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

[Dale Eason <atmpob@yahoo.com>]

Don,
Do audio amps have low enough frequency response?
I would think you need good response down to about .1 
Hertz.

Have you calculated the movement length you will need
and the size of the coil?  How much power you will
need to drive the mechanics?


Dale Eason

--- Don Clement <don_clement@charter.net> wrote:

> 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
> 
=== message truncated ===



 
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