On Saturday 26 June 2021 11:43:12 John Dammeyer 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 > Which is why I am in love with the 3 phase stepper servo's just now comiing on the market. They combine a 3 phase full step size of 1.2 degrees with a 1000 line encoder with a power saving citcuit that runs the motor dead cold as long as the following error is low. And if pushed beyond their ability, have a fault output that stops the machine as quick as it can. "home" cannot be lost with these and leave it running.
Currently available in nema 23 at 1NM, 2NM, and 3NM torque's. I have a 6 pack of 1NM's on order to see if they can run my 6040, one of which will go on an all printed harmonic drive to put some precision into the A axis supplied with the 6040 if you buy the 4 axis model. But my printed version of this drive is only 90mm in diameter, and w/o an output sprocket, only 20mm thick. 30/1 gear ratio. Output sprocket still being written. When its all done and working, the openscad file to make it will be published. But I've yet to test its longevity, I've not yet obtained the screws to mount it with, which I think will be good. 1st one is made of PLA, next one if needed from carbon fiber PETG. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
