Re: Servo torque requirements

on 2004-11-25 17:36:36 UTC

Well, after more consideration and a little more time to think about it...

I still seem to be as lost as before. I have a little more clear idea of what I want to do now,
so here we go...

- I am designing a 3 axis (for now) mill which will be used for machining small primarily
aluminum, but occasionally harder (likely inconel) parts.

- I will be using a cast iron table measuring 9x18"

- My spindle is yet undecided, but will either be an R-8 mini-mill spindle, or a modified
Sherline unit.

- I am using TKH LM Guides on all axis.

- 3 Parker Compumotor SM232B-N-FL-N Servos (1000 line encoders)
http://www.compumotor.com/literature/pdf/pg190_sm_sz23_encdr.pdf

- I think that I'm looking for around 300ipm max traverse rate but any feedback would be
great from you guys.

- I had originally planned to use the servos directly mounted to ground ballscrews. I have
one ballscrew with 8mm pitch, but decided to do a little research before buying any more.

- I will be using a PC based controller most likely with EMC. I think this is where the loop
gets closed.

- I would like to use the Parker Compumotor OEM770T Drivers for the Servos. They are
designed to operate together and I can pick them up reasonable cheap.
http://www.compumotor.com/manuals/OEM770T/0_OEM770T_Rev_A_Entire.pdf

Now, here's my dilemma. I want to produce parts for model gas turbines, so the ability to
work inconel will be a must. However, precision is a must. I have looked at some 4mm
lead ballscrews, but I still wonder what sort of feed rate I can get.

I think the thing that I'm getting most confused about is how to figure out what my feed
rates will be limited to. Now, I understand that most cards, such as ServoToGo or Vigilant
use some sort of quadrature something in processing the encoder signal. What confuses
me is that if a card says that it can handle PID bandwidth of 20KHz, does that mean that I
can only drive my servo at (1000lines x 4) = 4000 ----> 20000/4000=5 rev per second
or 300RPM? Somehow, I think I'm way off on this. Help!?

Discussion Thread