Re: [CAD_CAM_EDM_DRO] Basic EMC question

exeric1 wrote:

> I've been doing some reading about EMC and understand the push behind
> it was to create a standard control system that isn't hardware
> dependent. The big question: is the control board function
> implemented in software on the PC?

Control board? What is that?

EMC takes all functions into a program (really a set of about 5 cooperating
programs) that runs entirely on one PC. It can generate step/direction
signals for stepper drivers, or control servo drives through a suitable
interface.

> That would explain the big deal
> about an operating system that can output commands in real time - I
> understand that standard windows can't hack it and Unix,Windows NT
> and Linux can.

No, not quite. Unix is not real-time, Windows NT is most definitely not
real time. Both of these systems can accept add-ons, however, that also
make them suitable for real-time code to run under them. The problem
with NT was that the real-time extensions that were available at the time
NIST looked into it cost $2000 for each machine it was installed on!
There may be others, now.

> My other related question is this: Why is it so
> important to have a non-proprietary control system? It seems you will
> still need a separate outboard power supply and drivers that WILL be
> proprietary for each servo/stepper installation. I don't get it.

Microkinetics will sell you a complete 3-axis box under $1000. many
other outfits have similar units. For under $300, you can get all the
major pieces from several outfits and wire the power supply to the
drivers yourself, and supply your own box. Gecko drives will cost just
a little more.

Allen Bradley used to charge $50,000 for the basic CNC control, and servo
amps, digital I/O, etc. was extra. A Centroid 2-axis control was quoted to
me for $13,000 not very long ago. These have continued to come down,
but most commercial 3-axis controls will still cost well over $10,000.

EMC is free, so your only costs for a stepper system are :
1 Pentium PC with monitor, keyboard, and mouse
1 power supply
stepper drivers
stepper motors

> I'm
> not being a smart ass, I'm just learning. If it could ALL be
> implemented inside the PC including power supply for the drivers and
> drivers themselves then it would make sense to me.

The PC power supply does not have the right voltages or power capacity
for most machine controls. Most people start with a 10 A 48 V power supply
at the minimum. So, that is 480 W - your PC power supply is likely about
200 W, and the PC's electronics use up at least half that.

You COULD put a motor power supply and drivers inside a larger PC
case, if you really want to make it compact. As long as enough air
is moved through the case to prevent overheating, that should work out
just fine.

Jon