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"
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> Top 5 VFD parameter changes explained
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> Chris Vavra
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> Learning Objectives Setting five parameters can take care of most VFD
> programming. Consider VFD control met...
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> "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
> >>>
> >>>
> >>> _______________________________________________
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> >>
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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)
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 - Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/gene>


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