Re: Re: Low cost Servo Controller

Ray Henry wrote:

> From: Ray Henry <rehenry@...>
>
> Bertho
>
> I spent years keeping up a bunch of Hardinge lathes that were controlled by
> AB 73xx controllers. They used 15 bits from the digital to drive their D/A
> board. That's 1600+ steps plus direction if mscalc works the way I think it
> should.

Actually, 16384 discrete levels, + direction.

> They would do an excellent job on shallow tapers where one axis
> runs very slow compared to the other and on cutting a radius or half circle.
>
> To me that's the critical question. What are the very shallow tapers going
> to look like? What are the four corners (where axis motion slows to a stop
> and then reverses) of a milled circle going to look like? 128 steps are
> more than adequate for the high end of axis motion. Will they be enough
> for the low end of feedrates.
>
> The stg card uses 13 bit for both D/A and A/D. (8000+ levels)

I find very good results with EMC and the STG card, and my servo amps.
I am using 1000 cycle/rev encoders, so I get 4000 counts/rev, x 5 revs/inch,
to get .00005" / encoder count. This is part of the secret.

On my mill, I often bore out circular holes using circular interpolation.
If it is a critical part, I then bore it out to final size with a boring head.
But, just doing the circular interpolation with an end mill gives a VERY
good circle, maybe with a variation in diameter of .002" or so. Most
of that is due to a little bit of backlash in my ballscrews. The results
are VASTLY better than my AB7320 did, but then it was never properly
tuned for my machine. I also now have the following error holding
within .005" all the way up to 105 IPM, with a following error of
about .0005" or so at low feed rates.

Jon