Re: microstep accuracy was what comprises as step

Mariss,

I decided to leave out the reduced torque per microstep, thinking it
would be belaboring the point...

Your last paragraph confirms my intent. But I'll re-state it in a way
that is clearer (I hope).

Microstepping does not improve the positional accuracy of the typical
cnc system for machining tools we discuss here on CCED. Unless your
motors are ten times too big<G>

At our typical speeds, masses, and inertias, the benefit of
microstepping is mostly in smoothness. For most of our machines,
stick-slip will "eat" most of the micro-steps. As I said before, this
is not a new thing. Problem has been, much of the "precision" info
coming re: microsteppping steppers is related to arenas where it DOES
work: in things like semiconductor foundry machinery, with granite
tables, air bearings, and LOTS of dollars to spend.

Finally, I will add that this is not intended to cast doubt on the
gecko drives. I am quite sure that Mariss has designed them well.
This is just a reminder to consider that physics still rules.

Ballendo

P.S. I didn't know that the "square" motors had been re-designed
generally to support microstepping accuracy; phase currents vis a vis
shaft angle. Thank you.

--- In CAD_CAM_EDM_DRO@y..., "mariss92705" <mariss92705@y...> wrote:
> Hi,
>
> Actually microstepping does improve positional accuracy within
> certain constraints. As mentioned, a typical motor has a +/- 5% non-
> accumulative error. This means any step is within a 10% error band
of
> where you would expect it to be. This alo happens to mean a motor
has
> an overall accuracy of 1 part out of 2,000 or 1/10 of a full step.
>
> Many new "square" motors are linear (sin/cos angle vs. motor
> position) within 1%. This means the measured position is within 1%
of
> where it is predicted to be. Paricularly good motors in this
respect
> are the Vexta PK series, Sanyo Denki 103 series and PacSci M31
series
> among others.
>
> What limits the usefulness of this accuracy is the amount of torque
> required to move the motor off-position. At 10 microsteps/ step
this
> is about 10% of the motor's holding torque. At 100 microsteps/step
it
> would take 1% of the holding torque to move it off position 1
> microstep.
>
> Mariss
>
>
> --- In CAD_CAM_EDM_DRO@y..., "ballendo" <ballendo@y...> wrote:
> > Dave,
> >
> > Unless the motor, drive, and machine are matched you DO NOT get
> > increased "positional accuracy" from a microstep drive.
> >
> > What you get is smoothness. Quietly. Positional accuracy of any
> > stepper is limited by the construction of the motor, which is
> > typically rated as expecting any FULL step to be within 3% of
> where
> > it "should" be... And many motors are 5%.
> >
> > Hi-end microstepper systems used in um positioning are carefully
> > designed, made, matched, and integrated all the way through the
> > design process. Just changing the sin/cos values of the winding
> > current(s) to make smaller steps is not enough. Magnetic position
> is
> > not always(often) the same as the mathematical model would have
us
> > believe.
> >
> > You're damp, but so are a lot of others on this subject<G>.
> >
> > Hope this helps,
> >
> > Ballendo
> >
> >
> > --- In CAD_CAM_EDM_DRO@y..., "dave_ace_me" <davemucha@j...> wrote:
> > <Snip>
> > >If I am not mistaken, the Gecko uses a micro step and breaks
that
> > >into 10 parts of a step or 1/10 step per pulse. This would mean
> > >that it would drive a stepper 10 times slower, but with 10 times
> the
> > >positioning accuracy of a full step drive.
> > <snip>
> > > leadscrew revolutions per stepper revolution, but by using the
> > Gecko,the same leadscrew speed would be achieved, AND the same
> > positional accuracy would be had.
> > <snip>
> > >Am I right on or all wet ? (or maybe just a little damp?)
> > >
> > >
> > > Dave