Re: [ATM] DC Motor for grinding machine question

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

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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> >>
> >
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