Re: CNC / DNC
Posted by
Andrew Werby
on 2000-05-09 10:08:49 UTC
Jon Elson <jmelson@...>wrote:
Subject: Re: CNC / DNC
Andrew Werby wrote:
through the serial port" part, and it makes a lot more sense.
[Actually, that was my assumption, not what the Milltronics guy told me. So
I just have to send it regular G-code, as ascii characters, and let the
mill control do the translation itself?]
There will
be no step and direction signals anywhere. What you want is a CAD/CAM
program that generates RS-274D (also known as G-Code). This output
generally goes to a file. A number of the CAD/CAM packages have machine
interfaces that can either output step and direction to stepper motor
drivers, or send the G-code through the serial port (or, in some cases, the
parallel port). A 'BTR' (yes, behind the reader) usually attaches to the
parallel port, as it is closest to the paper tape reader interface.
[But since RS-232 is a serial communications link, I have to go through the
serial port, no?]
A CAD/CAM package (or other machine control) will work a lot better than an
off-the-shelf comm program. Especially, in some cases, the CNC requires the
tape to be read backwards (to back up a few program steps when a tool
breaks, for instance).
[You don't get that with DNC, though- it seems like a one-way street. As I
understand it, all I get to do is feed it a set of instructions- no backing
up. But I suppose I might be able to edit the program to resume cutting at
a given place, if I knew where that was.]
controlling the
machine's servo or stepper motors.
[That would require 2-way communication, which this set-up isn't going to
give me, to deal with the servo feedback. So EMC evidently isn't the
program for this job. I'm still interested in the DOS port, though, for my
other project- the from-scratch router.]
program run step and direction to stepper motors. You don't have these.
[Got it. ]
Do you have a paper tape reader?
[I think what is currently plugged into the RS-232 port is this weird old
mag-tape reader, which takes small cassettes that I've never seen anywhere
else.]
Don't be confused by the 25-pin D plug,
that is not RS-232, it is RS-2xx, a parallel standard for paper tape readers.
I don't remember the exact numbers, there.
[The plug labeled RS-232 is one of 6 round plugs. I didn't count the
prongs, but there are fewer than 25.]
But, you may have 2 possible
paths. I didn't have an RS-232 interface on mine, so I made a BTR. I could
also load the CNC executive from the PC, which was a nice improvement. But,
the RS-232, if it works, will be best for simplicity. Your only real concern
is to make sure the 'wait' signal is consistant, telling the PC to not send any
more data until the CNC is ready.
[Uh, what's a "wait" signal, and how do I assure its consistency?]
controlling data flow on RS-232 connections. They have nothing to do with a
BTR, which uses an electrical signal to control flow. Does your CNC control
use X-on and X-off? Or, does it use something else, like the clear to send
signal wire?
[According to the Centurion guy, it's software handshaking: x-on, x-off. ]
would
stop sending when it receives an X-off, and resume when it sees an X-on.
X-off is CTRL/S, or hex char code 13, decimal code 19. X-on is CTRL/Q, hex
code 11, decimal code 17.
[This would come back up the serial port? And the PC would have to
recognize it? Is this part of the standard null-modem stuff, or something I
have to put in there?]
Depending on how your CNC accepts programs from the serial interface, this
may limit what you can do. For instance, a program that returns to the
beginning and runs again will not work automatically with a comm program
sending from the PC, as it has no way to know the CNC wants to receive the
program again from the beginning. And, if you instruct the CNC to back up,
the comm program won't know how to do this.
[I'm not expecting that- all I want is to be able to run a big program once.]
Each CNC has it's own little language to express these operations, and a
program specifically
for DNC will know how to handle them. This is really what you are wanting,
DNC (Distributed Numeric Control), where a central server handles sending
programs to the CNC controls. You can run these completely from the CNC
machine, including writing a program at the CNC control and uploading it
for storage on the PC. To run a part program, you call
it up from the CNC control by name, and the CNC sends a message to the PC
asking for the program by name, and the PC begins to send the program to
the CNC.
Jon
[Can you recommend a DNC program to do this? At this point, I'm not sure
the CNC control that's on the machine is capable of asking for programs by
name- there seem to be mostly numbers on its keypad, with only a few
letters, like "G" and "M". Could I call a program by a numerical "name",
like "123" ? Anyway, thanks for the help, I really appreciate it. As you
can probably tell, I'm fumbling around in the dark here, although there
seems to be some light at the end of the tunnel...]
Andrew Werby
http://www.computersculpture.com
Andrew Werby - United Artworks
Sculpture, Jewelry, and Other Art Stuff
http://unitedartworks.com
Subject: Re: CNC / DNC
Andrew Werby wrote:
>Re: PROJECTS STILL ON THE BURNER?This is a muddle. leave out the "output my G-code as step and direction
>It now appears I can get my Beast (the 1984 Leadwell-Ramco) of a milling
>machine to accept drip-feed input through its RS-232 port. I tracked down
>the people who made the old Centurion IV control (they are called
>Milltronics now, and are located in the Minneapolis area) , called the
>number (952-442-1410) and talked to "the old guy in the back". He assured
>me that if I could be happy with a 1200 baud rate, could come up with some
>kind of "BTR" (Behind The Reader?) box and appropriate shielded cables, and
>found a control program that could output my G-code as step and direction
>through the serial port of my computer, using Microsoft's built-in
>Hyperterminal or some other null modem connection, then I'd be in biz- able
>to feed it unlimited-size files in DNC mode.
through the serial port" part, and it makes a lot more sense.
