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In the end I want to close the servo loops with the glass scales on each axis of my mill.

But for getting the breadboard going I was ass-u-ming that my 544 ABB/Isoflux servos where encoder equiped, especially as the diagram of the existing Seidel/Bobray amp is showing a feedback loop labeled 'tach'.

I found the documentation for the servos:





Oh Woe!

It turns out tach. and _tach. are 0.02V/rpm, although the servos are equiped 'with encoder resolver 2and shaft'.

So, what is the easy way out here? Electroncially convert the DC tacho to a pulse train (mechanically jimmy the commutator in the tach) or add a pupose made encoder?

What would be "best practise", given that the ultimate reference are the glass scales?

Thanks

The tachs are for _velocity_ feedback for the motor drives, and need to remain if
you are using the original velocity mode drives. They do not and cannot provide position
information. Position information must come from encoders/resolver/scales.

PCW wrote:
That is clear. My error was in assuming that the 7i29 would provide a trivial interface.

The problem remains, how to interface the analog velocity signal.

I have on order with mesanet 7i29 + 7i47s + 7i37ta, so no analog in.

Regards
_jC
.

IIRC the 7i29 connects directly to DC servos and takes back in encoder feedback... you don't connect a 7i29 to another drive.

Analog in to what?

John

Typically with a 7I29 , a shaft encoder is used for position and velocity feedback

PCW wrote:
And so my question is, and remains, what is the easy way to convert the analog signal to a pulse train. See original post.

I suppose the tacho generator has a commutator, maybe the simplest approach is to break that.

A negative logic pulse-train would be nice for safety reasons, and an out of the box (PLL?) circuit would be neat.

Cheers
_jC
.