PC based CNC system architecture

Hi again,

It seems to me the biggest issue we keep tripping over is system
architecture.

Servo amps and stepper drivers are pretty well defined black boxes. The
PC is _the_ generic cheapo number cruncher. It's the little matter of
how one connects the two that seems to be the most troublesome.

Multi-axis motor control is clearly a real time process. Generic PC
hardware and OS's were not designed as real time processing tools. I
trust I have not shocked anyone with those two statements.

EMC (for example) is proof that a PC can be successfully pressed in to
service as a real time controller. This does not come without some cost.

Among the costs I see are: The installation and system integration is
messy enough to drive many folks away; the RT subsystem negatively
impacts the performance of the user interface; the performance of the
stepper drive version is rather limiting.

My take on all this is that the system architecture is not partitioned
quite right.

We seem to be in general agrement that hooking motor drivers directly to
the PC printer port doesn't really cut it. We also seem to agree that
there is a missing piece of hardware that would go between the PC and
the motor drivers. It is, in my view, the exact form that this "black
box" might take that is the primary subject of debate, here.

It is tempting, for many of us, to try to go off by ourself and design
this "black box". If we do, we will, most likely, get tripped up by the
usual tendency to view a task in terms of the tools with which we are
most comfortable. I'm trying to resist this temptation.

To put that another way, I would like to see us more fully define the
functional role of this "black box" before we get too carried away with
figuring out just how it works.

I, of course, have some opinions on just what that functional role
should be, but I want to think about it a bit more first. (Besides, I'm
hungry now, time for lunch.)

Jeff