of balance between the output levels could then by shifted (by
> software) to generate different DC or low frequency output levels.
>
> Any other ideas for making precision low frequency outputs from computer
> control?
>
> Plan B involves using a laser interferometer to measure the mirror position
> and servoing the quadrature fringe signals.

The fringe signals might be the easier way to go. Just do a nice job of linearly driving the VC and then sense (on the fly) where
you are.

My line of thinking leads me from this to FTIR.....so what is your application?

A most intriguing project. Best of luck...

I still have a couple of 2 x 2 gratings around here that are supposed to find their way into a Czerny-Turner one of these days.
(years).

Dave

>
> Elliot Burke
>