Disclaimer: CNC Concepts, Inc.
accepts no responsibility for the use or misuse of
techniques shown in this web page. We simply publish
information we feel will be of interest to CNC users. In
all cases, the reader is totally responsible for
considering the implications, good and bad, of
implementing one or more of the techniques we show.
How does direct numerical
control
work?
Can somebody walk me through the steps to
setup the cnc and dnc software so the machine will run
the program directly from the computer when the
machine's memory is insufficient to hold the program.
Thank you, Mike Koch
Response:
Mike,
Frankly speaking, there's not all that much
to it as long as the CNC control truly allows direct
numerical control. For Fanuc models 6MB and more recent,
for example, as long as your communications protocol is
properly set up (baud rate, stop bits, handshaking,
etc.), the actual task of running a the CNC machine from
an off line computer is pretty easy.
This is pretty much the same protocol used
for distributive numerical control (transferring a
program in its entirety), but with an emphasis on
handshaking - usually with xon/xoff . Usually a setting
parameter controls whether the cycle start button will
activate a program in the control's memory or a program
from the serial communications port (computer). With
Fanuc controls, it's usually on the setting page and
labeled Input Device. For most control models, it must be
set to RMT (For remote) when you want to run directly
from a computer.
After ensuring that the connection is made
between the control and computer and parameter settings
are correct, most controls simply require that you first
turn on single block (so the program won't run until
you're ready for it to).
Next, you press the cycle start button. But
since there is no program coming through the serial port
(yet), and because of handshaking, the control will
simply wait.
Finally, you go to the computer and send it
to the machine (like you do for distributive numerical
control). When you get back to the machine, you'll
notice that it has executed the first command of the
program (the program number for a Fanuc control) and
stopped (since single block is on).
When you turn off single block and press
the cycle start button, the control will execute the
program.
With most controls, however, you won't see
much of the program on the display screen (as you do
when executing a program from memory). Only what's in
the look ahead buffer will be displayed. And of course,
you won't be able to edit the program at the control as
you can when executing a program from memory.
