Re: Digest Number 20

> From: Jon Elson <jmelson@...>
> Subject: Re: Servo Amp designs
>
> Ohh, there's the killer, right there. Just like all the other darn
> beautiful one-axis chips (Nat Semi LM628/629, HP HCTL1200
> etc.) when you need coordinated motion on 2 - n axes, it all falls
> apart. Especially for contouring or engraving, where you're following
> splines with a change in angle every few thousandths of an inch.
> That's the reason why everyone seems to come up with some way
> of using one processor to compute the trajectory for ALL the axes.

Yep, I've been forced to use single axis controllers to perform
interpolated moves. It's not the best way of doing it to say the least.
A multi-axis approach, though more expensive, is probably required.

> From: Tom Kulaga <tkulaga@...>
> Subject: Re: Digest Number 19
>
> If you plan to use steppers, well, you're running open-loop already,
> but I guess you could use the linear encoders as feedback to correct
> for missed steps. This assumes that you'll be writing a custom
> program to run the steppers, unless there's software out there to
> take advantage of the encoder feedback. I haven't seen any, but then
> again, I haven't looked. :)

Some of the commercial stepper cards do this, they move, check the
final position, and make corrections as specified by various
parameters. Not great, but workable. Especially since you then
know you had slippage or a stall and can correct for it or at
least stop the process.

> From: Jon Elson <jmelson@...>
> There is an Atlas/Craftsman list, and the metalworking web site has a fAQ,
> already. It probably has little specifically on CAD, CAM and EDM.
> It does have some pointers and comments about DROs.

I'll have to check that one out!

Jim Eckman