Linux vs. DOS

Jon Elson <jmelson@...> wrote:

Andrew Werby wrote:

> From: Andrew Werby <drewid@...>
>
> [I just got my new (old) mill delivered yesterday, and it's really a beast!
> This is a Ramco "Ramill", built to be a CNC mill in the mid-eighties. It
> has servo motors and ballscrews, which should save me some time and money
> over retrofitting an old Bridgeport, which was my first idea. Currently, it
> will accept instructions in g-code, either from the attached keyboard or
> from a tape drive. But I'd like to convert it to a more modern control
> system which wouldn't be limited to 999 instructions- some of the progams
> I've been generating run over 2 megs, (and I'm just getting started.) I
> think I can save the servo amplifiers and most of the relay switches, while
> gutting out the old computer and attaching a standard monitor. I'd be happy
> with something that ran in real time under DOS, if it could handle g-code.

I would suggest EMC. It runs under Linux, but Linux offers total MSDOS
file system compatibility. You can run text-based DOS programs in an
emulator window, as well as read and write DOS floppies directly in
Linux. In fact, if you mount a DOS floppy before starting EMC (or
later, using another window) you could execute a G-code program
directly off the floppy, if you wanted to.

The reason DOS is unacceptable, is that it is NOT a real-time environment.
Yes, it seems pretty real time to us slow humans, but for a motion
control system with a 1 KHz servo update rate (or better) DOS is
most emphatically NOT real-time. You would have to place hooks
on every interrupt entry point and write your own real-time
scheduler to get guaranteed priority for the realtime task. But,
the worst part is that the DOS environment is not secure!
Any haywire program could overwrite the motion control
code or data areas, and cause a hazardous crash! I sure wouldn't
use such a system!

[Oh. I really don't know anything about Linux, but it seems intimidating.
All the problems with "kernels", whatever they are, seem like they would
take over my life. I read some previous discussion here on the fine points
of running Linux , and I didn't understand thing one. Is there no
alternative? Does NT run in real time? Has anybody built a graphical user
interface for Linux that makes it more user-friendly? Is there a Linux for
Dummies?]

See my page at : http://ascc.artsci.wustl.edu/~jmelson/CNCconv.html
and http://ascc.artsci.wustl.edu/~jmelson/EMC.html

For EMC itself, see :
http://www.isd.cme.nist.gov/projects/emc/emcsoft.html

The software is available for download from the web.

The only thing it sounds like you'd need to buy would be the
Servo-to-Go card, and maybe a rack of solid-state relays to
drive the auxilliary stuff.

[Would that be better than leaving the old relays in place? Also, can you
tell me why there's a strong smell of methyl mercaptans in the mill's
control box? If I didn't know better, I'd swear it was leaking natural
gas...]

Servo-to-Go is at : http://www.servotogo.com/

If you have any questions, feel free to email me.

Jon

[If you'd rather, we could take this off-list, but it seemed we were still
discussing things of general interest, so I'm replying in "public". The 8
axis Servo-to go card sounds interesting at $888 - it certainly beats
paying $1500 per axis. They mention running NT in conjunction with their
card, and something about how it (and DOS) can be induced not to interrupt-
do you know anything about this? They also talk about writing your own
algorithms, though- so I'm not sure how hard this would be. ]

Andrew Werby

Andrew Werby - United Artworks
Sculpture, Jewelry, and Other Art Stuff
http://unitedartworks.com