Re: Balancing drivers to motors

The Parker OEM 650, and OEM750 to the best of my knowledge, has the
option

>of varying the wave form from a pure sine wave to a negative percent

of the

>third harmonic. In addition, there are tuning instructions for Phase

B,

>and Phase A offsets via trim pots. This coupled with the

Microstepping

>ability of the driver up to 50,800 steps/Rev are leaving me some what
>confused.

I would bet this functionality is to get the motor to perform better
at a specific RPM (like a tuned pipe for a race car). I would guess
that for some applications you can really bring up the torque at the
higher RPM's or really get the RPM's up there out of normal stepper
ranges.

For your application I would leave them alone.

Thanks
Aaron Moss
www.IndustrialHobbies.com

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
>
>
> Don Rogers wrote:
>
> >I've been following this group for almost a year now and it has
been a
> >wealth of information.
> >
> >I have put together a Taig CNC mill. I am using Parker Compumotor
OEM 650
> >drivers, and Pacific Scientific Powermax II M22 motors on X, Y,
and Z, and
> >a M21 in reserve for A. My interface to the mill is TurboCNC. I
have
> >varied the acceleration and max speeds to the point that I can
either make
> >a 0.0005" move or a 10.000" move and both are dead on with the
dial
> >indicator after repeated moves.
> >
> >The Parker OEM 650, and OEM750 to the best of my knowledge, has
the option
> >of varying the wave form from a pure sine wave to a negative
percent of the
> >third harmonic. In addition, there are tuning instructions for
Phase B,
> >and Phase A offsets via trim pots. This coupled with the
Microstepping
> >ability of the driver up to 50,800 steps/Rev are leaving me some
what
> >confused. The old mechanic in me the said "if it ain't broke,
don't fix
> >it" is clashing with the thought "if I tweaked this, it might be
better".
> >
> >
> There is a fallacy in thinking that these motors can actually MOVE
in
> increments
> of 1/50800 of a rotation. Just because the driver can produce
drive
> waveforms
> that split full steps to this resolution doesn't mean that the
motor can
> move
> with such fine resolution, or that it maintains such precision
under
> varying loads.
>
> You might do some experiments with it, such as making extremely
small
> moves, and using a dial indicator to detect when it "jumps". I can
almost
> guarantee that it will jump in small increments, perhaps from a few
tenths
> to something approaching a thousandth of an inch, when you have the
> program "creeping" in the smallest increments it can. In other
words, if
> you make moves of one microstep at a time, the machine will not
move at
> each microstep, but will suddenly jump many microsteps, when the
increasing
> force developed by the motor overcomes the static friction.
>
> >I have yet to do very much constructive work with the mill, but
what I have
> >done so far seems to work well. I have got the backlash down to
less than
> >0.001" and the ways are tight, but not binding. The X will track
to less
> >than 0.001" full left to full right. The Y is dead on, and I
still need to
> >do some tuning on the Z, but overall it is ready to cut.
> >
> >My question is about the waveform shape setup, and the Phase A and
Phase B
> >offsets. So far, I have been leaving them to whatever the factory
defaults
> >were, or in the case of the offsets, what ever they were set to
when I got
> >the drivers. Is there some tuning that I should do or should I
follow the
> >"if it ain't broke don't fix it" rule?
> >
> >
> I suspect you don't have the instruments to make these alignments.
They
> probably
> use a super precise encoder to measure extremely small angular
movements of
> the shaft, and adjust the drive waveforms to minimize cyclical
error within
> the steps. This would require angular resolution down to the tens
of
> arc seconds,
> but would be meaningless when frictional loads are added.
>
> Jon