I got the braking resistor installed, fiddled with all the DC injection braking and dynamic braking parameters on the machine, then started turning down the deceleration time. It looks like I only tuned the acceleration time when I originally installed the VFD because it was set to the default 10 seconds. I turned it down to 0.6 seconds and tested a reversal of direction up to 1000 RPM. Worked great. Also, since the mechanical brake kicks in automatically when stopping, the drive doesn’t fault out even when the varispeed head is set to max RPM. I can’t imagine I’ll need to tap at 1000 RPM, but I estimated that 1000 RPM to 0 RPM in 0.6 seconds should be approximately equal to 10 revolutions (assuming a linear deceleration). I didn’t bother to push it further. No idea how much the braking resistor helps, but it certainly doesn’t hurt.
Upon testing, I found that rigid tapping worked as intended, aside from one glitch on the first attempt after powering up where it hung in the down position and running in reverse. Not sure of the cause there, but I wasn’t able to reproduce the error. In practice, 560 RPM resulted in an overshoot equal to a bit under 3 revolutions. I figure if I allow 5 revolutions of margin to the bottom of the hole, I should be fine. I tested it repeatedly, including running a program tapping two holes in delrin. Thank you all for your help. I’ll run it a few more times before declaring it solved, but so far so good! As to configuring speed control of the VFD, that’s for another day. I plan to do it eventually, but for now I’m thrilled I didn’t need to resort to more sophisticated fixes. I’m fine with manually setting my speed. > On Jul 21, 2020, at 8:26 PM, Gene Heskett <ghesk...@shentel.net> wrote: > > On Tuesday 21 July 2020 18:40:35 Scott Harwell via Emc-users wrote: > >> Just got my new Control Engineering in the mail and saw this."Top 5 >> VFD parameter changes explained" >> >> >> >> >> >> >> >> >> >> >> >> Top 5 VFD parameter changes explained >> >> Chris Vavra >> >> Learning Objectives Setting five parameters can take care of most VFD >> programming. Consider VFD control met... >> >> >> >> >> >> >> >> "www.controleng.com/articles/top-5-vfd-parameter-changes-explained/" >> It may help. >> Scott >> >> On Tuesday, July 21, 2020, 12:17:05 PM CDT, Matthew Herd >> <herd.m...@gmail.com> wrote: >> >> Hi Rob, >> >> Thanks for the insights. I suspected something along these lines, >> even if I might have other problems with noise. I can confirm, the >> spindle stops way too slowly and definitely more than 10 revolutions >> pass before stopping. Long story short, I can’t readily run the >> machine in back gear and the slowest I can go at 60Hz is 560 RPM >> without backgear. > > But if you get the right control signal setup, you can drive that vfd at > 5 hertz! I am doing it. And I can do it for an hour at a time without > heating the motor so hot I can't touch it. All you need is to find the > register that sets the motors FLA, and transfer the FLA from the motors > nameplate to that register. That way you are assured that the motor > won't be quickly overheated and burned up at even very low speeds. You > may also have to locate the register that sets the minimum run speed as > its likely set to faster than that, possibly even turning itself off at > 30 hertz or more. There are registers also to control how fast it > accels or decels. The biggest problem is in translating the Chinglish > in the booklets into your local dialect that you understand. > > One thing I've found is that most vfd's are directly controllable by a > 12 volt swing from a pwm generator, running the pwm at 10 kilohertz. The > vfd's response averages that into an analog signal equivalent, so a 10% > duty cycle pwm will run the vfd at say 12 hertz. And I've some extra > stuff in my .hal to measure the overshoot so I'll demo, live, right now. > From 200 rpms, entering an m4 to reverse it, gets me a display of 1.0333 > revs that it overshot, or just a small hair over 1 full turn from 200 > revs. This is an E400 drive, running in 1st gear, and it has an 8" 4 jaw > chuck that weighs just short of 40 lbs mounted. This particular vfd is > controlled by a Mesa SpinX1 which has its own analog 0-10 volt output. > > Your B-Port doesn't have near that amount of flywheel, and it ought to > beat that time while spinning at 400 rpms. > >> I’ll play a bit more with how quickly I can stop >> the spindle with a braking resistor or I’ll attempt to get the HAL >> file to engage the mechanical brake to help transition faster. >> Nonetheless, 10 revolutions seems fairly ambitious based on my best >> guess of how long it might take to stop the spindle even with a >> braking resistor. That’s about 1 second, but should be achievable. >> Currently the VFD is configured based on the fastest stop time for max >> RPM, and there doesn’t seem to be a way to decrease stop time for >> different inertial loads (i.e. lower gear ratios/spindle speeds). >> However, I understand that the braking resistor should decrease stop >> time by approximately an order of magnitude based on some reading I >> did yesterday. >> >> Thanks! >> Matt >> >>> On Jul 21, 2020, at 1:00 PM, Robert Ellenberg <rwe...@gmail.com> >>> wrote: >>> >>> Based on the videos and your descriptions of the behavior, you may >>> be running into a TP issue I've seen (in simulation) with very >>> sluggish spindles or very high spindle speeds. Here's what I think >>> is going on: >>> >>> 1. The rigid tapping cycle allows a hard-coded 10 revolutions >>> >>> <https://github.com/LinuxCNC/linuxcnc/blob/master/src/emc/tp/tc.c#L8 >>> 56> of overtravel beyond the nominal bottom of the hole when >>> reversing direction. >>> 2. The spindle starts reversing direction only after the Z axis has >>> reached the bottom, so the spindle has to be able to stop in 10 >>> revolutions to stay within the budgeted overtravel. >>> 3. If the TP hits the end of the overtravel, it prematurely >>> declares the motion to be complete and stops following the spindle >>> motion. >>> >>> Do you still see this behavior if you run the spindle slower? Your >>> spindle seems to take a long time to reverse, so at high speeds you >>> may be hitting this limit. >>> >>> Best, >>> Rob >>> <https://github.com/LinuxCNC/linuxcnc/blob/master/src/emc/tp/tc.c#L8 >>> 56> >>> >>> On Tue, Jul 21, 2020 at 11:18 AM Matthew Herd <herd.m...@gmail.com> > wrote: >>>> Ahh, so I do use limit switches and a homing routine. So it’s >>>> homing to the same position (plus or minus a few thousandths or >>>> so). >>>> >>>>> On Jul 21, 2020, at 11:07 AM, Jon Elson <el...@pico-systems.com> >>>>> wrote: >>>>> >>>>> On 07/21/2020 04:20 AM, andy pugh wrote: >>>>>> On Tue, 21 Jul 2020 at 10:18, andy pugh <bodge...@gmail.com> > wrote: >>>>>>> We are not looking for noise, we are looking for spurious >>>>>>> encoder >>>> >>>> count resets. >>>> >>>>>> But, thinking further, even if there _is_ noise on the index >>>>>> line, the encoder counter should ignore it. It ignores all the >>>>>> _real_ indexes unless index-enable is set true in HAL. >>>>> >>>>> Yes, the only thing I can think of is he's hitting his soft >>>>> limits. Over >>>> >>>> time, starting and stopping LinuxCNC, >>>> >>>>> without homing, the machine limits will drift. If you have >>>>> rational >>>> >>>> limits in the .ini file, you will eventually reach the end of them >>>> and have really strange behavior. it can be fixed by homing in a >>>> safe position, >>>> >>>>> but best to put in home switches and actually home the machine to >>>>> a >>>> >>>> repeatable position every time. >>>> >>>>> Jon >>>>> >>>>> >>>>> _______________________________________________ >>>>> Emc-users mailing list >>>>> Emc-users@lists.sourceforge.net >>>>> https://lists.sourceforge.net/lists/listinfo/emc-users >>>> >>>> _______________________________________________ >>>> Emc-users mailing list >>>> Emc-users@lists.sourceforge.net >>>> https://lists.sourceforge.net/lists/listinfo/emc-users >>> >>> _______________________________________________ >>> Emc-users mailing list >>> Emc-users@lists.sourceforge.net >>> https://lists.sourceforge.net/lists/listinfo/emc-users >> >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users >> >> _______________________________________________ >> 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 > <http://geneslinuxbox.net:6309/gene>> > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net <mailto:Emc-users@lists.sourceforge.net> > https://lists.sourceforge.net/lists/listinfo/emc-users > <https://lists.sourceforge.net/lists/listinfo/emc-users> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
