Originally Posted by Al_The_Man I was looking into this some time back, I thought maybe that EMC had developed an interface for the dedicated type of servo card as in Galil, Delt-Tau etc, but as far as I can tell it is still software oriented and uses the common step and direction control through the parallel port to 'intelligent' drives, in other words the loop is not closed in the CNC software or controller, and in that case it does not appear that EMC integrates the servo encoder loop.
I hope someone can prove me wrong.
Al. |
Ahh! For once I caught you wrong!!
It does. In fact it even does this when running stepper motors.
You have several driver options. The ones I have used are:
Parallel port direct (freqmod) is one (I don't recommend it).
Now I use Pico-Systems Universal Stepper Controller. I'm thoroughly impressed! It drives the steppers very smoothly. They sound and move like servos. This hardware can use steppers with or without encoders, or with linear encoders by flipping some DIP switches. If no encoders, the step outputs are run directly back to the position counters, so the closed loop does not embrace the screw/axis. Nice thing is I can just put in an encoder, connect it and flip the switches if there is a need.
In both cases the PID values have to be tuned. There are also 3 FF terms.
Whether this is a good thing when using servo drives with their own PID controller is one thing I find interesting. But I guess a P of unity and the others to zero would pass on those resposibilities to the drive?
I'll probably find out, as I have a BLDC servo system I will set up with EMC.
For other drive options I'll have to pass you on to
www.linuxcnc.org, as I have not tried them. But I'm pretty sure they all have the PID running inside EMC. The user interface also have a logger/plotter that is very nice when tuning the PID. I did not realise this in the beginning, but once I was told of it, it made the motor tuning a one evening affair.