Hi Roger,
a modern AC servo leaves the ESS PID solution in the dust.
Of course you know that at this time it is limited to one pulse per rev. Andy has expressed interest in extending that to multiple pulses per rev. As you also probably
know many ENTRY level servos are shipping with 17 bit encoders, A Delta servo I've been giving a hand with in the forum has a potential encoder count of
160,000 per rev. Will Andy be able to squeeze that in?
My servo is about 10 years old, Allen Bradley and is equipped with a 8000 count per rev encoder.....very ho hum by todays standards but has proven to really REALLY
spin my wheels! I had to buy the software to program the EMPROM, I would have had it gratis had I bought new, but this is second hand.
Anyway the software has a database of all Allen Bradley servos, mine included and many of the basic parameters are set just by virtue of selecting your servo from
the list. The basic parameters include such things as rated speed, rated current, encoder count etc, all the usual stuff. What may not be apparent is the detail about each
servo, the resistance and inductance of the windings, a table of flux density verses current....yes that's a quasi linear approximation of hysteresis, thermal mass and
temperature rise. In short the database has more information that you could expect to find or measure yourself.
There is the opportunity to adjust the PID parameters if you wish however the database entries have proven to be better than me fiddling with them for hours.
Amongst the facilities of the software is an Oscilloscope where you can plot loop error verses time, just brill....I can see at a glance the damping factor a damn near
0.7071, just what I'd try to achieve if I were fiddling with it...and to have it displayed as a live oscilloscope trace!
In short modern AC servos and their drives with the software support from the manufacturer make old school PID loops look like crap. I bought my servo and drive
including shipping for $800 NZD or about $600 USD. Quite frankly for that sort of money why would you bother with a DC servo?
Craig