Re: [ATM] Voice coil actuators was: DC Motor for grinding machine question

["Don Clement" <don_clement@charter.net>]

Gary,



Voice coil actuators are neither complicated nor expensive. A good
explanation can be found here:
http://www.consult-g2.com/course/chapter11/chapter.html

Voice coil actuators are commonly found in just about everywhere in the form
of the loudspeaker. Voice coil actuators are simple enough to be built by
the ATMer. I plan to use voice coil actuators because of the simplicity of
driving them using off-the-self audio amplifier and off-the-self D/A cards
with a PC. The pseudo random driving signals are easily generated in
software in the PC. I am using my favorite all-graphical software NI LabView
to do this.



Don Clement

Running Springs, California



> Thanks Don,
>
> I looked up voice coil actuators - very interesting - though I didn't
understand much. The ones I saw looked like they weren't for continuous
motion. Is that true of all, or am I just not making sense of it? If so, how
would you use them for the machine?
>
> They also look expensive...
>
> With their rapid acceleration/braking/reversing and ability to move in
very small increments would these be better than other motors for scope
drives?
>
> Thanks,
>
> Gary Fuchs
>
>
>
> >
> >Gary,
> >
> >
> >
> >Periodic error by definition would produce a regular pattern. Machines
that
> >use the same drive for spindle rotation and also drive the tool will have
> >some synchronization and produce periodic component. That's why my
machine
> >will use two independently driven voice coil actuators to drive the tool.
We
> >could test that theory by using the Lyot phase-contrast method and look
for
> >any effects of periodic error on the machine polished surface.
> >
> >
> >
> >Don Clement
> >
> >Running Springs, California
> >
> >
> >
> >> (First, thanks for the VFD info. That's on my Christmas list.)
> >>
> >> Don, Mike, et al?,
> >>
> >> I'm probably in over my head here, but why wouldn't the periodic error
I
> >think you're talking about actually be beneficial, making the machine's
> >action just slightly irregular and more human-like? Don't typical
machines
> >have at least two places where periodic error would occur, but not at the
> >same time?
> >>
> >> Gary Fuchs
> >>
> >>
> >> >
> >> > Mike,
> >> >
> >> >
> >> >
> >> >We could test that theory.  Perhaps using technique mentioned by
Texereau
> >in
> >> >"How to make a Telescope", the Lyot phase-contrast method. One could
do a
> >> >spatial spectrum analysis on the machine polished surface using the
Lyot
> >> >phase-contrast method to detect any periodic contribution due to the
> >regular
> >> >arraignment of balls in a ball bearing race. Since spindle rpm is
known
> >and
> >> >the ball bearing race configuration is known, one would know what
spatial
> >> >frequencies to surface roughness to look for.
> >> >
> >> >
> >> >
> >> >
> >> >
> >> >Don Clement
> >> >
> >> >Running Springs, California
> >> >
> >> >
> >> >> Don,
> >> >>
> >> >> Don Clement wrote:
> >> >> > There is no contradiction.
> >> >>
> >> >> Yes, there was.  In one message you said there was no effect, then
in
> >> >> your next message you said there was.  Maybe it was a typo.  I was
> >> >> just trying to follow your reasoning.
> >> >>
> >> >> > Using a FFT Dynamic Signal Analyzer
> >> >> > (such as the Agilent 35670A) and the proper sensors one can see
the
> >> >> > effects of rotating equipment using ball bearing races. In fact,
> >> >> > one can determine detailed information on the ball bearing race
> >> >> > parameters (such as number of balls, etc) by examining the
spectrum
> >> >> > of rotating machinery. There is no doubt that regular spaced balls
> >> >> > in ball bearing races add some periodic component to a rotating
> >> >> > spindle of a polishing machine.
> >> >>
> >> >> I have no doubt you are correct in that statement - my day job is
> >> >> signal processing and I play with FFTs all day.  I also have no
doubt
> >> >> that the vibrations affect the quality of finish in metal working,
and
> >> >> I found your post about 3-phase motors and speed controllers very
> >> >> interesting and useful.
> >> >>
> >> >> However, I debate your assertion that the miniscule vibrations will
> >> >> cause measurable effects on the surface of a mirror being polished
on
> >> >> a machine.  I certainly haven't detected any on my DC motor/variac
> >> >> setup, or on a machine that uses a PWM controller.
> >> >>
> >> >> I guess you'll end up with a grinding machine that can double as a
> >> >> decent turntable for playing vinyl, should your Marantz experience
> >> >> problems.  :)
> >> >>
> >> >> (Yes, I know vinyl often sounds better.)
> >> >>
> >> >> Mike Lockwood
> >> >>
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