RE: [CAD_CAM_EDM_DRO] Re: Microstepping thru the Tulips

I'm with Phil on this.
To restate; at that time where the step rate becomes a single digit fraction
of the PWM freq or chop off time, the PWM is probably at 100% or the chopper
is never cutting in. So there is no way to microstep.

None of this is a problem though as the rotational inertia of the motor+
screw smooths things out nicely.
It does, however, highlight the validity of the generalisation that
microstepping isn't a precision improving technique. It's a low to mid speed
smoothing thing.

PK


_____

From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Phil Mattison
Sent: Tuesday, 15 August 2006 11:19 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Re: Microstepping thru the Tulips



Again, these traces illustrate my point, which is that when the step rate
gets to the point where the inductive phase shift of the motor winding
dominates the period during which the winding is energized, the chopper
simply turns off once during that phase, in effect acting like a single-step
driver. It doesn't matter at that point how many microsteps are processed,
the motor never sees them.
--
Phil Mattison
http://www.ohmikron <http://www.ohmikron.com/> .com/

----- Original Message -----
From: Mariss Freimanis <mariss92705@ <mailto:mariss92705%40yahoo.com>
yahoo.com>
To: <CAD_CAM_EDM_ <mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>
DRO@yahoogroups.com>
Sent: Monday, August 14, 2006 5:39 PM
Subject: [CAD_CAM_EDM_DRO] Re: Microstepping thru the Tulips

> Hi,
>
> For everyone who is interested in this thread, I took 8 scope pics of
> winding currents for a 3.9A/phase motor operated at 24VDC.
>
> The motor pics were taken at 3.75 RPM, 15 RPM, 150 RPM, 375 RPM, 750
> RPM, 1500 RPM, 3750 RPM and 7500 RPM.
>
> Yes, that's right, 7,500 RPM at 24VDC for a 3.9A NEMA-23 motor.
> That's 250,000 microsteps per second. That step pulse frequency IS
> 12.5 times higher than the 20kHz PWM switching of the drive. See how
> it all works, makes sense and doesn't violate any known law of
> physics.
>
> Please go to the Geckodrive Yahoo Group, Files section and see:
> Files > G203V step motor drive > MOTOR CURRENT WAVEFORMS
>
> The accompanying .pdf file by the same name describes the 8 gif scope
> pictures.
>
> Mariss
>
>
>
> --- In CAD_CAM_EDM_ <mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>
DRO@yahoogroups.com, "turbulatordude"
> <dave_mucha@...> wrote:
> >
> > --- In CAD_CAM_EDM_ <mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>
DRO@yahoogroups.com, "Steve Stallings"
> > <stevesng@> wrote:
> > >
> > > violent agreement indeed, except for your assumption
> > > of what most folks consider high speed.
> > >
> > > If we assume Gecko drives microstepping at 10 micro-
> > > steps per full step and the known appx. 20KHz PWM
> > > rate, then we get a possible 10 rev. per second or
> > > 600 RPM with microstepping still nominally functioning.
> > >
> > > Apply this to a Bridgeport with 5 TPI screws and
> > > 2:1 gearing (typical of Boss series) and you get
> > > 60 inches per minute. Not blindingly fast, but a
> > > long ways from slow.
> > >
> > > Cheers,
> > > Steve Stallings
> > > www.PMDX.com
> > >
> >
> > <HUGE snip>
> >
> > My understanding is that microstepping shows it's best face on slow
> > speeds and acceleration, and that at *some* point, becomes
> > inconsequential.
> >
> > but,
> >
> > those useful speeds are the most common to actually use the motor.
> > not rapids, but cutting speeds.
> >
> > Personally, I could care less of the smootheness of a rapid, as long
> > as there were no missed steps.
> >
> > It seems the question what speed is considdered slow enough to
> benifit
> > from microstepping and what is too fast to need it ? And that
> appears
> > to be dependant on power supply voltage, motor inductance and maybe
> > some other factors ?
> >
> >
> >
> > Dave
> >
>
>
>
>
>
>
>
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