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From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: large (5HP) DC motor controller design issues
Date: Fri, 27 Sep 2002 22:09:04 GMT
NNTP-Posting-Date: Fri, 27 Sep 2002 15:09:04 PDT
Richard Everett wrote:
> I would like to build a somewhat simple PWM controller for a largish DC
> brush motor (5HP). This is a shunt wound motor, with a 180V armature
> (guessing about 24 amps) and a 200V field (at 1 or 2 amps). I can live
> without field weakening if needed.
> One big problem is that I need to be able to control the motor position. It
> is the spindle motor in a cnc mill I picked up cheap because the spindle
> drive was shot ($7500 to replace)...the cnc mill has a tool changer and so
> the spindle has to stop in a certain position for a notch in the spindle
> taper to line up with a notch in the tool holder when changing tools.
> Ideally, I would like to build a solid state reversing drive (hbridge made
> up of IBGT devices, or mosfets) with quadrature encoder feedback. I have
> built discrete h-bridges for small motors and steppers, but have never
> tackled something of this power. I am worried about things like voltage
> spikes and inrush currents.
> A fairly exhaustive search of past posts has not yielded much information in
> larger DC motor control...any articles or sources of information would be
> apprecitated greatly!
I don't want to get into the power electronics because I have not done
high power stuff in many years but the spindle position is another
matter. Does your motor have an encoder on it? It would be usual on that
type of machine to have an encoder. If the encoder is fine enough, you
simply servo the spindle to the required angle. I don't have a taper
tool holder under my nose but I seem to recall that the 40 taper is self
aligning if you get the angle close enough. The tool holder will rotate
slightly when the draw bar pulls it home. Without an encoder, a roller
detent pulled away by a solenoid for normal operation is possible. A
microswitch can be used to sense when the roller falls into the detent.
For large DC motor control information, there is (or was) a magazine
called "Motion Control." The general topic of motion control might help
you anyway. Note that "Motion Control" is (or was) a free magazine and
you have to qualify for subscription. I don't know about back issues of
it at all.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org
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