RE: [CAD_CAM_EDM_DRO] Windows PC as CNC controller

A minor nit:

> But I haven't seen any stepper motor drivers which take
> velocity and return
> position. Have you?
>

Something similar to this was just brought up on a thread "Integrated
stepper/driver systems"

The issue is concurrency. A parallel port driving several axes of step and
direction lines offers absolute lockstep concurrency. If you are doing
simultaneous operations in more than one axis and if a command to one of
your axes gets delayed a bit, that workpiece is toast. If windows is
spitting out
Move X
Move Y
Move Z
Move X
Move Y
Move Z
...
commands, it could do this fast enough so that your finished work came out
fine enough but suppose that windows gets distracted for a millisecond, all
of a sudden, your X is OK but your Y is delayed and your Z is delayed a
little bit more.

Depending on feed rate, you will be off by a bunch of 'thou.

With step and direction, you bang out all of your axes at once:
X goes here, Y goes here, Z goes here
X goes here, Y goes here, Z goes here
...
Now, if windows gets distracted, the cutter will hang out for a few
milliseconds longer at that one position but nothing will be moving.

Parallel-port step and direction systems can do this off the shelf with zero
add-on software or electronics.

Any system trying to use velocity and position will have lots of problems
with this.

Velocity and position systems are out there -- you see them a lot on
conveyer automation (bottling lines, palletizing, assembly and painting
bots) but you do not generally see them on CNC machines. When you do, those
machines are 15-20 years old and are sitting in a warehouse corner with a
tarp thrown over the top.

There is a reason for this.


Good luck!
Dave