Re: [CAD_CAM_EDM_DRO] Re: PC based CNC system architecture

Wally K wrote:

>
> would this list be correct for plug in cards.
>
> 1) 4 axis servo card.
> 2) 4-16 bit DAC's.
> 3) 4 axis stepper rate generator card.
> 4) 4 axis encoder counter card.
> 5) Digital I/O card. With 16 opto inputs and 8 solid state relay
> outputs.

Not quite. there is no servo card. For servos, you use one encoder counter
card and one DAC card for every 4 axes. For steppers, the first
generation would use one encoder counter card (same as above) and
one stepper rate generator card for 4 axes. In either case, you could
use one or more digital I/O cards, as needed. One would be enough
for most small systems. With separate limit and home switches for each
axis, that is still only 12 inputs.

> If you would use the encoder counter card to count encoder pulses are
> there any special requirements for encoder resolution.

None in a servo system, other than the resolution should be greater than
whatever position accuracy you want by a factor of ten or so.

For steppers, I think having an encoder with more resolution than the
stepper could cause problems. But, we could put a dead zone in the
control loop to prevent fast hunting. (The planned design will cause steppers
to hunt at a rate of one step every .6 seconds, as that is as slow as the
rate generator can go.)

> With all the crying i have done about price i hesitate to ask for
> something that will add cost. But on your solid state relay
> outputs. Do you have a replaceable fuse not a solder type. Having
> to unsolder them from opto-22 stuff i think it is worth it. Also i
> can tell you that explaining to a customer on the phone what a pico
> fuse looks like and how to unsolder and replace it, is an hour job.

Sure, the socket pins are not too expensive. I can imagine what a
nightmare it would be to have to crawl halfway inside a control cabinet,
with a flashlight in your teeth, and unwire 52 wires from a board,
take it to a bench, unsolder the fuse and replace, and then reattach
all 52 wires correctly! (I don't even want to think about the customer
doing this!)

> So with a 8 slot motherboard. You could have up to 12 axis and 2 I/O
> cards.

Right! If you need more, extend the backplane with another one.

Jon