Hi,
you don't need it, as you say the loop is closed by the drive. You may have noted that there is an alarm that triggers if the servo deviates by
some small programmable amount, say 20 encoder counts. If you have a 10000 count per rev encoder that means your servo will alarm if it
lags by 3/4 of a degree from where its supposed to be....that's right 3/4 degree from where it supposed to be at say 1000 rpm! This thing is so
damn accurate it was intended as an axis servo not just a mere spindle motor.
The actual and programmed speed should be within a few parts per million.....you are wasting time and money if you try improve on that.
No doubt if I read the manual closely there will be an encoder output. This could be used by Mach to measure the rpm and display it if
you want to be totally anal retentive about it.
There is talk of the ESS having an API but given it has yet to get backlash compensation and THC support and I've been waiting for months I wouldn't
hold my breath....anoxia is a bad way to go! I don't intend this as a complaint about Warp9 either, I use an ESS and luv it, I just don't need a lot of
bull********* stuff.
I don't know whether you have done any control systems programming but PID programs are not for the faint hearted...you have to worry about loop
parameters, integrator wind up, how to generate a low numerical noise speed signal, usually done by a high gain integrator loop, and if you have to ask
you do not want to try it!
If you've already got full speed range control with step/direction signalling then using analogue voltage for speed control is going backwards...you already have
position control, and not just any position control but the full blown modern sense of position control...that is a final position accuracy of (programmable)
four encoder counts say, 8.6 min of arc, just a bit over a tenth of a degree!
The bottom line is you stumped up with I'm guessing $1000 for a servo and drive, ie you paid good and what you've got is good, in fact very good! If your
going to worry about stuff you might try worrying about who's going to win the next Melbourne Cup!
Craig