Re: [CAD_CAM_EDM_DRO] Rotor inertia.

----- Original Message -----
From: Jon Elson <elson@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Friday, October 31, 2003 5:17 PM
Subject: Re: [CAD_CAM_EDM_DRO] Rotor inertia.


>
>
> Jason Cox wrote:
>
> >Hello All,
> >
> >Just wondering when selecting servo motors what impact does rotor inertia
have on the final function of a cnc machine?
> >
> >>From my research motors with a far lower inertia are much cheaper, but
does this really matter. Surely the redution in inertia of the rotor would
be minimal say compared to the inertia of the machine table.
> >
> >
> Yes, essentially correct. Mariss Freimanis did some calculations that I
> seem to
> recall showed that it is not insignificant, but that common motors come
> out in
> the right range. Under some circumstances, a motor with too much, or too
> little inertia can make for an unstable servo system. This is especially
a
> problem when there is some springy element between the motor and the
> high-inertia load, such as a long thin leadscrew or couplings with too
much
> flex. You end up with a system comparable to two masses connected by a
> spring.
>
> Are you sure low-inertia motors are cheaper? I happen to have some low
> inertia Yaskawa super minertia motors that supposedly cost $5000 each.
> They were in computer tape drives, and had a fiber composite capstan
> with Beryllium hub, a ceramic shaft, ironless rotor motor of the "thimble"
> style, etc. But, in general, a low inertia motor of conventional
> construction
> is just smaller, that's all. So, a smaller motor qould be cheaper to
make.
>
> Jon
>
>
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