Re: Low cost Servo Controller

Les Watts wrote:

On the structural stuff, I guess you won't know until you get the whole machine assembled,
and then gauge the deflections or just make something and check the part.

> I would like to learn what the best controls will allow as far as high speed performance. My lm628
> software was tested with a small xyz voice coil driven machine and the very best I can do (following
> tech80 advice) is 1000 microsecond trajectory updates. If EMC can do 200 microsecond servo
> updates I would think one could go 5 times faster or one fifth following error given the proper
> amp and encoder. Perhaps even better considering feedforward.

I have been told that EMC has been run on modest Pentium processors (around 100 MHz)
up to 100 uS servo loops. The default is 500 uS (2 KHz). I have been running at 1 KHz
with a 100 MHz Pentium Classic, but could go higher. One problem with running very high
servo update rates is that you have to tune very carefully to avoid high frequency resonances,
such as torsional modes in the leadscrews. Since the torsional natural frequency varies as
the length between the motor and nut changes, it could be tricky to damp that out.

Jon