Re: digital servo controller to offload the Parallel Port?

["Les Watts" <leswatts-at-alltel.net>]

John, I see a dot somewhere in Texas on our world map... that
means someone at least has the software.

I previously used one of the many dedicated servo/motion control
ics (LM628) that was just commanded by the host. EMC easily
can outperform many of these chips simply because of the raw
power of Pentium class PCs.

The software is not perfect but I find it reliable enough for
commercial use. The very good G-code interpreter can be
used as a stand alone.

I believe most use EMC as a stepper controller, but it is really
designed as a high performance servo controller. I actually
think the servo version is easier to use... and it has much 
higher performance. It's just that experimenters have a hard
time justifying a few hundred to a thousand dollars for an interface
card. The card is not super complex; it just is some d/a and a/d,
quadrature decoder chips, and digital i/o. But I had to pay about
$1000 for this as not many are made. It is still cheap for a
commercial application though.

Even with an old Pentium 200 I get 2000 servo updates per
second with P, I, D, and position, velocity, and acceleration
feedforward updates. And look ahead.

Previously I would do these calcs by writing finite impulse
digital filter coefficients to a dedicated DSP.

Les

Leslie Watts
L M Watts Furniture
Tiger, Georgia USA
http://www.alltel.net/~leswatts/wattsfurniturewp.html
engineering page:
http://www.alltel.net/~leswatts/shop.html
Surplus cnc for sale:
http://www.alltel.net/~leswatts/forsale.html
----- Original Message ----- 
From: "John Griessen" <john_g-at-cibolo.com>
To: "Multiple recipients of list" <emc-at-nist.gov>
Sent: Thursday, December 19, 2002 10:38 AM
Subject: Re: digital servo controller to offload the Parallel Port?


> 
> Les,
> 
> I understand that emc uses the low cost of the mass produced PC to great
> effect.   It just seemed Till knew where a performance limit was when
> using the parallel port, and I was asking.  I have not played with an
> emc driven machine yet.  Is there anyone in  Austin TX using one?
> 
> John Griessen
> On Wed, 2002-12-18 at 16:30, Les Watts wrote:
> > 
> > Hi, John
> > 
> > The whole idea with EMC is really host signal processing.... the
> > computer cpu does all the servo loop calcs in a real time
> > operating system. Even a very slow old commodity computer has
> > enough processing power to do a high performance job. So it does
> > not need outboard processors.
> 
> 
> > Les
> > Leslie Watts
> > L M Watts Furniture
> 
> 
> 
>