> 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
