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

[GARY FUCHS <gary@rcn.com>]

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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>> >>
>> >
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