Re: [CAD_CAM_EDM_DRO] Re: Which Software?

> Jon,
>
> You are saying that "EMC" accepts feedback into itself, as
> software, to fully control this NC milling machine? That is exactly
> what I'm looking for. I have never worked blind and don't expect my
> help to either - human or mechanical (how fortunate we are as
> humans!) Now, what is EMC and are the servo drivers different for
> EMC than for, say: MACH1 and similar software?

Yes and No


EMC is the Enhanced Machine Controller, a piece of software put out by NIST
(National Institute of Standards and Technology). Since it is a government
agency, you allready paid for it with your taxes, so it is free. It was
written to retrofit older machines with good iron, but bad controllers. It
was originally written for driving analog servo amps, using a Servo To Go
card which plugs into an ISA slot on your computer. The STG card has inputs
for encoders and outputs an analog voltage of + or - 10 VDC to your servo
amps. This is true, full feedback motion control and it is how most, if not
all big machines operate. The controller 'knows' exactly what's moving and
how fast it's doing so. It continiously adjusts the analog output voltage to
the servo amps to keep everything going as it was instructed to do.
If the axis gets a few thousandths behind where it's supposed to be, the
controller will up the analog voltage to the amp to make it catch up to
where it's supposed to be. EMC runs under a realtime version of linux.

Mach1 and all of the other hobby controllers do not drive analog servo amps
like EMC does, they push steps out of the parallel port of your computer to
drive stepper motor amps. There really is no way to add feedback to the
controllers on them, (Mach1 may be an exception), so the controller really
has no way of 'knowing' what's happening with the motion, they just keep
spitting out steps, regardless of what's whats doing on. This is not a
problem, IF everything is working as it should.

OK, now this is where the lines begin to cross.

EMC was modified to also put step and direction pulses out of the parallel
port to drive stepper motors if that is what you want. Probably more people
using emc with step and direction than analog servos.

To further muddy the waters,

Along comes Gecko Drive, a company that makes great stepper amps, with an
amp that will take step and direction pulses and drive a servo motor. The
encoder feedback goes to the amp instead of the controller software, so the
controller still just puts out steps, and has no idea of the status of the
motion. The only feedback going back to the controller is a fault line from
the amp ( this fault line is not required, but a nice feature) If the actual
motion gets too far behind the commanded motion the amp will fault, and this
will trip the controller that something is wrong. Lots of people here using
a setup like this, myself included, and it works well. Not quite as
sophisticated as analog drive of servo motors, but better than blindly
driving steppers with no feedback at all. Also easier to set up, and less
expensive to implement. So now all of the hobby controllers can control
servo systems, just not an analog servo system. EMC can control either type

EMC has been further modified to accept other analog servo cards besides the
STG card, including Jon Elson's PPC stuff.

New stuff from Gecko Drive on the way that will complicate things further,
but have great promise.

Bill