ceturtd., 2025. g. 9. janv., plkst. 21:30 — lietotājs Todd Zuercher (<tzuercher1...@gmail.com>) rakstīja: > > Ona normal velocity PID loop, the command input and feedback are in > position units, only the output command is in velocity units. For a torque > command servo, if using a double nested loops the outer one would be a > regular position/velocity loop, but the inner one would be velocity command > input to torque command output. A single PID loop can be used with torque > command servos, but tuning them is a lot harder and they are a bit unstable > when loads change and at high or low speed. For such a loop tune with lots > of I term with an i-error limit set so the I term can never saturate the > output command. This allows a fast I reaction without windup induced > overshoot causing instability. >
This makes sense. Servodrives are Mesa 8i20, input value to the drive is current, which means "torque". I kind of have them running with single PID loop, nothing particular to complain but am not very happy as either the ferror is more than 0.06 mm or motors become noisy and are vibrating. This explains why I could not get ferror down to 0.01-0.02 mm... Nested /cascaded PID loops sound good, I found a forum thread mentioning that as well, but I have no idea how to start with that. I would appreciate any advice on how to actually tackle this. I suspect that I should start with inner loop first. I even found that P, I and FF1 parameters should be used for inner loop, P and FF1 parameters for outer loop. It is just that I am not sure what should be used for inner loop's command when outer loop is not there yet. Connect inner loop's pid.m.command to joint.n.vel-cmd? And should the "encoder.nn.velocity" linked to pid.m.feedback? And keeping in mind that I want some jerk limitation as well, what could possibly go wrong if I put limit3 component between both pid loops? It is acceptable that overall ferror will be around 0.05 mm with max accel of 800m/s^2, I just need to minimize those kicks when actual acceleration value instantly changes. Viesturs _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
