Re: G320s, New and Improved!

Jon,

It dithers in the absence of a tach simply because there is no
feedback from the encoder except on the edges. A PID servo has no
other option because of the integrator term.

My solution is to knock the proportional and differential co-
efficients (gain and damping) down to 5% of set value when the servo
is within +/- 2 counts of the command position. The interal co-
efficient is dominant within this range, so this is very effective.

Most inexpensive motors are not equipped with tachs, so it tells you
which way technology is trending these days. Though not perfect, a
motor and encoder sans tach gets you within 99.9% of perfect with a
modern drive.

Mariss

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> cadcamcenter@y... wrote:
>
> >
> > > First off there is virtually no dither noise. I do have one axis
> > that you
> > > can hear the motor shift back and forth very slightly and at a
very
> > slow
> > > rate (maybe one or two cycles per second) when it is stopped in
> > certain
> > > positions. There is absolutely no humming noise that I used to
get
> > on the
> > > old G320's.
> >
> > The presence of dither means that the servo is always seeking
> > the "correct" position means that servo is always overcorrecting,
> > then undercorrecting. Re: the old servo vs stepper "controversy".
>
> It can be argued that any servo which dithers with no other input
is not
> properly tuned. I can say that my servos do NOT dither, except
under
> very rare circumstances when a mechanical resonance has been
excited.
> That, in itself, is indication that I could tune it better, but it
is very
> much
> "Good Enough".