Re: +/- 10V Gecko

Jon,

Hi. What I'm designing is an amplifier. As such it can be configured
as a voltage amplifier or a transconductance amplifier. Any time you
close the loop, such as using a tachometer and/or encoder it becomes
a servo.

A voltage amplifier behaves exactly as you describe in closed loop
operation. This is primarily because of the additional 90 degree
phase lag introduced when compared against a transconductance
amplifier. IR compensation introduces phase lead which improves the
loop phase margin somewhat.

A voltage amplifier has uses other than driving a motor.

You caught me out regards to IR compensation. To be practical, the
feedback pot must be a multi-turn type because of the exquisite care
with which it has to be set to get decent speed regulation. I have it
front mounted.

I am looking at including tach feedback summing node but I am put off
by the interior loop feedback phase compensation adjustments. Witness
the plug-in capacitors and resistors necessary on Copley and other
amplifiers.

Mariss

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <jmelson@a...> wrote:

> We're a little out of sync on these messages, but I have an
important
> thing to say. As far as I'm concerned, this is NOT a velocity servo
> amp, in fact it is not even a servo amp. It is just a plain
voltage amp.
> I have tried this, and I can tell you with absolute certainty, that
it will
> perform extremely poorly in a CNC motion control system. If you
> turn up the DC gain enough to get low error when standing still,
> it will vibrate badly when moving. If you turn the gain down to
> eliminate the instability, it will have HUGE following errors when
> moving. The IR compensation will help, but only a little. Since
Mariss
> says there won't be room enough for a pot to adjust it, I don't
know how
> you will set the correct IR compensation, anyway. And, the IR comp
> needs to be set for each motor type.
>
> I still say that you can't do a velocity servo without velocity
feedback.
> That either takes a very high resolution encoder or a DC tach.
> I also still say that a true velocity servo is a very desirable
thing!
>
> Jon