Re: [CAD_CAM_EDM_DRO] emc servo question

Thanks, that is exactly the answer I was looking for. This stuff interests
me, and I'd like to think that I'll live long enough to build up a simple
circuit to play with.

- Steven Ciciora

At 12:07 AM 11/11/2003 -0600, you wrote:

>Steven Ciciora wrote:
>
> >I have a simple question about EMC and how it controls servos. Let's say I
> >have a way to get encoder signals into EMC. EMC does some calculations and
> >comes up with a number that is outputted to a D/A converter. This D/A
> >sends a voltage to drive a servo amp. Is this voltage simply amplified and
> >is proportional to the voltage sent to the servo motor, or is it
> >proportional to the current sent to the servo motor? How many bits is it
> >usually? I think the Geckos are internally 8 bits.
> >
> >
>Neither. The "classic" positioning servo has 3 loops. The outermost is
>a position loop, and involves the CNC control, in this case EMC. it
>looks at the velocity commanded by the toolpath program, the actual
>position at the last encoder reading, the commanded position it is supposed
>to be at now, and other things like feedforward and integral and derivative
>adjustments, and comes up with its best guess for a new velocity to move
>at to minimize error at the next reading. This velocity command is sent to
>the servo amplifier through a DAC.

<snip>