Re: Servo-PWM-DSP

PTENGIN@... wrote:

> From: PTENGIN@...
>
> In a message dated 09/10/1999 2:50:03 PM Hawaiian Standard Time,
> dhowland@... writes:
>
> << and some discussions I've read suggust that you can tell by looking at the
> tooled part if a CNC system was controlled by a stepper based or servo based
> controller. >>
>
> Dave,
> I have cut many parts on both stepper and servo based systems. I know
> speed is the biggest difference, the slowest servo system I've played with
> moved at 300 inches a min on a G0. In terms of part quality, I think many
> more economy machines were built with steppers. Thus the base machine is
> often not as stiff or backlash free as you would desire. Given the same basic
> frame of a Bridgeport sized mill, I think one would not be able to tell the
> difference in part quality if they were both setup properly.

The problem here is that all stepper systems have an inherent tradeoff between
top rapid speed and step size. If the steps are made very fine, then the top
speed will almost certainly have to be reduced. My servo system has a
resolution of .00005" for X and Y, and a resolution of .000025" on the Z.
It uses 1000-cycle encoders, giving 4000 counts/rev, and .2" leadscrews
for X and Y, and a .1" leadscrew on the Z axis.

Jon