Control.com - Nerds in Control

I am working on a magnetic levitation system which uses an electromagnet and optical sensors to suspend a ball in air. I am willing to use a DSP or UNAC controller but first i need some help finding out the minimum sampling rate for the system to work.

Does anybody have good references or any advice on that, i have some background in electrical engineering bu am a beginner in the field of control.

Thanks a lot,

Nathan

Magnetism is highly separation dependednt, so
you'll need extremely quick responses! If you're
a beginner, I'd suggest you work on a different
project - maybe using a column of air, blowing
out of a vacuum cleaner?

Nathan,

I can probably help you with this. I have built just such a device (as many students have), and I have worked on the controllers for several "real-world" maglev systems (stages for semiconductor photolithography).

For any control system, the sample rate is related to the closed-loop control bandwidth (there are other considerations, but this is the primary one for your system, in my opinion). If you can set the sample rate to 10-30 times the control bandwidth, everything will be pretty easy. You can get by with less, but there's no real reason to in this case.

Since this system is inherently unstable, the closed-loop bandwidth has a lower limit which is set by the time constant of this instability. This is determined by the size of your suspended mass, your actuator, etc. When you work out your control design, you'll see what I mean.

If this thing is just a small demonstration unit, a closed-loop bandwidth in the neighborhood of 10-50Hz is probably reasonable, so a sample rate of 1kHz should be more than sufficient. If it's something very large or very small, these numbers may not be "in the ballpark". I don't know what a UNAC controller is, but a DSP can handle this easily (I've done it at 1kHz with a 68000 before).

If you're having trouble getting started with the analysis, several textbooks use this as an example. Two that are in front of me at the moment are:

"Control System Design Using MATLAB", B. Shahian, M. Hassul, 1993, Prentice Hall

"Feedback Control of Dynamic Systems", G. F. Franklin, J. D. Powell, A. Emami-Naeini, 1987, Addison Wesley (I have the first edition, but there are several later editions.)

Good luck,
Tony Smith

You might want to check Shaum's "Feedback & Control Systems". It provides a good starting point in control & feedback theory.
Good luck.

I hope u will find good information on this guy site


http://eewww.eng.ohio-state.edu/~geminp/projects/proje cts.html


good luck

ok i m the student of computer information system engineering but i have done this project in my micro processor based system design i found it very difficult although upto some extent tht is done but unfortunately tht was left uncompleted I m interested in tht too. if u r interested lets do tht combine. ok
my e mail address is daniu16@hotmail.com