Re: [CAD_CAM_EDM_DRO] Re: Black Box

Alan Marconett KM6VV wrote:

> Hi to the list,
>
> Too bad FlashCut's "signal generator" is a "closed architecture", we
> might think of doing something along those lines. I have no more then
> a
> guess what is in FlashCut's box, but I like it.
>
> Jon, would your "black box" be along these lines?

I think it is probably better. I am guessing here, but I suspect the
flashcut box is either a fixed pulse generator used to interrupt the
processor at a fixed interval, or a programmable timer used to
cause interrupts at the desired rate.

What I am working on is a 4-channel programmable pulse generator
that would actually send the step and direction pulses to the stepper
driver. Each channel would be given a velocity value and a direction.
It would also generate quadrature pulses that followed the step and
direction signals, and could be used to drive old phase-drive type
stepper drivers, as well as be counted by an encoder counter, for
open-loop systems. For closed loop, the encoder counters would
read actual encoders on the motors, or on the machine itself.

I am running EMC with a 100 MHz Pentium, and updating the
servo loop at a 1 KHz rate, with plenty of CPU power to spare.
This type of device would look about the same to the CPU,
encoder values are read in, servo calculations are done, and a new
velocity command is written out.

A 24-bit counter/comparator circuit running at 10 MHz (100 nS
resolution) could output up to 5 Million steps / second (although the
jump from 3.333 to 5 million is obviously too big a jump).
But, reasonable step rates would be well in excess of 100,000/sec,
which might be needed for people using high microstepping
division ratios. And, the timing resolution there would still be
100 nS, giving extremely fine velocity control, no large jumps
in velocity, and smooth acceleration and running at any sped
desired.

The low end is one step every 1.6 seconds. The code could either
stop the counter if no steps are needed, or just let it bump every
1.6 seconds, first one way, then the other. This would cause
some VERY slow and small hunting, and might not be objectionable.
If it is, the code could shut off the pulses when the commanded
velocity is below some threshold, like .001" / sec.

Jon