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

[Dominic-Luc Webb <dlwebb@canit.se>]

I am not sure about "voice" coil actuators specifically, but have
seen very powerful selenoids, etc using same basic physics. I am
very confident such devices could be used.

Dominic

On Mon, 20 Nov 2006, GARY FUCHS wrote:

> Don,
>
> That was probably a basic explanation, but still mostly over my head.
>
> It looks like voice coil actuators move linearly. If that's true, won't you need to convert that to rotary motion? If so, how?
>
> And if it's going to be driven by an audio amplifier, won't the amplifier need to be pretty powerful if the voice coil actuator is going to be pushing a polishing tool around?
>
> What am I missing?
>
> Gary
>
>
> >
> >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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