On Saturday 06 March 2021 12:11:26 John Dammeyer wrote: > > From: Gene Heskett [mailto:ghesk...@shentel.net] > > > > On Friday 05 March 2021 18:59:19 John Dammeyer wrote: > > > net a-index-enable <=> pid.a.index-enable > > > net a-enable => pid.a.enable > > > net a-pos-cmd => pid.a.command > > > #net a-vel-cmd => pid.a.command-deriv > > > net a-pos-fb => pid.a.feedback > > > net a-output => pid.a.output > > > > So this is a position servo. Very similar to mine currently. > > I have an idb module which does an Inverse Dead Band between > > a-output and the pwmgen.value, with the amount at 9.5, about 2 short > > of making it hunt. > > > > That idb gives an offset in the currant value according to the > > direction, which helps to cancel the brush and bearing friction. The > > pwmgen is still pinging the driver about 7% when the motor has > > stopped. From either direction. I need to set the DEADBAND > > accordingly, as the idb module, when in balance would then shut the > > pwm off completely. That's the theory anyway. > > > > Thanks John D. > > Stay safe and well. > > > > Cheers, Gene Heskett > > Hi Gene, > I don't know if the following comments are helpful at all. I've > found with the step and direction (250 lines per rev or 1000 pulses > per rev) that when my servos stop that there is still a certain > amount of 'looseness'. If I adjust parameters like P I can make it > stiffer but then when it stops it's often noisy. Like it's trying to > move one encoder edge but can't quite mechanically get there. Or over > shoot perhaps? Then try to get back and friction too much. > > The Bergerda spindle did that when it stopped. I'd grab the spindle > at the end of the quill and just twist it a bit and the squeal would > stop. The Bergerda App Engineer told me what parameter to tweak and > the noise and that issue went away. > > But it sounds like you have PWM from LinuxCNC and the encoder is fed > back to LinuxCNC? Not that it should make any difference whether the > controller is the PC or standalone like what's in the STMBL drive Andy > and I have on our 4th Axis. > > Although, perhaps a question for Andy is whether he's running smart > serial or step/dir and does LinuxCNC get the encoder information back > from the STMBL? And does LinuxCNC do anything with that? Perhaps > Andy can provide his STMBL 4th axis LinuxCNC HAL information and that > might help you tune yours? > > More questions than answers. Sorry. > John Dammeyer > I should probably qualify that a bit. The encoder feedback path comes straight thru a modified and therefore filterless bob, on the p2 plug of a 5i25. Nanoseconds of lag. The encoder's both of them are in the 5i25's fpga. The encoders are running, both of them, with a 6 megahertz sample rate.
And because it was easier to use, the pwmgens are swapped, so that the complementary outputs of pwmgen.0, on the 7i76D, outputs could be used as a driver to a full H-Bridge. SSerial is not in that path, so the pulse outputs aren't more than 10 nanoseconds delayed from their actual outputs in the 5i25's fpga. Those outputs then can be seen on my new 350MHz 4 trace sampling scope on their way to drive the full wave bridge driver. There isn't enough delay in the hardware to bother trying to compensate for it. I should investigate a faster servo loop, but haven't yet. The newer 4 core I5 in this box can probably run 3 or 4 times faster than its current 1 kilohertz. Something that I expect htop can guide me on. I wish the halscope had even 10% of that scopes memory per event. I'd love to be able to observe a homing sequence in it entirety. I wish the other John, Big John Thornton would check in but its been quite a while since he last posted. I hope he is alright. Thanks John D. 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
