Re: [CAD_CAM_EDM_DRO] Machine security and safety

> Speaking of which, does anyone know who came up with "Gcode" and why they
> chose not to include some kind of safety checksum in the commands? I'd be
> more concerned about a garbled step command than someone 'hacking' into the
> machine...

Well, checksums are hard for people to calculate, and it is in fact
very usefull that someone can grab just about any text editor and
write gcode by hand. So I think that there is a good reason that the
format itself does not have a checksum. But it could be done as an
add on if you want - it would be easy to write tools to add in and
strip out the checksum from files for compatability with the standard.

If the motion commands are transmitted from a computer to some sort of
external processing box, then yes, they absolutely should have some
sort of error checking if there are enough 'smarts' in the processors
on both ends to handle it. One is also free to use error-correcting
storage devices to hold the files.

Stepper drives built from logic gates don't have those smarts. I'd
really rather see stepper drives that could be given more powerful
commands (perhaps move at so many steps per second until you have
moved this many steps or I tell you to do something else) which could
include error checking, but that requires defining a much more
complicated interface.

Step & direction is primitive and has its problems, but it works, and
is easy to generate with either a computer or a crude 555 pulse
generator circuit, and easy to receive with either a fancy chopper
drive, step servo drive, or a really basic full step constant voltage
'learning project' drive. Its versatility has made it the standard
for hobby cnc and quite a bit of small industrial motion stuff as
well.

Chris

-------------------------------------------------
Christopher C. Stratton
Engineer, Instrument Maker, and Horn Player
ccs@... 617 628 1062
http://web.mit.edu/~stratton/www/brassbuild.html