On Sunday 10 January 2021 13:53:55 Jon Elson wrote: > On 01/10/2021 12:27 PM, Gene Heskett wrote: > > On Sunday 10 January 2021 11:38:42 Jon Elson wrote: > >> On 01/10/2021 01:36 AM, Gene Heskett wrote: > >>> On Saturday 09 January 2021 20:57:24 Jon Elson wrote: > >>>> On 01/09/2021 06:39 PM, Gene Heskett wrote: > >>>>> Yes so idb drives it closer by overdriving it an "amount" so > >>>>> that the friction locked point is closer to the desired point > >>>>> without going over. The trick is to null the error without > >>>>> changing the sign of the error. If the sign changes, then it > >>>>> oscillates, hard. So you can narrow the friction caused deadband > >>>>> by a small amount of overdrive, but you also cannot change the > >>>>> sign of the error. > >>>> > >>>> Yes, that's the tricky part. Any time you introduce a > >>>> discontinuity into the transfer function, > >>>> it makes things unstable at that point. > >>>> > >>>> Jon > >>> > >>> Thinking along a different line, I am running the pwmgen at 4khz, > >>> mainly because my ears have a "carhart notch" at least 120 db deep > >>> so theres not a chance in hell I'd ever hear it. What would happen > >>> if I dropped the pwmgen frequency to 400 hz. that same percentage > >>> of a pulse coming into the controller would have 10x the length of > >>> time to actually move the motor, which may drive it closer to a > >>> null than tickling it with a 1% pulse 4k times a second. The > >>> trouble with that is that both pwmgens run at the same frequency, > >>> and Jon's servo, driving the spindle, may trip its current limits > >>> with the longer pulses. > >>> > >>> Jon? Can you opine on that? Is there a minimum frequency for > >>> those toroids? > >> > >> Well, at 50 KHz, which is what it was designed for, the > >> motor current is always continuous, but could look like a > >> sine wave with low inductance motors. At 4 KHz, it is > >> likely to already be discontinuous except maybe at high duty > >> cycles. So, it really won't make a difference to the > >> toroids. I suspect the > >> motors will "sing", maybe pretty loudly, with 400 Hz PWM, > >> but maybe you don't care. > >> > >> Yes, a long pulse with 400 Hz rep rate could allow current > >> to build a lot. But, in a PROPERLY tuned PID system, there > >> should not be sudden excursions in pulse width. Now, you > >> have to watch out for > >> excessive acceleration parameters in the .ini file. My PWM > >> servo amp has TWO current limits. > >> The first (adjustable by resistor) limit just cuts off the > >> PWM pulse early, and resets on the next PWM pulse. The > >> second limit (not adjustable) trips around 20 A and latches > >> the servo amp into E-stop. > > > > Requiring the pushbutton reset. With a nominally 17 amp limit set > > resistively, the other. triggering the shutdown can be counted on > > one, maybe 2 hands in all these years of using it for a spindle > > controller. > > > >> Oh, now one issue is with the PWM frequency being LOWER than > >> the servo period, that might make for some delay in updating > >> the PWM generator. Is this with a Pico controller or a > >> Mesa? I know my controller will immediately update the end > >> of the PWM pulse if the width is changed in the middle of a > >> cycle. I can't say for Mesa. > > > > mesa, and that possibility had not occurred to me, my bad. So I'd > > consider 2 khz as being the lowest workable minimum, and when the 17 > > amp kicks in I do hear a chirp from the iron in the motor so it > > obviously slower than the 4 khz pwm. And its possible its going to > > 100%. But IIRC theres a .98 max output set. But it is not set there. > > PWM_SCALE is 46 in this case. How does one figure that value to be > > 98% mathematically? > > I have a max duty cycle parameter in my ppmc driver for the > PWM generator. I have no idea > whether the Mesa has a similar function or not. > And I find when trying to add it, that the mesa version doesn't have that. So I need a way to set the pid.n.maxoutput to do the same thing but subtract the amount idb uses. How does that math work with as pwmgen scale of 46, and I can't recall the reason for that 7 years later. > Jon > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users
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
