rotations piezo system

i have cheked those products, but it seams that they can not reach a precision of 2 microradians.

I have contacted some manufacturers asking for a custom made solution. In any case, in my opinion the best solution is based on piezo system.

I have found this:

Andrea

this:

I wish I could find the information on the device I read about. If I remember it used a cascade of stages in one unit to achieve high precision. I hope you will write about your application and success with your project for us curious critters.

this:

I may be able to help you...

Renishaw make some very high precision angle encoders. In terms of resolution, we can offer products with resolutions to 0.005 arc seconds (that's 0.024 micro radians in real money). The question is... do you need 2 microradians resolution, or 2 microradians accuracy? Renishaw can help you with either case. If you need the former, then we can achieve that quite easily with a variety of different ring encoder products (take a look at renishaw.com and go to position encoders, then select angle encoders). RESR and SiGNUM will both be able to achieve that resolution - just select a ring size that fits and go to the resolution table in the product datasheet (also on-line) for the correct interpolation rate. If you need 2 microradians accuracy, then things get a little more tricky. There is a new product called REXM that offers very high accuracy. The product is specified to +/- 1 arc second total installed accuracy (+/- 4.8 micro radians), but they are actually a lot better than that. If you choose one of the larger ring sizes (300 mm +), the ring will achieve +/- 2 micro radians total installed accuracy. To give you a guide, 183 mm rings are specified at +/- 1 arc second total installed accuracy, but actually typically achieve +/- 0.22 arc seconds.

The REXM is designed for use with two readheads. We make a box called DSi that takes the signals from two heads and combines them so it appears as one very high accuracy encoder.

If you need to work with a smaller ring, you could use correspondingly more readheads and still achieve the required accuracy, but you will have to average the counts inside your controller. If you want the really highest accuracy, then you can use as many heads as you can fit around the ring. When you use a lot of readheads, the limiting factor on an encoder will be the sub-divisional error (sometimes called the "interpolation error" or "cyclic error"). This is the error within one scale period, so it will not be compensated by multiple readheads. Renishaw's SiGNUM encoder has just 30 nm sub-divisional error, compared to 200 nm for competitor products.

One final thing to mention... to get this level of accuracy, you really need to use a modular encoder. Using an enclosed encoder that has its own integral bearing will not work because the coupling errors will take up your entire error budget.

If you have any other questions, please let me know.

Best regards,

Corrie.

this:

Thanks, but it is Andrea who is looking for the encoder and

I saw that Renishaw manufactures an optical encoder that utilizes more than one pickup on the same encoder ring and that is the unit I thought would work for Andrea.

These guys make all sorts of stuff

Or these

But 2 µrad is pretty steep, or should we say, shallow.

robert

this:

Thanks for the reply. Sorry, I meant to reply to Andrea, but I'm new to this Google groups thing and screwed it up!!! Andrea has contacted me directly by e-mail and I've pointed her in the direction of some controller cards to go with the encoder. Many thanks again for the recommendation. I appreciate your help.

Corrie.

this:

I'm glad to share my limited intelligence, all my brain cells aren't dead yet. As a kid I was always getting into trouble for taking something apart to see how it worked. Things like the radio, lawnmower, the neighbor's cat, etc......

solution.

system.

this:

Had a turtle, saw a cartoon were the turtle took off it's shell and ran around, tried it, the turtle died. Little Monster.

solution.

system.

this:

And you grew up to be a medical examiner.