Re: microstepper drives

[mooney@aps.anl.gov (Tim Mooney)]

re...

> Pete writes:
> > ...
> > We (UNICAT) have got to choose a different technology than chopper
> > microsteppers.  Don't see any debate about this issue.
> > Thought that this problem is likely to be of importance to the
> > community of microstepper users here at APS and elsewhere.
> > ...
> 
> There is no doubt that chopper drivers generate noise.  The question is
> whether with reasonable care one can make this noise insignificant.  Putting
> drivers in different racks from amplifiers, using shielded cables and watching
> cable routing might be easier than abandoning chopper drives.  The only 
> non-chopper microstepper I know of is the Highland Technology one which SRI
> has tested and written software for.  Using it means you can't use your OMS
> drivers either.
> 
> Mark Rivers

Three things:

Grounding/shielding -- You probably already know this stuff, but anyway
the worst of the noise we ran into with chopper drives went away when
we made sure that the cable shield was grounded only at the driver end
and did not make electrical contact with the motor housing, and also
that the motor housing was grounded *very* solidly--in one case by
grounding the optical table on which everything was mounted with a
thick (e.g., 6 gauge) wire.

5-phase -- One of these days, Leo Bric is going to develop a 5-phase
bipolar full/half-step driver, which will be electrically silent when
it's not moving and have some of the advantages of a microstepper.  As
a prerequisite, ACS will have to figure out how they would make a
bipolar version of their standard driver--something we need anyway.
(Around a third of the microsteppers in use by SRI-CAT are in
applications that really just need bipolar drivers.)

The Highland Technology quiet microstepping drivers work by chopping at
100kHz (rather than the usual ~20 kHz) and sending motor current
through a 1kHz low-pass filter.  (I'm not giving away any trade
secrets; this is straight out of their product literature.) If we can
find a high-frequency chopper driver, we might be able to design our
own high-current low-pass filter, and make a quiet microstepper for the
StepPack chassis--or better, get a vendor to do it.  (By the way,
Highland microsteppers are no longer available from stock.  They lost a
supplier for one critical part and must redesign, which they won't do
for less that around a quantity 10--40 motors--order.  Even then, their
plan is to produce a 3-amp drive, instead of the 10-amp drive they sold
us.)

Tim Mooney