rotations piezo system

How far and how fast do you need to go?

Cheers,

Phil Hobbs

I bet a microstepping stepper motor and a toothed-belt reducer, or a little gearbox, could get into that ballpark. We did that, driving a ball screw thing, and got nice 90 nm steps.

John

And how big is the thing you need to rotate, and what's its moment of inertia?

Will a harmonic drive give you that level of precision?

Just curious but do you know why those things are so expensive? I know there is an ego tax but is there anything in the device itself that actually costs a significant portion of the price? (They seem to try and stick it to you if your just interested in 1 piece)

Microstepping drive will give small steps, but the actual precision is still limited by the nonsinusoidal profile of the pole fields in the stepper motor. Whether that's good enough will depend on the OP's application. Two microradians is less than half an arc second, so I'd also be worried about gear backlash and belt stretching. It's fairly rare to want an open-loop rotation stage to have that kind of resolution--22 bits' worth for a full turn--so I suspect that a much narrower range would be OK.

Settability of that order is much easier to get than accuracy of that order, but it's still very hard to guarantee if bearings are involved. It really doesn't take much of a surface irregularity to give you a dead zone of a five-millionth of a rotation.

Cheers,

Phil Hobbs

I'm curious here, what's the spec on "hard drives"?

Why I'm asking, is that perhaps a magnetizable disc could write a magetic bit and use that to rotate the disc, then degauss (remove) the bit. Ken

All true.

There are some very elegant, and small and cheap, servo motor-encoder-leadscrew things designed to focus microscopes, and they're very good. If the op can live with just a small segment of 360 degrees rotation, one of these and a loaded linkage would probably work nicely.

John

i need to make rotations of not more 5 milli-radiants, at steps of 2 micro-radiants. Speed is not important.

Best regards, Andrea

how do you translate those 90nm into rotational angle ? Which are dimension of the sytem you developed ?

Best regards, Andrea

could you give me more informations on those products ? Any brand ? Where to find them ?

Many thanks, Andrea

The final output was linear translation. We used a stepper motor, a toothed-belt reducer, and a recirculating-ball lead screw. The whole assembly was about a foot high. We measured it with an LVDT and got distinct 90 nM steps. It was for one of those huge segmented-mirror telescopes, but we didn't get the job. It was fun, anyhow.

It's around here somewhere. I'll post a pic if I can find it.

What is your project about?

John

I think we are speaking of two different things: i'm interested to rotational movements, not linear.

btw, congratulations for your good result.

Cheers, Andrea

how do you translate those 90nm into rotational angle ? Which are dimension of the sytem you developed ?

Best regards, Andrea

i need to make rotations of not more 5 milli-radiants, at steps of 2 micro-radiants. Speed is not important.

Best regards, Andrea

Looks like lots of people make these...

google "microscope focus servo" or such for more.

You could do piezo, too, inchworm or something.

Does it have to be motorized? You can do some outrageous manual stuff with a machinist's micrometer head and some linkages.

John

No clue here -- perhaps they have to sacrifice virgins?

Well s*it... then it should be cheaper?

As someone may already have suggesed, try asking at alt.lasers

Piezo translation / rotation transducers are routinely used for beam steering / focusing and other stuff those guys do. There are quite a few manufacturers of these things- too long ago for me to remember - sorry!