"Richard J Kinch" wrote in message
. ..

http://www.embedded.com/2000/0010/0010feat3.htm

Thanks for that. It explains the control problem quite well.

So, taking all that was said before, I take it the 320 solves to the
commanded position by controlling the servo's speed. An evenly spaced step
pulse train results in smooth movement at the target speed, which settles in
quickly if the gains are adjusted correctly. The smooth movement doesn't
suffer from a stepper's herky jerky motion, and is thus immune from the
related stepper resonance issues. The discrete nature of the step pulses and
the encoder stream would seem to be inherently noisy, but is easily averaged
out in steady state motion. OTOH, acceleration and deceleration would seem
strongly dependent on the controller being able to maintain sync, rather
than solely on the motor's available torque as is the case with a stepper. I
don't know how big the difference is, or if it's even measurable or
objectionable in CNC use.

So, how much can I expect to pay for a 400 oz-in servo?