RE: [CAD_CAM_EDM_DRO] Safety -- servo vs. stepper

Hi Rayhex

Yes, this is done by various companies using everything from PICS
to Basic Stamps to dedicated motion control chips like the $30
National LM 628/629.

The idea with emc was to use perhaps the easiest control platform
one could imagine...a commodity pc. Servo control is really not a
very demanding application, so an old $25 clunker pc can easily
run a machine tool...in fact it is capable of outperforming some $3000
machine controllers!

The only problem with this has been the interface. No one seems to
have come up with a REALLY low cost interface that would be in the
range hobbyists would be willing to spend to get the advantages of
full servo control.

My system is a good case in point: A $50 old pc with a $900 interface
card installed!

If someone came up with a $200 or less pc interface for full servo control
with emc the program would really take off. Something like frequency
modulation
on a couple of cheap sound cards (they don't go to dc) and/or parport.
Or USB 2.0.

I know this is a tough challenge though, because the user base is relatively
small.
Chicken and egg.

Les

Leslie M.Watts
L M Watts Furniture
Tiger Georgia USA
(706) 212-0242
http://www.lmwatts.com
Engineering page:
http://www.lmwatts.com/shop.html
CNC surplus for sale:
http://www.lmwatts.com/forsale.html
CNC carved signs:
http://www.lmwatts.com/signwp.html




-----Original Message-----
From: Raymond Heckert [mailto:jnr@...]
Sent: Friday, May 21, 2004 11:52 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Safety -- servo vs. stepper


Why can't a person make their own dedicated circuit board to process the
feedback loop? That would take the load off the PC. With the price of
x86nn computer chips, it oughta be cheap, and easy enough to do, no??? A
little machine language on an EPROM would be the controller???...Or, is
this already done on the commercial driver boards??

RayHex

----------

> From: Jon Elson <elson@...>
>

<snip>

> A true servo system where the feedback loop is processed through the
> CNC computer already has to update the velocity DACs every servo cycle.
> I have a hardware (CMOS analog, even!) watchdog that can cause an
> all-hardware E-stop if the computer fails to update the velocity

controlling

> part of the interface. On the PPMC (analog servo) it is on the DACs.
> On the UPC (PWM servo) it is on the PWM generators. And, on
> the Universal stepper controller, it is on the step rate generators.

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