Hey John, I guess i should've explained better, I was half awake when I asked that. I'm running dmm servos on my mill, which are currently driven on a 7i76e with step/dir and are only semi closed loop (closed loop from the motor to the drive, but not to LinuxCNC). I'm Curious if it's possible to use the external encoder feedback from the dyn4 to LinuxCNC to create a full closed loop arrangement using that encoder and step/dir or do the servos have to be controlled via analog signal and pid tuning to get the encoder feedback to be closed loop?
Also, I'm looking for the secret sauce to get full closed loop from my vfd to LinuxCNC if anyone has pointers on that. I have encoder feedback to LinuxCNC, but i feel like I'm missing a key element to get the pid working properly. Most of the adjustments I've made to pid never result in LinuxCNC compensating for the error (i.e. G97 S200 = S210 actual with p =0, changing P results in a runaway in most cases). I'm wondering what the magic net command might be to get everything working so I could thread on my lathe. Phil T. The Feral Engineer Check out my LinuxCNC tutorials, machine builds and other antics at www.youtube.com/c/theferalengineer Help support my channel efforts and coffee addiction: www.patreon.com/theferalengineer On Sat, Jun 26, 2021, 11:46 AM John Dammeyer <[email protected]> wrote: > > That being said, anyone ever use a 7i95 for full closed loop to LinuxCNC > > using step dir and encoders? I know a lot of guys are using the 7i77 that > > way with analog and there's the 7i97 that would be fun to check out as > well > > for analog setups. Curious if there's any kind of weirdness that happens > > using step pulse with encoder vs just using analog signal. > > > > > > Phil T. > > The Feral Engineer > > Hi Phil, > On the bench I have the Pi4 driving the Bergerda AC Servo spindle with > step/dir (smaller motor for bench testing) with an encoder coupled back > for feedback. At the moment I have P=0 and FF1=0 so I'm not using closed > loop control because it would probably fight with the Bergerda which has > its own set of PID parameters. > > I not sure you can really do that with a real stepper motor because at > high speeds once the motor loses position it locks up and you need to slow > down the step rate to get it to mechanically synchronize. For final > positioning though, since a stepper is only accurate to the nearest full > step position, an encoder could be used with LinuxCNC to add/subtract > micro-steps until the motor turned to the encoder expected position. > > The closed loop servo-steppers work slightly differently I believe. > (Haven't checked). I think they treat the two stepper windings as a two > phase AC motor with the AC waveforms recreated matching the encoder > resolution. Or if they are really clever they, like the Gecko, would > switch to full step square waves after the resonance point to raise the > torque from 0.707 of name plate to full. And they too would adjust the two > phase waveform when stopped to the expected encoder position based on step > count input. > > John Dammeyer > > > > > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
