Re: [CAD_CAM_EDM_DRO] DIY AC servodrive questions

Hi Les,

Thanks for the quick and informative reply.
It looks like I won't have to develop more microcontroller code then -
nice, since it's not my strength nor very interesting !

As I tried to describe the servodrive reads an analog voltage and
outputs sinwaves with this voltage amplitude. Wether that makes it a
speed or torque drive I don't know... In principle the drive input
controls speed, but it's open-loop, i.e. when there is load a higher
input needs to be applied.

When running in this mode (no speed or torque loops closed in servodrive
hardware), are there any special considerations for the PID loop that
runs in EMC ? (other than 'normal' PID tuning - which in itself seems
to be somewhat of a black art...)

AW

> Anders,
> Long ago when computers were slower and encoders therefore were coarser many
> systems offloaded the velocity loop to an analog tach with a feedback loop in the
> amp. This gave smoother response when the coarse encoder pulse rate got very slow.
> There is little need to do that these days. Generally amps are set up as
> voltage controlled current sources, and the computer PID sends out torque commands. The D in
> PID closes a velocity loop. Particularly with feedforward such systems produce very low following error with very high speed.
> If you do have a velocity drive take care not to use much D in the computer
> as that would create a potentially unstable fourth order system.
>