Hi,
Before I can justify spending thousands on AC servos I need to give these a fair go.
Ac servos are not free but they don't cost thousands either.
DMM 200V Off-line Servo and Drive:
750W 200V servo $239
230VAC Drive $218
3m power & encoder cables $71
Total $528
This is for a modern AC servo which will eat the old stuff alive, 16 bit encoder, direct offline power supply, a multitude of control modes including step/direction,
vastly flexible electronic gearing, acceleration and velocity limits, programmable following error, zero error, multiple error reporting modes, indexed position and
velocity and the list goes on.
Note that the servo and drive form the loop, the controller is just a plain (cheap) open loop step/direction source....no closed loop controller required!
Ye-ha! Reduce confusion and tuning problems to a mere nothing! An AC servo and drive is as easy to hook up as a stepper driver, Mach can't tell the
difference between the two.
My experience is that I bought a modern AC servo second hand but have been so impressed I wont consider the old stuff any more.
I know its too early but the runaway first occurred when the Tach was not connected. Does this illuminate the possibility of being wired backwards
No. If it runs with the tach disconnected it just means the amp operates without feedback. Look at the last diagram that I posted.....with the tach disconnected
then the feedback voltage Vfb is zero. Therfore error, e = Vin and the output current would be Iout= Vin.G, given that G is high even a modest input voltage will cause
significant output current and the motor will speed away. That's not faulty, that's just how it works.
If the tacho is connected and there is NO input, ie Vin=0 and the motor speeds away it means that the feedback voltage is generating its own input. This
is called positive feedback and is undesirable. If you reverse EITHER the tacho OR the servo then it becomes negative feedback which is what we want.
As I mentioned before could it be possible that the three-phase going into the drive needs the phases swapping to turn the motor the other way?
No, the three phases are rectified to produce DC. Phase reversal has no effect on the DC output.
Three phase induction motors will reverse the direction of rotation if one of the phases is swapped. If the direction of rotation is important, and it usually is
then attention to phase rotation is required. Your servos should be unaffected by phase reversal.
Totally agree with you about using a 10v pot its a great idea. Should I disconnect the encoder wires from the CSMIO whilst doing that or just turn it off?
For testing purposes 9 or 10V and a pot would be good. Whether the encoder is hooked to the CSMIO is immaterial, the CSMIO might as well be off, we don't need it,
with perhaps the exception of an enable signal, to drive the servo.
Craig