I believe this doc explains the spindle encoder feedback. http://linuxcnc.org/docs/2.4/html/examples_spindle.html John
> -----Original Message----- > From: John Dammeyer [mailto:jo...@autoartisans.com] > Sent: June-15-21 4:52 PM > To: 'Enhanced Machine Controller (EMC)' > Subject: Re: [Emc-users] Spindle Control > > > 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 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
