Hi,
yes you can drive an AC servo with either step/direction OR PWM. In most circumstances there is little in it.
If your controller is providing an analogue voltage , ie PMW output, the servo drive closes its speed loop on that input voltage, thus any
speed reduction by virtue of changing load will be corrected by the servo drive feedback.
If your controller is outputting step/direction then the drive, using the servo encoder, closes the feedback loop.
Both methods result in the speed being controlled by a feedback loop....ergo no difference. Given that the spindle in Mach3, and incidentally Mach4,
is natively PWM it is easier to apply PWM than step/direction, although either is possible.
Step/Direction input allows you to have position control for an indexing spindle for instance, or C axis control for rigid tapping. Quite frankly I think
trying to get Mach3 to do a Caxis properly is going to be trouble.
Spindle motor to C axis, just by using an Index input (1 per rev), but in that case I believe you trust on the inbuilt encoder spindle and it's power to don't slow down while threading or bye bye, something bad will happen since there is no real feedback on the spindle. Is this the case?
That is a misunderstanding, the servo encoder is an INPUT into the servo drive and it is COMPARED to the step/direction input and the drive attempts to reduce the
error. That IS FEEDBACK, and its fundemental to the way AC servos operate. Thus an AC servo is in feedback control at all times, its just that you, or rather Mach,
does not control the feedback loop, it is enacted entirely by the servo drive. Should the load be such that the servo cannot keep up then the drive will alarm out
and stop. The feedback enacted by a modern servo drive on a matching servo is superb, better I would say, than any general purpose feedback controller can ever
manage. The manufacturer of a servo knows EXACTLY the best way to control it and makes their drives to PERFECTLY match the servo. If you think you can program
a PID loop better than a servo manufacturer then this is the wrong place for you!
Regarding the UC300ETH, I have seen it has an analog port but does it mean that for instance it can create the 0-10V signal to drive a VFD without an additional board?
This is a misunderstanding also. A controller, be it an ESS OR a UC300 can produce a PWM output signal which is filtered by an A-to-D converter on the BoB to produce an
analogue 0-10V signal. What a UC300 has is an analog input channel. The UC300 measures an analog input, say a voltage from a potentiometer say, and convert that into
a digital number which can be read and manipulated by Mach.
. Then a Estop is automatically triggered and the changes are applied. I have also tried to trigger the Estop manually but that doesn't help, so there is some kind of refresh cycle that it's automatically elicited when you close the ports and pins tab. Do you know if it's possible to trigger the same refresh cycle with a VB command? Thanks
This is part of the way Mach3 works, any change to the profile results in an Estop and must be manually restarted. Mach4 on the other hand can programmatically change settings in the
profile, with or without a save cycle, and carry on running. Mach4 and its Lua coding language is VASTLY superior when it comes to doing this sort of tricky-dicky customisations.
Craig