[Actually, that was my assumption, not what the Milltronics guy told me. So
I just have to send it regular G-code, as ascii characters, and let the
mill control do the translation itself?]
There will
be no step and direction signals anywhere. What you want is a CAD/CAM
program that generates RS-274D (also known as G-Code). This output
generally goes to a file. A number of the CAD/CAM packages have machine
interfaces that can either output step and direction to stepper motor
drivers, or send the G-code through the serial port (or, in some cases, the
parallel port). A 'BTR' (yes, behind the reader) usually attaches to the
parallel port, as it is closest to the paper tape reader interface.
[But since RS-232 is a serial communications link, I have to go through the
serial port, no?]
A CAD/CAM package (or other machine control) will work a lot better than an
off-the-shelf comm program. Especially, in some cases, the CNC requires the
tape to be read backwards (to back up a few program steps when a tool
breaks, for instance).
[You don't get that with DNC, though- it seems like a one-way street. As I
understand it, all I get to do is feed it a set of instructions- no backing
up. But I suppose I might be able to edit the program to resume cutting at
a given place, if I knew where that was.]
>This sounds distinctly doable (much more so than the Brain Transplant), butEMC knows nothing about serial ports, and expects to be directly
>I've got some questions for the experts here:
>What control program should I use to communicate with this old DC
>servo-equipped mill? Is this a good excuse to try CNC Pro, or would
>something else be better? Is the DOS port of EMC really ready and for sale
>someplace? I think this would go fast enough on my P223, in DOS mode-
>wouldn't the low baud rate be the limiting factor? How many inches per min.
>should I expect, in contouring mode?
controlling the
machine's servo or stepper motors.
[That would require 2-way communication, which this set-up isn't going to
give me, to deal with the servo feedback. So EMC evidently isn't the
program for this job. I'm still interested in the DOS port, though, for my
other project- the from-scratch router.]
>Do I really need some special BTR box, or can I go direct from the 9-pinAgain, there is NO step and direction, anywhere. Lots of low-end CAD/CAM
>serial port of my computer? Does this machine need its code fed in some
>special way, which the BTR translates from standard step-and-direction?
program run step and direction to stepper motors. You don't have these.
[Got it. ]
Do you have a paper tape reader?
[I think what is currently plugged into the RS-232 port is this weird old
mag-tape reader, which takes small cassettes that I've never seen anywhere
else.]
Don't be confused by the 25-pin D plug,
that is not RS-232, it is RS-2xx, a parallel standard for paper tape readers.
I don't remember the exact numbers, there.
[The plug labeled RS-232 is one of 6 round plugs. I didn't count the
prongs, but there are fewer than 25.]
But, you may have 2 possible
paths. I didn't have an RS-232 interface on mine, so I made a BTR. I could
also load the CNC executive from the PC, which was a nice improvement. But,
the RS-232, if it works, will be best for simplicity. Your only real concern
is to make sure the 'wait' signal is consistant, telling the PC to not send any
more data until the CNC is ready.
[Uh, what's a "wait" signal, and how do I assure its consistency?]
>IfX-on and X-off are two characters in the ASCII code that are often used for
>I do need one, which is the most cost-effective (for an non-electronician)?
>What about the "software handshaking" it uses: x-on x-off? How does that
>work?
controlling data flow on RS-232 connections. They have nothing to do with a
BTR, which uses an electrical signal to control flow. Does your CNC control
use X-on and X-off? Or, does it use something else, like the clear to send
signal wire?
[According to the Centurion guy, it's software handshaking: x-on, x-off. ]
>Is this just a series of characters I need to insert at the beginning ofNo, the CNC would send these characters, if it uses them, to the PC, which
>each program, (and if so, how do I find out what they are?)
would
stop sending when it receives an X-off, and resume when it sees an X-on.
X-off is CTRL/S, or hex char code 13, decimal code 19. X-on is CTRL/Q, hex
code 11, decimal code 17.
[This would come back up the serial port? And the PC would have to
recognize it? Is this part of the standard null-modem stuff, or something I
have to put in there?]
Depending on how your CNC accepts programs from the serial interface, this
may limit what you can do. For instance, a program that returns to the
beginning and runs again will not work automatically with a comm program
sending from the PC, as it has no way to know the CNC wants to receive the
program again from the beginning. And, if you instruct the CNC to back up,
the comm program won't know how to do this.
[I'm not expecting that- all I want is to be able to run a big program once.]
Each CNC has it's own little language to express these operations, and a
program specifically
for DNC will know how to handle them. This is really what you are wanting,
DNC (Distributed Numeric Control), where a central server handles sending
programs to the CNC controls. You can run these completely from the CNC
machine, including writing a program at the CNC control and uploading it
for storage on the PC. To run a part program, you call
it up from the CNC control by name, and the CNC sends a message to the PC
asking for the program by name, and the PC begins to send the program to
the CNC.
Jon
[Can you recommend a DNC program to do this? At this point, I'm not sure
the CNC control that's on the machine is capable of asking for programs by
name- there seem to be mostly numbers on its keypad, with only a few
letters, like "G" and "M". Could I call a program by a numerical "name",
like "123" ? Anyway, thanks for the help, I really appreciate it. As you
can probably tell, I'm fumbling around in the dark here, although there
seems to be some light at the end of the tunnel...]
Andrew Werby
http://www.computersculpture.com
Andrew Werby - United Artworks
Sculpture, Jewelry, and Other Art Stuff
http://unitedartworks.com