RE: Testing Step Motors

Good morning;

I recently purchased a Microkinetics Driverack system. Not too happy with
it, but that's another story. I did, however, learn from first hand
experience that microstepping has significant advantages over conventional
halfstepping when using large (Nema 42) motors. With the old L/R drive
amplifiers, such as were found on the BOSS 5 Bridgeport mills, resonance was
annoying but tolerable. But the newer switching amplifiers are so harsh
that these large motors are almost unusable. Microstepping virtually
eliminates the vibration. Having started with halfstepping and later paid
for the upgrade I can vouch for the advantages.

Accuracy is not so much an issue as is repeatability. Halfstepping a 400
cog motor with 1:2 gearing yields .0005 resolution on a knee mill and that's
well within the repeatability of most low end machines. Repeatability
becomes and issue when vibration is so bad the motor skips steps, and that
is usually why they skip if we are assuming they were of adequate size to
begin with.

Doug Harrison

> -----Original Message-----
> From: Jon Elson [SMTP:jmelson@...]
> Sent: Wednesday, November 17, 1999 5:56 PM
> To: CAD_CAM_EDM_DRO@onelist.com
> Subject: Re: [CAD_CAM_EDM_DRO] Testing Step Motors
>
> From: Jon Elson <jmelson@...>
>
>
>
> Ray Henry wrote:
>
> > From: Ray Henry <rehenry@...>
> >
> > Read an interesting article in Test and Measurement World Nov 1999 that
> > discussed stepper motor applications, testing, and failure. Stuff there
> > that I didn't know about holding and dynamic torque and accuracy.
>
> Yes, very interesting. Nobody ever seems to talk about the positioning
> accuracy of stepper motors. They just assume that they precisely break
> a circle into however many steps they have per rev, which is far from
> true.
> And, especially with microstepping, people think they can divide each step
> into thousands of microsteps, with full accuracy. Clearly, the micro
> steps
> quickly become meaningless, if the step accuracy is something like 5 or
> 10%.
>
>
> Jon
>
> > Welcome to CAD_CAM_EDM_DRO@...,an unmoderated list for the
> discussion of shop built systems in the above catagories.
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> bill,
> List Manager