Re: Digital Servo

Hello again Arne,

Please re-read my posts. I am not proposing to do an external position loop or change the basic system design. The motion
control software, EMC for example would still control all functions just as usual.

I am proposing to get rid of the mechanical tach and to do the math in digital format instead of using analog circuits and
filters. The end result would be a more stable, lower cost system that does not drift over time or temperature and is software
tunable.

No other changes are proposed to the system and all tracking and channel syncs would work just as usual.

Bertho
=============================================

> "Arne Chr. Jorgensen" <instel@...> wrote:
>
> Hi,
>
> I have not read all, and I am just going to comment on something
> from Bertho Boman:
>
> As I said, I can't see that you are doing anything more than what
> is common. Someone mentioned the LM628/629, and let us see what
> they do.
>
> You send a couple of bytes to it, it has a position feedback,
> velocity feedback and acceleration feedback, a very good digital
> PID filter, and some other options too. It has modes for filter
> updating, resets, home positioning , velocity and position closed
> loops. The 628 can drive a H-bridge. Further it has 32bit counters,
> I believe. That is more than the STG board. And HP has another
> chip, but if my memory don't fail me, it use 24-bit counters.
>
> By the way, I believe the EMC started with boards using LM629 or
> similar. You could ask Fred Proctor.
>
> In DSP - there is some other options, and there is chips available
> that outperforms a LM629 many times over. But as I said, ask Fred
> about it, because the whole idea with the EMC is to overcome some of
> the problems using chips like this.
>
> I have also made something similar, - and it was a great educational
> experience. A real good demo of my own lack of knowledge ! ;-)
>
> Sorry, I don't want to discourage you. Hmmm....
>
> What if you forget the encoders, and just make a digital H-bridge
> drive ? Skip the DAC, PID , etc. Then a 8 bit processor would do
> it.
> A PIC could do it easy. This could be added to the DRO board that
> the others are making, and would fit much better with the EMC
> efforts.
>
> //ARNE