> From: Peter C. Wallace [mailto:p...@mesanet.com] > On Tue, 15 Jun 2021, John Dammeyer wrote: > > > Kind of cool to do an M3 S10 and see the what would be the spindle turning > > at > > 10 RPM with STEP/DIR control. (all on my test bench with a smaller motor at > > the moment and Pi4/7i92H instead of PC/7i92H. > > > > Been working on that all afternoon. Moved controllers around. Moved > > motors. > > Nothing. And yet the motor worked fine on the machine and under the Pi4 and > > 7i92 also ran correctly with PWM/DIR. But not STEP/DIR. Didn't seem to > > matter what parameters I changed in the servo motor. I'd switch back and > > forth between the two different .BIT files in the 7i92H. > > > > I took a step backward and started cloning the Z axis parameters into the > > spindle parameter in the INI file. The P parameter was 0.0 Once I set it to > > 1000.0 spindle stepping worked. Which makes sense. No Proportional Gain, > > no > > velocity. > > > > MAX_VELOCITY = 50.0 > > MAX_ACCELERATION = 300.0 > > P = 1000.0 > > I = 0.0 > > D = 0.0 > > FF0 = 1.0 > > FF1 = 0.0 > > FF2 = 0.0 > > BIAS = 0.0 > > DEADBAND = 0.0 > > MAX_OUTPUT = 3000.0 > > > > So when controlling an intelligent AC Servo Drive what is an ideal value for > > P? It's open loop at the moment, until I add an encoder to the spindle. > > Anything else required to make open loop reliable? Once there's an encoder > > on > > the spindle how much tuning is needed given that it's step/dir and not PWM > > with encoder feedback? > > > > Thanks > > John > > > > If you are outputing a velocity command (either a stepgen rate or a PWM > value), P=0 should be fine, because FF0=1 meaning the PID output that drives > the > stepgen or PWMgen will equal the input command. Basically the PID compoment is > just passing the commanded spindle RPM to its output so when P=0 (and I=0) you > are running open loop, but it should work in this configuration. If you are > using a stepgen, there should be no need for P (or PID) at all, since the > stegen > rate accuracy will be better than .01% or so. > Peter Wallace > Mesa Electronics
Ah. The problem was with the FF0=1.0 then. Setting FF0=0 and P=0 makes it work. What about for power tapping then. Is there even a need for an encoder or does it still require that index pulse and spindle feedback? I suspect yes because there is no guarantee that my pulleys are precisely the same diameter so what the motor thinks and what the spindle is doing may be out just a hair. And if I do change to the alternate step down pulleys to increase torque then the spindle won't be doing motor speed. Is the loop closed then with the system asking for say 200 RPM and the spindle reporting 207RPM, through the encoder inputs QCount0? Ie the stepgen will be told to reduce RPM until the target 200 on the spindle is reached? And although the motor has been configured for 5000 pulses per rev the encoder might only have 200 lines for 800 PPR. I should have an encoder wired to this test bench motor in the next day or so I can try this out. Thanks John _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
